Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1996-07-02
2001-01-16
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S165000, C349S074000
Reexamination Certificate
active
06175398
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an axial symmetric polarizing plate, a method for fabricating the axial symmetric polarizing plate, and a liquid crystal display device using the polarizing plate. More Specifically, the present invention relates to an axial symmetric polarizing plate having light transmission easy axes or light absorption axes arranged with axial symmetry so that the light transmission or light absorption of the polarizing plate for incident light is uniform omnidirectionally in one plane, and a method for easy fabrication of such an axis symmetric polarizing plate.
The present invention also relates to a liquid crystal display device where the viewing angle characteristics are uniform omnidirectionally by combining the above axial symmetric polarizing plate and the orientation of liquid crystal molecules of a liquid crystal display device.
2. Description of the Related Art
A liquid crystal display device having wide viewing angle characteristics is suitable, not only for personal display apparatuses such as wordprocessors and personal computers, but also for apparatuses such as portable information terminals which are viewed by a plurality of users, especially one which is viewed by several users gathering in front of the apparatus on a desk. This type of liquid crystal display device should be used both as a reflective liquid crystal device and a portable display device. Such a liquid crystal display device is now under development.
Hereinbelow, the principle for the improvement in the viewing angle characteristics of a liquid crystal display devise will be described.
FIGS. 24A
to
24
C illustrate the change in the orientation of liquid crystal molecules in a liquid crystal cell where the liquid crystal molecules are oriented in two different directions.
FIGS. 24D
to
24
F illustrate the change in the orientation of liquid crystal molecules in a liquid crystal cell of a conventional twisted nematic (TN) mode,
Referring to
FIGS. 24A
to C, a liquid crystal cell
11
corresponding to one pixel includes upper end lower substrates
2
and
1
facing each other and a liquid crystal layer formed therebetween. The liquid crystal cell
11
has two liquid crystal domains
8
a
and
8
b
where liquid crystal molecules
9
are initially oriented in different directions. The liquid crystal domains
8
a
and
8
b
are surrounded by a partition
7
made of polymer and the like. The reference numeral
10
denotes the boundary between the liquid crystal domains
8
a
and
8
b
. Referring to
FIGS. 24D
to
24
F, a liquid crystal cell
12
corresponding to one pixel is of the TN mode and includes liquid crystal molecules
13
oriented in one direction. Upper and lower polarizing plates (not shown) are disposed on the upper and lower substrates
2
and
1
of both the liquid crystal cells
11
and
12
so that the polarization axes thereof are perpendicular to each other (normally white mode).
In order to improve the viewing angle characteristics of a liquid crystal display device, it is necessary to form two or more domains where liquid crystal molecules are oriented in different directions in each liquid crystal cell corresponding to one pixel as shown in
FIGS. 24A
to
24
C.
The reason is that, as shown in
FIG. 24B
, in a gray-scale state of the liquid crystal cell
11
, i.e., in the state where the liquid crystal molecules are in transition between the horizontal orientation and the vertical orientation by the application of a voltage, the transmittances for light incident from directions A and B are averaged, and thus the same contrast ratio is obtained in the directions A and B. As a result, the viewing angle characteristics of the liquid crystal cell
11
in the gray-scale state are improved compared with that of the liquid crystal cell
12
of the TN mode.
However, in a saturated voltage application state of the liquid crystal cells
11
and
12
(FIGS.
24
C and
24
F), the liquid crystal molecules
9
and
13
are oriented along the electric field. Therefore, in the saturated voltage application state, the orientations of the liquid crystal molecules are the same in the liquid crystal cells
11
and
12
though they are initially different. In the saturated voltage application state, as for the optical characteristics in a direction inclined from the normal of the liquid crystal display device, a region where the viewing angle characteristics are comparatively poor is generated in the 45° directions from the polarization axes of the upper and lower polarizing plates. This is due to the synergistic effect of the viewing angle characteristics of the upper and lower polarizing plates and the light leakage by an elliptically polarized light component caused by retardation generated as light passes obliquely through the liquid crystal layer. Even a liquid crystal display device, including the liquid crystal cell
11
which has two domains where liquid crystal molecules are oriented in different directions, does not have omnidirectional viewing angle characteristics since the device itself is anisotropic for the viewing angle.
In other words, the problem that the display performance is comparatively poor in 45° directions from the polarization axes of the upper and lower polarizing plates arises because the polarization axes of the polarizing plates are arranged in a predetermined direction over the entire liquid crystal cell.
Next, some examples of conventional liquid crystal display devices of a wide viewing angle mode will be described.
(1) A method for electrically controlling the transparent state or the opaque state of a liquid crystal device using birefringence of liquid crystal molecules in a liquid crystal cell having polymer walls has been proposed. In this method, basically, the ordinary light refractive index of the liquid crystal molecules and the refractive index of a medium supporting the liquid crystal are set to be equal to each other. When a voltage is applied, the liquid crystal molecules become oriented in such a way as to allow the transparent state to be displayed. When no voltage is applied, the liquid crystal molecules become oriented in such a way as to allow the light scattering state to be displayed.
Japanese Laid-Open Patent Publication No. 61-502128 concretely discloses one such method. According to this method, a liquid crystal material and a photocurable or thermosetting resin are mixed. The liquid crystal material is deposited by curing the resin, forming liquid crystal drops in the resin. In this method, neither the polarizing plate nor the alignment treatment for liquid crystal molecules is required.
Japanese Laid-Open Patent Publication Nos. 4-338923 and 4-212928 disclose a wide viewing angle mode where the above liquid crystal device is combined with polarizing plates perpendicular to each other (crossed Nicols state).
More specifically, Japanese Laid-Open Patent Publication No. 4-338923 discloses a liquid crystal display device where a liquid crystal layer of a liquid crystal cell includes a liquid crystal medium, and liquid crystal capsules dispersed in the liquid crystal medium. Two polarizing plates having polarization axes perpendicular to each other are disposed on the opposite surfaces of the liquid crystal cell. A phase plate having a disk shape refractive index anisotropy is formed between the liquid crystal cell and one of the polarizing plates. In this type of liquid crystal display device, display is conducted by switching between whether light is scattered or not scattered by liquid crystal molecules in the liquid crystal capsules. Thus, the viewing angle dependence seldom occurs.
Japanese Laid-Open Patent Publication No. 4-212928 discloses a liquid crystal display device where a liquid crystal panel is constructed so that the orientation of liquid crystal molecules is disordered to scatter incident light when no voltage is applied, and that the incident light is allowed to pass through when a voltage is applied. A pair of polarizing plates having polarizing direc
Kozaki Shuichi
Okamoto Masayuki
Yamada Nobuaki
Duong Tai V.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Sikes William L.
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