DE2625864A1 - Liquid crystal indicator cells esp. for wrist watches - where liquid crystal layer contains regions permitting light transmission - Google Patents

Abstract

Visual indicator display cell has a front plate on the outside of a liq. crystal layer and a back plate made of a carrier material with a refractive index (RI) >1. A fluorescent plate is provided at the rear of the cell, and the individual display regions (1) posses light outlet windows; adjacent to regions (1) on the front plate are regions (2) permeable to light. At least during operation, the liq. crystal layer has a texture in regions (2) which permits the transmission of light, this texture being different from that in the display regions which are not switched on. One of several pref. cells has a dielectric, positive anisotropic nematic liq. crystal layer located between two linear polarisers possessing parallel polarising directions, and which also polarise the excitation light for the fluorescent plate. The two plates contg. the liq. crystal are pref. coated internally with the sequence: (a) an orientating layer of Al2O3 or Cr2O3; (b) SnO2; (c) SiO2; (d) an orientating layer; layers (b, c, d) are etched to define the display regions. The cells are pref. used in wrist watches.

Description

Liquid crystal display device with a fluorescent plate.

The invention relates to a display device according to the preamble of claim 1. Such a liquid crystal (LC) display is already the subject matter an older application (P 25 54 226).

The fluorescent plate is used for the display according to the older proposal To brighten up the symbols shown: The plate collects what falls on it Ambient light and bundles it from the individual light exit windows out again. The display contrast that can be achieved in this way is higher the greater the ratio of the light-absorbing to the light-emitting area of the fluorescent plate is, so that one generally has the fluorescent plate next to the FE cell must protrude.

Such a dimensioning is unsatisfactory when the landscape format of the display should be stumpy and in particular next to that claimed by the LC cell Area no additional space should be allocated (example: wristwatch).

The aforementioned patent application also suggests such cases the cell is at least partially translucent close, and zvar either by using polarizers which selectively apply the excitation light for the fluorescent substances to pass through unpolarized, or by making identical left near polarization breaks through at places outside the display areas. By the polarizer recesses allow light to enter the fluorescent plate unhindered, but because of the fluorescence scattering and subsequent (dot) reflections inside the plate emerge again only to a small fraction, so that the image background is only weak, the excited indicating areas, however, are strongly brightened and so overall results in a contrast enhancement.

However, the production prepares the proposed frequency-selective Polarizers significant technological difficulties and is also the manufacture and visually perfect placement of openwork, small-format advertisements extremely filigree polarizer films are not that easy.

To eliminate the deficiencies described, in particular to create of an LC display with fluorescent plate, in which the SK cell is also used as a collector surface is available and yet no special manufacturing or development problems gives up, are according to the invention in a display device of the type mentioned at the outset two alternatives are proposed, which are described in claim 1 and claim 11, respectively are.

Both proposed alternatives have in common that the light transmission occurs in certain cell areas without special polarizers; in particular no frequency or location sensitive polarizers are required. When the display device is based on a representation principle that requires one or more polarizers, you can fall back on the usual polarizer designs and have at the implementation of the invention in the first alternative only to pay attention to that the LC orientation in the translucent casual cell areas is matched to the specified polarizer configuration. If you choose instead alternative 2 with the optically isotropic medium in the light-permeable cell areas and if polarizers are present, they must be transparent in themselves Form a group.

A display device according to the invention also has the advantage that the Fi-texturing provided in the first alternative by known per se wçnd proven techniques (e.g. surface orientations or field orientations) and possibly even, since the BV layer has to be oriented anyway, without can generate additional operations. Also the filling of individual districts with a transparent, optically isotropic medium such as glass or plastic (alternative 2) is known per se and unproblematic.

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 excited in many different ways, for example according to the principle the rotary cell (DD-OS 21 58 563), with the help of the DAP effect (DT-OS 21 55 241) or for example through the incorporation of pleochroic dyes in the SK substance (DD-PS 14 62 919). If you decide on a mode of operation like a rotary cell, then the embodiments specified in more detail in claims 2 to 8 are special expedient. When choosing a cell that has the DhP effect in its display areas works, the arrangement should be made as it is characterized in claim 9 is.

If you want to cause a light modulation by adding dye, so it makes sense to take the measures mentioned in claim 10.

Further advantageous embodiments and developments of the invention are the subject of further claims.

The invention will now be based on particularly preferred exemplary embodiments will be explained in more detail in connection with the figures of the drawing. In the figures Corresponding parts are provided with the same reference numerals. Show it: 1 shows a first embodiment of a display device according to the invention based on rotating cells, in a side section; Fig. 2 shows a second embodiment, in a partially broken side cut; 3 shows a third embodiment, in the same manner of representation as FIG. 2; Fig. 4 in a partially broken away Side section of a further exemplary embodiment, which is based on the so-called "guest-host effect" is working; and FIG. 5 in a side section, also partially broken away another embodiment.

FIGS. 1 to 4 show variants of alternative 1, and FIG. 5 shows one Execution according to alternative 2. All for an understanding of the present invention not absolutely necessary individual parts of an LC display, for example the electrical supply lines, any required insulation or distancing elements are not designated in the drawing for the sake of clarity or are omitted entirely.

The display embodiment of Figure 1 is a seven segment display and works as a rotating cell in the display areas. It contains a front one in detail Linear polarizer 1, a front support plate 2, a rear support 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 mirrored on its side surfaces Fluorescent plate 5.

All parts mentioned are to be considered in the order in which they are listed arranged one behind the other.

The inner sides of the two carrier plates each have segment electrodes 6, which define the display areas of the FK cell7 and at their edges Connected tightly to one another via a frame 7 at a predetermined distance. In the chamber formed by the two carrier plates and the frame is located a liquid crystal layer 8. In the front of the fluorescent plate 5 are, a- each behind the individual segment electrodes 6, notches 16 made, through which the light collected in the plate emerges to the front again.

For more detailed manufacturing and operating details, please refer to the referenced patent application mentioned at the beginning.

So that the ambient light through the cell areas outside the display areas The FE layer is in these cell areas given a texture that interacts with the parallel Linerarpolarisatoren allows light to pass through and thus the expansion of the translucent Cell areas determined.

As is well known, the lowest transmission losses are obtained with a homeotropic or a uniformly homogeneous molecular orientation in the direction of the polarization axes. . There are many ways to create these textures; compare this for example 11RCA-Review11 Vol. 35, 1974, pp. 447-461, with further references.

In the embodiment of Fig. 1, the SK layer outside of the Segment electrodes a homeotropic texture generated by a surface orientation. The required wall orientation is produced as follows been: The heart surfaces of both carrier plates are successively with the following layers coated: first with an AlS03 layer, then with a conductive SnO2 layer, then an insulating SiO2 layer and finally an orienting layer parallel to the plate Layer. (The layers are entered in the figure and given the reference number 9,6,10 and 11 respectively.) The segment electrode surfaces and are then masked possibly the lead surfaces and then etches away all layers except for the bottom. Since the Al203 layer is oriented normal to the plate, the desired area results different BK-2 texture.

A permanent homeotropic texture can also be obtained by vapor deposition of perpendicularly orienting layers such as Al 2 O 3 or Cr 2 O 3 layers on the opposing plate surfaces outside the segments]. electrodes produce. A translucent orientation can also be obtained if if you only have one of the two electrode-carrying carrier plates partially with a vapor-deposited homeotropic orienting layer.

Should the SK layer get a uniformly homogeneous texture and if you want to use the reliable inclined vapor deposition method for this, then you can proceed as follows: You vaporize one carrier plate 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 oblique vapor deposition direction) and at the location of the translucent Areas in another direction (third oblique vapor deposition direction) in such a way that that when the PE cell is fully assembled, the projection of the third diagonal vapor deposition direction on the Plate plane parallel to the corresponding projection of the first Ycl-rräL = steaming direction and perpendicular to the corresponding projection the second oblique steaming direction lies. Two diagonal steaming directions instead of one carrier plate it would also be possible to choose the display areas at a different angle than to vaporize the translucent areas (cf. DU-OS 25 08 913).

Homeotropic or uniformly homogeneous molecular configurations can be achieved In addition to surface treatments, they can also be obtained conveniently using electrical fields. Thus, a nematic liquid crystal with a positive dielectric anisotropy takes place under sufficiently high fields directed perpendicular to the plane of the plate a homeotropic one Texture. In this case, you only need the carrier plates with additional ones To provide electrodes, the additional electrodes against the segment electrodes if necessary isolate and between) them in the operation of the display device a sufficiently large To create potential difference. A uniform, homogeneous orientation is also possible can be produced very easily with electric fields: it is sufficient if you just look at the inner surface one of the two carrier plates in addition to the segment electrodes with a system made up of interlocking comb electrodes and both comb electrodes are suitable sets different potentials. Both variants are shown in the drawing, namely, Fig. 2 shows 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, which is well known the two linear polarizers must be perpendicular to each other, so recommends the LC layer in the translucent areas like 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 adjacent polarizers lie.

At least one polarizer can be saved if you use the LC substance gives a pleochroic dye. Fig. 4 shows such an embodiment. In contrast to the previous examples, the rear linear polarizer is missing here.

Instead, the dielectrically positive anisotropic nematic FK-Sabstanz embedded pleochroic dye molecules, which in the case of plate-parallel LC orientation light passing through in the direction of the longitudinal axes of the molecule vibrates strongly absorb and with homeotropic texturing that the liquid crystal Let penetrating light pass through with practically no attenuation. The arrangement can thereby e.g. uniformly homogeneous, parallel to the polarization direction of the linear polarizer, is aligned and in the translucent areas a twisted homogeneous Has texture like a rotating cell. The ones adjacent to the polarizer are here LC molecules in the twisted phases perpendicular to its polarization direction.

You could even use the described variant with the addition of dye get by without any polarizer if you only linearly polarize the fluorescent plate Light can be decoupled (see patent application P ....................

(VPA 76 P 1051 BRD)). Such a design is particularly favorable, because with her the translucent cell areas have a very high degree of transmission can have.

Fig. 5 shows how one can also do so in other ways than by a specific one Texturing of the BE layer makes the FK cell translucent outside of its display areas can make, namely by covering these areas with an optically isotropic transparent Medium fills. In the present case, the medium exists from a Glass layer 15. Should the display work with a display pin that has the Requires the use of linear polarizers, these polarizers must be relative to one another lie parallel. This is for example a rotating cell with light characters the case against a dark background.

To even when looking at the display device under extremely large The individual display areas could be used to rule out any incorrect readings each surrounded by a light-impermeable edge. It is useful to to orient the liquid crystal in this edge area in the same way as in the display areas when not switched.

13 claims 5 figures

Claims (13)

P a t e n t a n s Q r ii c h e 1st drawing device, containing a Liquid crystal cell with a viewing direction behind a front panel liquid crystal layer located in certain areas (display areas) the} front plate can be switched between different optical states, and Pine, which is placed behind the liquid crystal cell and made of a substrate with a refractive index greater than 1, provided with a fluorescent additive is and the light exit window assigned to the individual display areas having, the 'liquid crystal cell remaining in the next to the display areas Area of their front panel (rust area) at least partially translucent is that the liquid crystal layer; (8) at least when the display device is in operation in the translucent cell areas has a texture suitable for light transmission that differs from the texture the liquid crystal layer in the non-switched display areas. 2. Display device according to claim 1, containing a liquid crystal cell with a dielektrise.hpositiv anisotropic nematic liquid crystal layer, with a linear polarizer in front of and behind the liquid crystal layer, the linear polarizers have mutually parallel directions of polarization and also the excitation light for polarize the fluorescent plate, as well as with two Dräger plates on their Provide inner surfaces with, if necessary, segmented electrode coatings (display electrodes) are and the liquid crystal layer with a specific wall orientation include between them that the Liquid crystal molecules in the display areas are oriented parallel to the plate and are twisted by at least approximately 900 in the direction of the plate normal and have a homeotropic texture in the translucent areas. 3. Display device according to claim 2, d a d u r c h g e k e n n z E i c h n e t that at least one of the two can be used to obtain the homeotropic texture Carrier plates (2,3) on their inner surface in the translucent cell areas a layer (9) oriented perpendicular to the plate, preferably made of Al203 or Cr203, wearing. 4. Display device according to claim 2, d a d u r c h g e k e n n z E i c h n e t that at least one of the two can be used to obtain the homeotropic texture Carrier plates have an Al 2 O 3 layer (9), a SnO 2 layer, one on top of the other on their inner surface (6), a SiO2 layer (10) and a plate-parallel layer (11) with the top three layers only covering the display areas and the bottom layer covers the carrier plate (2.5) continuously. 5. Display device according to claim 2, d a d u r c h g e k e n n z e i c h n e t that to obtain the homeotropic texture the display electrodes (6) both carrier plates are segented and both carrier plates (2,3) in addition to these segment electrodes in the translucent cell areas further, from the Segment electrodes wear electrically insulated electrodes (additional electrodes 12), to which different potentials can be applied during operation of the display device. 6. display device according to the preamble of claim 2, d a d u r c h e Ic e n n e i c h n e t that the liquid crystal molecules in the Display areas oriented parallel to the plate and in the direction of the plate normal are twisted by at least approximately 90 ° and in the opaque cell area eten have a uniformly homogeneous texture. 7. Display device according to claim 6, d a d u r c h g e k e n n z e i c h n e t that both carrier plates (2,3) on their inner surfaces each obliquely vapor-deposited, Wear layers oriented parallel to the plate, the layer of a carrier plate is vapor-deposited in a first direction and the layer of the other carrier plate in the display areas in a second and in the light-permeable areas is evaporated in a third direction and the projections of the first and third Bchänghzd.3mrJfungsri rect on the plate plane parallel to each other and to the corresponding Projection of the second oblique damping rioh1: lie vertically. 8. Display device according to claim 6, d a d u r c h g e k e n n z e i c h n e t 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 cell areas In addition to the segment electrodes, pairs of interlocking comb electrodes (1s, 14), the comb electrodes of each pair at different potentials can be laid. 9. Display device according to claim 1, d a d u r c h g e k c n n z It is clear that the liquid crystal cell is 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 Contains liquid crystal layer and two carrier plates (2,3) on their inner surfaces are provided with optionally arranged electrode coatings (display electrodes 6) and enclose the liquid crystal layer between them, and that the liquid crystal layer a homeotropic texture in the display areas and in the translucent cell areas has a homogeneous texture in which the liquid crystal molecules in the direction of the plate normal are twisted by at least approximately 900. 10. Display device according to claim 1, g e k e n n z e i c h -n e This is a liquid crystal cell containing a nematic liquid crystal layer (8 with positive dielectric anisotropy and a linear polarizer (1) the liquid crystal layer, the liquid crystal layer being a pleochroism Contains dye and uniformly homogeneous in the direction of the display areas The polarization axis of the linear polarizer is oriented as well as in the Zichtransparent 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 900 and stand in the vicinity of the linear polarizer perpendicular to its polarization axis. 11. Display device according to the preamble of claim 1, d a d u r c h e k e n n n z e i c h n e t that the liquid crystal layer (8) in the translucent areas through a transparent, optically isotropic medium (15), is preferably made of glass or plastic. 12. Display device according to a dox claims 1 to 11, d a d u It is noted that the display areas are each opaque from one another Edge are surrounded. 13. Display device according to one of claims 1 to 12, g e k e n e c h e its use in a wristwatch.