Illumination – Illuminated scale or dial – Edge illuminated modifier or light rod/pipe
Reexamination Certificate
2002-04-01
2004-11-23
Husar, Stephen F. (Department: 2875)
Illumination
Illuminated scale or dial
Edge illuminated modifier or light rod/pipe
C362S035000, C362S293000, C349S065000
Reexamination Certificate
active
06820989
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a light source device, a backlight assembly and a liquid crystal display device for preventing a light guide plate from being discolored due to light emitted by a lamp.
2. Description of the Related Art
Presently, information processing devices are developed for various shapes and functions and higher processing speed. The information processing devices convert various type of information into electrical signals. Display devices function as an interface between users and the information processing devices such that the users can identify the information processed by the information processing devices.
Recently, the display device manufacturing industry has been focusing on developing smaller and lighter liquid display devices. The liquid display devices provide richer and fuller colors and higher resolutions as compared with conventional display devices, such as a CRT (Cathode Ray Tube). As the result, the liquid display devices have been gaining its popularity among other display devices, for example, computer monitors, household television sets that are hung on a wall, and the like.
Generally, to operate a liquid crystal display device, a voltage is applied to the liquid crystal in the predetermined molecule arrays to change the liquid crystal in the other arrays, which alters the optical characteristics of the liquid crystal, such as a double refractivity, a rotatory polarization, a dichroism and a light scattering according to the molecule arrays of the liquid crystal to emit the light. Therefore, the liquid crystal display device can display the images according to the changes of the optical characteristics of the liquid crystal cell.
FIG. 1
is an exploded perspective view showing a liquid crystal display device according to the conventional art schematically, and
FIG. 2
is a sectional view of showing the constructions of a lamp shown in FIG.
1
.
FIG. 3
is a graph for showing a discoloration of a light guide plate due to light supplied by the lamp shown in FIG.
1
.
Referring to
FIGS. 1 and 2
, the liquid crystal display device comprises a liquid crystal display module for displaying images when image signals are applied thereto and a case (not shown) for accommodating the liquid crystal display module. The liquid crystal display module includes a display unit having a liquid crystal display panel for displaying the images.
The display unit
200
includes the liquid crystal display panel
210
, a printed circuit board
220
for transferring data signals, a printed circuit board
212
for transferring gate signals, a tape carrier package
230
for transferring data signals and a tape carrier package
250
for transferring gate signals.
The liquid crystal display panel
210
includes a thin film transistor board
212
which is normally a transparent glass on which the thin flhn transistors are formed in a matrix, a color filter board
214
having RGB pixels that are formed thereon by a thin film process and present predetermined colors while the light passes through the color filter board
214
, and liquid crystal (not shown).
When the thin film transistors of the thin film transistor board
212
are turned on, electric field is created between the pixel electrodes of the thin film transistor board
212
and the common electrodes of the color filter board
214
. The electric field changes the liquid crystal layer's array angle, and changes the light transmittivity. As a result, it is possible to gain the desired pixels.
A driving signal and a timing signal are applied to the gate lines and data lines of the thin film transistor in order to control the array angle of the liquid crystal and the time of arraying the liquid crystal in the liquid crystal display panel
210
. That is, the printed circuit boards
220
and
240
generate and apply the gate driving signal and the data signal for driving the liquid crystal display device and a plurality of timing signals for applying the gate driving signal and the data signal, to the gate lines and the data lines of the liquid crystal display panel
210
.
The backlight assembly
300
is provided under the display unit
200
to supply the light to the display unit
200
uniformly. The backlight assembly
300
includes a lamp
310
for generating the light. The lamp
310
is protected by a lamp cover
312
.
As shown in
FIG. 2
, the lamp
310
has a glass tube
301
in which inert gas is filled up and a hot electrode and a cold electrode
303
and
305
to which high voltage electricity and low voltage electricity are respectively applied are disposed at both ends respectively. Metal electrodes
303
a
and
305
a
are mounted at the hot and cold electrodes
303
and
305
, respectively, in the glass tube. As outer voltages discharge electricity between the two electrodes, the inert gas
309
is excited and ultraviolet rays are generated from the inert gas
309
. Some ultraviolet rays
311
are conversed into visible rays
313
by the fluorescent material in the glass tube
301
and then supplied to the light guide plate
320
.
The light guide plate
320
has a size corresponding to that of the liquid crystal panel
210
of the display unit
200
, which is disposed under the liquid crystal panel
210
to guide the light emitted by the lamp
310
toward the display unit
200
by changing a pathway of the light.
A plurality of optical sheets
330
are provided on the light guide plate
320
to make brightness of the light from the light guide plate
320
to the liquid crystal display panel
210
uniformly. In addition, a light reflecting plate
340
provided under the light guide plate
320
reflect leaking light to the light guide plate
320
so as to improve the efficiency of the light.
The display unit
200
and the backlight assembly
300
are supported by means of a mold frame
400
used as a receptacle. The mold frame
400
is provided with a top chassis
500
for preventing the display unit
200
from departing from the mold frame
400
while the printed circuit boards
220
and
240
are bent toward outside of the mold frame
400
and fixed to the bottom surface of the mold frame
400
.
The light guide plate
320
of polymethyl methacrylate (hereinafter, referred to as PMMA) effects the size and the weight of the liquid crystal display unit. As the size of the light guide plate
320
is directly related to a size of the liquid crystal display panel, however, researches have been continued to produce a liquid crystal display device that is light, thin and small by reducing the weight of the light guide plate
320
as much as possible.
Recently, for an example, a light guide plate which uses cycloolefin polymer (hereinafter, referred to as COP) has been developed to reduce the weight thereof. As shown in
FIG. 3
, however, the COP light guide plate is susceptible to the ultraviolet rays in the light emitted by the lamp
310
as compared with PMMA light guide plate.
For an example, when the PMMA light guide plate was aged at an ordinary temperature for 3300 hours, the PMMA light guide plate had changes &Dgr;X and &Dgr;Y in the order of 0.015 on X and Y color coordinates. However, the COP light guide plate had changes &Dgr;X and &Dgr;Y in the order of 0.025 and 0.032 on X and Y color coordinates. This is caused by a recombination reaction of the polyolefin resin composition to the ultraviolet rays, and the light guide plate is subjected to discoloration into yellow when used for a long period of time.
Besides, as shown in a graph in
FIG. 4
, when aged for about 3000 hours, a maintenance rate of brightness for the PMMA light guide plate is about 70%, while a maintenance rate of brightness for the COP light guide plate is about 60%.
Hence, COP light guide plate has the problems of discoloration and degradation of brightness characteristics as aged.
SUMMARY OF THE INVENTION
The present invention is directed to solving the aforementioned problems, and accordingly it is an object of
Kwak Meen-Woo
Lee Ik-Soo
Lee Jeong-Hwan
Lee Keun-Woo
Youn Sang-Hyuck
Husar Stephen F.
McGuireWoods LLP
Samsung Electronics Co,. Ltd.
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