Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2001-11-16
2003-12-02
Niebling, John F. (Department: 2812)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
Reexamination Certificate
active
06657685
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a liquid crystal display (LCD) device having an improved backlight unit and, more particularly, to the improvement of the structure of the optical sheet assembly in the backlight unit of the LCD device.
(b) Description of the Related Art
An LCD device has the advantages of smaller thickness and lightweight, and thus is used as a flat display panel in a variety of applications. The LCD device generally includes a display panel, a backlight unit for irradiating the display panel from the rear surface thereof, a housing for receiving therein the display panel and the backlight unit in one body so that the front screen of the display panel is exposed from a front opening of the housing, and a backlight chassis for positioning the backlight unit with respect to the LCD panel within the housing.
FIG. 1
shows a typical LCD device
10
in an exploded view thereof. The LCD device
10
includes an LCD panel
12
having a front screen, a backlight unit
14
disposed at the rear side of the LCD panel
12
for irradiating the LCD panel at the rear side, and a housing including a frame member
16
and a pair of holders
18
which support the LCD panel
12
and the backlight unit
14
at the top and bottom sides of the LCD panel in association with the frame member
16
, and a backlight chassis (not shown) for positioning the backlight unit
14
with respect to the LCD panel
12
within the housing. The LCD panel
12
mounts thereon drive circuits
32
and
34
at the edge of the LCD panel
12
.
The frame member
16
is made of a metallic body
16
which defines a window
20
for exposing therethrough the front screen of the LCD panel
12
. The frame member
16
acts as an electrostatic shield for the LCD device. The frame member
16
is engaged with the holders
18
to thrust the LCD panel
12
toward the backlight unit
14
.
FIG. 2
shows the top corner of the typical LCD device
10
, in a sectional view taken along line II—II in FIG.
1
.
In
FIG. 2
, the LCD panel
12
includes a color filter
26
and a TFT substrate
28
, which are sandwiched between a first (front) polarizing plate
22
and a second (rear) polarizing plate
24
. A black matrix
30
is disposed between the color filter
26
and the TFT substrate
28
to cover the periphery of the TFT substrate
28
for preventing the backlight from passing the LCD panel
12
.
The backlight unit
14
includes a light source
36
for emitting light, an optical guide plate
38
made of acrylic resin for passing therethrough the light emitted by the light source
36
, and a laminated, optical sheet assembly
48
including a first light scattering sheet
40
, a first lens sheet
42
, a second lens sheet
44
and a second light scattering sheet
46
, which are consecutively formed on the front surface of the optical guide plate
38
. A reflective sheet
50
is formed on the rear surface of the optical guide plate
38
for reflecting the light passing the rear surface of the optical guide plate
38
toward the internal thereof.
The optical guide plate
38
receives light from the light source
36
at the light receiving edge
38
b
thereof and passes the received light through the front surface
38
a
thereof. The first and second light scattering sheets
40
and
46
have a function for scattering the light passing therethrough to obtain a uniform brightness of the front screen. The first and second lens sheets
42
and
44
are made of a plastic material having a thickness of about 0.2 mm. Each of the first and second lens sheet
42
and
44
has a plurality of triangle prisms extending horizontally or vertically and arranged on the rear surface thereof. The first and second lens sheets
42
and
44
have a function for correcting the direction of the light passed from the optical guide plate
38
to form a substantially parallel ray on the front screen of the LCD panel
12
.
The light source
36
of the backlight unit
14
is implemented by a cylindrical elongate lamp extending along the light receiving edge
38
b
of the optical conductive plate
38
. A metallic reflecting member
54
having a “]” shape in cross section is disposed for encircling the lamp
36
. The metallic reflecting member
54
has a first edge abutted with the light receiving edge
38
b
near the front side thereof, and a second edge sandwiched between the holder
18
and the reflective sheet
50
disposed at the rear surface of the optical conductive plate
38
.
The backlight chassis
56
, as mentioned before, is made of an opaque plastic material and is disposed for positioning and supporting the optical conductive plate
38
, the optical sheet assembly
48
, the lamp
36
and the metallic reflecting member
54
with respect to the LCD panel
12
while encircling these members. A spacer
58
made of a plastic material is disposed between the backlight chassis
56
and the metallic reflecting member
54
.
FIG. 3
shows, in a sectional view, a side edge portion
60
of a conventional LCD device
10
A having configurations such as shown in
FIGS. 1 and 2
, wherein
FIG. 3
is taken along a line corresponding to line III—III in FIG.
1
. In
FIG. 3
, the optical conductive plate
38
has an edge
38
c
, other than the light receiving edge
38
b
, the edge
38
c
being flush with the edges of the first scattering sheet
40
, the first lens sheet
42
and the second lens sheet
44
of the optical sheet assembly
48
. The edge
38
c
opposes the inner surface
56
a
of the backlight chassis
56
. The second scattering sheet
46
of the optical sheet assembly
48
has an extended edge
46
a
protruding from the edges of the first scattering sheet
40
etc. of the optical sheet assembly
48
, and mounted on a step
56
b
of the backlight chassis
56
, with an intervention of a cushion member
57
disposed therebetween.
The LC drivers
32
and
34
are mounted on a support member
62
disposed at the rear side of the reflective sheet
50
. TCPs (tape carrier packages)
66
extend from the LC drivers
32
and
34
toward the front side of the LCD panel
12
for transferring driving signals for the LCD panel
12
.
FIG. 4
is a schematic view showing the situation wherein the screen of the conventional LCD device
10
A is observed by a human eye with an angle “a” which is the supplementary angle of the viewing angle of the LCD panel. In the vicinity of the black matrix
30
, the human eye observes a bright line, which passes the space between the edge
38
c
of the optical conductive plate
38
and the inner surface
56
a
of the backlight chassis
56
while being repetitively reflected by the edge
38
c
of the optical conductive plate
38
and the inner surface
56
a
of the backlight chassis
56
.
The bright line appearing in the vicinity of the image of the black matrix
30
of the LCD device significantly degrades the image quality of the LCD device, and is thus undesirable.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide an LCD device having an excellent image quality by suppressing the bright line as encountered in the conventional LCD device.
The present invention provides, in a preferred embodiment thereof, a liquid crystal display (LCD) device including: an LCD panel; a backlight unit including a light source, an optical conductive plate including a light receiving edge for receiving therein light from the light source, three remaining edges, and a light emitting surface for irradiating therethrough the light received through the light receiving edge toward the LCD panel, and an optical sheet assembly including a first light scattering sheet, a first lens sheet, a second lens sheet and a second light scattering sheet consecutively formed on the light emitting surface; and a backlight chassis for positioning the light source, the optical conductive plate and the optical sheet assembly with respect to the LCD panel, wherein at least the first and second lens sheets among the optical sheet assembly have extended edges adjacent to
Kasuga Koji
Sakaki Yoshinobu
Foley & Lardner
NEC LCD Technologies Ltd.
Niebling John F.
Stevenson André C
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