Electricity: circuit makers and breakers – Solid contact – Membrane type
Reexamination Certificate
2000-01-26
2002-05-21
Bradley, P. Austin (Department: 2832)
Electricity: circuit makers and breakers
Solid contact
Membrane type
C200S08500R
Reexamination Certificate
active
06392178
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a membrane switch that is buried for use, e.g., below an automobile seat and operates such that its contacts are closed by person's seating pressure.
2. Description of the Prior Art
Generally, in an existing membrane switch, a film-like first flexible insulating substrate at a part of which at least one first contact pattern is formed, and a film-like second flexible insulating substrate at a part of which at least one second contact pattern is formed are joined in facing relation via a thin spacer member so that corresponding first and second contact patterns are disposed in overlapped manner, wherein an opening is provided in each of areas in the thin spacer member in which the corresponding first and second contact patterns overlap one another, and each of the areas in which the corresponding first and second contact patterns overlap one another forms a contact of the switch. Wiring patterns respectively conductive-connected to the corresponding contact patterns are formed in one or both of the first flexible insulating substrate and the second flexible insulating substrate.
In the foregoing existing membrane switch, an area containing the formation portions of the contacts forms a switch body part, an area deriving from the switch body part forms a derivation part, and a tip area of the derivation part forms a terminal part (connection part) with connection terminals provided for connection with an external circuit. The contacts are conductive-connected with the connection terminals by the wiring patterns.
In this case, the existing membrane switch forms the first contact pattern, the second contact pattern, and the wiring patterns by printing them at required portions of the first flexible insulating substrate and the second flexible insulating substrate with a mixture of conductive silver powder and thermoplastic resin used as a binder material.
In the membrane switch having the foregoing structure, corresponding first and second contact patterns are usually out of contact; that is, each contact is usually open, and the first contact pattern and the second contact pattern are brought into conductive contact by pressure applied between the first contact pattern and the second contact pattern, so that the contact is closed.
This type of a membrane switch may be used in places where a change in the ambient temperature of the switch is relatively large. Particularly when the membrane switch is buried in an automobile seat so that it is used as a sensor element for judging whether an occupant uses the seat, if the periphery of the membrane switch is exposed to high temperatures and baggage is put on the seat of the parking automobile, pressure would remain applied to the membrane switch.
In the foregoing existing membrane switch, since the first contact pattern and the second contact pattern constituting the contacts are made of thermoplastic resin, if the ambient temperature of the membrane switch becomes high and pressure remains applied to the membrane switch, stress relaxation (creep) would occur at the contacts, reducing the actuating force to close the contacts. Specifically, there exists a problem in that prolonged stress applied to the membrane switch keeps the first contact pattern and the second contact pattern deformed and, as a result, the contacts are closed before normal (predetermined) pressure is applied to the contacts, disabling the correct operations of the sensor element.
SUMMARY OF THE INVENTION
The present invention has been made to solve such a problem and provides a membrane switch that, even if the ambient temperature of the switch becomes high and pressure is applied, is resistant to stress relaxation at the contacts and is capable of preventing the occurrence of contact malfunction.
To achieve the foregoing object, the present invention provides a membrane switch including the following means. A first flexible insulating substrate provided with a first contact pattern and a second flexible insulating substrate provided with a second contact pattern are disposed in facing relation via a spacer member, and wiring patterns are provided in at least one of the first flexible insulating substrate and the second flexible insulating substrate, wherein the wiring patterns are conductive layers containing resin made of a mixture of conductive powder and binder resin and at least one layer of the second contact pattern is a layer containing rigid resin that is more rigid than binder resin.
According to the foregoing means, since the wiring patterns are constituted by conductive layers containing resin made of a mixture of conductive powder and binder resin, in addition to the intrinsic flexibility of the first flexible insulating substrate and the second flexible insulating substrate, the entire membrane switch can be provided with satisfactory flexibility. Moreover, since a part of the second contact pattern is constituted by a layer containing more rigid resin than binder resin, even if the ambient temperature of the membrane switch becomes high during use, stress relaxation would occur at the contacts with less frequency and the heat resistance creep ability at the contacts could be increased.
In embodiments of the present invention, a membrane switch is constructed so that a first flexible insulating substrate at a part of which a first contact pattern is formed, and a second flexible insulating substrate at a part of which a second contact pattern is formed are joined in facing relation via a spacer member having an opening at an area in which the first contact pattern and the second contact pattern face each other; wiring patterns conductive-connected to corresponding contact patterns are formed on at least one of the first flexible insulating substrate and the second flexible insulating substrate; and the first contact pattern and the second contact pattern are conductive-connected by pressure applied to the formation portion of at least the second contact pattern, wherein the wiring patterns are conductive layers containing resin made of a mixture of conductive powder and binder resin, and at least one layer of the second contact pattern is a layer containing resin that is more rigid than the binder resin.
In a first concrete example of an embodiment of the present invention, in the membrane switch, binder resin to form the wiring patterns is thermoplastic resin and rigid resin to form the second contact pattern is thermosetting resin.
In a second concrete example of an embodiment of the present invention, in the membrane switch, the second contact pattern has a conductive layer at a layer below the layer containing thermosetting resin.
In a third concrete example of an embodiment of the present invention, in the membrane switch, the layer containing rigid resin comprises a conductive layer containing rigid resin formed by a mixture of conductive powder and binder resin that is more rigid than the binder resin of the wiring pattern.
In a fourth concrete example of an embodiment of the present invention, in the membrane switch, the wiring patterns are formed on the second flexible insulating substrate and the wiring patterns are constituted by two conductive layers, of which the lower uses silver powder as the conductive powder and thermoplastic resin as the binder resin, and the upper uses conductive carbon powder and thermoplastic resin as binder resin and covers the lower conductive layer; the layer containing rigid resin of the second contact pattern is constituted by a conductive layer containing rigid resin which contains a mixture of thermosetting resin as more rigid binder resin than the binder resin of the wiring patterns and carbon powder; and the lower conductive layer extends to the bottom (between the second flexible insulating substrate and the conductive layer containing rigid resin) of the conductive layer containing rigid resin.
In a fifth concrete example of an embodiment of the present invention, the membrane switch uses a polyester film as a
Alps Electric Co. ,Ltd.
Bradley P. Austin
Klaus Lisa N.
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