GB2261100A

GB2261100A - Light scatter film for a display

Info

Publication number: GB2261100A
Application number: GB9220928A
Authority: GB
Inventors: Reinhard Moller
Original assignee: TA Triumph Adler AG
Current assignee: TA Triumph Adler AG
Priority date: 1991-10-28
Filing date: 1992-10-05
Publication date: 1993-05-05
Anticipated expiration: 2012-10-05
Also published as: GB9220928D0; DE4135506A1; ITMI922220A0; CH686463A5; GB2261100B; SE9202761D0; SE9202761L; FR2683071B1; ITMI922220A1; DE4135506C2; IT1255835B; JPH0675223A; FR2683071A1

Abstract

A background illuminated display arrangement has a housing (1), a display (4) facing the viewer, a lights deflecting unit arranged behind the display (4) and covering the display unit area, and at least one light source (9) illuminating the light deflecting unit from behind. The light deflecting unit consists of a photographically produced transparent scatter film (6) whose photographic coating (8) is illuminated by each light source in the skimming manner of a dark field illumination and which has photographically produced scatter bodies, whose density distribution is inversely proportional to the light intensity distribution across the area of the scatter film (6). The scatter film is produced by exposing a photographic film while the film is in a recording device which imitates the actual illuminating conditions in the display. <IMAGE>

Description

I _1 11 a 1 DISPLAY DEVICE AND METHOD FOR MANUFACTURE OF LIGHT SCATTER

FILM FOR SUCH A DEVICE

The invention concerns a background illuminated display device, in particular a background illuminated LCD display for personal computers, and a process for the manufacture of a scatter film for such a background illuminated display device.

In display devices of this generic type, the problem arises that the areal, transparent, display unit facing the viewer - that is the plate containing the liquid crystal layer in an LCD display - is required to be illuminated as uniformly as possible by a light source arranged behind the display unit. Since such background illuminated display devices are often designed as so-called flat screens, in which the light source is arranged in the form of a fluorescent tube in the region of the lateral edge of the display unit, the problem of uniform illumination is critically important. Due to the inverse square dependency of the light intensity on the distance from the light source, an extremely irregular illumination of the display unit would result if no additional measures were taken, with intense brightness in the immediate vicinity of the light source, and only a very weak illumination at the lateral edge of the display unit opposite the light source.

To compensate, a light deflection unit is provided, covering the area behind the display unit, in the form of a reflecting film, plate or scatter disc, which has 2 - a reflection or scatter that increases as the distance from the light source increases, thereby compensating for the diminishing light intensity, to give a uniform illumination of the display unit.

It is known that an acrylic glass plate may be used as a light deflecting unit, in which grooves are tooled. With these grooves, a prismatic-type light deflection is achieved. The grooves become more concentrated (closer together) as the distance from the light source increases, whereby the decreasing light intensity is compensated and a uniform illumination of the display unit is achieved.

Such acrylic glass plates have the disadvantage that they are relatively complex to manufacture. In addition, an accurate adaptation of the density distribution of the grooves to the actual illuminating conditions, and hence a uniform illumination of the display unit can be obtained only with great difficulty.

The invention aims to provide a background illuminated display device such that a particularly even illumination of the display unit is ensured by simple design. In addition, it is intended that a particularly simple process for the manufacture of a light deflection unit for such a background illuminated display device be provided.

According to one aspect of the present invention there is provided a background illuminated display device with a housing, a planar transparent display unit arranged in an open side of the housing, a light deflecting unit arranged behind the display unit covering the area of the same, and at least one light source, wherein the light deflecting unit consists of a photographic transparent scatter film comprising a photographic coating which is illuminated by each light source from the rear and one side and has photographically produced scatter bodies whose distribution density is inversely proportional to the light intensity distribution across the surface of the scatter film.

The present invention makes use of the technique of dark field illumination, known in principle from microscopy, or the reproduction of a grossly underexposed negative in the dark field, as known from photoreproduction technology. Use is made of the finding that in a scanning illumination of the object, the illuminating light rays are bent at the object structures and radiate in particular to the front. Very small objects (scatter bodies) suitable for the bending of the light rays, are the silver particles which develop in the photographic process within the photographic coating and which are applied on a transparent film. The density of the distribution of silver particles and their size can be controlled by the illumination and development. If the transparent scatter film has photographically produced scatter bodies whose distribution density, dependent on the light intensity distribution across the area of the scatter film, is inversely proportional to the intensity of the light generated by the light source of the background illuminated display device, then the desired uniform illumination of the display unit is obtained.

Since the transparent scatter film can be made very thin, there are additional advantages of weight, compared to a solid acrylic glass plate, which are of special benefit in an LCD display for portable PCs, i.e. laptops or notebooks.

The scatter film may be flexible but is preferably constructed as a rigid transparent plate with a photographic coating. This can then be manipulated, better than a flexible scatter film, by automatic handling devices in the automatic assembly of background illuminated display devices.

- 4 A feasible alternative would further be to dispense with a film carrier and to design the scatter film as a photographic coating applied directly to the rear side of the display unit. This provides a particularly readily assembled alternative, since the display unit and the light deflection unit are combined within one component.

In a preferred embodiment an absorption screen is arranged at a distance behind the transparent scatter film, such that the light source radiates from the side into the separating gap between the film and the screen. Obliquely arranged membranes may be placed in front of the absorption screen pointing in the direction of the light source. These developments facilitate the suppression of scatter light effects which would disturb a uniform illumination.

The absorption screen may be formed as an absorption coating on the inside of the housing rear side. This refinement of the absorption screen in particularly simple and readily assembled.

A reflector may preferably be arranged on the rear side of the light source which faces away from the display unit to increase the light intensity available for the illumination of the display unit.

The light source is preferably surrounded by a screen device which limits the radiation angle of the light source. This again enables scattered light effects to be suppressed.

According to another aspect of the invention there is provided a method for the manufacture of a scatter film for a background illuminated display device as described above, comprising the following process steps:

a) in a recording device which imitates the actual illuminating conditions in the display device, a photographic film is exposed by means of a light source which is arranged and dimensioned as appropriate to the scatter film position, b) the exposed film is photographically developed into a negative film and fixed, and c) a transparent positive film which forms the scatter film is photographically produced from the negative film.

The method of the invention uses known and well developed photographic techniques. The manufacture of the scatter film does not require any material processing or shaping procedure steps, such as, for example, in the manufacture of polymethyl methacrylate plates with grooves. Moreover, due to the recording device which imitates the actual illumination conditions in the display device, the density of scatter body distribution in the photographic coating which is necessary for a uniform illumination of the display unit, is produced. Any special calculations, such as may be necessary for the shaping and distribution of the grooves in the known polymethyl methacrylate plates as light deflecting units, can be dispensed with altogether. Furthermore, the scatter films can be adapted to a changed geometry in the background illumination of the display unit without any significant changes in the manufacturing process. The only requirement is for the recording device to be adapted; whereas the use of a polymethyl methacrylate plate would require the entire groove arrangement to be recalculated and the tools for their manufacture to be modified accordingly.

Preferably, the positive film is produced by means of a photographic contact copy process, such that the manufacture of the scatter film is further rationalized and simplified. The same purpose is served by a further refinement of the method by which a multitude of transparent positive films is produced from a master negative film by means of a photographic contact process; the advantages of this being of particular significance in the batch production of scatter films. It is thus sufficient to - 6 manufacture just one master negative film, corresponding to the actual illumination conditions in the display device, for the manufacture of a scatter film for a certain type of background illuminated display device. This master negative film can subsequently be used to produce any number of transparent positive films by means of photographic contact copying.

It should pointed out that not only can LCD displays be used as display units in background illuminated display devices of the invention, but direct reading instrument scales, for example, can also be used.

Other features, details, and advantages of the invention can be gleaned from the description which follows, in which embodiments of the invention are more closely explained by way of example by means of the enclosed sketches.

Fig. 1 shows a schematic section through a background illuminated display device in a first embodiment of the invention;

Fig. 2 shows a schematic section through a background illuminated display device in a second embodiment; and

Fig. 3 shows a schematic section through a recording device for the manufacture of a scatter film for a background illuminated display device.

Fig. 1 shows a background illuminated display device in the form of an LCD display for a laptop. The. display device has a flat cuboid housing 1, the flat side 2 of which has a rectangular aperture 3. Behind this aperture 3 is a plate shaped transparent liquid crystal display unit 4, one flat side of which faces towards the viewer. The liquid crystal display unit 4 is known and commercially available.

7 Directly behind the display unit 4, a scatter film 6 is arranged which covers the area of the display unit and which consists of a carrier material 7 and a photographic coating 8. The latter is applied to that side of the carrier material 7 which faces away from the display unit 4.

Behind the plane of the scatter film 6 and at the side adjacent to the liquid crystal display unit 4, a fluorescent light tube 9 is arranged as a light source, which extends over the entire length of the narrow side 10 of the display unit 4 facing the light source. A strip-like reflector 11. which is formed concave towards the fluorescent light tube 9, is arranged on the rear side of the fluorescent light tube 9 which faces away from the display unit 4. The fluorescent light tube 9 is further flanked over its length by a screen device which limits its radiation angle and which consists of two screen plates 12, 13 arranged essentially parallel to the plane of the display unit 4.

The laterally extending fluorescent light tube 9 is arranged directly behind the plane of the scatter film 6 such that the scatter film 6 and in particular its photographic coating 8 is illuminated from the rear and one side by the light skimming across the rear and being scattered through the coating in the manner used in dark field illumination. In the scatter film itself, photographically produced scatter bodies in the form of silver particles are distributed, the density distribution of which, dependent on the intensity of the light radiated across the area of the scatter film 6 by the fluorescent light tube 9, is inversely proportional to the light intensity. Essentially, therefore, the density of the scatter bodies increases as the distance from the fluorescent light tube 9 increases, in accordance with a square function, since the light intensity decreases in accordance with an inverse square function as the distance from the fluorescent light tube 9 increases. On straight lines which run parallel to the longitudinal axis of the fluorescent light tube 9, the light intensity is constant, so that the density of the scatter bodies does not change in this direction.

Apart from the screen plates 12, 13 for the avoidance of scatter light effects, an absorption screen 15 is provided on the rear side of the housing 1 as a dark field in the form of a matt black coating 16 of the rear side inner wall of the housing. The coating 16 projects laterally beyond the outline of the display unit 4 and the scatter film 6, so that even when looking in from the side at the display unit 4, no disturbing reflections or the like can occur.

In the embodiment shown in fig.2, the housing 1, the liquid crystal display unit 4, the scatter film 6, the fluorescent light tube 9, and the reflector 11 are designed in accordance with the embodiment of fig. 1. To avoid repetition, reference is made to the description of figure 1. In contrast to the embodiment shown in fig. 1, the embodiment shown in fig. 2 has the two screen plates 12, 13 omitted. For the avoidance of scatter light effects, absorbing membranes 17 are used in this example, which are oblique and which point in the direction towards the fluorescent light tube 9 and which are fixed in a frame 18, which is schematically indicated. The absorption screen 15 itself is designed as a matt black box fitted to the rear side 14 of the housing 1.

A method in accordance with the invention for the manufacture of the scatter film 6 is described hereafter, with reference to fig. 3.

A recording device 19 is used, which imitates the actual illumination conditions in the display device, in which the scatter film 6 is to be used. For this purpose, the recording device 19 is constructed as a box 20, corresponding to the housing 1. Fitted to the inside wall of one flat side 21 in a position which corresponds to the position of the scatter film 6 in the housing 1, is a photographic film which is dimensioned corresponding to the dimensioning of the scatter film 6. The photographic coating 22 of the film faces towards the interior of the box 20.

A fluorescent light tube 23, identical to the fluorescent light tube 9 of the display device, together with an appropriate reflector 24, is arranged behind the plane of the film 22. On the rear side 25 of the box 20, opposite the flat side 21, an absorption screen 26 is arranged, which corresponds to the absorption screen 15 of the display device. The film 22 is briefly exposed by means of the recording device 19, and this can take place by means of a photographic shutter (not shown) in front of the fluorescent light tube 23, for example. The film, thus exposed, is photographically developed into a negative and is fixed. There are many silver particles on this negative film in areas of greatest exposure, whereas in poorly exposed areas which are at a greater distance from the fluorescent light tube 23, there are only a few of such silver particles. If the negative film were inserted in this form into the display device as a scatter film 6, it would demonstrate a scatter behaviour exactly opposite to the desired scatter behaviour. A transparent positive film which forms the scatter film 6 is therefore produced from the negative film by means of a photographic contact copy process. The positive film then has the desired density of scatter body distribution, the exact reverse of that of the negative film.

For batch production of scatter films 6, these can be produced in any number from just one master negative film by means of a photographic contact copying process.

- 10 If a scatter film for a large area LCD display is to be produced which is background illuminated by two opposing fluorescent light tubes, it is necessary for the recording device 19 also to have two such fluorescent light tubes at opposite sides of the film 22. The further process with development of the negative film and production of a transparent positive film takes place as described. It is also possible to manufacture scatter films accordingly for any configuration of fluorescent light tubes.

11 -

Claims

1. A background illuminated display device with a housing, a planar transparent display unit arranged in an open side of the housing, a light deflecting unit arranged behind the display unit covering the area of the same, and at least one light source, wherein the light deflecting unit consists of a photographic transparent scatter film comprising a photographic coating which is illuminated by each light source from the rear and one side and has photographically produced scatter bodies whose distribution density is inversely proportional to the light intensity distribution across the surface of the scatter film.

2. A display device in accordance with claim 1, wherein the transparent scatter film comprises a rigid transparent plate with a photographic coating.

A display device in accordance with claim 1, wherein the transparent scatter film comprises a photographic coating applied directly on the rear side of the display unit.

4. A display device in accordance with one of the claims 1 to 3, wherein an absorption screen is arranged at a distance behind the transparent scatter film, such that the light source radiates from the side into the gap separating the film and the screen.

5. A display device in accordance with claim 4, wherein obliquely arranged absorption membranes are placed in front of the absorption screen pointing in the direction of the light source.

12 - 6. A display device in accordance with claim 4, wherein the absorption screen is formed as an absorbing coating on the inside of the housing rear side.

7. A display device in accordance with one of the claims 1 to 6, wherein a reflector is arranged on the rear side of the light source which faces away from the display unit.

8. A display device in accordance with one of the claims 1 to 7, wherein the light source is surrounded by a screen device which limits the radiation angle of the light source.

9. A method for the manufacture of a scatter film for a background illuminated display device in accordance with one of the claims 1 to 6, comprising the following process steps:

a) in a recording device which imitates the actual illuminating conditions in the display device, a photographic film is exposed by means of a light source which is arranged and dimensioned as appropriate to the scatter film position, b) the exposed film is photographically developed into a negative film and fixed, and c) a transparent positive film which forms the scatter film is photographically produced from the negative f i lm.

10. A method in accordance with claim 9, wherein the positive film is produced by means of a photographic contact copy process.

11. A method in accoiaan-ce--wi-th claim 9 or 10, wherein, for the batch production of scatter films, a - 13 multitude of transparent positive films is produced from a master negative film by means of a photographic contact process.

12. A display device substantially as hereinbefore described with reference to the accompanying drawings.