HK1098545B - Multi-stage enamelled dial - Google Patents

Description

Multi-level enamel dial

Technical Field

The invention relates to a multi-level enamel dial, i.e. a dial whose substrate has one or more recesses or, conversely, projections, the surface of said substrate being coated with an enamel/enamel layer. Such a dial is particularly used in timepieces in which the recess defines, for example, a secondary dial, for example the dial of a small stopwatch or of a timepiece. This multi-level design also has purely aesthetic purposes.

Background

A common method for manufacturing multi-level enamel dials is to take a metal plate of very small thickness, usually made of copper, copper alloy or silver, and form, by successive deposition and sintering operations, a layer of enamel on the surface of the base plate, said (enamel) layer having a thickness of usually 600 to 800 μm, and a layer of lower-thickness back-side enamel (counter enameling) on the back side of the plate. The back enamel has one of the main technical functions, namely to resist the stresses generated in the metal plate during the successive sintering operation stages. Then, a hole of the desired size is cut for the secondary dial, the surface of the enamel disk produced in the same way is subsequently machined and cut to the size of the hole, which may reduce the thickness of the enamel, and finally the disk is welded into the hole, which creates a very visible mark on the back of the dial and may damage the secondary dial. The method described briefly above is very difficult to implement and has a very high rejection rate, which ultimately results in very high costs for the finished product.

In order to make the metallic enamel dial more three-dimensional without incurring the above-mentioned drawbacks of the prior art, it has been proposed to take a thicker substrate, to make a recess in the substrate, and then to coat the recess with a sufficiently thick enamel to conceal the underlying metallic surface. The enamel dial thus formed is very thick, which causes an increase in the size of the watch case, which is no longer compatible with the requirements of current watches.

It has also been proposed to deform a metal substrate, for example by stamping, and then glazing. The parts that have been deformed have altered thermal properties, so that the sintering operation often causes cracks in the enamel layer, which results in the rejection of the manufactured part.

Disclosure of Invention

The object of the present invention is therefore to overcome the drawbacks of the prior art described above by providing a multi-level dial that does not require the back enamel to be applied to the back of the dial or the welding of one part, for example in order to form a secondary dial in a recess.

The invention therefore relates to a multi-level enamel dial comprising a substrate, the surface of which comprises reliefs forming recesses or, conversely, projections, for decorative or technical purposes, for example to define a secondary dial in a timepiece, the whole surface of the dial and the reliefs being covered with an enamel layer. This dial is characterized in that the base plate is made of ceramic material, the relief being made by preforming said base plate before enamelling or by machining said enamel layer so as to penetrate the enamel layer or even the base plate. In fact, such a multi-level enamel dial can be obtained in a number of different ways.

In the first embodiment, in the process of manufacturing the ceramic substrate, the required concave-convex portions are formed on the surface of the dial, for example, by a CIM method (ceramic injection molding method) using an appropriate mold, and then the entire surface and the concave-convex portions are glazed by successive deposition and sintering operations to directly obtain the finished dial. Also, the concave-convex portion may be formed by machining the flat surface of the ceramic substrate.

According to a second embodiment, the entire surface of the substrate is first glazed, then a machining operation is carried out with spot facing or etching through the entire thickness of the enamel layer and partially through the substrate, followed by glazing the bottom of the recess thus formed. According to a variant, the enamel layer formed is sufficiently thick so as not to reach the bottom plate (substrate) when the recess is machined.

According to a third embodiment, the entire surface of the substrate is first enamel coated and then a through-hole is machined through the enamel layer and the substrate. A ceramic insert is separately prepared, the insert having the same dimensions as the through-hole and the visible surface of which comprises a layer of enamel which may be the same or different from the coating of the entire surface. The insert is then inserted into the through hole and held in place by bonding. Depending on the overall thickness of the insert and its enamel, an enamel dial can be formed with a concave portion or conversely with a convex portion.

It can be seen that given the very close thermal expansion coefficients of ceramics and enamels, a multi-level enamel dial made using ceramic substrates does not require welding and does not require the presence of a back enamel, thus not causing deformations that must therefore be compensated.

However, the seam between the base plate and the insert can be concealed by gluing, at the junction between the base plate and the insert, an additional plate having the same contour as the dial, which thus also acts to keep the insert in place.

Given the very limited technical functionality of the additional plate, this additional plate can be made of ceramic material, like the base plate, or of metal, depending on the aesthetic appearance required by the finished product comprising said dial.

According to a variant of the above embodiment, when the additional plate is made of ceramic material, it can be made in one piece with the insert. According to another variant, the additional plate may be provided with a foot for fixing the dial, the peripheral direction of said additional plate being arranged so that it can be inserted in the bottom of the base plate.

Drawings

Further characteristics and advantages of the invention are demonstrated in the following description of several embodiments of the invention, given as non-limiting examples, with reference to the attached drawings, in which:

FIGS. 1A, 1B and 1C illustrate in cross-section the steps of a first embodiment of the invention;

FIGS. 2A, 2B and 2C show a second embodiment;

fig. 3A and 3B show a modification of the second embodiment;

FIGS. 4A, 4B and 4C illustrate a third embodiment; and

fig. 5, 6 and 7 correspond to modifications of the third embodiment.

Detailed Description

For a better understanding of the figures, it should be noted first that the thicknesses are not all shown to the same scale, but only a part of the dial containing the relief.

Fig. 1A to 1C show a first embodiment in which the dial is made of a ceramic substrate 1 with two parallel and flat surfaces 3, 5 (fig. 1A) and a recess 4 is machined by spot facing or etching (fig. 1B). Then, an enamel layer is formed by successive deposition and sintering operations (fig. 1C). The base plate 1 can be cut from a large ceramic plate having a thickness of between 0.4mm and 0.9mm, such a value enabling the dial to obtain satisfactory mechanical properties. The substrate 1 may also be manufactured to be preformed directly to the required dimensions, for example by means of a ceramic injection moulding method (CIM) or pressing. In this case, the concave portions 4 may be formed at the same time. It is clear that in the same way by machining, pressing or CIM, it is possible to form the relief corresponding to the relief before the glazing step, and that finishing can also be carried out, for example, in order to improve the aspect ratio of the relief.

Ceramic materials, such as alumina-based ceramic materials, are known to have a low colour and may also contain colouring agents, so that the number of enamel layers necessary to form the desired final colour may be low, whereby the enamel layers have a thickness of between 0.1mm and 0.4mm, since the coefficients of thermal expansion of the ceramic and the enamel are very close, no tensions are generated during the sintering operation which tend to deform the substrate 1, so that no back enamel is required.

Fig. 2A to 2C show a second embodiment. Starting with the substrate 1 on the surface of which the first enamel layer 2 has been formed. Then, a concave portion 4 is formed so as to completely penetrate through the first enamel layer 2 and partially penetrate through the ceramic substrate 1. Subsequently, the second enamel layer 12 is formed at the bottom of the concave portion 4 by, for example, machining (damming). Thereby, the concave portion can be made to have a color different from that of the dial surface. It is clear that it is also possible to proceed as described in the first embodiment, i.e. to coat this second enamel layer on the whole dial surface and on the relief portions, using an enamel of the same or different colour as the first coating. According to a variant, shown in figures 3A and 3B, enamel layer 2 is sufficiently thick, for example 0.4mm, so that it can be machined without reaching ceramic substrate 1. In order to obtain a high level of surface state, it is desirable to perform additional sintering to obtain a fine finished product.

Fig. 4A to 4C relate to an embodiment which differs from those described above in that the substrate 1 and its enamel layer 2 are processed to form through-holes 9. An insert 10 with a ceramic substrate 11 is formed separately, which matches the contour 13 of the through-hole 9 and comprises a second enamel layer 12, which may be identical to or different from the first enamel layer 2. The insert 10 is disposed in the through-hole 9 and held therein by adhesion. In the finished product shown in fig. 4C, the thickness of the substrate 11 of the insert 10 is smaller than that of the substrate 1, so that the concave-convex portion thus formed is a concave portion. For the same reasons as above, the bottom of the substrate does not technically require any backside enamel.

However, for aesthetic purposes, for example to mask the contour 13 of the seam between the substrate 1 and the insert 10, an adhesive 15 may be applied to the bottom of the dial to adhere an additional masking plate 14. The material forming this additional plate may be ceramic, as with the base plate, or a metal, such as copper, silver, gold or platinum or an alloy of these materials, depending on the aesthetic effect sought by the timepiece.

Fig. 6 shows an alternative embodiment of the multi-level dial described above. It is first of all seen that the visible surface of the dial has a curved shape, which can be easily formed by using ceramic materials for the base plate and, in this case, for the insert, without generating any particular tension during glazing, i.e. without still requiring any back enamel. It can also be seen that the insert 10 has a thickness greater than the height of the through hole 9, so that the relief portion formed is a convex portion 8. Finally, it can be seen that the insert can be formed in one piece with an additional masking plate 14, which is obviously made of ceramic material.

Fig. 7 shows that, at the same time as the insert 10 and the additional plate 14 are formed, it is possible to form feet 18 that will position the dial, the additional plate shown in this example being arranged in the bottom 5 of the base plate. The foot 18 obviously can occupy a non-central position to allow the passage of the arbour when the recess 12 is a secondary dial.

It is clear that the above described embodiments and the embodiments corresponding to the finished product shown in fig. 1C, 2C, 3B, 4C, 5, 6 and 7 may be varied. By way of non-limiting example, the teachings of fig. 1C, 6 and 7 can be combined, without departing from the scope of the invention, to obtain a glazed ceramic dial comprising a secondary dial with an embossed surface in a recess, the base plate of which comprises a foot.

Claims (10)

1. A multi-level enamel dial comprising a substrate (1), the surface of which comprises reliefs forming recesses (4, 6) or protrusions (8), said surface and said reliefs being coated with an enamel layer (2, 12), characterized in that the substrate (1) is made of a ceramic material, the reliefs being made by preforming said substrate (1) before enamelling, or by machining said enamel layer (2) so as to penetrate the enamel layer or through the substrate (1).

2. The enamel dial according to claim 1, characterised in that the surface of the substrate (1) comprises at least one recess (4) formed by preforming or machining the substrate (1).

3. The enamel dial for multi-level enamel according to claim 1, characterised in that the entire surface of the base plate (1) comprises a first enamel layer (2), the recess (4) passing completely through the first enamel layer (2), the bottom of the recess (4) being coated with a second enamel layer (12) identical to or different from the first enamel layer (2).

4. The enamel dial for multi-level enamel according to claim 1, characterised in that the whole surface of the substrate (1) comprises a thick enamel layer (2), a recess (4) being machined in the enamel layer (2).

5. The enamel dial according to claim 1, characterised in that the entire surface of the base plate (1) comprises a first enamel layer (2), said first enamel layer (2) and said base plate (1) comprising through holes (9) closed by a ceramic insert (10), the ceramic insert (10) comprising a second enamel layer (12) identical to or different from the first enamel layer (2).

6. The enamel dial according to claim 5, characterised in that the thickness of the insert (10) together with the second enamel layer (12) is less than the thickness of the substrate (1), so as to form a recess (6) in the dial.

7. The enamel dial according to claim 5, characterised in that the thickness of the insert (10) together with the second enamel layer (12) is greater than the thickness of the substrate (1), so as to form a protuberance (8) on the dial.

8. The enamel dial for multi-level enamel according to claim 5, characterised in that an additional plate (14) is fixed to the back of the dial, the additional plate (14) having the same profile as the base plate (1).

9. The enamel dial for multi-level enamel according to claim 8, characterised in that the material forming the additional plate (14) is chosen from ceramics and metals.

10. The enamel dial according to claim 5, characterised in that the insert (10) comprises, at its bottom, an additional plate (14) integral with said insert (10), the additional plate (14) having a profile between the profile of the dial and the profile of the through hole (9) of the insert and being connected to the bottom of the base plate (1) or located in a cavity (16) formed in the base plate.