Abstract:
Dial ( 2 ) designed to equip a watch piece provided with luminous marks ( 32 ) lodged under a mother-of-pearl semi-transparent layer ( 20 ) inside blind hollows ( 35 ) made in the semi-transparent layer ( 20 ) and filled with a phosphorescent pigment ( 32 ). The luminous marks ( 32 ) form an image ( 61 ) visible in darkness and essentially invisible in daylight.

Description:
REFERENCE DATA  
         [0001]    This patent application claims priority from Swiss patent application No 2003CH-0561 filed on Apr. 1, 2003.  
         FIELD OF THE INVENTION  
         [0002]    The present invention concerns a dial for an instrument with an analog display and especially, but not exclusively, on a clock face designed to equip a wristwatch.  
         DESCRIPTION OF RELATED ART  
         [0003]    It is known to apply luminous indexes to a clock face to allow the time to be read in the dark. These indexes can take very different forms but, in most cases, they are shaped like a luminous stick or point and are applied, set or glued onto the upper face of the dial, in accordance with the position of the hours.  
           [0004]    To make luminous marks, one usually uses phosphorescent pigments, capable of being activated in day light and whose induced luminosity decreases sufficiently slowly to remain visible during the greater part of the night.  
           [0005]    One also knows luminous pigments in which the luminosity is induced by a radioactive substance mixed with a luminescent substance. Use of these pigments is however prohibited or restricted in most countries because of their danger.  
           [0006]    It is also known to add phosphorescent or luminous marks on a dial to obtain a particular aesthetic effect, for example to have a logo or an inscription appear. In this case, a layer of phosphorescent of luminescent material is applied onto the dial and it can, according to need, be covered with a coat of varnish or lacquer.  
           [0007]    An inconvenience of this type of construction is that the marks made with luminous material remain visible also in daylight with an aesthetic effect that is not always appealing.  
           [0008]    It is thus an aim of the present invention to propose a new dial that does not have the inconveniences of the prior art.  
           [0009]    This aim is achieved by the dial having the characteristics of the main claim and notably by a dial comprising: a substrate plate; a semi-transparent layer covering at least part of said substrate plate with a material allowing light to pass; phosphorescent, fluorescent or luminescent elements lodged between said substrate plate and said semi-transparent layer; in which said luminous elements form a luminous image visible in darkness, but essentially invisible in normal lighting conditions. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The present invention will be better understood by reading the description, the claims and the following figures, in which notably:  
         [0011]    [0011]FIG. 1 shows a cross section view of a watch dial according to the invention;  
         [0012]    [0012]FIG. 2 shows a cross section view of a watch dial according to a second embodiment of the invention;  
         [0013]    [0013]FIG. 3 represents a plane of a watch dial according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    The dial  2  represented in FIG. 1 comprises a substrate plate  10 , generally made of brass or of another metal and designed to supply a mechanical support to the construction. The substrate plate  10  is completely or partially covered by a semi-transparent layer  20  chosen according to the aesthetic effect one wishes to achieve. In a preferred construction embodiment, the semi-transparent layer  20  is constituted of a sheet of natural mother-of-pearl of 0.4 mm thickness. It is however possible to use other semi-transparent or translucent materials, such as a coat of varnish, lacquer, stained or matted glass, acrylic resin or epoxy or any other semi-transparent plastic resin. The thickness of the semi-transparent layer  20  can also vary according to the effect sought and the material chosen.  
         [0015]    For the construction of the dial  2 , the substrate plate  10  and the semi-transparent layer  20  are first cut out, embossed, stamped or machined according to the desired shape and size. During this step, the holes  51  necessary for the wheels and staffs of the hands as well as the apertures  54  for the date indicator, if required, are made in the substrate plate  10  and in the semi-transparent layer  20 .  
         [0016]    On the rear side  22  of the semi-transparent layer  20 , blind hollows  35  are made whose bottom is arranged in the direction of the visible side  21  of the semi-transparent layer  20 . The hollows  35  are then filled with a phosphorescent pigment of the desired color. The present invention allows use of several phosphorescent, luminescent or fluorescent materials, but one will preferably use high-performance non-radioactive phosphorescent pigments, for example Super-LumiNova® pigments commercialized by LumiNova SA.  
         [0017]    Once the hollows  35  are filled, a coat  25  of colored varnish is applied to the rear side  22  of the semi-transparent layer  20 . The function of the coat  25  is to give a shade of color to the dial  2  and to seal the pigment  32  to protect it from humidity.  
         [0018]    The color of the coat of varnish  25  and that of the pigment  32  are chosen so as to blend in normal lighting conditions, when the intrinsic luminosity of the pigment  32  is too weak to be perceived. In darkness, the light generated by the pigment  32  shines through the layer  20  and allows the silhouette of the hollow  35  to be seen, as a luminous image  61  on an obscure background, as can be seen in FIG. 3.  
         [0019]    Once application of the coat of varnish  25  has been completed, the semi-transparent layer  20  is fastened onto the substrate plate  10  to form the dial  2 . In the subsequent manufacturing phases, the upper side  21  of the dial  2  is polished and optionally provided with indexes  56  and/or other functional or decorative elements that are applied, glued, riveted, serigraphed, transferred, painted or realized through any other method.  
         [0020]    The luminous intensity of the image  61  depends on the thickness of the layer of pigment  32  and on the thickness d of semi-transparent matter  20  which the light emitted by the pigment  32  must pass through. It is consequently important that the hollows  35  be made with the greatest precision as any local variation of the thickness d will result in a considerable variation of luminous intensity because of the considerable absorption of light by the mother-of-pearl or the semi-transparent material. According to the manufacturing requirements and to the chosen material, the hollows  35  can be made by machining or selective chemical attack or by any other method.  
         [0021]    In another embodiment of the inventive dial, represented in FIG. 2, a layer of luminescent pigment  32  is applied by serigraphy, tampography, manually or by any other application method on the rear side  22  of the semi-transparent layer  20  and then covered by the protective layer  25 . This embodiment is very well suited to dials in which the thickness of the semi-transparent layer  20  is particularly thin.  
         [0022]    In a later embodiment of the inventive dial, also adapted to thin semi-transparent layers  20 , the blind hollows  35  are open in the substrate plate  10  and filled with the luminescent pigment  32 . The coat of colored varnish  25  can in this case be applied to the rear side  22  of the semi-transparent  20  or to the substrate plate  10 .