between both the electrodes, while when the depression
TOUCH PANEL force is removed, both the electrodes are maintained
separate from each other owing to the fluidity of the
BACKGROUND OF THE INVENTION insulating liquid. Thus, as there are absent the air layer
The present invention relates to a touch panel 5 ""d the dot spacer as mentioned previously between
adapted to be mounted on a display device such as CRT 1x5411 tne electrodes, the visibility may be improved, and
and detect a coordinate at a position of depression by a the resolution may be also improved because of no dead
finger, a pen, etc. zone.
Generally, the touch panel is formed by laminating Although such a touch panel utilizing the insulating transparent upper and lower electrodes with a spacer 10 fluid as a spacer exhibits a good function regarding the such as a dot spacer interposed therebetween, and sup- prevention of reduction in visibility and the improveporting the lower electrode to a transparent support ment in resolution, there still remains a problem. That is, plate. The touch panel thus formed is mounted on a the insulating liquid has a good fluidity in response to a display surface of a display device such as CRT or LCD depression force, but it is inferior in restorability when (liquid crystal display), and is depressed at a predeter- 15 removing the depression force. Accordingly, there is a mined position by means of a pen, a finger, etc. as possibility of both the electrodes erroneously contactviewed by an operator to detect a coordinate at such a ing with each other during a long service life. Further, depressed position, thus providing a coordinate input as a long restoring time is needed, operation feeling is device. rendered unsatisfactory.
In such a touch panel as mentioned above, it is known 20
that a filter permitting transmitting of a certain part of SUMMARY OF THE INVENTION
spectrum from the display device as a light source and rt js an object of the present invention to provide a
absorbing the other part is provided so as to improve a touch panel which may exhibit a fllter effect at a low
contrast at a display portion of the display device and manufacturing cost.
adjust a color tone. . 25 It is another object of the present invention to pro
Such a conventional filter is formed by uniformly vide a tQuch { which improve the visibility of
dispersing pigment or dyestuff made of organic or mor- ^ m t surface
ganic materials in a transparent acrylic resin, and the Jt is a further object of the resent invention to profilter is coated on a single surface or both surfaces of the yide a tQuch , which ffla %liminate m j t dead
upper electrode and the lower electrode. Alternatively, 30 r , . J r
■ *T. .. _. i * ■ * J zone and ensure a reliable input operation,
in the case that the transparent support plate is formed . _■• * * e
c . iU X vt, r ,. . According to one aspect of the present invention,
of a transparent synthetic resin such as acrylic resin, it_ i t_ i i_ •
pigment or dyestuff as mentioned above is kneaded in 'here "s P/ov'ded m a touch P"*1 ^avm8 a Pa,nel ^
the transparent support plate to integrally form the formed transparent upper and lower electrodes
filter with the support plate. As a result, the steps of 35 spaced a predetermined distance smd touch panel being
manufacturing the touch panel with such a filter as mounted on a front surface of a display device to detect
mentioned above are complicated to cause an increase a coordinate at a depressed position on said upper elec
m cost trode; the improvement comprising a transparent msu
Further, in the prior art touch panel as mentioned latin8 material filled between said upper and
above, an air gap is defined by the dot spacer between 40 lower electrodes and a coloring agent containing pig
the upper electrode and the lower electrode. Accord- ment or dyestuff dispersed m said liquid material,
ingly, there occurs reflection or refraction of light at an As described above, the liquid material such as oil or
air layer formed by the air gap, causing a reduction in gel is used as a spacer material, and the coloring agent
transmission rate of the touch panel as a whole. Addi- containing pigment or dyestuff is uniformly dispersed in
tionally, the outline of the dot spacer is readily visual- 45 the h<luid material. Accordingly, a filter effect may be
ized to generate a problem in visibility. exhibited by the coloring agent dispersed in the spacer
Furthermore, as the dot spacer is fixed on either of material without the necessity of providing a filter
the electrodes, there exists a non-contact area of both layer, thus reducing a cost. Further, the upper and
the electrodes, that is, a dead zone of the input device, lower electrodes are maintained spaced a predeter
causing incapability of minute coordinate detection. 50 mined gap by the liquid material filled therebetween.
Particularly in the case of forming the dot spacer by a Accordingly, it is possible to prevent a reduction in
general printing technique, a diameter of the spacer visibility due to an air gap.
tends to be greater at a bottom surface than a height According to another aspect of the present invention,
thereof in relation to the viscosity of the spacer. There- there is provided in a touch panel having a panel body
fore, the existence of the dead zone as mentioned above 55 formed by transparent upper and lower electrodes
cannot be ignored. spaced a predetermined distance, said touch panel being
Other documents disclosing a touch panel and a mounted on a front surface of a display device to detect membrane switch are co-pending U.S. patent applica- a coordinate at a depressed position on said upper election Ser. Nos. 07/187,263, filed Apr. 28, 1988, entitled trode; the improvement comprising a transparent insu"Membrane Switch" and 07/180,294, filed Apr. 12, 60 lating liquid material filled between said upper and 1988, entitled "Touch Panel". lower electrodes and an insulating fine powder dis
In another conventional touch panel as disclosed in persed in said liquid material.
Japanese Utility Model Laid-Open Publication No. In operation, when the touch panel is depressed from
60-112844, a transparent insulating liquid acting as a the upper electrode side at an arbitral position, the liq
spacer is enclosed between the upper electrode and the 65 uid material flows aside away from this position by the
lower electrode. When the touch panel is depressed depression force to allow the upper and lower elec
from the upper electrode side, the insulating liquid at a trades to come into contact with each other and be
depressed portion is moved aside to allow the contact electrically connected. At this time, since the insulating
