Membrane switch having layers containing rigid resin in contact parts

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 base material of at least one of the first flexible insulating substrate and the second flexible insulating substrate; includes a switch body part containing the formation areas of the contact patterns and a derivation part protruding from the switch body part; and derivation patterns conductive-connected to the wiring patterns are formed in the derivation part and polyester resin is used as binder resin of the derivation patterns.

In a sixth concrete example of an embodiment of the present invention, in the membrane switch, the second flexible insulating substrate includes the switch body part, the derivation part, and a connection part for connecting the derivation part to an external circuit, and the connection part includes terminals using the rigid resin or rigid binder resin as a formation material.

In a seventh concrete example of an embodiment of the present invention, in the membrane switch, the second contact pattern, at the outermost layer, uses a conductive layer containing rigid resin made of phenol resin as rigid binder resin.

In an eighth concrete example of an embodiment of the present invention, in the membrane switch, the spacer member is film-like and is integrated with the first flexible insulating substrate and the second flexible insulating substrate by an adhesive, and has an opening which is smaller than the formation areas of the first contact pattern and the second contact pattern.

In a ninth concrete example of an embodiment of the present invention, in the membrane switch, the outermost layer of the terminals is a conductive layer containing rigid resin made of a mixture of conductive powder and more rigid binder resin than the binder resin of the wiring patterns.

In a tenth concrete example of an embodiment of the present invention, in the membrane switch, the first contact pattern includes a conductive layer containing rigid resin made of a mixture of conductive powder and more rigid binder resin than the binder resin of the wiring patterns and applies pressure to the both flexible insulating substrates.

According to the embodiments of the present invention, since the wiring patterns, like existing membrane switches, 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, like existing membrane switches, the entire membrane switch can be provided with satisfactory flexibility. Moreover, since apart of the second contact pattern is constituted by a layer containing more rigid resin than binder resin, preferably a layer containing rigid resin containing thermosetting resin, even if the ambient temperature of the membrane switch becomes high during use (when the portion in which the second contact pattern is formed is pressed), stress relaxation would less frequently occur at the contacts and the occurrence of malfunction such as the contacts that are closed when a predetermined amount of pressure is not applied could be prevented.

Of the embodiments of the present invention, according to the embodiment that a conductive layer is provided at a layer below the conductive layer containing rigid resin to constitute the second contact pattern, with the conductivity of the second contact pattern maintained, contacts resistant to high temperatures can be formed.

As a layer containing rigid resin to constitute the second contact pattern, an additional insulating layer can be provided. However, in the embodiments of the present invention, if a silver layer containing a mixture of binder resin made of thermoplastic resin and silver powder is formed as the base of the wiring patterns and the second contact pattern, and the silver layer in the wiring pattern parts is covered with an upper conductive layer containing a mixture of binder resin made of thermoplastic resin and carbon powder, the conduction resistance of the wiring patterns and the second contact pattern can be reduced and there is no need to worry about the corrosion of the silver layer. Furthermore, the two types of carbon layers provide resistance to stress relaxation at the contacts without impairing the flexibility of the membrane switch.

Of the embodiments of the present invention, according to the embodiment that a polyester film is used as the base material of at least one of the first flexible insulating substrate and the second flexible insulating substrate and polyester resin is used as the binder resin of the wiring patterns (the derivation patterns), the wiring patterns (the derivation patterns) are brought into more intimate contact with the flexible insulating substrates, and even if the derivation part is used in a relaxed manner, the wiring patterns would not disjoin from the flexible insulating substrates.

Of the embodiments of the present invention, according to the embodiment that a film material is used as the spacer member and the opening of the spacer member corresponding to a contact is formed to be smaller than the formation areas of the first contact pattern and the second contact pattern, even if the first contact pattern and the second contact pattern are formed using a printing means so as to cause a wide range of film thickness variation, the gap between the contacts could be decided by the board thickness of the spacer member used as a film material, the variation of the gap would become small, and pressure for closing the contacts could be kept almost constant.

Of the embodiments of the present invention, according to the embodiment that more rigid binder resin than the binder resin forming the wiring patterns is used as the binder resin forming the terminals of the connection part, the terminals of the connection part would be little shaved by repeated insertion and extraction operations between the connection part and the connector, and trouble due to conductive clippings can be avoided.

Furthermore, of the embodiments of the present invention, according to the embodiment that rigid phenol resin is used as binder resin at the outermost layer of the second contact pattern, highly wear-resistant, long-life contact parts can be formed.

Also, of the embodiments of the present invention, according to the embodiment that the first contact pattern includes a conductive layer containing rigid resin, even if pressure is applied from any of the two flexible insulating substrates, stress relaxation occurs less frequently and the heat resistance creep ability can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described in detail based on the followings, wherein:

FIG. 1

is a schematic view of a membrane switch of a first embodiment according to the present invention, and is a cross-sectional view of a membrane switch of the first embodiment according to the present invention;

FIG. 2A

is a plan view of a first flexible insulating substrate and a second flexible insulating substrate in the first embodiment;

FIG. 2B

is a plan view of a spacer member in the first embodiment;

FIGS. 3A

is a plan view showing the neighborhood of a first terminal or second terminal constituting a connection part in the first embodiment;

FIG. 3B

is a cross-sectional view along a line

3

B—

3

B in

FIG. 3A

;

FIG. 4

is a schematic view showing a second embodiment of the membrane switch according to the present invention;

FIG. 5A

is a plan view of a first flexible insulating substrate in a second embodiment;

FIG. 5B

is a plan view of a second flexible insulating substrate in the second embodiment;

FIG. 6

is a schematic view showing a third embodiment of the membrane switch according to the present invention; and

FIG. 7

is a schematic view showing a fourth embodiment of the membrane switch according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1

is a schematic view of a membrane switch of a first embodiment according to the present invention, and is a cross-sectional view showing the neighborhood of its contact.

As shown in

FIG. 1

, the membrane switch of the first embodiment comprises: a first flexible isolating substrate

1

; a second flexible isolating substrate

2

; a spacer member

3

; a first contact pattern

4

; a second contact pattern

5

; a first wiring pattern

6

; a second wiring pattern

7

; an opening

8

; adhesive layers

9

; and contacts

10

.

The first flexible isolating substrate

1

and the second flexible insulating substrate

2

, each of which is made of a polyethylene naphthalate (PEN) base material of a polyester film, is about 75 to 100 &mgr;m in thickness, and has flexibility. The spacer member

3

is a polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) film of a polyester film, is about 100 &mgr;m in thickness, and has the opening

8

formed in the formation area of the contact

10

. The adhesive layers

9

, disposed between the first flexible isolating substrate

1

and one side of the spacer member

3

and between the second flexible isolating substrate

2

and another side of the spacer member

3

, are formed of adhesives having a thickness of about 25 &mgr;m in advance provided on both sides of the spacer member

3

constructed from a double-side adhesive sheet. The adhesive layers

9

integrate the first flexible isolating substrate

1

and the second flexible isolating substrate

2

so that they are disposed in facing relation at a predetermined interval.

The first contact pattern

4

and the second contact pattern

5

respectively consist of two layers, conductive layers

4

1

and

5

1

containing thermoplastic resin, and conductive layers

4

2

and

5

2

containing thermosetting resin. The first wiring pattern

6

and the second wiring pattern

7

respectively consist of two layers, lower conductive layers

6

1

and

7

1

containing thermoplastic resin, and upper conductive layers

6

2

and

7

2

containing thermoplastic resin.

In this case, conductive layers

4

1

and

5

1

containing thermoplastic resin, and lower conductive layers

6

1

and

7

1

containing thermoplastic resin have the same structure; a pasty mixture produced by mixing silver conductive powder and thermoplastic polyester binder resin in an organic solvent is coat-printed in the formation areas of the first contact pattern

4

and the first wiring pattern

6

on the first flexible insulating substrate

1

, and the formation areas of the second contact pattern

5

and the second wiring pattern

7

on the second flexible insulating substrate

2

, and the printed portions are heated to evaporate the organic solvent so that dry coats are formed. The conductive layers

4

2

and

5

2

containing thermosetting resin have the same structure; a pasty mixture produced by mixing conductive carbon powder (made from carbon black and graphite) and thermosetting phenol binder resin in an organic solvent is coat-printed on the formation area of the first contact pattern

4

on the first flexible insulating substrate

1

, and the formation area of the second contact pattern

5

on the second flexible insulating substrate

2

, and the printed portions are heated to evaporate the organic solvent so that dry coats are formed. The upper conductive layers

6

2

and

7

2

containing thermoplastic resin have the same structure; a pasty mixture produced by mixing conductive carbon powder (made from carbon black and graphite) and thermoplastic vinyl binder resin in an organic solvent is coat-printed on the formation areas of the first and second wiring patterns

6

and

7

on the first flexible insulating substrate

1

and the second flexible insulating substrate

2

, and the printed portions are heated to evaporate the organic solvent so that dry coats are formed.

The conductive layers

4

2

and

5

2

containing thermosetting resin and the upper conductive layers

6

2

and

7

2

containing thermoplastic resin are disposed and formed so that they respectively cover the conductive layers

4

1

and

5

1

containing thermoplastic resin, and the lower conductive layers

6

1

and

7

1

containing thermoplastic resin at a lower layer thereof, which contain silver powder, to prevent corrosion of the conductive layers

4

1

and

5

1

containing thermoplastic resin, and the lower conductive layers

6

1

and

7

1

containing thermoplastic resin. The first contact pattern

4

and the second contact pattern

5

are formed so that their size is slightly larger than the opening size of the spacer member

3

. The film thickness of each of the dried conductive layers is about 10 &mgr;m.

FIGS. 2A and 2B

are schematic views of the first flexible insulating substrate

1

and the second flexible insulating substrate

2

, and the spacer member

3

, which are used in the membrane switch of the first embodiment.

FIG. 2A

is a plan view (a front plan view and a back plan view) of the first flexible insulating substrate

1

and the second flexible insulating substrate

2

.

FIG. 2B

is a plan view of the spacer member

3

.

As shown in

FIGS. 2A and 2B

, the first flexible insulating substrate

1

and the second flexible insulating substrate

2

comprise: a switch body part

11

of nearly rectangular shape; a slim derivation part

12

protruding from the switch body part

11

; and a connection part

13

formed at the tip of the derivation part

12

. Components shown in

FIGS. 2A and 2B

that are identical to components shown in

FIG. 1

are identified by the same reference numerals.

The switch body part

11

has five contacts

10

formed thereon wherein the five contacts

10

comprise five first contact patters

4

on the first flexible insulating substrate

1

and five second contact patterns

5

on the second flexible insulating substrate

2

. On the first flexible insulating substrate

1

are formed five first wiring patterns

6

and a first wiring pattern coupling part

6

C wherein the five first wiring patterns

6

extend from the five first contact patterns

4

and the first wiring pattern coupling part

6

C, provided in the boundary with the derivation part

12

, couples the five first wiring patterns

6

. On the second flexible insulating substrate

2

are formed five second wiring patterns

7

and a second wiring pattern coupling part

7

C wherein the five second wiring patterns

7

extend from the five second contact patterns

5

, and the second wiring pattern coupling part

7

C, provided in facing relation with the first wiring pattern coupling part

6

C, couples the five first wiring patterns

7

. In this case, the first and second wiring pattern coupling parts

6

C and

7

C have a two-layer structure like the first and second wiring patterns

6

and

7

, and are formed at the same time when the first and second wiring patterns

6

and

7

are formed.

The derivation part

12

and the connection part

13

are formed by protruding the first flexible insulating substrate

1

and the first flexible insulating substrate

2

of the switch body part

11

. The derivation part

12

has a first wiring pattern

14

formed thereon as a derivation pattern leading to the first wiring pattern coupling part

6

C in the direction of the length of the first flexible insulating substrate

1

, and a second wiring pattern

15

formed thereon as a derivation pattern leading to the second wiring pattern coupling part

7

C in the direction of the length of the second flexible insulating substrate

2

. The connection part

13

has a first terminal

16

leading to the first wiring pattern

14

in the direction of the length of the first flexible insulating substrate

1

, and a second terminal

17

leading to the second wiring pattern

15

in the direction of the length of the second flexible insulating substrate

2

wherein the membrane switch and an external circuit are connected when the first terminal

16

and the second terminal

17

are coupled by a connector (not shown).

The first wiring pattern

14

consists of two layers, a lower conductive layer

14

1

containing thermoplastic resin, and an upper conductive layer

14

2

containing thermoplastic resin. The second wiring pattern

15

consists of two layers, a lower conductive layer

15

1

containing thermoplastic resin, and an upper conductive layer

15

2

containing thermoplastic resin (see FIG.

3

).

In this case, the lower conductive layers

14

1

and

15

1

containing thermoplastic resin have the same structure as the conductive layers

4

1

and

5

1

containing thermoplastic resin and the lower conductive layers

6

1

and

7

1

containing thermoplastic resin, and are formed at the same time when the conductive layers

4

1

and

5

1

containing thermoplastic resin and the lower conductive layers

6

1

and

7

1

containing thermoplastic resin are formed. The upper conductive layers

14

2

and

15

2

containing thermoplastic resin have the same structure as the upper conductive layers

6

2

and

7

2

containing thermoplastic resin, and are formed at the same time when the upper conductive layers

6

2

and

7

2

containing thermoplastic resin are formed. The conductive layers

16

2

and

17

2

containing thermosetting resign as shown in

FIG. 3

have the same structure as the conductive layers

4

2

and

5

2

containing thermosetting resin, and are formed at the same time when the conductive layers

4

2

and

5

2

containing thermosetting resin are formed.

FIGS. 3A and 3B

are schematic views of the neighborhood of the first terminal

16

or second terminal

17

constituting the connection part

13

.

FIG. 3A

is a plan view perspectively showing the interior thereof, and

FIG. 3B

is a cross-sectional view of the interior thereof along a line

3

B—

3

B in FIG.

3

A.

Components shown in

FIGS. 3A and 3B

that are identical to components shown in

FIGS. 2A and 2B

are identified by the same reference numerals.

As shown in

FIGS. 3A and 3B

, the connection part

13

comprises the first terminal

16

formed on the first flexible insulating substrate

1

and the second terminal

17

formed on the second flexible insulating substrate

2

wherein the first terminal

16

consists of two layers, a conductive layer

16

1

containing thermoplastic resin and a conductive-layer

16

2

containing thermosetting resin, while the second terminal

17

consists of two layers, a conductive layer

17

1

containing thermoplastic resin and a conductive layer

17

2

containing thermosetting resin.

In this case, the conductive layers

16

1

and

17

1

containing thermoplastic resin have the same structure as the conductive layers

4

1

and

5

1

containing thermoplastic resin, the lower conductive layers

6

1

and

7

1

containing thermoplastic resin, or the lower conductive layers

4

1

and

5

1

containing thermoplastic resin, and are formed at the same time when the conductive layers

4

1

and

5

1

containing thermoplastic resin, the lower conductive layers

6

1

and

7

1

containing thermoplastic resin, and the lower conductive layers

14

1

and

15

1

containing thermoplastic resin are formed. The conductive layers

16

2

and

17

2

containing thermosetting resign have the same structure as the conductive layers

4

2

and

5

2

containing thermosetting resin, and are formed at the same time when the conductive layers

4

2

and

5

2

containing thermosetting resin are formed.

The membrane switch of the first embodiment having the foregoing structure operates as follows.

The body part

11

of the membrane switch is buried in an operation area, e.g., an automobile seat (the interior of urethane foam). When an occupant sits on the seat, pressure is applied to at least one of the five contacts

10

by the occupant's weight, the first and second flexible insulating substrates

1

and

2

are partially deformed in opposition to the elasticity of the first and second flexible insulating substrates

1

and

2

themselves, and the first contact pattern

4

and the second contact pattern

5

are brought into contact so that the contact

10

is closed. When the contact

10

has been closed, there arises a change in the state of voltage or current between the first wiring pattern

6

connected to the first contact pattern

4

and the second wiring pattern

7

connected to the second contact pattern

5

, the change in the state of voltage or current is transferred to an external circuit via the first and second wiring pattern coupling parts

6

C and

7

C, the first and second wiring patterns

14

and

15

, and the first and second terminals

16

and

17

, and thereby it is detected that the membrane switch has been closed.

In this way, in the membrane switch of the first embodiment, highly flexible polyester films are used for the first flexible insulating substrate

1

and the second flexible insulating substrate

2

; and the first and second wiring patterns

6

and

7

, the first and second wiring pattern coupling parts

6

C and

7

C, and the first and second wiring patterns

14

and

15

respectively use conductive layers

6

1

,

6

2

,

7

1

,

7

2

,

14

1

,

14

2

,

15

1

, and

15

2

containing thermoplastic resin used as binder resin. Therefore, the flexibility of the switch body part

11

and the derivation part

12

can be kept satisfactory.

In the membrane switch of the first embodiment, PEN having higher heat resistance than PET is used for the first and second flexible insulating substrates

1

and

2

; and the first and second contact patterns

4

and

5

, and the first and second terminals

16

and

17

respectively use conductive layers

4

2

,

5

2

,

16

2

and

17

2

containing thermosetting resin used as binder resin. Therefore, even if the ambient temperature of the membrane switch becomes high during use, stress relaxation at the contacts

10

can be prevented whenever possible, the situation in which the contacts are erroneously closed when an applied pressure is insufficient can be avoided, the surface of the first and second terminals

16

and

17

would not be shaved by repeated insertion and extraction of the first and second terminals

16

and

17

to and from the connector, trouble due to conductive clippings can be avoided, and the operating life of the connection part

13

can be extended.

Furthermore, in the membrane switch of the first embodiment, each of the first and second contact patters

4

and

5

, the first and second wiring patterns

6

and

7

, the first and second wiring pattern coupling parts

6

C and

7

C, the first and second wiring patterns

14

and

15

, and the first and second terminals

16

and

17

has two conductive layers. Therefore, conductivity can be increased, as compared with those known that have only one conductive layer.

In the membrane switch of the first embodiment, polyester films are used for the first flexible insulating substrate

1

and the second flexible insulating substrate

2

; and the lower layers of the first and second wiring patterns

6

,

7

,

14

, and

15

consisting of two layers respectively use conductive layers

6

1

,

7

1

,

14

1

, and

15

1

containing thermoplastic resin made of polyester binder resin. Therefore, the first flexible insulating substrate

1

and the second flexible insulating substrate

2

are brought into more intimate contact with the conductive layers

6

1

,

7

1

,

14

1

, and

15

1

containing thermoplastic resin. For example, even if the derivation part

12

and the like are used in a relaxed manner, the conductive layers

14

1

and

15

1

containing thermoplastic resin would not disjoin from each other.

FIG. 4

is a schematic view showing a second embodiment of a membrane switch according to the present invention and is a cross-sectional view (no wiring patterns are shown) showing the neighborhood of contact

10

.

FIGS. 5A and 5B

are schematic views of a first flexible insulating substrate

1

and a second flexible insulating substrate

2

used in the membrane switch of the second embodiment.

FIG. 5A

is a plan view of the first flexible insulating substrate

1

and

FIG. 5B

is a plan view (a back plan view) of the second flexible insulating substrate

2

shown partially perspectively.

Components shown in

FIGS. 4

,

5

A, and

5

B that are identical to components shown in

FIGS. 1

,

2

A, and

2

B are identified by the same reference numerals.

The membrane switch of the second embodiment is similar to that of the first embodiment in the basic structure including the base material of the first flexible insulating substrate

1

and the second flexible insulating substrate

2

. However, the membrane switch of the second embodiment is structurally different from that of the first embodiment in the following point. When a conductive pattern is formed on the first flexible insulating substrate

1

and the second flexible insulating substrate

2

, the membrane switch of the first embodiment is constructed so that a variety of components are formed equally in both the first flexible insulating substrate

1

and the second flexible insulating substrate

2

, while the membrane switch of the second embodiment is constructed so that a variety of components are formed mainly in the first flexible insulating substrate

1

.

Specifically, in the second embodiment, in the switch body part

11

of the first flexible insulating substrate

1

, a pair of comb conductive patterns is disposed as a first contact pattern

4

to serve as a contact

10

, a first and a second wiring patterns

6

and

7

respectively leading to the pair of comb conductive patterns

4

are disposed, a first and a second wiring patterns

14

and

15

are, in a derivation part

12

, disposed as derivation patterns respectively leading to the first and second wiring patterns

6

and

7

, and first and second terminals

16

and

17

respectively leading to the first and second wiring patterns

14

and

15

are disposed in a connection part

13

, while, in the second flexible insulating substrate

2

, only the second contact pattern

5

to serve as a contact

10

is disposed in the switch body part

11

, but the second wiring pattern

7

is not disposed, and the derivation part

12

in which the second wiring pattern

15

is disposed, and the connection part

13

are not provided.

In the second embodiment, as in the first embodiment, a spacer member

3

(without a protrusion part disposed on the derivation part

12

) having an opening

8

is disposed between the first flexible insulating substrate

1

and the second flexible insulating substrate

2

at the contact

10

and is integrally joined to the first flexible insulating substrate

1

and the second flexible insulating substrate

2

by adhesive layers

9

. A pair of comb conductive patterns

4

and the second contact pattern

5

respectively consist of two layers, conductive layers

4

1

and

5

1

containing thermoplastic resin and conductive layers

4

2

and

5

2

containing thermosetting resin, which are constructed from the same material forming the first contact pattern

4

and the second contact pattern

5

of the first embodiment. The first and second wiring patterns

6

and

7

, and the first and second wiring patterns

14

and

15

, though not shown, consist of two layers, lower conductive layers

6

1

,

7

1

,

14

1

, and

15

1

containing thermoplastic resin and upper conductive layers

6

2

,

7

2

,

14

2

, and

15

2

containing thermoplastic resin, which are constructed from the same material forming the first and second wiring patterns

6

and

7

and the first and second wiring patterns

14

and

15

of the first embodiment.

The membrane switch of the foregoing structure of the second embodiment operates essentially like the membrane switch of the first embodiment and effects obtained by the membrane switch of the second embodiment are almost the same as those obtained by the membrane switch of the first embodiment. Therefore, a description of the operation and effects of the membrane switch of the second embodiment is omitted.

The structure of the membrane switch of the second embodiment may be changed so that the second contact pattern

5

consists of two layers, a conductive layer

5

1

containing thermoplastic resin and a conductive layer

5

2

containing thermosetting resin, while a pair of comb conductive patterns

4

to serve as a first contact pattern

4

consists of two layers, lower and upper conductive layers containing thermoplastic resin, like the first and second wiring patterns

6

and

7

. The changed structure of the membrane switch would raise practically little problem, except that, since a conductive pattern area in which a pair of comb conductive patterns

4

is formed is smaller than the conductive pattern area of the first contact pattern

4

of the first embodiment, the occurrence of stress relaxation at the contact

10

becomes more difficult to avoid than with a membrane switch of the first embodiment when the ambient temperature of the membrane switch becomes high.

FIG. 6

is a schematic view showing a third embodiment of a membrane switch according to the present invention, and is a cross-sectional view showing the neighborhood of a contact.

As shown in

FIG. 6

, the membrane switch of the third embodiment includes: a conductive layer

5

3

containing thermosetting resin; first conductive layers

4

′

1

and

5

4

containing thermoplastic resin; second conductive layers

4

′

2

and

5

5

containing thermoplastic resin; and a stationary plate

18

. Components shown in

FIG. 6

that are identical to components shown in

FIG. 1

are identified by the same reference numerals.

A second contact pattern

5

consists of three layers, a conductive layer

5

3

containing thermosetting resin at the bottom layer wherein the first conductive layer

5

3

serves as an insulating, conductive layer containing rigid resin, a first conductive layer

5

4

containing thermoplastic resin at a middle layer, and a second conductive layer

5

5

containing thermoplastic resin at the bottom layer. The stationary plate

18

is constructed from, e.g., a metallic plate made of steel having a thickness of 1 mm, and an open face of the first flexible insulating substrate

1

is joined to one face of the stationary plate

18

.

In this case, the conductive layer

5

3

containing thermosetting resin is fabricated by the same fabrication process as the process of fabricating the conductive layers

4

2

and

5

2

containing thermosetting resin of the first embodiment from which the process of introducing conductive powder is excluded. The first conductive layer

5

4

containing thermoplastic resin is fabricated by the same fabrication process as the process of fabricating the conductive layers

4

1

and

5

1

containing thermosetting resin of the first embodiment. The second conductive layer

5

5