EP0078237B1 - Watch with an analogue display device, of which the dial is formed of a liquid crystal display cell - Google Patents

Abstract

A watch display comprises time display hands (3, 4) and a reflecting digital display (5) which acts as dial for the hands, the display being transparent under the effect of an electric field and opaque in the absence of the field.

Description

The present invention relates to watches and, more particularly, to a watch comprising movable members for analog time display and a display cell acting as a dial for the movable members. The display cell comprises a composite layer, certain areas of which undergo a change in their opacity under the effect of an electric field produced in response to an external action, with a view to displaying information, this layer comprising a crystal layer. liquid. This cell further comprises a closed space defined by a front plate, a rear plate and closing means, inside which is the layer of liquid crystal, and means for reflecting and diffusing light arranged at the back of the composite layer.

Such cells are described in an article by SUN LU: "Continuous display technologies for electronic watches" (Wescon 77 conference record september 1977, Session 30/2), and in particular cells comprising a mixture of liquid crystals and pleochroic molecules.

We know from patent application GB-A-2 052 115 a watch with time display by hands, and date by an electro-optical display cell placed behind the hands.

Patent application JP-A-53-99,979 also describes a watch comprising hands and an electro-optical display cell placed behind them. This watch includes control means making it possible to erase the information carried by the cell.

In the last two examples, in the absence of a field, the cell lets in light and absorbs it in the presence of the field, so that the information appears in dark on light foud. It follows that the surface forming the dial is constituted by the reflector-light diffuser located at the rear of the cell.

These two known watches thus have the drawback of the unsightly effect due to the relatively large distance separating the hands from the surface forming the dial.

The object of the invention is to remedy this drawback.

To this end, according to claim 1, the watch comprises a liquid crystal display cell, the composite layer of which is transparent under the effect of the electric field and opaque when no electric field is applied to the crystal layer. liquid.

Thus, the aesthetics of the watch is improved thanks to the fact that the surface forming the dial, that is to say the surface furthest from the hands which reflects light capable of reaching the eye of the user, is located closer to the hands or other analog time display device, than the reflector-diffuser.

According to a currently preferred embodiment, the watch cell is of the type comprising a layer of liquid crystal containing a nematic compound with positive dielectric anisotropy, and pleochroic molecules having a substantial light absorption coefficient in most lengths visible waves. A polarizer is placed between said liquid crystal layer and the reflector-diffuser.

• - la figure 1 est une vue de dessus d'une montre selon un mode de réalisation de l'invention;
• - la figure 2 est une vue schématique en coupe verticale selon le plan A-A de la figure 1, montrant un premier exemple de réalisation de la cellule d'affichage à cristal liquide de la montre; et
• - la figure 3 est une vue schématique en coupe verticale suivant le plan A-A de la figure 1, montrant un deuxième exemple de réalisation de la cellule d'affichage à cristal liquide de la montre selon l'invention.

The advantages and characteristics of the invention will be better understood on reading the description which follows, of several embodiments, description made with reference to the appended drawings in which:

• - Figure 1 is a top view of a watch according to an embodiment of the invention;
• - Figure 2 is a schematic view in vertical section along the plane AA of Figure 1, showing a first embodiment of the liquid crystal display cell of the watch; and
• - Figure 3 is a schematic view in vertical section along the plane AA of Figure 1, showing a second embodiment of the liquid crystal display cell of the watch according to the invention.

The drawings represent a watch whose case includes a middle part I and a watch glass 2. This watch includes analog time display means comprising an hour hand 3 and a minute hand 4. These hands 3, 4 are arranged above a liquid crystal display cell 5 which forms a dial for the hands 3 and 4, and which extends over the entire area of the window 6 covered by the watch glass 2, of the case. The cell 5 has a bore 5a located substantially in its center; this bore is crossed by the axis 3a on which is fixed the hour hand 3, and by the axis 4a on which is fixed the minute hand 4.

The watch shown also comprises a control circuit represented diagrammatically by a rectangle bearing the reference 7 in FIGS. 2 and 3. The circuit 7 responds to an actuation signal supplied by a device 8, by applying to the input terminals 5b of the display cell 5 a suitable control signal. The actuating device 8 comprises means allowing the entry of information from outside the watch. These means are for example constituted by an operating member with crown 9 and by a pusher 10. Of course, the operating member with crown 9 and the pusher 10 can be replaced by any other device such as capacitive or element devices photosensitive, allowing information to be entered into the watch.

According to the information transmitted by the device 8 to the circuit 7, the latter applies a control signal to the terminals 5b of the cell 5 so that the latter displays particular information, chosen from several types of information. It can be, for example, time information such as the hour, minute and second, as shown in FIG. 1. It can also be date information, information of timed time, etc. Same As long as this information is displayed in digital form, cell 5 displays a characteristic sign of the type of this information. Thus, it can be seen in FIG. 1 that the cell 5 displays, in addition to the hour, minute and second information 11, arranged on the lower part of the surface of the cell 5, a stylized informative sign 12 indicating that this is hourly information. As shown in FIG. 1, it is advantageous to place the information sign 12 in a place in cell 5 which is not covered by the trajectory of the analog time display hands 3, 4. If, as shown in the FIG. 1, the shape of the window 6 is rectangular, informative signs such as 12 are advantageously placed near the two upper corners 6a, 6b of said window 6.

The circuit 7 comprises, as is well known, a generator of a time standard signal, such as a quartz oscillator, a divider, counters and a decoder receiving the counting information signals supplied by said counters . The device 8 comprises, for example, switches interposed between said decoder and the input terminals 5b of the display cell 5. Said switches are for example controlled by the pusher 10 forming part of the actuating device 8. Each depression the push-button 10 causes, for example, the closing of a contact connecting a voltage source to the input T of a type T flip-flop whose output Q is connected to the MOS transistor control electrodes constituting the above-mentioned switches. Thus, a first pressing of the push-button 10 causes the display by the cell 5 of information such as it and of a sign such as 12. A second pressing of the push-button 10 makes this display disappear.

FIG. 2 shows an exemplary embodiment according to which the display cell 5 is of the type which is described in the American patent US-A-3,731,986. This type of cell is generally called "twisted nematic liquid crystal".

The cell 5, according to FIG. 2, comprises a transparent front plate 13, a transparent rear plate 14, spacing and closing means 15 delimiting, in cooperation with the plates 13 and 14, a closed space situated between said plates. In this closed space is a nematic liquid crystal layer with positive dielectric anisotropy 16. The liquid crystal layer 16 has, in the absence of an electric field, a helical structure with an axis substantially orthogonal to this layer and having an angle 90 ° total torsion

The cell 5 further comprises two polarizers 17 and 18 placed, respectively, on either side of the assembly formed by the plates 13 and 14 and the liquid crystal layer 16, the optical axes of the polarizers being parallel to each other.

The cell 5 finally comprises a wall 19 whose face facing the assembly formed by the plates 13 and 14 and the polarizers 17 and 18 is reflecting and diffusing light. The liquid crystal layer 16 and the polarizers 17 and 18 form a composite layer whose opacity can be modified under the effect of an electric field.

To do this and in the display areas intended to display information such as time information 11 or the information sign 12, the front plates 13 and rear 14 are provided with electrodes 20 respectively 21.

When a potential difference is established between electrodes 20 and 21, the part of liquid crystal 16 located between these electrodes is subjected to an electric field having the effect of removing in said part the helical structure and replacing it with a structure homeotropic.

The axes of the polarizers 17 and 18 are parallel to each other. As a result, in the absence of an electric field applied to the liquid crystal layer 16, the composite layer is uniformly opaque. In this way, cell 5 appears uniformly dark over its entire extent. The analog time display hands 3, 4 which are advantageously of a clear and brilliant color, stand out and are therefore easily visible on this dark background which constitutes cell 5. In addition, the composite layer of this cell being opaque, the surface constituting the dial in front of which the hands 3 and 4 move is located at the front polarizer 17, therefore much closer to the hands than the reflecting surface of the reflector-diffuser 19.

It should be noted that the information which is displayed by cell 5 is clear on a dark background and it only appears at the request of the user of the watch, that is to say when the latter acts on pusher 10.

According to the example shown in the drawings, cell 5 is also provided with means for permanently displaying a sign or information, for example a mark of frabism, such as the mark represented schematically by the letters XYZ, 22 in FIG. 1 .

This permanent display can be obtained by a metal deposit 22a such as an aluminum layer deposited on one of the faces, for example on the internal face of the front plate 13.

Alternatively, the trademark sign could be displayed by means of electrodes, by applying an electric field to the layer of liquid crystal.

Advantageously, a partially reflecting layer 23 is placed at the front of the plate 13.

According to the example shown in Figure 3, the liquid crystal display cell 5 is of the type described in American patent US-A-3,551,026. This type of cell is generally designated by the name HEILMEIER of its inventor.

The cell of the watch shown in FIG. 3 differs from that of the watch shown in FIG. 2 in that it comprises a layer of liquid crystal 160 comprising, in addition to a nematic compound with positive dielectric anisotropy, a pleochroic dye, and that it has only one polarizer 180.

The liquid crystal layer 160 is disposed in a closed space delimited by a front plate 130, a rear plate 140, and spacing and closing means 150 hereinafter called spacer.

The pleochroic dye contained in the liquid crystal layer 160 advantageously has a relatively high absorption coefficient in most of the visible wavelengths, so that the cell is present at rest, that is to say in the absence electric field applied to said liquid crystal layer 160, a substantially black or slightly tinted color, depending on the proportions of pleochroic molecules constituting the dye. This dye is for example that which is described in the patent application in FRG DE-A-30.28.593.

The internal faces, that is to say the faces facing the liquid crystal layer 160, of the plates 130 and 140, comprise planar alignment layers capable of inducing an alignment of the nematic liquid crystal molecules and therefore of the pleochroic dye molecules, contained in layer 160, in a single direction, parallel to plates 130 and 140. The optical axis of polarizer 180 is oriented parallel to said single direction. Thanks to these provisions, in the absence of an electric field applied to the liquid crystal layer 160, the cell 5 of FIG. 3 has a uniformly dark black appearance.

When the user of the watch actuates the device 8 with a view to obtaining the display by cell 5 of FIG. 3, of information of any type, for example time information 11, the circuit 7 applies to terminals 5b a control signal such that a potential difference is established between certain electrodes 20 and certain electrodes 21 of the plates 130 and 140. As a result, the layer of liquid crystal 160 is subjected, at the locations located between said electrodes 20 and 21, to an electric field suppressing said planar alignment of the molecules of nematic liquid crystal and of pleochroic dye and replacing this alignment with a homeotropic alignment having the property of allowing polarized light to pass, whatever its frequency spectrum and whatever the orientation of its plane of polarization. As a result, the information displayed by cell 5 in FIG. 3 is in clear on a dark background.

In the absence of an electric field applied to the liquid crystal layer 160, the composite layer formed by the liquid crystal layer 160 and the polarizer 180, is uniformly opaque over the entire extent of the cell 5. When an electric field is applied between two electrodes 20 and 21 of certain display areas, this layer only becomes substantially transparent in these display areas, that is to say only in places where the liquid crystal layer 160 is subjected to an electric field. As a result, here again as in the case of FIG. 2, the surface forming the dial in front of which the hands 3 and 4 move is clearly above the reflecting surface of the reflector-diffuser 19.

The distance separating the hands 3 and 4 from the surface forming the dial is thus relatively small, which appreciably improves the aesthetics of the watch.

The spacer 150 is advantageously made of a resin-based bonding material and containing a pigmentation agent having substantially the same color as the pleochroic dye contained in the layer of liquid crystal 160. In this way, the closure means 150 make integral part of the dial surface.

This resin can be an epoxy resin, a polyester, a phenolic resin, an acrylic resin, a polyurethane, or a derivative of these constituents.

In order not to deteriorate the mechanical characteristics of the spacer, it is sought to have the lowest density of pigmentation agent. Due to the higher absorbency of inorganic pigments, it is possible to have an appearance similar to that obtained by pleochroic molecules, for a lower density.

The density of the pigmentation agent making it possible to obtain a suitable coloration of the material constituting the spacer is clearly lower than that of dye having the same effect.

When the dye is black, the pigmentation agent used can be: carbon black, smoke black, a metal oxide, etc., mixed or not with pleochroic molecules.

As a variant to the solution described above, the polarizer 180 can be placed at the front of the front plate 130 and not at the rear of the rear plate, as shown in FIG. 3.

According to another embodiment, cell 5 can be of the type described in American patent US-A-3,833,287. According to this embodiment, the liquid crystal layer 160 also contains a chiral compound inducing in said layer 160 a helical structure of pitch such that all the components of the light are absorbed.

Under the effect of an electric field applied in particular areas of the liquid crystal layer 160, the molecules of this layer are oriented, in these areas, perpendicular to the plates so that the light is no longer absorbed by the pleochroic molecules making these areas transparent.

In this case, the polarizer 180 becomes unnecessary and can therefore be omitted.

We have just described three embodiments of the invention making it possible to obtain a dark dial which, while offering the user a certain amount of additional information at the time, provides a remarkable aesthetic effect, because it appears very close to the needles.

It should be noted that the effect obtained is all the better as the amount of light reflected by the elements inserted between the layer of liquid crystal and the needles is large compared to the amount of light which passes through the composite layer after being reflected by the reflector- _{1 V.} broadcaster, taken globally across the width of the spectrum. This implies a judicious choice of the absorption characteristics of the reflector-diffuser, of the polarizers and / or of the pleochroic molecules.

Thus, if one wishes to display the information in gray on a black background, one chooses polarizers and / or pleochroic molecules absorbing throughout the width of the visible spectrum and a white reflector-diffuser. If it is desired to produce a display cell whose information is colored on a black background, polarizers and / or dichroic molecules absorbing across the entire width of the visible spectrum are chosen, associated with a colored reflector-diffuser. If you want to make a display cell whose dark background is slightly tinted and whose information is colorful, choose polarizers and / or dichroic molecules absorbing across the spectrum, except for a few lengths of waves and a colored reflector-diffuser.

Obtaining a tinted background is limited by the fact that the quantity of light passing through the composite layer is thus increased after being reflected by the reflector-diffuser. This limitation can be lifted thanks to the partially reflecting layer, which the front plate of the cell can carry.

This layer increases the amount of light reflected by the elements inserted between the liquid crystal layer and the needles, which also makes it possible to increase the amount of light which passes through the composite layer after being reflected by the reflector-diffuser, without for you might as well lose the desired effect.

If it is thus possible to tint the background more markedly, it should nevertheless be noted that an exaggeration in this direction leads to a reduction in the contrast of the display.

Claims (8)

1. A watch comprising:

(a) mobile analogue time display elements (3, 4); and

(b) a display cell (5) acting as a dial for said mobile elements and including:

- a composite layer (16-18; 160, 180) of which some regions vary in opacity under the effect of an electric field produced in response to an external action, to display information, said composite layer including a layer of liquid crystal (16; 160),

- a closed space defined by a front plate (13, 130) a rear plate (14, 140) and spacer and closure means (15, 150), inside which is located said layer of liquid crystal (16; 160); and

- light reflecting and diffusing means (19) behind said composite layer, characterised in that said cell is of the kind where the composite layer is transparent under the effect of the field and opaque in the absence of field, such that, in the absence of the field, said layer has a uniformly opaque appearance and hence itself acts as a dial for said analogue display.

2. A watch as in claim 1, characterised in that the composite layer includes two polarisers (17, 18) with one place in front of the liquid crystal layer (16) and the other sandwiched between the liquid crystal layer and the light reflecting and diffusing means (19), in that the liquid crystal layer has a helical structure with an axis at substantially right angles to the plane of said layer, the angle of twist of the helix being 90°, and in that the axes of the polarisers are parallel with one another.

3. A watch as in claim 1, characterised in that said composite layer further includes a polariser (180) and in that the liquid crystal layer (160) includes a nematic compound and pleochroic colouring.

4. A watch as in claim 3, characterised in that said polariser (180) is adjacent the light reflecting means (19).

5. A watch as in claim 1, characterised in that said liquid crystal layer (160) includes a nematic compound, pleochroic colouring and a chiralic compound inducing in the liquid crystal layer a helical structure.

6. A watch as in claims 3, 4 and 5, characterised in that the pleochroic colouring has a relatively high coefficient of absorption in most visible light wavelengths.

7. A watch as in any one of claims 3 to 6, characterised in that said spacer and closure means (15, 150) include adhesive material with which is associated a pigmenting agent having substantially the same colour as the pleochroic colouring.

8. A watch as in any one of claims 1 to 7, characterised in that front plate (13, 130) bears a partly reflecting layer (23) on one face thereof.

Images