JP2990972B2 - Membrane switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a membrane switch used for a switch part controlled by a computer used in a high humidity environment.

[0002]

2. Description of the Related Art A membrane switch is a pressure-sensitive adhesive mainly composed of an acrylic resin, a thermoplastic adhesive such as a nitrile resin, or a phenol resin-based adhesive as an adhesive between a spacer and a substrate and between a contact sheet and a spacer. Although a thermosetting adhesive is used, the contact layer is formed by this adhesive layer, and at the same time, it has the function of preventing the intrusion of moisture from the external environment. In addition, the contact sheet was bonded over almost the entire surface of the substrate including the vicinity of the contact.

Since the on / off operation of the contact portion on which silver or carbon paste is printed uses the rigidity of the contact sheet, the distance in the short direction of the contact chamber is affected by the material of the contact sheet. In the case of a polyethylene terephthalate sheet having a thickness of about 0.1 mm used, 10 to 20 mm
Set to about.

[0004]

A feature of the present invention is that a sealed air chamber is formed by bonding one surface of a spacer to the outer periphery of a substrate and bonding a contact sheet to the other surface of the spacer opposite to the substrate. Forming a contact chamber in the air chamber, which is a part of the spacer and communicates with the air chamber by a contact chamber forming spacer having the same thickness , and contacts the substrate and the contact sheet of the contact chamber respectively. And the contact chamber forming spacer forming the contact chamber is bonded only to either the contact sheet or the substrate.

[0005]

As described above, the membrane switch is provided with a contact chamber as its basic structure, and operates by bending the upper surface thereof by operating pressure. Has a closed sealed structure.

This is particularly necessary for products used in high humidity environments such as washing machines, dishwashers, clothes dryers, rice cookers and the like.

That is, it is intended to prevent corrosion of circuits and electronic components due to intrusion of moisture from the outside, malfunctions due to a decrease in insulation resistance between contacts, and the like.

However, in the case of a hermetic structure, there is a problem that the pressure in the contact chamber gradually decreases due to fluctuations in the temperature of the use environment, and the contact portion remains in a recessed state, adversely affecting the switch function.

This is because the internal air expands in a high-temperature environment, the internal pressure rises, and the air passes through the contact sheet and is gradually discharged to the outside. It is considered that the air permeability of the sheet is smaller than that at the time of high temperature, so that the sheet permeates again from the outside and does not sufficiently enter the contact chamber.

[0010] By repeating this heat cycle, the internal pressure continues to decrease, and eventually the contact portion is depressed until contact conduction is reached.

In order to prevent this, a structure has been adopted which alleviates the concentration of stress on the contact portion due to the decrease in the internal pressure of the closed system.

In this method, another air chamber communicating with the contact chamber is provided, and the rigidity of the upper surface of the air chamber is made smaller than that of the contact chamber, so that the depression corresponding to the decrease in the internal pressure is consumed on the upper surface of the air chamber, and the amount of depression of the contact section is reduced. The air chamber is designed using a space other than the front surface of the substrate, that is, a space other than the contact chamber on one side provided with contacts and circuits, and the back surface of the substrate provided with holes and communicating with the substrate.

In order to realize the pressure relief structure of such a concept, it is preferable to make the air chamber as wide as possible.
Particularly in the case of a rectangle, it is effective to increase the distance in the short direction.

That is, the relationship between the pressure and the amount of depression when the four sides are fixed is inversely proportional to the dimension in the short direction as shown in Expression 1.

As described above, in the conventional membrane switch, since the adhesive layer is provided on both surfaces of the spacer on the substrate, the air chamber must be provided in the remaining space other than the contact chamber on the surface, that is, the contact chamber surface. However, it was difficult to secure a sufficient area.

In particular, when the substrate has an elongated shape, a sufficient dimension in the short direction cannot be obtained from portions other than the contact chamber, and there has been a problem that the pressure relaxation effect is extremely reduced.

Many of the components of pressure-sensitive adhesives often used as adhesives contain a liquid plasticizer for the purpose of increasing flexibility, etc., but these are left to stand in a high-temperature environment for a long time. If so, it may ooze out.

In a structure in which the adhesive layer is exposed on the wall surface of the contact chamber as in the prior art, the exuded adhesive fixes the concave contact sheet as it is when the switch is operated, causing a change in operation pressure and a cause of poor conduction. There was a problem.

[0019]

A feature of the present invention is that a sealed air chamber is formed by bonding one surface of a spacer to the outer periphery of a substrate and bonding a contact sheet to the other surface of the spacer opposite to the substrate. Forming a contact chamber communicating with the air chamber by a contact chamber forming spacer that is a part of the spacer in the air chamber, and arranging contacts on the substrate and the contact sheet of the contact chamber, respectively.
The membrane switch, wherein the spacer for forming the contact chamber, which forms the contact chamber, is bonded to only one of the contact sheet and the substrate.

[0020]

The contact portion of the contact sheet needs to have a certain rigidity in order to regulate the operating pressure as a switch. For this purpose, a contact chamber forming spacer is protruded around the contact portion, and the contact sheet or the contact sheet is formed. The problem can be solved by adopting a structure in which only one of the substrates is bonded. In particular, when only the interface between the spacer and the substrate surface is bonded and fixed, the rigidity of the contact sheet is not affected, which is effective.

[0021]

1 and 2 show the structure of a conventional membrane switch.

FIG. 1 is a top view of the membrane switch, and FIG. 2 is a sectional view of a portion A in FIG.

The contact portion 2 is a double printed layer of silver and carbon printed on the surface of the contact sheet 3 and the substrate 1. Here, the substrate 1 is provided with a copper etching circuit on a paper-laminated phenolic resin plate, on which a multilayer resist film made of an ultraviolet curable resin and a heat curable resin is formed.

The contact sheet 3 is a polyethylene terephthalate resin having a thickness of 0.1 mm.
The same material as the 5mm spacer is used.

The adhesive layer 4 is a pressure-sensitive adhesive film based on an acrylic resin and has tackiness. This adhesive layer 4
Is kept at least 7 mm from the outer peripheral portion, and plays a role of preventing moisture and the like from entering the contact chamber 6 and the air chamber 7.

A spacer 5 protrudes around the contact portion 2 and is fixed by an adhesive layer 4. The size of the contact chamber is set to 10 mm in the short side direction to obtain an appropriate switch operating pressure.

Hereinafter, Embodiments 1, 2, and 3 of the present invention will be described in order with reference to FIGS. 3, 4, and 5, and Embodiment 4 will be described with reference to FIGS.

In the first embodiment, the material of each part is shown in FIGS.
However, there is no adhesive layer at the interface between the contact chamber forming spacer 5 forming the contact chamber 6 and the contact sheet 3.

Therefore, the adhesive on the upper surface is not exposed on the inner wall surface of the contact chamber 6. However, the entire surface of the contact chamber forming spacer 5 and the substrate 1 is fixed by the adhesive layer 4.

In this embodiment, the contact chamber forming spacer 5
Is not bonded to the contact sheet, the movable portion of the contact sheet 3 is within the range between the spacers 4 bonded to the outer periphery of the substrate 1. As a result, the rigidity of the contact sheet 3 decreases,
Even if the internal air expands in a high-temperature atmosphere, the pressure generated is lower than when the contact chamber forming spacer 5 is bonded.

Accordingly, at this time, the amount of air that passes through the contact sheet 3 and leaks to the outside is reduced, so that the degree of decrease in the internal pressure when cooled thereafter is also reduced, and the amount of depression in the contact portion is reduced.

Since the adhesive layer 4 does not exist at the interface between the inner wall surface of the contact chamber 6 and the contact sheet 3, the adhesive oozing out after being left in a high-temperature environment for a long time pulls the recessed contact sheet downward from the side. There is no problem of being fixed.

Next, in the case of the second embodiment shown in FIG. 4, the structure in which the adhesive layer 4 is not provided at the interface with the substrate 1 in the contact chamber forming spacer 5 around the contact chamber 6 is also used. Almost the same effect of reducing the generated internal pressure as in the case of Example 1 can be obtained.

The adverse effect due to the exuded adhesive is suppressed less than in the conventional configuration because the contact chamber forming spacer 5 itself is not fixed to the substrate and is movable.

In the third embodiment shown in FIG. 5, a nitrile resin-based thermoplastic adhesive is used for the adhesive layer 4. In the figure, a heating jig 11 for thermocompression bonding is used to heat and melt the adhesive, and only by tightening the adhesive while heating from above and below, only the contact portion is melted and an adhesive force is developed.

FIG. 5A shows a hot-melt adhesive portion 4A of the adhesive, which has the same size and shape as the heat-compression heating jig 11.
The adhesive portion 4B of the contact chamber forming spacer 5 is not heated, and therefore does not exhibit an adhesive force.

According to this method, unlike the first and second embodiments, the spacer 5 and the adhesive layer 4 do not need to be processed into different shapes, and there is an advantage that only the processing of the shape of the jig at the time of thermocompression bonding is required.

The fourth embodiment shown in FIGS. 6 and 7 is an application example of the present invention when the air chamber 7 is small or when the air chamber 7 is not installed.

In this embodiment, the dotted line in FIG. 6 indicates a range 5 mm outward from the contact chamber, but the contact sheet 3 and the spacer 5 are not bonded inside the dotted line.

When the contact room air expands, the inside of the dotted line becomes a movable portion, and the generated internal pressure rise is suppressed low, so that the effect of reducing the amount of leaked air can be obtained. Therefore, the degree of pressure reduction at low temperatures is also reduced, and the amount of depression is reduced.

[0041]

FIG. 8 shows a comparison between the effect of the conventional membrane switch shown in FIG. 2 and the effect of the membrane switch of the first embodiment shown in FIG.

The effect is as follows. The membrane switch of each structure is left in a cooling / heating cycle environment in which it is left at -20 ° C. for 1 hour after being left at 80 ° C. for 23 hours, and the dent amount of the contact portion of the contact sheet at 25 ° C. is measured with time. The result is shown.

The height of the contact chamber including the spacer and the adhesive layer is 0.4 mm, and when the recess becomes 0.4 mm, the contact is in a continuous conduction state and does not function as a switch. In FIG. 8, a curve 8 indicates the structure of the conventional product, and a curve 9 indicates the change in the amount of depression by the structure of the first embodiment of the present invention.

As is evident from the results, the dent amount is equal to 0.
The time required to reach 4 mm was about 1000 hours for the conventional product, whereas that of Example 1 was about 10,000 hours, which is a ten-fold life extension effect.

This is due to not only the effect of the structure for alleviating the rise in internal pressure, but also the effect of fixing the contact sheet by the adhesive that has clearly oozed into the contact chamber after about 500 hours in the conventional structure.

In this test, no key tapping operation was performed, but since the actual membrane switch is pressed many times as a switch, it is estimated that the effect of preventing the adhesive from oozing out will be added to the results of this test. Is done.

[Brief description of the drawings]

FIG. 1 shows a top view of a membrane switch.

FIG. 2 is a sectional view showing the vicinity of a contact portion of a conventional membrane switch (A portion in FIG. 1).

FIG. 3 shows a first embodiment of the present invention in a sectional view near a contact portion.

FIG. 4 is a cross-sectional view showing the vicinity of a contact portion according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view showing the vicinity of a contact portion according to a third embodiment of the present invention.

FIG. 6 shows a fourth embodiment of the present invention in a top view of a membrane switch.

FIG. 7 is a cross-sectional view showing the vicinity of a contact portion according to a fourth embodiment of the present invention.

FIG. 8 shows the results of a cooling / heating cycle test of Example 1 of the present invention in comparison with conventional components in terms of the amount of dent in the contact portion.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Contact part, 3 ... Contact sheet, 4 ... Adhesive layer,
4A: thermoplastic adhesive layer heat-fused portion, 4B: thermoplastic adhesive layer non-melted portion, 5: spacer, 6: contact chamber, 7: air chamber, 8: conventional product (contact portion adhesive structure), 9: Examples 1
(Contact part non-adhesive structure), 11: Heating jig for thermocompression bonding.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsuo Ishikawa 1-1-1 Higashitagacho, Hitachi City, Ibaraki Prefecture Within the Living Equipment Business Division, Hitachi, Ltd. (72) Inventor Noboru Fujita 1-chome, Higashitagacho, Hitachi City, Ibaraki No. 1-1 Hitachi, Ltd. Living Equipment Division (72) Inventor Tomoyuki Soma 1-1-1, Higashitagacho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Living Equipment Division (72) Inventor Shigeharu Nakano Ibaraki 1-1-1 Higashitaga-cho, Hitachi City, Japan Inside the Living Equipment Division of Hitachi, Ltd. (56) References JP-A-62-264521 (JP, A) JP-A 1-152417 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01H 13/00-13/76

Claims (1)

(57) [Claims] 1. A sealed air chamber is formed by bonding one surface of a spacer to an outer periphery of a substrate and bonding a contact sheet to another surface of the spacer opposite to the substrate to form a sealed air chamber. And a contact chamber communicating with the air chamber is formed by a contact chamber forming spacer having the same thickness and a contact is arranged on the substrate and the contact sheet of the contact chamber to form the contact chamber. A membrane switch, wherein the spacer for forming the contact chamber is bonded to only one of the contact sheet and the substrate.