Liquid crystal cells – elements and systems – Liquid crystal system – Liquid crystal writing tablet
Reexamination Certificate
2000-04-13
2004-07-20
Ngo, Julie (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Liquid crystal writing tablet
C349S098000, C349S119000, C345S173000
Reexamination Certificate
active
06765629
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 1999-12904, filed on Apr. 13, 1999, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polarizer, and more particularly, to a polarizer used in a liquid crystal display. Although the polarizer of the present invention is applicable to a wide range of applications, it is especially applicable to a touch panel and a flat panel display integrated with the touch panel.
2. Discussion of the Related Art
Generally, a “polarizer” is attached to each surface of a liquid crystal display (LCD) of a flat panel display device for linear polarization of a visible light ray. A “touch panel” is an input device used, instead of a keyboard or a mouse. Such applications for the touch panel include a CAD, a production system, a game machine, a KIOSK, a POS and medical applications. The touch panel is mounted to a display screen which is an output device so that a user can make various input operations for controlling the device by manually pressing a desired position in the screen while viewing the display screen.
A touch panel is classified into a resistive film system or a capacitance system depending on its operational principle. The touch panel of a resistive film system operates by sensing a voltage or current change at a contact point of two opposite conductive layers (or resistive films) that is pressed by a user and then converting it into a coordinate value when a voltage has been applied to the two opposite conductive layers.
On the other hand, in the touch panel of a capacitance system, a small amount of electric charges is accumulated in a single transparent conductive film or transparent conductive glass in accordance with a capacitance coupling between a stylus (a pen-type input device) and the transparent conductive film at a contact point pressed by a user when alternating charge and discharge states of the capacitance are being repeated. The capacitance system touch panel operates by reading the amount of electric charges from four input points and then converting it into a coordinate value. In such capacitance system touch panel, an electrical power is applied to the stylus.
The conventional flat panel display employing a touch panel of resistive film system will be described below.
FIG. 1
is a sectional view showing the structure of a conventional flat panel display of an additive type touch panel. In
FIG. 1
, touch panel
50
is added to an upper surface of flat panel display
40
including lower polarizer
10
, LCD
20
and upper polarizer
30
. In such a conventional additive type touch panel flat panel display, since touch panel
50
is located at the uppermost portion of the flat panel display and externally exposed, it is referred to as an “outer touch panel”.
In the additive type touch panel flat panel display, as shown in
FIG. 1
, lower polarizer
10
is provided with optical film
12
for polarizing light at the center thereof, upper film
13
and lower film
11
. The upper and lower films mechanically support optical film
12
at the upper and lower surfaces, respectively. LCD
20
includes lower glass
21
and upper glass
22
that surround a liquid crystal layer. The liquid crystal layer is provided between lower glass
22
and upper glass
22
. Upper polarizer
30
includes lower film
31
, optical film
32
, and upper film
33
in a similar manner to lower polarizer
10
.
Touch panel
50
is provided with lower sheet
51
including a transparent film at the lower portion thereof to serve as a resistive film, upper sheet
52
including a transparent film at the upper portion thereof to serve as a resistive film, bus bar
53
serving as an electrode for applying a voltage to two resistive films between the lower sheet and upper sheet
52
, tail
54
for connecting bar bus
53
to a controller over flat panel display
40
, and a plurality of dot spacers
55
positioned on lower sheet
51
to space upper sheet
52
from the lower sheet
51
. Lower sheet
51
includes a base film or glass layer and a conductive layer (or resistive film layer). Upper sheet
52
includes a conductive layer (or resistive film layer), a transparent conductive film layer and an anti-dazzling hard-coating layer. Adhesive
60
may be replaced by a double-face adhesive tape.
The conventional additive type touch panel flat panel display as described above has a problem in that, since touch panel
50
including lower sheet
51
and upper sheet
52
is added to the upper portion of flat panel display
40
which increases the entire bulk and weight, it is difficult to apply the touch panel to an LCD monitor, a notebook or personal computer, etc., which require light weight and thin characteristics. Also, the conventional additive type touch panel flat panel display has a problem in that, there is a large difference of refraction index with five boundary surfaces and a relatively large reflection as indicated by dotted lines in FIG.
1
. Such problem results in poor light transmissivity.
FIG. 2
is a sectional view showing the structure of a conventional integral type touch panel flat panel display. Referring to
FIG. 2
, the conventional integral type touch panel flat panel display includes lower polarizer
10
, LCD
20
, touch panel
50
and upper polarizer
30
that are sequentially disposed. Touch panel
50
is inserted into flat panel display
40
including lower polarizer
10
, LCD
20
and upper polarizer
30
to thereby form an integral type. In such a conventional flat panel display, since touch panel
50
is located at an inner side of the upper polarizer
30
, it is referred to as an “inner touch panel”.
Such a conventional integral type touch panel flat panel display has a structure almost analogous to the additive type touch panel flat panel display, except that touch panel
50
in the integral type is located between upper polarizer
30
and LCD
20
while touch panel
50
in the additive type is located over upper polarizer
30
. The light transmissivity in the integral type is somewhat improved over the additive type.
The conventional integral type as described above also has a problem in that, since touch panel
50
including lower sheet
51
and upper sheet
52
is used similarly to the conventional additive type which increases the entire bulk and weight, it is difficult to apply the touch panel to an LCD monitor, a notebook or a personal computer, etc., which require light weight and thin characteristics. Also, the conventional additive type touch panel flat panel display has a problem in that, there is a large difference in the refraction index with five boundary surfaces and a relatively large reflection as indicated by dotted lines in FIG.
2
. Such problem results in poor light transmissivity.
Furthermore, the conventional integral type touch panel flat panel display is limited in that, a light-isotropic film must be used for transparent conductive films of upper sheet
52
and lower sheet
51
of touch panel
50
because touch panel
50
is inserted between lower polarizer
10
and the upper polarizer. According to a disclosure in the Japanese Patent Laid-open No. 9-24571, if a light-isotropic film is not used for the transparent conductive films of upper sheet
52
and lower sheet
51
of touch panel
50
that is inserted between lower polarizer
10
and upper polarizer
30
, then an optical axis is not matched causing a coloration or a light interference due to an interference with lower polarizer
10
.
Yet another problem with the conventional touch panel integral type flat panel display is that because touch panel
50
is inserted between upper polarizer
30
and LCD
20
, mechanical characteristics such as a degree of hardness, heat-proof and scratch-proof, etc. related to upper sheet
52
of touch panel
50
must be provided to upper polarizer
30
.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a polarizer integrated with transparent conductive film that substantially obviates one or more
Ahn Young Soo
Jeong Byoung Hyun
Jeong Yun Cheol
Rhee Jang Youl
LG. Philips LCD Co. Ltd.
McKenna Long & Aldridge LLP
Ngo Julie
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