Title: Movable contact unit having press-down projections
Abstract: Movable contact unit of the present invention comprises a plurality of dome-like movable contacts made of electrically conductive metal sheets capable of making an inflective action when depressed, a base film having an adhesive layer for retaining upper surfaces of the plurality of movable contacts, and a plurality of press-down projections bonded by adhesive to an upper surface of the base film in positions corresponding to center portions of the respective movable contacts, wherein the upper surface of the base film and underside surfaces of the press-down projections are each provided with a pretreated layer. The above structure has an advantage of strengthening the bonding between the adhesive and each of the pretreated layers formed on the adhering surfaces of the base film and the press-down projections, so as to provide the movable contact unit with outstanding reliability in maintaining the bonded condition for a long duration.
Patent Number: 6,906,274 Issued on 06/14/2005 to Ito, et al.
| Inventors:
|
Ito; Masahiro (Okayama, JP);
Sera; Naoki (Okayama, JP);
Numoto; Nobuhiro (Okayama, JP)
|
| Assignee:
|
Matsushita Electric Industrial Co., Ltd. (Osaka, JP)
|
| Appl. No.:
|
700680 |
| Filed:
|
November 5, 2003 |
Foreign Application Priority Data
| Dec 13, 2002[JP] | 2002-362038 |
| Current U.S. Class: |
200/512; 200/341; 200/345 |
| Intern'l Class: |
H01H 001/02; H01H013/70.2 |
| Field of Search: |
200/512-517,341-345
400/490-495
428/910,913,425.2
|
References Cited [Referenced By]
U.S. Patent Documents
| 5888656 | Mar., 1999 | Suzuki et al.
| |
| 6084190 | Jul., 2000 | Kenmochi.
| |
| 6224278 | May., 2001 | Nishi.
| |
| 6604278 | Aug., 2003 | Sera et al.
| |
| 6723936 | Apr., 2004 | Ootsuka et al.
| |
| Foreign Patent Documents |
| 2002/-216582 | Aug., 2002 | JP.
| |
Primary Examiner: Scott; James R.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack, L.L.P.
Claims
1. A movable contact unit having press-down projections comprising:
base film having first film surface and second film surface;
adhesive layer covering said first film surface;
first pretreated layer covering said second film surface;
a plurality of dome-like movable contacts with outer surfaces held adhered to
said adhesive layer;
a plurality of press-down members, each having upper surface and underside surface;
and
second pretreated layer covering said underside surface,
wherein said second pretreated layer is bonded to said first pretreated layer
with adhesive in a position where each said press-down members confronts a center
portion of each said movable contacts.
2. The movable contact unit of claim 1, wherein at least one of said first pretreated
layer and said second pretreated layer is a resin layer comprising a coating of
any of Urethane resin and Ester resin.
3. The movable contact unit of claim 1, wherein said adhesive comprises UV-curable
adhesive resin.
4. The movable contact unit of claim 3, wherein said adhesive resin comprises
urethane acrylate.
5. The movable contact unit of claim 3, wherein said adhesive has an after-cured
hardness of HDD 80 to 65 as measured by a type D durometer according to JIS Standard
K 7215.
6. The movable contact unit of claim 1, wherein an underside surface of each
said press-down members has an outer diameter between ¼ and ½ of an outer
diameter of said movable contacts.
7. The movable contact unit of claim 1, wherein an underside surface of each
said press-down members has a surface area between {fraction (1/16)} to ¼
of a surface area of said movable contacts.
8. The movable contact unit of claim 1, wherein said first pretreated layer provides
said basefile with good wettability to said adhesive, and
said second pretreated layer provides said press-down members with good wettability
to said adhesive.
9. The movable contact unit of claim 1, wherein said first pretreated layer improves
adhesion between said basefile and said adhesive, and
said second pretreated layer improves adhesion between said press-down members
and said adhesive.
Description
TECHNICAL FIELD
The present invention relates to a movable contact unit provided with press-down
projections used in a control panel and the like of a variety of electronic apparatuses.
BACKGROUND OF THE INVENTION
With the increase in variety of electronic apparatuses for portable use such
as cellular phones, portable audio-video equipment, and the like in recent years,
there is continued advancement in multi-functional capability as well as reduction
in size, thickness and weight. Movable contact units of a type having a plurality
of movable contacts retained on an insulating plastic film are used in large number
as switches for control panels of the electronic apparatuses, as they can be made
thin, and provide good tactile response as well as stable electrical contact. The
movable contacts are made of electrically conductive metal sheets formed into a
dome-like shape.
Since these apparatuses are being carried and used anywhere, the switches are
operated so frequently that they require movable contact units of high durability
and stable tactile response in the switching operation.
Referring now to FIG. 7, a description is provided hereinafter of a conventional
movable contact unit of such kind used for the switch of a control panel.
In the conventional movable contact unit, as shown in FIG. 7, a plurality of
dome-like
movable contacts 3 are arranged independently with respect to one another,
with their upper surfaces retained by adhesion of adhesive layer 2 formed
on an underside surface of flexible insulating base film 1 having an external
shape formed into a predetermined shape.
Movable contacts 3 are sandwiched between separator 4 made
of an insulating film having a surface treated with release agent and base film
1. Separator 4 is held adhered to adhesive layer 2 on base
film 1 in a manner that it covers the entire underside surface of base film 1.
As separator 4 is placed in close adhesion to base film 1 in a manner
to completely cover the outer peripheries of movable contacts 3, it prevents
corrosion of movable contacts 3. In addition, separator 4 also prevents
adhesive layer 2 on base film 1 from sticking to other surfaces and
gathering foreign objects unintendedly during transportation and in the storage.
The conventional movable contact unit further has small cylindrical parts 5A,
which are fabricated by die-cutting a plastic film into a cylindrical shape, and
bonded to base film 1 by adhesive resin 5B composed of epoxy acrylate,
i.e. a kind of resin curable by ultraviolet rays. Each of cylindrical parts 5A
and adhesive resin 5B compose press-down projection 5.
FIG. 8 shows a structure of the conventional movable contact unit in the actual
application. After separator 4 is peeled off, base film 1 bearing
movable contacts 3 is attached to wiring board 7 using adhesive layer
2 so that movable contacts 3 are aligned in a manner to face with
their respective sets of stationary contacts 6 (6A and 6B).
FIG. 8 depicts wiring board 7 with the movable contact unit attached
to it. The center portion of movable contact 3 confronts the respective
one of central stationary contacts 6A, and the peripheral edge of movable
contact 3 lies on the corresponding outer stationary contact 6B,
so that each movable contact 3 and the corresponding stationary contacts
6 compose a single switch. In addition, actuator button 8 of the
apparatus is arranged above press-down projection 5.
A switch for control panel using the conventional movable contact unit constructed
as above operates in a manner which will be described now with reference to FIG. 9.
When actuator button 8 is depressed in a direction shown by an arrow
in FIG. 9, the depressing force is given on the upper surface of cylindrical press-down
projection 5, which is in contact to underside surface 8A of actuator
button 8. The depressing force is thus applied to the center portion of
movable contact 3 through press-down projection 5 and base film 1.
When the depressing force exceeds an inflectional strength of movable contact
3 of the dome-like shape, it bends into an inverted shape with a click-feeling,
and an underside surface in the center of movable contact 3 comes in contact
with central stationary contact 6A. This makes an electrical connection
between central stationary contact 6A and outer stationary contact 6B
on wiring board 7 via movable contact 3.
When the depressing force is removed, movable contact 3 regains its original
shape by an elastic restoring force of its own. This separates the underside surface
in the center of movable contact 3 from central stationary contact 6A,
to restore the state of electrical isolation between the central stationary contact
6A and the outer stationary contact 6B of wiring board 7.
By allowing the optimum click-feeling in the depressing operation, the above structure
provides the control panel switch with good tactile response.
Due to the rapid-paced advancement in the multi-functional capability in addition
to downsizing of portable apparatuses in the recent years, a number of functions
assigned to a single switch increases, which consequently increases frequency of
depressing operation of the switch. There is thus growing demand for improvement
of durability to the switching operation.
In other words, the desire continues to increase for a movable contact unit designed
to increase strength of adhesion of press-down projection 5 to base film
1 with steadiness of the tactile response even after repeated operations.
SUMMARY OF THE INVENTION
The present invention addresses the above problems, and it is intended to provide
a movable contact unit having press-down projections which can maintain the press-down
projections in a securely bonded condition to a base film without increasing a
number of components used and necessitating a complicated manufacturing process.
To achieve the above object, the movable contact unit of this invention comprises
a plurality of dome-like movable contacts made of electrically conductive metal
sheets capable of making an inflective action when depressed, a base film having
an adhesive layer for retaining upper surfaces of the plurality of movable contacts,
and a plurality of press-down projections bonded by adhesive to an upper surface
of the base film in positions corresponding to center portions of the respective
movable contacts, wherein the upper surface of the base film and underside surfaces
of the press-down projections are each provided with a pretreated layer. The above
structure has an advantage of strengthening the bonding between the adhesive and
each of the pretreated layers formed on the adhering surfaces of the base film
and the press-down projections, so as to provide the movable contact unit with
outstanding reliability in maintaining the bonded condition for a long duration.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectioned front view of a movable contact unit with press-down projections
according to an exemplary embodiment of the present invention.
FIG. 2 is a sectioned view of a portion of a control panel switch provided with
the movable contact unit according to the exemplary embodiment of this invention.
FIG. 3 is a drawing illustrating operation of the control panel switch shown
in FIG. 2.
FIG. 4 is a drawing illustrating a method of measuring bonding strength of the
press-down projections of the movable contact unit according to the exemplary embodiment
of this invention.
FIG. 5 is a graphical representation showing a test result of the bonding strength
corresponding to number of depressing operations.
FIG. 6 is a graphical representation showing another test result of the bonding
strength corresponding to number of depressing operations under high temperature
and high humidity environment.
FIG. 7 is a sectioned front view of a movable contact unit of the related art.
FIG. 8 is a sectioned view of a portion of a control panel switch provided with
the movable contact unit of the related art.
FIG. 9 is a drawing illustrating operation of the control panel switch of the
related art.
DESCRIPTION OF THE INVENTION
Referring to FIG.
1 through FIG. 6, description is provided hereinafter
of an exemplary embodiment of the present invention.
(Exemplary Embodiment)
Like reference numerals are used to denote like structural components as those
described in the background techniques section, and their details will be skipped.
FIG. 1 shows movable contact unit
100 provided with press-down projections
according to the present invention. As shown in FIG. 1, base film
11 composed
of a flexible resin film. (made of PET) having an external shape formed into a
predetermined shape has an underside surface (hereinafter referred to as first
film surface)
112 and an upper surface (hereinafter referred to as second
film surface)
111. Second film surface
111 is covered with a resin
layer serving as a pretreated layer (hereinafter designated first pretreated layer)
13 formed by coating Ester resin.
Base film
11 has adhesive layer
12 covering an entire surface
of first film surface
112, on which movable contacts
14 made of electrically
conductive metal sheets formed into a dome-like shape are bonded securely. The
plurality of movable contacts
14 are positioned independently with respect
to one another into a predetermined layout, with their upper surfaces retained
by adhesion. Movable contacts
14 positioned independently here means that
they are not in contact with each other.
Base film
11 may be so prefabricated that portions corresponding to respective
movable contacts
14 are convexed to fit the dome-like shape of movable contacts
14.
Separator
15 made of an insulating plastic film having a surface
treated with agent is adhered to adhesive layer
12 to cover the entire area
of first film surface
112 of base film
11 in the same manner as the
related example, in order to prevent corrosion of movable contacts
14, gathering
of foreign objects and the like.
In addition, small cylindrical parts (i.e. press-down members)
16 are
bonded
by adhesive resin
18 on their underside surfaces
162 to second film
surface
111 of base film
11 in respective positions corresponding
to the center portions of dome-like movable contacts
14, to thus compose
press-down projections
19 of this exemplary embodiment of the invention.
Each of small cylindrical parts
16 made of a PET film has resin layer (hereinafter
designated second pretreated layer)
17 composed of Ester resin coated on
its underside surface
162. Second pretreated layer
17 is bonded to
base film
11 with adhesive resin
18. Accordingly, small cylindrical
part
16, adhesive resin
18 and second pretreated layer
17
compose each of press-down projections
19. On the other hand, adhesive resin
18 bonds between second pretreated layer
17 on small cylindrical
part
16 and first pretreated layer
13 on base film
11, since
base film
11 has first pretreated layer
13 formed over second film
surface
111. A main ingredient of adhesive resin
18 used in this
exemplary embodiment is urethane acrylate, which is a kind of UV-curable resin.
What has been described above is the structure of movable contact unit
100
provided with a plurality of movable contacts
14, base film
11, and
press-down projections
19 in order of the manufacturing process.
Next, FIG. 2 shows a control panel switch assembled with the movable contact
unit having press-down projections according to this exemplary embodiment. Separator
15 is peeled off first from the movable contact unit having press-down projections,
which bears separator
15 adhered to it as shown in FIG.
1. The movable
contact unit is attached to wiring board
7 using adhesive layer
12
on the underside of base film
11, while movable contacts
14 are aligned
over wiring board
7 having an array of stationary contacts
6 (
6A
and
6B), in a manner that movable contacts
14 face the corresponding
sets of stationary contacts
6.
Here, each of movable contacts
14 is positioned with its peripheral
edge lying on the outer stationary contact
6B so that the bottom center
portion confronts the central stationary contacts
6A. Each of movable contacts
14 thus composes individual switch in combination with the corresponding
stationary contacts
6.
Actuator buttons
8 of the apparatus are then arranged above press-down
projections
19 in a corresponding manner. Accordingly, small cylindrical
parts
16 come in contact with actuator buttons
8 at their upper surfaces
161.
In the control panel switch of the above structure, depression of actuator button
8 in the direction of an arrow shown in FIG. 3 inflects movable contact
14 into an inverted shape, and causes the center portion of movable contact
14 lying on outer stationary contact
6B to come into contact with
central stationary contact
6A, so as to make switching operation.
Evaluation
Description is given next of test methods and results of various comparison
evaluations conducted on the movable contact unit having press-down projections
according to this exemplary embodiment.
Describing first pertains to details of measurements made on a plurality
of samples produced for bonding strength between press-down projections
19
and base film
11.
1. Embodied Samples
1 Through
4
Adhesive resin
18 used in the samples for the evaluation of bonding
strength is a kind of resin having a main ingredient of urethane acrylate with
four levels of hardness ranging between HDD80 and HDD65 at intervals of HDD5 as
measured by a type D durometer specified in JIS Standard K-7215 (hereinafter referred
to as durometer hardness), after the resin has been cured.
For this evaluation, tests were conducted on specially made samples provided
with round dome-like movable contacts
14 having 4 mm in outer diameter,
and press-down projections
19 having five different outer diameters ranging
from 0.5 mm to 2.5 mm at intervals of 0.5 mm.
2. Related Art Samples
Equivalent tests were carried out on separately prepared samples of the
related art, which employ epoxy acrylate resin with durometer hardness of HDD80
as adhesive resin
5B, and provided with same movable contacts
14
and press-down projections
19 as those of the embodied samples.
Test 1. Measurement of Bonding Strength
The samples prepared for measurement of bonding strength are as shown in FIG.
4. Movable contacts
14 and separator
15 placed on base film
11 were removed from each sample of movable contact units
100 described
in the above exemplary embodiment. In addition, the convexed portions in the areas
where movable contacts
14 were located on base film
11 were flattened,
and made the base film into generally a flat plate-like shape. After the above
preparation, a shearing load was applied in a direction indicated by an arrow in
FIG. 4 on the side of small cylindrical part
16 bonded to first film surface
111 of each sample, and a strength of the bonding was measured when press-down
projection
19 came off.
The results are shown in Table 1.
| |
Related art |
Embodied |
Embodied |
Embodied |
Embodied |
| |
Samples |
Samples 1 |
Samples 2 |
Samples 3 |
Samples 4 |
| Dia. of |
Hardness: |
Hardness: |
Hardness: |
Hardness: |
Hardness: |
| Press- |
HDD80 |
HDD80 |
HDD75 |
HDD70 |
HDD65 |
| down |
Bonding |
Judge- |
Bonding |
Judge- |
Bonding |
Judge- |
Bonding |
Judge- |
Bonding |
Judje- |
| Projection |
strength |
ment |
strength |
ment |
strength |
ment |
strength |
ment |
strength |
ment |
| |
| 0.5 mm |
9 |
X |
9 |
X |
9 |
X |
7 |
X |
5 |
X |
| 1.0 mm |
13 |
O |
19 |
O |
16 |
O |
14 |
O |
10 |
O |
| 1.5 mm |
18 |
O |
26 |
O |
23 |
O |
21 |
O |
20 |
O |
| 2.0 mm |
23 |
O |
34 |
O |
31 |
O |
28 |
O |
25 |
O |
| 2.5 mm |
28 |
O |
39 |
O |
37 |
O |
35 |
O |
31 |
O |
| |
| (Unit of bonding strength: N) |
Since the desired bonding strength is 10 N (Newtons) or greater as required
for the practical application, a mark "O" is used in the above table when the bonding
strength is 10 N or greater, and another mark "X" when the strength is less than
10 N.
Upon examination of the individual tested samples, it was confirmed initially
that press-down projections
5 had been torn off between the surfaces of
base films
1 and adhesive resins
5B shown in FIG. 7 in the related
art samples. It was thus considered that the bonding strength depends on the adhesion
between those components.
On the other hand, the embodied samples
1 through
4 showed that
press-down projections
19 have been torn off together with base films
11
at the areas where the projections
19 are bonded.
This result indicates strong adhesion between base films
11 made of PET
and first pretreated layers
13 formed of coated Ester resin, as well as
cylindrical parts
16 and second pretreated layers
17, and also strong
adhesion between first pretreated layers
13 and UV-cured adhesive resin
18 composed of urethane acrylate or between second pretreated layers
17
and the UV-cured adhesive resin
18.
First pretreated layers
13 and second pretreated layers
17 formed
of Ester resin, when provided in the above manner, improve wettability of base
films
11 made of PET and cylindrical parts (i.e. press-down members)
16
to the adhesive resin, thereby providing the strong bonding therebetween.
As shown in Table 1, the embodied samples
1 through
4 have comparatively
higher bonding strength than the related art samples, except for the one having
press-down projections
19 of 0.5 mm in the outer diameter, and the higher
the durometer hardness of adhesive resin
18, the greater the bonding strength
obtained by it. It was determined here that adhesive resin
18 gets better
adhesion to base film
11 the greater the hardness of it becomes after cured
by the ultraviolet rays.
However, the embodied samples
3 and
4 were not superior in
strength than the related art samples when outer diameters of their press-down
projections
19 were 0.5 mm or less and 1.0 mm or less respectively. In consideration
of the torn-off conditions, it was determined that press-down projections
19
in the diameter of 1.0 mm can satisfy the standard value (i.e. 10 N or greater
in the bonding strength), and have durability equal to or greater than the related
art devices even when unevenness of the adhesive and the like are taken into account.
Furthermore, the results showed lack of the bonding strength even on
the embodied samples
1 through
3 having adhesive resin
18
of durometer hardness HDD80 to 70 when press-down projections
19 were 0.5
mm in diameter, although they had sufficient strength when the diameter was 1.0
mm to 2.5 mm.
The related art samples also showed similar results. In consideration of the
fact that movable contacts
14 are 4 mm in outer diameter, and according
to the above test results, it was confirmed desirable that press-down projections
19 have a diameter equal to or larger than ¼ of the diameter of movable
contacts
14. Likewise, press-down projections
19 may have a surface
area equal to or larger than {fraction (1/16)} of the movable contacts
14
because they are ¼ in the outer diameter.
Test 2. Evaluation of Tactile Response
Next, same samples as the embodied samples
3 were used for depressing
operation, and their tactile responses were evaluated by comparison.
Table 2 shows the results. A mark "0" is used for a sample exhibiting good
tactile response and another mark "X" for any sample exhibiting poor tactile response
in Table 2.
| |
TABLE 2 |
| |
|
| |
Tactile Response to Operation |
|
| Diameter of |
Related art Samples |
Embodied Samples 3 |
| Press-down |
Hardness: HDD80 |
Hardness: HDD70 |
| Projection |
Judgment |
Judgment |
| |
| 0.5 mm |
O |
O |
| 1.0 mm |
O |
O |
| 1.5 mm |
O |
O |
| 2.0 mm |
O |
O |
| 2.5 mm |
X |
X |
| |
| Marks for judgment: "O" denotes good tactile response, and "X" denotes poor
tactile response. |
As shown in Table 2, both the related art samples and the embodied samples
3
exhibited the same result of tactile response to the depressing operation. In other
words, the samples having press-down projections
19 ranging from 0.5 mm
to 2.0 mm in outer diameter gave excellent click feelings, and the samples having
2.5 mm diameter gave poor click feelings.
These poor tactile responses are considered attributable to the outer diameter
of press-down projection
19 bonded to round dome-like movable contact
14,
in that the diameter of press-down projection
19, if made closer to the
outer diameter of movable contact
14, overlies near the rounded surface
of movable contact
14, which impedes the springy click motion of the dome-like
movable contact
14 although it is still inflective.
The above results also showed that the tendency of changes in the tactile response
is not dependent upon presence or absence of the coating of Ester resin serving
the pretreated layer, or properties of the UV-curable resin material, but it depends
only on size of press-down projection
19. In other words, the same results
were obtained on the samples irrespective of kind of the UV-curable resin, between
Urethane material and epoxy-base material.
According to the above result of examination on the tactile response, it
was found that press-down projections
19 of ½ or less in diameter of
the movable contacts
14 is desirable. It is therefore desirable that press-down
projections
19 have a relative surface area of ¼ or less to movable
contacts
14.
Test 3. Durability Test
As an evaluation of durability, test was carried out next on the bonding strength
with respect to number of depressing operations.
Test Method
First, separator
15 was peeled off, and the movable contact unit having
the press-down projections was placed on wiring board
7, to compose a panel
switch as shown in FIG.
2. Next, samples of the switch were operated by
depressing and releasing press-down projections
19 from the direction shown
by an arrow in FIG. 3 with a thrusting force of 3 N. The operation was repeated
by counting each inflection and restoration of movable contact
14 as one
cycle. On the other hand, bonding strengths were measured by the method described
previously with reference to FIG. 4, at the start of testing, after completion
of operations for 100,000 cycles, 500,000 cycles, 1,000,000 cycles, and 2,000,000 cycles.
Test samples
The tests were performed on samples prepared using press-down projections
19
having an outer diameter of 1.5 mm, and four different types of adhesive resin
18 in the hardness of HDD 80, 75, 70 and 65 (hereinafter designated as embodied
samples
5 to
8).
In addition, the same tests were also conducted for the comparison purpose on
the related art samples prepared by using press-down projections
19 of 1.5
mm diameter among those samples described above.
Test Result 1
The results are shown in Table 3.
| TABLE 3 |
| |
| |
Related |
|
|
|
|
| |
art |
Embodied |
Embodied |
Embodied |
Embodied |
| Test Samples |
samples |
sample 5 |
sample 6 |
sample 7 |
sample 8 |
| |
| Coating resin |
None |
Ester resin |
Ester resin |
Ester resin |
Ester resin |
| Adhesive |
| resin |
| (UV-curable |
| resin) |
| Basic |
Epoxy |
Urethane |
Urethane |
Urethane |
Urethane |
| composition |
Acrylate |
Acrylate |
Acrylate |
Acrylate |
Acrylate |
| Hardness |
HDD80 |
HDD80 |
HDD75 |
HDD70 |
HDD65 |
| Number of |
| Operations |
| Start |
18 |
26 |
23 |
21 |
20 |
| 100,000 |
16 |
24 |
21 |
20 |
19 |
| cycles |
| 500,000 |
14 |
17 |
20 |
18 |
18 |
| cycles |
| 1,000,000 |
12 |
13 |
19 |
18 |
17 |
| cycles |
| 2,000,000 |
5 |
10 |
17 |
15 |
15 |
| cycles |
| |
| Numerical values represent the bonding strengths (N). |
FIG. 5 is a graphical representation of the results shown in Table 3 for the
purpose of easy reference.
As is obvious from Table 3 and FIG. 5, the embodied sample
5 having durometer
hardness of HDD80 had the largest initial bonding strength, and they exhibited
a tendency of decreasing the bonding strength as the number of operating cycles
increases. However, these samples showed better performance on all of the tests
up to 2,000,000 cycles as compared to the results of the related art sample.
This tendency of the embodied sample
5 is considered attributable to
the excessive stiffness of adhesive resin
18, which makes it difficult to
absorb the repeated pressure of inflection and restoration of movable contact
14
caused by the depressing operations, thereby resulting in the decrease of bonding strength.
However, the bonding strength of the embodied sample
5 after the
completion of 2,000,000 cycles was 10 N, which remains still within a range of
the desirable bonding strength for the practical use.
On the other hand, it was found that the embodied samples
6 through
8
prepared with the adhesive material of HDD75 to 65 in the durometer hardness have
high durability, as they maintain bonding strengths higher than 80% of the initial
bonding strengths after 1,000,000 cycles of operation, and higher than 70% even
after the completion of 2,000,000 cycles of operation.
These results of the embodied samples
6 through
8 seem to be
the effects of elasticity provided by the low hardness of adhesive resin
18
composed of urethane acrylate, in that adhesive resin
18 functions as a
buffer to absorb the repeated pressure of the depressing operation mentioned above.
Test Result 2
Further tests were performed to evaluate the bonding strength under the high
temperature and high humidity environment. Those tests were carried out since the
elasticity of adhesive resin
18 might be obtained owing to the porous structure
of the material or might show high moisture permeability.
Similar tests were conducted and measurement results of bonding strength
against the number of operations were recorded on samples prepared in the same
manner as the embodied samples
5 through
8 as well as the related
art samples corresponding to them.
Bonding strengths were measured after the test samples were subjected to
the 100,000 cycles of depressing operation under an environment of 60° C.
in temperature and 90 to 95%-RH in humidity as the test condition.
The results are shown in Table 4 and a graph in FIG.
6.
| TABLE 4 |
| |
| |
Related |
|
|
|
|
| |
art |
Embodied |
Embodied |
Embodied |
Embodied |
| Sample |
sample |
sample 5 |
sample 6 |
sample 7 |
sample 8 |
| |
| Coating resin |
None |
Ester resin |
Ester resin |
Ester resin |
Ester resin |
| Adhesive |
| resin |
| (UV-curable |
| resin) |
| Basic |
Epoxy |
Urethane |
Urethane |
Urethane |
Urethane |
| composition |
Acrylate |
Acrylate |
Acrylate |
Acrylate |
Acrylate |
| Hardness |
HDD80 |
HDD80 |
HDD75 |
HDD70 |
HDD65 |
| Number of |
| Operations |
| Start |
18 |
26 |
23 |
21 |
20 |
| 100,000 |
6 |
11 |
18 |
16 |
10 |
| cycles |
| |
| Numerical values represent the bonding strengths (N). |
As is obvious from Table 4 and FIG. 6, it was confirmed that all of the embodied
samples
5 through
8 maintain high levels of bonding strength in absolute
value as compared with the related art sample, although the embodied samples
8
and
5 show a tendency of decrease in the relative bonding strength similar
to that of the related art sample.
The reduction in strength of the embodied sample
8 is thought to be due
to an increase in hygroscopic property of adhesive resin
19 as it might
be formed into a porous structure or a dynamic structure with elasticity, as discussed
above. The reduction in strength of the embodied sample
5 is thought to
be due to the stiffness of cured adhesive resin
19, as was seen in the previous
test on the bonding strength to the number of operations.
The embodied samples
6 and
7 have very high durability, as they
maintain bonding strengths higher than 75% of the initial bonding strengths even
after the test.
According to the confirmation tests for the bonding strengths of press-down
projections
19 to base film
11, as discussed above, it was verified
that the invention can strengthen the bonding strengths while maintaining the excellent
durability by the above structure, in which base film
11 made of PET having
round dome-like movable contacts
14 is provided with first pretreated layer
13 formed of coated Ester resin on it upper surface, small cylindrical parts
16 made of PET and constituting press-down projections
19 are each
provided with second pretreated layer
17 also formed of coated Ester resin
on the underside surface, and base film
11 and press-down projections
19
are bonded together via these pretreated layers.
In addition, the productivity can be improved to make the movable contact unit
less expensive when UV-curable urethane acrylate resin is used as adhesive resin
18, since it has fast curing reaction.
Furthermore, adhesive resin
18 can be formed with optimum elasticity
when its hardness is maintained within the range of HDD80 and 65 in the durometer
hardness, so as to make it function as a buffer to the force applied during repeated
depressing operation, and thereby improving the durability in addition to the bonding strength.
Like advantages can also be expected even when other types of adhesive resin
are used so long as the hardness is maintained to the same range of HDD80 and 65
in the durometer hardness, so as to provide the optimum elasticity as the adhesive
resin with buffering function.
Press-down projections
19 can provide excellent and stable operational
response when their outer diameter is designed to be ¼ to ½ the outer
diameter of the round dome-like movable contacts
14. This can provide a
large area of adhesion for press-down projections
19 to ensure strong adhesion
and to maintain the adhesion steady for a prolonged duration. A ratio of the surface
area of adhesion between {fraction (1/16)} and ¼ is thus suitable.
However, outer diameter of press-down projections
19 between ⅜
and ½ of the outer diameter of dome-like movable contacts
14 is rather
desirable, if adhesive resin
18 used is an UV-curable urethane acrylate
resin having HDD65 in the durometer hardness. A desirable relative surface area
in this case is between {fraction (9/64)} and ¼.
In this exemplary embodiment, although what has been described is an example
in
which pretreated layers are formed by coating Ester resin, this is not restrictive
and that the pretreated layers can be formed by coating Urethane resin. The coating
of Urethane resin can also improve wettability with the adjoining resin. In addition,
use of the above-said urethane acrylate resin as adhesive to form adhesive resin
18 can further improve adhesion between the preprocessing layers and adhesive
resin
18 since they are the same type of material.
According to this exemplary embodiment, what has been discussed is the
structure in which pretreated layers formed of coated Ester resin or Urethane resin
are provided on the surfaces of the press-down projections and the base film that
come to contact with each other, and these pretreated layers are bonded with UV-curable
urethane acrylate resin. This structure improves the wettability between the pretreated
layers and the adhesive to strengthen their adhesion, and achieves the movable
contact unit having press-down projections that can keep the adhesion for a long duration.
As discussed, the present invention has an outstanding advantage of providing
the highly reliable movable contact unit having press-down projections which can
maintain the press-down projections in a securely bonded condition to the base
film without increasing a number of components used and necessitating a complicated
manufacturing process.
*
