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BACKGROUND OF THE INVENTION
This invention relates to a method of manufacturing a framed keytop sheet
for a push-button switch, such keytop sheet being of reduced size and
thickness and being suitable for integration.
The reduction in the size and thickness of electronic devices that has been
achieved in recent years has been accompanied by a demand to reduce the
size and thickness also of a keytop sheet for push-button switches used in
control panels of such devices.
In an effort to meet this demand, a keytop sheet has been proposed in which
a plurality of keytops made of synthetic resin are fixedly molded to a
film sheet comprising a single film made of resin, and a frame made of
synthetic resin is fixedly molded to the periphery of the film sheet so as
to encircle the plurality of keytops. A switch contact is disposed below
each keytop so that if the keytop is pressed, the switch underlying it
will be closed. At such time the film sheet surrounding the keytop is
tensioned slightly in the downward direction. Push-button switches using a
keytop sheet of this type include some that are used in environments in
which there is the danger of humidity and moisture penetrating to the
interior of the switch. In such case, there are instances in which it is
preferred that the keytop sheet have a so-called waterproof structure in
which humidity and moisture will not penetrate the underside of the sheet
from the top side thereof. To achieve this, it is required that the film
sheet be entirely devoid of holes.
When the conventional keytop sheet is such that the spacing between the
keytops and the frame or the spacing between the keytops themselves is
reduced for the sake of miniaturization, the following problems arise.
Specifically, FIGS. 20(A) and 20(B) show the relationship among an angle of
inclination A of a film sheet 210, L and .DELTA.L, where L represents the
spacing between a keytop 220 and a frame 230 to which film sheet 210 has
been affixed, and .DELTA.L represents the amount by which the film sheet
210 must stretch when the keytop 220 is depressed by 0.3 mm. As indicated
by the graph of FIG. 20(A), the smaller the spacing L, the much greater
the amount of stretch .DELTA.L and the angle of inclination A. In other
words, the smaller the spacing L is made, the more difficult it is to
depress the keytop 220. If the keytop 220 is pressed too strongly in such
case, there is the danger that the film sheet 210 will be deformed.
Further, when any single keytop is pressed, a keytop alongside it is pulled
slightly toward the pressed keytop. However, when the spacing between
mutually adjacent keytops is made small, the amount of pull becomes much
larger by reason of a principle similar to that described above in
connection with FIG. 20. Consequently, when one keytop is pressed, there
is the danger that the keytop alongside will be moved toward the pressed
keytop to a noticeable extent.
If it is unnecessary to provide the keytop sheet itself with a waterproof
function, then it will suffice to provide the portion of the film sheet
surrounding each keytop with a C-shaped cut-out in order to solve the
above-mentioned problem. If such an arrangement is adopted, the film sheet
surrounding a keytop will not be pulled when the keytop is pressed,
thereby facilitating operation of the keytop. However, when the film sheet
is provided with a cut-out, the cut-out is visible from above the keytop
sheet and detracts from the appearance of the device.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a method of
manufacture of a keytop sheet of a push-button switch having a simple
structure in which each keytop can be pressed smoothly even if the keytop
sheet is miniaturized.
Another object of the present invention is to provide such a method of
manufacture of a keytop sheet of a push-button switch in which the keytop
sheet itself can readily be provided with a waterproof structure as
necessary.
A further object of the present invention is to provide such a method of
manufacture of a keytop sheet in which an attractive external appearance
is maintained even if the film sheet is provided with a cut-out.
According to the present invention, the above objects are achieved by
providing a method of manufacture of a keytop sheet of a push-button
switch in which a keytop arranged above a switch contact and having an
underside provided with a pushing portion for opening and closing the
switch contact by pressing it is molded at a prescribed position on a film
sheet comprising a resin film, wherein the film sheet surrounding the
portion thereof on which the keytop is molded is provided with a curved
projection which protrudes in a downward and/or upward direction from the
surface of the film sheet, so as to encircle the keytop. When the keytop
is pressed to cause it to recede, the curved projection provided in the
film sheet about the keytop is deformed, thereby making it easier to press
the keytop.
According to another aspect of the present invention, the film sheet
surrounding the portion thereof on which the keytop is molded is provided
with a cut-out leaving a hinge portion, and a nameplate comprising a resin
film and provided with a hole shaped so that the keytop may be passed
therethrough is attached to the film sheet so as to cover the cut-out and
hinge portion of the film sheet. In this aspect of the invention, the
keytop is connected to the surrounding film sheet solely by the hinge
portion, as a result of which the keytop can be pressed smoothly.
Moreover, since the cut-out in the film sheet is covered by the nameplate,
the cut-out cannot be seen from the surface and an attractive appearance
is maintained as a result. Further, though the hinge portion develops a
wrinkle when the keytop is pressed, the hinge portion also is covered by
the nameplate so that the attractive appearance of the keytop sheet is
maintained in this sense as well.
According to a further aspect of the present invention, a nameplate is
mounted on the film sheet and comprises a resin film having an outer
diameter greater than that of the film sheet, a frame made of synthetic
resin is molded on an underside of the film sheet on a peripheral portion
thereof so as to be affixed to the film sheet, and an outer peripheral
portion of the nameplate that protrudes beyond the film sheet is bent and
fixed to an outer peripheral side surface of the frame. Since the outer
peripheral portion of the nameplate is thus fixed to the outer peripheral
side surface of the frame, an upper edge portion on the outer periphery of
the keytop sheet is covered by the nameplate. Therefore, even if the upper
edge portion on the outer periphery of the keytop sheet protrudes somewhat
from the surface of a case accommodating the keytop sheet, an attractive
appearance in terms of design is maintained. Further, since the nameplate
completely covers the film sheet and even extends up to the side face of
the frame, the nameplate will peel off the film sheet only with great
difficulty.
Other features and advantages of the present invention will be apparent
from the following description taken in conjunction with the accompanying
drawings, in which like reference characters designate the same or similar
parts throughout the figures thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side sectional view illustrating a push-button switch including
a framed keytop sheet manufactured according to a first embodiment of the
present invention;
FIGS. 2(A) and 2(B) respectively are a plan view and a side view thereof;
FIGS. 3(A) and 3(B) respectively are a plan view and a side view of a film
sheet used in manufacture thereof;
FIG. 4 is a diagrammatic section illustrating a method of forming the
keytop sheet of FIG. 1 by resin molding;
FIG. 5 is a schematic side sectional view illustrating a push-button switch
including a keytop sheet formed according to a second embodiment of the
present invention;
FIGS. 6(A) and 6(B) illustrate a keytop sheet formed according to a third
embodiment of the present invention, FIG. 6(A) being a side sectional view
taken along line 6(A)--6(A) of FIG. 6(B), and FIG. 6(B) being a plan view
of a principal portion;
FIGS. 7(A), 7(B) and 7(C) illustrate a portion of a keytop sheet formed
according to a fourth embodiment of the present invention, FIG. 7(A) being
a plan view, FIG. 7(B) being a side sectional view taken along line
7(B)--7(B) of FIG. 7(A) and FIG. 7(C) being a bottom view, and FIG. 7(D)
is a plan view of a film sheet used in formation of the keytop sheet of
this embodiment;
FIGS. 8(B), 8(B) and 8(C) illustrate a portion of a keytop sheet formed
according to a fifth embodiment of the present invention, FIG. 8(A) being
a plan view, FIG. 8(B) being a side sectional view taken along line
8(B)--8(B) of FIG. 8(A) and FIG. 8(C) being a bottom view;
FIGS. 9(A) and 9(B) are partial sections illustrating other configurations
of curved projections formed according to the present invention;
FIG. 10 is a side sectional view illustrating a push-button switch
including a keytop sheet formed according to a sixth embodiment of the
present invention;
FIGS. 11(A) and 11(B) respectively are a plan view and a side view thereof;
FIGS. 12(A), 12(B), 12(C) are plan views illustrating a procedure for
manufacturing a film sheet thereof;
FIGS. 13(A), 13(B), 13(C) are plan views illustrating a procedure for
manufacturing a nameplate thereof;
FIG. 14 is a diagrammatic section illustrating a method of forming the
keytop sheet of FIG. 10 by resin molding;
FIG. 15 is an enlarged view of an encircled portion B in FIG. 10;
FIG. 16 is a side sectional view illustrating a push-button switch
including a keytop sheet formed according to a seventh embodiment of the
present invention;
FIG. 17 is a diagrammatic section illustrating a method of forming the
keytop sheet of FIG. 16 by resin molding;
FIG. 18(A) is a schematic view of a principal portion of the push-button
switch of FIG. 10 accommodated in a case, and FIG. 18(B) is a schematic
view of a principal portion of the push-button switch of FIG. 16
accommodated in a case;
FIG. 19 is a side sectional view illustrating a push-button switch
including a keytop sheet formed according to an eighth embodiment of the
present invention; and
FIGS. 20(A) and 20(B) respectively are a graph and a section showing the
relationship among an angle of inclination A of a film sheet, L and
.DELTA.L, where L represents the spacing between a keytop and a frame to
which a film sheet has been affixed, and .DELTA.L represents the amount by
which the film sheet must stretch when the keytop is depressed by 0.3 mm.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will now be described in
detail with reference to the accompanying drawings.
FIG. 1 is a side sectional view illustrating a push-button switch including
a keytop sheet formed according to a first embodiment of the present
invention. As shown in FIG. 1, a push-button switch 1 includes a switch
substrate 60 formed by superimposing an upper sheet 61, a spacer 63 and a
lower sheet 65, and a keytop sheet 10 obtained by fixing a frame 40 to the
outer periphery of the underside of a film sheet 20 provided with a keytop
50. A click spring 69 is attached to the switch substrate 60 over a switch
contact 68, and the frame 40 of the keytop sheet 10 is affixed to the
outer periphery of the switch substrate 60 via a sheet 71 having an
adhesive on both sides thereof.
FIGS. 2(A) and 2(B) illustrate the keytop sheet 10, in which FIG. 2(A) is a
plan view and FIG. 2(B) a side view. It should be noted that FIG. 1 is a
sectional view taken along line 1--1 in FIG. 2(A). As shown in FIGS. 2(A)
and 2(B), the keytop sheet 10 has three keytops 50 provided on the central
portion of the film sheet 20, and the frame 40 is attached to the
underside of the film sheet 20 along the outer periphery thereof. Further,
the film sheet 20, at portions thereof surrounding portions on which the
keytops 50 are molded, is provided with curved projections 25, each of
which protrudes in a downward direction from the surface of the film sheet
20, so as to surround the respective keytops 50.
In order to manufacture the keytop sheet 10, first the film sheet 20 is
prepared. As shown in FIGS. 3(A) and 3(B), the film sheet 20 is
manufactured by cutting a thermoplastic synthetic-resin film (e.g.,
polyethylene terephthalate, polyethylene naphthalate, etc.) into
rectangular shape and printing a desired design (not shown) on the top
side or underside of the sheet. Next, as illustrated in FIG. 4, the film
sheet 20 is clamped between an upper mold D and a lower mold E. The upper
mold D is provided with a cavity D1 for forming the keytop 50, and the
lower mold E is provided with a cavity E1 for forming the frame 40 and a
cavity E2 for forming the pushing portion 51 of the keytop 50. Further,
the cavities E1, E2 of the lower mold E are provided with pin gate E10,
E20, respectively. The portion of the upper mold D surrounding the cavity
is provided with a ring-shaped projection D2 having a semicircular cross
section. The lower mold E is provided with a ring-shaped cavity E3 at a
position opposing the projection D2. The cavity E3 has a semicircular
cross section and is formed to have such dimensions that a gap equivalent
to the thickness of the film sheet 20 will be delimited between the cavity
E3 and the projection D2 when the upper mold D and the lower mold E are
closed.
When a molten resin under conditions of high temperature and pressure is
forcibly introduced through the pin gates E10, E20, the frame 40 is formed
on the outer peripheral portion on the underside of the film sheet 20, and
the portion of the film sheet 20 situated at the cavity D1 is urged
upwardly and is deformed against the inner surfaces of mold D defining the
cavity D1, as indicated by the dashed lines in FIG. 4 thus forming a
cavity within film sheet 20. At the same time, the cavity within film
sheet 20 and the cavity E2 are filled with the molten resin. In other
words, the film sheet 20 is formed to include a cavity or bulge 21 (see
FIG. 1) having the shape of the inner surfaces defining the cavity D1, and
the cavity 21 is filled with charged resin 23 that is allowed to harden to
unify with the film sheet 20, thereby forming the keytop 50. Since the
molten resin introduced at this time is at a high temperature and pressure
and the film sheet 20 consists of thermoplastic resin, the forcibly
introduced resin and film sheet 20 are directly and strongly fused
together and the film sheet 20 will not peel off. The portion of the film
sheet 20 clamped between the projection D2 and the cavity E3 shown in FIG.
4 is thermoplastically deformed into the clamped shape by the heat of the
introduced molten resin and the heat from the upper and lower molds D, E
themselves. As a result, the curved projection 25 is formed in the film
sheet 20. As an alternative to forming the curved projection 25 in the
film sheet 20 by the upper and lower molds D, E, the film sheet may be
furnished with the curved projection 25 in advance by a forming process,
after which the film sheet may be clamped between the upper and lower
molds D, E. Separating the upper and lower molds D, E completes formation
of the keytop sheet 10 shown in FIGS. 1, 2(A) and 2(B).
As shown in FIG. 1, the switch substrate 60 is an ordinary membrane switch
and is produced by superimposing the upper and lower sheets 61, 65 with
the spacer 63 sandwiched between them. The spacer 63 is provided with a
hole 67 within which electrode patterns formed on respective ones of the
upper and lower sheets 61, 65 are arranged in opposition to each other so
as to construct the switch contact 68. The lower sheet 65 is provided with
an air-venting hole 66. The click spring 69, which is made of metal or
resin, is attached over the switch contact 68.
Sheets 71, 73, both sides of each of which are provided with an adhesive,
are affixed to the upper and lower surfaces, respectively, of the switch
substrate 60. The double-sided adhesive sheet 71 on the upper side is
affixed so as to surround the entire outer periphery of the top side of
the switch substrate 60, and the double-sided adhesive sheet 73 on the
lower side covers the entire underside of the switch substrate 60 and is
affixed in such a manner that an air-venting hole 75 therein is situated
at a prescribed position relative to the switch substrate 60. It should be
noted that a separator 77 is affixed to the underside of the lower
double-sided adhesive sheet 73. Bonding the upper double-sided adhesive
sheet 71 to the underside of the frame 40 of the keytop sheet 10 completes
the push-button switch 1. When the push-button switch i is secured to
another member, it will suffice to peel the separator 77 off and affix the
underside of the double-sided adhesive sheet to the other member.
When the keytop 50 of the keytop sheet 10 is pressed, the pushing portion
51 presses the click spring 69, which snaps back to produce a clicking
sensation, as well as the switch contact 68 to close the same. The curved
projection 25 of film sheet 20 is deformed when the keytop 50 is pressed,
as a result of which the pressing operation is facilitated. The reason for
this is that when the keytop 50 is pressed, the stretching of the film by
an amount equivalent to the stroke of the keytop 50 is compensated for
(absorbed) by the shape deformation of the curved projection 25.
Further, since the film sheet 20 of the keytop sheet 10 is not provided
with any holes, water cannot penetrate the push-button switch 1 to the
underside of the film sheet 20 even if the switch is exposed to water from
above.
In the embodiment described above, the keytop 50 can be brightly
illuminated from its lower side if the resin 23 consists of a transparent
material and a light-emitting element is disposed at a prescribed position
below the keytop 50.
Further, in the embodiment described above, a membrane switch comprising a
flexible substrate is used as the switch substrate 60. However, it is
permissible to use switch substrates of other types, such as a rigid
substrate.
Although the frame 40 is provided on the periphery of the underside of film
sheet 20 so as to surround the keytop 50, it is not always necessary for
the keytop sheet in this invention to have the frame 40. More
specifically, a keytop sheet devoid of a frame may be arranged directly on
a switch substrate, or a keytop sheet devoid of a frame may be retained by
another member and this member may be arranged on the switch substrate.
Further, in the first embodiment described above, there are instances in
which the adhesion between the film sheet 20 and keytop 50 is weak,
depending upon the quality and thickness of the film sheet 20 or the
quality and melting temperature of the molding resin used to form the
keytop 50 and the frame 40. In such case the union between the film sheet
and keytop can be strengthened if an adhesive layer is interposed
therebetween.
FIG. 5 is a schematic side sectional view illustrating a push-button switch
1-2 including a keytop sheet 10-2 formed according to a second embodiment
of the present invention. Since a switch substrate 60-2 is identical with
the switch substrate 60 of the first embodiment, the outline of the switch
substrate 60-2 is indicated by dashed lines in FIG. 5.
This embodiment differs from the first embodiment in that a nameplate 30-2
is affixed to the upper side of a film sheet 20-2. The nameplate 30-2 is
provided with a circular hole 31-2 through which keytop 50-2 passes. More
specifically, the nameplate 30-2 is affixed to the film sheet 20-2 in such
a manner that the keytop 50-2 passes through the hole 31-2. In this
arrangement, curved projection 25-2 provided on the film sheet 20-2 will
no longer be visible to the eye. In addition, printing can be provided on
the top side or underside of the nameplate 30-2 in a variety of ways.
FIGS. 6(A) and 6(B) illustrate a keytop sheet 10-3 formed according to a
third embodiment of the present invention, FIG. 6(A) being a side
sectional view taken along line 6 (A)--6(A) of FIG. 6(B) and FIG. 6(B)
being a plan view of a principal portion. The keytop sheet 10-3 shown in
FIGS. 6(A) and 6(B) includes a film sheet 20-3 provided with a hole 90-3,
and a keytop 50-3 molded by charging molten resin above and below the film
sheet 20-3 via the hole 90-3. In this embodiment, a pushing portion 51-3
of the keytop 50-3 is situated on the underside of the keytop 50-3 at the
central portion thereof, just as in the first and second embodiments.
Further, a curved projection 25-3 is provided surrounding the keytop 50-3.
FIGS. 7(A), 7(B) and 7(C) illustrate a portion of a keytop sheet 10-4
formed according to a fourth embodiment of the present invention, FIG.
7(A) being a plan view, FIG. 7(B) being a side sectional view taken along
line 7(B)--7 (B) of FIG. 7(A) and FIG. 7(C) being a bottom view. FIG. 7
(D) is a plan view of a film sheet 20-4 used in formation of the keytop
sheet 10-4. Film sheet 20-4 is provided with eight holes 90-4 in a
ring-shaped configuration, as shown in FIG. 7(D), and a keytop 50-4 is
molded by charging molten resin above and below the film sheet 20-4 via
the holes 90-4. According to this embodiment, the film sheet 20-4 is
clamped and secured by a film fixing portion 55-4 molded on the outer
periphery of the top side of keytop 50-4 and a ring-shaped film retaining
portion 52-4 molded on the underside of the film sheet 20-4. The periphery
of the keytop 50-4 is surrounded by a curved projection 25-4 of film sheet
20-4.
FIGS. 8(A), 8(B) and 8(C) illustrate a portion of a keytop sheet 10-5
formed according to a fifth embodiment of the present invention, FIG. 8(A)
being a plan view, FIG. 8(B) being a side sectional view taken along line
8(B)--8(B) of FIG. 8(A) and FIG. 8(C) being a bottom view. A film sheet
20-5 is provided with holes 90-5 in a ring-shaped configuration in a
manner similar to that shown in FIG. 7(D), a large hole 91-5 is provided
at the center of the ring, and a keytop 50-5 is molded by charging molten
resin above and below the film sheet 20-5 via the holes 90-5, 91-5. The
periphery of the keytop 50-5 is surrounded by a curved projection 25-5 of
film sheet 20-5.
In the first through fifth embodiments described above, the curved
projection protrudes downwardly from the surface of the film sheet.
However, as shown in FIG. 9(A), a curved projection 25-A may be formed so
as to protrude upwardly from the surface of a film sheet 20-A, or, as
shown in FIG. 9(B), curved projections 25-B may be formed so as to
protrude upwardly and downwardly in the manner of a wave relative to the
surface of a film sheet 20-B. In the latter case, the greater the length
of the curved projections 25-B in comparison with the other embodiments,
the easier it is to press the keytop.
FIG. 10 is a side sectional view illustrating a push-button switch 1-6
including a keytop sheet 10-6 formed according to a sixth embodiment of
the present invention. As shown in FIG. 10, the push-button switch 1-6
includes keytop sheet 10-6 including nameplate 30-6 and a frame 40-6
secured above and below a film sheet 20-6 provided with a keytop 50-6, and
a switch substrate 60-6 (only the outline of which is shown) that is the
same as the switch substrate 60 depicted in FIG. 1. FIGS. 11(A) and 11(B)
illustrate the keytop sheet 10-6 of FIG. 10, FIG. 11(A) being a plan view
and FIG. 11(B) being a side view. FIGS. 12(A), 12(B) and 12(C) are plan
views illustrating a procedure for manufacturing the film sheet 20-6, and
FIGS. 13(A), 13(B) and 13(C) are bottom views illustrating a procedure for
manufacturing the nameplate 30-6.
In order to manufacture the film sheet 20-6, first a thermoplastic
synthetic resin 21-6 (e.g., polyethylene terephthalate, polyethylene
naphthalate, etc.) is prepared, as shown in FIG. 12(A), and a bonding
agent 26-6 such as epoxy resin or urethane resin is printed on the top
side of the film sheet 21-6 to a thickness of 25.about.30 .mu.m. The
bonding agent 26-6 is applied to the entirety of the film sheet 21-6 with
the exception of the interior of a circle a1-6, and to a ring-shaped
portion 26A-6 located within the circle a1-6. The ring-shaped portion
26A-6 is a portion between two circles a2-6 and a3-6. Next, as shown in
FIG. 12(B), decorative printing 25-6 comprising a desired design or the
like is applied to a prescribed position of the film sheet 21-6. The
decorative printing 25-6 is applied inwardly of a circle a4-6 between the
circle a1-6 and the circle a2-6 illustrated in FIG. 12(A). It should be
noted that the thickness of the decorative printing 25-6 is on the order
of 5.about.7 .mu.m. Next, as shown in FIG. 12(C), a portion between the
circles a1-6 and a2-6 of the film sheet 21-6 is cut away to provide a
C-shaped cut-out 22-6. As a result, a structure is obtained in which a
circular keytop portion 23-6 is connected to the film 21-6 solely by a
hinge portion 24-6 of small width.
In order to manufacture the nameplate 30-6, first a synthetic resin film
31-6 (e.g., polyethylene terephthalate or the like, a thermoplastic resin
need not necessarily be used) is prepared and printing 33-6 such as a
desired design is applied over the entire underside of the film 31-6, as
illustrated in FIG. 13(A). Next, as shown in FIG. 13(B), a bonding agent
35-6 such as epoxy resin or urethane resin is printed on the printing
33-6. It should be noted that the bonding agent 35-6 is not printed on the
inner side of a circle b1-6. The diameter of the circle b1-6 is made the
same as that of the circle a3-6 shown in FIG. 12(A). The portion of the
film 31-6 on which the bonding agent 35-6 has not been printed is cut
away, as shown in FIG. 13(C), thereby providing a circular hole 32-6. The
diameter of the hole 32-6 is the same as the diameter of the circle b1-6.
The nameplate 30-6 shown in FIG. 13(C) is placed upon the film sheet 20-6
of FIG. 12(C) in such a manner that the two layers of bonding agents 26-6,
35-6 contact each other. The nameplate 30-6 and film sheet 20-6 are bonded
strongly together by thermocompression bonding.
Next, the keytop 50-6 and frame 40-6 are provided simultaneously, by resin
molding, on the unitary body comprising the film sheet 20-6 and nameplate
30-6. This method will now be described with reference to FIG. 14. The
film sheet 20-6 and nameplate 30-6 united in the manner set forth above
are clamped between an upper mold D-6 and a lower mold E-6. The upper mold
D-6 is provided with a cavity D1-6 for forming the keytop 50-6, and the
lower mold E-6 is provided with a cavity El-6 for forming the frame 40-6
and a cavity E2-6 for forming a pushing portion 51-6 of the keytop 50-6.
The cavities E1-6, E2-6 of the lower mold E-6 are provided with pin gates
E10-6, E20-6, respectively.
When a high-temperature, high-pressure molten resin is forcibly introduced
through the pin gates E10-6, E20-6, frame 40-6 is formed on the outer
periphery of the underside of the film sheet 20-6, and a keytop portion
23-6 of the film sheet 20-6 is urged upwardly and deformed so as to adhere
to the inner surfaces of the mold D-6 defining cavity D1-6, as indicated
by the dashed lines in FIG. 14, thus forming a cavity within portion 23-6.
At the same time, the cavity within portion 23-6 and the cavity E2-6 are
filled with the molten resin. Since the thermoplastic molten resin
introduced at this time is at a high temperature and pressure and the film
sheet 20-6 consists of thermoplastic resin, the forcibly introduced resin
and film sheet 20-6 are directly and strongly fused together so that the
film sheet 20-6 will not peel off. It should be noted that an adhesive
layer may be interposed between the resin and the film sheet, as described
earlier in connection with the first embodiment. In other words, the
portion of the film sheet 20-6 having the keytop portion 23-6 is caused to
protrude and deform upwardly, thereby forming a bulge having the shape of
the inner surface of the cavity D1-6, and the synthetic resin is caused to
fill the interior of the bulge and is allowed to harden so as to integrate
the resin and the film sheet and form the keytop 50-6. Separating the
upper and lower molds D-6, E-6 completes formation of the keytop sheet
10-6 shown in FIGS. 10-11(B).
As shown in FIGS. 10 and 11(A), the cut-out 22-6 [see FIG. 12(C)] provided
in the film sheet 20-6 is concealed by being covered by the nameplate 30-6
and therefore cannot be seen from upper side. This makes it possible to
maintain an attractive appearance of the keytop sheet 10-6. Further,
though the hinge portion 24-6 [see FIG. 12(C)] of the film sheet 20-6
develops a wrinkle when the keytop 50-6 is pressed, the hinge portion 24-6
also is covered and concealed by the nameplate 30-6 so that the attractive
appearance of the keytop sheet is maintained in this sense as well.
FIG. 15 is an enlarged view of portion B in FIG. 10. As illustrated in FIG.
15, since the layer of bonding agent 26-6 of the film sheet 20-6 and the
layer of bonding agent 35-6 of the nameplate 30-6 are in direct contact
with each other, the two are bonded together by heat. However, since the
decorative printing 25-6 has been applied to the ring-shaped portion
26A-6, the two are not bonded together at this portion even though heat is
applied. In other words, the two members are merely in contact with each
other at this portion. The ring-shaped portion 26A-6 is provided for the
following reason. If the ring-shaped portion 26A-6 of a prescribed
thickness were not provided, a gap would be produced between the bonding
agent 35-6 of the nameplate 30-6 and the decorative printing 25-6 of the
film sheet 20-6 in this region. When clamped between the molds D-6, E-6
shown in FIG. 14, the film sheet 20-6 of the ring-shaped portion 26A-6 and
the nameplate 30-6 could not be clamped together strongly and fixedly
secured. If this portion cannot be fixedly secured, the molten resin will
flow out from the gap to the side of the cut-out 22-6 of the film sheet
20-6 when the molten resin is charged. Such a molding operation is
unsatisfactory.
A particular characterizing feature of this embodiment is that the
thickness of the portion where the film sheet 20-6 of the ring-shaped
portion 26A-6 and the nameplate 30-6 overlap is equal to the sum of the
thickness of the film 21-6, the thickness of the ring-shaped portion
26A-6, the thickness of the decorative printing 25-6, the thickness of the
bonding agent 35-6, the thickness of the decorative printing 33-6 and the
thickness of the film 31-6. By contrast, the thickness of the portion
where the film sheet 20-6 and nameplate 30-6 overlap is equal to the sum
of the thickness of the film 21-6, the thickness of the bonding agent
26-6, the thickness of the bonding agent 35-6, the thickness of the
decorative printing 33-6 and the thickness of the film 31-6. In other
words, the thickness of the portion where the film sheet 20-6 of the
ring-shaped portion 26A-6 and the nameplate 30-6 overlap is greater than
that of other portions by the thickness of the decorative printing 25-6.
As a consequence, the clamping of this portion by the molds D-6, E-6 is
strengthened and made more certain.
In the above-described embodiment, the film sheet 20-6 and the nameplate
30-6 are bonded together by a thermocompression bonding step. However,
this step is not always necessary. The reason is that if the
above-mentioned members are clamped between the upper and lower molds D-6,
E-6 shown in FIG. 14 in a state in which the film sheet 20-6 and nameplate
30-6 are merely superimposed (i.e., without being bonded together by
thermocompression) and the molten resin is forcibly introduced, the two
layers of bonding agents 25-6, 35-6 are melted and bonded together by the
pressure and heat of the molten resin and the temperature of the
high-temperature molds D-6, E-6.
If the keytop sheet 10-6 is attached to the switch substrate 60-6 and the
keytop 50-6 of the keytop sheet 10-6 is pressed, the pushing portion 51
presses the click spring of the switch substrate 60-6 and the switch
contact, thereby closing the switch contact. When the keytop 50-6 is
pressed, the hinge portion 24-6 flexes since the film sheet 20-6 is
provided with the cut-out 22-6 and the keytop 50-6 is merely connected to
the film sheet 20-6 by the hinge portion 24-6. As a result, the keytop
50-6 is very easy to depress.
In the embodiment described above, the keytop 50-6 can be brightly
illuminated from its lower side if the charged resin consists of a
transparent material and a light-emitting element is disposed on the
switch substrate 60-6.
In the sixth embodiment described above, the hinge portion 24-6 is provided
at only one location. However, the invention is not limited to such an
arrangement, and hinge portions may be provided at a plurality of
locations.
FIG. 16 is a side sectional view illustrating a push-button switch 1-7
including a keytop sheet 10-7 formed according to a seventh embodiment of
the present invention. Though this embodiment has approximately the same
structure as that of the sixth embodiment, it differs from the sixth
embodiment in that a nameplate 30-7 is formed to have an outer dimension
greater than that of a film sheet 20-7 by a predetermined amount, and the
outer peripheral portion of the nameplate 30-7 that extends beyond the
film sheet 20-7 is bent transversely and secured to a side face of a frame
40-7.
FIG. 17 illustrates a method of forming the keytop sheet 10-7 of FIG. 16 by
resin molding. As shown in FIG. 17, an upper mold D-7 has an outer
peripheral portion surrounding a cavity D1-7, and such outer peripheral
portion is extended downwardly and has a second cavity D2-7. When molten
resin is forcibly introduced from pin gates E10-7, E20-7, the outer
peripheral portion of the nameplate 30-7 is urged against an outer
peripheral side face of mold D-7 that defines the second cavity D2-7.
The reason for adopting this configuration is as follows. In the case of
the push-button switch 1-6 according to the sixth embodiment shown in FIG.
10, an outer peripheral face f of the keytop sheet 10-6 is plate-shaped
[see FIG. 18(A)]. As a result, when it is attempted to conceal the keytop
sheet 10-6 by a case 80-6 for the sake of design and so that the film
sheet 20-6 will not peel off the nameplate 30-6, it is necessary to make
the surface of the top h of the push-button switch 1-6 lower than the top
g of a side wall 81-6 of the case 80-6 when the push-button switch 1-6 is
fitted into the case 80-6. Consequently, dust tends to accumulate at a
stepped portion 83-6 produced by the two top surfaces g, h. Owing to
possible errors in assembly of the push-button switch 1-6, some
dimensional error can develop in the thickness of the push-button switch
16. Owing to this error in the thickness direction, there is the danger
that the surface h may exceed that of the surface g. This means that
assembly errors in the thickness direction of the push-button switch 1-6
must be reduced. Accordingly, strict measurement must be taken to deal
with assembly errors in the thickness direction.
By contrast, in the case of a push-button switch 1-7 using the keytop sheet
10-7 according to the seventh embodiment, an upper edge i of the outer
periphery of the keytop sheet 10-7 is covered by nameplate 30-7, as shown
in FIG. 18(B). As a result, even if the upper edge i on the outer
periphery is made to project somewhat from the top side g of a side wall
81-7 of a case 80-7, there is no problem in terms of design and there is
no danger that the film sheet 20-7 will peel off the nameplate 30-7.
Accordingly, no problems arise even if there is some dimensional error in
the thickness of the push-button switch 1-7. This means that especially
strict measures need not be taken to deal with assembly errors in the
thickness direction of the push-button switch 1-7. This facilitates
operability and fabrication as well.
Further, the underside | | |
