HK1078655B - Backlighting device for an information display element of a portable object - Google Patents

Description

Backlight device for information display element of portable object

Technical Field

The present invention relates to a backlighting device for an information display element of a portable object such as a wristwatch. The backlight device comprises a light guide plate with a front surface and a back surface, a light reflector on the back surface of the light guide plate, and a visible light source. The visible light source provides a beam of light at an edge or boundary of the guide plate. The light beams propagate between the two faces of the light guide plate to be guided to illuminate a display screen located above the front face of the guide plate. The apparatus further includes a layer disposed opposite to a rear surface of the display element of the portable object from a side of the front surface of the guide plate. The layer also has at least one region having a partial opacity which decreases from the limit close to a boundary region of the guide plate receiving the light beam of the light source. This attenuates the intensity of light passing through the region.

Technical Field

In the case of an object such as a watch, the display element is understood to be a watch face on which the hour hand indicates the time, a liquid crystal display displaying time, text and image information, or a combination of a watch face and a display.

Devices for backlighting displays, in particular liquid crystal displays, have already been described in the prior art, which are referred to as backlights. Such devices are used in particular for objects such as wireless mobile telephones, portable computers or other types of portable objects currently in use.

In those larger sized objects, it is generally simpler to illuminate a display element from its back surface over its entire viewing surface. For this purpose, backlighting can be achieved by using one or more light sources arranged opposite layers of a light guide plate. The light source emits light into the light guide plate, so that the light is directed to the display element. When several light sources are arranged at a large distance apart with respect to the viewable portion of the display element, the display element can be illuminated more evenly.

In the case of a watch, it is difficult to provide several light sources to illuminate the display from behind, because the space available in the case is limited. Since the number of components mounted in the case must be reduced to achieve all the intended functions of the watch, a single light source is usually provided to ensure the illumination of the display element.

In the case of a conventional backlight device, the light source is mounted within the housing of the watch below the display element at a location adjacent to the viewable portion of the display element. Even if the light source is partially hidden under the display element, its light emission may result in the formation of a halo (halo) around the light source, which halo is visible from the outside through the display element.

Because the halo has a greater intensity of light than the light illuminating the remainder of the display element, the illumination of the display element from behind is non-uniform. This is a major drawback of such a backlight device if it is used, for example, in high-end watches.

Document US 2823476 describes a backlight of a dial. The device comprises a light guide plate, at the boundary of which a light source is arranged to propagate a light beam into the light guide plate between a back side and a front side of the plate. A compensation film is arranged on the front surface of the light guide plate to make the brightness of the dial plate uniform. The opacity of the compensation film is gradually reduced from the edge of the light guide plate receiving the light beam.

To implement the compensation film, a photographic emulsion must first be applied to the film, the film is placed on the device, the light source is turned on, and the emulsion is developed in a dark room to obtain an area of decreasing opacity. All said operations are complex and costly, which is a drawback, in order to obtain such a compensation film.

Disclosure of Invention

The main object of the present invention is therefore to overcome the above drawbacks by providing a backlight device for an information display element of a portable object, which allows to uniformly illuminate the display element, in particular in an area surrounding the light source, and which is easy to implement.

On this basis, the invention relates to a backlight device for an information display element of a portable object, such as a wristwatch, characterized in that the partially opaque region is obtained by: by applying a dark white or silver dye to the layer or disposing said dye integrally with the layer; or through a semi-transparent metal coating of varying thickness; or through a metal overlay penetrated by a plurality of holes of varying diameter and spacing having dimensions less than the resolution of the human eye; or by a metal coating formed by a plurality of metal dots of varying diameter and spacing so that the beam is partially reflected and returned into the light guide plate to reduce the loss of useful photons.

An advantage of the backlight according to the invention is that halos caused by a light source located under and close to the visible part of the display element can be attenuated by areas with a decreasing opacity obtained by said dye or said cover layer. Thus, due to the regions of decreasing opacity, the display elements of the portable object may be uniformly illuminated, which may also depend on the viewing angle of the display elements. Thus, a single light source is sufficient to illuminate the display element. The light source may be a light emitting diode mounted on a printed circuit board and positioned within a chamber that is open at the top of a connector mounted on the printed circuit board.

Of course, because the intensity of light moving from the light source to the halo at a predetermined distance from the light source gradually decreases, the partial opacity of the region of the layer must also decrease as one moves away from the light source. Since the decrease in the intensity of the halo is non-linear as a function of distance, the decrease in opacity for a given distance over which the region extends on the layer is also non-linear.

The partially reduced opacity zone is preferably obtained by a dye applied to or integrally disposed in the layer, or by offset printing (offset), or by a semi-transparent metal coating of variable thickness, or by a metal coating penetrated by a plurality of holes of varying diameter and spacing, or formed by a plurality of metal dots of varying diameter and spacing as a function of the resolution of the human eye. The dye used may be a gradually weakening (shade) black, white or silver. The dye is for example an ink applied by a printing machine. White is advantageous when the layer with partially opaque areas forms an integral part of the front face of the light guide plate to diffusely reflect a portion of the light for redistribution within the light guide plate.

The layer having the partially opaque region may also be a light diffusion film or a light correction film on the front surface of the light guide plate.

Advantageously, the light guide plate has a rounded corner in its circumferential direction covered by a light-reflecting layer, which may be a completely opaque white paint coating or a metal cover layer. The light emitting diodes are thus arranged below the rounded corners to provide a light beam in a vertical direction. In this way, the light beam can be reflected by the reflective layer at the edge of the light guide plate to pass into the light guide plate between the front and back faces.

A tab made of silicon material allows the upper portion of the LED to engage the rounded lower surface of the printed circuit board to limit optical losses. The joint is selected to have a refractive index intermediate between the refractive index of the transparent material of the light emitting diode and the refractive index of the light guide plate.

Advantageously, the light guide plate, the reflector and the partially opaque region form a single element.

Drawings

The objects, advantages and features of the backlight of an information display element of a portable object will become apparent from the following description of at least one embodiment of the invention, taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a three-dimensional exploded view of a backlight according to the present invention;

FIGS. 2a and 2b show a top view and a perspective view of a backlight according to the invention with all elements assembled together;

FIGS. 3a and 3b show top views of two embodiments of a diffuser film of a backlight according to the invention;

FIG. 4 schematically shows a partial cross-sectional view of a first embodiment of a backlight device according to the invention at a light source;

FIG. 5 schematically shows a partial cross-sectional view of a second embodiment of a backlight device according to the invention at a light source;

fig. 6 is a simplified graph showing the light intensity of light emitted from the backlight without intensity attenuation and with intensity attenuation as a function of distance from the light source.

Detailed Description

In the following description, those elements of the backlight device which are well known to those skilled in the art will not be described in detail. The embodiments relate specifically to a backlight device for an information display element of a wristwatch. The display element may be a liquid crystal translucent type screen or a watch face having regions transparent to visible light.

Fig. 1 shows a three-dimensional exploded view of an embodiment of a backlight 1 suitable for a wristwatch. In this embodiment, a backlight 1 for an information display element (not shown) first comprises a printed circuit board 3 on which a light source, such as a vertically illuminated light emitting diode 2, and at least one electronic component 4 are fixed. The leds are powered by a power source (not shown), such as a battery or accumulator, which is electrically connected to the printed circuit board 3.

A frame-like, preferably white or black, coupling member (cross) 12 made of plastic material is detachably mounted on the printed circuit board. The coupling is positioned using a mounting structure formed by posts 26 that contact the edge of the printed circuit board 13. A chamber 5 is provided outside the coupling member 12 to accommodate the light emitting diode. The chamber has a plurality of vertical walls partially surrounding the diodes 2.

The chamber may of course also be provided with vertical walls completely surrounding the light emitting diodes so that they provide a light beam only in the vertical direction. An opaque frame (not shown) may also be interposed between the walls of the chamber and the leds.

The backlight 1 for a display element further comprises a light guide plate 7, a light reflector 6 of the diffusing (reflective) or specular type mounted on the back of the light guide plate and a layer provided between the front of the light guide plate and the display element, the layer having a partially opaque region 10'. On a part of the front surface of the light guide plate 7, a lens device 7 of, for example, a nanometer order or other size is provided. The lens device may also be disposed on a portion of the back surface of the light guide plate.

The light guide plate 7 also has a rounded corner 8 covered by an opaque white paint coating or metal cover. The leds 2 in the chamber 5 are arranged just below the rounded corners at the edge of the light guide plate. The light-emitting diode provides light beams perpendicularly at the rounded edges, so that these light beams are reflected diffusely by the white paint coating or specularly by the metal cover layer. After being reflected at the rounded corners, the light beams travel between the front and rear surfaces of the light guide plate to be reflected by the reflectors and refracted by the nano-scale lens devices.

The light guide plate 7 and its nano-scale lens arrangement may be made of PC (polycarbonate) or PMMA (polymethylmethacrylate/plexiglass).

In this embodiment, the layer with partially opaque areas is a flexible light diffusing film 9 on which a flexible light restifier film 11 can be mounted. The flexible light correction film 11 may be a T-BEF 90/24 film manufactured by 3M company. The correction film may include micro prisms on its front or back surface to correct and direct light toward the display elements. The rows of microprisms may preferably be arranged perpendicular to the axis of light transmission in the light guide plate to better collimate and maximize the intensity of the light. Two correction films with intersecting rows and columns of prisms may also be used to maximize the intensity of light at a predetermined viewing angle of the display element.

Said partially opaque regions extend over the diffuser film 9 to a limit 25 representing the borderline of the visible part of a display element within a predetermined distance d1 from the light source, as can be seen more clearly with reference to fig. 3a and 3 b. The distance d1 may depend on a natural viewing angle of the display element, which in the case of a watch is not necessarily perpendicular to the display element.

It should be noted that the visible portion of the display element is preferably defined by an opaque raised support (not shown) of the watch crystal, which support holds the display element. In case the raised support and the case bezel (bezel) or case of the watch are both substantially transparent, it may be necessary to provide a partially or completely opaque layer 10, e.g. black as shown in fig. 3b, on the diffuser film 9 around the visible part of the display element.

The light intensity of the halo caused by the light source and visible from the outside of the display element decreases non-linearly from the limit 25 to a distance d1, from which distance d1 the light intensity is substantially uniform. Thus, similar to the light intensity of the halo, the opacity of the region must decrease non-linearly from limit 25 to a distance d1 from the light source to ensure that the entire display element is uniformly illuminated. The partial opacity of this region may decrease from about 80% at boundary 25 to 0% at distance d 1.

Fig. 6 simply shows the light intensity on the display element as a function of the distance from the light source position. It can be seen that the light intensity of the halo decreases non-linearly up to distance d1, which can be considered more or less constant from distance d 1. The intensity of light transmitted through the display element when no layer with partially opaque regions is provided is shown by curve a. In the presence of such a layer, the light intensity is shown by curve b to be uniform under the attenuating effect of the opaque areas as indicated by the hatched portions. As a result, the opacity at each location of the area must correspond to the intensity level shown on curve a.

The partially opaque regions 10' on the diffuser film 9, which are shown in simplified form in fig. 1, 3a and 3b, can be obtained by means of a dye deposited on the flexible diffuser film or provided integrally with the diffuser film, or by means of an offset printing (offset). The dyes used may be black, silver or white gradations. For example, black dye is an ink applied by a printer. In the case of black, light passing through the partially opaque region is partially absorbed and lost, but in the case of white, the light is partially reflected in a diffuse manner and returns to the light guide plate to reduce the loss of useful photons. The recovered photons may be directed to other less bright areas of the light guide plate 7.

The partially opaque region 10' may also be obtained by a semitransparent metallic coating of varying thickness, or by a metallic coating pierced by a plurality of holes of varying diameter and spacing as a function of the resolution of the human eye, or by a metallic coating formed by a plurality of metallic dots of varying diameter and spacing obtained by means of a template having pierced holes, instead of a dye. The metal overlay may be achieved by a vacuum metallization process and the holes of the thin coating or template may be made by punching with a laser beam or other photolithographic methods.

As shown in fig. 3b, it is conceivable that the diffuser film comprises a further partially opaque area in order to form a specific pattern 9, such as at least one letter, at least one symbol or an image, on the background of the display element. Depending on the change in opacity of the region, a monochrome image may be displayed.

Of course the partially opaque region may be formed from a different layer than the diffuser film. The region may be formed directly on the front surface of the light guide plate, on the correction film 11, or on the back surface of the display element. In the case where a region is provided on the light guide plate, it is preferable to select a white dye which gradually weakens from a boundary corresponding to a boundary line of a visible portion of the display element from the light source side. With white color deposited directly on the light guide plate, light can be partially reflected in a diffuse manner, so that useful photons can be recovered as described above.

Since the backlight must be easy to handle during the operation of fitting into the watch case, all the elements forming the backlight must be pre-fitted together. To this end, according to fig. 1, the coupling piece in the form of a frame 12 first comprises a first inner shoulder 13, on the side wall of which first shoulder 13 two resilient fingers 15 are provided. The reflector 6 and the light guide plate 7 are held between a supporting surface of the first shoulder and the two resilient fingers 15.

In the case where it is envisaged that a diffuser film 9 and/or a correction film 11 should be mounted, the coupling member further comprises a second inner shoulder 14 located above the first shoulder 13. The diffuser film 9 is first placed against the second shoulder and held by a tab 20 in the inserted housing 16 of a side wall of the second shoulder. The correction film 11 is then placed against the diffuser film and, similarly to the case of the diffuser film, is held by a projection 21 which is also inserted into the housing 16. In this way all the light transmitting or reflecting elements are held within the coupling piece, which itself is mounted to the printed circuit board on which the light emitting diodes 2 are fixed.

The surface areas of the reflector 6, the light guide plate 7, the diffusion film 9, and the correction film 11 are each greater than or equal to the surface area of the visible portion of the display element.

As can be seen in fig. 1, a portion of the diffuser film on which the regions of decreasing opacity have been provided is located on this rounded corner 8. As also shown in fig. 3, this portion of the diffuser film is covered by a completely opaque black layer 10, which layer 10 extends to the limit of the beginning of the region of decreasing opacity.

The shape of the backlight, all its elements assembled together, can be better seen from fig. 2a and 2 b. The elements forming the device in fig. 2a and 2b will not be described, as these elements have been described above, in particular with reference to fig. 1.

In addition, two variations of the backlight device are also described with reference to fig. 4 and 5. Those elements which have already been described above naturally have the same reference numerals and will only be described briefly.

The backlight device shown in a partial sectional view includes a printed circuit board 3, light emitting diodes 2 fixed on the printed circuit board, a coupling member 12 of a chamber 5 having the diodes 2, a reflector 6, a light guide plate 7, a diffusion film 9, and a correction film 11.

As shown in fig. 4, the light emitting diode 2 may be located directly below the rounded corner at a short distance from the back surface of the light guide plate. Thus, the upper side of the diode 2 is separated from the rounded corner 8 by a gap. One edge of the reflector 6 is flush with the upper edge of the chamber. The edge of the reflector may preferably be located directly on the edge of the light outlet of the light emitting diode, so that no reflected light is lost via rounded corners.

Since there is provided a region 10' of partial opacity which decreases with increasing distance from the diode, the light F redirected and directed by all the light propagation and emission elements_LIs substantially the same at each location so that the display element can be uniformly illuminated.

In the variant shown in fig. 5, a silicon tab 17 is provided to engage the upper portion of the led 2 with the rounded lower surface of the printed circuit board. Preferably, the joint has a refractive index intermediate between the refractive index of the transparent material of the light emitting diode and the refractive index of the light guide plate.

The portion of the coupling 12 defining the chamber 5 that completely houses the light emitting diodes 2 may define a completely opaque enclosure. This avoids the stray light effect in the case of a watch case clasp or case of the watch being transparent.

Of course, it is also conceivable to place the diodes in the same plane as the light guide plate so that the diodes can provide light beams in a horizontal direction through an edge of the light guide plate. In this case, the light guide plate no longer has rounded corners.

From the above description, a person skilled in the art will be able to envisage many variants of the backlight device without departing from the scope of the invention as defined by the claims. In the case where it is desired to deliberately attenuate the light intensity to give a particular effect through the display element, one or more further partially opaque regions may be provided on the layer. The further region may be disposed on a side of the front or back of the light guide plate. The partially opaque regions may be realized with a bright dye. One possible idea of the device is to use only a reflector and a light guide plate on which one or more partially opaque regions are arranged to reduce production costs. The reflector and the light guide plate may form only one element.

Claims (14)

1. Backlight device (1) for an information display element of a portable object, said device comprising: a light guide plate (7) having a front surface and a back surface; a light reflector (6) on the back of the light guide plate; a visible light source (2) for providing a light beam to a boundary or edge of the guide plate, said light beam propagating within said light guide plate between two faces of the light guide plate; and a layer, said layer being arranged from the side of the front face of the guide plate towards the rear face of the display element of said portable object, said layer having at least one region (10 ') with a partial opacity that gradually decreases from a limit (25) close to a border region of said guide plate receiving the light beam of the light source, said light source being located below and close to the visible part of the display element, to attenuate the intensity of the light passing through said region, characterized in that said region (10') with partial opacity is obtained in such a way that: by a fading white or silver dye applied on or integrally disposed in said layer; or by a translucent metal cover layer of varying thickness; or through a metal overlay penetrated by a plurality of holes of varying diameter and spacing, the size of the holes being smaller than the resolution of the human eye; or through a metal cladding formed of a plurality of metal dots of varying diameter and spacing so that the light beam can be partially reflected and returned back into the light guide plate to reduce the loss of useful photons.

2. Backlight (1) according to claim 1, characterized in that it is used in a wristwatch, the partial opacity of said area (10') decreasing non-linearly from the limit close to the edge of said light-guide plate.

3. Backlight device (1) according to claim 2, characterized in that the layer with partially opaque areas (10') forms an integral part of the front side of the light guide plate (7) or serves as a polarizing film for the display element.

4. Backlight device (1) according to claim 2, characterized in that the layer with partially opaque areas (10') is a light diffusing film (9) or a light correcting film (11) on the front side of the light guide plate (7).

5. Backlight device (1) according to claim 1, characterized in that the backlight device comprises a single light source for illuminating the display elements from behind, which light source is a light emitting diode.

6. Backlight device (1) according to claim 4, characterized in that: the backlight device comprises a coupling member (12) forming a frame in which a reflector (6), the light guide plate and a diffuser are held, and a printed circuit board (3) on which the light source is fixed, the light source being a light emitting diode; and a chamber (5) is formed by insertion in the circumferential direction of the coupling member to accommodate the light emitting diode (2), the coupling member being detachably mounted and positioned on the printed circuit board by a mounting structure (26).

7. Backlight device (1) according to claim 6, characterized in that the coupling member (12) comprises two resilient fingers (15) arranged on the side of a first inner shoulder (13) to hold the reflector (6) and the light guide plate (7) inserted between a supporting surface of the first shoulder and each resilient finger.

8. Backlight device (1) according to claim 7, characterized in that: above the resilient fingers (15), the coupling piece comprises a second inner shoulder (14) to receive a flexible diffuser film (9) held by a projection (20) inserted into the housing (16) in the side on which the second shoulder of the coupling piece is located; and a flexible, transparent light correction film (11) is located on the diffuser film and held by another protrusion (21) in the housing (16) of the second shoulder.

9. Backlight device (1) according to any of the preceding claims, characterized in that the light-guiding plate (7) has a rounded corner (8) covered by a light-reflecting layer (8 ') and a means (7') of microprisms or lenses having a nanometric size located on a portion of the front or back of the light-guiding plate; and the light source is arranged below the round angle to provide light beams along a direction perpendicular to the light guide plate, so that the light beams are reflected by the reflecting layer at the edge of the light guide plate and spread into the light guide plate between the front surface and the back surface of the light guide plate, and the light source is a light emitting diode (2).

10. A backlight device (1) according to claim 9, characterized in that: a portion of a diffuser film (9) is arranged above said rounded corners (8) of the light-guide plate (7), said portion of diffuser film being covered by a completely opaque black layer (10) extending to the limit of the beginning of said area with decreasing opacity; and the round corners are covered by an opaque white layer or a metal covering layer.

11. Backlight device (1) according to claim 6, characterized in that: the light-emitting diodes (2) are housed in the chambers of the coupling comprising side walls which partially or completely surround the diodes from an upper surface of the printed circuit board (3); and an edge of the reflector is flush with an upper edge of the chamber.

12. Backlight device (1) according to claim 6, characterized in that a joint (17) made of silicon material, having an intermediate refractive index between the refractive index of the transparent material of the light emitting diodes and the refractive index of the light guide plate, allows the upper part of the light emitting diodes (2) to be joined to a lower surface of the rounded corner of the printed circuit board.

13. Backlight device (1) according to claim 1, characterized in that the light guide plate (7), the reflector (6) and the partially opaque region form a single element.

14. Backlight device (1) according to claim 1, characterized in that the backlight device comprises one or more further areas (19) with partial opacity on the layer to arbitrarily attenuate the light intensity passing through the further areas to produce a specific effect or pattern by the display elements.