Liquid crystal cells – elements and systems – Particular structure – Holder – support – frame – or housing
Reexamination Certificate
2000-04-14
2002-12-03
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Holder, support, frame, or housing
C349S065000, C348S838000, C361S032000
Reexamination Certificate
active
06490015
ABSTRACT:
CROSS REFERENCE
This application claims the benefit of Korean Patent Application No. 1999-13095, filed on Apr. 14, 1999, under 35 U.S.C. §119, the entirety of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a structure of a liquid crystal display module having a light waveguide plate and a main supporting frame.
2. Description of Related Art
Liquid crystal displays (LCDS) are gaining in popularity for use in systems such as television receivers, computer monitors, avionics displays, aerospace displays, and other military-related displays where the elimination of cathode ray tube (CRT) technology is desirable for several reasons. In particular, CRTs are characterized by large depth dimensions, undesirably high weight, and fragility. Additionally, CRTs require a relatively high voltage power supply in order to sufficiently accelerate electron beams for displaying images.
The aforementioned shortcomings of CRTs are overcome by flat panel liquid crystal displays in which matrix arrays of liquid crystal picture elements or pixels are arranged in a plurality of rows and columns. Patterns of information are thereby defined by the two dimensional array of pixels, which because of differences in the orientation of the liquid crystal material within each pixel, are caused to appear either darkened or transparent.
FIG. 1
is a perspective view illustrating a conventional LCD module, and
FIG. 2
is a cross-sectional view taken along line II—II of FIG.
1
. As shown in
FIGS. 1 and 2
, the LCD module
10
generally includes a display panel
20
comprising two substrates with a liquid crystal layer interposed therebetween, a back light device
30
having a lamp
36
as a light source arranged along a side of the LCD module
10
, a metal frame
70
supporting the display panel
20
and the backlight device
30
together with a main frame
40
.
The backlight device
30
further includes a protecting sheet
31
, a diffusing sheet
32
, a prism sheet
33
, a light waveguide plate
34
, and a reflecting sheet
35
, which are stacked in above-described order. The light waveguide plate
34
serves to uniformly direct a light from the lamp
36
to the display panel
20
, and its three side walls contact with corresponding portions of the main frame
40
. The other side wall
50
of the light waveguide plate
34
contacts with the lamp
36
through a lamp housing
60
that surrounds the lamp
36
(see FIG.
3
).
FIG. 3
is a perspective view illustrating a structure of a conventional LCD module having the light waveguide plate and the main frame. As shown in
FIG. 3
, the main frame
40
has a recessed portion
42
and the light waveguide plate
34
has a protruding portion
34
a
around a center of its side wall which is perpendicular to the longitudinal direction of the lamp
36
. So the light waveguide plate
34
is accommodated in the main frame
40
when the protruding portion
34
a
is aligned with the recessed portion
42
. Movement of the light waveguide plate
34
that may damage the lamp
36
is prevented owing to the engagement of the protruding portion
34
a
and the recessed portion
42
.
FIG. 4
shows a different structure of another conventional LCD module having the waveguide plate and the main frame. As shown in
FIG. 4
, the main frame
40
has fixing portions
44
at both end portions thereof adjacent to the lamp
36
and the light waveguide plate
34
has recessed portions
34
b
at locations corresponding to the fixing portions
44
of the main frame
40
such the light waveguide plate
34
is accommodated in the main frame
40
. Thus, movement of the light waveguide plate
34
that may damage the lamp
36
is prevented.
However, the structures of the light waveguide plate and the main frame described above have the following disadvantages.
As shown in
FIG. 2
, since the light waveguide plate
34
is generally fabricated through an injection molding process using a metal mold and the open portion of the mold corresponds to an upper edge of the light waveguide plate
34
, it has burrs
38
formed on its upper edge. The burrs
38
are formed after the molding process due to the open portion. When the light waveguide plate
34
having the burrs is accommodated in the main frame
40
or when the light waveguide plate
34
moves, friction between the burrs
38
of the light waveguide plate
34
and the main frame
40
produces alien substances, leading to a bad display characteristics of the LCD.
Next, in general, dimensions of the light waveguide plate vary with the surroundings. And the dimension variation of the light waveguide plate is a product of a length and the coefficient of linear expansion. Therefore, when the coefficient of linear expansion is constant, its dimension variation becomes greater as it get far from a reference point of the light waveguide plate. But the main frame
40
seldom changes its dimension since it is usually made of polycarbonate whereas the light waveguide plate is usually made of acrylic resin. Referring to
FIG. 3
, note that the side wall
50
of the light waveguide plate
34
is a reference point since at that point the light waveguide plate
34
and the main frame
40
are fixed by the lamp housing
60
. Since the protruding portion
34
a
of the light waveguide plate
34
is far from the side wall
50
of the light waveguide plate
34
, the dimension variation difference between the recessed portion
42
of the main frame
40
and the protruding portion
34
a
of the light waveguide plate
34
is much larger. As a result, variation of a space “A” between the recessed portion
42
and the protruding portion
34
a
becomes as large as about ±0.3 mm. Therefore the light waveguide plate
34
may get out of the lamp housing of the lamp
36
during an impact test or being carried, leading to a problem in that light leakage (a bright line) may occur in the vicinity of the end portion of the display panel
20
. In order to overcome such a problem, the structures of the light waveguide plate and the main frame in
FIG. 4
have been introduced whose the fixing portion
44
and the recessed portion
34
b are formed at both end locations adjacent to the lamp
36
. In general, between the fixing portion
44
and the recessed portion
34
b,
a space “B” of 0.3 mm is required. This is because the light waveguide plate
34
is expanded during a high temperature test and gets bent so that the sheets
31
,
32
and
33
(see
FIG. 2
) arranged over the light waveguide plate
34
get bent. Thus, space “B” of 0.3 mm between the fixing portion
44
and the recessed portion
34
b
is necessary. However, such a space “B” of 0.3 mm causes the light waveguide plate
34
to get out of the lamp housing
60
of the lamp together with dimension variation difference between the light waveguide plate
34
and the main frame
40
due to the surroundings such a temperature and humidity during an impact test or being carried, leading to a problem in that light leakage (a bright line) may occur in the vicinity of the end portion of the display panel
20
.
SUMMARY OF THE INVENTION
In order to overcome problems described above, a preferred embodiment of the present invention provides a liquid crystal display device having good display characteristics and capable of preventing a bright line from occurring.
In order to achieve the above object, the present invention provides A liquid crystal display device module which includes a backlight device having a) a lamp; b) a lamp housing surrounding the lamp; c) a reflecting sheet for reflecting light from the lamp; d) a light waveguide plate having four side walls, one of the four side walls fixed to the lamp housing and another side wall adjacent to the fixed side wall having a protruding portion, the light waveguide plate being located on the reflecting sheet, and e) a plurality of sheets located on the light waveguide plate; a liquid crystal panel located on the backlight device;
Birch & Stewart Kolasch & Birch, LLP
LG. Philips LCD Co. Ltd.
Ngo Julie
Sikes William L.
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