Liquid crystal cells – elements and systems – Particular structure – Holder – support – frame – or housing
Reexamination Certificate
1998-09-29
2001-04-17
Malinowski, Walter J. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Holder, support, frame, or housing
C349S065000
Reexamination Certificate
active
06219116
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal panel module, and to a liquid crystal display device using the liquid crystal panel module.
2. Description of the Related Art
Most notebook computers and dedicated laptop wordprocessors available today use a liquid crystal display (LCD) device mounted on the inside of a cover for a monitor. Such LCDs typically comprise a transparent liquid crystal panel, a light guide for guiding illumination light to the LC panel, a lamp disposed to one side of the light guide, and a reinforced plastic or metal frame in which these and other components are housed.
In the market for notebook computers in particular, however, demand remains great for ever smaller, lighter, and thinner systems. This has driven demand for thinner LCD devices.
FIG. 9
is a sectional view of a conventional LCD device
100
such as is commonly used in notebook computers. As will be known from the figure, this LCD device
100
has a liquid crystal panel module
102
disposed in a frame
101
with a mask frame
103
affixed to the top.
The liquid crystal panel module
102
comprises, assembled in sequence on a plastic frame
104
, a backlight unit
105
, stacked films
109
comprising an optical diffusion sheet and a lens sheet, and TFT LC panel unit
110
.
The backlight unit
105
comprises a light guide
106
with a reflective sheet affixed to the bottom side thereof as seen in
FIG. 9
, a reflector
107
with a circular cross section, and a lamp
108
.
Metal chassis
11
a
and
111
b
for securing the liquid crystal panel module
102
to the frame
101
are provided at the left and right sides of the panel module
102
.
Note that U.S. Pat. No. 5,504,605, for example, teaches the construction of a liquid crystal module using a plastic frame.
With a liquid crystal panel module
102
as described above and shown in
FIG. 9
, there are three major factors limiting the reduction in module thickness. These are described below.
FIG. 10
is a view of the plastic frame
104
in the above-described liquid crystal panel module
102
. As shown in
FIG. 10
, the plastic frame
104
is manufactured with a uniform thickness except for the lamp housing, both to reliably secure components therein, and to ensure sufficient strength in the liquid crystal panel module
102
. The thickness of this plastic frame
104
is a first factor limiting thinner liquid crystal panel modules
102
.
While making the LCD device
100
thinner, it is still essential to ensure a certain minimum strength. The strength of the LCD device
100
, however, is more dependent on the strength of the frame than on the strength of the liquid crystal panel module
102
.
This suggests that the liquid crystal panel module
102
could be made thinner by making the plastic frame
104
thinner, thus solving the first problem noted above. Doing so, however, creates a further problem, specifically, reliably securing the TFT LC panel unit
110
to the backlight unit
105
becomes difficult.
Circuits and wiring harnesses for the gate and control signal buses used for controlling the operation of the TFT LC panel unit
110
are also disposed between the plastic frame
104
and light guide
106
. A plurality of protrusions are also provided on the top of the plastic frame
104
for supporting the light guide
106
.
When the gap between the plastic frame
104
and light guide
106
is narrowed by an external force applied to the plastic frame
104
, the light guide
106
is pushed up by one or more protrusions
115
on the plastic frame
104
. This causes the light guide
106
to push up on the film
109
and thereby on the TFT LC panel unit
110
. This results in display irregularities on the screen of the TFT LC panel unit
110
.
To prevent such display irregularities from appearing on the screen of the TFT LC panel unit
110
in a typical liquid crystal panel module
102
as described above, a certain minimum gap is typically maintained between the plastic frame
104
and light guide
106
. In addition, this gap also normally has sufficient extra tolerance, and is the second major factor limiting further reduction in the thickness of liquid crystal panel module
102
.
It would also seem that the liquid crystal panel module
102
could be made thinner by narrowing the sufficient gap between the plastic frame
104
and light guide
106
to the same thickness as the thickest circuit and protrusion interposed to this gap. In this case, however, small vibrations induced by operating the keyboard, opening and closing the cover, and other operations can cause the circuit and protrusion to contact the light guide
106
. Display irregularities can again result easily.
Variations in manufacturing precision can also produce distortion in the light guide
106
. A specific gap is therefore provided between the light guide
106
and the TFT LC panel unit
110
in a typical liquid crystal panel module
102
as described above to prevent the distorted part of the light guide
106
from pushing up from below on the TFT LC panel unit
110
and causing display irregularities as described above. This gap is a third major factor limiting further reduction in the thickness of liquid crystal panel module
102
. In addition, small contaminants and foreign objects can easily penetrate this gap, resulting in black spots, luminance errors, and other display irregularities.
The liquid crystal panel module
102
can again be made thinner by narrowing this gap, but when there are distortions in the light guide
106
and these distortions are pressed against the TFT LC panel unit
110
, display irregularities will still occur.
As described above, it is difficult to resolve the problems associated with the above three factors to reduce the thickness of the thinner liquid crystal panel module
102
with a construction as described above.
A further problem is related to the reflector
107
with a circular section that is used in the backlight unit
105
of a typical liquid crystal panel module
102
as shown in FIG.
12
. In this case, the thickness, or more specifically the diameter D as shown in the figure, of the reflector
107
must be reduced to achieve a thinner LCD device. Reducing the diameter D of the reflector
107
, however, is complicated by the following problems.
Specifically, when the reflector
107
is made thinner, the diameter of the lamp
108
, which is supported on both ends inside the reflector
107
, must also be reduced. Reducing the lamp
108
diameter, however, can make it more difficult to precisely position the lamp
108
inside the reflector
107
due to variations in component dimensions and applied force.
Reducing the diameter of the lamp
108
also reduces its rigidity and resistance to loads, including gravity, vibration, and impact, applied perpendicular to the longitudinal axis of the lamp. In addition, vibrations caused by typing on the keyboard can also cause the position of the lamp
108
to shift.
FIG. 13
is a graph showing the relationship between the distance X from the center point A of the reflector
107
to the center point B of the lamp
108
, and the incidence efficiency (%) of light from the lamp to the light guide. As will be known from
FIG. 13
, a slight change in the position of the lamp
108
results in a significant change in the efficiency with which a circular section reflector
107
makes the emitted light incident on the light guide
106
.
As will therefore be understood, when a small diameter lamp
108
is used and the distance of the lamp
108
from the center of the reflector
107
is different at the two ends of the lamp, light from the lamp
108
cannot be guided to the light guide
106
with uniform luminance along the entire axial length of the lamp.
Furthermore, even if the lamp
108
is positioned to the reflector
107
with a uniform distance therebetween throughout the entire length of the lamp, variations in this distance to the center of the reflector
107
in different LC panel modules can easily produce variations in the luminance o
Kawabe Sin
Matsumoto Sadayuki
Sasagawa Tomohiro
Shimojo Kazutoshi
Umesaki Mitsumasa
Leydig , Voit & Mayer, Ltd.
Malinowski Walter J.
Mitsubishi Denki & Kabushiki Kaisha
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