Method of manufacturing a keytop

Abstract: A method of manufacturing 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 pressing said movable contact, wherein there are provided an upper mold having cavities the shapes thereof are the same as those of the upper part of a keytop portion, a lower mold having cavities the shapes thereof are the same as those of the lower part of said keytop portion, and a resin film, said method including the steps of: clamping said resin film between said upper mold and said lower mold; injecting a molten resin into the cavities the shapes thereof are the same as those of the lower part of said keytop portion from a pin gate provided in either said upper mold or said lower mold, whereby said resin film is deformed by pressure and heat of said molten resin so as to bring the deformed resin film into adhering contact with the inner surface of the cavities in said upper mold, thereby allowing said molten resin to fill each of the cavities; and parting said upper and lower molds after said molten resin has hardened.

Description: The invention relates to a method of manufacturing the keytop of a push-button switch. 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. From US-A-4 799 083 a membrane switch having first and second contacts, a graphic overlay supporting a tactile actuator and a bezel combination is known. Upon application of pressure to said actuator, the contacts engage. The present invention has been devised in view of the foregoing points and its object is to provide a method of manufacturing a keytop for a keytop sheet for use in a push-button switch suited for a reduction in size and thickness. According to the present invention, there is provided a method of manufacturing the keytop according to which there are provided an upper mold having cavities the shapes whereof are the same as those of the upper part of said keytop portion and said film fixing portion, a lower mold having cavities the shapes thereof are the same as those of the lower part of said keytop portion and said film retaining portion, and a resin film, said method including the steps of: printing a member, symbol or symbol mark on the side of said resin film at a portion thereof where the upper portion of said keytop is situated; clamping said resin film between said upper mold and said lower mold; injecting a molten resin into the cavities the shapes whereof are the same as those of the lower part of said keytop portion and said film retaining portion from a pin gate provided in either said upper mold or said lower mold, whereby said resin film is deformed by pressure and heat of said molten resin so as to be brought into adhering contact with the inner surface of the cavities in said upper mold; allowing said molten resin to flow, through a hole provided in said resin film, into the cavity the shape whereof is the same as that of said film fixing portion in said upper mold; allowing said molten resin to fill each of the cavities; and parting said upper and lower molds after said molten resin has hardened. Other features and advantages of the present inventi-5 on 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) 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, in which Fig. 1(A) is a plan view, Fig. 1(B) is a sectional view taking along line 12(B) - 12 (B) of Fig. 1(A), and Fig. 1(C) a bottom view; Fig. 2 is a partial sectional view showing the first embodiment of the structure of a keytop of a push-button switch according to the present invention; Fig. 3 is a plan view showing the shapes of holes in a resin film; Fig. 4 is a diagram showing the symbol and the shapes of holes in a resin film which forms a keytop; Fig. 5(A) and 5(B) are diagrams for describing a method of manufacturing the keytop; and Fig. 6(A) to 6(C) are diagrams illustrating another structure of a keytop of a push-button switch according to the present invention, in which Fig. 6(A) is a plan view, Fig. 6(B) a sectional view taken along line 17(B) - 17(B) of Fig. 6(A), and Fig. 6(C) a bottom view. Figs. 1(A) to 1(C) are diagrams illustrating a first embodiment of the structure of a keytop for a push-button switch according to the present invention. Fig. 1(A) is a plan view, Fig. 1(B) a sectional view taken along line 12(B) - 12(B) of Fig. 1(A), and Fig. 1(C) a bottom view. A keytop 12-3 has a keytop portion 12-3b consisting of resin material and formed as an integral part thereof, and film retaining portions 12-3c provided on the periphery of the keytop portion 12-3b as an integral part thereof. A resin film 10-3 is disposed on the top side of the keytop portion 12-3b so as to cover the same, and the resin film 10-3 is fixedly sandwiched between the film retaining portion 12-3c and film fixing portions 12-3d integrally provided on the upper parts of the film retaining portions 12-3c. A thermoplastic polycarbonate resin or acrylic resin may be used as the material for the keytop 12-3. The keytop 12-3 has a pressing protrusion 12-3a, which is for pressing a movable contact, integrally provided on the lower part of the film retaining number 12-3c spaced away from the center of the button surface of the keytop portion 12-3b. The pressing protrusion 12-3a for pressing the movable contact is provided at a position offset from the centre of the bottom surface of keytop portion 12-3b. As a result, it is unnecessary to dispose the contact portion of the switch below the centre of the bottom surface of the keytop portion 12-3b. Accordingly, by using a light-transmissive resin material for the resin film and keytop, 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 keytop. More specifically, by printing a number, symbol or other indicia as necessary on the portion of the resin film 10-3 at which the keytop portion 12-3b is located, the number, symbol or indicia will be clearly visible through the keytop portion 12-3b. Such a keytop presents an excellent appearance. Fig. 2 is a diagram illustrating the structure of a push-button switch using the keytop 12-3 having the structure shown in Fig. 1. 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 12-13a 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 centre of the keytop portion 12-3. The drip-proof frame 11 surrounds a plurality of the keytops 12 and is maintained in a watertight state with respect to the resin film 10. 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 watertightly 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 watertight 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 watertightly affixed to the resin film 10. In addition, since the elongated groove 11a and elongated portion projection 14a are fitted together watertightly, 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. Described next will be a method of manufacturing a switch control panel 1-3 obtained by integrally molding a drip-proof frame 11-3 and keytops with the resin film 10-3. Fig. 3 is a plan view showing the external form of the resin film 10-3. As shown in Fig. 3, the resin film 10-3 is rectangular in shape and the portion thereof on which the drip-proof frame 11-3 is formed is provided at prescribed intervals with a number of holes 20-3 through which molten resin flows at the time of molding. Further, the portion of the resin film 10-3 on which the keytops 12-3 are formed is provided at prescribed interval with hole groups 21-3 each having small holes 21-3a (at three locations in this embodiment) and one large hole 21-3b (at one location in this embodiment) through which the molten resin flows. If required, as shown in Fig. 4, a number, symbol or character 24-3 is printed on the resin film 10-3 at a portion thereof where the keytop portion 12-3b is located. The printing can be performed either on the top side or underside of the resin film 10-3. Fig. 5(A) and Fig. 5(B) are diagrams showing a structure, in which the resin film is clamped between upper and lower molds, for describing the method of manufacturing a keytop according to this embodiment. Fig. 5 is a cross sectional view of the molds 105-3, 106-3 corresponding to a cross section of the keytop 12-3 taken along line 12(D) - 12(D) but not shown in Fig. 1(A), and Fig. 5(B) is a view corresponding to a cross section of the keytop 12-3 taken along line 12(B) - 12(B) of Fig. 1(A). As illustrated in these drawings, the resin film is clamped between an upper mold 105-3 and a lower mold 106-3. The upper mold 105-3 has a cavity 110-3 of the same shape as the upper part of keytop portion 12-3b (see Fig. 1) and a cavity 112-3 of the same shape as the film fixing portion 12-3d. The lower mold 106-3 has a cavity 111-3 of the same shape as the lower part of keytop portion 12-3b, a cavity 113-3 of the same shape as the film retaining portion 12-3c, and a cavity 114-3 of the same shape as the pressing protrusion 12-3a. Thus, the resin film 10-3 is clamped by the upper mold 105-3 and the lower mold 106-3, and a molten resin is injected from a pin gate 107-3 situated above the large hole 21-3b. As a result, the molten resin flows into the cavities 114-3, 111-3 and 113-3 of the lower mold 106-3 through the hole 21-3b formed in the resin film 10-3. At this time, as shown in Fig. 5(B), film 10-3 facing other than the cavities 111-3, 113-3 and 114-3 formed in the lower mold 106-3 are strongly clamped by the upper and lower molds, and therefore the molten resin which has flowed in deforms the film 10-3 and forces it into intimate adhering contact with the inner wall of the upper mold 105-3. The molten resin flows into the cavity 110-3 of the upper mold 105-3 and flows also into the cavity 112-3 of the upper mold 105-3 through the hole 21-3a formed in the resin film 10-3. As a result of the foregoing, the resin film 10-3 is deformed and comes into intimate adhering contact with the inner wall of the cavity 110-3 of upper mold 105-3, as indicated by the dashed line. When the upper mold 105-3 and lower mold 106-3 are parted after the molten resin has hardened, the result is the keytop 12-3, in which the surface of the keytop portion 12-3b is covered with the resin film, as illustrated in Figs. 1(A) to 1(C). In the embodiment described above, the upper mold 105-3 is provided with the pin gate 107-3, and the molten resin is charged into the cavities 111-3, 113-3 and 114-3 of the lower mold 106-3 through the large hole 21-3b formed in the resin film 10-3. However, it is permissible to provide the pin gate in the cavity 114-3 of the lower mold 106-3 and charge the molten resin directly into the cavity 114-3. The gist of the method of manufacture according to this embodiment of the invention resides in molding the keytop 12-3 in the resin film 10-3 while the resin film is deformed into the shape of the cavity 110-3. Accordingly, the results are influenced by the shape of the keytop 12-3 and the charging conditions of the molten resin. According to this embodiment, a keytop was manufactured in which the thickness of the resin film was 0,2 mm and the height of the keytop 12-3 was made less than 1/2 the diameter. The result was that the resin film 10-3 was deformed into intimate contact with the inner wall of the cavity 110-3 of upper mold 105-3, as indicated by the dashed line. At charging of the molten resin, it is necessary to set the temperature of the molten resin, the injection (charging) pressure, the injection need, the injection time and the temperature of the molds to suitable values. In this embodiment, molding at a high yield was achieved by setting the temperature of the molten resin to 240°C, the mold temperature to about 80°C, the injection time to about 3 sec., cooling time to about 10 sec., the injection pressure of the injection molding machine to 1400 kg, and the injection speed to 15 mm/sec. Figs. 6(A) to 6(C) are diagrams illustrating a second embodiment of the structure of a keytop for a push-button switch according to the present invention. Fig. 6(A) is a plan view, Fig. 6(B) a sectional view taken along line 17(B) - 17 (B) of Fig. 6 (A), and Fig. 6(C) a bottom view. A keytop 12-4 has a keytop portion 12-4b consisting of a resin material and formed as an integral part thereof, and a film retaining portion 12-4c provided on the periphery of the keytop portion 12-4b as an integral part thereof. As in the keytop shown in Figs. 1(A) - (C), the resin film 10-4 in the embodiment is disposed on the top side of the keytop portion 12-4b so as to cover the same, and the resin film 10-4 is fixedly sandwiched between the film retaining portion 12-4c and a film fixing portion 12-4d integrally provided on the upper part of the film retaining portion 12-4c. This keytop 12-4 differs from the keytop of Figs. 1(A) - (C) in that a pressing protrusion 12-4f which presses the movable contact is projectively provided beyond the underside of the film retaining portion 12-4c at the centre of the lower part of the keytop portion 12-4b. Also, as in the keytop 12 of Fig. 1, a thermoplastic polycarbonate resin or acrylic resin may be used as the material for the keytop 12-4. Furthermore, the only difference in the method of manufacture is that the shape of the cavity in the lower mold is changed in dependence upon the shape of the keytop 12-4. In other aspects, the method of manufacture is the same as that for the keytop of Fig. 1 and need not be described again. In this embodiment, a light-transmissive resin material is used for the resin film 10-4 and keytop 12-4. By printing a number, symbol or other indicia as necessary on the portion of the resin film 10-4 at which the keytop portion 12-4b is located, the number, symbol or indicia will be clearly visible through the keytop portion 12-4b. Such a keytop presents an excellent appearance. It should be noted that the shape of the keytop portion 12-4b of the keytop 12-4 is not limited to that described in the foregoing embodiment. For example, it goes without saying that the planar configuration can be rectangular or polygonal and need not be circular. Further, though four of the film retaining portions 12-4c are provided in radiating fashion on the outer circumference of the keytop portion 12-4b on the bottom thereof, the film retaining portions 12-4c are not limited to this arrangement. In order to increase the strength of adherence between the keytop 12-4 and the resin film 10-4, the radiating film retaining portions 12-4c may be increased. In addition, the film fixing portions 12-4d may be connected in the form of a ring. In other words, so long as the resin film 10-4 is capable of being strongly clamped by the upper mold 105-4 and lower mold 106-4 at the locations of the keytop 12-4, the film remaining portions 12-4c and film fixing portions 12-4d may be of any number and of any shape. 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 unnecessary 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 claim.

Claims: A method of manufacturing a keytop (12) of a push-button switch having a fixed contact (17a) and a movable contact (16a) arranged to oppose each other, and a keytop (12-3) arranged above the movable contact (16a) pressing said movable contact (16a), wherein there are provided an upper mold (105-3) having cavities (110-3) the shapes thereof are the same as those of the upper part of a keytop portion, a lower mold (106-3) having cavities (111-3) the shapes thereof are the same as those of the lower part of said keytop portion (12-3b), and a resin film (10-3), said method including the steps of: printing a member, symbol or symbol mark (24-3) on the side of said resin film at a portion thereof where the upper portion of said key top (12-3b) is situated; clamping said resin film (10-3) between said upper mold (105-3) and said lower mold (106-3); injecting a molten resin into the cavities the shapes thereof are the same as those of the lower part of said keytop portion from a pin gate (107-3) provided in either said upper mold (105-3) or said lower mold (106-3), whereby said resin film (10-3) is deformed by pressure and heat of said molten resin so as to bring the deformed resin film into adhering contact with the inner surface of the cavities in said upper mold (105-3), thereby allowing said molten resin to fill each of the cavities; and parting said upper and lower molds (105-3; 106-3) after said molten resin has hardened.

Inventors: HARI ATSUSHI, INAGAKI JIROH, KAKU YASUTOSHI, SHINOKI TAKASHI, YAGI NOBUYUKI, HARI, ATSUSHI, INAGAKI, JIROH, KAKU, YASUTOSHI, SHINOKI, TAKASHI, YAGI, NOBUYUKI, Shinoki, Takashi, c/o Teikoku Tsushin Kogyo Co.Ltd
Applicants: TEIKOKU TSUSHIN KOGYO KK, TEIKOKU TSUSHIN KOGYO CO. LTD.
Application year: 1991
Main classification: H01H13
IPC codes: H01H13, B29C45, H01H11