Display panel with electroluminescent illumination

Abstract: According to the present invention, a display panel integrated with an electroluminescent lamp panel (EL) can be obtained by printing EL at the back of a light permeable substrate, covering the front surface of the substrate and the rearface of EL with a moisture proof film for insulating and protecting the EL from the surrounding atmosphere, or covering the substrate and EL entirely, printing an indication mark at the surface of the moisture proof film, or printing EL at the back of the light permeable substrate having an indication mark printed on the surface thereof, covering the front surface of the substrate and the rearface of EL with a moisture proof film for insulating and protecting EL from the surrounding atmosphere, or covering the substrate and the EL entirely, so that production of the display panel can be simplified as compared with a case of attaching EL as an independent member to the display panel after manufacture of the production.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention concerns a display panel in which an indication mark is illuminated by light emission from the rear face and, more in particular, it relates to a display panel suitable to use as a number plate for an indication instrument. 2. Description of the Prior Art For instance, in an automobile indicator, indication marks such as scales or numerical figures printed on the front surface of a number plate can be seen clearly during night or in a dark circumstance. Specifically, a light permeable substrate is adopted for the number plate and it is formed such that an indication mark is in the form of negative indication (indication mark appears bright) or positive (opposite to the negative) indication and an illumination member comprising lamps is disposed at the back of the number plate (for example, refer to US Patent Nos. 4878387 and 5047761). In the above-mentioned indicator, the brightness of the indication mark becomes not uniform depending on the difference in the distance from the illumination member and it is difficult to see. Further, in view of the heat generation from illumination member, an expensive heat resistant material has to be used for a casing containing the indicator. Further, since a gap has to be large between the illumination member and the casing in view of the heat generation from the illumination member, the size of the casing is enlarged. As a countermeasure for overcoming such problems, an electroluminescent lamp panel (hereinafter referred to as "EL") is sometimes disposed at the back of the number plate (for example, refer to U.S. Patent No. 5036249 and Japanese Utility Model Laid-Open Sho 62-40518 and Sho 62-124510). The foregoing problems can be solved by adopting EL for the illumination of the number plate. However, when EL is at the back of the number plate, the position between EL and the number plate has to be aligned accurately for satisfactory illumination of the indication mark on the number plate by the EL emission. In addition, since EL is thin and easy to flex distort, EL has to be protected from the surrounding atmosphere such as external vibrations and a rigid rear frame has been attached at the back of EL for instance. Accordingly, assembling operation between the number plate and EL or the number plate, EL and the rear frame becomes too complicated and makes the production troublesome. An object of the present invention is to overcome the foregoing problem and provide a display panel integrated with EL and, particularly, a display panel suitable to use as a number plate for use in an indicator. SUMMARY OF THE INVENTION In the present invention, EL is printed at the back of a light permeable substrate, the front surface of the substrate and the rearface of the EL are covered with a moisture proof film for insulating and protecting EL from the surrounding atmosphere, or the substrate and EL are covered entirely and an indication mark is printed on the surface of the moisture proof film. In the present invention, EL is printed on the rearface of a light permeable substrate having an indication mark printed on the surface thereof, the front surface of the substrate and the rearface of EL are covered with a moisture proof film for insulating and protecting EL from the surrounding atmosphere, or the substrate and EL are entirely covered. In the present invention, a light permeable front electrode, a light emission layer and a back electrode are successively printed at the back of the light permeable substrate having an indication mark printed on the front surface, an insulation layer for insulating and protecting the front electrode, the light emission layer and the back electrode from the surrounding atmosphere is formed at the back of the substrate and, particularly, the insulation layer is formed by printing an insulation material. Japanese Patent Application No. JP 880038067 (Publication No. JP1213988) discloses an electroluminescent element which has an improved moisture-proof seal comprising a nonwoven fabric which supports a moisture proof wax. The fabric is wrapped around the element and the device is sealed with an adhesive sealant. Japanese Patent Application No. JP 870332782 (Publication No. JP1171994) discloses a display board comprising an electroluminescent display. The front surface of the display board is transparent or translucent so that writing on the front surface is illuminated by the electroluminescent display. European Patent Application No. 0,357,443 discloses an electroluminescent device which is made by forming between suitable conductive layers a printed dielectric layer and a printed phosphor layer, preferably using a UV-curable binder that reduces the moisture sensitivity of the device. European Patent Application No. 0,432,930 discloses an electroluminescent display panel which comprises transparent and base electrodes with dielectric and phosphorescent layers therebetween and an insulation layer behind the base layer. A moisture barrier layer is also provided on the back of the panel. The phosphorescent layer may include phosphor particles that have an etched surface which improves the brightness of the device. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view partly cut away of a first embodiment of a display panel; Fig. 2 is a cross sectional view for a portion of the embodiment described above; Fig. 3 is a cross sectional view for a portion of a second embodiment of a display panel; Fig. 4 is a cross sectional view for a portion of a third embodiment of a display panel; Fig. 5 is an exploded perspective view of an embodiment according to the present invention; Fig. 6 is a cross sectional view for a portion of the embodiment described above; and Fig. 7 is a back view in a state where a front electrode and a bus bar are formed to the substrate of the embodiment described above. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figs. 1 and 2 show a first embodiment of a display panel in which EL2 is printed on the rear face of a light permeable substrate 1 and EL2 is formed by laminating, at the back of the substrate 1, a moisture absorbing layer (Sumicagel. nylon or the like) 21, a light permeable front electrode (coating type ITO) 22, a light emission layer 23, an insulation layer 24, a reflective back electrode (Ag foil) 25 and a moisture absorbing layer 26 successively (Sumicagel. Nylon and ITO are registered trademarks). Then, the front surface of the substrate 1 and the rearface of EL2 are covered with a moisture proof film 3 for insulating and protecting EL2 from the surrounding atmosphere, terminals (leads) 22a, 25a for the electrodes 22, 25 are exposed to the outside of the moisture proof film 3, the periphery of the moisture proof film 3 is sealed, and an indication mark 4 in a negative display is printed at the front surface of the moisture film on the side of the front surface of the substrate 1. Fig. 3 shows a second embodiment of a display panel, in which the moisture proof film 3 in the first embodiment covers the substrate 1 and EL2 entirely, and an indication mark 4 is printed on the surface of the moisture proof film 3. Fig. 4 shows a third embodiment of a display panel, in which an indication mark 4 is previously printed to the front surface of the light permeable substrate 1, EL2 of the same constitution as that in first or second embodiment is printed at the back of the substrate 1, and the substrate 1 and EL2 are entirely covered by a moisture proof film 3 for insulating and protecting EL2 from the surrounding atmosphere like that in the second embodiment. In the third embodiment, the moisture proof film 3 may cover the front surface of the substrate 1 and the rearface of EL2 like that in the first embodiment. According to the first to third embodiments, the light emission layer 23 emits light by application of a predetermined voltage to each of the terminals 22a, 25a for the electrodes 22, 25 and the light emission illuminates the indication mark 4 from the back. Then, according to the first to third embodiments, a number plate integrated with EL2 can be obtained. Accordingly, manufacture of the number plate can be simplified as compared with the prior art (manufacturing EL as an independent member, it is attached to a number plate). Figs. 5, 6 and 7 show an embodiment according to the present invention as defined in the claims in which a number plate 51 is formed by successively printing, at the back of a light permeable substrate 52, a light permeable front electrode (coating type ITO) 53, a light emission layer 54, a back electrode 55 followed by drying and, further, forming an insulation layer and then printing and drying an indication mark 57 showing a running speed and fuel residue to the front surface of the substrate 52, in which an electrode 53, a light emission layer 54, an electrode 55 and an insulation layer 56 correspond to EL2 (refer to Fig. 1 - 4) of the first to third embodiments. The substrate 52 is a panel (of about 1.5 mm thickness) made of a resin, for example, polycarbonate like that existent number plate for the indicator and, in a case of indicating an indication mark 57 in the negative form, it can be obtained by printing the indication mark 57 with a white or like other light permeable paint and printing other portion with a light impermeable paint of black or like other color and a positive indication is attained by opposite procedures. In this embodiment, a negative indication mark 57 is formed by the same printing means as for the existent number plate, by printing the indication mark 57 with a white paint 57a while painting other portion with a black paint 57b. The front electrode 53 is formed by preparing a light permeable conductive material by kneading a metal oxide comprising indium oxide containing tin and adsorbing a dispersant composed of an anionic surface active agent and a binder resin comprising a vinyl acetate resin and adjusting a viscosity by a solvent comprising butyl cellosolve acetate and printing and drying the conductive material in a shape corresponding to the indication mark 57 (about 5 um thickness), a bus bar 58 comprising a low resistance material of a silver paste is formed by printing and drying so as not to oppose the indication mark 57 at the periphery of the front electrode 53, and a portion of a bus bar 58 is led to the end at the back of the substrate 52 as a terminal 59 (about 5 um thickness). The light emission layer 54 is formed by using a fluorescent paste prepared by dispersing a fluorescent material comprising a matrix of zinc sulfide mixed with a copper activator and, as required, a chlorine activator into a thermosetting epoxy resin of low water absorption and printing and drying the same substantially in the same shape (identical or somewhat greater) of the electrode 53 (about 40 um thickness). The back electrode 55 is formed by printing and drying a reflecting conductive material of a silver paste so as to oppose to the front electrode 53 by way of a light emission layer 54 followed by drying, and a portion of the back electrode 55 is led out to the end of the rearface of the substrate 52 as a terminal 60 (about 10 um thickness). Then, the light emission layer 54 emits light by applying a predetermined voltage between terminals 59 and 60, that is, between electrodes 53 and 55 and the light illuminates the indication mark 57 at the back. It will be apparent that the electrodes 53, 55 and the terminals 59 and 60 have to be designed and formed with such a care as not causing short circuit between each of them. An insulation layer 56 serves to insulate and protect the front electrode 53, the emission layer 54 and the back electrode 55 from the surrounding atmosphere such as moisture or impact shock, which can be formed by appending a high molecular weight insulation material such as a thin nylon sheet or a polyethylene naphthalate film to the back of the substrate 52, excepting for the terminals 59, 60. As shown in Figs. 5 and 6, if a thermosetting polymeric material such as an epoxy resin incorporated with a spacer material of glass beads is formed by printing and drying as an insulation material (about 15 um thickness), the entire thickness and the weight of the number plate can be reduced than in the case of using the insulation material and the entire portion including the front electrode 53 and the insulation layer 56 can be formed by printing and, accordingly, the production step can be simplified more than in the case of using the insulation material. Although not illustrated, it will be effective for improving the light emission performance of the light emission layer 54, if necessary, to interpose a dielectric layer (corresponding to insulation layer 24 in the first to third embodiments shown in Figs. 1 - 4) between the electrodes 53 and 55. Such a dielectric layer is formed by printing a dielectric paste prepared by dispersing a dielectric material of barium titanate in an thermosetting epoxy resin of low water absorption and drying the same (about 40 um thickness). Reference numeral 61 in Fig. 7 denotes an alignment mark printed simultaneously upon printing the front electrode 53 with the identical material and it is disposed at the back of the substrate 52 not opposing to the indication mark 57, and the indication mark 57 is formed to the front surface of the substrate 52 by aligning a printing mask (not illustrated) having a pattern for the indication mark 57 as a reference. Further, an indication member situating at the back of the number plate 51 can be illuminated by making the front electrode 53 - back electrode 55 greater than the indication mark 57 and making the back electrode 55 light permeable. A number plate having the foregoing constitution is disposed on an indicator not illustrated and the terminals 59 and 60 are connected by way of a switch (not illustrated) to a driving circuit (not illustrated). Then, when the switch is turned ON during night or in a dark circumstance, the light emission layer 54 emits light to illuminate the indication mark 57 brightly. In the embodiment of the present invention, a number plate integrated with EL can be obtained. Accordingly, manufacture can be simplified as compared with the prior art in which EL was manufactured as an independent member. Further, since the front electrode 53 and the subsequent members are formed at the back of the substrate 52 for the number plate 51, it is possible to improve the emission efficiency while suppressing the decay of emission from the emission layer 54 and improve the brightness of the indication mark 57 under the application of an identical voltage as compared with the case of the first to third embodiments. Further, when the insulation layer 56 for insulating an protecting the front electrode 53, the light emission layer 54 and the back electrode 55 from the surrounding atmosphere is printed at the back of the substrate 52 of the insulation layer 56, the entire thickness and the weight of the number plate 51 can be reduced and the entire portion including the front electrode 53 as far as the insulation layer 56 can be formed by printing and, accordingly, the manufacturing step can be simplified. The present invention is also applicable, in addition to each of the above-mentioned embodiments, to display members such as a guide plate indicating an emergency exit and a decorative sign board. Further, it will be apparent that the materials used can be selected variously and the color of light emission can optionally be selected depending on the material of the light emission layers 23, 54. Furthermore, if the back electrode 25, 55 are made of the same light permeable material as that for the front electrodes 22, 53, light emitted from the light emission layers 23, 54 are illuminated also to the backward and, for instance, an integrating meter (not illustrated) can also be illuminated. In the present invention including each of the foregoing embodiments, various appropriate printing methods can be adopted for "printing" such as screen printing method and it also includes a film coating method such as roll coating.

Claims: An electroluminescent display panel (51) comprising: a light-permeable substrate (52) having an indication mark (57) on a front surface thereof; and a light-permeable electrode (53), a light-emission layer (54), a base electrode (55) and an insulation layer (56) successively formed on a back surface of said light-permeable substrate (52); the display panel (51) being characterised in that: (i) the light-permeable electrode (53), the light-emission layer (54), the base electrode (55), and the insulation layer (56) are formed by printing, and (ii) the insulation layer (56) insulates said light-permeable electrode (53), said light-emission layer (54) and said base electrode (55) and prevents moisture ingress into said device. A display panel (51) as claimed in claim 1, wherein the indication mark (57) is illuminated from the back by applying a voltage between the base electrode (55) and the light-permeable electrode (53). The display panel (51) according to claim 1 or claim 2, wherein the light-permeable electrode (53) is in a shape corresponding to the indication mark (57). The display panel (51) according to claim 1, 2 or 3, wherein the insulation layer (56) is formed by applying an insulating material in liquid form. The display panel (51) according to any one of claims 1 to 4, wherein said light-emission layer (54) has substantially the same shape as the light-permeable electrode (53). The display panel according to any preceding claim wherein said insulation layer (56) comprises a thermosetting polymeric material incorporating a spacer material of glass beads. The display panel according to claim 6, wherein said thermosetting polymeric material is an epoxy resin. The display panel according to any one of claims 1 to 5, wherein said insulation layer (56) comprises a material of high molecular weight. The display panel according to claim 8, wherein said material of high molecular weight is nylon. The display panel according to claim 8, wherein said material of high molecular weight is polyethylene napthalate.

Inventors: MIYASHITA SADAMASA R D, ZHANG LAIYING R D, MIYASHITA, SADAMASA, ZHANG, LAIYING, Miyashita, Sadamasa, R&amp;D Center Nippon Seiki K.K., Zhang, Laiying, R&amp;D Center Nippon Seiki K.K.
Applicants: JAPAN ENGINE VALVE MFG, NIPPON SEIKI K.K.
Application year: 1992
Main classification: G01D11
IPC codes: B60Q3, G01D11, G09F13, B60K35