Abstract:
An electro-optic display material comprising a first and a second set of fibers, each fiber having a longitudinal conductive element the two sets forming a matrix structure of junctions, preferably woven. The structure further comprises an electro-optically active (EOA) substance at least partially coating the fibers of the first set; and a transparent or translucent conductive layer covering the EOA substance and having electric contact with the fibers of the second set at contact zones in the vicinity of the junctions. The conductivity of the conductive layer is limited to a predetermined value thereby defining, in the vicinity of each contact zone, an electro-optical activity zone (EOA zone) constituting a display element. Alternatively, the conductive layer is laid over the matrix structure in separated spots, each spot overlaying at least one junction and defining an EOA zone constituting a display element.

Description:
FIELD OF THE INVENTION 
     This invention relates to flexible electro-optic displays, in particular to matrix displays built from two sets of fibers. 
     BACKGROUND OF THE INVENTION 
     An electro-optic display is a device designed to change its optical behavior in response to an applied electric or magnetic field. Such a display usually comprises a plurality of display elements or pixels including an electro-optically active (EOA) substance, organized in a matrix or other pattern. Hereinafter, “EOA substance” is meant to denote any substance capable of changing its optic properties such as color, transparency, reflectivity, etc., or capable of emitting light, in response to changes of applied electric or electromagnetic field, and thereby suitable for displaying images. Flexible electro-optic displays may be made on flexible polymer films, where the EOA substance and patterns of electrodes are laid in thin layers over a polymer substrate, or may be built of a plurality of flexible filaments or strips, each having EOA layer, conductive layers, carrying layers, etc. 
     U.S. Pat. No. 5,962,967 and U.S. Pat. No. 6,072,619 disclose a display made of two sets of fibers arranged in a two-dimensional array. Each fiber includes a longitudinal conductor, and the fibers of at least one set are coated with light-emitting or other EOA substance. A display element (pixel) is formed at each junction where a fiber of one set transverses a fiber of the other set. The two-dimensional array may be formed by overlapping fibers of one set with the fibers of the other set, but preferably and advantageously the two sets of fibers are interlocked in a woven arrangement. Fibers may have round or flat cross-section. The manufacture process of fibers does not pose limitations to their length and, using known weaving techniques, flexible displays of large sizes may be produced. Woven displays do not need patterning (printing) of electrodes or of EOA substance, since the matrix structure with quite uniform pixel spacing is inherent in the nature of the textile fabric. Woven displays are also more flexible and robust than integral film displays. 
     However, the area of the display element, which is formed by the zone of electro-optical activity (EOA zone) at the junction of two fibers, is limited by the contact zone area of the two fibers or by the overlapping area of the conductive wires or layers in these fibers. Also, conductive wires normally used in such fibers are not transparent and they obscure the EOA zone. As a result, a relatively small quantity of the EOA substance, and a relatively small part of each fiber used in the woven display, may actually be engaged in producing an optical image on the display. 
     SUMMARY OF THE INVENTION 
     The present invention is concerned with an electro-optic display material comprising a first and a second set of fibers, each fiber having a longitudinal conductive element, the two sets forming a matrix structure of junctions, which structure further comprises an EOA substance at least partially coating the fibers of the first set, and a transparent or translucent conductive layer covering the EOA substance and having electric contact with the fibers of the second set at contact zones in the vicinity of said junctions. The fibers of the two sets are preferably interlocked in woven arrangement, and they can include conductive elements of any structure or have the form of flat strips or tapes. The introduction of the conductive layer over the EOA substance allows to obtain EOA zones and display elements of larger area than the area of a contact zone area between two fibers known in the prior art. The enlarged display elements may be obtained in different ways, according to different aspects of the present invention. 
     According to a first aspect of the invention, the conductivity of the transparent conductive layer is limited to a predetermined value thereby defining, in the vicinity of each contact zone, an EOA zone constituting a display element. 
     In one embodiment, the conductivity is selected so as to provide a display element at each junction while avoiding overlapping of adjacent display elements. In an alternative embodiment, the fibers of the two sets are arranged in groups, the space between adjacent groups being larger than the space between fibers within a group. The conductivity of the conductive layer is selected so as to allow the overlapping of adjacent display elements associated with fibers within a group but to prevent overlapping of display elements across adjacent groups, thereby forming a clustered display element over the intersection of a group of first set fibers with a group of second set fibers. 
     In accordance with a second aspect of the present invention, the transparent conductive layer is laid over the matrix structure in separated spots, each spot overlaying at least one junction and defining an EOA activity zone constituting a display element. Preferably, each spot overlays a plurality of contact zones between the conductive layer and the fibers of the second set thereby forming a clustered display element. The spots may have a rectangular shape to form another matrix over the initial matrix structure, or they may have any other shape and may form any desired pattern. The EOA substance also may be laid over the matrix structure in spots which are separated from each other and/or have different optical properties, thereby forming a visible image. 
     In accordance with a third aspect of the present invention, the transparent conductive layer is laid over the fibers of the first set in the form of separated sections, each section overlaying a plurality of junctions. The sections define EOA zones constituting clustered display elements. 
     The display material according to the above three aspects of the present invention may be produced from fibers coated with EOA substance, arranged in a matrix structure and then coated with a transparent conductive layer. Also, fibers may be first coated with EOA substance and a conductive layer thereabove, and then arranged in a matrix structure. 
     The display materials according to the first and second aspects of the present invention may also be produced from a matrix structure comprising a first and a second set of conductive wires, in which the wires of the first set have an insulating layer, by a method including a) covering the matrix structure with a layer of EOA substance so as to leave exposed parts of each wire of the second set; b) covering the matrix structure, over said layer of EOA substance, with at least one transparent or translucent conductive layer, so that the conductive layer is in electric contact with the exposed wires of the second set. This method allows to avoid creating of internal stresses and cracks in the EOA substance and the transparent conductive layer during weaving. 
     For the purposes of the present disclosure, it should be understood that if one entity is “covering” another entity, this does not exclude the presence of other entities between the first two. For example, when a layer of EOA substance coves a wire, this wire may have or may not have some protective or insulating layer on its surface. In a similar way, an “electric contact” between two objects should be understood as a proximity which allows such propagation of electric field or energy between these objects as necessary for functioning. For example, an alternating electric current may pass through a dielectric material or a gap between the two objects (capacitance electric contact). 
     The electro-optic display materials of the present invention have all the advantages of the woven flexible displays outlined in the background and additionally enable an extremely efficient controlled utilization of the EOA substance and length of the electro optic fibers invested in the display. In the case of EL display, for example, the material of the present invention allows to produce displays of unlimited size and resolution, enhanced brightness and low power consumption. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic illustration of known display material; 
     FIG. 2 is a schematic illustration of a display material with enlarged pixels according to a first aspect of the present invention; 
     FIG. 3 is a schematic illustration of a display material with clustered pixels according to the first aspect of the present invention. 
     FIG. 4 is a schematic illustration of a display material according to another aspect of the present invention; 
     FIG. 5 is a schematic illustration of a clustered pixel in accordance with still another aspect of the present invention; 
     FIG. 6 is a schematic illustration of display material obtained by a method of the present invention and operating as shown in FIG. 2; 
     FIG. 7 is a schematic illusion of display material obtained by the method of the present invention and operating as shown in FIG. 5; 
     FIG. 8 is a schematic illustration of another display material obtained by the method of the present invention; and 
     FIG. 9 is a schematic illusion of a display material according to the present invention with clustered pixels of arbitrary form. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1, there is shown a schematic illustration of the structure and operation principle of a prior art electro-optic material of the kind to which the present invention refers. For the sake of explanation, without any limitation to the scope of the invention, an example of light-emitting electroluminescent (EL) display will be used, the inventive idea being applicable to display materials based on any kind of electro-optically active substance. 
     In a simplified and conventional way, FIG. 1 presents a sectional view and an associated plan view of a piece of electro-optic material  10  comprising two weft electro-optic fibers  12  and one warp fiber  14 . It will be appreciated that denominations “weft” and “warp” are given here only for clarity, without reference to an actual textile structure. 
     The electro-optic fiber  12  comprises a conductive element (wire)  16  and an EL layer  18  therearound. It will be appreciated that a conductive wire may have any structure suitable for conducting electricity. For example, it may have round or flat section; be made of solid metal; be in the form of a dielectric fiber or strip covered or intertwined with a conductive fiber or layer, multiple-core twisted, spun, plaited wire; etc. 
     The warp fiber  14  may have the same structure as the weft fiber  12 , or may comprise only a conductive wire without an EL layer, as shown. An EL pixel is formed in the contact zone  24  between the overlapping parts of the wires  16  and  14  and light is emitted from the small electro-optic activity zone (EOA zone)  26 . As it can be seen in the plan view, the light-emitting zone  26  is partly-obscured by the non-transparent wire  16 . 
     FIG. 1 also includes a graph showing the distribution of the operative electric voltage U between the electrodes  16  and  14  of the EOA zone along the length of the fiber  12 . Light is emitted when and where this voltage exceeds a threshold value U t . It will be appreciated that for a different EOA substance, a different characteristic of the electric field may be relevant, such as current, frequency, etc. 
     With reference to FIG. 2, there is shown a schematic illustration of the structure and operation principle of an electro-optic material in accordance with one aspect of the present invention. FIG. 2 presents a sectional view and an associated plan view of a piece of electro-optic material  30  comprising two weft electro-optic fibers  32  and a warp fiber  34 . The weft fiber  32  comprises a conductive wire  36  and an EL layer  38  therearound and has an additional conductive layer  40  in the form of a coaxial cylindrical electrode laid over the EL layer  38 . The conductive layer  40  is transparent or translucent and has a predetermined conductivity. The warp fiber  34  is a wire in contact with the conductive layer  40  in the contact zone  44 . It will be appreciated that in this case an EOA zone  46  is formed between the wire  36  and the conductive layer  40 , which extends at both sides of the contact zone  44 . The EOA zone  46  occupies a range of the fiber where the operative voltage U in the conductive layer  40  exceeds the threshold value U t , as shown in the graph above the fibers. This range grows with the conductivity of the layer  40 . Thus, an enlarged pixel is created where the whole volume of the EL substance associated with the pixel is involved in light emission. The conductivity of the conductive layer  40  is limited so as to terminate the light-emitting zone half-way to the contact zone of the next pixel and to avoid the mere of two adjacent pixels. 
     Another embodiment of the same aspect of the invention is a display material with clustered pixels shown in FIG. 3 in enlarged sectional and plan view. The woven display material  50  comprises a matrix of warp wires  51  and weft fibers  52  including a conductive wire  53  and an EOA layer  54 . The warp wires  51  and weft fibers  52  are arranged in groups  55  and  56 , the space  57  between adjacent warp groups being larger than the space  58  between wires or fibers within a group. An additional transparent conductive layer  60  is applied over the matrix. The conductivity of the additional layer  60  is limited to a value allowing overlapping of adjacent EOA zones associated with fibers within a group but preventing overlapping of EOA zones across adjacent groups. This is illustrated by the graph in FIG. 3 showing the distribution of the operative electric voltage U along the length of the fiber  52 . The dotted lines in the graph show the operative voltage around individual warp wires  51  while the solid line is the total voltage. Light is emitted when and where this voltage exceeds a threshold value U t . Thus, a clustered display element  62  is formed over the area of intersection of a group  55  of warp wires  51  with a group  56  of weft fibers  52 . In the example shown in FIG. 3, the clustered display element  62  encompasses sixteen contact zones  64 . The necessary spacing between groups may be achieved by adding non-conductive fibers  66  between the wires  51 . It will be appreciated that the display material may be arranged from uniformly spaced and identical fibers in each respective direction but some of these fibers may be not connected to the electric circuitry in order to provide the necessary spacing between the groups of fibers. 
     With reference to FIGS. 4 and 5, there is shown a schematic illustration of the structure and operation principle of two kinds of electro-optic material in accordance with another aspect of the present invention. In FIG. 4, a piece of electro-optic material  70  comprises two weft electro-optic fibers  72  and two warp wires  73  and  74  contacting in contact zones  75  and  76 . The weft fibers  72  are similar to the fibers  32 , in that they comprise a conductive wire  36 , an EL layer  38  therearound, and an additional outer conductive layer  80 . However, the conductive layer  80  is not of specially limited conductivity but is laid over the electro-optic fiber  72  in separated sections  82 . As seen in FIG. 4, the light-emitting zones associated with contact zones  75  and  76  are merged in one EOA zone  84  extending as a continuous cylinder between the boundaries of one section  82 . Thus, all EOA zones belonging to one section of the conductive layer  80  define one clustered pixel. 
     FIG. 5 shows an enlarged sectional and plan view of a display material  110  with clustered pixels. The display material  110  comprises warp wires  112  and weft fibers  114  made of conductive wires  116  and EL layer  118 , arranged in a woven matrix structure. A transparent conductive layer  120  is applied on the matrix structure in square spots  122 , each spot overlaying nine contact zones and defining one clustered pixel  123  with three EOA zones  124  instead of nine regular pixels. To produce light, the clustered pixel  123  is connected to a power source  126  by Y-lines powering the weft fibers  114 , and by X-lines powering the wires  112 . It will be appreciated to some of the X-lines in the clustered pixel may be omitted since all wires  112  powering the pixel  123  are connected in parallel through the conductive layer  120 . It is also possible to apply the conductive layer in stripes which are continuous along the warp wires  112 , since the division into clustered pixels in this direction is defined only by the wiring of the weft fibers  114 . 
     From the viewpoint of the obtained EOA zones, it is not material whether the EOA substance is first laid on the wires which are then arranged into a matrix display structure, or the wires are first arranged into a matrix and then covered with EOA substance. Therefore, structures similar to the ones shown in FIGS. 2,  3  and  5 , and operating on the same principles may be obtained by applying layers of EOA substance and of transparent conductive material over an arranged matrix of two sets of conductive wires. In any case it is important to isolate the conductive wires of the one set from the wires of the other set. 
     FIG. 6 shows in a cross-sectional view a matrix display material  130  comprising warp wires  132  and weft wires  134  spaced by a layer of insulation  133  covering the wires  132 , and a layer of EOA substance  136 . One or two transparent conductive layers  138  and  140  are applied on one or both sides of the matrix display material, in electric contact with the weft wires  134  in contact zones  142 . An enlarged EL pixel is defined by an EOA zone  144  between the insulated warp wire  132  and one of the conductive layers  138  or  140  around each contact zone  142 . The EOA zone  144  extends around the contact zone  142  within an area where the operative voltage U in the conductive layer  138  exceeds the threshold value U t , as shown in the graph above the cross-section. Similarly to the materials shown in FIGS. 2 and 3, this area grows with the conductivity of the layer  138 . The conductivity is limited so as to terminate the EOA zone  144  half-way to the contact zone of the next pixel and to avoid the visible merging of two adjacent pixels. 
     Alternatively, the wires  132  and  134  may be arranged in groups, the space between adjacent groups being larger than the space between the wires within a group, as explained with reference to FIG.  3 . In this case, the conductivity of the conductive layer  138  may be limited to a value allowing the merging of adjacent EOA zones associated with the wires within a group but preventing merging of the EOA zones across adjacent groups. Thus, clustered pixels may be formed in a manner similar to the described with reference to FIG.  3 . 
     FIG. 7 is a cross-sectional view of a matrix display material  146  differing from the material  130  in FIG. 6 in that the conductive layers  138  and  140  are laid in separated spots  138   a  and  140   a . A clustered pixel  148  is defined by the EOA zone  149  formed between the warp wires  132  and the conductive layers in the whole area covered by spots  138   a  and  140   a.    
     When producing structures shown in FIGS. 6 and 7, the contact between the transparent conductive layer  138  or  140  and the warp wires  134  may be provided by exposing parts of warp wires in a number of ways. For example, the EOA layer  136  may be laid with thickness small enough as to leave each warp wire  134  at least partly exposed above or below the overlapping zones thereof with the weft wires  132 . Also, the EOA layer may be laid to entirely cover wires  134  but then an outer sublayer thereof may be removed, so as to expose partly each wire  134 . These methods of exposure are especially suitable for a woven matrix structure where warp wires  134  are protruding from the material at each junction with weft wires  132 . 
     Another technique to expose parts of warp wires  134  is similar to the photolithography process and includes: sputtering the matrix structure with removable particles of suitable size ensuring that at least one such particle is attached to each warp wire  134 ; covering the matrix structure with a layer of EOA substance  136  so as to leave the removable particles at least parlay exposed; and removing the particles by dissolving, etching, washing or otherwise. The resulting display material structure  150  is shown in FIG. 8 where the positions  152  of the removable particles are denoted by broken lines. It will be appreciated that this technique is suitable both for woven and non-woven matrix structures. If the transparent conductive layer is applied in spots, then it is preferable to have at least one particle attached to each warp wire  134  in each spot. If a continuous layer of limited conductivity is used, as shown in FIG. 6, then it is necessary to ensure at least one particle for each overlapping zone of warp wire  134  with weft wire  132  in order to obtain the contact  142 . The more contact zones  142  are obtained, the less may be the conductivity of the transparent layer  138  or  140 . Thus, cheaper transparent conductive polymers may be used instead of indium-tin oxide (ITO). 
     While the clustered pixels of the kind shown in FIG. 3 or  5  are parts of a matrix display where the display elements are arranged in rows and columns parallel to the warp and weft wires, clustered pixels of the kind shown in FIGS. 7 and 8 may have arbitrary shape in plan view. FIG. 9 shows an embodiment  160  of the material shown in FIG. 7, wherein clustered pixels of non-orthogonal form  161 ,  162 ,  163  are formed on a prepared orthogonal matrix of X-Y wires  166  and  168 , respectively. The EOA substance  170  and the transparent conductive layer  172  are laid only within the contours of the pixels. The remaining surface of the matrix may be covered with insulating material  174 . The pixel  163  is shown in light-emitting state. 
     It is also understood that a whole display may be made as a single clustered pixel, for example, if the spots  122  in FIG. 5 or the EOA substance  170  and the transparent conductive layer  172  in FIG. 9 are laid as one continuous layer. In this case, a static display will be obtained, e.g. a display that lights up as a whole. Nevertheless, a static display with the structure of FIG. 9 may carry an image consisting of elements with different color and brightness which are made of different EOA substance. 
     Although a description of specific embodiments bas been presented, it is contemplated that various changes could be made without deviating from the scope of the present invention as it is outlined in the claims. For example, both warp and weft fibers may be coated with an EOA substance before weaving, or the fibers may be in the form of flat strips or tapes. Also, the structures shown here on woven display material may be created on non-woven material and vice-versa.