CH715981A2 - Method for marking a sapphire watch crystal. - Google Patents

Abstract

The invention relates to a method for marking a sapphire watch crystal (1) by the interaction between a laser beam (4) and the sapphire. The beam is focused on a point (5) inside the ice and the interaction is such that it generates a rectilinear opaque zone (6) which is parallel to the upper surface (2) of the ice or perpendicular to it. said surface (2). The orientation of the opaque area depends on the operating mode applied. Depending on the hatching mode of operation, the beam (4) is scanned along one or more linear paths, generating opaque lines (6) inside the glass, which are parallel to the upper surface. The perforation mode of operation generates distinct opaque areas, obtained by a discontinuous operation of the beam (4) on a number of juxtaposed points (5). According to this latter mode of operation, the opaque zones extend in the direction perpendicular to the upper surface of the ice.

Description

Technical area

The present invention relates to watchmaking, in particular to the marking of a watch crystal to add to the ice a serial number, a drawing or logo, or any other type of computer and / or aesthetic mark. . The invention is focused more particularly on the marking of a sapphire watch crystal.

State of the art

[0002] A known technique for obtaining a marking consists in etching the ice using a laser. On sapphire crystals, it is known to use a laser which is focused on the upper surface of the crystal, and to scan the laser over part of the surface, so as to remove material, thus creating a break in the crystals. crystalline mesh, thus making the material opaque. The removed material must be disposed of as dust, which is a downside to this approach, since dust can contaminate the marking.

Another technique for marking watch glasses made of sapphire or other materials consists in the engraving of the material by a laser focused inside the crystal, but carried out in a dotted manner. Document WO-A-9921061 describes such a technique which consists in creating a series of impacts of the laser juxtaposed inside the material, so as to produce a pattern. The etching conditions are such that the impact generates an internal star-shaped defect, having a non-controllable cross section. This imposes a limit on the minimum distance between two consecutive impact zones, thus limiting the visibility of certain markings or drawings.

Summary of the invention

[0004] The present invention aims to provide methods for producing markings in a sapphire watch crystal which do not suffer from the drawbacks identified above. This object is achieved by a method and by a crystal as well as a watch according to the appended claims.

[0005] The invention relates to a method for marking a sapphire watch crystal, by the interaction between a laser beam and the sapphire. The beam is focused on a point inside the ice and the interaction is such that it generates a rectilinear opaque zone which is parallel to the upper surface of the ice or perpendicular to said surface. The orientation of the opaque area depends on the operating mode applied. Depending on the hatching mode of operation, the beam is scanned along one or more linear paths, generating opaque lines inside the ice, which are parallel to the upper surface. The perforation mode of operation generates distinct opaque zones, obtained by a discontinuous operation of the beam on a number of juxtaposed points. According to this latter mode of operation, the opaque zones extend in the direction perpendicular to the upper surface of the ice.

[0006] Other characteristics and advantages of the present invention will appear from the following description of preferred embodiments, presented by way of non-limiting example with reference to the accompanying drawings. A number of ranges of parameter values are identified in the detailed description and in the claims. The limits of these ranges are included in the ranges in question.

Brief description of the figures

[0007] <tb> <SEP> FIG. 1 represents two sections in a sapphire crystal according to the invention, during the marking of the crystal according to a first mode of operation, called the hatching mode, as well as a specific detail. <tb> <SEP> FIG. 2 represents the marking according to the first mode of operation, in which two hatching steps are carried out in a crossed manner. <tb> <SEP> FIG. 3 represents two sections in a sapphire crystal according to the invention, during the marking of the crystal according to a second operating mode, called the perforation mode. <tb> <SEP> Figure 4 shows a detail of the sapphire crystal, marked according to the perforation marking method.

Detailed description of embodiments of the invention

In the two modes of operation according to the invention, illustrated respectively in Figures 1 and 3, a transparent sapphire watch crystal 1 is marked by a laser beam 4 oriented perpendicular to the upper surface 2, and focused on a point 5 inside the mirror.

[0009] In the examples shown but not limited to, the mirror 1 has an upper surface 2 and a lower surface 3 which are essentially plane and parallel to one another. According to the first mode of operation (FIG. 1), the beam 4 is scanned over part of the surface of the ice 1, following a number of juxtaposed linear paths, thus carrying out a marking by hatching. The distance 'a' between the focal point 5 of the laser and the upper surface 2 remains essentially fixed during the scan. The parameters applied to achieve the hatching are such that each sweep along a linear path will generate an opaque zone 6 inside the sapphire, the zone being essentially rectilinear and perpendicular to the direction of the beam (or parallel to the upper surface of the sapphire). ice cream). The detail in Figure 1 shows that the opaque zone 6 is characterized by its width D and its height H.

[0010] According to a preferred embodiment, these dimensions can be controlled as a function of the power of the laser and of the design to be engraved. The height H is of the order of magnitude from a micrometer up to a few hundred micrometers, for example up to 200 micrometers. Without being bound by any theory, it is believed that each opaque area is made up of a plurality of microcracks which extend in the direction of the scan path.

The main parameter which makes it possible to obtain the areas 6 rectilinear and parallel to the upper surface 2 of the ice, is the scanning speed. This speed is considerably higher than the speeds applied for etching by removing material from a sapphire crystal.

[0012] Preferably, the scanning speed according to the invention is between 2m / s and 3m / s, for example 2.5 m / s. In addition, it is necessary for the laser to operate in an applicable regime for engraving a watch crystal. Table 1a gives preferred values for the operational parameters of the laser applied in the first mode of operation: <tb> Pulse length <SEP> 200 fs - 10 ps <tb> Wavelength <SEP> 500 nm - 1200 nm <tb> Pulse frequency <SEP> 200 kHz - 1.5 MHz <tb> Laser energy <SEP> 1 µJ - 20 µJ

Table 1a

Table 1b gives preferred values of a number of geometric parameters applied in the first mode of operation: <tb> Distance between two adjacent opaque zones 6 (measured between the central lines of zones 6 <SEP> 10 µm - 20 µm <tb> Depth of laser focal point 5 (distance 'a' in figure 1) <SEP> 0.5 mm - 1 mm

Table 1b

According to a specific embodiment of the first mode of operation, a second hatching step is performed in a direction transverse to the direction of the first step. FIG. 2 represents the partial result of two cross hatching steps in which the two series of opaque lines 6a and 6b formed by the respective steps are perpendicular to each other. The second hatching step is performed with the focal point 5 of the laser located at the same depth 'a' as the first step. Preferably, the distance between two adjacent lines 6a or 6b is equal during the two steps. The angle between the direction of lines 6a and 6b is preferably between 30 ° and 90 °.

The hatching mode of operation can be used to create a three-dimensional shape, by performing the hatching at several levels in the material. This process begins with a first hatching step (single or crossed), focusing the laser at a distance a1from the upper surface 2, followed by one or more consecutive steps, at distances a2, a3, ... which are progressively lower at the initial distance a1. In this way, a 3D shape is obtained which includes several layers. The distance between two layers is chosen so as to avoid a partial superposition of two adjacent layers.

According to a second mode of operation, illustrated in Figure 3, a laser beam 4 is focused consecutively and each time for a defined opening time, on a series of juxtaposed points 5 located inside of a sapphire watch crystal 1, at a fixed distance 'a' from the upper surface 2 of the crystal. This method, known as the “perforation operating mode”, is therefore similar to the method described in document WO-A-99/21061. However, the method parameters are configured so that the defects generated by the impact of the laser are different from the previous methods.

According to the method of the invention, the interaction between the laser and the sapphire generates an opaque rectilinear zone 10 which extends in the direction of the beam, ie perpendicular to the upper surface 2 of the crystal 1. As shown in detail in FIG. 4, each zone 10 is defined by its diameter D and by its height H. These dimensions can be controlled as a function of the power of the laser and as a function of the opening time of the laser applied for each point. . The diameter D is preferably of the order of magnitude of a micrometer, for example between 1 and 30 micrometers. The height H can for example be between 1 and a few hundred micrometers. As for the first mode of operation, and without being bound by any theory, it is estimated that each zone 10 consists of a plurality of microcracks which extend in the direction of the laser beam 4. Unlike the shape defects. stars described in document WO-A-99/21061, the zones 10 represent a shape well defined by the dimensions D and H, which are moreover controllable by the parameters of the laser. This allows more efficient control of the distance between two points of impact, as well as the thickness of a marking.

Table 2a groups together the laser parameters which are preferably applicable to achieve marking according to this second mode of operation. <tb> Pulse length <SEP> 200 fs - 10 ps <tb> Wavelength <SEP> 500 nm - 1200 nm <tb> Pulse frequency <SEP> 200 kHz - 1.5 MHz <tb> Laser energy <SEP> 1 µJ - 20 µJ <tb> Laser opening time <SEP> 0.01 ms - 0.1 ms

Table 2a

Table 2b gives preferred values of a number of geometric parameters applied in the second mode of operation: <tb> Distance between two adjacent zones 10 (measured between the centers of two zones <SEP> 0.01 mm - 0.03 mm <tb> Depth of the laser focal point (distance 'a' in figure 3) <SEP> 0.5 mm - 1 mm

Table 2b

Analogously to the first mode of operation, a 3-dimensional marking can be obtained by carrying out the perforation marking at several levels in the thickness of the glass 1. This process begins with a first perforation step, in focusing the laser at a distance a1 from the upper surface 2, followed by one or more consecutive steps, at distances a2, a3, ... which are progressively smaller than the initial distance a1. In this way, a 3D shape is obtained which consists of several layers. The distance between two layers is chosen so as to avoid a partial superposition of two adjacent layers.

The method according to the invention also works when an antireflection layer, for example a layer of MgF2 or SiO2, is present on the upper surface 2 of the ice.

[0022] The invention also relates to a sapphire watch crystal marked by any one of the methods described above, as well as a watch provided with this crystal.

Claims (19)

1. Method for marking a sapphire watch crystal (1), the crystal having a flat upper surface (2) and a lower surface (3), using a laser beam (4) directed perpendicularly to the upper surface (2) ), and focused at a point (5) inside the material of the crystal (1), characterized in that the interaction between the laser and the sapphire at the focal point (5) generates at least one zone opaque rectilinear (6,10) which extends in a direction parallel to the upper surface (2) or in a direction perpendicular to said upper surface (2). 2. The method of claim 1, wherein the beam (4) is scanned relative to the ice (1), following a linear path, while remaining focused on a point (5) at a fixed distance from the lens. upper surface (2) of the lens, and wherein said rectilinear opaque area (6) is substantially parallel to the upper surface (2) of the lens (1). 3. The method of claim 2, wherein the beam (4) follows a plurality of juxtaposed paths, so as to mark a first portion of the ice by a first hatching step. 4. The method of claim 3, wherein a second hatching step is performed in the transverse direction relative to the first step, the second step being performed on a second portion of the ice which at least partially covers the first portion, the second hatching step being carried out at the same distance from the upper surface (2) as the first hatching step. 5. The method according to any one of claims 3 or 4, wherein several hatching operations, comprising one or two stages, are carried out at successive levels in the material, so as to obtain a 3-dimensional marking, and in which the rectilinear opaque zones (6) formed at two adjacent levels are separated from each other. 6. The method according to any one of claims 2 to 5, wherein the scanning speed is between 2 m / s and 3 m / s. 7. The method according to any one of claims 2 to 6, wherein a number of laser parameters are defined as follows: <tb> Pulse length <SEP> 200 fs - 10 ps <tb> Wavelength <SEP> 500 nm - 1200 nm <tb> Pulse frequency <SEP> 200 kHz - 1.5 MHz <tb> Laser energy <SEP> 1 µJ - 20 µJ 8. The method according to any one of claims 2 to 7, wherein a number of geometric parameters are defined as follows: <tb> Distance between two adjacent linear opaque areas <SEP> 10 µm - 20 µm <tb> Laser focal point depth <SEP> 0.5 mm - 1 mm 9. The method of claim 1, wherein the laser beam (4) is focused consecutively at a plurality of juxtaposed points (5), and located at the same distance from the upper surface (2), and wherein the opaque area rectilinear (10) is generated at each of the points, said areas extending in the direction perpendicular to the upper surface (2). 10. The method of claim 9, wherein several marking steps are performed at successive levels in the material, so as to obtain a 3-dimensional marking, and wherein the opaque rectilinear areas (10) formed at two adjacent levels are separated from each other. 11. The method according to any one of claims 9 and 10, wherein the values of a number of parameters of the laser are defined as follows: <tb> Pulse length <SEP> 200 fs - 10 ps <tb> Wavelength <SEP> 500 nm - 1200 nm <tb> Pulse frequency <SEP> 200 kHz - 1.5 MHz <tb> Laser energy <SEP> 1 µJ - 20 µJ <tb> Laser opening time <SEP> 0.01 ms - 0.1 ms 12. The method according to any one of claims 9 to 11, in which a number of geometric parameters are defined as follows: <tb> Distance between two adjacent points <SEP> 0.01 mm - 0.03 mm <tb> Depth of the laser focal point (distance 'a' in figure 3) <SEP> 0.5 mm - 1 mm 13. The method according to any preceding claim, wherein the upper surface (2) of the lens is provided with an anti-reflective layer. 14. Sapphire watch crystal (1) provided with a marking inside the crystal, the crystal having a flat upper surface (2) and a lower surface (3), in which the marking comprises at least one zone opaque rectilinear (6,10) which extends in a direction parallel to the upper surface (2) or in a direction perpendicular to said upper surface (2). 15. Watch crystal (1) according to claim 14, wherein the marking comprises one or more opaque rectilinear areas (6) juxtaposed, oriented in a direction parallel to the upper surface (2), and at a fixed distance from said surface. upper (2). 16. Watch crystal (1) according to claim 15, wherein the marking comprises two series of juxtaposed rectilinear opaque areas (6a, 6b), at the same distance from the upper surface (2), oriented transversely with respect to one another. to the other and in which the second series at least partially covers the first series. 17. Watch crystal (1) according to claim 14, wherein the marking comprises in a dotted manner a plurality of juxtaposed rectilinear opaque areas (10) which extend in the direction perpendicular to the upper surface (2) of the crystal ( 1). 18. Watch crystal (1) comprising a 3-dimensional marking, comprising several layers, in which each layer consists of a marking according to claim 15 or according to any one of claims 16 and 17. 19. Watch comprising a sapphire crystal (1) according to any one of claims 14 to 18.