In particular, a method for manufacturing a ceramic housing element for a timepiece and a corresponding housing element

Abstract

The present invention relates to a manufacturing method of a casing element (1) made of ceramic, for the watchmaking or jewelry manufacturing field, which makes it possible to obtain a casing element (1) which is substantially homogeneous in its structure and mechanical properties and which has original and unique tonal and / or color variations on its surface. This manufacturing method notably comprises a machining step which aims to make different layers of respective different properties visible on the surface of the casing element (1).

Description

Technical Field

[0001] The present invention relates to a method for manufacturing ceramic housing elements for use in the fields of watches or jewelry, which makes it possible to obtain housing elements that are substantially homogeneous from the perspective of their structure and mechanical properties and exhibit hue and / or color variations on their surface.

[0002] The present invention also relates to housing elements intended for use in the field of watches or jewelry. Background Technology

[0003] Various methods for manufacturing ceramic components are known, and by means of these methods, the corresponding housing components exhibit a variety of colors on their surfaces.

[0004] Therefore, for example, patent CH707424B1 discloses a method for manufacturing a ceramic case element for watches, which allows for obtaining a case element with two parts of different colors. To achieve this result, a composition comprising powder intended for a sintering process to produce ceramic and a first pigment is prepared, followed by molding. Before the sintering process, the molded part is partially exposed to a treatment intended to dope the exposed part with a second pigment (preferably one or more metals), such that the final case element obtained after the sintering process exhibits two different colors between the part treated with the second pigment and the untreated part. According to the patentee, this method advantageously allows for the production of case elements exhibiting a clear and precise boundary between the two parts, particularly suitable for manufacturing, for example, two-tone bezels for diving watches or GMT functions. In this case, one color is associated with daytime, and the other with nighttime.

[0005] JP 2014-12615A discloses another method for manufacturing case elements, particularly for bezels of watches, such as diving watches. The document describes an embodiment in which such a bezel can be manufactured to present a common case formed of a first ceramic having a first predetermined color, and to produce an inscription within it made of a second ceramic having a second predetermined color. To achieve this result, the corresponding invention includes injecting two different compositions into the same mold and then subjecting them together to a conventional sintering process. Following the latter, a "HIP" ("hot isostatic pressing") process is performed directly, which is crucial for ensuring good density of the final ceramic and therefore good cohesion between different regions of the final products produced separately based on the different compositions.

[0006] In all cases, the method proposed in this Japanese publication aims to produce precise and predetermined patterns for display or decorative purposes. As mentioned above, the method disclosed in the first prior art also relates to the manufacture of housing elements with display functions, which involves achieving a precise distribution between ceramics of different colors, as in the case of producing predetermined patterns. Therefore, both methods represent a common trend in industrial research aimed at defining the parameters of manufacturing methods so that repeatable process conditions can be implemented to produce more or less identical parts. Summary of the Invention

[0007] A primary objective of this invention is to provide a method for manufacturing ceramic housing elements that is an alternative to known methods, enabling the acquisition of housing elements exhibiting an original and unique appearance. Another objective of this invention is to provide a ceramic housing element for timepieces or jewelry that is substantially homogeneous in terms of its structure and mechanical properties, and exhibits an original appearance compared to housing elements known in the prior art, particularly by achieving at least two distinct hues and / or colors overall.

[0008] Therefore, the present invention relates more particularly to a method for manufacturing a ceramic housing element of the above type for use in watches or jewelry, comprising the following steps:

[0009] - Prepare a first basic composition comprising powder intended for a sintering process to produce ceramics.

[0010] - Prepare a second basic composition comprising powder intended for a sintering process to produce ceramics.

[0011] - Prior to the sintering process, at least one of the first and second basic compositions is treated to introduce at least one pigment therein, and the respective reagents of the first and second compositions are defined.

[0012] The first and second reagents have similar but distinct properties, such that when they are sintered together, a substantially homogeneous ceramic product is obtained from the perspective of its structure and mechanical properties, and the final ceramic product exhibits variations in hue and / or color.

[0013] - The first and second reagents are placed in a mold in at least two layers that are at least partially adjacent to each other to define an interface of a predetermined form between them.

[0014] - Implement a sintering process applied to a mold containing the first and second reagents.

[0015] The method of the present invention is characterized by including at least one machining step of the ceramic product obtained after a sintering process, the step including at least one material removal process along a path intersecting the interface, such that at least a portion of the interface is visible on the surface of the housing element, and the latter exhibits a unique appearance on its surface with hue and / or color variations, the distribution of which appears substantially random and is unrelated to any predetermined pattern or any function associated with an indicated display.

[0016] Different colors can be conventionally identified, for example, by their coordinates in L*a*b* space.

[0017] Advantageously, as is known, each basic composition contains powder intended to form ceramics during the sintering process, as well as stabilizers and possibly binders, so that a greenbody-type agent can be obtained after the introduction of one or more pigments.

[0018] These characteristics allow for control over the overall trends in color and hue of ceramic products, while maintaining the free transfer of one or more pigments at the interface between the two layers during the sintering process, thereby creating a random influence on the appearance of the product obtained after sintering.

[0019] Subsequent machining steps also allow for the production of two significantly different housing elements from the same sintered ceramic product, based on the path followed in material removal. Therefore, manufacturers can choose to further emphasize or conversely reduce variations in hue and / or color on the surface of the housing element, building upon the same sintered ceramic product.

[0020] It is also important to note that one of the known difficulties in the manufacture of ceramic components lies in achieving good reproducibility of the color and hue of the finished product. In particular, the larger the component, the more difficult it becomes to guarantee perfect homogeneity of color and hue across its entire surface. Similarly, achieving the same color and hue for different parts of a complex product is also difficult, such as watch centerpieces, case backs, chronograph crowns, possibly pushers, bezels, and sometimes even links, studs, or bracelet clasps. In fact, once these components are assembled together, even the slightest variation in color or hue between two adjacent parts becomes immediately visible.

[0021] Returning to the manufacturing method of the present invention, this method also takes a view contrary to conventional methods, particularly in this case, aiming to improve the reproducibility of the manufacturing method by precisely controlling the hue and color obtained from the manufactured housing elements. In fact, instead, this method allows the use of color and hue palettes to emphasize variations not only on the surface of a given part, but also, where appropriate, between adjacent parts. Thus, this method not only alleviates the burden on the manufacturer of precisely controlling the hue and color of the products he or she manufactures, but also enables the production of products with original and unique appearances, which is exactly the opposite of the current general trend of aiming to produce parts with a uniform appearance.

[0022] Finally, it is important to note that the significant difference between the method of the present invention and the aforementioned prior art lies not only in the objective result of producing unique products rather than identical ones, but also in the substantial simplification of the process of placing reagents in the mold prior to the sintering process. This is because the housing element of the present invention is not intended to include a predetermined pattern, as is the case with housing elements obtained by implementing the aforementioned prior art methods. Similarly, the machining steps are significantly simplified compared to those disclosed in the aforementioned Japanese literature, as its purpose is only to disclose the general form of the housing element to be manufactured, without specifically considering the distribution of colors or hues produced by different reagents placed in the mold before sintering, which is crucial for obtaining the predetermined pattern.

[0023] In the case of the present invention, it is advantageous to provide that the first and second reagents are placed in the mold without any precise control over how they are distributed relative to each other within the mold in order to produce a predetermined pattern.

[0024] Typically, it can be provided that the interface between the layers placed in the mold has an intermediate plane, and the machining steps are performed in such a way that the housing element has at least one surface defining a median general plane, which is inclined at an angle of 10° to 90° relative to the intermediate plane of the interface. Therefore, by simply modifying the path followed during material removal, a number of different housing elements can potentially be produced from a given ceramic product obtained from sintering.

[0025] Advantageously, the method of the present invention may include a supplementary step of preparing a third reagent comprising powder intended for a sintering process to produce ceramics. This third reagent has properties similar to but different from at least one of the first and second reagents, and is selected in such a manner that when the first, second, and third reagents are sintered together, a substantially homogeneous ceramic product is obtained from the perspective of its structure and mechanical properties. The third reagent is then also placed in a mold along with the first and second reagents, defining at least one supplementary interface with at least one of them for sintering together. During the material removal process, at least a portion of one or more of these supplementary interfaces becomes visible on the surface of the housing element.

[0026] Therefore, a wider range of possible variations in the hue and color of housing elements manufactured in this way are achieved.

[0027] In this case, it may also be provided that each of the interface and supplementary interface or supplementary interface presents one or more inclinations of 0° to 20° between them, so as to define an intermediate plane for all interfaces, and the machining steps are performed in such a way that the housing element has at least one surface defining an intermediate total plane, which presents an inclination of 10° to 90° relative to the intermediate plane of all interfaces.

[0028] Advantageously, it can also be provided that each reagent contains a maximum weight percentage of 15% pigment.

[0029] Typically, preferably, the sintering process includes a flash sintering process.

[0030] In this context, it is advantageous to provide a flash sintering process comprising the following steps: using a conductive mold connected to two electrodes spaced apart from each other, applying a voltage greater than 1 volt and less than or equal to 10 volts between them, preferably associated with a current of 1A to 25000A, and preferably applying a pressure of 5MPa to 1000MPa between them for a duration of 2 to 30 minutes.

[0031] Furthermore, it is preferable that the flash sintering process then constitutes a single heat treatment process in the method applied to the mold, while the mold contains reagents.

[0032] The present invention also relates to a ceramic case element for use in watches or jewelry, comprising first and second portions adjacent by an interface at least partially visible on the surface of the case element, the first and second portions having distinct hues and / or colors and distinct properties, such that the case element is substantially homogeneous from the perspective of its structure and its mechanical properties. The case element of the present invention is characterized by:

[0033] - It has at least two mutually orthogonal transverse cutting planes, and each transverse cutting plane cuts two parts, and

[0034] - It has a unique appearance with hue and / or color variations on its surface, the distribution of which appears to be largely random and is unrelated to any predetermined pattern or any function associated with the indicated display.

[0035] Preferably, the housing element of the present invention has a structure in which the minimum size of each part of different colors is less than or substantially equal to 5 mm.

[0036] Advantageously, the housing element of the present invention can be a watch housing element, particularly a part of a watch case, such as a middle piece, bezel, or back piece, or a part of a watch strap, such as a link, stud, or buckle, or even a housing element of jewelry.

[0037] Typically, it is preferable to provide that the toughness between two adjacent portions of different hues and / or colors varies by up to 5% along their interface range. Attached Figure Description

[0038] Other features and advantages of the invention will become more apparent upon reading the following detailed description of preferred embodiments given with reference to the accompanying drawings, which are provided by way of non-limiting example, and in which:

[0039] - Figure 1 This is a schematic diagram illustrating the first implementation step of a preferred embodiment of the method of the present invention.

[0040] - Figure 2 This is a schematic diagram illustrating the second implementation step of the method according to a preferred embodiment of the present invention.

[0041] - Figure 3 This is a schematic diagram illustrating the third implementation step of the method according to a preferred embodiment of the present invention.

[0042] - Figure 4 This is a schematic diagram illustrating the implementation steps of a method according to a preferred embodiment of the present invention, in relation to supplementary examples, and...

[0043] - Figure 5a and Figure 5b This is a schematic diagram illustrating a preferred feature mode of the housing element of the present invention. Figure 5a Corresponding to housing elements that do not conform to the features of this invention, Figure 5b Corresponding to the housing element of the present invention. Detailed Implementation

[0044] As previously stated, the manufacturing method of the present invention specifically includes combining several reagents, wherein at least one reagent contains at least one pigment, so as to simultaneously sinter all the reagents and obtain ceramic products having portions that present different hues and / or colors from one another.

[0045] The manufacturing method is based on the principle that the resulting housing element exhibits structural homogeneity, that is, it does not contain any joints that could embrittle it, and its properties, especially mechanical properties, are homogeneous across its entire surface and even its entire volume.

[0046] Therefore, juxtaposing reagent layers with very different properties after sintering is not a satisfactory solution in order to obtain shell elements that exhibit different hues and / or colors after sintering, because the resulting shell elements will not exhibit the desired homogeneity.

[0047] In particular, an important characteristic to consider in order to achieve the desired homogeneity is that the different reagents involved must be chemically inert to each other and have similar sintering temperatures.

[0048] The similar temperature in the sense of this invention should be understood to mean that the different sintering temperatures of the different reagents used should preferably be in the range of about 20°C.

[0049] Therefore, in the context of this method, it is preferable to use only compositions in powder form that exhibit similar sintering temperatures. Furthermore, when using binders, they are preferably selected from the same series of binders; even the same binder can be used to bond different compositions together. The same applies to the stabilizers used in the different compositions involved. If appropriate, the respective proportions of binders and stabilizers used in the different compositions should be selected such that the sintering temperatures of the different compositions remain similar.

[0050] Finally, it should be noted that adding one or more pigments to the base composition also affects the sintering temperature of the resulting green body. Therefore, starting from the same base composition, it is preferable to limit the weight percentage of one or more pigments in the green body to 15%, thereby limiting variations in the sintering temperature.

[0051] As a non-limiting illustrative example, the following detailed description is intended to describe a method for manufacturing a ceramic housing element for the field of watches or jewelry according to a preferred embodiment of the present invention.

[0052] More specifically, according to the embodiments shown and described, the housing element 1 manufactured by implementing the manufacturing method is in the form of a watch bezel for a watch case. However, those skilled in the art will, of course, be able to implement the manufacturing method of the invention as defined in the claims to produce other housing elements without departing from the scope of the invention.

[0053] The method of the present invention includes preparing different reagents or green bodies for sintering when they are placed together in a mold, by introducing at least one pigment into at least one basic composition to define one of the reagents or green bodies.

[0054] At least one other green body can be used as a reagent, without necessarily including any pigment.

[0055] As an alternative, the same pigment can be added to other base compositions, but in different proportions, to achieve hue variations on the final housing element.

[0056] As mentioned above, at least one different pigment can also be introduced into each basic composition used to manufacture the desired housing element.

[0057] Figures 1 to 3 This is a schematic diagram illustrating different steps of a manufacturing method according to a preferred embodiment, wherein the same pigment or a mixture of the same pigments is added to the same basic composition, but in different proportions, thus defining four different reagents or green bodies, each with a similar sintering temperature.

[0058] For example, a basic composition intended to produce ceramics after a sintering process can be considered prepared from zirconium oxide (ZrO2) (particularly with a particle size suitable for the desired properties of the obtained ceramic). Those skilled in the art will not have particular difficulty in selecting the powder and its particle size according to their specific needs.

[0059] What can be provided is that the basic composition includes a stabilizer, such as yttrium oxide (Y2O3) as described herein, and an optional binder, such as polyvinyl alcohol (PVA), each in proportions ranging from 0% to 10% by weight.

[0060] According to the present invention, several different reagents can be prepared by adding different proportions of the same pigment to the above-described basic composition, wherein the weight proportion of zirconium oxide in the final green body is preferably between 80% and 98%.

[0061] For example, as a non-limiting illustrative example, iron oxides (ranging from red or brown to black depending on the degree of iron oxidation), aluminum oxide (white), bismuth oxide (blue), and / or chromium oxide (green) may be used.

[0062] Preferably, it is capable of introducing pigments or pigment mixtures to obtain a green body in which one or more pigments are present in a proportion of about 0% to 15% by weight.

[0063] Therefore, for example, four reagents or green bodies 100, 200, 300, and 400 can be prepared based on the above composition, containing different proportions of pigment according to the information in the table below:

[0064] Layer numbering Pigment ratio Obtained color intensity 100 Low Very pale shades 200 maximum Very dark tones 300 average weak color tone 400 high Dark tones

[0065] like Figure 1 As shown, these reagents 100 to 400 are then placed in a mold in the form of adjacent layers for a sintering process. As a non-limiting illustrative example, reagent 100 is used here to produce two layers.

[0066] Each layer will advantageously be able to have an average thickness of about 0.5 mm to 5 mm, preferably 0.5 mm to 3 mm.

[0067] The essentially planar layer distribution here produces four interfaces 2, 4, 6 and 8, each defined at the junction between two adjacent layers.

[0068] As a non-limiting illustrative example, interfaces 2, 4, 6, and 8 are substantially planar and parallel, defining the orientation of the intermediate plane of all interfaces. Of course, those skilled in the art will be able to deposit different layers, particularly layers of variable thickness, according to their specific needs, thereby defining interfaces that are not necessarily parallel to each other.

[0069] As stated above, since the method of the present invention is not intended to produce a predetermined pattern on the final obtained housing element, placing different reagents in the mold does not require any particularly precise control over the arrangement of the different layers relative to each other.

[0070] The sintering process produces ceramic products in block form 10, the form of which is defined by the form of the mold used, such as... Figure 2 It is shown schematically.

[0071] It can be seen that this ceramic product has different parts, and as a whole, it exhibits different hues depending on the proportion of pigments used to dope the corresponding reagents.

[0072] Typically, the sintering process of the present invention preferably adopts the form of flash sintering process (or SPS, "spark plasma sintering", or current-assisted sintering or FAST, "field-assisted sintering technology").

[0073] More specifically, the flash sintering process may include the following steps: using a conductive mold connected to two electrodes spaced a distance apart, and applying a voltage greater than 0 volts and less than or equal to 10 volts between them, preferably associated with a current of 1A to 25000A flowing between the two electrodes. This current allows at least the mold to be heated, at a very rapid rate (approximately 500°C / min to 1000°C / min), and even the reagent (when it is conductive) to be heated.

[0074] Applying pressures from 5 MPa to 1000 MPa can accelerate sintering, sometimes lower the sintering temperature (and thus reduce the intensity of the applied current), and improve the density of the resulting product. Typically, the pressure is applied directly by the electrode itself, and is therefore unidirectional.

[0075] Typically, depending on the nature of the reagents and the process conditions being maintained, the duration of a flash sintering process ranges from 2 to 30 minutes. It can be performed while the mold is kept in a vacuum or a controlled atmosphere (e.g., in argon, hydrogen, or nitrogen).

[0076] It should be noted that in the case of rapid sintering, the use of binders is not necessary. Furthermore, in this case, since a debinding step is not required, the flash sintering process constitutes the only heat treatment process applied to the mold when the mold contains reagents.

[0077] Referring to the above-cited document JP 2014-12615A, it should be noted that this method not only reduces the duration of the sintering process from several hours to at most tens of minutes, but also eliminates the hot isostatic pressing (HIP) step necessary in existing methods to obtain the mechanical properties required for the final product.

[0078] The manufacturing method of the present invention provides a step of machining the obtained ceramic product, which makes it possible to obtain a housing element 1 that exhibits hue and / or color variation on its surface, in this case, a bezel for a watch case.

[0079] Therefore, the machining step advantageously includes at least one material removal process along a path intersecting at least one of interfaces 2, 4, 6 and 8, such that at least a portion of the interface is visible on the surface of the housing element 1.

[0080] Figure 2The possible positioning of the bezel within the ceramic block 10 is schematically shown, which allows all interfaces 2, 4, 6, and 8 visible on the bezel surface to be simultaneously presented once the machining steps are completed (here, as a non-limiting illustrative example, the bezel is octagonal, which explains the presence of edges regularly distributed along its periphery). For this purpose, the selection of the path followed by material removal for the housing element 1, which has a general form that defines its central plane, is preferably such that this central plane is inclined relative to the central plane of all interfaces.

[0081] Depending on the desired final effect, the number of layers, their thickness, form, and the size of the shell elements, an infinite number of different results can be obtained based on the direction of the path followed by the material removal for a given ceramic block 10.

[0082] Typically, and particularly, it can be provided that when the block 10 comprises at least two interfaces, they advantageously define two corresponding intermediate planes exhibiting a relative inclination of about 0° to 20°. Furthermore, it can also be provided that the overall intermediate plane of the housing element 1 or at least one of its faces (if appropriate) has an inclination of 10° to 90° relative to the intermediate planes of all interfaces.

[0083] The ceramic block 10 is then machined, preferably using a CNC machine or by laser, to release the bezel from it, such as... Figure 3 As shown.

[0084] Figure 3 Four interfaces 2, 4, 6 and 8 are shown to be visible on the surface of housing element 1.

[0085] Therefore, depending on the form of the housing element to be manufactured, the machining steps of the present invention are relatively simple, as the step only involves releasing the housing element from the ceramic block obtained after the sintering process. Once the overall form of the housing element is defined, it must simply be applied to the ceramic block, oriented such that one or more interfaces between different color areas can be cut.

[0086] Generally, those skilled in the art will not have particular difficulty in applying this teaching to define the appropriate number of layers, their thickness, or the properties of their composition, as needed, provided that the green bodies used result in a substantially homogeneous ceramic product from the perspective of its structure and mechanical properties when they are sintered together.

[0087] Different green blanks will now be presented as supplementary, non-limiting examples, along with relevant process conditions that enable the manufacture of the housing element 1 of the present invention.

[0088] Therefore, it is possible to prepare, for example, zirconium-based compositions combined with yttrium oxide as a stabilizer, wherein the proportion of yttrium oxide is 1% to 5% relative to zirconium oxide.

[0089] Advantageously, a binder can be added to obtain a ceramic slurry, comprising 0% to 7% by weight of the binder relative to the ceramic slurry. In a non-limiting manner, the binder can be selected from polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyoxymethylene (POM), or even polyvinylpyrrolidone.

[0090] As described above, by adding different proportions of the same pigment or different pigments in similar or different proportions to the basic composition, several different green bodies can then be advantageously prepared.

[0091] For example, pigments mentioned above can be used, particularly iron oxides (ranging from red or brown to black depending on the degree of iron oxidation), aluminum oxide (white), bismuth oxide (blue), and / or chromium oxide (green). Preferably, pigments can be added to obtain a green body in the proportion of one or more pigments from about 0% to 15% by weight.

[0092] From the perspective of this invention, the green bodies thus obtained are compatible with each other, that is, they have similar sintering temperatures.

[0093] As previously mentioned, the green body can be arranged alternately in layers in the mold, preferably by pressure injection. In particular, the white, green, red (and / or brown to black) and blue layers from the above-mentioned reagents can be placed alternately in any order. Each layer is preferably able to have a thickness of about 0.5 mm to 5 mm.

[0094] Then, at temperatures ranging from 800°C to 1600°C, conventional sintering processes are applied to molds containing different reagent layers or green bodies.

[0095] Alternatively, it is preferable not to use a binder and to place the powder in a flash sintering mold (e.g., typically graphite, silicon carbide, or tungsten carbide) and then perform a flash sintering process on the latter.

[0096] Those skilled in the art will be able to perform the flash sintering process using any suitable equipment without departing from the scope of the invention as defined by the appended claims. For example, he or she will be able to use one or another SPS machine sold by Fuji Electronics (see https: / / www.fdc.co.jp / sps / products / e_products.html).

[0097] Depending on the nature of the reagent to be treated, the flash sintering process can include one or more heating ramps without departing from the scope of the invention as defined by the appended claims.

[0098] After cooling, the sintered ceramic block is machined (e.g., using a CNC machine) to release the desired housing elements from it, particularly for use in the watchmaking or jewelry industry.

[0099] As Figure 2 and Figure 3 As already mentioned in the example shown, it is advantageous to provide that, during this machining step, the central plane of the housing element or at least one of its faces (if appropriate) has an inclination of 10° to 90° relative to the central plane of all interfaces.

[0100] These properties ensure that the maximum number of interfaces between different layers are visible on the surface of the final housing element, thus giving it a wide variety of hues and / or colors.

[0101] In order to characterize the conditions for obtaining the ceramic housing element of the present invention, that is, the conditions under which the ceramic element can be considered substantially homogeneous from the perspective of its structure and its mechanical properties, additional exemplary embodiments will now be described.

[0102] As an illustration, the additional example provides the production of a ceramic housing element comprising six distinct sections, each exhibiting a different color and hue due to the use of two different pigments or pigment mixtures (C1 and C2) in variable proportions, as shown in the table below.

[0103] Layer numbering Layer color Pigment ratios for the hues to be considered Obtained color intensity 104 C1 weak Very pale shades 204 C1 average Light color tone 304 C1 high Average tone 404 C2 average Dark tones 504 C2 weak Average tone 604 C2 Maximum value Very dark tones

[0104] Figure 4 This is a schematic diagram of the ceramic block 40 obtained according to the above process conditions.

[0105] In fact, this supplementary exemplary embodiment provides several different methods for preparing green bodies by adding two pigments or mixtures of two different pigments in varying proportions to the same basic composition, then placing these green bodies in a mold in the form of a stack and subjecting them to a sintering process.

[0106] Then block 40 is obtained, which has six different parts, corresponding to layers 104, 204, 304, 404, 504, and 604, as follows: Figure 4 As shown.

[0107] This can be achieved by moving laterally to different layers (i.e., essentially parallel to) Figure 4The plane P (referenced in the text) applies a load to block 40 to measure toughness, thereby defining the acceptable level of structural homogeneity of block 40.

[0108] Figure 5a This is a schematic diagram showing the ratio between the toughness of the ceramic block, which does not conform to the present invention, at different points in a direction parallel to plane P, and the toughness of the first layer 104.

[0109] It can be seen that the toughness varies significantly along the ceramic block, which is reflected in a certain structural heterogeneity. This structural heterogeneity can cause the block to crack under certain specific mechanical stresses, which is undesirable in the context of this invention.

[0110] Figure 5b This is a schematic diagram showing the ratio between the toughness of the ceramic block of the present invention at different points in a direction parallel to plane P and the toughness of the first layer 104.

[0111] Figure 5b The diagram schematically represents the ideal case where the toughness is constant along the entire plane P, which reflects the fact that, according to the standards of the present invention, the corresponding ceramic bulk is homogeneous from the perspective of its structure and its mechanical properties.

[0112] In practice, it is preferable to consider that the homogeneity criterion of the present invention is met when the toughness variation between two adjacent layers is at most 5%.

[0113] With the help of the manufacturing method just proposed, ceramic housing elements with an original and unique appearance can be produced in a variety of shades and / or colors, and their mechanical properties are comparable to those of conventional ceramic housing elements with uniform shades and colors.

[0114] The implementation of this invention is not limited to the compositions provided as non-limiting examples. In fact, those skilled in the art will not have particular difficulty in applying these teachings to the implementation of methods for manufacturing ceramic housing elements with properties different from those described and manufactured by compositions with properties different from those provided as examples, without departing in any way from the scope of the invention as defined by the claims.

Claims

1. A manufacturing method for a ceramic casing element (1) for the horology or jewelry field, comprising the following steps: - preparing a first base composition comprising a powder suitable for producing a ceramic when a sintering procedure is performed, - preparing a second base composition comprising a powder suitable for producing a ceramic when a sintering procedure is performed, - before performing the sintering procedure, treating at least one of the first base composition and the second base composition to introduce at least one pigment therein and define a first and a second respective agent (100, 200), the first and second respective agents having respective properties that are similar but different from each other, so that when they are subjected together to a sintering procedure, a ceramic product (10) is obtained that is homogeneous from the point of view of its structure and its mechanical properties, and the ceramic product (10) obtained finally exhibits a change in tone and / or color, - placing the first and second respective agents (100, 200) in a mold in the form of at least two layers that are at least partially adjacent to define an interface (2) of predetermined form between them, - performing a sintering procedure applied to the mold containing the first and second respective agents (100, 200), the method being characterized in that it comprises at least one machining step of the ceramic product (10) obtained after the sintering procedure, said step comprising at least one material removal procedure along a path that intersects the interface (2), so that at least one portion of the interface (2) is visible on the surface of the casing element (1) and the latter exhibits a unique appearance with a change in tone and / or color on its surface, the distribution of which appears to be random and independent of any predetermined pattern or any function related to an indicated display.

2. The method of claim 1, wherein, The first and second respective agents (100, 200) are placed in the mold without any precise control of the way in which they are distributed in the mold relative to each other that is intended to produce a predetermined pattern.

3. The method of claim 1, wherein, it comprises a supplementary step of preparing a third agent (300) comprising a powder suitable for producing a ceramic when a sintering procedure is performed, the third agent (300) having properties that are similar but different from at least one of the first and second respective agents (100, 200) and being chosen in such a way that when the first and second respective agents (100, 200) and the third agent (300) are subjected together to a sintering procedure, a ceramic product (10) is obtained that is homogeneous from the point of view of its structure and its mechanical properties, and the third agent (300) is also placed in a mold together with the first and second respective agents (100, 200), defining at least one supplementary interface (4) with at least one of them to be subjected together to a sintering procedure, at least one portion of the supplementary interface (4) or each supplementary interface (4) appearing to be visible on the surface of the casing element (1) when a material removal procedure is performed.

4. The method of claim 1, wherein, said interface (2) has a median plane and said machining step is performed in such a way that said casing element (1) has at least one face which defines a median overall plane which presents an inclination of 10° to 90° with respect to said median plane of said interface (2).

5. The method of claim 3, wherein, said interface (2) and said supplementary interface (4) or each of said supplementary interfaces present one or more inclinations between them of 0° to 20° so as to define a median plane for all of said interfaces (2) and said supplementary interface (4), and said machining step is performed in such a way that said casing element (1) has at least one face which defines a median overall plane which presents an inclination of 10° to 90° with respect to said median plane of all of said interfaces (2) and said supplementary interface (4).

6. The method of claim 1, wherein, said first and second respective agents (100, 200) each comprise pigments in a maximum proportion by weight of 15%.

7. The method of claim 3, wherein, said first and second respective agents (100, 200) and said third agent (300) each comprise pigments in a maximum proportion by weight of 15%.

8. The method of claim 1, wherein, said first and second respective agents (100, 200) comprise the same pigments in different proportions.

9. The method of claim 3, wherein, said first and second respective agents (100, 200) and said third agent (300) comprise the same pigments in different proportions.

10. The method of claim 1, wherein, at least one of said first and second respective agents (100, 200) contains particles of at least one noble metal.

11. The method of claim 1, wherein, said sintering procedure comprises a flash sintering procedure.

12. The method of claim 11, wherein, said flash sintering procedure comprises a step which comprises the use of an electrically conductive mould connected to two electrodes at a distance from each other and the application between them of a voltage greater than 1 volt and less than or equal to 10 volts for a duration of 2 minutes to 30 minutes.

13. The method of claim 12, wherein, the application between said two electrodes of a voltage greater than 1 volt and less than or equal to 10 volts is associated with a current of 1 A to 25 000 A.

14. The method of claim 12, wherein, a pressure of 5 MPa to 1000 MPa is applied between said two electrodes.

15. The method of claim 11, wherein, said flash sintering procedure constitutes a single heat treatment procedure of the method applied to said mould, while said mould contains at least said first and second respective agents (100, 200).

16. A ceramic casing element (1) for the watchmaking or jewellery field, comprising at least a first and a second portion which are adjacent by an interface which is at least partially visible on the surface of said casing element (1), said first and second portions exhibiting respectively different shades and / or colours and having respective properties, so that said casing element (1) is homogeneous from the point of view of its structure and of its mechanical properties, characterized in that said casing element has at least two mutually orthogonal transverse cutting planes and each of said transverse cutting planes cuts said at least first and second portions, and said casing element exhibits a unique appearance with a change in shades and / or colours on its surface, the distribution of which appears to be random and is independent of any predetermined pattern or any function related to an indicated display.

17. The casing element (1) as claimed in claim 16, characterized in that, It comprises at least a third portion, of a different shade and / or color than at least one of said first and second portions, and of properties such that said case element (1) is homogeneous from the point of view of its structure and of its mechanical properties, said third portion defining at least one supplementary interface with at least one of said first and second portions, and Each of said transverse cutting planes cuts at least two of said first, second and third portions.

18. A housing element (1) as claimed in claim 16, characterized in that The minimum dimension of each of said first and second portions is less than or equal to 5 mm.

19. A housing element (1) as claimed in claim 17, characterized in that The minimum dimension of each of said first, second and third portions is less than or equal to 5 mm.

20. A housing element (1) as claimed in claim 16, characterized in that It is a watch case element, comprising a component of a watch case, or a component of a wristband of a watch, or a case element of jewelry.

21. A housing element (1) as claimed in claim 20, characterized in that Said component of a watch case is a middle, a bezel or a bottom, said component of a wristband of a watch is a link, a stud or a buckle.

22. The housing element (1) according to any one of claims 16 to 21, characterized in that The tenacity between two adjacent portions varies by at most 5% along the corresponding interface.

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