Liquid crystal cells – elements and systems – Liquid crystal system – Liquid crystal writing tablet
Reexamination Certificate
2002-07-10
2004-08-31
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Liquid crystal writing tablet
C349S062000, C345S104000, C345S173000, C178S018050
Reexamination Certificate
active
06784948
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a touch panel for a display device, which is disposed close to a display surface of a display device, such as a liquid crystal display device, and which outputs a predetermined signal corresponding to a position at which an operator presses on a panel surface with a pen or a finger based on information displayed on the display surface.
2. Description of the Related Art
Since, in this type of touch panel, an area corresponding to the display surface of the display device can be used for both displaying and inputting information, the utilization factor of the area is increased, and therefore the touch panel is increasingly demanded for compact information processors and communications equipments, in particular, mobile communications terminals.
FIG. 2
is a sectional view of a conventional touch panel (disclosed in FIG. 2 of Japanese Patent Laid-open No. 2000-187197 A).
As shown in
FIG. 2
, a touch panel
10
A is basically composed of a pair of resistive layers (first and second resistive layers)
12
and
13
disposed opposite to each other across a plurality of insulating dot spacers
11
, and a light-transmissible flat plate, for example, a transparent glass plate
16
, for protecting the second resistive layer
13
which is laid on the glass plate
16
. The touch panel
10
A is disposed close to a display device
30
such that the glass plate
16
faces toward the display surface of the display device
30
.
In this construction, when the outer surface of the first resistive layer
12
is touched to be pressed, a touched portion of the first resistive layer
12
is brought into contact with a portion of the second resistive layer
13
opposite thereto, and a signal corresponding to the contact position (touched position) is generated.
In a practical construction, a transparent layer, for example, a polyethylene terephthalate (hereinafter referred to as PET) film
15
, is laminated on the outer surface of the first resistive layer
12
for protection thereof, so the touching operation is implemented on this PET film
15
.
The first and second resistive layers
12
and
13
are combined at their peripheries by means of a sealing member
14
to be dustproof and waterproof.
A light unit is added to the display device
30
to illuminate the display surface brightly for easier observation. A front light unit
20
to shed light on the front face (display surface) of the display device
30
is often used as the light unit in recent years.
In
FIG. 2
, the touch panel
10
A is attached to the display device
30
having the front light unit
20
described above. The front light unit
20
comprises a light source
21
and a light conductive plate
22
disposed facing the display surface of the display device
30
and adapted to guide light emitted from the light source
21
located at an end of the light conductive plate
22
toward the display surface of the display device
30
. Light made incident on the display surface is reflected thereat or inside of the display device
30
, travels through the light conductive plate
22
and the touch panel
10
A, and exits out (refer to an arrow indicated by a broken line in the figure), whereby an image on the display surface is visualized.
The light conductive plate
22
has an array of prisms, whose respective ridges are parallel to one another, formed on a surface thereof opposite to a surface facing toward the display device
30
, thereby guiding light, which has come into the light conductive plate
22
through its end face, toward the display surface of the display device
30
.
However, in the conventional structure shown in
FIG. 2
, since the touch panel
10
A and the front light unit
20
are constituted discretely from each other, the touch panel
10
A is handled individually and easily subjected to vibration and shock during transportation or assembly. And also the touch panel
10
A is required to be strong enough against vibration and shock even after mounted on the device body. Therefore, the glass plate
16
is increased in thickness so as to reinforce the touch panel
10
A and also to prevent itself from getting damages. However, this gives a disadvantage that the display device
30
has its whole thickness D increased when attached to the touch panel
10
A, and also a problem that since the light conductive plate
22
is brought into direct contact with the glass plate
16
, the light conductive plate
22
may be damaged or broken by the glass plate
16
when vibration or shock is applied to the touch panel
10
A.
Accordingly, a touch panel for a display device (as shown in FIG. 1 of the above-described Japanese Patent Laid-open) was disclosed, where, as shown in
FIG. 3
, a second resistive layer
13
of a touch panel
10
B is in close contact with a surface of a light conductive plate
22
, on which an array of prisms are formed.
In this touch panel, a member (the glass plate
16
in
FIG. 2
) interposed between the light conductive plate
22
and the second resistive layer
13
of the touch panel
10
B is eliminated, and the touch panel
10
B is integrated with a front light unit
20
, and thus the whole thickness D can be reduced when the touch panel and the front light unit are attached to a display device
30
. Further, the glass plate
16
in
FIG. 2
is not present, and this solves the problem that the light conductive plate
22
is damaged or broken by the glass plate
16
when vibration or shock is applied to the touch panel
10
B.
Furthermore, the present inventors proposed countermeasures to overcome the problems of the touch panel disclosed in FIG. 2 of the above-mentioned Japanese Patent Laid-open, and disclosed the details thereof in Japanese Patent Application No. 2000-387641 that was filed on Dec. 20, 2000 and has not been open to the public (therefore, the related invention in the Japanese Patent Application does not constitute prior art under 35 U.S.C. §102). In short, as shown in
FIG. 4
, a layer of a transparent gel material with a low refractive index
17
(
17
b
) is disposed between a glass plate
16
and a light conductive plate
22
, whereby vibration or shock applied to a touch panel
10
C can be absorbed, the glass plate
16
can be made thinner, and visibility of reflected light from a display device
30
can be secured. In addition, as shown in
FIG. 5
, a touch panel
10
D is also disclosed in which a layer of a transparent gel material
17
(
17
c
) and a transparent film
19
made of a material with a low refractive index are disposed between a glass plate
16
and a light conductive plate
22
thereby obtaining a similar advantage.
However, there is a problem described below in the conventional touch panel shown in FIG.
3
.
Since the second resistive layer
13
is in close contact with the surface of the light conductive plate
22
, on which the array of prisms are formed, as described above, the second resistive layer
13
is uneven corresponding to the surface of the array of prisms, and insulating dot spacers
11
are interposed between the uneven second resistive layer
13
and a flat first resistive layer
12
.
Accordingly, it becomes difficult to secure the linearity of resistance value at each position on a touch panel operation surface (the PET film
15
), and errors occur easily in positional information obtained.
In addition, this makes it difficult to dispose individual insulating dot spacers
11
with an even height on the second resistive layer
13
, whereby the PET film
15
constituting the touch panel operation surface tends to undulate deteriorating display quality.
Furthermore, this gives a problem that, with a long term use, protrusions on the array of prisms of the light conductive plate
22
and protrusions on the second resistive layer
13
covering the light conductive plate
22
are liable to damages, resulting in inferior durability.
Still furthermore, in the touch panels shown in
FIGS. 4 and 5
, the transparent gel material
17
(
17
b
) with a low refractive index and the transpar
Ishigami Katsuji
Kawashima Satoshi
Minebea Co. Ltd.
Nath Gary M.
Nath & Associates PLLC
Nguyen Hoan C.
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