Method for marking on a clay-based ceramic part

Abstract

Method for marking on a ceramic piece (1) based on clay, comprising a laser marking operation implementing a marking by means of a laser (2) of a pattern (3) on the raw or softened ceramic piece (1), followed by a final firing operation of the ceramic piece (1) after the laser marking operation to obtain the ceramic piece (1) fired and marked with the pattern (3), where the laser marking operation comprises a laser ablation step followed by a selective laser sintering step in the engraving obtained at the end of the laser ablation step. The invention finds a preferred, and non-limiting, application for decorating or personalizing a ceramic piece used in the fields of tableware, kitchenware or decorative items.

Description

[Technical field]

[0001] The invention relates to a method of marking on a clay-based ceramic part.

[0002] It relates more particularly to a method comprising a laser marking operation implementing marking by means of a laser of a pattern on a ceramic piece based on clay.

[0003] The invention finds a preferred, and non-limiting, application for decorating or personalizing a ceramic piece used in the fields of tableware, cooking or decorative items. [State of the art]

[0004] In a known manner, a ceramic part can be marked using a laser, as described for example in document EP1040017 which implements marking by selective laser sintering, and in document US5554335 which implements marking by laser ablation.

[0005] However, this laser marking is applied to a fired ceramic piece, that is to say a ceramic piece which has undergone final firing, typically between 900 and 1400 degrees Celsius, so as to have a finished ceramic piece, ready for use; and it is this fired ceramic piece which is the subject of laser marking.

[0006] The state of the art can also be illustrated by the teachings of documents WO2020 / 179699, WO2016 / 083909 and ES2154237, which propose carrying out marking by laser ablation on a raw, non-clay ceramic part.

[0007] Although these laser marking processes on fired or raw ceramic pieces are generally satisfactory, there is a need to improve the fineness of the marking, particularly on clay-based ceramic pieces, in other words to have a pattern with fine, clean lines and possibly also with material effects. [Summary of the invention]

[0008] To this end, the invention proposes a method of marking on a clay-based ceramic part, comprising a laser marking operation implementing a marking by means of a laser of a pattern on the raw or softened ceramic part, followed by a final firing operation of the ceramic part after the laser marking operation to obtain the fired ceramic part marked with the pattern.

[0009] Furthermore, the laser marking operation includes: at least one laser ablation step implementing one or more passes of the laser over a surface so as to remove material from the surface to form an etching defining the pattern; and at least one selective laser sintering step, carried out after the laser ablation step, and implementing one or more passes of the laser in the etching obtained at the end of the laser ablation step, so as to locally sinter the internal surface of the etching.

[0010] Thus, the process consists of carrying out laser marking on a ceramic piece which is raw or softened, in other words a ceramic piece which has not yet undergone final firing; a raw ceramic piece being a ceramic piece which has not undergone any firing, and a softened ceramic piece being a ceramic piece which has undergone pre-firing (also called first non-final firing or half-firing) the objective of which is mainly to dehydrate the softened ceramic piece and which takes place at a pre-firing temperature lower than the firing temperature which will be carried out later during the final firing operation.

[0011] This process allows for the obtaining of unique finishes of the pattern, which cannot be achieved with laser marking on fired or raw ceramic pieces with simple laser ablation, and at the same time are compatible with current food contact standards.

[0012] First, the laser ablation step allows material to be removed from the surface of the ceramic part, raw or hardened, based on clay and, secondly, what is particularly advantageous, is the selective laser sintering step which follows the laser ablation and which is implemented in the engraving obtained by the laser ablation.

[0013] Indeed, selective laser sintering involves passing the laser over the internal surface of the engraving to locally sinter this internal surface, and thus change the surface condition. This change in surface condition obtained thanks to localized selective sintering in the engraving, contributes to obtaining, after firing the clay-based ceramic part, a precise and unique finish, with clean and fine lines; which cannot be obtained with simple laser ablation followed by firing.

[0014] It is in fact observed that, the cooking, which occurs after the localized laser sintering in the engraving, makes it possible to reveal the marking and in particular to obtain rounded, well-defined edges for the lines of the pattern, in other words to round off the edges of the marking previously sintered by the laser sintering; which contributes to obtaining fine and precise markings.

[0015] It should be noted that the selective laser sintering step concerns selective sintering in the sense that the laser sintering takes place in selected areas, namely in the etching obtained at the end of the laser ablation step.

[0016] This selective sintering is therefore to be distinguished from the final firing operation of the ceramic piece which leads to a global sintering of the entire ceramic piece. Also, it is quite clear that in the engraving, and therefore on the pattern, two consecutive sinterings are carried out, the first corresponding to the selective sintering and the second corresponding to the final firing.

[0017] In a first embodiment, the laser marking operation is carried out on the raw or rough ceramic part which is in a raw state, i.e. without a coating layer. Thus the laser marking is carried out directly on the raw surface of the raw or rough ceramic part.

[0018] In a second embodiment, the method comprises, before the laser marking operation, a covering operation implementing a covering of the ceramic part with at least one coating layer, so that the laser marking operation is implemented on the at least one coating layer which covers the raw or roughened ceramic part.

[0019] In this second embodiment, the ceramic part is covered by one or more coating layers, including an outer coating layer and possibly one or more sub-coating layers. Thus, the laser marking is carried out on the outer coating layer, and possibly in the sub-coating layer(s), or even optionally until reaching the surface of the ceramic part.

[0020] According to one feature, the coating operation implements an enameling step and / or an engobing step, such that the at least one coating layer comprises at least one enameling layer and / or at least one engobing layer.

[0021] According to a first embodiment, the laser marking operation comprises at least one laser ablation step implementing one or more passes of the laser over a surface so as to remove material from the surface to form an engraving defining the pattern.

[0022] According to one possibility, the laser ablation step is implemented on the surface of the green or rough ceramic part which is in the raw state, in order to form the etching directly in the green or rough ceramic part.

[0023] Alternatively, the laser ablation step is performed on the surface of the at least one coating layer to form the etching at least in said at least one coating layer.

[0024] According to one variant, the at least one coating layer comprises a single coating layer, and the laser ablation step is implemented to form the etching over at least the entire thickness of said single coating layer by exposing the ceramic part under said single coating layer.

[0025] According to another variant, the at least one coating layer comprises at least two superimposed coating layers comprising an outer coating layer and an undercoating layer, and the laser ablation step is implemented to form the etching: over at least the entire thickness of the at least two superimposed coating layers by exposing the ceramic part under said at least two superimposed coating layers; or over the entire thickness of the outer coating layer by exposing the undercoating layer under said outer coating layer.

[0026] This makes it possible to choose which surface will be exposed, either that of the undercoat or one of the undercoats or that of the ceramic piece, thus making it possible to create original aesthetic effects, such as variations in shade.

[0027] In a particular embodiment, the method comprises, before the laser marking operation, an operation of coloring the raw or roughened ceramic piece in order to be colored in the mass.

[0028] In an advantageous embodiment, the laser used during the laser marking operation is a pulsed laser.

[0029] Indeed, this pulsed technology is particularly suitable for working on a ceramic piece made from clay, raw or softened, in terms of precision and fineness of marking, whether by ablation or selective sintering.

[0030] Advantageously, during the laser marking operation, the laser is operated with a power between 20 and 50 watts.

[0031] This laser power is well suited for implementing the process, as it promotes precision without harming the ceramic material.

[0032] In a particular embodiment, during the laser marking operation, the laser is operated at a wavelength in the infrared range, and for example at 1064 nm.

[0033] Alternatively, during the laser marking operation, the laser is operated with a pulse frequency between 20 and 200 kHz.

[0034] Alternatively, during the laser marking operation, the laser is moved with a movement speed of between 100 and 5000 millimeters per second, and for example between 300 and 3000 millimeters per second.

[0035] This speed of movement promotes the finesse of the marking.

[0036] According to one characteristic, the raw or rough ceramic piece includes a mass percentage of clay excluding kaolin which is less than 10%.

[0037] According to another characteristic, the final firing operation of the ceramic piece is carried out at a maximum firing temperature which is between 900 and 1400 degrees Celsius, and for example between 1000 and 1350 degrees Celsius. [Brief description of the figures]

[0038] Other characteristics and advantages of the present invention will appear on reading the detailed description below, of several non-limiting examples of implementation, made with reference to the appended figures in which: [ Fig 1 ] is a schematic view of four steps of a marking process implementing laser ablation directly in the green or annealed ceramic part, to form an etching in the green or annealed ceramic part, then selective laser sintering in the etching, and finally final firing; [ Fig 2 ] is a schematic view of five steps of a marking process using laser ablation to form an etch in a coating layer exposing the raw or roughened ceramic part, then selective laser sintering in the etch, and finally final firing; [ Fig 3] is a schematic view of five steps of a marking process involving laser ablation in an outer coating layer to form an etch exposing an undercoating layer, before selective laser sintering in the etch, and finally final firing; [ Fig 4 ] is a schematic view of five steps of a marking process involving laser ablation in an outer coating layer and in an undercoating layer to form an etching exposing the green or roughened ceramic part, before selective laser sintering in the etching, and finally final firing; [ Fig 5 ] is a schematic view of two photographs of an example of a ceramic part having undergone a laser ablation step, without the selective laser sintering step; [ Fig 6 ] is a schematic view of two photographs of an example of a ceramic piece having undergone the process of the Figure 2, with the laser ablation step followed by the selective laser sintering step. [Detailed description of several embodiments of the invention]

[0039] The detailed description which follows relates to several embodiments of the marking method on a ceramic part 1 based on clay, and more precisely which comprises a mass percentage of clay excluding kaolin which is less than 10%.

[0040] These embodiments all have in common the following: a laser marking operation implementing a marking by means of a laser 2 of a pattern 3 on the ceramic part 1 which is raw or softened; and a final firing operation of the ceramic part 1, carried out after the laser marking operation, to obtain the ceramic part 1 fired and marked with the pattern 3.

[0041] Furthermore, these embodiments also all have in common that the laser marking operation on the ceramic part 1 which is raw or roughened, comprises: a laser ablation step implementing one or more passes of the laser 2 over a surface so as to remove material from the surface to form an etching 20 defining the pattern 3; and a selective laser sintering step, carried out after the laser ablation step and before the final firing, and implementing one or more passes of the laser 2 in the etching 20 obtained at the end of the laser ablation step, so as to locally sinter the internal surface of the etching 20.

[0042] Thus, the laser marking operation (which combines laser ablation and selective laser sintering) is carried out on a ceramic part before final firing, which limits the effects of laser treatment on the technical characteristics.

[0043] Indeed, laser ablation on a fired ceramic part can lead to the appearance of microcracks in this fired part. In the case of the method described in the present application, this defect is limited by the fact that the ceramic part is treated by the laser before its final firing, and the selective laser sintering contributes to modifying the surface state locally in the engraving so that, once the final firing is carried out, fine engraving lines are obtained. Similarly, if the fired ceramic part is glazed and / or engobed, the edges of the treated area may be irregular and have small chips, which deteriorates the aesthetics of the part. Carrying out the laser marking operation as described above on a glazed and / or engobed part before the final firing makes it possible to eliminate these defects while obtaining a very fine pattern.Indeed, during the final firing, the enamel layer and / or the engobing layer fuses, which causes the edges of the treated area to round off. When the enamel layer and / or the engobing layer fuses, it does not spread over the treated area, allowing for very fine marking.

[0044] In addition, this laser marking operation prior to firing allows, thanks to selective laser sintering, to modify or even fuse the components on the treated internal surface of the engraving (whether for the raw ceramic, for the enamel layer and / or for the engobing layer), thus resulting in a different behavior during firing. This difference in behavior thus allows the appearance of the pattern according to well-defined and clear contours. In the case of ceramic bodies containing a colorant, this selective laser sintering can generate a reaction of the colorant, which will react differently during firing, thus resulting in a modification of the color on the area treated by the laser.

[0045] During the laser marking operation, the laser 2 used is a pulsed laser which operates under the following conditions: a power between 20 and 50 watts; a wavelength in the infrared range, for example 1064 nm; a pulse frequency between 20 and 200 kHz; a movement speed between 100 and 5000 millimeters per second, for example 300 and 3000 millimeters per second.

[0046] In the processes of Figures 1 to 4 , the laser marking operation first comprises a laser ablation step consisting of a removal of material under the effect of the laser 2 to engrave the pattern 3.

[0047] In the realization of the Figure 1 , the raw or softened ceramic part 1 is provided in a raw state (step a)), i.e. without a coating layer, and the laser ablation step is carried out on the surface of the raw or softened ceramic part 1 which is in the raw state so as to form an engraving 20 on this surface of the ceramic part 1 (step b)).

[0048] In the realization of the Figure 2, the raw or roughened ceramic part 1 is provided in a raw state (step a)), then it is covered with a coating layer 4, which may be an enamel layer or an engobing layer (step b)), then the laser ablation step is carried out on the surface of the coating layer 4 so as to form an engraving 20 on this surface of the coating layer 4 by exposing the ceramic part 1 under this coating layer 4 (step c)).

[0049] In the realization of the Figure 3, the raw or roughened ceramic part 1 is provided in a raw state (step a)), then it is covered by two superimposed coating layers 41, 42 comprising an outer coating layer 41 and a coating sub-layer 42, which may be enamel layers or engobing layers (step b)), then the laser ablation step is carried out on the surface of the outer coating layer 41 so as to form an etching 20 exposing the coating sub-layer 42 (step c)).

[0050] In the realization of the Figure 4, the raw or roughened ceramic part 1 is provided in a raw state (step a)), then it is covered by two superimposed coating layers 41, 42 comprising an outer coating layer 41 and a sub-coating layer 42, which may be enamel layers or engobing layers (step b)), then the laser ablation step is carried out on the two coating layers 41, 42 so as to form an engraving 20 exposing the raw or roughened ceramic part 1 (step c)).

[0051] In the processes of Figures 1 to 4 , the laser marking operation comprises, following the laser ablation step, a selective laser sintering step implementing one or more passes of the laser located in the engraving 20 which was obtained at the end of the laser ablation step, so as to locally sinter the internal surface of the engraving 20 to define the pattern 3.

[0052] In the realization of the Figure 1, the selective laser sintering step (step c)) is implemented in the etching 20 carried out on this surface of the ceramic part 1 on the surface of the raw or softened ceramic part 1 so as to form a sintered part 10 of the ceramic part 1 inside this etching 20 (at the bottom and on the edges of the etching 20), and finally the final firing is implemented (step d)) to obtain the ceramic part 1 fired and marked with the pattern 3

[0053] In the realization of the Figure 2 , the selective laser sintering step (step d)) is implemented on the engraving 20 so as to form a sintered part 10 of the ceramic part 1 (at the bottom of the engraving 20) and sintered parts 40 of the coating layer 4 (at the edge of the engraving 20), and finally the final firing is implemented (step e)) to obtain the fired, enameled or engobed ceramic part 1, and marked with the pattern 3 defined by the engraving 20.

[0054] In the realization of the Figure 3 , the selective laser sintering step (step d)) is implemented on the etching 20 so as to form a sintered part 420 of the coating underlayer 42 (at the bottom of the etching 20) and sintered parts 410 of the outer coating layer 41 (at the edge of the etching 20), and finally the final firing is implemented (step e)) to obtain the fired, glazed or engobed ceramic part 1, and marked with the pattern 3 defined by the etching 20.

[0055] In the realization of the Figure 3, the selective laser sintering step (step d)) is implemented on the etching 20 so as to form a sintered part 10 of the ceramic part 1 (at the bottom of the etching 20) and sintered parts 412 of the outer coating layer 41 and of the undercoating layer 42 (at the edge of the etching 20), and finally the final firing is implemented (step e)) to obtain the fired, enameled or engobed ceramic part 1, and marked with the pattern 3 defined by the etching 20.

[0056] Figure 9 shows a ceramic piece made with black ceramic tinted throughout and covered with a coating layer which is here a white enamel layer, thus forming a ceramic piece glazed with a white enamel. Photograph a) shows the ceramic piece after a laser ablation step to reveal an engraving forming a logo and writing. This laser ablation treatment removes the enamel to reveal the black paste at the engraving. The ceramic piece then undergoes the final firing operation, at high temperature, which allows the enamel to vitrify, allowing it to round off the edges of the engraving, as visible in photograph b). It should be noted that the very fine markings "17" and "68" were covered by the enamel during the final firing. The process implemented for this example therefore does not include the selective laser sintering step.

[0057] On the Figure 6 a ceramic piece is visible made with a black ceramic tinted in the mass and covered with a coating layer which is here a layer of white enamel; for this example, the ceramic and the enamel used are identical to those of the example of the Figure 5 . The ceramic piece was also treated by laser ablation in order to reveal the black colored paste at the engraving level. In addition, so that the fine markings are not covered during the final firing, a selective laser sintering step is also carried out in the engraving. Photograph a) shows the ceramic piece after laser ablation and selective laser sintering, before the final firing, and no difference in fineness can be seen compared to the example in photograph a) of the Figure 5. The ceramic piece then undergoes the final firing operation, at high temperature, which allows the enamel to vitrify, except that this time it is observed that the enamel has vitrified without covering the finest markings, as visible in photograph b). The process implemented for this example of the Figure 5 corresponds to the process of the Figure 2 , and illustrates the fact that the selective laser sintering step in the engraving obtained at the end of the laser ablation step is particularly advantageous for obtaining a clean and fine marking of the desired pattern.

Claims

1. A method of marking on a ceramic part (1) based on clay, comprising a laser marking operation implementing a marking by means of a laser (2) of a pattern (3) on the raw or softened ceramic part (1), followed by a final firing operation of the ceramic part (1) after the laser marking operation to obtain the ceramic part (1) fired and marked with the pattern (3), in which the laser marking operation comprises: - at least one laser ablation step implementing one or more passes of the laser (2) on a surface so as to remove material in the surface to form an engraving (20) defining the pattern (3); and - at least one selective laser sintering step, carried out after the laser ablation step, and implementing one or more passes of the laser (2) in the engraving (20) obtained at the end of the laser ablation step, so as to locally sinter the internal surface of the engraving (20).

2. Marking method according to claim 1, in which the laser marking operation is carried out on the raw or roughened ceramic part (1) which is in a raw state, i.e. without a coating layer (4).

3. Marking method according to claim 1, comprising, before the laser marking operation, a covering operation implementing a covering of the ceramic part (1) by at least one coating layer (4; 41, 42), so that the laser marking operation is implemented on the at least one coating layer (4; 41, 42) which covers the raw or softened ceramic part (1).

4. Marking method according to claim 3, wherein the covering operation implements an enameling step and / or an engobing step, so that the at least one coating layer (4; 41, 42) comprises at least one enameling layer and / or at least one engobing layer.

5. Marking method according to claim 3 or 4, wherein the at least one coating layer (4; 41, 42) comprises a single coating layer (4), and the laser ablation step is carried out to form the etching (20) over at least the entire thickness of said single coating layer (4) by exposing the ceramic part (1) under said single coating layer (4).

6. Marking method according to claim 3 or 4, wherein the at least one coating layer (4; 41, 42) comprises at least two superimposed coating layers (41, 42) comprising an outer coating layer (41) and a sub-coating layer (42), and the laser ablation step is carried out to form the etching (20): - over at least the entire thickness of the at least two superimposed coating layers (41, 42) by exposing the ceramic part (1) under said at least two superimposed coating layers (41, 42); or - over the entire thickness of the outer coating layer (41) by exposing the sub-coating layer (42) under said outer coating layer (41).

7. Marking method according to any one of the preceding claims, comprising, before the laser marking operation, an operation of coloring the raw or softened ceramic part (1) in order to be colored in the mass.

8. Marking method according to any one of the preceding claims, wherein the laser (2) used during the laser marking operation is a pulsed laser.

9. Marking method according to claim 8, wherein, during the laser marking operation, the laser (2) is operated with a power of between 20 and 50 watts.

10. Marking method according to claim 8 or 9, wherein, during the laser marking operation, the laser (2) is operated at a wavelength in the infrared range, and for example at 1064 nm.

11. Marking method according to any one of claims 8 to 10, wherein, during the laser marking operation, the laser (2) is operated with a pulse frequency of between 20 and 200 kHz.

12. Marking method according to any one of claims 8 to 11, wherein, during the laser marking operation, the laser (2) is moved with a movement speed of between 100 and 5000 millimeters per second, and for example between 300 and 3000 millimeters per second.

13. Marking method according to any one of the preceding claims, in which the raw or softened ceramic part (1) comprises a mass percentage of clay excluding kaolin which is less than 10%.

14. Marking method according to any one of the preceding claims, in which the final firing operation of the ceramic part (1) is carried out at a maximum firing temperature which is between 900 and 1400 degrees Celsius, and for example between 1000 and 1350 degrees Celsius.

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