DE2625864B2 - Liquid crystal display device with a fluorescent panel - Google Patents

Description

The invention relates to a display device according to the preamble of claim 1. Such a display device Liquid crystal (LC) display is already the subject of the earlier application DE-OS 25 54 226.

In the case of the display according to the older proposal, the fluorescent plate is used to brighten the displayed Symbols: The plate collects the ambient light falling on it and bundles it out of the individual light exit windows off again. The display contrast that can be achieved in this way is all the higher, the greater the ratio of the light-receiving to the light-emitting area of the fluorescent plate, so that you generally have to let the fluorescent plate protrude laterally next to the LC cell. One Such dimensioning is unsatisfactory when the landscape format of the display should be compact and in particular, no additional space is allocated in addition to the area occupied by the LC cell should (example: wrist watch).

For these cases, the aforementioned patent application has already suggested, at least the cell partially translucent, either by using polarizers that are selective let the excitation light for the fluorescent substances pass unpolarized, or by using ordinary Breaks through linear polarizers at locations outside the display areas. Through the polarizer recesses light can enter the fluorescent plate unhindered, but because of the fluorescence scattering and subsequent (total) reflections inside the plate emerge only to a small fraction, so that the image background is only weakly, the excited display areas, on the other hand, have been brightened up and this results in an overall contrast enhancement.

However, the production of the proposed frequency-selective polarizers prepares considerable technological Difficulties and is also the production and optically perfect placement of openwork, With small-format advertisements, extremely filigree polarizer foils are not that easy.

To eliminate the deficiencies outlined, in particular to create an LC display with a fluorescent plate, in which the LC cell is also used as a collector surface is available and yet does not pose any particular manufacturing or development problems a display device of the type mentioned at the outset according to the invention by the features of claim 1 marked.

In the case of the display according to the invention, the light transmission is achieved without special polarizers; in particular, no frequency or location sensitive polarizers are required. If the display device is based on a display principle that requires one or more polarizers, one can fall back on the usual polarizer designs and only has to ensure that the LC orientation in the translucent areas is matched to the specified polarizer configuration.

A display device according to the invention also has the advantage that the LC texturing can be produced without additional work steps using known and proven techniques (for example surface orientations or field orientations) and possibly even, since the LC layer has to be oriented anyway.
The display proposed here is mainly used where compact transverse dimensions are important; it is particularly suitable for use in wristwatches.

The switchable display areas of the proposed display device can be set to the most varied Way to be excited, for example according to the principle of the rotary cell (DT-OS 21 58 563), with the help of DAP-Etfekts (DT-OS 2155 241) or about by Storage of pleochroic dyes in the LC substance (DT-PS 14 62 919). If you decide for a mode of operation in the manner of a rotary cell, then those are specified in claims 2 to 8 Versions particularly useful. When choosing an FK cell that has the DAP effect in its display areas works, the arrangement should be made as it is characterized in claim 9. You want to go through Dye additives cause light modulation, so it makes sense to take the measures mentioned in claim 10 to take.

The invention will now be based on particularly preferred exemplary embodiments in conjunction with the figures the drawing will be explained in more detail. In the figures, parts corresponding to one another are identified by the same Provided with reference numerals. It shows

F i g. 1 a first exemplary embodiment! one according to the invention Rotary cell-based display device, in a side section;

F i g. 2 shows a second exemplary embodiment, in a partially broken away side section;

F i g. 3 shows a third embodiment in the same way Representation like F i g. 2; and

4 shows, in a partially broken away side section, a further exemplary embodiment which works with the so-called “guest-host effect”.
For the sake of clarity, all individual parts of an LC display that are not absolutely necessary for an understanding of the present invention, for example the electrical supply lines, possibly required insulation or spacing elements, are not designated in the drawing or are omitted entirely.

The display version of FIG. 1 is a seven-segment display and works as a rotating cell in the display areas. In detail, it contains a front one Linear polarizer 1, a front carrier plate 2, a rear carrier plate 3, a rear linear polarizer 4, the polarization axis of which is parallel to the polarization axis of the front linear polarizer, and one on Fluorescent plate mirrored on its side surfaces 5. All parts mentioned are in the order of their Listed one behind the other in the viewing direction.

The inner sides of the two carrier plates each have segment electrodes 6, which form the display areas the FK cell set, provided and at their edges on a frame 7 in a predetermined Distance tightly connected. In the one formed by the two support plates and the frame Chamber is a liquid crystal layer 8. In the front of the fluorescent plate 5 are, respectively

behind the individual segment electrodes 6, notches 16 introduced through which the light collected in the plate exits again to the front. For details For manufacturing and operating details, reference is made to the patent application already mentioned at the beginning.

So that the ambient light through the cell areas outside the display areas into the interior of the Fluorescent plate can occur, the LC layer in these cell areas is given a texture that in the Interaction with the parallel linear polarizers enables light to pass through and thus determines the extent of the translucent cell areas. The lowest transmission losses is known to be obtained with a homeotropic or uniformly hornogenic in the direction of the polarization axes Molecular orientation. There are many ways to create these textures; compare to this for example "RCA Review" Vol. 35, 1974, pp. 447-461, with further references.

In the embodiment of FIG. 1, the LC layer outside the segment electrodes has a through a Surface orientation created homeotropic texture. The required wall orientation is as follows generated:

The inner surfaces of both carrier plates have been coated one after the other with the following layers: first with an AbCh layer, then with a conductive one SnO2 layer, then an insulating SiCh layer and finally a layer which is oriented parallel to the plate. (The layers are shown in the figure and provided with the reference numerals 9, 6, 10 or 11). The segment electrode surfaces and, if necessary, the lead surfaces are then masked and then all of them are etched Layers down to the bottom. Since the AbOa layer Oriented to the normal to the panel, the desired FK texture, which is different in areas, results.

A permanent homeotropic texture can also be achieved by vapor deposition of vertically oriented Layers such as Al2O3 or CrjCV layers on the opposing plate surfaces outside of the segment electrodes. One translucent orientation can also be obtained if only one of the two electrodes is used Carrier plates partially vapor-deposited with a homeotropically orienting layer.

Should the LC layer have a uniformly homogeneous texture and should the reliable inclined vapor deposition method be used for this then you can proceed as follows:

One of the carrier plates is vaporized in a single direction (first oblique vapor deposition direction) and the second carrier plate at the location of the display areas in one direction (second diagonal vapor deposition direction) and at the location of the transparent areas in a different direction (third oblique vapor deposition direction), in such a way that when the FK cell is fully assembled, the projection of the third oblique vapor deposition direction onto the plane of the plate parallel to the corresponding projection of the first oblique vapor deposition direction and is perpendicular to the corresponding projection of the second oblique vapor deposition direction. Instead of on To choose two diagonal vapor deposition directions on a carrier plate, it would also be possible to use the display areas to vaporize at a different angle than the translucent areas (cf. DT-OS 25 08 913).

Homeotropic or uniformly homogeneous molecular orientations can also be achieved through surface treatments can also be gained conveniently through electric fields. So takes a nematic liquid crystal with a positive dielectric anisotropy under sufficiently high fields directed perpendicular to the plane of the plate a homeotropic texture. In this case, you only need the carrier plates with additional electrodes to provide, if necessary, to isolate the additional electrodes from the segment electrodes and between them in the Operation of the display device to create a sufficiently large potential difference. Also a uniform Homogeneous orientation can be produced very easily with electric fields: It is sufficient if one the inner surface of one of the two carrier plates in addition to the segment electrodes with a system interlocking comb electrodes occupied and both comb electrodes to suitably different Lays potential. Both variants are shown in the drawing, namely FIG. 2 a version with Additional electrodes on both carrier plates (additional electrodes 12) and FIG. 3 illustrates an embodiment with Comb electrodes (comb electrodes 13, 14) on one of the two carrier plates.

If you want to represent with the help of the DAP effect, in which the two linear polarizers are known to each other must stand vertically, it is advisable to use the LC layer in the translucent areas as in a rotary cell twisted to give a homogeneous texture. It is irrelevant whether the LC molecules close to the wall parallel or perpendicular to the polarization axes of the respective adjacent polarizers.

At least one polarizer can be saved by adding a pleochroic dye to the LC substance adds. Fig.4 shows such an embodiment. In In contrast to the previous examples, the rear linear polarizer is missing here. Instead, in the dielectrically positive anisotropic nematic LC substance pleochroic dye molecules embedded in plate-parallel LC orientation light passing through that oscillates in the direction of the longitudinal axes of the molecules, strongly absorb and with homeotropic texturing the light penetrating the liquid crystal is practical let through undamped. The arrangement can, for. B. be taken so that the liquid crystal in the Display areas uniformly homogeneous in the idle state, parallel to the direction of polarization of the Linear polarizer, is aligned and a twisted homogeneous texture in the translucent areas like a rotary cell. The LC molecules adjacent to the polarizer are in the twisted one Phases perpendicular to its direction of polarization.

With the variant described, with the addition of dye, one could even use no polarizer get by if you let the fluorescent plate only decouple linearly polarized light (see Patent application P 27 18 526.8). Such a design is particularly favorable because it is translucent Cell areas can have a very high degree of transmission.

Even when the display device is viewed from extremely large angles, there is any incorrect reading to exclude, one could each display areas with an opaque border surround. It is useful to orient the liquid crystal in this edge area in the same way as in the Display areas in the non-switched state.

1 sheet of drawings

Claims (12)

Patent claims: 1. Display device with a liquid crystal layer extending between a viewing direction front and a rear support plate is located and in display areas between different optical states can be switched, as well as with one arranged behind the carrier plates Plate made of a material with a refractive index greater than 1 with a fluorescent one Is provided and has light exit windows assigned to the individual display areas, at least the remaining area of the carrier plates next to the display areas is partially translucent, thereby characterized in that the liquid crystal layer (8) is in the transparent areas at least during operation of the display device has a texture suitable for light transmission, which differs from the texture of the liquid crystal layer (8) in the non-switched display areas. 2. Display device according to claim 1, with a dielectrically positive anisotropic nematic liquid crystal layer, with a linear polarizer in front of and behind the liquid crystal layer, the Linear polarizers have mutually parallel polarization directions and so do the excitation light polarize for the fluorescent plate, as well as with two carrier plates that have on their inner surfaces Display electrodes are provided and the liquid crystal layer with a certain wall orientation include between them, characterized in that the liquid crystal molecules in the Display areas oriented parallel to the plate and -15 are twisted in the direction of the plate normal by at least approximately 90 ° and in the translucent areas have a homeotropic texture. 3. Display device according to claim 2, characterized in that to obtain the homeotropic texture at least one of the two carrier plates (2,3) on its inner surface in the translucent areas a plate-perpendicularly orienting layer (9), preferably Al ₂ Oj or Cr ₂ Os, wearing. 4. Display device according to claim 2, characterized in that to obtain the homeotropic texture at least one of the two carrier plates on its inner surface one above the other an A1 ₂ O3 layer (9), an SnO ₂ layer (6), an SiO ₂ layer (10) and a plate-parallel orienting layer (11), with the top three layers only covering the display areas and the The bottom layer covers the carrier plate (2,3) continuously. 5. Display device according to claim 2, characterized in that for obtaining the homeotropic Texture the display electrodes (6) of both carrier plates are segmented and both carrier plates (2, 3) in addition to these segment electrodes & o those in the translucent cell areas, wear electrically isolated electrodes from the segment electrodes (additional electrodes 12) to which the im Operation of the display device different potentials can be applied. 6. Display device according to claim 1, with a dielectrically positive anisotropic nematic liquid crystal layer, with a linear polarizer in front of and behind the liquid crystal layer, the Linear polarizers have mutually parallel polarization directions and so do the excitation light polarize for the fluorescent plate, as well as with two carrier plates that have on their inner surfaces Display electrodes are provided and the liquid crystal layer with a certain wall orientation include between them, characterized in that the liquid crystal molecules in the Display areas oriented parallel to the plate and in the direction of the plate normal by at least are twisted approximately 90 ° and are uniform in the translucent cell areas have a homogeneous texture. 7. Display device according to claim 6, characterized in that both carrier plates (2, 3) their inner surfaces each wear obliquely vapor-deposited layers oriented parallel to the plate, with the layer of a carrier plate is vapor-deposited in a first direction and the layer of another carrier plate in the display areas in a second and in the translucent ones Areas in a third direction is evaporated and the projections of the first and third Inclined vapor deposition direction on the plane of the plate parallel to each other and to the corresponding projection the second oblique vapor deposition direction are perpendicular. 8. Display device according to claim 6, characterized in that the display electrodes (6) at least one of the two carrier plates (2, 3) are segmented and this carrier plate (2) in the translucent areas pairs of intermeshing comb electrodes (13, 14) carries, wherein the comb electrodes of each pair can be placed at different potentials. 9. Display device according to claim 1, characterized by a nematic liquid crystal layer (8) with a negative dielectric anisotropy, a linear polarizer (1) in front of and a linear polarizer (4) crossed to this polarizer behind the liquid crystal layer (8) and two carrier plates (2, 3) which are provided with display electrodes (6) on their inner surfaces and which Enclose liquid crystal layer (8) between them, the liquid crystal layer (8) in the display areas a homeotropic texture as well as a homogeneous one in the translucent cell areas Has texture in which the liquid crystal molecules in the direction of the plate normal by at least are twisted approximately 90 °. 10. Display device according to claim 1, characterized by a nematic liquid crystal layer (8) with positive dielectric anisotropy and a linear polarizer (1) in front of the liquid crystal layer, wherein the liquid crystal layer contains a pleochroic dye and in the Display areas uniformly homogeneously oriented in the direction of the polarization axis of the linear polarizer is, as well as in the translucent areas, either a uniformly homogeneous orientation perpendicular to the polarization axis of the linear polarizer or has a homogeneous texture in which the Liquid crystal molecules are twisted in the direction of the plate normal by at least approximately 90 ° and stand in the vicinity of the linear polarizer perpendicular to its polarization axis. 11. Display device according to one of the claims ehe 1 to 10, characterized in that the display areas are each opaque Edge are surrounded. 12. Display device according to one of claims 1 to 11, characterized by its use in a wrist watch.