AU701407B2 - Method for laser marking a glass object, and resulting marked glass object, particularly a mould for an ophthalmic lens - Google Patents

Description

WO 96/32221 PCT/FR96/00533 1 "Method for laser marking a glass object, and resulting marked glass object, particularly a mold for an ophthalmic lens" The present invention is generally concerned with the marking of a glass object of any kind, for example to apply to it a serial number, a reference or any other inscription.

The object can be a container or a windshield, for example.

However, the present invention is more particularly, although not necessarily exclusively, concerned with marking molds used to mold synthetic material ophthalmic lenses.

To identify these molds, and thus to enable them to be traced, in particular during a process of fabrication of ophthalmic lenses, it is necessary to mark them with all the required information, in encoded form or otherwise.

One proposal is to print them, for example using a cement applied by offset printing, i.e. using a transfer stamp, and thereafter annealed by heating.

A drawback of a method of this kind is its lack of flexibility in use, given that it is sometimes desirable to be able to change the mark or pattern to be printed quickly.

Furthermore, the mark obtained necessarily has relatively large dimensions so that, even if it is applied to the edge of a mold, in projection it necessarily encroaches upon at least part of the active area of the mold.

The cement employed is in practise usually opaque to ultraviolet radiation.

Thus in this case the mark can be an impediment to the process of fabricating an ophthalmic lens if the polymerization of the corresponding synthetic material 7-; i)

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2 WO 96/32221 PCTIFR96/00533 2 implies exposure to such radiation.

Another proposal is to use an etching process, more particularly a laser etching process, to reduce the dimensions of the mark obtained.

An "excimer" type laser can be used for this, for example, but a laser of this kind, which attacks the glass by sublimation, is heavy, bulky and costly.

It is also possible, and more practical, to use a C02 type laser, but with a laser of this kind the glass is chipped away and, if not properly controlled, this can lead to the formation of microcracks.

Finally, it is possible to use a YAG type laser which is as practical and as economic as a C02 type laser but does not have the disadvantages of the latter.

In this case, the effect on the glass is similar to a surface melting leading to simple frosting.

However, the glass being transparent at the A wavelength of the corresponding laser beam, the latter must be caused to interfere with a layer of an appropriate material applied for this purpose to the surface of the glass to be treated.

An etching process of the above kiild is described in French patent application n 92 05644 of 7 May 1992, publication number 2 690 862.

In practise, in the above French patent application, the material of the layer employed i) opaque at the wavelength of the laser beam.

This layer has a merely passive role in regard to the glass, transferring to the latter the heat due to the focusing of the laser beam, which is sufficient to raise the temperature locally to the value needed to obtain the required melting.

The major drawback of an etching process of the above kind concerns the lack of contrast in the mark ,1 obtained, which in practise makes subsequent reading of the WO 96/32221 PCT/FR96/00533 3 mark by means of an automatic reading device impossible.

A general aim of the present invention is to obtain an additional advantageous benefit from the layer of material employed in order to improve the conditions of use of the mark obtained.

To be more precise, the present invention consists in a method of marking a glass object of the kind in which a layer of a material is applied to the surface of said glass object and a laser beam is caused to interfere with it, characterized in that the material of the layer is a material capable of reacting with the glass; it also consists in any glass object and in particular any mold including at least locally a mark obtained by application of the above method.

The material of the layer employed is preferably a material capable of physical reaction with the glass, to be more precise a material capable of diffusing into the latter.

It is a cement, for example.

Be this as it may, by virtue of the reaction that occurs between this material and the glass, the etched mark obtained advantageously has a degree of coloration.

In other words, in accordance with the invention, to obtain the required mark, an etching operation that assures a permanent mark by mechanical means, increasing its resistance to abrasion and to chemical attack, and therefore its durability, is advantageously associated with a coloring operation which, by increasing its contrast, facilitates its subsequent reading and makes the latter more accurate.

Particularly favorable results are obtained when, in contrast to what is described in French patent application no 92 05644 mentioned hereinabove, the material chosen for the layer employed is a material at least in part permeable to the laser beam and the laser beam I C- ::11 5 WO 96/32221 PCT/FR96/00533 impinges directly on this layer, i.e. on the side of the latter opposite to the object to be marked.

As an alternative to this, however, the laser beam can also impinge on the material of the layer through the object.

The features and advantages of the invention will emerge from the following description given by way of example with reference to the accompanying diagrammatic drawings, in which: figure 1 is a view in axial section of a glass object to be marked by the method of the invention; figure 2 shows part of figure 1 to a larger scale, illustrating a first embodiment of the marking method of the invention; figure 3 is a fragmentary view of the marked glass object, to the same scale as figure 2; figure 4 is a view analogous to that of figure 2 for a second embodiment of the marking method of the invention.

By way of example, these figures show the situation in which the glass object 10 to be marked is a mold adapted to form, with a mold 10' of the same type and a seal 11 disposed at the periphery of the combination, a molding cavity 12 for molding an ophthalmic lens.

The corresponding arrangements are well known in themselves and are not relevant in themselves to the present invention, so they will not be described in more detail here.

Suffice to say that the glass object 10 is in the general form of a domed disk of substantially uniform thickness, the peripheral contour 13 of which is circular, for example, with an inside face 14A on the same side as the molding cavity 12 and an outside face 14B on the opposite side.

The inside face 14A is concave and the outside face i i k ,r 4i6 WO 96/32221 PCT/FR96/00533 14B is convex, for example.

Be this as it may, the aim is to mark this glass object 10, in other words to apply a mark 15 to it, in order to identify it.

The mark 15 is preferably applied to the external face 14B of the glass object 10, in the immediate vicinity of its peripheral contour 13, and it must have the smallest possible dimensions so as not to encroach in projection on its active area.

The mark 15 is applied by an etching process, in a manner known in itself, and to this end a layer 16 of a material 17 is applied to the external face 14B of the glass object 10. A laser beam 18, i.e. radiation emitted by a laser 19 and focused at a point 20 on the outside face 14B by a control device 21 enabling deviation to be varied at will along the trace of the mark 15 to be obtained, is caused to interfere with the material 17.

The corresponding arrangements are also well known in themselves and therefore not relevant to the invention, so they will not be described here.

Suffice to say that, in practise, the laser 19 employed is preferably a YAG type laser having a wavelength equal to 1.06 pm.

In accordance with the invention, the material 17 of the layer 16 is a material 17 capable of reacting with the glass.

A material 17 capable of diffusing into the glass is preferably chosen.

It is a cement, for example, and to be more precise a cement including a mixture of copper salts and at least one other metallic salt.

The copper salts can be sulfates and/or phosphates, for example, and by way of other metallic salts they can be associated with an oxide or a phosphate of silver and/or various other metallic oxides.

WO 96/32221 PCT/FR96/00533 6 The material 17 employed is preferably chosen to be at least partially permeable to the laser beam 18, for example.

Accordingly, and as shown in figure 2, it is possible for the laser 19 to impinge directly on the layer 16, i.e. from the side of the layer 16 opposite that in contact with the glass object 10 to be treated.

The material 17 employed is mixed with an oil such as a paraffin oil for its application to the glass object 10, for example.

It can be applied using a brush or by any other application or printing means.

When it is irradiated by the laser beam 18, a temperature increase occurs at the corresponding focusing point 20 which causes the required etching by surface melting, in practise in the form of simple frosting, and coloration within the corresponding recesses by migration (diffusion) of the material 17 into the glass.

The control device 21 traces the mark 15 to be obtained by deflecting the laser beam 18.

Of course, it can be controlled to this end by a computer, not shown, programmed accordingly.

If required, the mark 15 can be encoded.

For example, it can be encoded in the forms of rows and columns of dots, using a matrix type code.

Be this as it may, each etched dot obtained has an overall width in the order of 0.1 mm and an overall depth of 5 im.

With a matrix type code it is possible to obtain a mark 15 having 21 rows and 21 columns within a square having a side length of 3 mm.

In other words, the mark 15 does not encroach more than 3 mm onto the external face 14B of the glass object Of course, after the intervention of the laser 19 4-

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I _I WO96/32221 PCT/FR96/00533 7 the layer 16 of material 17 is washed off, for example using a jet of hot water at moderate temperature, in the order of 601C, and at a relatively low pressure, in the order of about 4 bars.

This leaves just the required mark 15, fixed into the external face 14B of the glass object 10, as shown in figure 3.

In the alternative embodiment shown in figure 4 the laser beam 18 impinges on the side of the layer 16 in contact with the glass object The laser beam 18 therefore passes through the glass object The material 17 of the layer 16 can in this case be opaque to the laser beam 18 and it is preferably effectively opaque to the latter.

Of course, the present invention is not limited to the embodiments described and shown, but encompasses any variant execution thereof.

In particular, the material employed for the layer applied to the glass object to be marked could be capable of chemical reaction with the glass, provided that this chemical reaction leads to coloratior of the etching obtained.

Further, it goes without saying that, as previously mentioned, the field of application of the invention is not limited to marking molds for molding ophthalmic lenses but to the contrary extends equally well to marking any glass object.

Claims (8)

1. Method of marking a glass object by etching it, of the kind in which a layer of a material is applied to the surface of said glass object and a laser beam is caused to interfere with it, characterized in that the material of the layer is a material capable of reacting with the glass and adapted to produce coloration within the etching obtained.

2. Method according to claim 1 characterized in that the material of the layer is a material capable of diffusing into the glass.

3. Method according to claim 2 characterized in that the material of the layer is a cement.

4. Method according to claim 3 characterized in that the material of the layer is a cement including a mixture of copper salts with at least one other metallic salt. Method according to any one of claims 1 to 4 characterized in that the laser beam impinges directly on the layer.

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6. Method according to any one of claims 1 to 4 characterized in that the ,laser beam impinges on the layer through the glass object.

7. Method according to any one of claims 1 to 6 characterized in that the laser beam is emitted by a YAG type laser.

8. Glass object including at least locally a mark characterized in that its mark is formed in accordance with any one of claims 1 to 7. DATED this 6th day of November, 1998. ESSILOR INTERNATIONAL (COMPAGNIE GENERALE D'OPTIQUE) WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 ~AUSTRALIA (DOC 23 AU5504896.WPC IAS/KMH/ML) I r lU^, I