Liquid crystal cells – elements and systems – Particular structure – Holder – support – frame – or housing
Reexamination Certificate
2000-09-26
2003-01-28
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Holder, support, frame, or housing
C349S065000
Reexamination Certificate
active
06512557
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device attached to the cover body of a laptop computer, a notebook type personal computer or the like to display images and a portable information terminal device having such a device.
2. Description of the Related Art
A portable information terminal device such as a laptop computer is provided with a keyboard at the top of the main body. The cover body to be lifted up and down and cover the keyboard is pivotally supported along the upper edge of the main body. The cover body is provided with a liquid crystal display device to display images.
The liquid crystal display device has an integral structure having a liquid crystal display panel (hereinafter as the “LCD panel”) held between a backlight unit and a picture frame-like presser casing. In the backlight unit, a plurality of diffusion sheets, a plurality of prism sheets, an optical guide plate and a reflector sheet are sequentially placed upon one another. At the lower part of the optical guide plate, a light source lamp and a reflector mirror (reflector) are provided. These are secured to a plate-like frame body (hereinafter as “chassis”) serving as a base.
The optical guide plate serves to propagate light emitted from the light source lamp upward and evenly supply the light over the entire display surface of the LCD panel. The optical guide plate has a rectangular shape when viewed two-dimensionally and a wedge-shaped cross section, for example. More specifically, the lower edge side closer to the light source lamp is thicker and the upper edge side farther from the light source lamp is thinner.
FIGS. 1A and 1B
are schematic views showing how the optical guide plate is: secured to the chassis. On both side edges of the optical guide plate
101
, there is a projection
102
projecting outward. Meanwhile, at a height in alignment with the projection
102
on the side frame of a chassis
100
, a recessed portion
103
is formed. The engagement of the projection
102
with the recessed portion
103
secures the optical guide plate
101
at a prescribed position of the chassis
100
.
Thus, even if for example the portable information terminal device having the liquid crystal display device is dropped, and large impact is applied upon the liquid crystal display device, the light source lamp can be prevented from being damaged as a result of the optical guide plate
101
moving downward to press the light source lamp (not shown).
It should be noted that the liquid crystal display device shown in
FIG. 1B
has a broader display surface than that shown in
FIG. 1A
, and an inner side
105
of the frame is positioned closer to the edge portion of the optical guide plate
101
in
FIG. 1B
than that shown in FIG.
1
A.
The portable information terminal devices have been reduced in size to cope with the demand in the market, and the model whose main body is almost as small as the size of the keyboard has been recently marketed. There has also been a demand for a device with an enlarged display surface as well while there has been the demand for reducing the size of the main body. In order to satisfy these demands in the market, the frame portion of the cover body tends to be narrowed in recent portable information terminal devices.
For example, in a laptop computer, the cover body has an outer size almost the same as the main body. Therefore, if the size of the main body is further reduced, the cover body is reduced in size accordingly. When the display surface is to be expanded in the cover body whose size is to be further reduced, only the display surface is expanded with the width of the frame being narrowed.
It is generally known that in a conventional liquid crystal display device, as shown in
FIGS. 1A and 1B
, a luminescent spot
106
(hatched) is generated at a position in close proximity to the upper part of the projection
102
. This is caused because the projections
102
are provided at both side edges of the optical guide plate
101
through which light must be homogeneously propagated at any positions. More specifically, the reflection state of the light changes by the presence of the projections
102
, and the homogeneity of propagation is lost, which causes light and dark areas to be generated at the position in the close proximity of the upper part to the projections
102
.
The luminescent spot
106
is hidden by the frame
105
of the cover body if the frame
105
has a relatively large width as shown in FIG.
1
A. Therefore, the spot does not appear in the actual display surface and it was not a significant problem before the attempt to reduce the width of the frame
105
as described above. However, as the width of the frame has come to be narrowed as described above, as shown in
FIG. 1B
, the luminescent spot
106
appears on the display surface. Therefore, an image near the frame is difficult to view.
It will be described how such a fixed structure as shown in
FIGS. 1A and 1B
have come to be employed in the conventional device.
As stated above, it would be readily conceived to provide projections on the side edge of the optical guide plate and recesses on the chassis and let them engage with each other in order to prevent the light source lamp from being damaged by the optical guide plate. However the positions where the projections and recesses are provided are not arbitrary. More specifically, the presence of the luminescent spot itself is a problem to be addressed even if it could be covered by the frame. Therefore, the possibility of providing them at the upper or lower part of the side edges believed to be less susceptible to the influence of the luminescent spot was originally considered, but the idea was turned down for the following reasons.
The optical guide plate lets light emitted from the light source lamp upward and supplies light homogeneously over the entire display surface as described above. The optical guide plate can carry out the function successfully if it has a wedge-like cross section with a thicker lower edge side and a thinner upper edge side. Therefore, in order to reduce the weight of the liquid crystal display device as much as possible, the wedge shape as described above is employed for the optical guide plate. If a projection is provided on an upper portion of a side edge of the optical guide plate having the wedge shape, however, impact applied thereupon by falling could cause a crack at the base of the projection because the thickness at the part of the optical guide plate is small. This is a reason for turning down the idea of providing a projection at the upper part (the first reason).
The amount of light propagated through the optical guide plate increases toward the lower edge (closer to the light source lamp) and decreases toward the upper edge (farther from the light source lamp). This is because the light scatters from the display surface as it propagates. Therefore, if a projection is provided at a lower portion of the side edge of the optical guide plate, the amount of light is greater at the portion with the projection and greater difference results between the dark and light areas in the closer proximity with the projection. As a result, the luminescent spot becomes clearly visible. This is a reason for turning down the idea of providing the projection at the lower part (the second reason).
In view of the first reason, the projection is preferably provided at a position closer to the lower edge (thicker side). Meanwhile, in view of the second reason, the projection is preferably provided at a position closer to the upper edge (farther from the light source lamp). As a result, the fixed structure having the projection at the center of the side edge as shown in
FIGS. 1A and 1B
has been employed as a compromise between the first and second reasons. In this structure, the luminescent spots appear in the middle stages on both sides of the display surface, but they were not such a significant problem when there was not much need for reducing the width of the
Dudek James
Hayes & Soloway PC
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