Display module for a timepiece including a solar cell

A display module for a timepiece, including a dial, on a lower face of which is secured a digital information display device, a solar cell, and a plate. The solar cell is accommodated in the plate such that the solar cell is underneath and at a small distance from the dial. The assembly formed by the dial and the digital information display device is disposed atop the solar cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a National phase Application in the United States of International patent Application PCT/EP2014/052192 filed Feb. 5, 2014 which claims priority on European patent Application 13165115.0 filed Apr. 24, 2013. The entire disclosure of the above patent application are hereby incorporated herein by reference.

The present invention concerns a timepiece including a digital information display device. More precisely, the invention concerns such a timepiece in which the digital information display is more attractive and easier to read.

Wristwatches provided with a digital information display device, such as a liquid crystal cell, have been known for a long time. Such wristwatches typically include a dial, under and away from which is arranged, for example, a liquid crystal cell. An aperture provided in the watch dial allows the user to read the time or other information displayed by the liquid crystal cell. The liquid crystal cell is secured on a main plate housed in the watch case away from the dial. There is therefore an unattractive space between the surface of the dial and the display surface of the liquid crystal cell. Further, depending on the angle at which the user looks at the watch, his view may be impaired by the shadow projected by the edges of the aperture onto the liquid crystal cell display surface.

Further, the liquid crystal cells fitted to wristwatches of the aforecited type usually include glass substrates joined to each other by means of a sealing frame. These glass substrates are usually of square or rectangular shape since, although it is technically possible to give such glass substrates shapes other than a square or rectangle, this is difficult to envisage from an economic point of view.

DE Patent No 19857997 discloses a dial under the surface of which a liquid crystal cell and a solar cell are simultaneously fixed.

It is an object of the present invention to overcome the aforementioned problems, in addition to others, by providing a timepiece fitted with a digital information display device in which the display of information is more attractive and easier to read.

To this end, the present invention concerns a display module for a timepiece, this display module including, on the one hand, a dial on a lower face of which is secured a digital information display device, and on the other hand, a solar cell and a plate, the solar cell being accommodated in the plate such that the solar cell is underneath and at a small distance from the dial, the assembly formed by the dial and the digital information display device being disposed atop the solar cell. Advantageously, the display module is completed by a backlight device disposed on a lower face of the plate and removably secured thereto.

There is thus obtained a complete display module which can be exchanged, part for part, in the event of malfunction. In the event of a problem, it is even possible to remove the display module and only replace the defective component(s), which is very advantageous from an economic point of view.

The present invention also concerns a method for manufacturing a timepiece including a dial underneath which is disposed a digital information display device, an aperture provided in the watch dial allowing the user to read the information displayed by the digital information display device, the dial having an upper face and a lower face and the digital information display device having an upper information display surface, the method being characterized in that the upper information display surface is provided with an adhesive layer and in that the digital information display device is laminated on the lower face of the dial by means of the adhesive layer.

According to a complementary feature of the invention, once the digital information display device is secured to the dial, the assembly is placed in an autoclave in order to expel any air trapped between the adhesive layer and the dial. Preferably, the pressure in the autoclave is 6 bars, the treatment temperature is on the order of 50° C. and the treatment time is around 30 minutes.

The present invention proceeds from the general inventive idea which consists, in the case of a timepiece including a dial on the lower face of which is fixed a digital information display device, in removably housing a solar cell in a plate disposed under the dial. In the event of failure of the digital information display device or the solar cell, it is possible to remove the display module and replace only the defective component(s), which is very advantageous from an economic point of view. In particular, if the solar cell fails, it is not necessary to remove the dial which is an expensive component.

FIG. 1is an exploded perspective view of a first example embodiment of a display module for a timepiece according to the invention. Designated as a whole by the general reference numeral1, this display module includes a dial2which, in the illustrated example, is of generally circular shape. It will be understood, however, that the shape of the dial may differ from a circular profile and may, for example, be square or rectangular. Dial2has an upper face4and a lower face6and is pierced at the centre with a hole8for the passage of a set of arbors for the hour and minute hands (not shown in the drawing). An aperture10is provided in dial2. In the case where dial2is made of a transparent material, the decorative layer coating dial2is omitted from the place corresponding to aperture10. Another solution for forming aperture10consists in piercing dial2at the desired location.

Display module1also includes a digital information display device. In the example shown in the drawing, this digital information display device is formed of a flexible liquid crystal display cell12which has a substantially semi-circular shape. This liquid crystal display cell12includes a front substrate14, which defines an upper display surface, and a rear substrate16. Front substrate14and rear substrate16are made from a flexible plastic material and connected to each other in a conventional manner by a sealing frame (not shown in the drawing) which delimits a closed volume for containing the liquid crystal. It goes without saying that this example is given purely by way of illustration and that the digital information display device may be of the electrophoretic type or even use an electronic ink. A flexible electrical connector18connects the electrodes of the liquid crystal display cell12to an electronic control circuit (not shown).

According to the invention, the front substrate14of liquid crystal display cell12is coated with an adhesive layer20formed of an optically transparent adhesive and by means of which liquid crystal display cell12is attached to the lower face6of dial2. Preferably, but in a non-limiting manner, liquid crystal display cell12is mechanically laminated against lower face6of dial2, then the assembly formed by dial2and liquid crystal display cell12is placed in an autoclave in order to expel any air trapped between adhesive layer20and dial2. By way of example, the pressure in the autoclave is 6 bars, the treatment temperature is on the order of 50° C. and the treatment time is around 30 minutes.

The assembly is completed by a first solar cell22. It will be understood that utilisation of this solar cell22corresponds to the preferred embodiment of the invention but that, in the basic variant of the invention, display module1includes only dial2and liquid crystal display cell12. In the example illustrated inFIG. 1, solar cell22has a substantially semi-circular shape complementary to the shape of liquid crystal display cell12. The sum of the area of liquid crystal display cell12and solar cell22substantially corresponds to the area of dial2.

Solar cell22is disposed underneath and at a small distance from dial2. It is therefore accommodated in a plate24whose dimensions and shape are adapted to those of dial2. For axially maintaining solar cell22, plate24includes a bearing surface26, the area of which is substantially equal to that of solar cell22. For radially maintaining solar cell22, the outer perimeter thereof is provided with at least one, and preferably with two lugs28, which are engaged in two corresponding housings30provided on the periphery of plate24. As shown in the drawing, bearing surface26is pierced with two diametrically opposite through holes32in which are engaged springs34, which ensure the electrical contact between the two terminals of solar cell22and the electric power supply circuit of the watch (not shown).

The assembly formed by dial2and liquid crystal display cell12is disposed atop solar cell22and rests on a peripheral rim36of plate24. It is seen that liquid crystal display cell12is plumb with an opening38, which is provided in plate24and whose area substantially corresponds to the area of liquid crystal display cell12. This opening38allows a backlight device40mounted from underneath plate24to backlight liquid crystal display cell12.

Finally, the assembly formed by dial2, liquid crystal display cell12and solar cell22is removably locked on main plate24by means of flexible locking hooks42. There is thus obtained a complete display module1which can be exchanged, part for part, in the event of malfunction. In the event of a problem, it is even possible to remove display module1and only replace the defective component(s), which is very advantageous from an economic point of view.

FIG. 2is an exploded perspective view of a second example embodiment of a display module for a timepiece according to the invention. In the following description, any elements similar or identical to those already described with reference toFIG. 1will be designated by the same reference numerals.

FIG. 2shows that dial2includes an aperture10whose dimensions and shape are adapted to those of front substrate14which defines the upper display surface of liquid crystal display cell12. It is also seen that a second solar cell220has substantially the same dimensions as dial2and is provided with an opening221which houses liquid crystal display cell12when solar cell220is disposed underneath dial2. It is understood that, when a solar cell of the same dimensions as dial2is placed underneath dial2, part of the surface of the solar cell will be concealed by liquid crystal display cell12. It was realised that the photovoltaic conversion efficiency of a solar cell with a given active surface is worse when the solar cell is partially obscured than when the active surface of the solar cell is reduced due to the presence of a shaped opening in which the digital information display device is housed.

Otherwise, the display module illustrated inFIG. 2is identical to that described above with reference toFIG. 1. Liquid crystal display cell12is secured to the lower face6of dial2, preferably by lamination, and solar cell220is accommodated in plate24. Thereafter, the assembly formed by dial2and liquid crystal display cell12is disposed atop solar cell220, so that solar cell220is underneath and at a small distance from dial2and liquid crystal display cell12is housed inside opening221. A backlight device40mounted from underneath main plate24backlights liquid crystal display cell12through the opening38provided in plate24. The assembly formed by dial2, liquid crystal display cell12and solar cell220is removably locked on plate24by means of a plurality of flexible locking hooks42.

As seen in the drawing, bearing surface26is pierced with two through holes32which are disposed in proximity to each other on a portion of the diameter of bearing surface26, and in which are engaged springs34which ensure the electrical contact between the two terminals of solar cell220and the electric power supply circuit of the watch (not shown). It is also seen that, to radially maintain solar cell220, at least one, and preferably three notches44, which cooperate with three corresponding lugs46of plate24, are provided at the periphery of solar cell220.

In the case where the timepiece is of the solar watch type, dial2must be at least partially transparent in order to allow through a sufficient amount of light for solar cell22,220to efficiently charge the watch battery while concealing the solar cell22,220from the wearer's view.

By way of example, dial2may be made of a transparent plastic material and be coated with a layer of paint, the opacity of which is adjusted according to the thickness of the paint layer and/or the concentration of pigments in the paint. The transmittance of a transparent plastic dial2coated with paint is on the order of 45%. In other words, 45% of the incident light is transmitted to solar cell22,220and the rest of the light is absorbed by dial2, which is sufficient to conceal solar cell22,220from the user's view. According to another example, plastic dial2may be coated with a mother-of-pearl layer whose thickness is typically 150 μm±20 μm and whose transmittance is adjusted to 35%. The mother-of-pearl layer is fixed to upper surface4of dial2by means of a layer of optically transparent adhesive.

According to another aspect of the invention, it is sought to give plastic dial2the appearance of a carbon fibre type composite material. It is known that such a composite material is obtained by means of intertwined carbon fibres impregnated with resin, the surface state of the resulting material having periodically repeated slightly raised areas.

To imitate this texture, two solutions are envisaged. The first solution consists in machining structured portions in the inner wall of the mould into which the plastic material is injected which will form as many raised areas on the surface of dial2. The second solution uses the principle of conventional pad printing (transfer with a cliché) or electronic printing, which can also be envisaged from a technical point of view, but which provides a slightly less satisfactory finish to the eye. As illustrated inFIGS. 3A and 3Bannexed to this Patent Application, the carbon effect is obtained by the alternate and periodic repetition of horizontal lines48and vertical lines50. Although horizontal lines48seem lighter, this is only due to the angle of incidence of the light. This effect makes it possible to bring the dial “to life” with light and this is exactly the same as with real carbon. The lines are black (horizontal lines and vertical lines). A mixture of black (vertical lines) and grey (horizontal lines) could also have been used to obtain the carbon effect, but in that case the effect would be independent of light and quite static.

It goes without saying that the present invention is not limited to the embodiments that have just been described and that various simple modifications and variants can be envisaged by those skilled in the art without departing from the scope of the invention as defined by the annexed claims. It will be noted, in particular, that in the embodiment illustrated inFIG. 1, liquid crystal display cell12and the first solar cell22each have a recess, respectively52and54, for the passage of the hour and minute hand arbors. Likewise, a through hole56is provided on the edge of bearing surface26of main plate24and backlight device40is pierced with a hole58. In a similar manner, the second solar cell220is pierced at the centre with a hole60and plate24is provided with a hole62delimited by a guide collar64.