Push-button switch and keytop

Abstract: The keytop of a push-button switch includes a keytop portion situated on the top side of a resin film at a prescribed position thereof, and a retaining portion situated on the underside of the resin film at the prescribed position. The keytop portion and retaining portion are formed into a unitary body by resin-molding through a hole provided in the resin film, and the resin film is sandwiched between the keytop portion and the retaining portion. In another embodiment, the retaining portion is loop-shaped and is formed into a unitary body with the keytop portion by resin-molding through a plurality of holes provided in the resin film along the loop-shaped circumference of the retaining portion. The resin film is sandwiched in a water-tight state between the keytop portion and the loop-shaped retaining portion.

Description: This invention relates to the keytop of a push-button switch, and the push-button switch which uses the keytop. A keytop of the type according to the pre-characterising part of claim 1 is known from US-A-4 799 083. The reduction in the size of electronic devices that has been achieved in recent years has been accompanied by a demand to reduce the size and thickness also of the push-button switches used on the control panels of these devices. In addition, electronic devices often are used in a variety of environments, and there is a need for a push-button switch having a so-called drip-proof structure, namely a structure which prevents humidity and moisture from penetrating into the contact portion of the switch from the outside. The conventional keytop of the push-button switch of this type is complicated in structure, has a large number of component parts and possesses a hinge mechanism of a prescribed length. Consequently, such a keytop does not lend itself to a reduction in size and thickness. In addition, a keytop of this kind is not well suited for use in a switch having the aforementioned drip-proof structure which prevents external humidity and moisture from invading the contact portion through the keytop. The present invention has been devised in view of the foregoing points and its object is to provide a keytop of a push-button switch suited to a reduction in size and thickness, as well as a method of manufacturing such a keytop. Another object of the present invention is to provide an outstanding push-button switch having a drip-proof structure in which the penetration of humidity and moisture from the side of the keytop can be prevented, the number of component parts is few and which lends itself to a reduction in size and thickness, as well as keytop of this push-button switch and a method of manufacturing the keytop. According to the present invention, there is provided a keytop of a push-button switch according to claim 1. Other preferred features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. Figs. 1(A) through 1(C) are diagrams illustrating a first embodiment of the structure of a keytop of a push-button switch according to the present invention, in which Fig. 1(A) is a plan view, Fig. 1(B) a sectional view taken along line 1(B) - 1(B) of Fig. 1(A), and Fig. 1(C) a bottom view; Fig. 2 is a partial sectional view showing the structure of a push-button switch which uses the keytop of the present invention; Fig. 3 is a plan view showing a control panel of push-button switches having the keytop structure and drip-proof frame structure of the present invention; Fig. 4 is a sectional view taken along line 4-4 of Fig. 3; Fig. 5 is an underside view of the control panel of the push-button switches, in which the keytop structure and the structure of the drip-proof frame are illustrated; Fig. 6 is a sectional view taken along line 6-6 of Fig. 3; Fig. 7 is a plan view showing the shapes of holes in a resin film; Fig. 8 is a diagram showing the shapes of holes in a resin film which forms a keytop; Fig. 9 is a diagram for describing a method of manufacturing the keytop; Fig. 10 is a diagram for describing a method of manufacturing the drip-proof frame; Figs. 11(A) through 11(D) are diagrams illustrating a second embodiment of the structure of a keytop of a push-button switch according to the present invention, in which Fig. 11(A) is a plan view, Fig. 11(B) a sectional view taken along line 11(B) - 11(B) of Fig. 11(A), Fig. 11(C) a bottom view, and Fig. 11(D) is a plan view of a resin film provided with holes; Fig. 12 is a diagram showing a third embodiment of a push-button switch having a drip-proof structure according to the present invention; Fig. 13 is a plan view showing a switch control panel; Fig. 14 is a sectional view taken along line 20-20 of Fig. 13; Fig. 15 is an underside view of the switch control panel; Fig. 16 is a sectional view taken along line 22-22 of Fig. 13; Figs. 17(A) to 17(C) are plan, sectional and underside views, respectively, of a keytop according to the present invention; Fig. 18 is a plan view showing the shapes of holes in a resin film; Fig. 19 is a plan view showing the shape of upper and lower resin sheets constituting a switch portion; 20 Fig. 20 is a diagram for describing the resin mold of a keytop; Fig. 21 is an exploded, perspective view showing a fourth embodiment of the structure of a push-button switch using the keytop of the invention; Fig. 22 is an enlarged perspective view of a portion of a switch sheet shown in Fig. 21; Fig. 23 is a perspective view showing the underside of a keytop sheet; Fig. 24 is a perspective view showing a film; Figs. 25(A) to 25(C) are diagrams illustrating a method of molding a keytop on a film, in which Fig. 25(A) is a diagram showing the manner in which a film is clamped by upper and lower molds, Fig. 25(B) is a diagram illustrating the manner in which the upper and lower molds are filled with a synthetic resin, and Fig. 25(C) is a diagram showing a molded keytop; Fig. 26 is a side sectional view showing an assembled push-button switch: Fig. 27 is an enlarged side sectional view showing a portion of one push-button switch within a push-button switch; Fig. 28 is a side sectional view for describing operation of the push-button switch; Fig. 29 is a perspective view showing a fifth embodiment of the structure of a keytop sheet according to the present invention; Figs. 30(A), 30(B), 30(C) and 30(D) are a plan view showing the keytop sheet of Fig. 29, an underside view of the keytop sheet, an enlarged sectional view taken along line 36(C) - 36(C) of Fig. 30(A), and an enlarged sectional view taken along line 36(D) - 36(D) of Fig. 36(A), respectively; and Figs. 31(A) to 31(C) are diagram for describing a method of manufacturing the keytop sheet, in which Fig. 31(A) is a diagram showing a flexible film, Fig. 31(B) is a diagram showing the manner in which patterns are printed on the film, and Fig. 31(C) is a diagram showing the manner in which patterns are formed on the film as well as the manner in which openings and through-holes are provided in the film. Figs. 1(A) to 1(C) are diagrams illustrating a first embodiment of the structure of a keytop of a push-button switch according to the present invention. As shown in Figs. 1(A) through 1(C), a keytop 12 includes a keytop portion 12b situated on the top side of a resin film 10, and a loop-shaped retaining portion 12c situated on the underside of the resin film. The loop-shaped portion 12c, which is located directly below the keytop portion 12b in concentric relation therewith, is circular and extends along the outer circumference of the bottom surface of the keytop portion 12b. As will be described later in greater detail, the keytop portion 12b and loop-shaped retaining portion 12c are integrally formed by resin-molding through a plurality of holes provided in the resin film 10 along the loop-shaped retaining member 12c, and the resin film 10 is water-tightly sandwiched between the keytop portion 12b and the loop-shaped portion 12c. A polycarbonate resin or acrylic resin, which are thermoplastic resins, may be used as the material for the keytop 12. The keytop 12 has a pressing protrusion 12a, which is for pressing a movable contact, provided as an integral part of the loop-shaped retaining member 12c spaced away from the center of the button surface of the keytop portion 12b. Thus, the pressing protrusion 12a for pressing the movable contact is provided at a position offset from the center of the bottom surface of keytop portion 12b. As a result, it is unnecessary to dispose the contact portion of the switch below the center of the bottom surface of pressing protrusion 12a. Accordingly, by using a keytop material through which light can pass, as will be described later, the surface of the keytop can be made to stand out by light from a light-emitting element if such an element is placed below the central portion of the bottom of the keytop portion 12b. More specifically, by printing a number, symbol or other indicia on the portion of the resin film 10 at which the keytop portion 12b is located, the number, symbol or indicia will be clearly visible through the keytop portion 12b. Such a keytop presents an excellent appearance. Though the material of the keytop 12 is a light-transmissive resin which is illuminated by a light-emitting element in the foregoing embodiment, the indicia on the keytop can readily be seen from the outside even without being illuminated by a light-emitting element. Fig. 2 is a diagram illustrating an example of the structure of a push-button switch using the keytop 12 having the structure described above. In Fig. 2, numerals 16, 17 denote films on which a movable contact pattern 16a and a fixed contact pattern 17a, respectively, are formed. The films 16, 17 are superimposed with the contact patterns 16a, 17a made to oppose each other through the intermediary of a spacer interposed therebetween, and the films 16, 17 are secured to the lower portion of a drip-proof frame 11. A click spring 19 is disposed on the top side of the film 16 at the position where the contact pattern 16a is located, and the pressing protrusion 12a of the keytop 12 is situated on the upper portion of the click spring 19. A light-emitting element 23, such as a light-emitting diode, is disposed below the center of the keytop portion 12b. The aforementioned drip-proof frame 11 surrounds a plurality of the keytops 12 and is maintained in a water-tight state with respect to the resin film 10, as will be described later. The assembly which includes the keytops 12, drip-proof frame 11 and films 16, 17 defines a control panel 1, which is housed in a case 15. A panel 14 is placed upon the upper portion of the case 15 and is provided with an elongated projection 14a that is water-tightly fitted into an elongated groove 11a formed in the drip-proof frame 11. The material constituting the drip-proof frame 11 is a thermoplastic or thermosetting synthetic resin. In order to improve the water-tight fit of the frame 11, the material constituting the frame preferably is a resilient styrene-type elastomer or a resilient polyester elastomer. By adopting the foregoing structure for the push-button switch, humidity or moisture which seeps in from the gap between the keytop 12 and the panel 14 will not reach the switch contact portion because the keytop 12 and drip-proof frame 11 are water-tightly affixed to the resin film 10. In addition, since the elongated groove 11a and elongated projection 14a are fitted together water tightly, moisture will not penetrate from between the drip-proof frame 11 and panel 14. The push-button switch thus has a structure exhibiting an excellent drip-proof property. Figs. 3 through 6 are diagrams illustrating the structure of the control panel 1 of the push-button switches obtained by molding the drip-proof frame 11 and keytops 12 with the resin film. Fig. 3 is a plan view, Fig. 4 a sectional view taken along line 4-4 of Fig. 3, Fig. 5 an underside view of the control panel 1, and Fig. 6 a sectional view taken along lines 6-6 of Fig. 3. As shown in these drawings, the drip-proof frame 11 surrounds a plurality (six in this embodiment) of the keytops 12 and is maintained in a water-tight state with respect to the resin film 10. More specifically, as shown in Fig. 6, the drip-proof frame 11 includes an upper portion 11b and a lower portion 11c formed to sandwich the resin film 10 between them, and the elongated groove 11a, which has a rectangular cross section, is formed in the top side of the upper portion 11b. Further, as depicted in Fig. 5, the underside of the drip-proof frame 11 is integrally formed to have fixing portions 13 for being fixed to a substrate or the like. Here the drip-proof frame 11 is such that the resin film 10 is sandwiched between the loop-shaped upper portion 11b and loop-shaped lower portion 11c, and the upper portion 11b and lower portion 11c are merely connected through holes 20 shown in Figs. 6 and 7. Consequently, humidity and moisture cannot seep in from between the drip-proof frame 11 and the resin film 10. In other words, a water-tight structure which keeps out humidity and moisture is formed between the resin film 10 and the drip-proof frame 11. Described next will be a method of manufacturing the switch control panel 1 obtained by integrally molding the drip-proof frame 11 and keytop 12 with the resin film 10. Fig. 7 is a plan view showing the external form of the resin film 10. As shown in Fig. 7, the resin film 10 is rectangular in shape and the portion thereof on which the drip-proof frame 11 is formed is provided at prescribed intervals with a number of holes 20 through which molten resin flows at the time of molding. As illustrated in Fig. 8, holes 21 for forming the keytop 12 include small holes 21a and one large hole 21b in a circular array, as shown in Fig. 7. The small holes 21a are situated at ribs 12d of the keytop 12, and the large hole 21b is situated at the protrusion 12a of the keytop 12. A number, symbol or character 24 is printed on the resin film 10 at a portion thereof where the keytop portion 12b is located. The printing can be performed on either the top side of the resin film 10, namely on the side having the keytop, or on the underside of the resin film 10. In either case, the number, symbol or character will be clearly visible. A method of manufacturing the keytop 12 will now be described. First, as shown in Fig. 9, the resin film 10 is clamped between an upper mold 105 having a cavity 110 of the same shape as the keytop 12 (see Fig. 1) and a lower mold 106 having a cavity 111 of the same shape as the annular retaining portion 12c (see Fig. 1). Next, a molten resin is injected from a pin gate 107 provided at a location above the protrusion 12a of the keytop 12. As a result, the molten resin flows into the cavity 110 of the upper mold 105 and also into the cavity 111 of the lower mold 106 through the holes 21a, 21b in the resin film 10. When the upper mold 105 and lower mold 106 are parted after the resin has hardened, the result is the keytop 12. A method of manufacturing the drip-proof frame 11 will be described next. First, as depicted in Fig. 10, the resin film 10 is clamped between an upper mold 101 having a cavity 112 of the same shape as the upper portion 11b of the frame (see Fig. 6) and a lower mold 102 having a cavity 113 of the same shape as the lower portion 11c of the frame (see Fig. 6). Next, a molten resin is injected from a pin gate 103, whereby the molten resin flows into the cavity 112 of the upper mold 101 through a resin reservoir 22 and also into the cavity 113 of the lower mold 102 through the holes 20 in the resin film 10. When the upper mold 101 and lower mold 102 are parted after the resin has hardened, the result is the drip-proof frame 11, which surrounds a prescribed area of the resin film 10. Figs. 11(A) through 11(D) are diagrams illustrating a second embodiment of the structure of a keytop of a push-button switch according to the present invention, in which Fig. 11(A) is a plan view, Fig. 11(B) a sectional view taken along line 11(B) - 11(B) of Fig. 11(A), Fig. 11(C) a bottom view, and Fig. 11(D) is a plan view of a resin film provided with holes. A keytop 12-2 shown in Fig. 11(A) differs from the keytop 12 of Fig. 1 in that whereas the pressing protrusion 12a for pressing the movable contact of the keytop 12 is provided as an integral part of the loop-shaped retaining portion 12c offset from the center of the lower portion of the keytop portion 12b in Fig. 1(A), the keytop of Figs. 11(A) - 11(D) is such that a pressing protrusion 12-2a is provided passing through the resin film 10-2 approximately at the center of the lower portion of the keytop portion 12-2. Furthermore, since the pressing protrusion 12-2a is formed approximately at the center of the lower portion of the keytop portion 12-2, the resin film 10-2 at the location situated at the center of the keytop 12-2 is cut away in the form of a circle. It should be noted that the shapes of the keytop portions 12b, 12-2b of the keytops 12 and 12-2 are not limited to those described in the foregoing embodiments. For example, it goes without saying that the planar configuration can be rectangular or polygonal and need not be circular. In this case, the retaining portions 12c, 12-2c also should have a rectangular or polygonal loop shape to conform to the shape of the keytop portion. In addition, the shape of the drip-proof frame 11 is not limited to that described above. For example, if the drip-proof frame is made of an elastomer having resilience, then a structure may be adopted in which the panel 14 is made flat, the surface of the drip-proof frame 11 is made a curved surface having the shape of semicircular cylinder, and the panel 14 and frame 11 are brought into pressured contact. In other words, it will suffice if the loop-shaped drip-proof frame 11 forms a water-tight seal together with the resin film by being molded onto the resin film so as to surround a prescribed area of the film. Fig. 12 is a sectional view showing a third embodiment of a push-button switch according to the present invention. In Fig. 12, numeral 29 denotes a substrate, whose top side is a curved surface, placed upon the corner portion of the case of an electronic appliance. Upper and lower resin sheets 16-5, 17-5 having a spacer 18-5 interposed between them are arranged on the top side of the substrate 29. The lower resin sheet 17-5 is formed to have a fixed-contact pattern 17-5a of a switch, and the upper resin sheet 16-5 is formed to have a movable contact 16-5a of the switch. The fixed contact 17-5a and the movable contact 16-5a oppose each other. A click spring 19 is disposed on the position formed with movable contact of the upper resin film 16-5, and a keytop 12-5 provided water-tightly on the resin film 10-5 is disposed on the click spring 19-5, as will be described later in greater detail. Numeral 11-5 denotes a drip-proof frame provided water-tightly on the resin film 10-5 so as to surround a prescribed area of the film, as will be described later. Numeral 14-5 designates the aforementioned panel, which defines a curved surface. The upper portion of the keytop 12-5 penetrates a hole 24A provided in the panel 12-5 and is exposed from above. As will be set forth later, the drip-proof frame 11-5 and the panel 14-5 are fitted together in a water-tight state by means of mating a projection with a groove. The drip-proof frame 11-5 also is attached to the substrate 29 in a water-tight state. The arrangement is such that pressing the keytop 12-5 causes the movable contact 16-5 to come into abutting contact with the fixed contact 17-5a. As will be set forth below, the keytop is attached to the resin film 10-5 in a water-tight state, and the drip-proof frame 11-5 is attached to the resin film 10-5 in a water-tight state. As a result, the structure is such that moisture or humidity which seeps in from holes in the panel 14-5 will not invade the contact portion, which comprises the resin sheet 16-5, 17-5 and the like. The structure of each portion of the push-button switch constructed as set forth above will now be described in detail. As illustrated in Figs. 13 to 16, the loop-shaped drip-proof frame 11-5 is formed on the resin film 10-5 by being molded with the film 10-5 in a water-tight state so as to surround a prescribed area of the film. The keytop 12-5 is formed within the drip-proof frame 11-5 in a water-tight state with respect to the resin film 10-5. As shown in Fig. 16, the drip-proof frame 11-5 has an upper portion 11-5b and a lower portion 11-5c which sandwich the resin film 10-5 between them. The top side of the upper portion 11-5b is formed to have an elongated groove 11-5a having a rectangular cross section, and a fixing portion 11-5d for being fixed to the substrate is formed as an integral part of the underside of the drip-proof frame 11-5. Here the drip-proof frame 11-5 is formed so that the resin film 10-5 is sandwiched between the loop-shaped upper portion 11-5b and loop-shaped lower portion 11-5c, and the upper and lower portions 11-5b, 11-5c are integrally connected through a hole 20-5 formed in the resin film 10-5. Consequently, humidity and moisture cannot seep in from between the drip-proof frame 11-5 and the resin film 10-5. In other words, a water-tight structure which keeps out humidity and moisture is formed between the resin film 10-5 and the drip-proof frame 11-5. The material constituting the drip-proof frame 11-5 is a resilient synthetic resin, such as a styrene-type elastomer or a polyester elastomer. As depicted in Figs. 17(A) - (C), the keytop 12-5 includes a keytop portion 12-5b formed on the upper portion and an annular retaining portion 12-5c on the lower portion so as to sandwich the resin film 10-5, and the underside is formed to have a protrusion 12-5a for pressing the movable contact of the switch. The material constituting the keytop 12-5 consists of a thermoplastic resin, namely polycarbonate resin or acrylic resin. Here the keytop 12-5 is such that the resin film 10-5 is sandwiched between the keytop portion 12-5b and the annular retaining portion 12-5c, and the keytop portion 12-5b and annular retaining portion 12-5c are integrally connected through a hole 21-5 shown in Fig. 17(B). Fig. 18 is a plan view of a resin film 10-5 having the holes 20-5 for molding the drip-proof frame 11-5, the holes 21-5 for molding the keytops 12-5, and holes 22 to project the protrusions 12-5a. Consequently, humidity and moisture cannot seep in from between the keytop 12-5 and the resin film 10-5. In other words, a water-tight structure which keeps out humidity and moisture is formed between the resin film 10-5 and the keytop 12-5. Fig. 19 is a plan view showing the shapes of the upper and lower resin sheets 16-5, 17-5. As shown in Fig. 19, the upper and lower resin sheets 16-5, 17-5 are formed by cutting a single resin sheet. Formed on the lower resin sheet 17-5 are fixed-contact patterns 17-5a, 17-5a, 17-5a and a wiring pattern 17-5b serially connecting the fixed-contact patterns 17-5a, 17-5a, 17-5a. Formed on the upper resin sheet 16-5 are movable-contact patterns 16-5a, 16-5a, 16-5a and wiring patterns 16-5b, 16-5b, 16-5b connected to respective ones of the movable-contact patterns 16-5a, 16-5a, 16-5a. In order to facilitate folding, the upper resin sheet 16-5 is provided with grooves 25-5 between the movable-contact patterns 16-5a, 16-5a. Cut-outs 23-5 are formed between the upper resin sheet 16-5 and the lower resin sheet 17-5. Contact portions are formed by folding the upper resin sheet 16-5 and lower resin sheet 17-5 about the cut-outs 23-5 through the intermediary of a spacer, which is not shown. The formation of the keytop 12-5 by resin molding will be described below. As depicted in Fig. 20, the resin film 10-5 is clamped between an upper mold 105-5 having a cavity 110-5 of the same shape as the keytop portion 12b [see Figs. 17(A) to 17(C)], and a lower mold 106-5 having a cavity 111-5 of the same shape as the annular retaining portion 12-5c [see Figs. 17(A) to 17(C)] and a cavity 112-5 of the same shape as a protrusion 18-5a. Next, a molten resin is injected from a pin gate 107-5, whereby the molten resin flows into the cavity 110-5 of the upper mold 105-5 and the cavity 112-5 of the lower mold 106-5. The molten resin flows also into the cavity 111-5 of the lower mold 106-5 through holes 21-5 in the resin film 16-5. The keytop 12-5 is formed by allowing the molten resin to harden. The formation of the drip-proof frame 11-5 is substantially the same as the method described in connection with Fig. 10 and need not be explained again. The manner in which the push-button switch is mounted on the main body of an appliance will now be described. First, as shown in Fig. 18, the resin sheets 16-5, 17-5 on which the fixed-contact pattern 17-5a and movable-contact pattern 16-5b are formed are folded about the cut-outs 23-5 through the intermediary of the spacer 18-5, and the resin sheets thus folded are placed upon the curved surface of the substrate 29. Next, the fixing portions 11-5d (ten of which are provided in this embodiment) of the drip-proof frame 11. 5 are press-fitted into fitting holes provided in the surface of the substrate 29. The reason for providing more than two pairs of the fixing portions 11-5d in the longitudinal direction of the drip-proof frame 11-5 is so that the switch control panel will be maintained at a fixed distance from the curved substrate surface. Next, a fitting projection 14-5a provided on the panel 14-5 having the form of a curved surface is fitted into the elongated groove 11-5a formed in the top side of the drip-proof frame 11-5. This completes the mounting of the push-button switch in this embodiment. Fig. 21 is an exploded, perspective view showing a fourth embodiment of the structure of a push-button switch using the keytop of the invention. As shown in Fig. 27, a push-button switch 70 comprises, in superimposed relation, a lower case 60, a switch sheet 30, a keytop sheet 40 and an upper case 50. Each of the components constituting the push-button switch 70 will now be described. A number of click plates 34 are attached to the top side of the switch plate 30, and a membrane switch is disposed on the underside of each switch plate. Fig. 22 is an enlarged, exploded perspective view showing the A portion (one membrane switch) of the switch sheet 30 shown in Fig. 21. The switch sheet 30 illustrated in Fig. 22 comprises a first substrate 31 consisting of a resilient synthetic resin film provided with a contact pattern 31a at a predetermined position on the top side thereof, a spacer 32 consisting of a resilient synthetic resin film provided with a through-hole 32a at a predetermined position, and a resilient synthetic resin film. The switch sheet 30 further comprises a second substrate 33 provided with a contact pattern 33a at a predetermined position of the underside thereof. The substrates 31, 33 and spacer 32 are bonded together in such a manner that the contact pattern 31a of the first substrate 31 and the contact pattern 33a of the second substrate 33 will oppose each other via the through-hole 32a of the spacer 32. The switch sheet 30 is thus constructed. It should be noted that one membrane switch is constructed at the portion where the fixed contact patterns 31a and 33a oppose each other. The click plate 34, which consists of an upwardly bent resilient metal plate, is bonded to the top side of the second substrate 33 at the position where the two contact patterns oppose each other. Further, as illustrated in Fig. 21, light-emitting elements 35 are attached to the top side of the switch sheet 30 at prescribed positions. Next, the keytop sheet 40 to which the present invention is applied is constructed by directly attaching a number of keytops 41 to a film 45 made of synthetic resin. Fig. 23 is a perspective view showing the underside of the keytop sheet 40. As shown in Figs. 21 and 23, each keytop 41 comprises an actuating portion 41a formed on the top side of the film 45, and a pressing portion 41b protruding from the underside of the film 45. The actuating portion 41a and pressing portion 41b of the keytop 41 are integrally molded via a hole 46 provided in the film 45. The method of manufacturing the keytop sheet 40 will be described next. Fig. 24 is a perspective view showing the film 45. As shown in Fig. 24, the film 45 is formed out of a synthetic resin in the form of a flexible thin sheet and is provided with small holes 46 at positions corresponding to the click plates 34 of the switch sheet 30 shown in Fig. 21. Fig. 25(A) to Fig. 25(C) are diagrams illustrating a method of resin molding the keytops 41 on the film 45. It should be noted that Fig. 31 illustrates only one keytop 41 among the plurality thereof. First, as depicted in Fig. 25(A), the film 45 is clamped from above and below by an upper mold 105 and a lower mold 106-6. The portion of the upper mold 105-6 corresponding to the hole 46 is provided with a cavity 110-6 for molding the actuating portion 41a of the keytop 41. The upper mold 105-6 is provided also with a pin gate 107-6 in the vicinity of the outer circumference of the cavity 110-6. The portion of the lower mold 106-6 corresponding to the hole 46 is provided with a cavity 111-6 for molding the pressing portion 41-b of the keytop 41. Next, as shown in Fig. 25(B), a synthetic resin is injected from the pin gate 107-6 so as to fill the cavities 110-6 and 111-6. As illustrated in Fig. 25(C), the upper mold 105-6 and lower mold 106-6 are removed after the injected synthetic resin has hardened. This completes the formation of the keytop 41 on which the actuating portion 41a and pressing portion 41b are integrally molded via the hole 46 of film 45. When the keytop 41 is thus directly molded on the film 45, the underside of the actuating portion 41a of the keytop is closely adhered to the top side of the film, and the top side of the pressing portion 41b is closed adhered to the underside of the film 45. Next, the upper case 50 shown in Fig. 21 is molded out of synthetic resin, and the keytop sheet 40 is provided with circular holes 51 at positions corresponding to the keytops 41. The lower case 60 shown in Fig. 21 is then formed from a metal plate the periphery of which is provided with an upstanding edge 63. Portions of the upstanding edge 63 are provided with tabs 61, each of which has a mounting hole 62. In order to assemble the push-button switch 70, the switch sheet 30 is placed upon the lower case 60, as shown in Fig. 21. An adhesive is applied to an adhering surface 47 (the entire surface of the periphery of the top side of film 45) of the keytop sheet 40, and the keytop sheet 40 is bonded to the underside of the upper case 50. The upper case 50 is then placed upon the lower case 60 and secured thereto to complete the construction of the push-button switch 70. Fig. 26 is a side sectional view illustrating the push-button switch 70 thus assembled. As illustrated in Fig. 26, a screw 71 is inserted into the mounting hole 62 of the tab 61 provided on the lower case 60, the lower case 60 is fitted into the upper case 50 within the outer circumferential wall thereof, and the two cases are secured to each other. The click plates 34 are situated beneath respective ones of the keytops 41, as shown. Fig. 27 is an enlarged side sectional view showing one push-button switch portion of the push-button switch 70 The lower case 60, it should be noted, is deleted from the drawing. As shown in Fig. 27, the push-button switch 70 is such that the click plate 34 and corresponding keytop 41 are arranged above a membrane switch composed of a contact pattern 31a and a contact pattern 33a which oppose each other via the through-hole 32a of the spacer 32. If the actuating portion 41a of the keytop 41 is pressed, as illustrated in Fig. 28, the film 45 is flexed and presses against the click plate 34, which performs a snap action. In addition, the second substrate 33 is pressed downward and causes the contact pattern 33a to contact the contact pattern 31a, thereby turning on (i.e., closing) the two contacts. When the pressing force is removed from the keytop 41, the latter is restored to the original position by a restoration force which attempts to return the click plate 32 and film 45 to their original states. As a result, the membrane switch is turned off (i.e., opened). In this embodiment of the present invention, as described above, the underside of the actuating portion 41a of keytop 41 and the top side of the pressing portion 41b are closely adhered to the upper and lower surfaces of the film 45, and therefore gaps do not form between the film 45 and the keytop 41. That is, the hole 46 provided in the film 45 is plugged by the keytop 41. Consequently, even if a water droplet invades the keytop 41 or film 45 from the hole 51 in the upper case 50, the water droplet will not seep down into the switch from the hole 46 in the film 45. Further, in the present invention, the fact that a number of the keytops 41 are directly molded on the thin film 45 makes it possible to considerably reduce the thickness of the group of keytops 41. As the keytop 41 consists of a light-transmissive material, light emitted by the light-emitting element 35 shown in Fig. 21 will be introduced to the interior of the keytop 41 to clearly illuminate the same. Though an example of a push-button switch using the keytop according to the present invention has been described in detail, the invention is not limited to the illustrated arrangement, and various modifications are possible, as set forth below. Though the switch arranged below the keytop is a membrane switch in the foregoing embodiment, the switch to which the keytop of the invention is applied is not limited thereto. A membrane switch of a different structure may be employed, and the push-button switch may be provided with a structure other than that of a membrane switch. The shape of the keytop is not limited to that of the foregoing embodiment. As long as a film is provided with a plurality of holes and the keytop is one molded from the top side to the underside of the film via each hole, the keytop may have any desired shape. Fig. 29 is a perspective view showing a fifth embodiment of the structure of the keytop sheet 40-7 according to the present invention. As shown in Fig. 29, a keytop sheet 40-7 is constructed by directly molding three keytops 41-7 on a film 45-7 made of synthetic resin. Figs. 30(A) to 30(C) are diagrams illustrating the keytop sheet 40-7, in which Fig. 30(A) is a plan view, Fig. 30(B) an underside view, Fig. 30(C) an enlarged sectional view taken along line 36(C) - 36(C) of Fig. 30(A), and Fig. 30(D) an enlarged sectional view taken along line 36(D) - 36(D) of Fig. 30(A). The keytop sheet 40-7 shown in Fig. 30 includes a flexible, transparent film 45-7 made of synthetic resin (e.g., polyethylene terephthalate) provided with holes 45-7a at four locations, and has keytops 41-7 made of synthetic resin directly molded on three circular keytop-mounting surfaces remaining between the holes 45-7a. Each keytop 41-7 is molded from a transparent synthetic resin and includes an actuating portion 41-7a provided on the top side of a film 45-7, three film fixing portions 41-7b provided on the underside of the film 45-7 via holes 45-7c provided in the film 45-7, and a protruding portion 41-7c provided on the underside of the film 45-7. As shown in Fig. 30(A), a prescribed light-transmissive symbol 46b is printed on the underside of the film 45-7 to which the keytop 41-7 is attached (namely the underside of the keytop-mounting surface 45-7e of film 45-7), and the periphery of the symbol 46-7b is printed so as to have an opaque portion 46-7a (indicated by the slanted lines). Accordingly, the symbol 46-7b is visible from the top side of the keytop 41-7 via the transparent film 45-7 and actuating portion 41-7a. If illuminated with light from the lower side of the film 45-7, the symbol 46-7b shows up very clearly. The method of manufacturing the keytop sheet 40-7 will now be described. Fig. 31(A) to Fig. 31(C) are diagrams showing the method of manufacturing the keytop sheet 40-7. First, as shown in Fig. 31(A), a thin, flexible film 45-7 consisting of a polyethylene plate is prepared. Next, as illustrated in Fig. 31(B), a prescribed pattern 47-7 is printed on a predetermined position of the film 45-7 (namely on a portion of the film which will become the keytop-mounting surface 45-7e in the following step). As illustrated, the pattern 47-7 is constituted by a circular opaque portion 47-7a of color black, by way of example, and a light-transmissive symbol 47-7b of color white, for example. Next, as depicted in Fig. 31(C), the holes 45-7a are provided in both sides of the film 45-7 at the portions furnished with the patterns 47-7 (namely at the portions serving as the keytop-mounting surfaces 45-7e to which the keytops 41-7 are attached), and the through-holes 45-7c are provided at three locations for each of the keytop-mounting surfaces 45-7e. Hinge portions 45-7b, 45-7b are left above and below the keytop-mounting surfaces 45-7e. The method of forming the keytops 41-7 of the keytop sheet 40-7 is substantially the same as in Fig. 31 and need not be described again. The keytop of the push-button switch according to the present invention is not limited to that of the foregoing embodiment and can be modified in various ways. In the present embodiment, the film 45-7 is transparent. However, so long as the character, number or symbol on the film 45-7 can be directly distinguished from above the keytop, this will suffice. Therefore, if the material constituting the keytop is transparent or semi-transparent, the film 45-7 may be opaque. One of the two hinge portions for each switch can be eliminated by cutting the hinge portion 45-7b along line C-C shown in Fig. 31(C). By constructing the keytops in the manner set forth above, the printing of the symbols is performed on the film. As a result, it is unnecessary to print characters, numbers or symbols on the keytops, as is done in the prior art, thereby making it easy to perform printing. In the prior art, it is necessary to print characters, numbers or symbols on the keytops and attach a transparent sheet to the keytops to protect these marks. By contrast, in accordance with the present invention, the keytops can be manufactured merely by being molded directly on a film. As a result, not only is manufacture facilitated, but mass production is expedited, cost is reduced and the keytops can be made much smaller in thickness. Many apparently widely different embodiments of the present invention can be made without departing from the scope thereof, as defined in the appended claims.

Claims: A keytop of a push-button switch having a fixed contact and a movable contact arranged to oppose each other, and a keytop arranged above the movable contact for pressing said movable contact, said keytop including a keytop portion situated on the top side of a resin film at a prescribed position thereof, and a retaining portion situated on the underside of said resin film at the prescribed position thereof, said keytop portion and said retaining portion being integrally formed by resin molding, and said resin film being sandwiched between said keytop portion and said retaining portion, characterized in that a number, symbol or symbol mark is printed on the top side or underside of said film at a portion thereof where the keytop is situated, and a transparent or semi-transparent resin material is used as the keytop portion at said portion of the film. The keytop according to Claim 1, wherein said retaining portion is loop-shaped, and said resin film is sandwiched in a water-tight state between said keytop portion and said loop-shaped retaining portion. The keytop according to Claim 2, wherein a pressing protrusion for pressing the movable contact of said keytop is provided as an integral part of said loop-shaped retaining portion offset from the center of the lower part of said keytop portion. A push-button switch having a fixed contact and a movable contact arranged to oppose each other, and a keytop according to one of the claims 1-3 arranged above the movable contact for pressing said movable contact, wherein a loop-shaped drip-proof frame is formed in a water-tight state with a resin film by being resin-molded on said resin film so as to surround a prescribed area thereof, a keytop portion is situated on the top side of said resin film at a prescribed position thereof within said loop-shaped drip-proof frame, a retaining portion is situated on the underside of said resin film at the prescribed position thereof, said loop-shaped drip-proof frame, said keytop portion and said retaining portion are integrally formed by resin molding, and said resin film is sandwiched in a water-tight state between said keytop portion and said retaining portion.

Inventors: HARI ATSUSHI, INAGAKI JIROH, KAKU YASUTOSHI, SHINOKI TAKASHI, YAGI NOBUYUKI, HARI, ATSUSHI, INAGAKI, JIROH, KAKU, YASUTOSHI, SHINOKI, TAKASHI, YAGI, NOBUYUKI
Applicants: TEIKOKU TSUSHIN KOGYO KK, TEIKOKU TSUSHIN KOGYO CO. LTD.
Application year: 1991
Main classification: H01H13
IPC codes: B29C45, H01H13, H01H11