Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-12-14
2002-11-12
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S103000, C349S065000
Reexamination Certificate
active
06480248
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of illuminating a liquid crystal layer and a liquid crystal display (hereinafter, LCD) using the same, and more particularly, to a method of illuminating a liquid crystal utilized in an LCD and capable of decreasing manufacturing costs as well as enhancing both brightness characteristics depending on visual angles and whole brightness characteristics, and an LCD using the illuminating method.
2. Description of the Related Art
Generally, an LCD is defined as one of flat panel displays which display data processed in an information processing device as characters, images and moving pictures using an optical property of liquid crystal in which light transmittance is varied depending on an intensity of an applied electric field.
Liquid crystal in an LCD controls transmittance of an incident light wave or beam depending on the intensity of an applied electric field to allow an image to be displayed. This means that all LCDs using such a liquid crystal require a light for displaying an image.
Such light is provided by an electrical energy internally charged in the LCD itself or from an external light source.
Where internally charged electrical energy is used in an LCD as a light source, an image can be displayed without being effected by an external environment of the LCD, such as existence or nonexistence of an external light source or intensity of light.
In the meantime, where the external light source is used for supplying light to an LCD, an image can be displayed with very small power consumption but the display is greatly affected by an external environment. For example, the display is not possible where there is no externally available light, or the quality of the display is greatly degraded where the intensity of an existing external light is insufficient.
Therefore, an LCD utilizing internally charged electrical energy for providing light to a liquid crystal layer, herein referred to as a “transmission type LCD”, has been widely used.
The transmission type LCD generally includes an LCD panel for controlling a liquid crystal and various elements for effectively using light which is supplied to the LCD panel after being generated from a lamp.
Specifically, as shown in
FIG. 1
, a conventional transmission type LCD
80
includes an LCD panel
20
and a backlight assembly
40
.
The LCD panel
20
includes a TFT substrate
16
having a selected effective display area, a color filter substrate facing the TFT substrate
16
, a liquid crystal layer (not shown) interposed between the TFT substrate
16
and the color filter substrate
14
, a lower polarizing plate
18
attached to an outer surface of the TFT substrate
16
and an upper polarizing plate
12
attached to an outer surface of the color filter substrate
14
.
The LCD panel
20
requires an incident light having an optical distribution of a planar light source and a uniform brightness in order to display an image with a uniform quality throughout the entire area of the effective display area.
However, since an optical distribution of a planar light source is difficult to obtain as an incident light, the backlight assembly
40
is used in the LCD
80
.
The backlight assembly
40
includes a lamp assembly, a light guiding plate
35
, a reflection plate
38
, a diffusion plate
34
, a prism sheet
33
, a reflection polarization film
32
, and a reflection polarization film protection sheet
31
.
The lamp assembly includes a CCFT (Cold cathode fluorescent tube) type lamp
37
for generating a white light that is similar to natural light and having a long life time and an easy manufacturing characteristic, and a lamp reflector
36
for directing the white light toward one direction.
Since the CCFT type lamp
37
generates light having an optical distribution of a linear light source, a member is required to transform the generated light into light having an optical distribution of a planar light source.
Specifically, in order to transform the light generated by the CCFT type lamp
37
having the optical distribution of the linear type into the light having the optical distribution of the planar type, the light guiding plate
35
is used.
The light guiding plate
35
has a plate-shaped parallelepiped structure. An incident light having the optical distribution of the linear light source is uniformly reflected throughout the entire area of the light guiding plate
35
, and the optical distribution of the planar light source is thus obtained.
The light illuminated from the light guiding plate
35
has the optical distribution of the planar light source but it has a low uniformity of brightness. Therefore, it is difficult to display an image having a high quality using the light guiding plate
35
alone.
To overcome this drawback, the diffusion plate
34
for diffusing the light illuminated from the light guiding plate
35
is provided on the light guiding plate
35
.
The light outputted from the diffusion plate
34
has an improved optical uniformity, however the light has an irregular progressive direction. Thus, a visual angle at the front side is significantly decreased.
To improve the visual angle at the front side, one sheet or two sheets of prism sheet
33
is disposed on the diffusion plate
34
.
The light passes through the CCFT type lamp
37
, the light guiding plate
35
, the diffusion plate
34
, the prism sheet
33
, the lower polarizing plate
18
, the TFT substrate
16
, the liquid crystal layer, the color filter substrate
14
, and the upper polarizing plate
12
to display an image.
The light that generated from the CCFT type lamp
37
has two kinds of wave forms, i.e., a P wave and an S wave. The P wave light passes through the lower polarizing plate
18
but the S wave light does not pass through the lower polarizing plate
18
and is dissipated.
Here, the P wave and the S wave are classified depending on the polarizing axis which the waves pass through. Particularly, the light that passes through the lower polarizing plate
18
is defined as the P wave and the light that does not pass through the lower polarizing plate
18
is defined as the S wave. This means that only 50% of the light output from the CCFT type lamp
37
arrives at a user's eye.
To improve the low light efficiency, the reflection polarization film
32
is disposed on the prism sheet
33
. The reflection polarization film
32
passes the P wave but it reflects the S wave and converts the reflected S wave into the P wave.
The reflection polarization film
32
is easily contaminated or scratched due to foreign particles and is susceptible to a Moire phenomenon due to a relationship between the prism sheet and a pattern of the TFT substrate. Also, the reflection polarization film
32
has a non-uniform visual angle.
In order to prevent these problems, the protection sheet
31
is disposed on the reflection polarization film
32
.
The protection sheet
31
is usually made of a polycarbonate (PC)-based material, which is manufactured by an extrusion process into a form of a thin sheet. The protection sheet
31
has a vague polarizing axis as shown in FIG.
2
. Therefore, the protection sheet
31
prevents a lowering of the brightness even if an angle between a polarizing axis of the reflection polarization film
32
and a polarizing axis of the protection sheet
31
is not adjusted, and it also remedies disadvantages of the reflection polarization film
32
.
Although the protection sheet
31
made of the PC-based synthetic resin guarantees a certain level of brightness regardless of the polarizing axis, the film experiences a deformation such as a wrinkling and shrinkage due to a considerably high thermal expansion coefficient and increases the manufacturing cost of the LCD due to a high cost of the extrusion process.
SUMMARY OF THE INVENTION
Accordingly, in one aspect of the present invention, there is provided a method for illuminating a liquid crystal layer, which allows an image display with a high brightness while reducing overall manufacturing
Kim Kyu-Seok
Lee Jeong-Hwan
Cantor & Colburn LLP
Dudek James
Samsung Electronics Co,. Ltd.
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