NO173078B - LIQUID CRYSTAL DEVICE AND PROCEDURE FOR REPRESENTATIVES BY SUCH A DEVICE - Google Patents

Description

The invention relates to a liquid crystal device comprising a liquid crystal to selectively diffuse light primarily or, in response to a prescribed input signal, to transmit light, the liquid crystal comprising operationally nematic liquid crystal material with positive dielectric anisotropy, and a carrier medium for supporting the liquid crystal.

The invention also relates to a liquid crystal display and a method for displaying clear characters or other information on a relatively dark background using liquid crystal material.

Liquid crystal material is currently used in many different devices, including for example optical devices, such as visual display devices. A property of liquid crystals (liquid crystals) that enables use in visual display devices is the ability to scatter and/or absorb (especially when pleochroic dye is mixed with the liquid crystal) light when the liquid crystals are in a random alignment, and the ability to transmit light when the liquid crystals are in an ordered alignment.

A visual display device using liquid crystals often displays dark characters on a gray or relatively light background. Under different circumstances, however, it would be desirable when using liquid crystal material to be able to easily display relatively bright or clear signs or other information,

etc. on a relatively dark background. It would also be desirable to improve the effective contrast between the displayed character and the background of the display device itself.

An example of an electrically sensitive liquid crystal material and its application can be found in US Patent 3,322,485. Certain types of liquid crystal material are sensitive to temperature in that they change the optical properties, such as the random or ordered alignment of the liquid crystal material, in response to temperature of the liquid crystal material.

Currently, there are three categories of liquid crystal materials, namely cholestric, nematic and smectic. Different principles according to the invention can be used together with a different or different of the other known types of liquid crystal material or combinations thereof. The present invention preferably uses nematic liquid crystal material or a combination of nematic and some cholesteric type. More specifically, the liquid crystal material is operationally nematic, i.e. it acts like a nematic material and not like the other types. Operationally, nematic means that structural distortion of the liquid crystal in the absence of external fields is dominated by the orientation of the liquid crystal at its boundaries or edge regions instead of by volume effects, such as very strong twists as in cholestric material, or layer formation as in smectic material. Thus, for example, chiral constituents, which induce a tendency to twist but cannot overcome the effects of boundary alignment, would still be operationally nema.ti.ske.- Such material must have a positive dielectric anisotropy. Although various properties of the various liquid crystal materials are described in the prior art, one known property is the property of reversibility. In particular, nematic liquid crystal material is known to be reversible, but cholesteric material is usually not reversible.

Pleochroic dyes have been mixed with the liquid crystal material to form a solution with it. The pleochroic dye usually aligns with the structure of the liquid crystal material. Such pleochroic dyes would therefore tend to act optically in a similar manner to the liquid crystal material in response to a varying parameter, such as application or non-application of an electric field. Examples of the use of pleochroic dyes together with liquid crystal material are described in US patents 3,499,702 and 3,551,026. One advantage of using pleochroic dyes together with the liquid crystal material is the elimination of the need for a polarizer. In the nematic form, however, a pleochroic device has relatively low contrast. In the past, cholestric material could be added to the nematic material along with the dye to improve the contrast ratio.

See, for example, an article by White et al. in "Journal of Applied Physics", Vol. 45, No. 11, November 1974, pages 4718-4723. Although nematic material is reversible, depending on whether an electric field is applied to it or not, cholestric material will not usually tend to its original zero-field shape when the electric field is removed. Another disadvantage of using pleochroic dye in solution with liquid crystal material is that the absorption of the dye is not zero in the field-on state. Absorption in the field-on state instead follows an ordering parameter that is proportional to or a function of the relative alignment of the dyes.

Typically, liquid crystal material is anisotropic both optically (birefringent) and, for example in the case of nematic material, electrically. The optical anisotropy is apparent due to the scattering of light when the liquid crystal material is in random alignment, and the transmission of light through the liquid crystal material when it is in ordered alignment. The electrical anisotropy can be a connection between the dielectric constant or the dielectric coefficient in relation to the alignment of the liquid crystal material.

In the past, devices using liquid crystals, such as devices for visual display, have been relatively small. One reason is the fluidity of the liquid crystal figures (the liquid crystal material may have a tendency to flow, so that areas of the display device are formed which have different thicknesses). As a result, the optical properties of the display device may lack uniformity, have different contrast properties in different parts of the display device, etc. The thickness variations in turn cause variations or gradual transitions in the optical properties of the liquid crystal device. The varying thickness of the liquid crystal layer will also cause corresponding variations in the liquid crystal layer's electrical properties, such as capacitance and impedance, so that the uniformity of a large liquid crystal device is further reduced. The varying electrical properties of the liquid crystal layer can then also cause a corresponding variation in the effective electric field that is applied over the liquid crystal material, and/or as a reaction to a constant electric field they would react in a different way in areas of the liquid crystal that have different thicknesses.

To overcome such problems, the liquid crystal material must have an optimal, uniform thickness. (As used herein, the term "liquid crystal" material means the liquid crystals themselves and, depending on the context, the pleochroic dye in solution with these.) There must also be an optimal distance between the electrodes by means of which the electric field is applied to the liquid crystal material .

In order to maintain such optimal thickness and spacing, relatively tight tolerances must be maintained. In order to maintain tight tolerances, there is a limit with regard to the size of the device that uses such liquid crystals, because it is quite difficult to maintain tight tolerances over: for example, large surface areas.

One typical, previously known display device may comprise a carrier medium and liquid crystal material which is supported by this. The display device is relatively flat and is viewed from a viewing side from which a so-called front surface or front surface is viewed. The rear surface of the carrier medium can have a bright, reflective coating which serves to make the surface appear relatively light or clear compared to relatively dark characters that are formed in areas where there is liquid crystal material. (The designations rear, front, upper, lower, etc. are used only for convenience,

and there is no compulsion that the viewing direction during operation must be, for example, as shown only from the top or upper side, etc.) When the liquid crystal material is in an ordered alignment, incident light from the viewing direction passes through the liquid crystal material to the bright, reflective coating, and also where there is no liquid crystal material, the light passes directly to the bright, reflective coating, and no sign is observed from the viewing direction. However, when the liquid crystal material is in random alignment, it will absorb some and scatter some of the incident light to form a relatively dark character on a relatively light colored background, such as gray or another color depending on the type of light reflective coating . In this type of display device, it is not desirable for the liquid crystal material to scatter light, due to the fact that some of this scattered light will be directed back in the viewing direction and there-

by reduces the darkness or contrast of the character in relation to the background of the display device. Pleochroic dye is often added to the liquid crystal material to increase the degree of absorption and thus the contrast when the liquid crystal material is in random alignment.

It is an object of the invention to provide a display device which, by using liquid crystals, is able to display relatively bright or clear signs or other information on a relatively dark background.

Another object of the invention is to provide a liquid crystal device which, by means of isotropic dispersion and total internal reflection, provides increased contrast and clarity in the formation of the displayed characters.

The above-mentioned purpose is achieved by means of a liquid crystal device of the type indicated at the outset which, according to the invention, is characterized in that the carrier medium comprises a containment medium to contain the liquid crystal in several volumes, the containment medium comprising a surface device for aligning the liquid crystal to effect essentially isotropic scattering of light in the absence of a prescribed input signal, and that a reflective device is provided to effect total internal reflection of light scattered by the liquid crystal.

An advantageous embodiment of the liquid crystal device is characterized by the fact that the liquid crystal and the containment medium are formed by a layer of encapsulated liquid crystal, and that the device further comprises electrodes which are placed between the carrier medium and the aforementioned layer of encapsulated liquid crystal, in order to apply an electric field to align the liquid crystal in comparison to this.

According to the invention, a liquid crystal display is also provided for displaying clear signs or the like on a dark background, and comprising a liquid crystal, which display is characterized by the characterizing features set out in claims 3 9 and 40.

According to the invention, there is also provided a method for displaying clear signs or other information on a relatively dark background using liquid crystal material, which method is characterized by

the characterizing features according to claim 42.

The use of encapsulated liquid crystals in accordance with the present invention has enabled the satisfactory use of liquid crystals in relatively large display devices, such as notice boards, etc.

and another application on a large (or small) scale can be as an optical shutter to control the passage of light from one area into another, e.g. in a window or window-like area of a building.

As used here with regard to the present invention, encapsulated liquid crystal material means liquid crystal material in a substantially closed containment medium, such as discrete capsules or cells, and may preferably be in the form of an emulsion of the liquid crystal material and the containment medium. Such an emulsion should be a stable emulsion.

In one embodiment, which may contain, but preferably does not contain pleochroic dye, the invention relates briefly to the isotropic scattering of light by means of liquid crystal material, and the use of such isotropically scattered light to provide a white or clear appearance of a sign, an information, etc, especially in relation to a background, when a liquid crystal material is in a state of decoupled field or distorted alignment, and a colored or dark appearance, e.g. the same as the background, when a liquid crystal material is in a state of coupled field and parallel or ordered alignment. The liquid crystal material is preferably almost completely isotropically scattering when in distorted alignment. Isotropic scattering means that when a light beam enters the liquid crystal material, there is virtually no way to predict the exit angle of scattered light. Pleochroic dye is preferably not used in this embodiment because the dye would absorb light to reduce clarity when scattering and brightening would be intended.

As used with respect to the present invention, the terms distorted alignment, random alignment and field-of-state mean essentially the same thing, namely that the directional orientation of the liquid crystal molecules is distorted into an effectively curved configuration. Such a distortion is caused, for example, by the wall of the respective capsules. The particular distorted alignment of liquid crystal material in a given capsule will usually always be substantially the same in the absence of an electric field. As used with regard to the present invention, on the other hand, the terms parallel aligned, ordered alignment and field-on state mean that the liquid crystal material in a capsule is usually aligned in relation to an externally imposed electric field. The term operationally nematic is defined above.

A capsule refers to a containment device or , a containment medium that confines a given amount of liquid crystal material, and "encapsulating medium" or "encapsulating material" is the medium or material from which such capsules are formed. An "encapsulated liquid crystal" or an "encapsulated liquid crystal material" means a given amount of liquid crystal material that is enclosed or contained in separate or discrete volumes in the encapsulating medium, for example in a solid material, such as individual capsules or dried, stable emulsions.

Capsules according to the present invention usually have an approximately spherical shape (although this in itself is not a necessity for the invention) with a diameter from approx. 0.3 to 100 ym, preferably 0.1 to 30 ym, and especially 3-1.5 ym, for example 5-15 ym. In the context of the invention, encapsulation and similar expressions refer not only to the formation of such articles which are usually referred to as capsules, but also to the formation of stable emulsions or dispersions of the liquid crystal material in a medium (an encapsulating medium) which results in the formation of stable particles with preferably of approximately uniform size in a uniform surrounding medium. Techniques for encapsulation, commonly referred to as microencapsulation due to the capsule size, are well known in the art (see, e.g., "Microcapsule Processing and Technology" by Asaji Kondo, published by Marce Dekker, Inc.), and taking into account the present description, it will be possible for one skilled in the art to determine suitable encapsulating agents and encapsulating methods for liquid crystal materials.

In the liquid crystal device according to the invention, an operational nematic material in which a pleochroic dye is dissolved can be placed in an essentially spherical capsule. In the absence of an electric field, the capsule wall distorts the liquid crystal structure, so that the liquid crystal and the dye will tend to absorb light regardless of its polarization direction. When a suitable electric field is applied over such a capsule, for example over an axis thereof, the liquid crystal material will tend to align itself parallel to this field, causing the absorption property of the material to be reduced to a value assumed when the liquid crystal material is in the plane configuration. To help ensure that a sufficient electric field is applied over the liquid crystal material in the capsule, and not just over or through the encapsulating medium, and in reality with a minimal voltage drop across the wall thickness of the respective capsules, the encapsulating material preferably has on one side a dielectric constant which is nothing less than the liquid crystal material's lowest dielectric constant, and on the other hand a relatively large impedance. Ideally, the dielectric constant of the encapsulating medium must be close to the highest dielectric constant of the liquid crystal.

The contrast of a liquid crystal device using encapsulated liquid crystals can be improved by choosing an encapsulating medium that has a refractive index that is matched to the normal refractive index of the liquid crystal material (ie the refractive index parallel to the optical axis of the crystal. See e.g. "Optics" by Borne & Wolf, or "Crystals and the Polarizing Microscope" by Hartshorne & Stewart).

The encapsulating medium can be used not only to encapsulate liquid crystal material, but also to hold the capsules to a substrate for support thereon. Alternatively, a further binder can be used to hold the liquid crystal capsules in relation to a substrate. In the latter case, however, the additional binder preferably has a refractive index that is adapted to the refractive index of the encapsulating medium, in order to maintain the improved contrast property discussed above. Due to the fact that the refractive index of a material is usually stress- or deformation-dependent, and deformation can be caused in e.g. the encapsulating medium, it may be necessary to take this effect into account when matching the refractive indices of the liquid crystal, the encapsulating medium and the binder, if present. If iridescence (play of color) is to be avoided, it may also be desirable to adjust the refractive indices to the greatest extent possible over a range of wavelengths, instead of just one wavelength.

A distinctive feature of the spherical or otherwise

capsule provided with a curvilinear surface that delimits the liquid crystal material therein in accordance with the invention, is that the liquid crystal material tends to follow the curvature or otherwise align itself essentially parallel to the curved surfaces of such a capsule. Thus, the liquid crystal structure tends to be forced or distorted into a particular shape, in a sense bending back on itself as it follows the capsule wall, so that the resulting optical property of a given capsule containing liquid crystal material is such that essentially all light emitted to it will be affected, for example scattered (when no pleochroic dye is present) or absorbed (when pleochroic dye is present) when no electric field is applied, regardless of the polarization direction of the incident light. Even without dye, this effect can cause spreading and thus opacity.

Another distinctive feature is the ability to control the effective thickness of the liquid crystal material contained in the capsule, by controlling the internal diameter of such a capsule. Such diameter control can be accomplished by means of a size fractionation separation process during the preparation of the encapsulated liquid crystals using any of a variety of conventional or novel sorting techniques, as well as by controlling the mixing process, the amounts of ingredients and/or the nature of the ingredients. which is provided during mixing. By controlling this thickness parameter to relatively narrow tolerances, the later tolerance requirements when the final liquid crystal device is manufactured using the encapsulated liquid crystals, will not be as critical as what was previously necessary for non-encapsulated devices.

However, a further and very important feature of the present invention is that there does not seem to be any limitation on the size of a high-quality liquid crystal device that can be produced by using the encapsulated liquid crystals in accordance with the invention.

Specifically, by providing for the confinement of discrete amounts of liquid crystal material, for example, in the prescribed capsules, the various problems relied upon in the past which prevented the use of liquid crystal material in large size devices are overcome, for each individual capsule may in fact still act as an independent liquid crystal device. Further, each capsule preferably has physical characteristics that enable it to be mounted in virtually any environment including an environment containing a number of additional such liquid crystal capsules mounted to a substrate or otherwise supported for application in response to pressure and removal of some type of excitation source, such as an electric or magnetic field. This feature also enables placement of the liquid crystal material on only selected areas of the optical device, such as in large display devices (e.g. bulletin boards), optical shutters, etc.

Important factors in accordance with the invention, and discoveries made by the inventor, are that an encapsulating medium with electrical properties that are matched in a prescribed manner to the electrical properties of a liquid crystal material encapsulated by it, and which is also preferably optically matched according to optical properties of such liquid crystal material, allows efficient high-quality operation of the liquid crystal material in response to excitation or non-excitation by an external source, and that the interaction of the encapsulating medium with the liquid crystal material distorts the latter in a prescribed manner that changes an operating mode for the liquid crystal material. With respect to the latter feature, by forcing the liquid crystal structure to distort or deform into substantially parallel or conformal alignment with the capsule wall, the liquid crystals will absorb or block rather than transmit light when not exposed to an electric field, and will be functional with respect to all modes of incident light without regard to the possible direction of polarization of such incident light.

In accordance with the invention can as mentioned

a liquid crystal display device produces relatively clear or white characters, information, etc. on a relatively dark background. The clear or bright sign is produced by

liquid crystal material that is randomly aligned (preferably without pleochroic dye that would absorb and reduce scattering). The background is caused, for example, by means of liquid crystal material which is in an ordered alignment and thus essentially optically transparent, and/or by means of areas of the display device where no liquid crystal material is found. When the liquid crystal material is in parallel or ordered alignment, only the relatively dark background, e.g. formed by an absorber, appear. The foregoing is achieved by using relatively low power requirements, minimal liquid crystal material, and lighting either from the viewing side or the viewing direction or from the rear or non-viewing side of the display device.

The invention shall be described in more detail in the following with reference to the drawings which show certain illustrative embodiments of the invention, as these, however, only indicate a few of the different ways in which the principles of the invention can be applied.

In the drawings, fig. 1 a schematic representation of a liquid crystal device in accordance with the invention, fig. 2 and 3 show enlarged, schematic illustrations of a liquid crystal capsule according to the invention respectively in a state without a field (field-off state) and in a state with an applied electric field (field-on state), fig.

4 and 5 show schematic representations of a liquid crystal device according to one embodiment of the invention in a state without a field and in a state with an applied electric field, fig. 6 shows a schematic representation of another embodiment of a liquid crystal device according to the invention where an air gap is used to produce total internal reflection, fig. 7 and 8 show schematic representations of another embodiment of a liquid crystal device according to the invention which uses optical interference principles under a state without a field and a state with an applied electric field respectively, fig. 9 shows an isometric view of a liquid crystal display device according to the invention and which can be formed by any of the embodiments shown here, fig. 10 shows an incomplete schematic side view of another embodiment of a liquid crystal device using continuous layers of liquid crystal material and interrupted electrodes, and FIG. 11 shows a schematic isometric view, partially cut away, of the embodiment in fig. 10; fig. 12 shows a schematic view of an approximately proportioned liquid crystal display device according to the invention and shows a more accurately representative size ratio between the carrier medium layers and the encapsulated liquid crystal layer for the many embodiments described, fig. 13 shows a schematic illustration of a nematic liquid crystal capsule with the addition of cholestric material, which can be used together with the many designs described, fig. 14 and 15 show schematic illustrations of yet another embodiment of a liquid crystal device with a light control film guiding device which is provided with incident illumination from the non-viewing side in the field-on and field-off states, respectively, Figs. 16 shows a schematic illustration similar to fig. 14 and 15, but with the light control film guide cemented to the carrier, Figs. 17 shows a schematic illustration similar to fig. 2 and 3 and shows an alternative embodiment of an encapsulated liquid crystal, fig. 18 shows a schematic representation of a liquid crystal device according to the invention which uses pleochroic dye in the liquid crystal, fig. 19 shows an enlarged, partially cut-away partial view of a portion of the liquid crystal display device, the arrangement of FIG. 9, but extensive pleochroic dye, for example as in the embodiment in fig. 18, and fig. 20 shows a schematic electrical connection diagram of a liquid crystal capsule according to the invention with an imprinted field.

In fig. 1, 2 and 3 show an encapsulated liquid crystal material used in accordance with the present invention. Fig. 1 shows a schematic representation of a liquid crystal device 10 according to the invention. The device 10 comprises encapsulated liquid crystal material

which is represented by a single capsule 11 in fig. 1-3. Although the capsules shown in the drawings are shown in two dimensions and therefore in planar form, it will be realized that the capsules are three-dimensional, and preferably spherical. The capsule 11 is shown mounted in a preferably transparent carrier medium 12 with upper and lower parts 12a, 12b which can be formed in one piece with each other. The device 10 also comprises two electrodes 13, 14 for applying an electric field over the liquid crystal material when a switch 15 is closed to energize the electrodes from a conventional voltage source 16.

A main feature of the present invention is that such an encapsulated liquid crystal material will isotropically scatter light that strikes it when it is in a field-off state with random alignment, and that this material in the field-on state with ordered alignment will be essentially optically transparent.

The capsule 11 may be one of many capsules which are formed separately or, more preferably, are formed by mixing the liquid crystal material with a so-called encapsulating material or containment medium to form an emulsion, preferably a stable one. The emulsion may be applied to or sandwiched between the carrier medium portions 12a, 12b and the electrodes 13, 14, as shown. If desired, the carrier medium 12

and the so-called encapsulation material or containment medium be the same material. As a further alternative, the upper and lower carrier medium parts 12a, 12b, or one of these, can be a preferably transparent mounting or frame material which is plastic-like, or made of glass or the like. In this latter case, the electrodes 13, 14 can be applied to such mounting material, and the encapsulated liquid crystal material or the encapsulated liquid

crystal emulsion, including e.g. many capsules 11 can be inserted between such mounting material 12a, 12b to form the device 10, as will be described in more detail below.

A reflection medium (reflectance medium) 18 forms an interface 19 with the lower carrier medium part 12b to achieve the desired internal total reflection function. As a result of the functional principle of total internal reflection, the liquid crystal material in the capsule 11 will be illuminated by means of incident light, for example represented by a light beam 17, and with light which it spreads isotropically in the device 10, so that from the viewing area 20 outside the upper carrier medium part 12a will the liquid crystal material 11 appear white or relatively bright or clear in a non-field state, e.g. with switch 15 open. The principle of total internal reflection according to the present invention increases the isotropic dispersion and thus makes clearer the visual/optical appearance of characters formed by the encapsulated liquid crystal material. A light absorbing layer 21 of black or colored material may be applied to the lower or rear surface of the reflective medium 18 at a distance from the interface 19 to absorb light incident on the layer 21.

The electrode 13 can be vacuum-deposited indium tin oxide which is applied to the lower carrier medium part 12b, and the electrode 14 can be electrically conductive, ink applied directly to the liquid crystal material or can be similar to the electrode 13. A different electrode material or a different attachment device for this can also be used for each electrode. Examples include tin oxide and antimony doped tin oxide. The electrodes are preferably relatively thin, for example approx. 200 Angstroms (= 0.02 um) and transparent so that they do not significantly affect the optics of the liquid crystal device 10.

The encapsulated liquid crystal material contains a liquid crystal 30 which is contained within the boundary or inner volume 31 of a capsule 32. Each capsule 32 can be a separate capsule, or alternatively the liquid crystal 30 can be contained in a stable emulsion of an encapsulation medium or so-called encapsulation material 33 which acts in the direction of forming a large number of capsule-like environments to contain the liquid crystal material. For convenience of illustration, the capsules 32 are shown as separate capsules in and preferably formed by the total amount of containment medium or encapsulation material 33. The capsule 32 is preferably substantially spherical, and the liquid crystal 30 is nematic or operationally nematic liquid crystal material with positive dielectric .. anisotropy. However, the principles of the invention would apply when the capsule 32 has a shape other than spherical.

Such a form must provide the desired optical and electrical properties which will interact satisfactorily with the optical properties of the liquid crystal material, e.g. refractive index, and will allow a sufficient portion of the electric field to act across the liquid crystal 30 itself to cause the desired ordered or parallel alignment of the liquid crystal when a field-on condition is desired. The shape must also tend to distort the liquid crystal material when it is in a decoupled field or random alignment state. A particular advantage of the preferred spherical shape of the capsule 32 is the distortion or deformation it causes to the liquid crystal 30 contained therein when in a field-off state. This distortion is due at least in part to the relative sizes of the capsules and the division of the liquid crystal. They are preferably of approximately the same or at least approximately the same order of magnitude. Nematic liquid crystal material also has fluid-like properties that facilitate its adaptation or distortion to the shape of the capsule wall in the absence of an electric field. In the presence of an electric field, on the other hand, such nematic material will relatively easily change to an ordered alignment in relation to such a field.

Liquid crystal material of a type other than nematic or combinations of different types of liquid crystal material and/or other additives can be used together with or inserted instead of the preferred nematic liquid crystal material as long as the encapsulated liquid crystal is operationally nematic. However, cholestric and smectic liquid crystal materials are usually volume or mass driven. It is more difficult to break up its mass structure for compliance with the capsule wall's shape and energy factors i

the capsule.

In fig. 2 and 3 show a schematic representation

of the individual capsule 32 containing the liquid crystal 30 in the field-off and field-on states respectively. The capsules 3 2 have a mainly smooth, curved inner wall surface 50 which forms the boundary of the volume 31. The relevant dimensional parameters for the wall surface 50 and the total capsule 32 are in relation to the amount of liquid crystal 30 contained in the capsule, and possibly to other properties to the individual liquid crystal material therein. The capsule 3 2 also exerts a force on the liquid crystals 30 which tries to create excess pressure or at least maintain the pressure in the volume 31 essentially constant. As a result of the foregoing, and as a result of the surface wetting nature of the liquid crystal, the liquid crystals, which in their free form would normally attempt to be parallel even though they might be randomly distributed, are distorted to curve in a direction that is normally parallel to a relatively close part of the inner wall surface 50. As a result of this distortion, the liquid crystals store elastic energy. For purposes of simple illustration, a layer or layer 51 of liquid crystal molecules 52 whose directional orientation is represented by respective dashed lines,

shown in the most immediate vicinity of the inner wall surface 50. The directional orientation of the liquid crystal molecules 52 is distorted to curve in the direction parallel to a nearby region of the wall surface 50. The directional pattern of the liquid crystal molecules away from the boundary layer 51- in the capsule is represented at 53. The liquid crystal molecules is directionally represented in layers or layers, but it will be realized that the molecules themselves are not limited to such layers. The organization in an individual capsule is thus predetermined by the organization of the structure at the wall and is fixed unless it is influenced by external forces, e.g. an electric field. On removal of the electric field, the directional orientation will return to the original one, such as that shown in fig. 2.

Nematic type material usually assumes a parallel configuration and is usually optical polarization direction sensitive. However, since the material 30 in the encapsulated liquid crystal 11 is distorted or forced into a curved shape in all three dimensions of the capsule 32, such a nematic liquid crystal material in such a capsule acquires an improved property in that it becomes insensitive to the direction of optical polarization of incident light. The present inventor has also discovered that when the liquid crystal material 30 in the capsule 32 has pleochroic dye dissolved therein, such dye, which would normally also be expected to have optical polarization sensitivity, is no longer polarization sensitive due to the dye attempting to follow the same type curvature orientation or distortion as the individual liquid crystal molecules 52.

The liquid crystal 30 in the capsule 32 has a discontinuity 55 in its essentially spherical orientation as a result of the liquid crystal's inability to align uniformly in a manner compatible with parallel alignment with the wall 50, and a need for minimal elastic energy. This discontinuity is in three dimensions and is effective in causing a distortion of the liquid crystal 30 to further reduce the possibility that the liquid crystal 30 will be sensitive to optical polarization direction of incident light. The discontinuity protrusion 55 will tend to cause scattering and absorption within the capsule, and the tangential or parallel alignment of the liquid crystal molecules with respect to portions of the capsule's inner wall surface 50 also causes scattering and absorption within the capsule 32. When the electric field is applied , for example as shown in fig. 3, the discontinuity will no longer exist, so that this discontinuity will have a minimal effect on optical transmission when the encapsulated liquid crystal 30 is in a field-on state or aligned state.

Although the preceding description has assumed a homogeneous orientation of the liquid crystal material (parallel to the capsule wall), this is not a requirement for the invention. All that is necessary is that the interaction between the wall and the liquid crystal produces an orientation in the liquid crystal near this wall which is essentially uniform and piecemeal continuous, so that the spatial average orientation of the liquid crystal material over the capsule volume is strongly curved and there is no significant parallel orientation direction of the liquid crystal structure in the absence of an electric field. It is this highly curved orientation that results in the scattering and polarization insensitivity in the field-off state, which is a distinctive feature of the invention.

In the field-on state, or in any other state that results in the liquid crystal being in ordered or parallel alignment, as shown in FIG. 3, the encapsulated liquid crystal 11 will transmit essentially all the light that falls on it, and will tend not to be visible in the carrier medium 12. In the field-off state, when the liquid crystal is in a distorted alignment, sometimes denoted here as random alignment, for example as shown in fig. 2, on the other hand, some of the incident light will be absorbed, but part of the incident light will also tend to be scattered isotropically in the carrier medium 12. By using total internal reflection, such isotropically scattered light can be redirected to the encapsulated liquid crystal 11, thus making it brighter or clearer and tending to make it appear white to a viewer or viewing instrument.

The refractive index of the encapsulating medium 32 and the normal refractive index of the liquid crystal 30 must be matched as much as possible when the liquid crystal is in the state of impressed field or ordered alignment, in order to avoid optical distortion due to refraction of incident light passing through the crystal. However, when the liquid crystal material is in a distorted or random alignment, i.e. there is no applied field, there will be a difference in refractive indices at the boundary of the liquid crystal 30 and the wall of the capsule 32. The extraordinary refractive index of the liquid crystal is greater than the refractive index of the encapsulating medium. This causes refraction at the interface between the liquid crystal material and the containment or encapsulation medium, and thus further scattering. Light that is further scattered in this way will be internally reflected to make the liquid crystal appear even brighter or clearer. Such appearance of different refractive indices is known as birefringence. The principles of birefringence are described in "Optics" by Sears and in "Crystals and the Polarizing Microscope" by Hartshorne and Stewart, the relevant disclosures of which are incorporated herein by reference. The encapsulation or containment medium 33^ and the carrier medium 12 preferably have the same refractive index in order to appear optically essentially as the same material, so that a further optical interface is avoided.

As long as the liquid crystal material's normal or ordinary refractive index is closer to the refractive index of the so-called encapsulating medium than the extraordinary refractive index, a change in dispersion will appear when you go from the field-on to the field-off state and vice versa. Maximum contrast occurs when the ordinary refractive index corresponds to the medium's refractive index. The accuracy of the refractive index matching will depend on the desired degree of contrast and transparency in the device, but the ordinary refractive index of the crystal and the refractive index of the medium will preferably differ by no more than 0.1, preferably 0.03, even more preferably 0.01, and especially 0.001. The permitted difference will depend on the capsule size.

It is desirable that the electric field E shown in fig. 3, is pressed onto the liquid crystal 30 in the capsule 32 over the greater part of it instead of being consumed or dropped to a significant extent in the encapsulation material. There should be no significant voltage drop across or through the material of which the wall 54 of the capsule 3 2 is formed. Instead, the voltage drop should occur across the liquid crystal 3 0 in the volume 31 of the capsule 3 2 .

The encapsulation medium's electrical impedance must in reality be sufficiently large in relation to the impedance of the liquid crystal in the encapsulated liquid crystal 11 so that a short circuit will not occur exclusively through the wall 54, e.g. from a point A via just the wall to a point B, bypassing the liquid crystal. Therefore, for example, the effective impedance to induced current or displacement current flowing through or via just the wall 54 from point A to point B should be greater than the impedance that would be encountered in a path from point A to point A' within the inner wall surface 50, via the liquid crystal material 30 to a point B' which is still in the volume 31, and finally back to point B. This condition will ensure that there will be a potential difference between point A and point B. This potential difference must be sufficiently large to produce an electric field above the liquid crystal material which will attempt to align it. It will be appreciated that due to geometrical considerations, namely the length through just the wall from e.g. point A to point B, this condition can still be met even if the real impedance of the wall material is lower than the impedance of the liquid crystal material in the capsule.

The dielectric constants of the material of which the encapsulation medium is formed and of which the liquid crystal is made up, and the effective capacitance values of the capsule wall 54, particularly in the radial direction, and of the liquid crystal over which the electric field E is applied, must all be so related that the capsule's 3 2 wall 54 does not significantly reduce the magnitude of the applied electric field E. Ideally, the capacitance-dielectric constants of the entire layer or layer 61 (Fig. 4) of encapsulated liquid crystal material must be substantially the same for the field-on condition.

The liquid crystal 30 will have a dielectric constant value which is anisotropic. It is preferred that the dielectric constant of the wall 54 is not lower than the dielectric constant of the anisotropic liquid crystal material 30 to help meet the above conditions for optimal operation. It is desirable to have a relatively high positive dielectric anisotropy in order to reduce the voltage requirements for the electric field E. The difference between the dielectric constant of the liquid crystal 3 0 when no electric field is applied, which must be relatively small, and the dielectric constant of the liquid crystal when it is aligned when an electric field is applied, which must be relatively large, must be as large as possible. The critical relationship between dielectric values and applied electric field must be such that the field applied over the liquid crystal material in the capsule or capsules is sufficient to cause alignment of the liquid crystal structure in relation to the field. The lowest dielectric values for commonly used liquid crystals are, for example, as low as approx. 3.5 to as high as approx. 8.

The capsules 3 2 can be of different sizes.

The smaller the size, however, the higher the requirements will be for the electric field to effect alignment of the liquid crystal in the capsule. However, the capsules must preferably have uniform size parameters so that the various properties, such as the optical and electrical properties, of a device, such as a display device, which uses the encapsulated liquid crystal, will be essentially uniform. The capsules 3 2 must furthermore be at least 1 µm in diameter, so that they appear as discrete capsules in relation to an incident light beam. A smaller diameter would result in the light beam "seeing" the capsules as a continuous, homogeneous layer and would not undergo the necessary, isotropic dispersion. The capsules can e.g. have a size of from 1-30 µm in diameter.

A preferred liquid crystal material in accordance with the best embodiment of the invention is the nematic material NM-8 250, an ester sold by American Liquid Xtal Chemical Corp., Kent, Ohio, USA. Other examples can be ester combinations, biphenyl and/or biphenyl combinations, and the like.

Several other types of liquid crystal material which are effective in accordance with the invention include the following four examples, each of which is a recipe for the respective liquid crystal materials. The so-called 10% material has approx. 10% 4-cyano-substituted materials, the 20% material has approx. 20% 4-cyano-substituted materials, etc.

10% material

20%- material 40%- material 4 0%- MOD

The encapsulating medium which forms respective capsules 32 should be of a type which is essentially completely unaffected by and which does not affect the liquid crystal material. Various resins and/or polymers can be used as encapsulation medium. A preferred encapsulation medium is polyvinyl alcohol (PVA) which has a good, relatively high dielectric constant and a refractive index which is relatively precisely matched to the refractive index of the preferred liquid crystal material. An example of preferred PVA is an approx. 84% hydrolyzed resin with a molecular weight of at least approx. 1000. Use of a PVA from the Monsanto Company designated as Gelvatol 20/30 represents the best embodiment of the invention.

A method for producing emulsified or encapsulated liquid crystals 11 may comprise mixing the containment or encapsulation medium, the liquid crystal material, and possibly a carrier medium, such as water. Mixing can be carried out in many different mixing devices, such as a mixer, a colloid mill, which is most preferred, or the like. What occurs during such mixing is the formation of an emulsion of the ingredients, which can later be dried to eliminate the carrier medium, such as water, and to satisfactorily cure the encapsulating medium, such as the PVA material. Although the capsule 32 of each encapsulated liquid crystal 11 thus prepared may not be a perfect sphere, each capsule will be substantially spherical in shape due to the fact that a sphere represents the lowest free energy state for individual droplets, small spheres or capsules of the emulsion, both when originally formed and after drying and/or curing.

The size (diameter) of the capsule should preferably be uniform in the emulsion to achieve uniform operation with regard to effect on incident light and response to electric field. As an example of capsule size range, this can range from approx. 0.3 to approx. 100 ym, preferably 0.3-30 ym, especially 3-15 ym, for example 5-15 ym.

Different techniques can be used to form the carrier medium 12 which can be of the same or a similar material as the encapsulation or containment medium. For example, the lower support medium 12b can be formed using a molding or casting process. The electrode 13 and the liquid crystal material can be applied for support by means of this medium 12b. The electrode 14 can be placed by e.g. printing. Then, the upper support medium portion 12a can be poured or cast in place to complete containment of the encapsulated liquid crystal material and electrodes. Alternatively, the carrier medium parts 12a, 12b can be an essentially transparent plastic-like film or a plate of glass, as described e.g. in the following Example 1.

If the reflection medium 18 is e.g. a solid substance, this can be applied to the carrier medium portion 12b by means of a further molding or molding technique, and the lower coating 21 of black or colored light-absorbing material can be applied to the back surface of the reflection medium 18, i.e. the surface which is at a distance from the interface between the medium and the lower carrier medium part 12b. Alternatively, the reflection medium can be an air gap or another fluid gap between the carrier medium part 12b and the absorber 21, or a matched dielectric layer can be applied by means of a conventional evaporation technique directly to the lower surface of the lower carrier medium part 12b instead of the reflection medium 18, as will be described in more detail. below.

In the following, several examples of materials and methods for the production of liquid crystal display devices and their operating characteristics in accordance with the invention are given.

Example 1

An example of an isotropic spreading material was produced by mixing approx. 2 grams of nematic liquid crystal of type 8250 (an ester from American Liquid Xtal) with approx. 4 grams of a 20% solution of Airco 4 05 polyvinyl alcohol (the remaining 80% of the solution was water). The material was mixed in a small low shear homogenizer to form an emulsion. When using a scraper blade with a setting of approx. 0.13 mm, the emulsion was coated on an electrode of Intrex material already placed in position on a polyester film base with a thickness of approx. 0.13 mm. The film was of the type known as Mylar. Another sheet of such film with such an electrode was placed on the encapsulated liquid crystal layer, so that the latter was sandwiched between the respective electrodes and films. The individual, encapsulated, operationally nematic liquid crystal capsules or particles had a diameter of approx. 4-5 ym, and the total layer of encapsulated liquid crystal material had a thickness of approx. 20-30 etc.

The device produced according to Example 1 was tested. The resulting material scattered light in a state of zero electric field (hereafter commonly referred to as the zero-field or field-off state). At an applied field of 10 volts the scattering decreased, and at 40 volts the scattering stopped entirely.

Although a homogenizer was used, other types of mixers, etc. can be used to effect the desired mixing.

Example 2

An example of the isotropic spreading material was produced by mixing approx. 2 grams of nematic liquid crystal of type 8250 with approx. 4 grams of a 22% solution (78% water) of polyvinyl alcohol of the type Gelvatol 20/30 (from Monsanto). The material was mixed in a small low shear homogenizer to form an emulsion. The emulsion was applied to an Intrex film electrode and a Mylar film polyester base, as in Example 1, with a scraper blade at a setting of approx. 0.13 mm, and the layered assembly (sandwich) was completed as in Example 1. The nematic capsules or particles had a diameter of approx. 3-4 ym, and the encapsulated liquid crystal layer was approx. 25 ym thick.

The device produced according to Example 2 was tested. The resulting material scattered light in a zero-field or field-off state. At an applied field of 10 volts the scattering decreased, and at 40 volts the scattering stopped entirely.

Example 3

An example of the isotropic spreading material was produced by mixing approx. 2 grams of nematic liquid crystal of type E-63 (a biphenyl from British Drug House, a subsidiary of E. Merck, West Germany) with approx. 4 grams of a 22% solution of polyvinyl alcohol of the type Gelvatol 20/30 (from Monsanto). The material was mixed in a small low shear homogenizer to form an emulsion. The emulsion was applied to an Intrex film electrode and a Mylar film polyester base with a scraper blade at a setting of approx. 0.13 mm,

and the sandwich was completed as above. The thickness of the encapsulated liquid crystal layer was approx. 25 ym, and the nematic capsules or particles had a diameter of approx. 4-5 etc.

The device produced according to Example 3 was tested. The resulting material scattered light in a zero-field or field-off state. At an applied field of 7 volts the spread decreased, and at 3 5 volts the spread stopped entirely.

Example 4

An example of the isotropically scattering material

was produced by mixing approx. 2 grams of liquid crystal of type 8250 with approx. 4 grams of a 22% solution of Gelvatol 20/30 polyvinyl alcohol. The material was mixed in a small low shear homogenizer to form an emulsion. The emulsion was applied to an Intrex film electrode and a Mylar polyester film base with a scraper blade at a setting of approx. 0.13 mm, and the sandwich was completed as indicated above. The thickness of the encapsulated liquid crystal layer was approx. 25 ym, and the nematic capsules or particles had a diameter of approx. 4-5 etc.

To improve emulsion stability and coating uniformity, 0.001% GAF LO 63 0, a non-ionic surfactant (detergent), was added prior to the mixing step. Improved behavior in terms of stability of the emulsion and in terms of coating of the emulsion on the electrode/polyester film base was noted. The operation results were otherwise essentially the same as those stated above with regard to Example 1.

It will thus be realized that a surface-active substance, preferably a non-ionic surface-active substance, a cleaning agent or the like, according to the invention can be mixed with the encapsulated liquid crystal material prior to deposition on the electrode-coated film, as just described above.

Example 5

The steps according to Example 1 were followed using the same materials as in Example 1, except that a glass plate with a thickness of approx. 3.2 mm was inserted in place of the Mylar film. The function was essentially the same as described with regard to example 1.

Example 6

A mixture was formed of nematic liquid crystal

of type 8250 and a solution of 15% AN169 Gantrez in 85% water. Such Gantrez is polymethyl vinyl ether/maleic anhydride, a polymaleic acid product of GAF Corporation. The mixture was 15% liquid crystal and 85% Gantrez as containment medium. The mixture was homogenized at low shear for

to form an emulsion which was applied to an electrode/carrier film as indicated above. This carrier film was approx. 0.03 mm thick. After drying the emulsion, the resulting liquid crystal emulsion responded to an electric field essentially as stated above, with dispersion in a field-off state, exhibiting a threshold of approx. 7 volts to start reducing dispersion, and had a saturation level of essentially no dispersion at approx. 4 5 volts.

Another example of an acid-type containment medium effective in connection with the invention is carbopol (carboxy-polymethylene polymer from B.F. Goodrich Chemical Company), or polyacid.

Other types of carrier media 12 that can be used include polyester materials, and further polycarbonate material, such as Kodel film. Tedlar film, which is very inactive, can also be used if sufficient adhesion of the electrode can be achieved. Such media 12 should preferably be mainly optically transparent.

Several different polymer containment media that can be used are listed in Table I below. The table also indicates several properties for the respective polymers.

Other Gelvatol PVA materials that may be used include those designated by Monsanto as 20-90, 9000, 20-60, 6000, 3000, and 40-10.

A preferred quantity ratio between liquid crystal material and containment medium is approx. one part by weight of liquid crystal material to approx. three parts by weight containment medium. An acceptable, encapsulated liquid crystal emulsion which is operative in accordance with the invention can also be obtained by using a quantity ratio of approx. one part liquid crystal material to approx. two parts containment medium, e.g. Gelvatol PVA. Although a ratio of 1:1 will also work, it will usually not work as well as material in the ratio range from approx. 1:2 to approx. 1:3.

Referring now to fig. 4 and 5, there is shown a part 60 of a liquid crystal display device according to the invention. The part or device 60 is a completion of the liquid crystal device 10 which is described above with reference to fig. 1, in that a number of encapsulated liquid crystals 11, actually several layers of such crystals, are contained in a carrier medium 12. The sizes, thicknesses, diameters, etc., of the many parts shown in fig. 4 and 5, are not necessarily to scale, but the sizes are instead as necessary to illustrate the many parts and their operation.

The electrodes 13, 14 are used to apply a desired electric field to effect selective alignment of the liquid crystal material in the manner shown e.g. on fig. 3. A device other than electrodes can be used to supply some type of input signal to the display device 60 for the purpose of effecting ordered or random alignment of the liquid crystal.

The encapsulated liquid crystals 11 are arranged in several layers 61 inside the display part 60. The layers 61 can be divided into several parts that represent the different characters or parts of characters that are intended to be displayed using the display device 60. For example, the longest, left portion 61L of the layers 61 shown in fig. 4, represent a cross-section through one part of a well-known 7-segment display pattern, and the relatively short,

right part 61R of those in fig. 4, layer 61 may represent a portion of another 7-segment character display. Different patterns of liquid crystal material can be used in accordance with the invention. A zone 62 of carrier medium 12 fills the area between the liquid crystal layer portions 61L, 61R. Later reference to the layers 61 will be collective, i.e. refer to the layer 61 as if it contains the many levels or layers containing the same. As an example, the composite thickness of such a layer 61 may be from approx. 0.0075 mm to approx. 0.254 mm. Uniform thickness is preferred to achieve uniform response to electric field, dispersion, etc.

Such an arrangement or pattern of encapsulated liquid crystal material layer portions 61L and 61R which are separated in the zone 62 by means of the carrier medium 12 or another material is facilitated, or also made possible, as a result of the confinement or confinement of the liquid crystal in separate confinement media, as it is formed by means of the preferred, stable emulsion. The encapsulated liquid crystal material can therefore, especially on a relatively large device, such as a display device, a notice board, an optical shutter, etc., be applied to the carrier medium 12 only where it is necessary to provide the selectable optical properties. Such patterning can reduce the amount of such material required for a particular application. Such pattern formation is further made possible as a result of the desired functional operation which is described in more detail below.

The display device 60 can be used, for example, in an air environment, as such air is represented by the reference number 63, and the air forms an interface 64 with the carrier medium 12 on the viewing side or from the viewing direction 20. The refractive index n for the outer medium 63 is different from the refractive index n ' for the encapsulation medium 12, the latter being usually larger than the former. As a result of this, a light beam 65 which arrives mainly from the viewing direction 20, as it passes through the boundary surface 64 into the carrier medium 12, will be bent in the direction towards the normal, which is an imaginary line 66 normal to the boundary surface 64. This light beam 65a inside the carrier medium 12 will lie closer to the normal than the incident light beam 65, as it satisfies the relation n sin 9- = in' sin 0' where ø is the angle of the incident light beam 65 in relation to the normal and Ø<1> is the angle of the light beam 65a in relation to the normal.

A corresponding mathematical relation will apply at the interface 19, in the following way: n' sin 0<*> = n" sin 0". In order to achieve the desired total internal reflection in accordance with the invention, the refractive index ri" of the reflection medium 18 is smaller than the refractive index n<1> of the carrier medium 12. Consequently, for example, the light beam 65a, if it were r capable of and actually passed through interface 19, be deflected away from the normal at interface 19 to the angle 0" relative to the normal. Since the light beam 65, 6 5a is not actually scattered off course due to the liquid crystal material in the layers 61, i.e. due to passing through the zone 62, it is indeed likely to exit through the interface 19.

In operation of a liquid crystal display device 60 (Fig. 4), the operationally nematic liquid crystal 30 is in distorted or random alignment as a result of the existence of a field-off condition. An incident light beam 70 enters the carrier medium 12 at the interface 64 and is deflected as the light beam 70a which, as incident light, hits the layer 61 of encapsulated liquid crystal. The randomly aligned or distorted encapsulated liquid crystal material will isotropically scatter this incident light. There are therefore several possibilities for how such an incident light beam 70a will tend to be scattered, as indicated below: A. One possibility is that the incident light beam 70a will be directed towards the boundary surface 19 in accordance with the dotted line 70b. The angle at which the light beam 70b hits the boundary surface 19 lies within the solid angle a shown (defined in the planar direction of the drawing in Fig. 4 by means of the dashed lines 71) for a so-called lighting cone. Light that falls within such a spatial angle a or illumination cone has too small an angle in relation to the normal at the boundary surface 19 to be totally internally reflected at this boundary surface. The light beam 70b will therefore pass through the interface 19 at the same time as it is bent away from the normal to form the light beam 70c. The light beam 70c passes into the reflective ion medium 18 and is absorbed by the layer or layer 21. B. Another possibility is that the light beam 70a will be dispersed isotropically in the direction of the light beam 70d outside the cone angle a. Total internal reflection will occur at the interface 19, so that the light beam 70d is caused to be reflected as a light beam 70e back to the layer 61 of encapsulated liquid crystal material where it will be treated as another, independently incident light beam thereto, in the same manner as the light beam 70a from which it was derived. The light beam 70e will therefore undergo isotropic scattering again as described here. C. A further possibility is that the incident light beam 70a, or that which is derived from it, such as the light beam 7Oe, will be dispersed in an isotropic manner in the direction of the boundary surface 64 at an angle that is so close to the normal at this boundary surface 64 that the light beam will pass through the interface 64 into the "medium" 63, such as the air, to be seen by an observer or observation instrument. The solid angle a' of an illumination cone, like the above-mentioned cone angle a, within which such a scattered light beam 70e must fall in order to be emitted through the boundary surface 64, is represented by the dashed lines 72. A light beam 70f represents such a light beam emitted in this way from the display device 60. It is this light, e.g. the sum of such emitted light rays 70f exiting at the interface 64 which causes the layer 61 of encapsulated liquid crystals 11 to give the appearance of a white or bright character as viewed from the viewing direction 20. D. Yet another possibility is that the light beam 70a can be spread isotropically in the direction of the light beam 70g. The light beam 70g lies outside the solid angle a<1> and will therefore undergo total internal reflection at the boundary surface 64, after which the reflected beam 70h will bounce back against the layer 61 as a virtually independent, incident light beam, in the same way as the above-mentioned beam 70e and with a similar effect.

The refractive index of the electrodes 13, 14 will usually be greater than the refractive index or indices of the containment medium and the carrier medium, and the refractive indices of the containment medium and the carrier medium are preferably at least approximately the same. The light that passes from the containment medium into the electrode material will therefore be deflected in the direction towards the normal, and the light that passes from the electrode into the carrier medium will be deflected away from the normal, so that the net effect of the electrode is thus zero or essentially negligible. The majority of total internal reflection will thus occur at the interface surfaces 19, 64.

As viewed from the viewing direction 20, the zone 62 will appear black or colored in accordance with the composition of the absorbent layer 21. This is due to the fact that the light beam 65, 65a, 65b, which represents the majority of light passing through the zone 62, will tend to pass through the interface 64, the carrier medium 12, the interface 19 and the reflection medium 18, as it is bent in the direction towards or away from the normal, at respective interfaces as shown, as it is ultimately mainly absorbed by the layer 21.

While briefly referring to fig. 5, this figure shows the field-on state (ordered alignment) and the operation of the encapsulated liquid crystal layer 61 in the display device 60. The encapsulated liquid crystals 11 in the layer 61 of fig. 5

are similar to those shown in fig. 3. Like the light beam 65, 65a, 65b which passes through the zone 62 and is absorbed by the layer 21, the light beam 70, 70a, 70i will therefore follow a similar path as it is also transmitted through the arranged and thus in reality transparent or non-scattering layer 61. At the boundary surface 19, the light beam 70a will be bent away from the normal, and later the light beam 70i will be absorbed by the layer 21. Whatever visual appearance the light beam 65 will try to effect with regard to an observer at the viewing location 20, will consequently also the light beam 70 causes the same effect as it passes through the ordered aligned encapsulated liquid crystal material. Thus, when the display device 60, and in particular the encapsulated liquid crystal material therein, is in the ordered aligned state or the field-on state, the area in which the liquid crystal is located will have essentially the same appearance as the zone 62.

It should be noted that if one or the other of the incident rays 65, 70 should ..enter the carrier medium 12" at the interface 64 at such a large angle, in relation to" the normal there that it finally collides with the interface 19 in a angle that is greater than an angle that falls within the so-called light cone angle a, such a beam would be internally totally reflected at the interface 19. However, such reflected light would probably remain inside the carrier medium 12 as a result of later transmission through the layer of liquid crystal material 61 and later total internal reflection at interface 64, etc.

In fig. 6, the preferred reflection medium 80 is shown to be air. In fig. 6, marked reference numbers denote elements that correspond to the elements designated by the same unmarked reference numbers in fig. 4 and 5. The display device 60' has an interface 19' formed with the air 80. To achieve absorption of the light transmitted through the interface 19' and the medium 80, a black or colored absorber 81 can be placed at a location offset from the interface 19'. The preferred absorber 81 is carbon black which may be mounted on a support surface which is placed in the main case as shown in fig. 6. The preferred liquid crystal is NM 8250, the preferred containment medium is PVA, and the preferred carrier medium 12 is polyester. It is further preferred that the refractive index of the carrier medium 12a, 12b and the refractive index of the containment medium for the liquid crystal are at least essentially the same. This helps to ensure that the total internal reflection will occur mainly at the interfaces 19', 64' and not very much, if at all, at the interface between the containment medium and the carrier medium. This minimizes optical distortion while maximizing contrast. The display device 60' works in the main in the same way as the display device 60 which is described above with reference to fig. 4 and 5.

Referring now to fig. 7 and 8, a modified liquid crystal display device 90 comprises a carrier medium 12 with a layer of encapsulated liquid crystal material 61, as in the foregoing. At the interface 19, however, there is a matched dielectric interference layer 91. The thickness of the dielectric layer 91, which is exaggerated in the drawings, is preferably a different integer function or multiple of A divided by two, such as 3X/2, 5X/2, etc. , where X is the wavelength of the light in the display device 90. The matched, dielectric interference layer 91 can be applied to the back surface of the carrier medium 12 by means of a conventional vapor deposition technique. Such a dielectric layer can consist of barium oxide (BaO), lithium fluoride (LiF) or another material which provides the desired optical interference function. Such a layer preferably has a smaller refractive index than the medium 12 in order to achieve an interface 19 at which total internal reflection of light within a cone angle a will be internally reflected. A comprehensive description of optical interference can be found in "Optics" by Born and Wolf, in "Fundamentals of Physics", second edition, 1981, by Resnick and Halliday, pages 731-735, and in "University Physics" by Sears and Zemansky, whose relevant statements are incorporated into the present description by reference.

In the field-off or random liquid crystal alignment condition shown in FIG. 7, the display device 90 will work in the main in the same way as the display device 60 described above with regard to (a)

isotropic scattering of light by means of the encapsulated liquid crystal material layer 61, (b) total internal reflection of the light falling outside the solid angle a, this as a result of the interface 19 shown in fig. 7 (or a<1> with respect to light scattered isotropically to the interface 64), and (c) the transmission of light, such as the light beam 70f, towards the viewing direction 20 to produce the appearance of a white character on a relatively dark background .

By using the tuned dielectric interference layer 91 and optical interference, the illumination caused by the encapsulated liquid crystal layer 61 in the field-off state is further enhanced. More specifically, the effective light cone angle a is reduced to the angle (j> shown in Fig. 7. In general, an incident light beam 92

which impinges on the boundary surface 64, be deflected as the light beam 92a which is then incident on the layer or layer 61. If the light beam 9 2a is spread isotropically as the beam

92b at an angle outside the original angle a, the operation with total internal reflection, which is described above in connection with the display device 60, will occur. If, however, the light beam 9 2a is spread isotropically as a light beam 9 2c at an angle that falls within the light cone angle a, but outside the cone angle $, it will in fact be reflected and constructive optical interference will occur to further enhance the illumination of the encapsulated liquid crystal layer 61 .

More specifically, when the light beam 9 2c enters the tuned dielectric interference layer 91, at least a part 92d will in reality be reflected back towards the boundary surface 19. At the boundary surface 19, constructive interference with another incident light beam 93 will take place, which increases the effective intensity of the internally reflected, resulting light beam 94 which is directed back towards the encapsulated liquid crystal layer 61 so that its illumination is amplified. The result of such constructive interference is that the display device 90 provides more light rays that are scattered up to or reflected up to the layer 61 than the display device 60. There is, however, a disadvantage in that the viewing angle at which the display device 90 will work effectively is smaller than the viewing angle at which display device 60 will work effectively. More specifically, incident light entering the carrier medium 12 at an angle equal to or less than the angle a relative to the interface 64 will tend to be totally reflected due to the fact that the rear or reflective surface of the tuned dielectric interference layer 91 will tend to act like a mirror, so that a certain contrast will go

lost in the display device 90. In connection with the display device 60, the angle a, if it exists at all, will tend to be smaller than the angle a of the display device 90.

The light beams 95 and 96 (Fig. 7) passing through the zone 62 of the display device 90, and the light beams 92' (Fig. 8) passing through the ordered aligned (field-impressed) liquid crystal layer 61 and falling within the cone angle $, will undergo destructive, optical - interference. From the viewing area 20, the zone 62 and the area where the field-on liquid crystal is arranged will therefore appear relatively dark/dark, i.e. as a dark background in relation to the white or brightly lit liquid crystal layer part 61 which has a field-off state and diffuses the light. If desired, an absorber (black or colored) can be used outside the layer 91. Also, the color of the background can be changed as a function of the thickness of the layer 91.

Referring now to fig. 9, there is shown an example of a liquid crystal device 100 according to the invention in the form of a liquid crystal display device which appears as a figure eight 101 with right-angled corners inside the substrate or carrier medium 12 which in this case is preferably a plastic material, such as Mylar, or alternatively can be another material, such as glass. The shaded area that appears in fig. 9 to form the number eight with right-angled corners, is constituted by one or more layers 61 of encapsulated liquid crystals 11 which are arranged in one or more layers on and are adhered to the substrate 12. An enlarged, incomplete cross-sectional view of a portion of the number eight 101 is shown in fig. 4 as the display device 60, 60' or 90 which is described above with reference to fig. 4-8. Each of the seven segments of the number eight 101 can be selectively energized or not energized to form different numerals. Energization here means placing the respective segments in such a state that they appear bright or clear in relation to the background. Energization therefore means a field-off state or random alignment for, for example, segments 101a and 101b to display "1" while the other segments are in the field-on state with ordered alignment.

Figs. 10 and 11 respectively show in incomplete section and incomplete isometric view an embodiment of the invention which represents the preferred arrangement of the liquid crystal layer 61" and the electrodes 13", 14" in the carrier medium 12". In fig. 10 and 11, double-marked reference numbers denote parts which correspond to the parts which are denoted by unmarked reference numbers in fig. 4 and 5, or marked reference numbers on fig. 6. According to the illustration on fig. 10 and 11, it is particularly preferred that the layer 61" and the electrode 13" in the display device 60" are essentially continuous over the whole or at least a relatively large part of a display device. The electrode 13" can e.g. be connected to a source of electrical ground potential. The electrode 14" can be divided into a number of electrically isolated electrode portions, such as those shown at 14a, 14b, each of which can be selectively connected to a source of electric potential to complete the application of an electric field over the liquid crystal material located between such an energized electrode portion 14a or 14b and the second electrode 13". Therefore, for example, an electric field can be applied over the electrodes 14a, 13",

so that the encapsulated liquid crystal material falling mainly directly therebetween is brought into order

field-on alignment and thus effectively optically transparent in the manner described above. At the same time, it may happen that the electrode 14b is not connected to a source of electrical potential, so that the liquid crystal material between this electrode 14b and the electrode 13" will be in a distorted or random alignment and will therefore appear relatively bright or clear from the viewing direction 20". A small space 120 between the electrodes 14a, 14b provides electrical isolation therebetween to allow the just described energization or non-energization thereof.

While briefly referring to fig. 12, the preferred embodiment and best form of the invention is shown as the display device 60'''. In fig. 12, the different parts or lots which are denoted by triple-marked reference numbers correspond to the parts which are denoted by equal reference numbers and are described above. The display device 60'<11> is produced in the main case in accordance with the numbered examples indicated above. Specifically, the lower support medium 12b'<11> is formed of Mylar film with an indium-doped tin oxide Intrex electrode 13''' thereon, and the layer or layer 61'<11> of encapsulated liquid crystal material was applied to the coated surface of the electrode , as shown. Several electrode portions 14a''', 14b''', etc, with a respective space 120''' in between, were applied either directly on the surface of the layer 61''' opposite to the carrier medium 12b''' or on the carrier medium 12a''' , and the latter was placed on the one in fig. 12 shown way to complete a sandwich of the display device 60'''. Furthermore, the reflection medium 80''' was air, and a carbon black absorber 81'', mounted on a carrier shown in fig. 12, was placed opposite the air gap 80"''

in relation to the carrier medium 12b''', as can be seen from the figure. The operation of the display device 60''' is in accordance with the operation described above, for example with reference to fig. 4-6 and 10.

Referring to fig. 13, there is shown an encapsulated liquid crystal 130 of the type described in the following Example 7. This capsule 130 comprises a spherical capsule wall 131 of containment material 132, operational nematic liquid crystal material 133 inside the capsule, and a cholesteric chiral additive 134. The additive 134 is usually in solution with the nematic material 133, although the addition of fig. 13 is shown in a central location due to its function being primarily with respect to the liquid crystal material at a distance from the capsule wall, as described in more detail below. The capsule 130 is shown in a distorted field-of-state with the liquid crystal material distorted in the manner described above, for example in connection with fig. 2. The liquid crystal material nearest the wall 131 tends to be forced into a shape which is curved like the inner boundary of this wall, and there is a discontinuity 135 analogous to that of FIG. 2 showed discontinuity 55..

Example 7

The steps of Example 1 were followed using the same materials and steps as in Example 1 except that 3% cholesterol oleate (chiral addition), a cholesteric material, was added prior to the mixing step, and then the mixing was carried out at very low shear force. The resulting capsules were somewhat larger than those produced in Example 1. The encapsulated liquid crystal material was still operationally nematic.

When operating the material formed in Example 7, it was found that chiral addition improved (reduced) the response time of the operationally nematic encapsulated liquid crystal material, particularly by returning to the distorted alignment that essentially follows the wall shape of the individual capsules, immediately after transition from a field-on to a field-off state. In the case of such relatively large capsules, e.g. approximately of the order of at least 8 um total diameter, it is the usual case upon transition to the field-off state that the liquid crystal material near the capsule wall will return to the distorted alignment that follows the shape or curvature of the capsule wall, faster than the liquid crystal material closer to the center of the capsule will . This non-uniformity tends to reduce the overall response time of the material. However, the chiral addition causes a tendency for the structure to twist. This effect on the nematic material is most noticeable at a distance from the capsule wall and thus accelerates the return of such relatively distant material to distorted alignment, preferably influenced by the shape of the capsule wall. Such chiral addition can be in the range from approx. 0.1% to approx. 8% of the liquid crystal material, and a preferred range is from approx. 2% to approx. 5%. The amount may vary depending on the additive and the liquid crystal and may also lie outside the specified range as long as the capsule remains operationally nematic.

It will be appreciated that the encapsulated liquid crystal 130 of FIG. 13 can be used in various embodiments of the invention described in the present description, instead of or in connection with other encapsulated liquid crystal material described here. The operation will be essentially the same as described in Example 7.

Another addition can also be used to reduce and/or otherwise control the viscosity of the liquid crystal during the production of e.g. a device 60. The reduced viscosity can have a positive effect on emulsion formation and/or on the process of applying the emulsion to an electrode-coated carrier medium 12. An example of such an addition can be chloroform, which is water-soluble and leaves the emulsion on drying .

Example 8

An emulsion was prepared using approx. 15 grams of 22% (the rest was water) medium-hydrolysis PVA with low viscosity, approx. 5 grams of 8250 liquid crystal (from American Liquid Xtal) which contained approx. 3% (percentages are relative to the weight of the liquid crystal) cholesterol-oleate, approx. 0.1% of a 1%

(the rest was water) solution of L.O. 630 surfactant, and 15% chloroform.

This material was mixed at high shear i

about. 3 minutes. The capsules produced were approx. 1-2 ym in diameter. A layer or bed of such encapsulated liquid crystal was applied to an electrode-coated carrier medium using a scraper blade with a gap setting of approx. 0.13 mm. The material was dried and worked essentially like the materials described above.

A modified liquid crystal display device

140 according to the invention is shown schematically in fig. 14 and 15.

In the device 140, the primary illumination source is derived from a light source 141 on the viewing device's so-called back side or non-viewing side 142. More specifically, the display device 140 comprises a layer or layer 61 of encapsulated liquid crystal between two electrodes 13, 14 which are supported on upper and lower carrier media 12a , 12b in the main case in the manner described above, e.g. with reference to fig. 12. The reflection medium 80 is an air gap, as was described in connection with the above preferred embodiment.

A light control film (LCF) sold by the 3M Company is shown at 143. The preferred film is identified by the product designation LCFS-ABRO-30°-OB-60°-CLEAR-GLOS-.030. The light control film 143 is a thin plastic sheet, preferably of black, essentially light-absorbing material, which has black micro-shutters 144 leading through the film from the back surface 145 towards its front surface 146. Such a film or a similar material can be used in connection with the various embodiments of the invention. Such a film may actually tend to collimate the light passing through the film to impinge on the liquid crystal material.

The micro-blinds act as a blind to direct light from the source 141, e.g. light rays 150, 151, into and through the display device 140, and in particular through the carrier medium 12 and the liquid crystal layer 61, at an angle that will usually lie outside the viewing angle line of sight for an observer looking at the display device 140 from the viewing direction 20, this when the liquid crystal is aligned or essentially optically transparent. Such an aligned field-on condition is shown in fig. 14 where the light beams 150, 151 mainly pass through the display device 140 outside the line of sight. Also, light, such as a light beam 152, incident on the display device 140 from the viewing direction 20 will usually pass through the carrier medium 12 and the aligned liquid crystal layer 61 in the field-on state for absorption by means of the black film 143 acting e.g. such as the absorber 81'<11> in connection with fig. 12.

As can be seen from fig. 15, however, when the liquid crystal layer 61 is in the field-off state, i.e., the liquid crystal is distorted or randomly aligned, the light rays 150, 151 from the source 141 are scattered isotropically by the layer of liquid crystal material 61, causing total internal reflection and clearer appearance of the liquid crystal material in the manner described above. Thus, for example, the beam 151 is shown to be dispersed isotropically as a beam 151a, to be. totally internally reflected as a beam 151b, and further be isotropically scattered as a beam 151c which is directed out through the boundary surface 64 towards the viewing direction 20. The display device 140 in fig. 14, 15 is particularly useful in situations where it is desirable to provide light from the rear or non-viewing side. However, such a display device will also work in the manner described above, for example with regard to the display device 60'<11> in fig. 12, even without the rear light source 141 as long as sufficient light is provided from the viewing direction 20. The device 140 can therefore be used for example in daylight, being illuminated on one or both sides by ambient light with or without the light source 141, and for example at night or in other cases where the ambient light is insufficient for the desired clarity, by using the lighting provided by the source 141.

A display device 160 in fig. 16 is similar to the display device 140 except that the light control film 161 at 162 is cemented directly to the device, or is otherwise placed in contact with the carrier medium material 12b. Total internal reflection will occur in the manner described above when the display device 160 is illuminated with light from the viewing direction 20, primarily as a result of the interface 64 of the carrier medium 12a with air. There may also be some total internal reflection at the boundary surface 162. However, since the LCF film is directly placed on the carrier medium 12b, a relatively large amount of the light that reaches the boundary surface 162 will be absorbed by the black film. In the display device 160, it is therefore particularly desirable to provide a rear light source 141 to ensure sufficient illumination of the liquid crystal material in the layer 61 to achieve the desired, bright or clear character display function in accordance

with the invention.

While briefly referring to fig. 17, there is shown an alternative embodiment of encapsulated liquid crystal material 200 which can be inserted instead of the various other shown and described embodiments of the invention. The encapsulated liquid crystal material 200 comprises operationally nematic liquid crystal material 201 in a capsule 202 which preferably has a substantially spherical wall 203. In fig. 17, the material 200 is in the field-off state, and in this state the structure 204 of the liquid crystal molecules is oriented so that it stands normally or essentially normally on the wall 203 at the interface 205 with it. At the boundary surface 205, the structure 204 is thus generally oriented in a radial direction in relation to the geometry of the capsule 20 2 . As one moves closer to the center of the capsule 202, the orientation of the structure 204 of at least some of the liquid crystal molecules will tend to curve to utilize, i.e. fill, the volume of the capsule 202 with an arrangement of the liquid crystal in the capsule with substantially minimal free energy, for example as shown in the drawing.

Such alignment is believed to occur as a result of the addition of an additive to the liquid crystal material 201 which reacts with the carrier medium to form normally oriented steryl or alkyl groups at the inner capsule wall. More specifically, such an additive may be a chromium-steryl complex or Werner complex which reacts with the PVA substance in the carrier medium (12) forming the capsule wall 203 to form a relatively rigid shell or wall with a steryl group or "moiety" which tend to penetrate radially into the liquid crystal material itself. Such a protrusion tends to cause the recorded radial or normal alignment of the liquid crystal structure. Such an alignment of the liquid crystal material also still conforms to the above-mentioned, strongly curved distortion of the liquid crystal structure in the field-off state due to the fact that the directional derivative taken at right angles to the general molecular direction is different from zero.

An example of such a material 200 is given below:

Example 9

To a 5 gram sample of 8250 nematic liquid crystal was added 0.005 gram of a 10% solution of Quilon M, a chromium-sterile complex manufactured by DuPont, along with 3 grams of chloroform. The resulting material was homogenized at low shear with 15 grams of a 22% w/w solution of Gelvatol 20/30 PVA (the remaining 78% of this Gelvatol solution was water).

The result was an encapsulated liquid crystal in which the capsule wall reacted with the Quilon M solution to form an insoluble shell.

When observing with polarized light, it was found that the capsule wall aligned the liquid crystal in a radial direction.

A film was cast onto a Mylar support already having an Intrex electrode on it, as indicated above, using a scraper blade with a gap setting of approx. 0.13 mm. The resulting film had a thickness of 0.025 mm on drying. An auxiliary electrode was attached. The material started to align in the capsule at 10 volts and was fully aligned at 40 volts. Such an arrangement will be similar to that shown in fig. 3.

The invention can be used in a number of different ways to effect the display of data, characters, information, images, etc. on both a small and large scale. According to the preferred embodiment and best form of the invention, the liquid crystal material is placed in the carrier medium 12 only in the areas where characters, etc. are to be formed. Alternatively, the layer or layer 61 may extend over the entire carrier medium 12, and only the areas where characters are to be displayed will have electrodes for controlling field-on and field-off states with respect to the adjacent portions of the liquid crystal layer 61. As an optical shutter, the invention can be used to adjust the effective and/or apparent brightness or clarity of light viewed on the viewing side. Various other constructions can also be used, as may be desired, utilizing the enhanced scattering caused by the total internal reflection and/or the optical interference principles according to the invention.

Referring now to fig. 18, a liquid crystal device according to the invention is shown at 310. The device 310 comprises an encapsulated liquid crystal 311 which is supported by a mounting substrate 312 over which an electric field can be applied via electrodes 313, 314.

The electrode 313 can e.g. be a certain amount of vacuum-deposited indium-tin oxide that is applied to the substrate 312, and the electrode 314 can e.g. be an electrically conductive ink. A protective layer or coating 315 may be placed over the electrode 314 for protective purposes, but such a layer 315 will not usually be necessary for supporting or delimiting the encapsulated liquid crystal 311 or the electrode 314. Voltage may be applied to the electrodes 313, 314 from an alternating voltage or DC voltage source 316, a selectively closable switch 317, and electrical wiring 318,

319 in order to in turn apply an electric field over the encapsulated liquid crystal 311 when the switch 317 is closed.

The encapsulated liquid crystal 311 comprises liquid crystal material 320 which is contained within the boundaries or inner volume 321 of a capsule 322. According to the preferred embodiment and the best form of the invention, the capsule 322 is essentially spherical. However, the principles of the invention would apply when the capsule 322 has a shape other than the spherical one. Such a form must provide the desired optical and electrical properties which will satisfactorily coexist with the liquid crystal material's 320 optical properties, e.g. refractive index, and which will allow a sufficient part of the electric field to act over the liquid crystal material 320 itself to effect the desired alignment of the liquid crystal structure when one wishes to have a field-on state. A particular advantage of the preferred spherical shape of the capsule 322 will be described below with respect to the distortion it causes to the liquid crystal structure.

The mounting substrate 312 and the electrodes 313, 314 as well as the protective coating 315 can be optically transmitting, so that the liquid crystal device 310 is able to control the transmission of light through it in response to whether or not an electric field is applied over the electrodes 313, 314, and thus over the encapsulated liquid crystal 311. Alternatively, the mounting substrate 312 may be optically reflective, or an optically reflective coating may be applied thereto, so that reflection by means of this reflective coating of incident light received through the protective coating 315 will be a function of whether an electrical field is imprinted or not over the encapsulated liquid crystal 311 .

According to the preferred embodiment and best form of the invention, a number of encapsulated liquid crystals 311 will be applied to the mounting substrate 312 in such a way that the encapsulated liquid crystals adhere to the mounting substrate 312 or to an interface material, such as the electrode 313, for subsalting by means of the mounting substrate 312 and retention in a fixed position in relation to the other encapsulated liquid crystals 311. It is most preferable that the encapsulating medium from which the capsule 322 is formed is also suitable for binding or otherwise adhering the capsule 322 to the substrate 312. Alternatively, a further bonding medium (not shown) is used to adhere the encapsulated liquid crystals 311 to the substrate 312. Since the capsules 322 are adhered to the substrate 312, and since each capsule 322 provides the necessary confinement for the liquid crystal material 320, a second mounting substrate, such as the additional substrate which usually is necessary in the early re known liquid crystal devices, usually not be necessary. For the purpose of providing protection against scratching, electrochemical degradation, e.g. oxidation, or the like, of the electrode 314, however, a protective coating 315 can be provided on the side or surface of the liquid crystal device 310 which is opposite to the mounting substrate 312, the latter providing the desired physical protection on its own side of the device 310.

Since the encapsulated liquid crystals 311 are relatively solidly glued to the substrate 312, and since there will usually be no need for an additional substrate, as mentioned above, the electrode 314 can be applied directly to the encapsulated liquid crystals 311.

An enlarged, incomplete sectional view of a portion 332 of a liquid crystal display device, for example, equal to the number eight 101 and the substrate 12 of FIG. 9, is shown in fig. 19. As can be seen from fig. 19, it is on the surface of the substrate 12 (312 in Fig. 19), which can be approx. 0.254 mm thick, deposited a 200 Angstrom (= 0.02 ym) thick electrode layer 333 of e.g. indium tin oxide or another suitable electrode material, such as gold, aluminum, tin oxide, antimony tin oxide, etc. One or more layers 334 of a plurality of encapsulated liquid crystals 311 are placed on and adhered directly to the electrode layer 333. Such sticking or adhesion according to the preferred embodiment and best form for the invention is effected by means of the encapsulating medium which forms respective capsules 322, although, if desired, as mentioned above, a further adhesive or binding material can be used for such adhesive purposes. The thickness of the layer 334 can be, for example, approx. 0.007-0.254 mm, preferably 0.018-0.101 mm, more preferably 0.02-0.03 mm and especially 0.025 mm. Other thicknesses can also be used, depending among other things on the ability to form a thin film and the film's electrical penetration properties. A further electrode layer 335 is deposited on the layer 334, either directly on the material from which the capsules 322 are formed, or alternatively on the further binding material used to bind the individual, encapsulated liquid crystals 311 to each other and to the mounting substrate 312. The electrode layer 335 can f .ex. be approx. 0.013 mm thick and may be formed, for example, of electrically conductive ink or of the materials mentioned above for layer 333. A protective coating layer 336 for the purposes described above with respect to coating 315 in fig. 18, can also be arranged as shown in fig. 19.

A distinctive feature of the invention utilizing the encapsulated liquid crystals 311 is that a versatile substrate 312 can be formed such that it is capable of displaying virtually any desired display as a function of only the selective segments of conductive ink electrodes that are printed thereon. the liquid crystal material. In this case, the entire surface 331 of the substrate 312 may be coated with electrode material 333, and also the entire surface of this electrode material may be coated substantially continuously with the layer 334 of encapsulated liquid crystals 311. Then, a prescribed pattern of electrode segments of conductive ink 335 may be printed where desired on layer 334. A single electrical wire may connect surface 331 to a voltage source, and respective electrical wires may connect respective conductive ink segments via respective controlled switches to such voltage source. Alternatively, the encapsulated liquid crystals 311 and/or the electrode material 333 can be applied to the surface 331 only in the areas where display segments are desired. The ability to apply encapsulated liquid crystals to only a desired area or a number of areas, such as the segments of a display device, using essentially conventional processes (such as screen printing or other printing processes), is particularly attractive compared to the prior art which has the problem of trapping liquid crystals between flat plates.

The encapsulated liquid crystals in the layer 3 34 act to dampen or not dampen light incident thereon, depending on whether an electric field is applied over the layer or not. A pleochroic dye is preferably present in solution with the liquid crystal material to provide substantial attenuation by absorption in the "field-off" state, but to be substantially transparent in the "field-on" state. Such an electric field may be e.g. a field produced as a result of the connection of the electrode layer portions 333, 335 at an individual segment, such as the segment 101a of the liquid crystal device 10' (Fig. 9), to an electric voltage source The magnitude of the electric field necessary to switch the encapsulated liquid crystals 311 from a no-field state (de-energized) to a field-on state (energized), may be a function of several parameters, including, for example, the diameter of the individual capsules and the thickness of the layer 334, which in turn may depend on the diameter of the individual capsules 3 22 and the number of such capsules in the thickness direction of the layer 334. One will realize the essential feature that when liquid cr the crystal material 320 is bounded in respective capsules 322, and since the individual, encapsulated liquid crystals 311 are attached to the substrate 312, the size of the liquid crystal device 10' or any other liquid crystal device that uses encapsulated liquid crystals in accordance with the invention is practically unlimited. In the areas where it is intended to effect a change in the optical properties of the encapsulated liquid crystals in such a device as a reaction to a no-field or field-on condition, it will of course be necessary that in such areas electrodes or other devices to apply an appropriate electric field to such liquid crystals.

The electrode layer 333 can be applied to the substrate 312 by evaporation, by vacuum deposition, by spraying, by printing or by means of another conventional technique. Furthermore, the layer 334 of encapsulated liquid crystals 311 can be applied, for example, by means of a plate or gravure printing roll or by means of counter roll printing techniques. The electrode layer 335 may also be applied using various printing or stenciling techniques or other techniques. If desired, the electrode layer 333 may be fabricated as a complete coating of the substrate 312, such as Mylar, as described above, as part of the process in which the Mylar sheet material is fabricated, and the layer 334 may also be placed as part of a such manufacturing process.

The inventor has further discovered that when the liquid crystal material in the capsule 32 (Fig. 2) has pleochroic dye dissolved in it, such dye, which would normally also be expected to have optical polarization sensitivity, is no longer polarization sensitive due to the dye trying to follow it same type of curvature orientation or distortion as the liquid crystal structure. It should be noted here that the discontinuity 55 in the capsule 3 2 further distorts the liquid crystal structure, which in turn further reduces the possibility that the liquid crystal material 3 0 would be sensitive to the optical polarization of the incident light. When the liquid crystal structure and the pleochroic dye are distorted to essentially fold in on themselves in the manner shown, for example, in FIG. 5, the encapsulated liquid crystal will usually absorb or block light from being transmitted through it when no electric field is applied over the encapsulated liquid crystal, and in particular over its liquid crystal material.

However, when an electric field is applied over the encapsulated liquid crystal in the manner shown in fig. 3, the liquid crystal and any pleochroic dye in solution with it will align with respect to the electric field in the manner shown in this figure. Such alignment allows light to be transmitted through the encapsulated liquid crystal 11 .

In order to optimize the contrast properties of a liquid crystal device such as that shown at 10' in FIG. 9, which comprises encapsulated liquid crystals 11 with pleochroic dye therein, and more particularly to avoid optical distortion as a result of refraction of incident light passing from the encapsulation medium into the liquid crystal material and vice versa, the refractive index of the encapsulation medium and the ordinary refractive index of the liquid crystal material must be matched as follows that they are as much as possible the same. The accuracy of the refractive index adjustment will depend on the desired degree of contrast and transparency in the device, but the ordinary refractive index of the liquid crystal and the refractive index of the medium will preferably not differ by more than 0.1, most preferably 0.01, and especially 0.001. The permissible difference will depend on the capsule size and the intended use of the device. The article "Optics" by Sears, published by Addison-Wesley, contains a thorough discussion of birefringence relevant to the foregoing, and the relevant portions of that article are incorporated into the present specification by reference.

However, when no field is applied, there will be a difference in refractive indices at the boundary between the liquid crystal and the capsule wall as a result of the extraordinary refractive index of the liquid crystal being greater than the refractive index of the encapsulation medium. This causes refraction at the interface and consequently further scattering and is a reason why the encapsulated, nematic liquid crystal material according to the invention will in particular act so as to prevent the transmission of light, even without the use of pleochroic dye. With such a dye, however, a significant absorption will occur

of the scattered light entering the capsule.

Typically, the encapsulated liquid crystals 311 will be applied to the substrate 312 such that the individual encapsulated liquid crystals 311 are relatively randomly oriented and preferably several capsules thick to ensure a sufficient amount of liquid crystal material, thereby providing the desired level of light blocking and/or light- transfer characteristics for e.g. a liquid crystal device 10' or the like.

In a liquid crystal device such as that shown at 10' in FIG. 9, which comprises a liquid crystal material 3 20 containing pleochroic dye to form encapsulated liquid crystals 311 according to the invention (Fig. 18), it has been discovered that the degree of optical absorption is at least approximately the same as the degree of absorption of relatively free (non- encapsulated) liquid crystal material containing pleochroic dye. It has also been unexpectedly discovered that when the electric field is applied in the manner shown in e.g. fig. 3, the clarity or lack of opacity of the encapsulated liquid crystal material 30 containing pleochroic dye is at least approximately the same as the clarity in the usual case in the previously known devices which have dye in solution with relatively free liquid crystal material.

A schematic electrical connection core representing the circuit over which the electric field E in fig.

3 is imposed, is shown in fig. 20. The electric field is diverted from the voltage source 316 when the switch 317 is closed. A capacitor 370 represents the capacitance of the liquid crystal material 30, 320 in the encapsulated liquid crystal 11, 311 when this electric field is applied in the manner shown in fig. 3. A capacitor 371 represents the capacitance of the capsule wall 54 in an upper area (the direction appropriately refers to the drawing, but has no other particular meaning). A capacitor 372 similarly represents the capacitance of the lower portion of the capsule exposed to the electric field E. The capacitance values of each capacitor 370-372 will be a function of the dielectric constant of the material of which the respective capacitors

is formed, and of the distance between these effective plates.

It is desirable that the voltage drop that occurs across the respective capacitors 371, 372 will be smaller than the voltage drop across the capacitor 370. The result is then the application of a maximum proportion of the electric field E over the liquid crystal material 30, 320 in the encapsulated liquid crystal 11, 311

for achieving optimal operation, i.e. alignment, of its liquid crystal structure with a minimal requirement for total energy for the voltage source 316. However, it is possible that the voltage drop in one or both capacitors 371, 372 will exceed the voltage drop across the capacitor 370. This is operationally acceptable as long as the voltage drop across the capacitor 370 (the liquid crystal material) is sufficiently large to produce an electric field which tries to align the liquid crystal material to and/or in the direction of e.g. the field-on condition of fig. 3.

In connection with e.g. the capacitor 371 is the dielectric material the material of which the capsule wall 54

is formed relatively close to the upper part of the capsule 32, 322.

The effective plates in such a condenser 371 are the outer and inner capsule wall surfaces, and the same applies to the condenser 372 in the lower part of the capsule. By making the wall 54 as thin as possible, while providing sufficient strength to contain the liquid crystal material, the sizes of the capacitors 371, 372 can be maximized, especially compared to the relatively thick or long distance between the upper and lower portions of the liquid crystal material in the capsule which in an approximate or equivalent manner, the plates of the same number in the capacitor form 370.

The liquid crystal material 320 will have a dielectric constant value that is anisotropic. This value is therefore referred to as the dielectric coefficient. It is preferred that the dielectric constant of the wall 54 is not lower than the lower dielectric coefficient of the anisotropic liquid crystal material 320 to help meet the above conditions. As a typical lower dielectric coefficient for liquid crystal material is approx. 6, this indicates that the dielectric constant of the encapsulation material is preferably at least approx. 6. This value can vary greatly depending on the liquid crystal material used, as it is, for example, as low as approx. 3.5 and as high as approx. 8 in the commonly used liquid crystals.

The encapsulated liquid crystal 311 has such distinctive features that when the liquid crystal structure is distorted and when the pleochroic dye is similarly distorted, absorption or blocking of light transmission through the encapsulated liquid crystals will be very effective when no electric field E is applied over them. As a result of both the effective application of an electric field over the liquid crystal material 320 in the encapsulated liquid crystals 311, in order to align the liquid crystal molecules and the dye together with these, as well as the previously mentioned, preferred adaptation of refractive indices, i.e. for the encapsulation medium and for the liquid crystal material, such that incident light will not be refracted or deflected at the interface between the capsule wall and the liquid crystal material 320 when an electric field is applied, on the other hand the encapsulated liquid crystal 311 will have a good optical transmission property.

Since a large number of encapsulated liquid crystals 11, 311 are usually required to construct a final liquid crystal device, such as the device 10' of FIG. 9, and as these encapsulated liquid crystals are usually present in several layers or layers, it is desirable that the liquid crystal material has a relatively high dielectric anisotropy in order to reduce the voltage requirements for the electric field E. More specifically, the difference between the dielectric constant of the liquid crystal material must not reach any electric field is applied, which constant must be relatively small, and the dielectric constant of the liquid crystal material when it is aligned by application of an electric field, which constant must be relatively large, be as large as possible in compatibility with the dielectric constant of the encapsulation medium.

As noted above, the larger the capsule size, the smaller the electric field that is necessary to effect alignment of the liquid crystal molecules therein. However, the larger the capsule or ball, the longer the response time. In view of the present disclosure, one of ordinary skill in the art should have no difficulty in determining an appropriate or optimal capsule size for a given application.

The encapsulating medium which forms capsules must be of a type which is essentially completely unaffected by and does not react with or otherwise chemically affect the liquid crystal material or the pleochroic dye. The dye must be soluble in the liquid crystal material and not subject to absorption by the encapsulation medium. In order to achieve the desired relatively high impedance for the encapsulation medium,

moreover, this medium must have a relatively high degree of purity. Especially when the encapsulation medium is produced as an aqueous dispersion or by means of ion polymerization, etc., it is important that the level of ionic (conductive) contaminants must be as low as possible.

Examples of pleochroic dyes that can suitably be used in the encapsulated liquid crystals 11 according to the present invention are indophenol blue, Sudan black B, Sudan 3 and Sudan 2, and D-37, D-43 and D-85 from the aforementioned company E .Merck.

Example 10

A 0.45% Sudan Black B pleochroic dye was dissolved in a liquid crystal composed of aromatic esters. This combined material is sold commercially under the designation NMB250 by American Liquid Xtal Chemical Corp., Kent, Ohio. This material was mixed with a solution

of 7% PVA which had been purified to remove all salts. The solution was also formed with ASTM-100 water. The resulting mixture was introduced into a colloid mill with a cone gap setting of 0.1 mm and the material was mixed for four minutes to give a fairly uniform particle suspension size. The result was a stable emulsion with a suspended particle size of approx. 3 etc. The emulsion was cast onto a Mylar film which was previously coated with an indium tin oxide electrode of 200 ohm per surface unit purchased from the company Sierracin. A scraper blade was used to cast the emulsion material onto the Mylar film on the electrode coated side.

A 0.18 mm deposit of the emulsion material was placed on such an electrode and allowed to dry to a total thickness of approx. 0.02 mm. A second layer of such an emulsion was later superimposed on the first with a resulting aggregated layer of liquid crystal droplets in a polyvinyl alcohol matrix having a thickness of approx. 0.04 mm. The encapsulated liquid crystals can preferably be deposited in a single layer with a thickness of one or more capsules.

The liquid crystal device thus formed, including the layer of Mylar, electrode and encapsulated liquid crystals, was then tested by applying an electric field, whereupon the material changed from black to almost clear transparent. The material exhibited a very wide viewing angle, i.e. the angle at which light was transmitted, and the contrast ratio was 7:1 with an applied electric field of 50 volts. The switching speed was approx. 2 milliseconds on and approx. 4 milliseconds off.

Example 11

900 grams 7% fully hydrolyzed high viscosity polymer (SA-72 from American Liquid Xtal Chemical Corp.), 100 grams 8250 nematic liquid crystal material (also from American Liquid Xtal Chemical Corp.), 0.45 grams C26510 Sudan Black B , and 0.15 gram of C26100 Sudan III (the last two components were pleochroic dyes) were used. The polymer was weighed into a beaker. The liquid crystal was weighed and then placed on a hot plate and heated slowly. The dye was weighed on a scale and added very slowly to the liquid crystal, the mixture being stirred in until all the dye dissolved.

The liquid crystal and dye solution was then filtered through a standard Millipore filtration system using 8 m filter paper. The filtered liquid crystal and dye solution was stirred into the polymer using a Teflon rod. This mixture was encapsulated by placing it in a colloid mill which was operated at moderate shear for five minutes. The emulsion film was then pulled onto a conductive polyester sheet.

During operation of a liquid crystal structure according to this example, the liquid crystal structure began to align upon application of an electric field of 10 volts, achieving met-

ning and maximum optical transmission at 4 0 volts.

Example 12

The steps of Example 11 were carried out using the same ingredients and steps except that a 5% high viscosity, fully hydrolyzed polymer, such as SA-72, was substituted for the 7% polymer of Example 11. The operating results were the same as in Example 11.

Example 13

The process of Example 11 was carried out to form an emulsion using 4 grams of 20% medium-viscous, partially hydrolyzed polymer (such as 4 05 set forth in the preceding Table I), and 2 grams of 8250 nematic liquid crystal material with 0.08 % D-37 magenta pleochroic dye (a pleochroic dye, a brand name manufactured and/or sold by E. Merck, West Germany) in solution with the liquid crystal.

An object or specimen slide was taken using a Teflon rod and on examination showed capsules of average size of approx. 3-4 ym in diameter. The material was filtered through a Millipore screen filter, and a new slide was taken. On examination, there was very little change in capsule size from the first-mentioned examination.

The emulsion was drawn off on a conductive polyester carrier film as in Example 11 using a scraper blade with a gap setting of approx. 0.13 mm. During operation, the encapsulated liquid crystal material began to align upon application of an electric field of 10 volts, and was in saturation or fully on state at voltages from approx. 40 to 60 volts.

Example 14

Using a glass rod that had been cleaned and washed with deionized ASTM-100 water, 2 grams of 40% 8250 nematic liquid crystal material with 0.08% D-37 pleochroic dye dissolved therein was mixed in 4 grams of "405 " (see Table I) desalted 20% by weight medium-hydrolyzed, medium-viscous polymer very carefully for approx. 15 minutes. The material was then filtered through a Millipore screen filter with a size of approx. 4 etc. A preparation glass was taken after the bubbles had dissolved.

A film was then subtracted with a spacing setting of approx. 0.13 mm on an electrically conductive Intrex electrode film material which was placed on a polyester support of Mylar material. During operation, it was obvious that the liquid crystal material began to align upon application of an electric field of 5 volts. The contrast was good and the liquid crystal material was in a fully on state or saturation when an electric field of 40 volts was applied.

Example 15

In this example, 8 grams of D-85 pleochroic dye dissolved in E-63 biphenyl liquid crystal was used. Such material is sold premixed by British Drug House which is a subsidiary of E. Merck, West Germany. The example also used 16 grams of 20% PVA medium-viscous, medium-hydrolyzed polymer as encapsulation medium. The solution of liquid crystal and pleochroic dye was carefully mixed by hand into the polymer at a slow speed. The combined material was then sieved or screened at low shear. A preparation glass was taken and observation showed capsules with a size of approx. 3 etc. A film of such an emulsion was drawn onto an electrically conductive polyester sheet, as indicated above, using a gap setting of approx. 0.13 mm. The film was in the on state or started to have an aligned liquid crystal structure with an applied electric field of approx. 6 volts, and was in saturation or fully on state at 24 volts.

Example 16

A mixture was formed of 8250 nematic liquid crystal with 0.08% D-37 pleochroic dye in solution therewith, and a solution of 15% AN169 Gantrez in 85% water. The mixture was 15% liquid crystal and 85% Gantrez as containment medium. The mixture was homogenized at low shear to form an emulsion which was applied to an electrode/carrier film as indicated above. This carrier film was approx. 0.03 mm thick. After drying the emulsion, the resulting liquid crystal emulsion responded to an electric field essentially as stated above, essentially absorbing or at least not significantly transmitting light in the field-off state, exhibiting a threshold of approx. 7 volts to begin transmission, and had a saturation level for essentially maximum transmission at approx. 4 5 volts.

In accordance with the present invention, the quantities of components for the production of the encapsulated liquid crystals 11, for example in the manner described above, can be as follows:

The liquid crystal material

This material can be from approx. 5% to approx. 20% and preferably approx. 50% (and in some cases even more, depending on the nature of the encapsulation material) included the pleochroic dye, at 25% (when using Gelvatol as an encapsulation medium) volume of the total solution delivered to the mixing apparatus, such as a colloid mill. The actual amount of liquid crystal material used must usually exceed the volume amount of encapsulation medium, e.g. PVA, to optimize the capsule size.

The PVA material

The amount of PVA in the solution must be of the order of magnitude from approx. 5% to approx. 50%, and possibly even more, depending on the hydrolysis and molecular weight of the PVA material, and preferably, as described above, approx. 22%. If, for example, the PVA material has too high a molecular weight, the resulting material will be similar to glass, especially if too much PVA is used in the solution. If, on the other hand, the molecular weight is too low, the use of too little PVA will result in too low a viscosity of the material, and the resulting emulsion will not hold well, nor will the droplets in the emulsion solidify in a filling manner into the desired, spherical , encapsulated liquid crystals.

The carrier medium

The remainder of the solution will be water or another, preferably volatile, carrier medium, as described above, with which the emulsion can be formed and the material deposited in a suitable manner on a substrate, an electrode or the like.

It will be appreciated that as the uncured capsules or droplets of encapsulation medium and liquid crystal material are carried in a liquid, various conventional or other techniques can be used to sort the capsules according to size, so that the capsules can be reshaped if they are of an undesirable size, by that they are fed again, e.g. through the mixing device, and so that the capsules finally used will have a desired uniformity for the reasons mentioned above.

Although the encapsulation technique has been described in detail in connection with emulsification, since the production of liquid crystal devices is made easy due to the fact that the encapsulation material and the binder are the same, the production of separate capsules of liquid crystal material can sometimes be advantageous, and the use of such separate capsules ( with a binder) is within the scope of the invention.

Although the currently preferred embodiment of the invention operates in response to the application and removal of an electric field, operation can also be effected by the application and removal of a magnetic field.

Indication of industrial use

The invention can be used, among other things, to produce a controlled, optical display device.

Claims (44)

1. Liquid crystal device comprising a liquid crystal (30) for selectively primarily scattering light or, in response to a prescribed input signal, transmitting light, the liquid crystal comprising operational nematic liquid crystal material with positive dielectric anisotropy, and a carrier medium (12) for support of the liquid crystal, CHARACTERIZED IN THAT the carrier medium comprises a containment medium (11, 33) to contain the liquid crystal (30) in several volumes (31), the containment medium comprising a surface device for aligning the liquid crystal to effect essentially isotropic scattering of light in the absence of a prescribed input signal, and that a reflective device (18, 19) is provided to effect total internal reflection of light scattered by the liquid crystal. 2. Device according to claim 1, CHARACTERIZED IN THAT the liquid crystal (30) and the containment medium are formed by a layer of encapsulated liquid crystal (11), and that the device further comprises electrodes (13, 14) which are placed between the carrier medium (12) and the aforementioned layer of encapsulated liquid crystal, to apply an electric field to align the liquid crystal (30) relative thereto. 3. Device according to claim 1 or 2, CHARACTERIZED IN THAT the liquid crystal material (30) has an ordinary refractive index which is mainly adjusted to the refractive index of the containment medium (33) in order to maximize optical transmission in the presence of an electric field, and an extraordinary refractive index which is different from the confinement medium's refractive index to effect essentially isotropic scattering in the absence of an electric field. 4. Device according to one of claims 1-3, CHARACTERIZED IN THAT the carrier medium (12) has a viewing side (20) and an opposite side, a reflection medium (18) being located on at least one of the viewing side and the opposite side, and that the carrier medium's (12) index of refraction is greater than the index of refraction of the reflective medium (18) as the reflective device (18, 19) comprises an interface (19) between one of the mentioned sides and the nearby reflective medium (18) to cause total internal reflection of light in the carrier medium (12) which falls on the aforementioned interface (19) at an angle that exceeds a predetermined light cone angle at which light will be transmitted through the interface. 5. Device according to claim 4, CHARACTERIZED IN THAT the liquid crystal (30) is operative in the absence of an electric field to scatter a substantial part of light at an angle that exceeds the angle of total internal reflection for the carrier medium (12) at the aforementioned interface ( 19). 6. Device according to claim 5, CHARACTERIZED IN THAT the carrier medium further comprises a carrier for supporting the aforementioned volumes of the liquid crystal in the containment medium. 7. Device according to claim 5, CHARACTERIZED IN THAT the reflection medium is located on both the viewing side and the opposite side, that the carrier medium (12)'s refractive index is greater than the refractive indices of the reflection medium (18) on both the viewing side and the opposite side, and that the reflective device comprises the interfaces between both of the mentioned sides and the respective nearby reflection medium to effect the total internal reflection. 8. Device according to one of claims 4-7, CHARACTERIZED IN THAT it further comprises a light directing device (143) for directing incident light into the carrier medium (12a, 12b) on the said opposite side thereof, the light directing device comprising a device for directing such incident light into the carrier medium in a direction which lies mainly outside the normal line of sight for viewing from the said viewing side (20). 9. Device according to claim 8, CHARACTERIZED IN THAT the reflective device comprises a space (80) between the carrier medium (12a, 12b) and the light directing device (143) to effect a total internal reflection between the carrier medium and said space. 10. Device according to claim 9, CHARACTERIZED IN THAT the light directing device comprises a light control film (143) which has light-transmitting and light-absorbing parts (144 and 145 respectively), the absorbing part being placed in such a way in relation to the mentioned interface that it absorbs in the least any light that is transmitted through the interface. 11. Device according to one of claims 1-4, CHARACTERIZED IN THAT the containment medium (132) is operative to contain separate amounts of operational nematic liquid crystal material (133) and to distort the liquid crystal material into non-parallel alignment in the absence of an electric field, and to allow substantially parallel alignment of the liquid crystal material (133) in the presence of an electric field. 12. Device according to claim 11, CHARACTERIZED IN that it further comprises an addition device (134) in the operational nematic liquid crystal material (133), to accelerate such distortion and return to non-parallel alignment upon removal of the electric field. 13. Device according to claim 12, CHARACTERIZED IN THAT the addition device (134) comprises a chiral addition. 14. Device according to one of claims 1-13, CHARACTERIZED IN THAT the carrier medium (12') comprises an optical absorption device (81) for absorbing light that is transmitted through the opposite side of the carrier medium in relation to the viewing side. 15. Device according to claim 11, CHARACTERIZED IN THAT it further comprises a device for trying to force at least a part of at least some of the liquid crystal material (201) into essentially normal alignment with the surface device (203) in the absence of the prescribed input signal. 16. Device according to one of claims 1-15, CHARACTERIZED IN THAT the liquid crystal material (30) is optically anisotropic, and that the difference between the liquid crystal material's ordinary refractive index and the surface device's (32) refractive index is not more than approx. 0.3. 17. Device according to claim 16, CHARACTERIZED IN THAT the containment medium (11) forms capsule-like volumes (31) containing liquid crystal material, and that the size of the capsule-like volumes is from approx. 0.3 pm to approx. 100 p.m. 18. Device according to one of claims 1-17, CHARACTERIZED IN THAT the said volumes (31) have a diameter of from approx. 1 pm to approx. 30 p.m. 19. Device according to claim 18, CHARACTERIZED IN THAT the liquid crystal material (30) has an extraordinary refractive index which is different from the refractive index of the surface device. 20. Device according to one of claims 16-19, CHARACTERIZED IN THAT it comprises a substrate (12) for supporting a layer of the liquid crystal material and the containment medium, the layer having a thickness of from approx. 0.007 mm to approx. 0.254 mm. 21. Device according to one of claims 16-20, CHARACTERIZED IN THAT the surface device affects the natural structure of the liquid crystal material to cause a distorted alignment of this in the absence of an electric field, to reduce optical transmission regardless of polarization. 22. Device according to one of claims 16-21, CHARACTERIZED IN THAT the surface device comprises a number of containment devices (32) with curved surfaces to cause a distorted alignment of the liquid crystal material which, in reaction to such distortion, at least either scatters or absorbs light when pleochroic dye is present in the liquid crystal material (30) and which, in response to an electric field such as the prescribed input signal, reduces the degree of such scattering or absorption at least in the direction of the applied electric field. 23. Device according to claim 22, CHARACTERIZED IN THAT the said alignment runs at least partially parallel to the curvature of the said volumes. 24. Device according to claim 23, CHARACTERIZED IN THAT the curved volumes (31) comprise separate curved volumes containing separate amounts of liquid crystal material. 25. Device according to one of claims 16-24, CHARACTERIZED IN THAT the containment medium is selected from the group comprising resin, polymer, gelatin, Carbopol, Gantrez, polyvinyl alcohol, carboxy-polymethylene polymer and polymethyl vinyl ether/maleic anhydride. 26. Device according to one of claims 1-15, CHARACTERIZED IN THAT the containment medium comprises a dried, stable emulsion. 27. Device according to one of claims 1-15, CHARACTERIZED IN THAT the containment medium comprises a dispersion of the liquid crystal material and a containment material. 28. Device according to claim 2, CHARACTERIZED IN that at least one of the electrodes (13, 14) comprises electrically conductive ink. 29. Device according to claim 28, CHARACTERIZED IN THAT the electrically conductive ink is optically reflective. 30. Device according to claim 2, CHARACTERIZED IN THAT at least one of the electrodes (13, 14) is applied by means of at least one of the methods evaporation, vacuum deposition, spraying, printing, plate-roll printing, gravure-roll printing, counter-roll printing, stenciling and silk-screen printing printing. 31. Device according to claim 2, CHARACTERIZED IN THAT the electrodes (13, 14) comprise at least one component from the group consisting of indium tin oxide, gold, aluminium, tin oxide and antimony tin oxide. 32. Device according to claim 2, CHARACTERIZED IN THAT several volumes of liquid crystal material in a containment medium cover a substantial part of a carrier medium. 33. Device according to claim 32, CHARACTERIZED IN THAT it comprises several electrodes (14a, 14b) for applying electric fields to selected parts of the liquid crystal material (61), the electrodes being placed over relatively smaller areas of the carrier medium (12) and the liquid crystal material (61 ) than the substantial part of the liquid crystal material covering the carrier medium. 34. Device according to claim 2, CHARACTERIZED IN THAT one of the electrodes is formed by a plate-like electrode which covers a substantial surface of the carrier medium. 35. Device according to claim 2, CHARACTERIZED IN THAT it further comprises a circuit (15, 16) for providing electrical energy to the electrodes (13, 14). 36. Device according to one of claims 1-35, CHARACTERIZED IN THAT the lowest dielectric constant for the liquid crystal material lies between approx. 3.5 and approx. 8. 37. Device according to one of claims 1-36, CHARACTERIZED IN THAT the surface device comprises a device for causing a non-linear alignment of the liquid crystal material, thereby diffusing light in the absence of the prescribed input signal. 38. Device according to one of claims 1-5, 11-13, 15 or 29-35, CHARACTERIZED IN THAT the containment medium and the carrier medium comprise the same material. 39. Liquid crystal display for displaying clear characters or the like on a dark background, and comprising a liquid crystal (30), CHARACTERIZED IN THAT the liquid crystal scatters light that falls on it in an essentially isotropic manner, the liquid crystal comprising several volumes (31) of operational nematic liquid crystal material with positive dielectric anisotropy in a containment medium (11, 32), the volumes being bounded by walls (50) of the containment medium, the walls being operative in the absence of an electric field to interact with the liquid crystal material (30) to effect scattering of light, and the liquid crystal material reacts to the application of an electric field to align itself in relation to this, thereby reducing the degree of such scattering, and that the display further comprises a reflection device (18, 19) to reflect light that is scattered in an isotropic manner of the liquid crystal, back to the liquid crystal for further scattering by means of it. 40. Liquid crystal display for displaying clear characters or the like on a dark background, and comprising a liquid crystal (30), CHARACTERIZED IN THAT the liquid crystal scatters light that is incident on it in an essentially isotropic manner, and that the display further comprises a reflection device (18, 19) to reflect light that is scattered isotropically by the liquid crystal (30) back to the liquid crystal for further scattering by means of this, the reflection device comprising a carrier medium (12) for supporting the liquid crystal and performing total internal reflection of light in this, the carrier medium having a viewing surface (64) through which light scattered isotropically by the liquid crystal within a prescribed angle can be transmitted to provide such clear character appearance, and the carrier medium having an area in which light is not reflected through the viewing surface, thereby cause the appearance of a relatively dark background, the said area comprising an area n is the liquid crystal which is essentially optically transmitting, the liquid crystal comprising at least one layer (61) of encapsulated, operationally nematic liquid crystal material in the carrier medium, the liquid crystal material having positive dielectric anisotropy and an ordinary refractive index which is essentially matched to the refractive index of the carrier medium in order to maximize optical transmission in the presence of an electric field, and to effect substantially isotropic scattering in the absence of an electric field. 41. Display according to claim 40, CHARACTERIZED IN THAT it comprises an optical absorbing device (21) for absorbing light that is transmitted through the liquid crystal material (61) and the carrier medium (12) at a distance from the device's viewing side. 42. Method for displaying a clear sign or other information on a relatively dark background using liquid crystal material, where the liquid crystal material is contained in volumes that are formed in a containment medium, the liquid crystal material being operationally nematic, having positive dielectric anisotropy, and having an extraordinary refractive index which is different from the refractive index of the encapsulating medium, and an ordinary refractive index which is essentially matched to the enclosing medium's refractive index, CHARACTERIZED IN THAT it includes the steps of shaping the enclosing medium so that the structure of the liquid crystal material is aligned to effect essentially isotropic scattering of at least some light which incident on the liquid crystal material, to provide an interface with a refractive index difference to cause total internal reflection of isotropically scattered light back to the liquid crystal material to refresh it, and to transmit at least some of the light that e r scattered by the liquid crystal material, into a viewing area to form the said character or other information. 43. Method according to claim 42, CHARACTERIZED BY the fact that an electric field is selectively applied to the liquid crystal material to adjust it for transparency to form a relatively dark background. 44. Method according to claim 42 or 43, CHARACTERIZED IN THAT at least some of the light transmitted by the liquid crystal material is absorbed.