Abstract:
A set of a transparent electrode layer and a luminescent layer in which phosphor particles are dispersed are formed on a transparent resin film, and this set is formed layer by layer to create more than one luminescent layer. One or more luminescent layers are divided into multiple luminescent color regions. Or, the transparent electrode layer is electrically separated into two or more regions. This configuration enables the display of multiple patterns in multiple luminescent colors using one dispersed EL lamp. Accordingly, the multicolor EL lamp, which is aesthetically appealing as well as good visibility, can be provided for a display unit of a range of electronic equipment and backlight for LCDs.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of dispersed multicolor electroluminescent (EL) lamps employed as backlights of liquid crystal displays and switch keys in a variety of small mobile equipment, and more particularly to dispersed multicolor EL lamps and EL lamp units employing thereof which not only satisfy practical functions such as visibility but also are aesthetically appealing. 
     BACKGROUND OF THE INVENTION 
     A conventional dispersed multicolor EL lamp is described using its sectional view in FIG.  9 . In FIG. 9, the thickness dimension is magnified for illustrative purposes. 
     In FIG. 9, indium tin oxide, for example, is deposited on a transparent resin film  1  using a deposition method such as vacuum sputtering to form a transparent electrode  2 . Then a phosphor layer  3  is formed by dispersing phosphor particles such as zinc sulfide doped with copper in a resin with high dielectric constant such as cyanic resin or fluororubber resin. A dielectric layer  4  is made of the same synthetic resin system as the phosphor layer  3  in which ferroelectric powder such as barium titanate is dispersed. A back electrode layer  5  is made of silver resin system or carbon resin system paste. An insulative cover resist  6 , followed by external electrodes  7 A and  7 B are then formed. 
     When multicolor text or graphics are displayed using the above conventional EL lamp, the text or graphics are directly drawn onto the surface of the transparent insulative film  1  using optically transmissive color paint; or a sheet on which text or graphics are drawn with optically transmissive color paint is attached to the transparent insulative film  1 . Alternatively, the luminescent color of the phosphor layer  3  is partially changed to match the text or graphics. 
     In the above conventional dispersed multicolor EL lamps, however, only one type of text or graphics can be displayed. 
     SUMMARY OF THE INVENTION 
     In the dispersed multicolor EL lamp in accordance with an exemplary embodiment of the present invention, a first transparent electrode layer is formed on a transparent resin film, and then a first luminescent layer at least containing a phosphor layer in which phosphor powder is dispersed is formed. Then, a transparent electrode layer and luminescent layer are formed layer by layer as a set to form N (N is an integer of N≧2) transparent electrode layers and N luminescent layers. One or more layers in the first to Nth luminescent layers are divided into multiple luminescent color regions for the required text or graphics in the same luminescent layer. A back electrode layer is then formed on the Nth luminescent layer. 
     The above configuration enables the display of multiple text and graphics in multiple luminescent colors using a single dispersed EL lamp. 
     In the dispersed multicolor EL lamp in accordance with an exemplary embodiment of the present invention, one or more layers in the first to Nth luminescent layers which are divided into multiple luminescent color regions show an almost colorless monocolor in the same luminescent layer when they are not illuminated, but emit multiple luminescent colors when they are illuminated. When the first to Nth luminescent layers are illuminated independently, multiple divided regions are illuminated in multiple luminescent colors without mutually affecting the coloring of each luminescent layer. 
     Also in the dispersed multicolor EL lamp in accordance with an exemplary embodiment of the present invention, one or more layers in the first to Nth transparent electrode layers or back electrode layer are electrically separated into two or more regions in the same transparent electrode layer or back electrode layer. This makes it possible to illuminate each divided region of the first to Nth luminescent layers in more than one luminescent color. 
     Also in the dispersed multicolor EL lamp in accordance with an exemplary embodiment of the present invention, each of the first to (N−1)th luminescent layers is formed of two layers. The first layer is a phosphor layer in which phosphor particles are dispersed. The second layer is formed of a light transmissive insulation layer with higher dielectric constant than that of the first layer. This enables even higher luminance to be achieved when any of the first to (N−1)th luminescent layers are illuminated. 
     In the dispersed multicolor El lamp in accordance with an exemplary embodiment of the present invention, the Nth luminescent layer is practically formed of two layers. The first layer is a phosphor layer in which phosphor particles are dispersed. The second layer is formed of a white insulation layer with higher dielectric constant than that of the first layer. This makes it possible to achieve even higher luminance when the Nth luminescent layer is illuminated. 
     Furthermore, in the dispersed multicolor EL lamp in accordance with an exemplary embodiment of the present invention, transparent electrode layers at least other than the first transparent electrode layer are formed of light-transmissive conductive paste with sheet resistance of 50 k or less by printing and drying transparent synthetic resin in which conductive indium tin oxide powder is dispersed. This facilitates the manufacture of the transparent electrode layer, such as by screen printing, at low cost. 
     Still furthermore, in the dispersed multicolor EL lamp in accordance with an exemplary embodiment of the present invention, the light-transmissive conductive paste for transparent electrode layers may be colored. This allows the overall luminescent color of each of the first to Nth luminescent layers to be changed. 
     In an EL lamp unit in accordance with an exemplary embodiment of the present invention, a microcomputer is employed to control the turning on and off and flashing of the first to Nth luminescent layers of the dispersed multicolor EL lamp separately or in combination. This makes it possible to automatically turn on, turn off, or flash each of the first to Nth luminescent layers independently or in combination in accordance with predetermined conditions. 
     Furthermore, in the EL lamp unit in accordance with an exemplary embodiment of the present invention, the microcomputer controls each of the electrically separated electrodes in the first to Nth transparent electrode layers and back electrode layer to automatically apply, shut, or intermittently apply voltage to each of the electrode layers electrically separated into multiple regions independently or in combination. This makes it possible to automatically turn on, turn off, or flash each of divided regions in the first to Nth luminescent layers corresponding to electrically separated electrode layers in the first to Nth transparent electrode layers and back electrode layer independently or in combination, in accordance with predetermined conditions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a dispersed multicolor EL lamp, displaying text, in accordance with a first exemplary embodiment of the present invention. 
     FIG. 2 is a sectional view taken along a line  2 — 2  in FIG.  1 . 
     FIG. 3 is a sectional view taken along a line  3 — 3  in FIG.  1 . 
     FIG. 4 is a front view of the dispersed multicolor EL lamp, displaying another text different from that in FIG. 1, in accordance with the first exemplary embodiment of the present invention. 
     FIG. 5 is a plan view of a second transparent electrode layer of a dispersed multicolor EL lamp in accordance with a second exemplary embodiment of the present invention. 
     FIG. 6 is a plan view of a back electrode layer of the dispersed multicolor EL lamp in accordance with the second exemplary embodiment of the present invention. 
     FIG. 7 is a sectional view of the dispersed multicolor EL lamp in accordance with the second exemplary embodiment of the present invention. 
     FIG. 8A is a plan view of a first luminescent layer of dispersed multicolor EL lamp in accordance with a third exemplary embodiment of the present invention. 
     FIG. 8B is a plan view of a second luminescent layer of dispersed multicolor EL lamp in accordance with the third exemplary embodiment of the present invention. 
     FIG. 9 is a sectional view of a dispersed multicolor EL lamp of the prior art. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Exemplary Embodiment 
     A first exemplary embodiment of the present invention is described with reference to FIGS. 1 to  4 . Components having the same configuration as those of the prior art are given the same numbers, and thus their detailed explanation is omitted here. 
     FIG. 1 shows a plan view of a dispersed multicolor electroluminescent lamp (hereafter referred to as an EL lamp) in accordance with the first exemplary embodiment of the present invention. FIG. 2 shows a sectional view taken along a line  2 — 2  in FIG.  1 . FIG. 3 shows a sectional view taken along a line  3 — 3  in FIG.  1 . FIG. 4 shows a front view of the dispersed multicolor EL lamp displaying another text different from that in FIG. 1. A light-emitter of an EL lamp  8  of the present invention consists of the lamination of a first light-emitter  9  and second light-emitter  12 . Looking at the plan view in FIG. 1, the first light-emitter  9  includes a text light-emitter  10  for “PLAY” and background light-emitter  11 . The second light-emitter  12  includes a text light-emitter  13  for “STOP” and background light-emitter  14 . Looking at its sectional view in FIG. 2, the first light-emitter  9  includes a first luminescent layer and first transparent electrode layer  18 . The first luminescent layer includes a first phosphor layer  19  and first dielectric layer  20 . A part of the first phosphor layer  19  corresponding to the text light-emitter  10  is  19 A, and a part of the first phosphor layer  19  corresponding to the background light-emitter  11  is  19 B. The second light-emitter  12  includes a second luminescent layer, a second transparent electrode layer  21 , and a back electrode layer  24 . The second luminescent layer includes the second phosphor layer  22  and second dielectric layer  23 . A part of the second phosphor layer  22  corresponding to the text light-emitter  13  is  22 A, and a part of the second phosphor layer  22  corresponding to the background light-emitter  14  is  22 B. Each of the above layers is protected by an insulation layer  25 . The second transparent electrode layer  21 , first transparent electrode layer  18 , and back electrode layer  24  are respectively connected to the external electrodes  15 ,  16 , and  17 . 
     In FIGS. 2 and 3, the part  19 A of the first phosphor layer  19  corresponding to the text light-emitter  10  and the part  19 B corresponding to the background light-emitter  11  consist of a phosphor with different luminescent color. The part  22 A of the second phosphor layer  22  corresponding to the text light-emitter  13  and the part  22 B corresponding to the background light-emitter  14  also consist of a phosphor with different luminescent color. When an AC electric field is applied between the external electrodes  15  and  16  to illuminate the first luminescent layer, the text light-emitter  10  for “PLAY” and its background light-emitter  11  in FIG. 1 are displayed in different luminescent colors. When an AC electric field is applied between external electrodes  15  and  17  to illuminate the second luminescent layer, the text light-emitter  13  for “STOP” and its background light-emitter  14  in FIG. 4 are displayed in different luminescent colors. 
     In this exemplary embodiment, each of the transparent electrode layers  18  and  21 , and back electrode layer  24  are uniformly formed on the entire EL light-emitting regions , and each phosphor layer is divided into multiple luminescent color regions in the same phosphor layer. 
     In the above configuration, a transparent conductive film pre-deposited on a polyester film by sputtering or electron beam evaporation is employed as the first transparent electrode layer  18 . For the second transparent electrode layer  21 , a light transmissive sheet which is a conductive paste with sheet resistance of 50 kΩ or below made by dispersing indium tin oxide dendrite powder in polyester resin, epoxy resin, acrylic resin, phenoxy resin, fluororubber resin, or the like is employed. For the first phosphor layer  19  and second phosphor layer  22 , paste is made by dispersing EL phosphor powder with different luminescent colors for the text and background in resin with high dielectric constant such as cyano ethyl cellulose resin, cyano ethyl pullulan resin, or fluororubber resin containing fluorovinylidine. For the first dielectric layer  20 , milky-white optically transmissive paste is made by dispersing a small amount of ferroelectric powder, typically of barium titanate, in the same resin system as the phosphor layer paste. For the second dielectric layer  23 , paste which reflects white light is made by dispersing ferroelectric powder, typically of barium titanate, in the same resin system as the phosphor layer paste. For the back electrode layer  24  and external electrodes  15 ,  16 , and  17 , silver resin paste or carbon resin paste which is normally used for membrane switches is employed. For the insulation layer  25 , electrically insulating paste typically of a polyester system, urethane system, or epoxy system is employed. The above pastes for each layer are printed into a predetermined pattern, typically by screen printing, and then dried to form each layer. 
     The first transparent electrode layer  18  may also be formed by screen printing the same material as the second transparent electrode layer  21 . 
     As described above, in the first exemplary embodiment, the first luminescent layer is formed of the first phosphor layer  19  and first dielectric layers  20  and the second luminescent layer are formed of the second phosphor layer  22  and second dielectric layer  23 . By configuring the dielectric layers  20  and  23  with materials having a higher dielectric constant than that of the phosphor layers  19  and  22 , voltage can be more effectively applied to the phosphor than if configuring the luminescent layer only with the phosphor layer, thus achieving higher luminance light emissions. 
     The first and second phosphor layers may also be colored by adding phosphor dye or phosphor pigment to both pastes. This makes it possible to achieve luminescent color that is different from the natural color of the phosphor. 
     For the second phosphor layer, phosphor dye or phosphor pigment may be added to the phosphor layer paste for coloring, as well as EL phosphor, when adjusting the luminescent color of the text and background. Addition of phosphor dye or phosphor pigment is not apparent from the light-emitting side when the EL lamp is not turned on. At the same time, there is less color interference when the first phosphor layer is lighted. 
     In the first exemplary embodiment, the luminescent layer is made of two layers, i.e., the first and second luminescent layers. It is naturally possible to laminate three or more layers. In general, N layers (N is a positive integer) of the luminescent layer may be laminated by providing a transparent electrodes in-between. 
     In the first exemplary embodiment, each phosphor layer is divided into two luminescent color regions in the same phosphor layer. It may also be divided into three or more, in general to M (M is an integer of N≧2) luminescent color regions. 
     In the first exemplary embodiment, the external electrodes  15 ,  16  and  17  are disposed on opposite ends of the EL light-emitting region. It is apparent that each external electrode may also be disposed on any end independently or all together. 
     As described above, the dispersed EL lamp in the first exemplary embodiment enables the display of multiple indications by emitting multiple colors from the same light-emitting face. 
     Second Exemplary Embodiment 
     Points that differ in a dispersed multicolor electroluminescent (EL) lamp in accordance with the second exemplary embodiment of the present invention from the first exemplary embodiment are as follows. The second transparent electrode layer and back electrode layer are divided into two regions, and an external electrode is provided for each divided region. 
     FIG. 5 shows a plan view of the second transparent electrode layer of the dispersed multicolor EL lamp in the second exemplary embodiment. FIG. 6 is a plan view of the back electrode layer. FIGS. 5 and 6 show that the second transparent electrode layer and the back electrode layer in the first exemplary embodiment are divided into two regions. FIG. 7 shows a sectional view of the dispersed multicolor EL lamp in the second exemplary embodiment, which corresponds to FIG. 2 illustrating the first exemplary embodiment. 
     In FIG. 5, a text electrode  26 A is a region of a second transparent electrode layer  26  formed at a position corresponding to the text light-emitter  10  for “PLAY” in FIG. 1. A background electrode  26 B is a region of the second transparent electrode layer  26  corresponding to the background light-emitter  11 . An external electrode  27 A is an electrode for the text electrode  26 A, and an external electrode  27 B is an electrode for the background electrode  26 B. In FIG. 6, a text electrode  28 A is a region of a back electrode layer  28  which is formed in a position corresponding to the text light-emitter  13  for “STOP” in FIG. 4. A background electrode  28 B is a region of the back electrode layer  28  corresponding to the background light-emitter  14 . An external electrode  29 A is an electrode for the text electrode  28 A, and an external electrode  29 B is an electrode for the background electrode  28 B. The first transparent electrode layer is uniformly formed on the entire face. 
     The materials used for each layer of the EL lamp in the second exemplary embodiment is the same as that used in the first exemplary embodiment. 
     In the second exemplary embodiment, as described below, different indications may be displayed by changing the combination of selected transparent electrode layers and the back electrode layer when applying voltage to each transparent electrode layer and back electrode layer through each external electrode. 
     First, when voltage is applied between the first transparent electrode layer  18  and the text electrode  26 A of the second transparent electrode layer  26 , i.e. voltage is applied between the external electrode  16  and external electrode  27 A, the lamp may be controlled to illuminate only the text light-emitter  10  for “PLAY” without illuminating the background light-emitter  11 . In the same way, when voltage is applied between the first transparent electrode layer  18  and the background electrode  26 B of the second transparent electrode layer  26 , i.e. voltage is applied between the external electrode  16  and external electrode  27 B, the lamp may be controlled to illuminate only the background light-emitter  11  for “PLAY” without lighting the text light-emitter  10 . When the external electrode  27 A and external electrode  27 B of the second transparent electrode layer  26  are short circuited, and voltage is applied between the short circuited part and external electrode  16 , the text light-emitter  10  for “PLAY” and its background light-emitter  11  are both illuminated simultaneously in different luminescent colors. 
     In the same way, when the external electrode  27 A and external electrode  27 B of the second transparent electrode layer  26  are short circuited, and voltage is applied between the short circuited part and the external electrode  29 A for the text electrode  28 A of the back electrode layer  28 , only the text light-emitter  13  for “STOP” is lighted. When the external electrode  27 A and external electrode  27 B of the second transparent electrode layer  26  are short circuited and voltage is applied between the short circuited part and the external electrode  29 B for the background electrode  28 B of the back electrode layer  28 , only the background light-emitter  14  for “STOP” is lighted. When voltage is applied between a short circuited part of the external electrode  27 A and external electrode  27 B for the second transparent electrode layer  26  and a short circuited part of the external electrode  29 A and external electrode  29 B for the back electrode layer  28 , the text light-emitter  13  for “STOP” and its background light-emitter  14  are both illuminated simultaneously in different luminescent colors. 
     As described above, in the second exemplary embodiment, a range of indications which are also aesthetically appealing may be displayed by selecting the transparent electrode layer and back electrode layer to apply voltage to change the display color and background color as well as the display pattern. 
     For easier understanding, in the second exemplary embodiment, each of the boundary between different luminescent color regions in the first phosphor layer is patterned such that it approximately coincides with the boundary between electrically separated regions in the second transparent electrode layer. Also the boundary between different luminescent color regions in the second phosphor layer approximately coincides with the boundary between electrically separated regions in the back electrode layer. However, the present invention is not limited to this configuration. A boundary between different luminescent color regions in the phosphor layer and a boundary between electrically separated regions in the transparent electrode layer or back electrode layer may be varied to achieve a wider range of indications. 
     In this exemplary embodiment, EL lamp includes two luminescent layers: the first and second luminescent layers. Three or more luminescent layers may be laminated by providing a transparent electrode in-between, each luminescent layer may be divided into multiple different luminescent color regions, and each transparent electrode layer may be electrically separated into two or more regions. 
     Third Exemplary Embodiment 
     FIG. 8A and 8B show top views of flying image patterns of butterflies  34  and  36  in the first luminescent layer  32  and the second luminescent layer  33  respectively in a dispersed multicolor electroluminescent (EL) lamp in a third exemplary embodiment of the present invention. Each luminescent layer is composed of a phosphor layer and a dielectric layer, as described in the previous exemplary embodiments. 
     In this EL lamp, an orange EL phosphor is used for the butterflies  34  and  36 , and green EL phosphor is used for backgrounds  35  and  37  to form the first luminescent layer  32  and second luminescent layer  33  respectively. 
     Each layer is formed using the same materials as in the first exemplary embodiment. 
     There are two methods for partially changing the luminescent color of the EL lamp: 1) Changing the luminescent color of the EL phosphor contained in the phosphor layer, and 2) additionally dispersing phosphor dye or phosphor pigment, colored to a different color from the luminescent color of the EL phosphor, in the phosphor layer. The light generated in the second phosphor layer must pass through the first phosphor layer before it is finally emitted from the transparent resin film. Therefore, if the luminescent color of the butterfly part and the background in the first phosphor layer are changed using method 2), it is anxious that the color emitted from the second phosphor layer is affected or interfered by the added phosphor dye or phosphor pigment in the first phosphor layer. 
     Thus, in the third exemplary embodiment, the luminescent color of each EL phosphor for butterflies  34  and  36  and backgrounds  35  and  37  of the first and second luminescent layers  32  and  33  are respectively changed. With this configuration, both first and second luminescent layers  32  and  33  are virtually colorless when they are not illuminated, so the coloring of the first luminescent layer  32  does not affect the second luminescent layer  33  when only the second luminescent layer  33  is lighted. When the first and second luminescent layers  32  and  33  are lighted independently, the butterflies  34  and  36  are illuminated in orange, and the backgrounds  35  and  37  are illuminated in green. 
     If the EL lamp of the present invention is configured as an EL circuit unit, controlled by the microcomputer  44  (as shown in FIG.  7 ), to illuminate the first and second luminescent layers  32  and  33  alternately, the butterfly may be made to appear as if it is flying by alternately turning on the first and second luminescent layers  32  and  33 . 
     It is apparent that the EL lamps described in the first and second exemplary embodiments may also be configured to be controlled by a microcomputer to automatically change, turn on, turn off, or flash the displayed indication by selecting the transparent electrode layer or back electrode layer to which voltage is to be applied. 
     As described above, the present invention offers a dispersed EL lamp which enables multiple colors to be emitted from the same light-emitting face of a single EL lamp. Furthermore, multiple text or graphics may be displayed independently or simultaneously. 
     Reference Numerals 
       1  transparent resin film 
       2  transparent electrode 
       3  phosphor layer 
       4  dielectric layer 
       5  back electrode layer 
       6  cover resist 
       7 A,  7 B external electrode 
       8  EL lamp 
       9  first light-emitter 
       10 ,  13  text light-emitter 
       11 ,  14  background light-emitter 
       15 ,  16 ,  17 ,  27 A,  27 B,  29 A,  29 B external electrode 
       18  first transparent electrode layer 
       19 ,  32  first phosphor layer 
       19 A,  22 A part corresponding to text light-emitters  10  and  13   
       19 B,  22 B part corresponding to background light-emitters  11  and 
       20  first dielectric layer 
       21 ,  26  second transparent electrode layer 
       22 ,  33  second phosphor layer 
       23  second dielectric layer 
       24 ,  28  back electrode layer 
       25  insulation layer 
       26 A,  28 B text electrode 
       26 B,  28 B background electrode 
       34 ,  36  butterfly 
       35 ,  37  background 
     Reference Numerals 
       1  transparent resin film 
       2  transparent electrode 
       3  phosphor layer 
       4  dielectric layer 
       5  back electrode layer 
       6  cover resist 
       7 A,  7 B external electrode 
       8  EL lamp 
       9  first light-emitter 
       10 ,  13  text light emitter 
       11 ,  14  background light-emitter 
       15 ,  16 ,  17 ,  27 A,  27 B,  29 A,  29 B external electrode 
       18  first transparent electrode layer 
       19 ,  32  first phosphor layer 
       19 A,  22 A part corresponding to text light-emitters  10  and  13   
       19 B,  22 B part corresponding to background light-emitters  11  and  14   
       20  first dielectric layer 
       21 ,  26  second transparent electrode layer 
       22 ,  33  second phosphor layer 
       23  second dielectric layer 
       24 ,  28  back electrode layer 
       25  insulation layer 
       26 A,  28 B text electrode 
       26 B,  28 B background electrode 
       34 ,  36  butterfly 
       35 ,  37  background