Patent Publication Number: US-6670750-B2

Title: Luminous EL sheet having a domed diaphragm and a switch employing the EL sheet

Description:
TECHNICAL FIELD 
     The present invention relates to an EL sheet employed as a back light in an operating section of various electronic apparatuses, and to a switch employing the EL sheet. 
     BACKGROUND ART 
     Electronic apparatuses, as being diversified recently, includes a switch-key to be identified and operable even in a dark place. The switch-key includes a back light disposed at a rear part of an operating section. Many of the back lights employ EL sheets. A switch including the conventional EL sheet discussed above will be described hereinafter with reference to FIG. 7, in which dimensions in a thickness direction are enlarged for better understanding. 
     FIG. 7 shows a lateral sectional view of the switch employing an EL sheet. Light-transmissible insulating film  1  made of, e.g., polyethylene terephtalate has domed diaphragm  2 , which swells upward, formed at a given place. Beneath the entire lower face of film  1 , light-transmissible electrode layer  3 A, made of tin indium oxide, is formed by a spattering or an electron beam method. 
     Luminous layer  3 B, dielectric layer  3 C, back electrode layer  3 D, and insulating layer  3 E are laid one after another beneath layer  3 A by printing beneath layer  3 A except bent section  2 A around the root of diaphragm  2 , so that EL element layer  3 , as a whole, may be constructed. Luminance layer  3 B includes high dielectric resin, made of fluoro rubber or cyano-system resin in which zinc sulfide, which is a base material for light emission, is dispersed. Dielectric layer  3 C includes high dielectric resin in which barium titante is dispersed. Back electrode layer  3 D is made of silver or carbon resin system. Insulating layer  3 E is made of epoxy resin or polyester resin. 
     Beneath EL element layer  3 , formed on the lower face of diaphragm  2 , a movable contact  4  is printed, so that EL sheet  5 , as a whole, may be constructed. Movable contact  4  is made of epoxy resin or polyester resin in which conductive particles such as silver or carbon are dispersed. 
     Circuit board  6  made of an insulating film such as polyethylene terephtalate is disposed under EL sheet  5 , and a pair of fixed contacts  6 A—facing movable contact  4  with a given clearance—are disposed on the upper face of board  6 . Plural wiring patterns (not shown) are coupled to fixed contacts  6 , so that a switch as a whole may be constructed. 
     Beneath insulating film  1 , having an entire lower face covered with light-transmissible electrode layer  3 A, EL element layer  3 , which includes luminous layer  3 B, dielectric layer  3 C, back electrode layer  3 D and insulating layer  3 E, is printed. Movable contact  4  is also printed on the top of that. Then diaphragm  2  is formed using a mold, so that EL sheet  5  may be completed. EL sheet  5  is bonded to circuit board  6  with adhesive or by thermal bonding so that the switch may be completed. 
     The switch is mounted to an operating section of an electronic apparatus, and an alternating current (AC) voltage from a circuit of the apparatus is applied between light-transmissible electrode layer  3 A and back electrode layer  3 D of EL sheet  5 , so that luminous layer  3 B may emit light. The light illuminates the operating section of the apparatus from the back of the operating section, and thus a user can identify and operate the operating section easily even in a dark place. 
     Diaphragm  2  is depressed from above the diaphragm through, e.g., a key-button, then diaphragm  2  is bowed on a fulcrum, i.e., bent section  2 A or its vicinity with a click feel, and thereby, movable contact  4  moves downward to contact with fixed contacts  6 A. Movable contact  4  thus contacts electrically with fixed contacts  6 A. When the depression is released, diaphragm  2  is restored to the status shown in FIG. 7 by resilient restoring force of the diaphragm. 
     The conventional EL sheet in the switch includes light-transmissible electrode layer  3 A made of metallic hard film formed beneath the entire face of insulating film  1 . This structure degrades the click feel and the flexibility of diaphragm  2  during operation. Thus, light-transmissible electrode layer  3 A may crack when diaphragm  2  is formed or depressed repeatedly. Further, the depressing force through diaphragm  2  tends to change. 
     SUMMARY OF THE INVENTION 
     An EL sheet generates a stable click feel during an operation and is easy to be processed. A switch employs the EL sheet. The EL sheet includes the following elements: 
     (a) a light-transmissible insulating film having a domed diaphragm swelling upward; 
     (b) an EL element layer including a light-transmissible electrode layer, a luminous layer, a dielectric layer, and a back electrode layer laminated beneath the insulating film in this order except at a bent section and its vicinity around the root of the diaphragm; 
     (c) a first conductive pattern coupled to the light-transmissible electrode layer and formed beneath the insulating film; and 
     (d) a second conductive pattern being coupled to the back electrode layer and formed beneath the insulating film. 
     The switch includes the EL sheet and contacts being disposed under the diaphragm to resiliently and electrically contact each other. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a lateral sectional view of a switch employing an EL sheet in accordance with a first exemplary embodiment of the present invention. 
     FIG. 2 is a cross sectional view of the EL sheet. 
     FIG. 3 is a cross sectional view of the EL sheet. 
     FIG. 4 is a lateral sectional view of the EL sheet. 
     FIG. 5 is a lateral sectional view of the EL sheet. 
     FIG. 6 is a lateral sectional view of a switch employing an EL sheet in accordance with a second exemplary embodiment of the present invention. 
     FIG. 7 is a lateral sectional view of a switch employing a conventional EL sheet. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Exemplary embodiments of the present invention will be explained hereinafter with reference to the accompanying drawings, FIG.  1  through FIG.  6 . For easy understanding, the dimensions in a thickness direction are enlarged. Elements similar to those used in the background art are denoted by the same reference numerals, and detailed descriptions thereof are thus omitted here. 
     Exemplary Embodiment 1 
     FIG. 1 is a lateral sectional view of a switch employing an EL sheet in accordance with a first exemplary embodiment of the present invention. FIG. 2 is a cross sectional view of the EL sheet. Light-transmissible insulating film  1 , made of, e.g., polyethylene terephtalate, swells upward at a given place, so that domed diaphragm  2  may be formed. Light-transmissible electrode layer  13 A is printed beneath diaphragm  2  and the flat section of insulating film  1 , except for bent section  2 A and its vicinity around the root of diaphragm  2 . Light-transmissible electrode layer  13 A is made of light-transmissible resin such as phenoxy resin, epoxy resin, or fluoro rubber, in which conductive particles such as tin indium oxide, tin oxide or indium oxide are dispersed. Beneath layer  13 A, luminous layer  3 B, dielectric layer  3 C, back electrode layer  3 D and insulating layer  3 E are formed by printing one after another in this order, so that EL element layer  13 , as a whole, may be constructed. Luminance layer  3 B includes high dielectric resin, made of fluoro rubber or cyano-system resin, in which zinc sulfide, which is a base material for light emission, is dispersed. Dielectric layer  3 C includes high dielectric resin, in which barium titante is dispersed. Back electrode layer  3 D is made of a silver or carbon resin system. Insulating layer  3 E is made of epoxy resin or polyester resin. 
     Further, conductive patterns  14 A and  14 B have respective first ends coupled to layer  13 A and layer  3 D, and run through bent section  2 A. Second ends of conductive patterns  14 A and  14 B extend to a tail section (not shown) protruding from the outward appearance. Conductive patterns  14 A and  14 B are formed by printing epoxy resin or polyester resin in which silver or carbon is dispersed. 
     Beneath EL element layer  13  formed on the lower face of diaphragm  2 , movable contact  4  is printed, so that EL sheet  15 , as a whole, may be constructed. Movable contact  4  is made of epoxy resin or polyester resin, in which silver or carbon is dispersed. 
     Circuit board  6  made of insulating film such as polyethylene terephtalate is disposed under EL sheet  15 , and a pair of fixed contacts  6 A, which face movable contact  4  via a given clearance, are disposed on the upper face of board  6 . Plural wiring patterns (not shown) are coupled to fixed contacts  6 , so that a switch as a whole may be constructed. EL sheet  15  is bonded to circuit board  6  with adhesive or by thermal bonding, so that the switch may be completed. 
     In the structure discussed above, the switch is mounted to an operating section of an electronic apparatus, and an AC voltage is supplied from a circuit of the apparatus to conductive patterns  14 A and  14 B coupled respectively to light-transmissible electrode layer  13 A and back electrode layer  3 D of EL sheet  15 . The voltage causes layer  3 B to emit light. The light illuminates the operating section of the apparatus from behind the operating section, and a user can thus identify and operate the operating section easily even in a dark place. 
     Diaphragm  2 . is depressed from above the diaphragm through a key-button, then diaphragm  2  is bowed with a click feel on a fulcrum, i.e., bent section  2 A or its vicinity, where only conductive patterns  14 A and  14 B are formed, thereby moving movable contact  4  downward to contact with fixed contact  6 A. Movable contact  4  thus contacts electrically with fixed contact  6 A. When the depression is released, diaphragm  2  is restored to the status shown in FIG. 1 by the resilient restoring force of the diaphragm. 
     According to the first embodiment, EL element layer  13  is not formed at bent section  2 A and its vicinity which functions as a fulcrum, where diaphragm  2  is bowed by a depression. But only conductive patterns  14 A and  14 B, which are flexible, are formed in this area. Thus, the sheet generates a stable click feel during operation, and has diaphragm  2  which is easy to be processed. As a result, an EL sheet, and a switch employing the EL sheet with a stable click feel, are obtainable. 
     Light-transmissible electrode layer  13 A is formed by printing flexible light-transmissible resin in which conductive particles are dispersed, so that the resin may increase the flexibility of diaphragm as a whole. Thus, the switch generates a better click feel during operation. 
     Since movable contact  4  is formed on the lower face of the EL element layer disposed beneath diaphragm  2 , the switch can be constructed easily by just combining circuit board  6  including fixed contacts  6 A with EL sheet  15 . 
     As shown in the cross sectional view of FIG. 3, respective conductive patterns can be formed integrally with layer  13 A and layer  3 D. In this case, a conductive pattern coupled to layer  13 A and the other conductive pattern coupled to layer  3 D can be printed simultaneously. Thus the number of printings to form the EL element layer can be reduced, which lowers the cost of the EL sheet. 
     In the above description, EL element layer  13  is formed beneath diaphragm  2  and a flat section of insulating film  1  except at bent section  2 A and its vicinity around the root of diaphragm  2 . However, as shown in FIG. 4, EL element layer  13  can be formed only beneath diaphragm  2 . Further, as shown in FIG. 5, EL element layer  13  can be formed only beneath the flat section of insulating film  1 , and only movable contact  4  can remain beneath diaphragm  2 . In these cases, the conductive patterns are not formed at bent section  2 A or its vicinity functioning as a fulcrum around the root of diaphragm  2 , and insulating film  1  exposes itself, thereby further increasing the flexibility. As a result, a more stable and moderate feeling can be obtained. 
     Exemplary Embodiment 2 
     The elements similar to those in the first embodiment are denoted by the same reference numerals, and the detailed descriptions thereof are thus omitted here. FIG. 6 is a lateral sectional view of a switch employing an EL sheet in accordance with a second exemplary embodiment of the present invention. Diaphragm  2  is formed in insulating film  1 . EL element layer  13  is formed beneath diaphragm  2  and insulating film  1  except at bent section  2 A and its vicinity around the root of diaphragm  2 . This structure is the same as that of embodiment  1 . Conductive patterns are respectively coupled to light-transmissible electrode layer  13 A and back electrode layer  3 D of EL element layer  13 , similar to embodiment  1 . 
     EL sheet  16  has no movable contact formed beneath EL element layer  13 . Beneath EL sheet  16 , is disposed switch contact  22  of a membrane type being placed on insulating substrate  21 , and thereby forming a switch. This membrane switch contact  22  includes upper sheet  23  and lower sheet  24 . Upper sheet  23  includes flexible insulating film  23 A and movable contact  23 B formed beneath film  23 A under the center of diaphragm  2 . Lower sheet  24  includes insulating film  24 A and fixed contact  24 B, which faces movable contact  23 B, formed on film  24 A. Movable contact  23 B is formed on upper sheet  23  and made of epoxy resin or polyester resin in which silver or carbon is dispersed. 
     Upper sheet  23  is bonded to lower sheet  24  with adhesive (not shown) applied on both faces of an insulating film  25 A, which is a part of a spacer  25 . Between movable contact  23 B and fixed contact  24 B, a given clearance is provided at opening  25 B. 
     The switch is mounted to an operating section of an electronic apparatus, and an alternating current (AC) voltage is applied from a circuit of the electric apparatus between light-transmissible electrode layer  13 A and back electrode layer  3 D, so that EL sheet  16  may emit light similarly to the first embodiment. 
     Diaphragm  2  is depressed from above the diaphragm through a key-button, then diaphragm  2  is bowed with a click feel on a fulcrum, i.e., bent section  2 A and its vicinity, similarly to the first embodiment. At this moment, the lower face of diaphragm  2  is pushed to upper sheet  23  via EL element layer  13 , and upper sheet  23  of membrane-switch contact  22  bows downward at opening  25 B. Movable contact  23 B is thus moved downward to contact with fixed contact  24 B, thereby making electrical contact between movable contact  23 B and fixed contact  24 B. When the depression is released, diaphragm  2  is restored to the status shown in FIG. 6 by the resilient restoring force of the diaphragm. 
     According to the second embodiment, switch contact  22 , which turns on and off by depression, is disposed under diaphragm  2  of EL sheet  16 . Thus, a switch generating a stable click feel and having excellent flexibility can be provided. 
     Instead of membrane-switch contact  22 , an independent push switch can be combined with EL sheet  16 , or a pressure sensitive resistor, in which the resistor value is changed by depression, can be combined with EL sheet  16  to effect the advantage of the present invention. These combinations produce various switches, and thus various electrical signals can be generated. 
     Light-transmissible electrode layer  13 A is formed by printing light-transmissible resin in which conductive particles are dispersed. Instead of this method, a light-transmissible electrode layer may be once formed beneath the entire insulating film  1  by a spattering or an electron beam method, and then the light-transmissible electrode layer can be formed at a given place by etching. 
     The present invention relates to an EL sheet employed as a back light in an operating section of various electronic apparatuses, and a switch employing the EL sheet. The EL sheet can be processed easily and can generate a stable click feel and can provide a switch employing the EL sheet.