METHOD FOR OBTAINING MARKED GLASS PLATES

Abstract

A method for obtaining a glass plate marked on a portion of one of its faces with code-forming symbols, includes a stage of etching the symbols by laser radiation on a glass sheet obtained by floating on a bath of molten tin, the etching being carried out on the face which has been in contact with the bath of molten tin.

Claims

1. A method for obtaining a glass plate marked on a portion of one of its faces with code-forming symbols, comprising a stage of etching said symbols by means of laser radiation on a glass sheet obtained by floating on a bath of molten tin, said etching being carried out on the face which has been in contact with said bath of molten tin.

2. The method as claimed in claim 1, such that the laser radiation is ultraviolet radiation.

3. The method as claimed in claim 2, such that the ultraviolet radiation results from a laser chosen from: excimer lasers, lasers comprising a YAG (yttrium aluminum garnet) or YVO.sub.4 matrix coupled to a frequency tripler or quadrupler, fiber lasers doped with ytterbium.

4. The method as claimed in claim 1, comprising, prior to the etching stage, a stage of floating on a bath of molten tin in order to obtain said glass sheet, followed by a stage of annealing said glass sheet, followed by a cutting stage, the etching stage being carried out during the annealing stage or between the annealing stage and the cutting stage.

5. The method as claimed in claim 1, wherein the etching stage is carried out after at least one cutting stage, on glass plates of finished sizes.

6. The method as claimed in claim 1, such that the symbols are at at most 10 mm from an edge face of the glass sheet or of the glass plate.

7. The method as claimed in claim 1, such that the symbols exhibit a mean size of between 50 and 180 m.

8. The method as claimed in claim 1, such that the code is a two-dimensional code.

9. A glass plate obtained by the method of claim 1, formed from a glass sheet obtained by floating on a bath of molten tin, said plate being marked with code-forming symbols etched by means of laser radiation on a portion of the face which has been in contact with said bath of molten tin.

10. The glass plate as claimed in claim 9, such that the symbols are at at most 10 mm from an edge face of the plate.

11. The glass plate as claimed in claim 9, such that the symbols exhibit a mean size of between 50 and 180 m.

12. The glass plate as claimed in claim 9, such that the code is a two-dimensional code.

13. A method for reading, via the edge face, code-forming symbols marked on a glass plate as claimed in claim 9.

14. The method as claimed in claim 3, wherein the YAG (yttrium aluminum garnet) or YVO.sub.4 matrix is doped with neodymium or with ytterbium.

15. The method as claimed in claim 6, such that the symbols are at at most 7 mm from an edge face of the glass sheet or of the glass plate.

16. The method as claimed in claim 7, such that the symbols exhibit a mean size of between 60 and 160 m.

17. The method as claimed in claim 8, wherein the code is a Datamatrix code.

18. The glass plate as claimed in claim 10, such that the symbols are at at most 7 mm from an edge face of the plate.

19. The glass plate as claimed in claim 11, wherein the symbols exhibit a mean size of between 60 and 160 m.

20. The glass plate as claimed in claim 12, wherein the code is a Datamatrix code.

Description

[0039] FIGS. 1 and 2 are photographs of codes displayed via the edge face, respectively for a comparative example and for an example according to the invention.

[0040] A sheet of clear soda-lime-silica float glass, of the type sold by the applicant company under the Planiclear name, was subjected to irradiation by means of a UV lamp (wavelength of 254 nm), in order to identify the tin face of the sheet.

[0041] In an example according to the invention, a Datamatrix code was subsequently etched on the tin face of the sheet, by means of a pulsed laser emitting ultraviolet radiation, more specifically a Nd:YVO.sub.4 laser pumped using a laser diode and combined with a frequency tripler, so as to produce radiation with a wavelength of 355 nm. The code, with a total size of 3*3 mm.sup.2, is formed of circular points with a diameter ranging from 50 to 120 m, the points closest to the edge face being located at a distance of 2 mm from the latter.

[0042] In this example, the etching was carried out on the glass sheet while it was in rectilinear movement at a rate of 18 meters per minute.

[0043] In a comparative example, the same code was etched in the same way but on the atmosphere face of the glass sheet.

[0044] The codes were subsequently read via the edge face by means of a camera under an angle of approximately 30 with respect to a normal to the edge face.

[0045] The image taken by the camera in the case of the comparative example is represented in FIG. 1. It may be seen that the quality of the image is mediocre, the points forming the code being in places discernible with difficulty from one another. It would appear that this reduced visibility of the points is due to the presence of microcracks which propagate between the points, which microcracks are invisible during face reading but which scatter the light so as to affect the reading via the edge face. The reading of the code is then difficult and can even result in reading errors.

[0046] The image taken by the camera in the case of the example according to the invention is represented in FIG. 2. It is seen here that the image is of good quality, the points being well separated from one another. The reading of the code is then greatly facilitated and the risk of reading error minimized.

[0047] On the other hand, it should be noted that, seen through the face, the codes of the example according to the invention and of the comparative example do not exhibit visible differences. To the naked eye, the etching appears slightly more obvious when the etching was carried out on the atmosphere face but, in the event of reading the code through the face, no difference is observed.

[0048] Similar results were obtained in other etching tests, carried out on static glass plates.