Ceramic article with color gradient and method of producing the same

Abstract

To provide a production method capable of mass production of a ceramic part with a color gradient, in particular a bezel of a timepiece, and to provide such a ceramic part.SOLUTION: The present invention produces a ceramic part using uniaxial pressing by a method involving the injection of at least two differently-colored ceramic materials, the ceramic materials being mixed in different weight ratios to create a plurality of mixed materials forming a color gradient.SELECTED DRAWING: Figure 3a

Description

[Technical field]

[0001] The present invention relates to ceramic parts, and more particularly to watch parts such as bezels, made by uniaxial pressing of multiple ceramic materials of different colors that form a continuous change in color to decorate the watch part. [Background technology]

[0002] Ceramic or cermet watch parts are generally obtained by a method involving the injection of material followed by sintering. These parts often feature decorations such as indices or numbers on the bezel that are of a different color than the rest of the part. The decorative elements are generally brazed or glued to the sintered blank part. This mechanical assembly between the blank part and the decorative elements can be costly and complicated to implement.

[0003] An alternative to this mechanical assembly is to manufacture blank parts by injecting several materials of different colors with the color intended to form the decoration after machining. However, manufacturing parts made of ceramics or cermets of different colors is a complex process. In fact, significant shrinkage of up to 30% is observed during sintering. The shrinkage rate depends on several factors, such as the choice of material and the amount of material injected. In the bi-injection method or the more common multi-injection method, differential shrinkage can occur during sintering, which can lead to separation at the joints of the various materials or diffusion of pigments from one color to another.

[0004] To remedy this drawback, US Pat. No. 5,399,633 proposes forming a green body and impregnating a portion of this body with a solution containing a metal that acts as a pigment before sintering. However, a drawback of this method is that it is difficult to obtain a uniform color throughout the entire colored part. Also, Patent Document 2 describes a method for obtaining a ceramic material with a continuous change in color to form a dental prosthesis. However, such a method generally uses isostatic pressing, which is time-consuming and demanding. Moreover, such a method cannot be industrially applied for mass production. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent Application Publication No. 2746243 [Patent Document 2] European Patent Application Publication No. 2965713 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention aims to remedy the above drawbacks by providing a new uniaxial pressing method for obtaining ceramic parts with color gradations. [Means for solving the problem]

[0007] To this end, the present invention relates to a method for producing a ceramic component with a color gradation.

[0008] More specifically, the method of producing a part by uniaxial pressing according to the invention comprises the steps of: providing at least a first ceramic material and a second ceramic material, the first ceramic material being different in color from the second ceramic material; Providing a press tool having an impression; - placing a grid within the impression to form compartments within the impression; preparing a plurality of mixtures of the first and second ceramic materials in different weight ratios to produce a continuous variation in the desired color; depositing the materials in the compartments in ascending or descending order according to their weight ratio; removing the grid and uniaxially pressing the material to form a green body; debinding the green body to obtain the brown body; sintering the brown body to form a blank part; finishing the blank part to obtain a part; Includes.

[0009] The invention also relates to the ceramic parts obtained from this manufacturing method.

[0010] According to another advantageous variant of the invention, The first ceramic material and the second ceramic material include any one of zirconium oxide powder, aluminum oxide powder, titanium nitride powder, silicon nitride powder, titanium carbide powder, chromium carbide powder, tungsten carbide powder, or a mixture of at least two of these powders. The first ceramic material and the second ceramic material each include a different pigment that imparts a different color to the first ceramic material and the second ceramic material. · The pigments are metal oxides or spinels. The pigments are selected from chromium oxide, cobalt oxide, iron oxide, titanium oxide, manganese oxide, molybdenum oxide, cerium oxide, vanadium oxide, zinc oxide, aluminum oxide or mixtures of these oxides. The pigments are cobalt / iron / chromium spinels or cobalt / aluminium spinels. The first ceramic powder and the second ceramic powder each include a binder. The sintering step is carried out at a temperature between 1,200°C and 1,800°C for 30 minutes to 20 hours. The sintering step is carried out in an oxidizing or reducing environment.

[0011] The present invention also relates to a ceramic part having a color gradation.

[0012] The part according to the invention comprises several different ceramic materials that differ in color and more generally in aesthetic appearance. According to the invention, the decorated part is monolithic and there are no discontinuities between the ceramic materials of the part in order to obtain the color gradation. Other characteristics and advantages of the invention will become apparent in the following description of preferred embodiments, given as non-limiting examples with reference to the attached drawings, in which: [Brief description of the drawings]

[0013] [Figure 1a-1c] 1 shows an exemplary embodiment of a ceramic part with a continuous change in color obtained using a manufacturing method according to the present invention. [Diagram 2] 1 shows a plan view of a blank part having a grid used to form a bezel using a manufacturing method according to the present invention. [Figure 3a] 5 illustrates steps in a manufacturing method according to the present invention. [Figure 3b] 5 illustrates steps in a manufacturing method according to the present invention. [Figure 3c] 5 illustrates steps in a manufacturing method according to the present invention. [Figure 3d] 5 illustrates steps in a manufacturing method according to the present invention. [Figure 3e] 5 illustrates steps in a manufacturing method according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention relates to a ceramic part, such as an exterior part or watch part for use in watches and jewellery, which has a colour gradation throughout its entire mass. A "colour gradation" (colour gradient) refers to a continuous change in colour, where at least two colours are used as the basis for creating the continuous change. Of course, the continuous change in colour can have three or more base colours.

[0015] The component according to the invention is made of a ceramic, which may be, for example, zirconium oxide, aluminium oxide, titanium nitride, silicon nitride or a carbide, such as titanium carbide, chromium carbide, tungsten carbide, or a mixture of these ceramics.

[0016] "Ceramic material" refers to any type of material, such as, for example, powder or granules, known to those skilled in the art for making ceramic components.

[0017] At least one of the ceramic materials includes a pigment that colors the material. The pigment is a metal oxide or spinel selected depending on the color desired. Examples include chromium oxide, cobalt oxide, iron oxide, titanium oxide, manganese oxide, zinc oxide, molybdenum oxide, cerium oxide, vanadium oxide, aluminum oxide, or mixtures of these oxides (e.g., iron oxide / chromium oxide, etc.). For example, for blue, the pigment can be cobalt oxide, for green, the pigment can be chromium oxide, and for brown, the pigment can be iron oxide.

[0018] The part according to the invention can also be a decorative part, such as a component part of a watch, a jewel, a wristlet, etc. In the field of watchmaking technology, the part can be an exterior 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. The part can also be a part of a movement, such as a vibration weight, platinum, etc. By way of example, the part is a bezel 1 made of multiple ceramics of different colors, for example with a gradation from black to turquoise blue. By way of further example, the part can be an acronym of the crown of the watch or an index of the bezel.

[0019] The parts are manufactured using uniaxial pressing of various ceramic materials to form green bodies. The manufacturing process is illustrated below for a part containing seven successive different colored materials, but the part may also be a part containing two, three, four, etc. materials with different colors, different compositions, or different pigment concentrations.

[0020] The method for manufacturing by uniaxial pressing includes the following steps with reference to the figure. · Providing at least a first ceramic powder 2 and a second ceramic powder 3. The first ceramic powder differs from the second ceramic powder by its colour and therefore by its chemical composition. Prepare impression 5. A grid 6 is placed in the impression 5 to form segments 4 in the impression. The segments optionally have a wide variety of shapes. In the case of the bezel shown, the segments can be in the form of sectors, vertical strips or vertical lines. Of course, any other shape is possible, for example a wave shape. The grid is at least 4 mm high and the number of segments formed depends on the desired final decoration. A plurality of mixed materials 20, 21, 22, 23, 24 in which the first ceramic material 2 and the second ceramic material 3 are mixed in different weight ratios are prepared, varying the weight ratio from 0 to 100% to form a continuous change in the desired color. Thus, when using two ceramic materials, the mixed materials can have weight ratios of 100 / 0, 90 / 10, 80 / 20, 70 / 30, 60 / 40, 50 / 50, 40 / 60, 30 / 70, 20 / 80, 10 / 90, 0 / 100, etc. A person skilled in the art would have no difficulty in using more than two ceramic materials, for example three, four or five ceramic materials, to obtain the desired color and the desired color gradation. The mixed materials 20, 21, 22, 23, 24 are deposited in the compartment 4 in ascending or descending order according to the desired weight ratio or gradation. The height of the mixed materials deposited in the compartment is at least 0.5 mm and does not exceed the height of the grid. · The grid 6 is removed and the mixed material is uniaxially pressed to form the green body 7. This is a particularly useful step in terms of obtaining good color uniformity throughout the part. In fact, when the grid 6 is removed, the mixed material settles slightly due to the spaces left by the grid. The green body 7 is thermally degreased to obtain the brown body. Sintering the brown body to form a blank part. Finishing a blank part to form part 1.

[0021] Several layers of mixed ceramic materials or powders can be stacked to form a particular color pattern that is visible from the side of the part.

[0022] An example using two powders is shown, which would not be particularly difficult for a person skilled in the art to prepare.

[0023] The ceramic materials used are primarily ceramic powders.

[0024] The green body is thermally desorbed at temperatures ranging from 100° C. to 800° C. This step allows the Brownian body to be obtained.

[0025] The brown body is sintered at a temperature range of 1,200°C to 1,800°C, preferably 1,350°C to 1,450°C, for 30 minutes to 20 hours. Those skilled in the art know that each color has an optimal temperature during sintering and an optimal sintering time so that the color appears quickly after sintering. Therefore, in creating a continuous transition, it is particularly useful to select multiple colors with similar sintering temperatures and times, and sinter at a temperature that is the average of the ideal sintering temperatures of the selected multiple colors.

[0026] 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 decreased at a rate of 100° C. to 200° C. per hour.

[0027] The brown body is sintered in an oxidizing or reducing environment, depending on the pigments used and the color desired. For example, sintering can be carried out in an oxygen-containing atmosphere, which can be normal air or an artificially created atmosphere that combines oxygen with other gases. For simplicity and cost-effectiveness, normal air is preferred. The oxygen-containing atmosphere can be static or there can be a constant or intermittent flow of gas.

[0028] Depending on the needs of the person skilled in the art, several sintering steps can be performed to achieve the desired result.

[0029] To form the bezel, the blank part is machined to the dimensions of the desired part.

[0030] The method may include a laser ablation process to form decoration on the part. The decoration may consist of, for example, indexes, graduations, or logos.

[0031] After the laser ablation process, the manufacturing method includes finishing steps such as polishing, satin finishing, matte finishing, etc. Also, post-sintering machining can help to make continuous changes in color or specific patterns stand out more clearly depending on the cross-section of the part.

[0032] Typically, the method according to the invention is used to obtain a bezel 1 according to figures 1a-1c, which has a colour gradient from black to turquoise blue. Naturally, other gradients based on other colours can be obtained using this method.

Claims

1. A method for producing a ceramic part (1) with a color gradation by uniaxial pressing, comprising the steps of: - providing at least a first ceramic material (2) and a second ceramic material (3), said first ceramic material (2) being different in color from said second ceramic material (3); - preparing an impression (5); - placing a grid (6) within said impression (5) to form compartments (4) within said impression; - preparing a plurality of mixed materials (20, 21, 22, 23, 24) in which the first ceramic material (2) and the second ceramic material (3) are mixed in different weight ratios, while varying the weight ratio to form a desired color gradation; - depositing said materials in said compartment (4) in ascending or descending order according to said weight ratio; - removing said grid (6) and uniaxially pressing said material to form a green body (7); - degreasing said green body (7) to form a Brown body; - sintering the brown body to form a blank part; - machining the blank part obtained to obtain the part (1); The method includes:

2. 2. The method according to claim 1, characterized in that the first ceramic material (2) and the second ceramic material (3) comprise any one of zirconium oxide powder, aluminum oxide powder, titanium nitride powder, silicon nitride powder, titanium carbide powder, chromium carbide powder, tungsten carbide powder, or a mixture of at least two of these powders.

3. 2. The method according to claim 1, characterized in that the first ceramic material (2) and the second ceramic material (3) respectively contain different pigments that give the first ceramic material (2) and the second ceramic material (3) different colors.

4. 2. The method of claim 1, wherein the pigment is a metal oxide or a spinel.

5. 5. The method according to claim 4, characterized in that the pigment is selected from chromium oxide, cobalt oxide, iron oxide, titanium oxide, manganese oxide, molybdenum oxide, cerium oxide, vanadium oxide, zinc oxide, aluminum oxide or mixtures of these oxides.

6. 5. The method of claim 4, wherein the pigment is a cobalt / iron / chromium spinel or a cobalt / aluminium spinel.

7. 2. The method of claim 1, wherein the first ceramic powder (2) and the second ceramic powder (3) each comprise a binder, the binder being present between X% and Y% by weight.

8. 2. The method of claim 1, wherein the sintering step is performed at a temperature between 1,200° C. and 1,800° C. for 15 minutes to 20 hours.

9. The method of claim 1 , wherein the sintering step is performed in an oxidizing or reducing environment.

10. A ceramic part (1), characterized in that it has a color gradation.

11. Component (1) according to claim 10, characterised in that the component is an exterior component or a watch component used in the movement.

12. 11. The component (1) according to claim 10, characterized in that the watch components used in the exterior components or in the movement are selected from the list comprising: middles, backs, bezels, bezel inserts, buttons, crowns, wristlet links, buckles, dials, hands, bars, racks, dial indexes, oscillating weights and platinum.

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