Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-06-29
2004-06-15
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C359S859000, C359S869000, C362S347000
Reexamination Certificate
active
06750930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflector that can be suitably used for a reflection type liquid crystal display device that uses ambient light as a light source. More particularly, the present invention relates to a reflector providing desirable reflectance over a wide angle and a particularly high reflectance in an intended range of directions in which light is reflected, and a reflection type liquid crystal display device providing a wide viewing angle and suitable directionality so that a display surface appears bright within a typical range of viewing angle for a display device incorporated in certain devices such as a notebook personal computer.
2. Description of the Related Art
In recent years, a reflection type liquid crystal display device using ambient light as a light source is widely used as a display part of a handy personal computer and the like particularly because of its low power consumption. A reflection type liquid crystal display device has a reflector which reflects incident light coming through the display surface side back to the display surface side so that the user can view a display that is produced according to the arrangement of liquid crystal molecules in a liquid crystal layer.
When a reflector having a flat surface is used for a reflection type liquid crystal display device, the reflector has high reflectance in a particular reflection angle corresponding to an incident angle. However, the range of reflection angle showing high reflectance is narrow, i.e., the viewing angle is narrow. To solve such a problem, there are several attempts so as to obtain good reflectance in wider range of direction, for example, by forming many concave portions or grooves each being a part of a sphere on a reflector surface, or by providing depressions and projections randomly.
FIG. 15
shows a reflector provided with many concave portions being a part of a sphere on a reflector surface. A reflector
71
shown in this figure is formed as follows. On a substrate
72
made of a glass or the like, a flat-plate resin base material
73
(a base material for a reflector) made of a photosensitive resin layer or the like is provided. On a surface of the base material
72
, many concave portions
74
whose inner surfaces being a part of a sphere are formed continuously so as to overlap each other. A reflection film
75
made of a thin film of aluminum, silver or the like is deposited or printed on the concave portions
74
.
The concave portions
74
are formed with random depth in a range of 0.1 &mgr;m to 3 &mgr;m and are arranged randomly with the pitch between adjacent concave portions ranging from 5 &mgr;m to 50 &mgr;m. An inner surface of each of the concave portions
74
is a curved surface which is a part of a single sphere.
The term “depth of a concave portion” as used herein means the distance from the reflector surface to the bottom of the concave portion, and the term “pitch of concave portions” as used herein means the distance between the center of a concave portion (which has a circular shape as viewed in a plan view) and the center of an adjacent concave portion.
The reflector
71
has a reflection property shown as &bgr; in a comparative example of
FIG. 7
or FIG.
12
. Each of FIG.
7
and
FIG. 12
is a graph showing a reflection property when the incident angle is 30°, wherein the vertical axis is reflectance (reflection intensity), and the horizontal axis is the reflection angle. The term “incident angle” as used herein means an angle &ohgr;
0
between incident light J and a normal line H extending to the surface of the reflector
71
as shown in FIG.
16
. Likewise, the term “reflection angle” as used herein means an angle &ohgr; between the normal line H and reflection light K on a plane including the incident light J and the normal line H. As &bgr; shown in the comparative example of
FIG. 7
or
FIG. 12
, the reflector
71
shows relatively good reflectance, which is in a range of 15°≦&ohgr;≦45° centered about the reflection angle 30°.
The conventional reflector
71
described above enables one to obtain relatively good reflectance over a relatively wide angle due to the concave portions. However, as &bgr; shown in the comparative example of
FIG. 7
or
FIG. 12
, the relatively higher reflection intensity peaks at the reflection angles 15° and 45°, which appear symmetrical with the reflection angle 30° being an axis of symmetry.
Nevertheless, a display device incorporated in devices such as notebook personal computers, in which a display surface is inclined during its use, is generally viewed from near the direction normal to the display surface as shown in
FIG. 17
even though it may vary depending on a degree of inclination of the display surface or a position of the light source.
FIG. 17
shows a notebook personal computer having a main body
81
and a cover portion
82
, illustrating a situation in which the computer is used. In
FIG. 17
, P represents a direction normal to a conventional display device
83
, Q incident light, &ohgr;
0
an incident angle (e.g., 30°), R
1
reflection light whose reflection angle &ohgr; is the same as the incident angle &ohgr;
0
, R
2
reflection light whose reflection angle &ohgr; is smaller than the incident angle &ohgr;
0
, and R
3
reflection light whose reflection angle &ohgr; is greater than the incident angle &ohgr;
0
.
As seen in
FIG. 17
, directions in which a user usually looks at the display device
83
are concentrated in a range of the direction of the reflection light R
2
near the normal line P as opposed to a range of the reflection light R
3
in which the user has to look up at the display device
83
from a lower direction making it more difficult to see it. Therefore, for convenience of the users, it is desirable to secure a wide viewing angle while enhancing reflectance in the direction in which the reflection angle is smaller than reflection light.
To the contrary, a display device on a horizontal surface such as a table-type game machine is generally looked at from a direction near parallel to the surface as shown in FIG.
18
.
FIG. 18
shows a display device
85
provided horizontally on a table
84
, illustrating a situation in which the device is used. In
FIG. 18
, W represents a direction normal to the display device
85
, S incident light, &ohgr;
0
an incident angle (e.g., 30°), T
1
reflection light whose reflection angle &ohgr; is the same as the incident angle &ohgr;
0
, T
2
reflection light whose reflection angle &ohgr; is smaller than the incident angle &ohgr;
0
, and T
3
reflection light whose reflection angle &ohgr; is greater than the incident angle &ohgr;
0
.
As seen in
FIG. 18
, directions in which a user usually looks at the display device
85
are concentrated in a range of the direction of the reflection light T
3
whose reflection angle is greater than reflection light T
1
. Meanwhile, the reflection light T
2
is in the range of the direction where a user has to look into the display device, thus making it awkward to see it. Accordingly, for convenience of users, it is desirable to obtain a wide viewing angle and particularly high reflectance in a range of directions in which the reflection angle is greater than the incident angle.
SUMMARY OF THE INVENTION
The present invention has been achieved to solve above-described problems. It is therefore an object of present invention to provide a reflector having desirable reflectance over a wide angle, wherein the reflectance can be selectively enhanced in desirable directions such as the reflection angles smaller (including negative values) or greater than the incident angles; and a reflection type liquid crystal display device having a wide viewing angle by incorporating the reflector, and having suitable directionality corresponding to a normal viewing angle under a particular condition such as in cases where the display surface is used inclined, horizontally, or the like.
It is another object of the present invention to provide a reflector having light-di
Kano Mitsuru
Moriike Tatsuya
Omote Kenji
Yoshii Katsumasa
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Kim Robert H.
Nguyen Hoan
LandOfFree
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