Contact key switch and method for its manufacturing the same

Abstract: A contact key switch according to the present invention is a highly reliable contact key switch allowing the prevention of rise of a resistance, easy integral molding, no need of selection of an adhesive and adhesion process for use accomplished by forming the surface of the electroconductive contact portion with a fabric or a nonwoven fabric made of a electroconductive fiber like a carbon fiber, and by using same material the rubber-like elastic body of the main body of the contact switch.

Description: The present invention relates to a contact key switch used as an input key for an electronic instrument such as a telephone, a calculator, or an AV instrument, or an automobile component such as a power window or a remote controlled door mirror, and a method for its manufacture. As a rule, the rubber-like elastic key pad of the main body of a contact key switch is manufactured using as a material an insulating rubber-like elastic body represented by natural rubber, synthetic rubber, or a thermoplastic elastic body, by processing with various methods such as compression molding, injection molding, etc. As the rubber-like elastic body, silicone rubber is frequently used having many characteristics, such as electric insulation, low temperature resistance, heat-proof ability, chemical resistance, precision molding ability, and resilience elasticity, necessary for a contact key switch. A contact portion is exemplified by those molded integrally with an electroconductive chip on the contact portion of the key pad in a given shape by mixing carbon black and metal powder in a rubber-like elastic material, those formed by preparing a layer of electroconductive ink on the contact portion by screen printing or PAD printing after previous making the main body of the contact key switch, and those molded integrally after preparing the electroconductive chip by punching a layering body, that is made by layering a metal layer plated on a rubber layer, in a given shape. Attention is also drawn to the disclosures of DE-4 314 193 C and US-4 164 634 A. However, said contact portion has been made by mixing carbon black and metal powder, which are electroconductive media, in an elastic material or ink. Therefore, compounding a large quantity of an electroconductive medium yields a contact resistance of some 10 ohms or higher, not allowing use suitable for low contact resistance of some ohms or lower. In addition, the contact portion of a contact switch made by plating of a metal on a rubber layer is, as described in Japanese Patent Publication 06(1994)- 93335 and Japanese Patent Laid-Open 08(1996)-276435, made of a metal, and suitable for low resistance use. However, silicone as the material of the keypad is normally difficult to adhere to a metal as known from its use as a release agent. Therefore, the adhesive and adhering procedure should be selected to make adhesion of both materials possible. On the other hand, both sides of the electroconductive chip consist of a metal layer and an insulating rubber layer. Therefore, the metal layer should contact with the mold surface at insertion of the mold in a molding step. This step makes the efficiency of manufacture worse and costs higher. To solve the aforementioned problem, the present invention provides a contact key switch suitable the for low resistance use by making the surface of a contact portion of the contact switch of electroconductive woven fabric or electroconductive nonwoven. The present invention in one aspect provdes a contact key switch including a key pad composed of a rubber-like elastic body, wherein: the key pad has a contact portion formed at a part thereof; and a surface of the contact portion is made of (a) an electroconductive woven fabric of a carbon fiber having a composition of a number of wales of 10 to 30 per 25 mm and a filament number of 1000 to 6000, or (b) an electroconductive nonwoven fabric of a carbon fiber having a carbon mass rate of 0.03 to 2.5 g/cm 2 . The invention also provides a contact key switch including a key pad composed of a rubber-like elastic body, wherein the key pad has a contact portion formed at a part thereof, and the contact portion is a layered contact portion in which an electroconductive woven fabric of a metal fiber or an electroconductive nonwoven fabric of a metal fiber is layered on both sides of a rubber layer. The invention in another aspect provides a method for manufacture of a contact key switch, wherein an unvulcanized rubber penetrates in the opening portion of an electroconductive woven fabric or an electroconductive nonwoven fabric and is hardened to form a layered body, the layered body is punched in a given shape to make a layered contact portion and to form it as a part of a key pad made of a rubber-like elastic body so as to make the electroconductive woven fabric or the electroconductive nonwoven fabric as a surface. In one preferred method of the invention, penetration of an unvulcanized rubber in the opening portion of an electroconductive woven fabric or an electroconductive nonwoven fabric is carried out by compression molding. In another preferred method of the invention, an unvulcanized rubber penetrates in the opening portion of the electroconductive woven fabric or the electroconductive nonwoven fabric to apply or print by using a roll or a blade, or the like and is hardened in a hardening furnace to make a layered body. In the method of the invention, a rubber-like elastic keypad is suitably made of silicon rubber. The invention also provides a method for manufacture of a contact key switch, wherein after an electroconductive woven fabric or an electroconductive nonwoven fabric is put in a mold for injection molding, a thermoplastic elastomer is injected in a mold, a melted thermoplastic elastic body is deposited on the electroconductive woven fabric or the electroconductive nonwoven fabric or penetrated in an opening portion thereof to make a layered body, the layered body is punched in a given shape to make a layered contact portion and a part of a key pad made of a rubber-like elastic body is formed to make the electroconductive woven fabric or the electroconductive nonwoven fabric as a surface. In preferred embodiments of said method of the invention: (a) the electroconductive woven fabric is composed of a carbon fiber having a composition of a number of wales of 10 to 30 per 25 mm and a filament number of 1000 to 6000; (b) the electroconductive nonwoven fabric is composed of a carbon fiber having a carbon mass rate of 0.03 to 2.5 g/cm 2 ; (c) the layered body is formed by layering an electroconductive woven fabric or an electroconductive nonwoven fabric on both sides of a rubber layer. The material of the rubber part of the main body of the contact switch and layered body is, as used as the contact switch, not especially restricted if having a high resilience elasticity, but is preferably an insulating rubber-like elastic body represented by a synthetic rubber selected from at least one of natural rubber, ethylene-propylene rubber, silicone rubber, butadiene rubber or a thermoplastic elastic body selected from at least one of styrene, esters, olefins, urethanes, and vinylated compounds. On the other hand, the constituent of the electroconductive woven fabric or electroconductive nonwoven fabric is not especially restricted if at least one of warp fibers or woof fibers consist of electroconductive fibers. Further, the present invention provides a contact key switch having excellent characteristics such as low temperature resistance, heat-proof ability, chemical resistance, precision molding ability, and resilience elasticity, by using silicone rubber for a rubber-like elastic body. Furthermore, the present invention provides a contact key switch suitable for low resistance use by using material selected from carbon fiber and metal fiber for an electroconductive woven fabric or an electroconductive nonwoven fabric. According to the present invention, carbon fiber constituting the electroconductive woven fabric or the electroconductive nonwoven fabric is selected from fiber composition of number of wales of 10 to 30 per 25 mm and filament number of 1000 to 6000 in the electroconductive woven fabric or carbon mass rate of 0.03 to 2.5 g/ cm 2 in the electroconductive nonwoven fabric. A fiber constitution smaller than that of the respective number ranges increases surface resistance by invasion of unvulcanized rubber, in the surface of a layered contact portion due to large opening portion of the electroconductive woven fabric or the electroconductive nonwoven fabric. A fiber constitution larger than that of respective number ranges easily allows surface dissociation by lowered holding performance of vulcanized rubber and fibers caused by no invasion of unvulcanized rubber between fibers due to small opening portions of the electroconductive woven fabric or the electroconductive nonwoven fabric. The method for manufacture of carbon fibers is not especially restricted, and can be selected from fibers prepared by carbonizing through heat treatment of fibers made by spinning of organic fibers such as rayon and polyacrylonitrile and purified petroleum pitch in an inert gas atmosphere. The material of metal fiber is not specially restricted, and may be fibers such as gold, gold alloy, silver, copper, copper alloy, iron, nickel, brass, and when corrosible material is used, those of which the entire surface has been plated with a material, such as gold or gold alloy, not easily corrosible. The layered contact portion is manufactured by penetrating unvulcanized rubber into the opening portion of the electroconductive woven fabric or the electroconductive nonwoven fabric to harden and make a layered body, and by punching the layered body in a given shape. The layered body made of the rubber layer and the electroconductive woven fabric or the electroconductive nonwoven fabric, of the present invention, is manufactured by layering the electroconductive woven fabric or the electroconductive nonwoven fabric on the unvulcanized rubber to be subject to compression molding. The layered body made of the rubber layer and the electroconductive woven fabric or the electroconductive nonwoven fabric, of the present invention, is manufactured by layering evenly the unvulcanized rubber on the electroconductive woven fabric or the electroconductive nonwoven fabric using a roll or a blade, and if necessary, by further layering the electroconductive woven fabric or the electroconductive nonwoven fabric on the unvulcanized rubber, and by using a hardening furnace with far infrared rays, near-infrared rays, or heat air. According to aforementioned method, the unvulcanized rubber is hardened after penetrating into the opening portion of the electroconductive woven fabric or the electroconductive nonwoven fabric to allow easy formation of the layered contact portion. Thus, selection use of an adhesive and adhesion process is not necessary. The condition of the unvulcanized rubber of the present invention is not restricted to either a liquid form or a solid form. However, when the unvulcanized rubber is evenly layered on the electroconductive woven fabric or the electroconductive nonwoven fabric by using a roll or a blade, the liquid form is preferable for easy penetration into the opening portion of the electroconductive woven fabric or the electroconductive nonwoven fabric. In the use of silicone rubber for the rubber layer, if silane coupling agent is applied to the electroconductive woven fabric or the electroconductive nonwoven fabric, the holding performance of the electroconductive woven fabric or the electroconductive nonwoven fabric is increased. In addition, the rubber layer is not restricted to insulating or electroconductive material. However, if electroconductive rubber is used, the contact resistance of the contact portion shows a tendency to fall to a lower value. The layered contact portion is formed by punching the layered body in a given shape. The layered contact portion is engaged to the contact part of the mold of the rubber-like elastic key pad to fit the surface of the electroconductive woven fabric or the electroconductive nonwoven fabric to the mold, followed by integrated molding by inserting the rubber-like elastic material in the mold. The layered body made of the rubber layer and the electroconductive woven fabric or the electroconductive nonwoven fabric, of the present invention, is manufactured by applying the electroconductive woven fabric or the electroconductive nonwoven fabric to the mold for injection molding, extruding the thermoplastic elastic body to the mold, and applying the melted thermoplastic elastic body to the electroconductive woven fabric or the electroconductive nonwoven fabric or penetrating into the opening portion of the electroconductive woven fabric or the electroconductive nonwoven fabric. Layering the electroconductive woven fabric or the electroconductive nonwoven fabric on both sides of the rubber layer gives electroconductivity to both surfaces of the layered contact portion. Therefore, a jig or an apparatus for identifying the side of the layered contact portion is not necessary for insertion of the layered contact portion in the contact part of the mold to allow efficient manufacture. The invention will be further described with reference to the accompanying drawings, in which: Fig. 1 is a sectional view of a contact key switch; Fig. 2 is a perspective side view of a layered body made of a rubber and fiber fabric; and Fig. 3 is a perspective side view of a layered contact portion. Embodiments of the present invention are given below. Fig. 1 is a sectional view of a contact key switch, showing an embodiment of the present invention. In Fig. 1, the main body 1 of the contact key switch is made of a non-operation portion 1a , an operation portion 1b , a thin skirt portion 1c connecting them, and a projecting portion 1d projecting downward integrally with an elastic body. The surface of a layered contact portion 2 is made of electroconductive woven fabric or electroconductive nonwoven fabric. In the embodiment, silicone rubber was used for the main body 1 of the contact key switch. For carbon fiber forming the electroconductive woven fabric or the electroconductive nonwoven fabric of the surface of the contact portion, carbon fiber fabric (Torayca Fabric, produced by Toray Industries, Inc. was used for the electroconductive woven fabric and carbon fiber Mat (Torayca Mat, produced by Toray Industries, Inc. was used for the electroconductive nonwoven fabric. Electroconductive silicone rubber was used for the rubber layer. The rubber layer of layered electroconductive portion is not especially restricted if integrated hardening is possible by vulcanizing the main body of the contact switch and carbon fiber fabric. However, a rubber-like elastic body made of the same material as that of the main body of the contact switch is preferable. Silicone rubber containing 50 weight part of carbon black was used. The contact resistance of the layered contact portion was 2 to 3 Ω. A method for manufacture of the layered contact portion of the present invention is described below using the carbon fiber fabric according to Fig. 2. As shown in Fig. 2, a layered body 2 made by layering a rubber sheet 2b on a carbon fiber fabric 2a and layering the carbon fiber fabric 2a on the rubber sheet 2b was subjected to compression molding under 190 kgf/cm 2 using unvulcanized electroconductive silicone rubber layer and carbon fiber fabric (Torayca Fabric, produced by Toray Industries, Inc.), vulcanized and integrated, and punched in a given shape to manufacture the layered contact portion as shown in Fig. 3. In the case of using carbon fiber Mat (Torayca Mat, produced by Toray Industries, Inc.) as the carbon fiber nonwoven fabric for a layered contact portion, manufacture was carried out by same method as that of the carbon fiber fabric. The contact key switch was manufactured by putting the layered contact portion in a mold and putting silicone rubber as a rubber-like elastic body of the main body 1 of the contact switch in the mold to mold integrally. The compression pressure at the compression molding is not restricted if the layered contact portion can be molded in a given thickness. However, the pressure is preferably 100 to 200 kgf/cm 2 in either unvulcanized rubber of liquid form or solid form. Table 1 presents the results of the electroconductive woven fabric in the layered contact portion made of carbon fibers. Similarly, Table 2 presents the result of the electroconductive nonwoven fabric. As regards the evaluation of resistance (contact resistance), holding performance, molding performance, and processibility for die cutting, the results of embodiments (e) and (k) were good in all the items. Other embodiments are presented as comparative embodiments in respective tables. The contact resistance is represented by o ○ for resistance less than 2Ω, ○ for 2 to 10Ω , and × for more than 10Ω. Holding performances are represented by ○ for a case of no problem in close contact of rubber with fibers and × for unsatisfactory performance. The molding performances are represented by ○ for a case in which the shape of fibers have been kept after molding and × for a case in which the shape of fibers have not been kept by moving of fibers after molding. The processibility was represented by ○ for a case in which a section is clearly punched by punching in a given shape after molding and × for a case in which many burrs have occurred by falling down of fibers pulled out by a blade. Electroconductive woven fabric number of wale X (25mm) number of filament y resistance holding performance molding performance processibility a X < 10 y < 1000 × ○ × ○ b " 1000≦y≦6000 × ○ × ○ o " 6000 < y × ○ ○ × d 10≦ X ≦30 y < 1000 ○ ○ × ○ e " 1000≦y≦6000 o ○ ○ ○ ○ f " 6000 < y o ○ × ○ × g 30 < X y < 1000 ○ × ○ ○ h " 1000≦y≦6000 o ○ × ○ ○ i " 6000 < y o ○ × ○ × The contact key switch of the present invention has the surface of the electroconductive contact portion made of woven fabric or nonwoven fabric of electroconductive fibers. Thus, the same low resistance was yielded as that of the contact portion made of a metal plate. Further, manufacture of the layered contact portion by punching the layered body in a given shape, of which both surfaces of the rubber layer are covered by the electroconductive woven fabric or the electroconductive nonwoven fabric, gives electroconductivity to both surfaces of the layered contact portion. Therefore, a jig or an apparatus or the like for identifying the side of the layered contact portion is not necessary for insertion of the layered contact portion in the contact part of the mold to allow efficient manufacture at low cost. The main body of the contact key switch and the electroconductive woven fabric or the electroconductive nonwoven fabric are easily and integrally molded by using the same material for the rubber layer of the layered contact portion and the rubber-like elastic body of the main body of the contact switch. Thus, selection of an adhesive and adhesion process for use is not necessary. Furthermore, the use of carbon fibers for the electroconductive woven fabric or the electroconductive nonwoven fabric prevents increasing resistance caused by oxidation which easily occurs in a metal and provide a contact key switch of high reliability. The carbon fibers are selected from a composition of number of wales of 10 to 30 per 25 mm and filament number of 1000 to 6000 for the electroconductive woven fabric and having a carbon mass rate of 0.03 to 2.5 g/ cm 2 for the electroconductive nonwoven fabric. By this, a high quality contact key switch having a low contact resistance and a high durability is obtained.

Claims: A contact key switch including a key pad (1b) composed of a rubber-like elastic body, the key pad having a contact portion (2) formed at a part thereof; characterized in that a surface (2a) of the contact portion is made of (a) an electroconductive woven fabric of a carbon fiber having a composition of a number of wales of 10 to 30 per 25 mm and a filament number of 1000 to 6000, or (b) an electroconductive nonwoven fabric of a carbon fiber having a carbon mass rate of 0.03 to 2.5 g/cm 2 . A contact key switch including a key pad (1b) composed of a rubber-like elastic body, the key pad having a contact portion (2) formed at a part thereof, characterized in that the contact portion is a layered contact portion in which an electroconductive woven fabric of a metal fiber or an electroconductive nonwoven fabric of a metal fiber is layered on both sides (2a) of a rubber layer. A method for manufacture of a contact key switch, characterized in that an unvulcanized rubber penetrates in the opening portion of an electroconductive woven fabric or an electroconductive nonwoven fabric and is hardened to form a layered body, the layered body is punched in a given shape to make a layered contact portion and to form it as a part of a key pad made of a rubber-like elastic body so as to make the electroconductive woven fabric or the electroconductive nonwoven fabric as a surface. A method for manufacture of a contact key switch as claimed in claim 3, characterized in that penetration of an unvulcanized rubber in the opening portion of an electroconductive woven fabric or an electroconductive nonwoven fabric is carried out by compression molding. A method for manufacture of a contact key switch as claimed in claim 3, characterized in that an unvulcanized rubber penetrates in the opening portion of the electroconductive woven fabric or the electroconductive nonwoven fabric to apply or print by using a roll or a blade, or the like and is hardened in a hardening furnace to make a layered body. A method for manufacture of a contact key switch as claimed in any of claims 3 to 5, characterized in that a rubber-like elastic keypad is made of silicone rubber. A method for manufacture of a contact key switch, characterized in that after an electroconductive woven fabric or an electroconductive nonwoven fabric is put in a mold for injection molding, a thermoplastic elastomer is injected in a mold, a melted thermoplastic elastic body is deposited on the electroconductive woven fabric or the electroconductive nonwoven fabric or penetrated in an opening portion thereof to make a layered body, the layered body is punched in a given shape to make a layered contact portion and a part of a key pad made of a rubber-like elastic body is formed to make the electroconductive woven fabric or the electroconductive nonwoven fabric as a surface. A method for manufacture of a contact key switch as claimed in any of claims 3 to 7, characterized in that the electroconductive woven fabric is composed of a carbon fiber having a composition of a number of wales of 10 to 30 per 25 mm and a filament number of 1000 to 6000. A method for manufacture of a contact key switch as claimed in any of claims 3 to 7, characterized in that the electroconductive nonwoven fabric is composed of a carbon fiber having a carbon mass rate of 0.03 to 2.5 g/cm 2 . A method for manufacture of a contact key switch as claimed in any of claims 3 to 7, characterized in that the layered body is formed by layering an electroconductive woven fabric or an electroconductive nonwoven fabric on both sides of a rubber layer.

Inventors: HORIUCHI WATARU, HORIUCHI, WATARU, Horiuchi, Wataru, Polymatech Co., Ltd.R &amp; D center
Applicants: POLYMATECH CO LTD, POLYMATECH CO., LTD.
Application year: 1999
Main classification: H01H13
IPC codes: H01H1, H01H11, H01H13