An electroluminescent display

Abstract: An EL display in which a luminescent area is enlarged by arranging such that a non-luminescent area is not projected toward the outside, in which connecting positions connected with a driving circuit are not limited to a narrow range and which requires no high precision positioning is provided at low cost. A transparent electrode layer 2 is formed on the back of a transparent substrate 1; part of the peripheral portion of the transparent electrode layer is left as an exposed portion 1a and a luminescent layer 3, a first insulation layer 4 and a back electrode layer 5 are laminated and formed on the remaining whole face thereof. A part of the back electrode layer is left as an exposed portion 5a and a second insulation layer 6 is coated on the remaining whole face thereof. A contact layer 5b is formed on the exposed portion 5a of the back electrode layer and a contact layer 2c which conducts with the exposed portion 2a of the transparent electrode layer is formed on the back of the second insulation layer 6. Contact terminal portions for an external driving control circuit are connected with the respective contact layers 2c and 5b of the transparent electrode layer and the back electrode layer.

Description: The present invention relates to an electroluminescent (EL) display in particular for use as an electroluminescent (EL) face of a watch and the like. An EL element in a previously known EL display is formed by laminating a transparent electrode layer, a luminescent layer, an insulation layer and a back electrode layer. Electrode connecting portions are formed so as to project respectively from the transparent electrode layer and from the back electrode layer as means for applying an AC electric field between the transparent electrode layer and the back electrode layer. Flat cables and the like are connected to the electrode connecting portions to electrically connect with an external driving control circuit. Further, a previously known EL display used in a wristwatch as shown, for example, in US 5,265,071, has a transparent electrode layer connected with an electrode by an electrode connecting portion formed by projecting the transparent electrode layer, and a back electrode layer connected with an electrode by an electrode contact layer provided on the back of the back electrode layer. The transparent electrode layer is connected with the electrode by winding the electrode connecting portion of the transparent electrode layer around the side of a frame and by screwing to the electrode of a circuit board provided on the back of the frame. However, if the electrode connecting portion is formed so as to project toward the outside as described above, the luminescent area covers correspondingly less than the whole area, because the electrode connecting portion is a non-luminescent area. Further, a cavity portion corresponding to that projection has to be provided on the side of the case thus requiring a complicated mould and increasing the cost. Still more, since the electrode connecting portion is provided so as to project within a small area at an extremely limited specific position in order to minimise the non-luminescent area, the position of the connection with the driving circuit is naturally limited to a narrow range, and high precision positioning is required, thus increasing the cost of the assembly process. The arrangement shown in US 5,265,071 has an additional drawback, in that it requires high precision work in narrow sections to provide screw holes for example on the electrode connecting portion, the frame and the circuit board to screw the electrode connecting portion of the transparent electrode layer. According to the present invention, there is provided an EL display comprising: a transparent substrate onto which a transparent electrode layer, a luminescent layer, a first insulation layer, a back electrode layer, and a second insulation layer have been successively laminated; characterised in that a part of the peripheral portion of said transparent electrode layer is left as an exposed portion, and a first contact layer which is electrically conductive with the exposed portion of the transparent electrode layer is formed on the back of the second insulation layer; and a part of the back electrode layer is left as an exposed portion and a second contact layer is formed on the exposed portion of the back electrode layer. Thus, according to the present invention, a pair of contact layers corresponding to a driving control circuit are disposed on the back of a back electrode which is superimposed on a luminescent area of an EL element by making the most use of the screen printing technology without extending a non-luminescent area toward the outside, in order to increase a luminescent area and to facilitate the connection with the driving circuit. Preferably, the respective contact layers of the transparent electrode layer and the back electrode layer are formed in a shape of concentric arcs. Further, preferably, the contact layer of the back electrode layer is formed in a circle at the center part and the contact layer of the transparent electrode layer is formed in a surrounding annular shape at the peripheral portion of the circle. Still more, preferably, the contact layer of the back electrode layer is formed in a semi-circle and the contact layer of the transparent electrode layer is formed in another semi-circle which opposes to the semi-circle. Preferably, a back protection layer which is made of an insulating material and which is formed such that the respective part of each contact layer is exposed is formed on the back of the respective contact layers of the back electrode layer and the transparent electrode layer. For a better understanding of the present invention, and to show how it may be brought into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a section view showing an arrangement in accordance with this invention; Figure 2 is a rear view of the contact layer arrangement shown in Figure 1 prior to the formation of the back protection layer; Figure 3 is a rear view showing another contact layer arrangement; Figure 4 is a rear view showing a further contact layer arrangement; Figure 5 is a rear view showing a yet further contact layer arrangement; Figure 6 is a rear view showing an additional contact layer arrangement; Figure 7 is a rear view showing the contact layer arrangement prior to the formation of the back protection layer for an EL display having a different external shape; Figure 8 is a rear view showing another contact layer arrangement; Figure 9 is a rear view showing a further contact layer arrangement; Figure 10 is a rear view showing a yet further contact layer arrangement. Figure 1 shows a section of an EL display according to the invention, in which a transparent electrode layer 2 is formed by evaporating indium tin oxide (ITO) onto a transparent substrate 1 which is made of a synthetic resin such as a polyethylene terephthalate (PET) film. Then, leaving a part of the peripheral portion of the transparent electrode layer 2 as an exposed portion 2a, a luminescent layer 3, a first insulation layer 4 and a back electrode layer 5 are formed sequentially on the remaining face, for example by screen printing. Ink produced by mixing and agitating a luminescent substance in which copper is doped in zinc sulphide, i.e. a luminescent material, with fluororesin binder may be used for the luminescent layer 3. Ink produced by mixing and agitating barium titanate, i.e. a high dielectric substance, with fluorine binder may be used for the first insulation layer 4. The back electrode layer 5 may be made from carbon paste. A connection electrode 2b of the transparent electrode layer 2 is formed by carbon paste on the exposed portion 2a of the transparent electrode layer 2 at the part of the peripheral portion of the transparent electrode layer 2 in such a way as to be insulated from the back electrode layer 5. This connection electrode 2b is formed by printing at the same time as the back electrode layer 5 is printed. A second insulation layer 6 is formed on the back electrode layer 5. While the same ink as that used for the first insulation layer 4 may be used for the second insulation layer 6, ink produced by mixing and agitating a low dielectric substance with fluorine binder may be also used. As shown in Figure 2, a C-shaped arc aperture 6a is formed on the second insulation layer 6 and the back electrode layer 5 is exposed in the aperture as an exposed portion 5a of the back electrode layer. A contact layer 5b of the back electrode layer 5 is formed on the exposed portion 5a by using silver paste. A C-shaped arc contact layer 2c of the transparent electrode layer 2 is formed on the second insulation layer 6 by using silver paste so that it is electrically connected to the connection electrode 2b of the transparent electrode layer 2. The contact layer 5b of the back electrode layer 5 and the contact layer 2c of the transparent electrode layer 2 are formed in the shape of concentric arcs. The contact layer 2c is formed on the periphery of the EL display, as shown. Finally, a back protection layer 7, which is formed such that part of the contact layers 2c and 5b of the transparent electrode layer and the back electrode layer, respectively, are exposed, is formed by an insulating material such as silicon and vinyl chloride. The contact layer 5b of the back electrode layer 5 is exposed by means of an aperture 7a of the back protection layer 7 and the contact layer 2c of the transparent electrode layer 2 is exposed by means of an aperture 7b. Owing to the construction described above, the contact terminal portions for the driving control circuit may be connected selectively to arbitrary points on the C-shaped arc contact layers 2c and 5b, thus allowing the connection to be made readily. Further, because these connection points are located on the back of the luminescent area, they will not reduce the luminescent area and the non-luminescent area corresponds only to the area of the exposed portion 2a, which is very localised and is limited to part of the peripheral portion of the transparent electrode layer 2. For example, the contact terminal portion 8a of the driving control circuit may be connected selectively to an arbitrary point so long as it is on the circular arc of the contact layer 5b and the contact terminal portion 8b may be connected selectively to an arbitrary point so long as it is on the circular arc of the contact layer 2c. It is noted that because the positions of the contact terminal portions 8a and 8b for the driving control circuit are determined in advance, it is possible to form the apertures on the back protection layer 7 at positions corresponding to the contact terminal portions 8a and 8b and to cover and protect all of the other parts except the apertures. That is, if the contact layers 2c and 5b are formed as described above in advance, it is possible to make the printing screens of each of the other layers from the transparent electrode layer 2 to the second insulation layer 6 as well as the contact layer 2c all in common and easily to accommodate different models in which the contact terminal portions are positioned in a variety of positions merely by changing the printing screen of the back protection layer 7 so that the apertures are formed at the positions corresponding to the positions of the contact terminal portions 8a and 8b of the driving control circuit. Figure 3 shows an embodiment in which a contact layer 12c of the transparent electrode layer and a contact layer 15b of the back electrode layer are formed in the shape of concentric rings, wherein a back protection layer (not shown) is formed in the same manner as that described above after positioning the contact layer 15b within an annular aperture 16a of a second insulation layer 16 and forming the annular contact layer 12c on the second insulation layer 16. Contact terminal portions 8a and 8b of the driving control circuit are shown by two-dot chain lines, respectively. Figure 4 shows an embodiment in which an arc aperture 26a is opened at the peripheral portion of a second insulation layer 26 and a contact layer 25b of the back electrode layer is provided within the aperture when the positions of the contact terminal portions for the driving control circuit are limited further. A contact layer 22c of the transparent electrode layer is also formed in an arc at the other part of the peripheral portion of the second insulation layer 26. Figure 5 shows an embodiment in which the contact terminal portions for the driving control circuit may be connected selectively to a greater area of the surface. A circular aperture 36a is opened at the center part of a second insulation layer 36 and a contact layer 35b of the back electrode layer is provided within the aperture. An annular contact layer 32c of the transparent electrode layer is formed at the peripheral portion of the aperture 36a of the second insulation layer 36. In other respects, the structure is the same as that described above. This structure allows the contact terminal portion 8a for the driving control circuit to be connected at any position within the contact layer 36a and the contact terminal portion 8b to be connected at any position on the annular peripheral contact layer 32c. Figure 6 shows an embodiment in which the second insulation layer 46 is formed on a part of the back electrode layer, such as the left hand half as shown, and a contact layer 45b of the back electrode layer is formed on a further part, such as the right hand half as shown. A contact layer 42c of the transparent electrode layer is formed on the second insulation layer 46. This structure allows the contact terminal portion 8a for the connection to the driving control circuit to be formed at any position on the right semi-circular part and the contact terminal portion 8b for connection to the driving control circuit to be formed at any position on the left semi-circular part. Figures 7 to 10 show embodiments of the invention in which the outer shape of the EL display is octagonal. Figures 7 and 8 show embodiments of the invention in which the same contact layers 2c and 5b as those described in Figure 2 and the same contact layers 12c and 15b as those described in Figure 3, respectively, are provided. Figures 9 and 10 show embodiments of the invention in which contact layers are formed with a predetermined width parallel to each side of the octagonal outer shape, wherein contact layers 52c and 55b whose part corresponding to one side is cut in Figure 9 and contact layers 62c and 65b continue octagonally in Figure 10. All of the other structures of all the embodiments shown in and after Figure 3 are substantially the same as those shown in Figures 1 and 2. As described above, the embodiment in which the contact layers are formed in the shape of concentric arcs or rings allows a large dislocation in the direction of rotation in mounting to be accommodated. Further, the embodiment in which the contact layers are formed of linear portions, such as an octagon, enables large linear movements during mounting to be accommodated. As described above, the respective contact layers of the transparent electrode layer and the back electrode layer of the EL display to be connected with the contact terminal portions of the driving control circuit are formed on the back of the back electrode layer superimposed on the luminescent area. In this way, the non-luminescent area is not projected toward the outside and almost the whole area may be act as the luminescent area. Further, because the positions of the contact terminal portions for the driving control circuit are not limited to a narrow range and no precision positioning is required, it becomes easy to assemble. When the contact layers are formed in the shape of concentric arcs, it becomes possible to accommodate a large dislocation in the direction of rotation in mounting, so that the assembly works becomes easy. The exposed contact layers may be minimised and damages which might be otherwise caused by contact and the like may be prevented by providing the back protection layer.

Claims: An EL display comprising: a transparent substrate (1) onto which a transparent electrode layer (2), a luminescent layer (3), a first insulation layer (4), a back electrode layer (5), and a second insulation layer (6) have been successively laminated; characterised in that a part of the peripheral portion of said transparent electrode layer (2) is left as an exposed portion (2a), and a first contact layer (2c) which is electrically conductive with the exposed portion (2a) of the transparent electrode layer (2) is formed on the back of the second insulation layer (4); and a part of the back electrode layer (5) is left as an exposed portion (5a) and a second contact layer (5b) is formed on the exposed portion (5a) of the back electrode layer (5). The EL display as claimed in claim 1, wherein contact terminal portions (8a,8b) for an external driving control circuit are connected with respective first and second contact layers (2c,5b). The EL display according to claim 1 or 2, wherein the first and second contact layers (2c,5b) are formed as concentric arcs. The EL display according to one of claims 1 or 2, in which the second contact layer (5b) is formed in a circle at the center part and the first contact layer (2c) is formed in an annular shape at the peripheral portion of said circle. The EL display according to claim 1 or 2, wherein the first and second contact layers (2c,5b) are formed in opposing semi-circles. The EL display according to any of claims 1 to 5, also comprising a back protection layer (7) made of an insulating material which is formed such that the respective part of each of the first and second contact layers is exposed. The EL display according to claim 1 or 2, wherein the shape of the first contact layer corresponds to the external shape of the EL display.

Inventors: MIYAUCHI YOSHIAKI, YAMAZAKI HIROSHI, MIYAUCHI, YOSHIAKI, YAMAZAKI, HIROSHI
Applicants: SEIKO PRECISION KK, SEIKO PRECISION INC.
Application year: 1996
Main classification: H05B33
IPC codes: H05B33, G04B19