Patent Publication Number: US-6659666-B2

Title: Key top assembly integrated with a film

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     This invention relates to a key top assembly which is integrated with a film and is built into the input portion of equipment such as a telephone, a mobile communications device, an acoustic equipment, a television set, a video cassette recorder, a facsimile machine, a copying machine, and an on-vehicle device. 
     2. Related Art 
     In conjunction with the fact that electric and electronic devices have become compact and portable, there is a demand for smaller, thinner and lighter push-button switches for use in the operational portions of such devices. 
     By way of a measure to meet such a demand is known a key top assembly integrated with a film as shown in FIG. 7, wherein required characters and symbols are printed on the upper surface or on the undersurface of a transparent or translucent flexible resin film  17 , and a key top body  18  is attached, by a technique such as fusion or bonding, to the interior of each recess formed by the above-mentioned resin film  17  bent upward. The arrangement of this key top assembly integrated with a film, as it is mounted on a device, is such that each key top body  18  is placed separately from others inside one of the frames of a mounting  19 . 
     In recent years, as regards push button switches used in carrying out a retrieval function of devices such as cellular telephones and portable terminals, there has been a growing demand for a push button switch designed in such a way that a core key top is placed inside an annular key top. In the event that a key top assembly thus designed is mounted on a pertinent device, then it follows that an annular key top and a core key top are placed inside a single frame, with the result that the clearance between the two adjacent key tops is very small. 
     Problems to be Solved by the Invention 
     However, in the case of a prior art key top assembly integrated with a film, wherein the clearance between adjacent key tops is small, when one of the key tops is pressed, at least one of the adjacent key tops becomes interlocked, thus presenting a problem. For the purpose of avoiding the interlocking of adjacent key tops, the two following types are available: a key top assembly integrated with a film as shown in FIG. 8, wherein a groove  20  is formed at approximately the center of that portion of a resin film which is located between adjacent key tops; and a key top assembly integrated with a film as shown in FIG. 9, wherein slits  22  are machined in those portions of a resin film which are located between adjacent key tops. 
     It is true that the interlocking of key tops can be prevented in the case of the above-mentioned types, but it is necessary that the clearance between adjacent key tops be rendered large. Therefore, in the case of an arrangement wherein a plurality of key tops are placed inside one of the frames of a mounting, those portions of a resin film which are located between adjacent key tops are exposed, resulting in a crude appearance. 
     Means To Solve the Problems 
     The present invention, which seeks to solve the above-mentioned problems, provides a key top assembly integrated with a film in which a plurality of key tops can be placed inside one frame and which has the following features: clearances between adjacent key tops are rendered small; no key top interlocks with any other key top; and a good appearance is presented. 
     Namely, in the case of this key top assembly integrated with a film, a core key top is placed inside a circumferential outer key top, and that portion of a resin film which connects the body of the above-mentioned key top to the body of the above-mentioned core key top is formed into a bent shape in such a way that the lower end of this bent portion is located at a position lower than the lower ends of the areas where the above-mentioned resin film is bonded to the bodies of the above-mentioned two key tops. 
     Furthermore, as regards this key top assembly integrated with a film, the interior portion of the base of the above-mentioned circumferential outer key top is cut out, resulting in the interior portion of the above-mentioned base being formed at a position higher than that of the exterior portion of the above-mentioned base. 
     Moreover, as for this key top assembly integrated with a film, the body of the above-mentioned circumferential outer key top is annular. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a top view of the present invention. 
     FIG. 2 is a longitudinal sectional view of an embodiment of the present invention. 
     FIG. 3 is a longitudinal sectional view of another embodiment of the present invention. 
     FIG. 4 shows the operation of a switch of an embodiment of the present invention. 
     FIG. 5 is a longitudinal sectional view of the example of the present invention. 
     FIG. 6 shows the operation of a switch of the example of the present invention. 
     FIG. 7 is a longitudinal sectional view of a prior art key top assembly integrated with a film. 
     FIG. 8 is a longitudinal sectional view of another prior art key top assembly integrated with a film. 
     FIG. 9 is a longitudinal sectional view of yet another prior art key top assembly integrated with a film. 
     FIG. 10 contains top views of two other embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A detailed description of the present invention will be given below by referring to drawings. 
     FIG. 1 is a top view of a typical embodiment of the present invention. As shown in FIG. 1, this embodiment comprises a core key top  2  located at the center and a circumferential outer key top surrounding the outside of the core key top  2  and is built into a frame  3 . 
     By way of specific examples of longitudinal sectional views of embodiments of the present invention, the following views can be enumerated: a longitudinal sectional view as shown in FIG. 2, wherein a resin film  5  is pierced by a push stud  10 ; a longitudinal sectional view as shown in FIG. 3, wherein a key top body  7  made from resin is integrated with a resin film  8  formed over the key top body  7  by being so bent as to have the same shape thereof. In FIG. 8 are shown resin films  5  and  8  which are transparent and the reverse side of each of which has a printed layer (shown hatched). 
     Referring to FIG. 4, a description of the operation of the switch pertaining to the key top assembly integrated with a film, as shown in FIG. 3, will be made. A connection portion  9 , which is part of the resin film  8  and is located between a circumferential outer key top  1  and a core key top  2 , is formed into a bent shape in such a way that the lower end of this bent portion is located at a position lower than the lower end of the area where the resin film  8  is bonded to the key top body  7 . Consequently, when a required key top is depressed, the other adjacent key top does not become interlocked in spite of the fact that that the clearance between the circumferential outer key top  1  and the core key top  2  is small. In fact, when a key top was depressed, it was possible to have a distinct clicking feel caused by a Belleville spring  11 . 
     In the event that those bottom portions of two key top bodies which are adjacent to each other are cut out to form cutouts  16  shown in FIG. 5, then the switch stroke can be adjusted appropriately depending on the dimension of a height h, as is evident from the description given of the switch operation in FIG.  6 . Furthermore, the depth of drawing required to bend downward that portion of the resin film  8  which is located between the two key tops is less than in the case of the embodiment shown in FIG. 3, thereby facilitating drawing work. 
     The cross-sectional shape of that connection portion of the resin film of the present invention that is formed into a bent shape may comprise either a curved portion only or a combination of a curved portion and of a straight portion. However, in the event that the above-mentioned connection portion comprises a curved portion only, then the clearance between the key tops can be rendered smaller than otherwise. 
     The shape of that circumferential outer key top of the present invention which surrounds the outside of the core key top may be either annular or polygonal as shown in FIGS. 1 and 10. 
     Embodiment 
     The description of the example of the present invention is as follows. As shown in FIG. 5, which is a longitudinal sectional view of the example of the present invention, a circumferential outer key top  1  is an annular key top, inside which was formed a core key top  2 . 
     In this case, the arrangement of the key top assembly integrated with a film is as follows. On the undersurface of a transparent resin film  13  made from polyethylene terephthalate are printed some symbols to provide an indication portion. Also printed on the above-mentioned undersurface is a layer which is colored white. The resin film  13  was drawn by means of a jig into an upward bent shape, and then polycarbonate resin was injection-molded inside the resulting bent portion, thereby forming a key top body  12 . The bottom face of the body of the circumferential outer key top  1  was formed at a high position by being cut out. The bottom face of the body of the core key top  2  was formed at the same height as that of the bottom face of the body of the circumferential outer key top  1 . Moreover, a connection portion  14 , which is part of the resin film  13  and is located between the body of the circumferential outer key top  1  and the body of the core key top  2  was formed into a bent shape in such a way that the lower end of this bent portion is located at a position lower than lower ends  16  of the area where the resin film  13  is bonded to cutouts  15  of the body of the circumferential outer key top  1  and of the body of the core key top  2 . 
     FIG. 6 shows the operation of a switch of this example. When the key top was depressed, as shown in FIG.  6 ( a ), it was possible to have a distinct clicking feel caused by a Belleville spring  11  placed underneath a push stud  10 . When each of the four indication portions provided on the annular key top  1  was depressed, as shown in FIG.  6 ( b ), the core top key  2  did not go so far as to press the Belleville spring  11 , thus avoiding interlocking. 
     According to the present invention, that portion of a resin film which is located between a circumferential outer key top and a core key top is formed by being bent downward, thereby being capable of providing a compact key top assembly integrated with a film whereby: 
     no key top interlocks with any adjacent key top even if the clearance between key tops is rendered small; and moreover, 
     a good appearance is presented. 
     Another advantageous effect, among others, of this arrangement, which it was not possible to embody until now, is that inside an annular key, another key top having a different function can be placed, thereby permitting a plurality of key tops to be placed inside one frame. 
     Furthermore, since that portion of the resin film which is located between key tops is formed into a bent shape, any key top returns to its original position after being pressed. 
     Moreover, the since the structure of the metal mold for molding key tops are simplified, it becomes possible to increase the rate of turnout of products, thereby permitting production costs to be reduced.