Patent Application
20250115523
The present invention relates to a ceramic part. It relates more particularly to a watch component such as a bezel, made by uniaxial pressing of differently-coloured ceramic materials forming a colour progression to decorate the watch component.
Ceramic or cermet watch components are generally obtained by a method involving the injection or a method involving the uniaxial or isostatic pressing of a material followed by sintering. These components often feature decoration, such as indexes and numerals on a bezel, in a colour that is different from the rest of the component, or simply a two-tone decoration throughout. The decorative elements are generally brazed or glued onto the sintered blank part. This mechanical assembly between the blank part and the decorative elements can be costly and complicated to implement.
An alternative to this mechanical assembly is to produce a blank part by injecting differently-coloured materials with a colour intended to form the decoration after machining. However, manufacturing ceramic or cermet components in different colours is a complex process. In fact, significant shrinkage, up to 30%, is observed during sintering. The shrinkage rate will depend on several factors, including the choice of material and the volume of material injected. In bi-injection or, more generally, multi-injection methods, shrinkage differences can appear during sintering, leading to separation at the junction between the various materials.
To remedy this drawback, document EP 2 746 243 proposes forming a green body and impregnating part of this green body before sintering with a solution comprising a metal acting as a pigment. However, the drawback to this method is that it is difficult to obtain a uniform colour throughout the coloured part.
Document EP 2 965 713 also describes a method for obtaining a ceramic material with a colour progression and forming a dental prosthesis. However, such a method uses isostatic pressing, which is generally time-consuming and demanding. Moreover, such a method cannot be applied industrially for mass production.
The present invention aims to remedy the aforementioned drawbacks by providing a new uniaxial pressing method for obtaining a ceramic part with a colour gradient.
To this end, the present invention relates to a method for manufacturing a ceramic part with a colour gradient.
More specifically, the method for manufacturing the part according to the invention comprises the following steps:
The present invention also relates to the ceramic part resulting from the manufacturing method.
According to other advantageous variants of the invention:
The invention also relates to a ceramic part with a colour gradient.
The part according to the invention comprises several different ceramic materials that vary in colour and, more generally, in aesthetic appearance. According to the invention, the decorated part is in one piece and with no discontinuity between the ceramic materials of the part so as to obtain a colour gradient.
Other features and advantages of the present invention will become apparent in the following description of a preferred embodiment, presented by way of non-limiting example with reference to the appended drawings.
The present invention relates to a ceramic part such as an external part used in horology or in jewellery, or even a watch component with a colour gradient throughout its entire mass. “Colour gradient” refers to a colour progression with at least two colours used as the basis for creating the progression. Of course, the colour progression can have more than two base colours.
The component according to the invention is made of ceramic. For example, it can be zirconium oxide, aluminium oxide, titanium nitride, silicon nitride or even a carbide such as titanium carbide, chromium carbide or tungsten carbide, or even a mixture of these ceramics.
At least one of the ceramic materials comprises a pigment that colours the material. The pigment is a metal oxide or a spinel chosen according to the desired colour. Examples include chromium oxide, cobalt oxide, iron oxide, titanium oxide, manganese oxide, zinc oxide, molybdenum oxide, cerium oxide, vanadium oxide, aluminium oxide or a mixture of these oxides such as an iron/chromium oxide, for example. For example, for a blue colour the pigment can be a cobalt oxide, for a green colour the pigment can be a chromium oxide, for a brown colour the pigment can be an iron oxide.
The part according to the invention can also be a decorative part such as a constituent component for watches, jewels, wristlets, etc. In the field of horology, this part can be an external part such as a middle, a back, a bezel, a bezel insert, a button, a crown, a wristlet link, a clasp, a buckle, a dial, a hand, a dial index, etc. It can also be a component of the movement such as an oscillating weight, a platinum, etc. By way of illustration, the part is a bezel 1 made with differently-coloured ceramics, for example with a gradient ranging from black to turquoise blue. As a further example, it could be an acronym on a watch crown or even an index on a bezel.
The part is made by injecting various materials to form a green body and by sintering said green body. The manufacturing method is illustrated below for a part comprising seven successive differently-coloured materials, but it could be a part comprising two, three, four etc. materials with different colours and/or compositions for each of the successive materials injected.
The method for manufacturing by uniaxial pressing includes the following steps with reference to the figures:
Several layers of mixed ceramic materials can be stacked to form a particular colour pattern visible from the sides of the part.
The compartments of the filling shoe can be straight or not, depending on the needs of the person skilled in the art and on the desired pattern.
The ceramic material can be predominantly ceramic powder or a feedstock that is a mixture of ceramic powder and of an organic binder.
If a feedstock is used to form the mixed materials, a debinding step is necessary before sintering the green body 8. Debinding can be done in a solvent to remove materials such as wax, paraffin, etc. It can be followed by thermal debinding in a temperature range comprised between 100 and 800° C.
The brown body is sintered in a temperature range comprised between 1,200 and 1,800° C., and preferably between 1,350 and 1,450° C., for a time comprised between 30 minutes and 20 hours. The person skilled in the art knows that each colour has an optimum temperature and an optimum sintering time during sintering so that the colour comes out right after sintering. Thus, when creating a progression, it is particularly useful to choose colours with similar sintering temperatures and times and to sinter at a temperature that is the average of the ideal sintering temperatures of the chosen colours.
Preferably, the temperature is increased to the required sintering temperature at a rate of 100° C. to 200° C. per hour. Once sintering is complete, the temperature is gradually lowered at a rate of 100° C. to 200° C. per hour.
The sintering step is carried out in an oxidising or reducing environment. For example, sintering can be carried out in an oxygenated atmosphere, which can be ordinary air or an atmosphere created artificially by combining oxygen and other gases. The oxygenated atmosphere may be static or there may be a constant or intermittent flow of gas.
Depending on the needs of the person skilled in the art, several sintering steps can be carried out to achieve the desired result.
To form a bezel, the blank part is machined to the dimensions of the desired part.
The method can comprise laser ablation machining to form decorations in the part. The decorations can consist of indexes, a graduation or a logo, for example.
After laser ablation machining, the manufacturing method includes a finishing step such as polishing, satin-finishing, mattifying, etc. Post-sintering machining also helps make the colour progression or a particular pattern stand out more clearly, depending on the section of the part.
Typically, a bezel 1 according to
| Number | Date | Country | Kind |
|---|---|---|---|
| 23202754.0 | Oct 2023 | EP | regional |
