Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-08-28
2002-08-06
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06429919
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflector which provides uniform brightness and whiteness over an extensive range, a manufacturing method for the same, and a reflection type liquid crystal display device that employs the reflector.
2. Description of the Related Art
In recent years, a reflection type liquid crystal display device has been extensively used as the display unit of a handy type computer or the like. The reflection type liquid crystal display device is equipped with a reflector for reflecting the light which has entered the display surface thereof to provide display. In the past, reflectors having mirror surfaces or reflectors having random pits and projections on the surfaces thereof have been used.
Among the aforesaid conventional reflectors, a conventional reflector
260
equipped with a surface with random pits and projections is illustrated in FIG.
16
. This reflector is produced by heating a polyester film
261
which is, for example, 300 to 500 &mgr;m thick, to form an uneven surface
261
a
having projections of a few &mgr;m high, then further forming a reflection film
262
composed of aluminum, silver, etc. on the uneven surface
261
a
by employing such a process as vapor deposition.
As illustrated in
FIG. 17
, in the conventional reflection type liquid crystal display device employing this type of reflector
260
, transparent electrode layers
253
and
254
are provided on the opposed surfaces of a pair of glass substrates
251
and
252
, respectively. Further, oriented films
255
and
256
of liquid crystal are respectively provided on the transparent electrode layers
253
and
254
and a liquid crystal layer
257
is disposed between the oriented films
255
and
256
. A first polarizing plate
258
and a second polarizing plate
259
are provided on the outer sides the glass substrates
251
and
252
, respectively, the reflector
260
being mounted on the outer side of the second polarizing plate
259
so that the surface thereof facing the reflection film
262
is oriented toward the second polarizing plate
259
.
In the reflection type liquid crystal display device
250
having the constitution described above, the light which has entered the first polarizing plate
258
is linearly polarized through the polarizing plate
258
, and the polarized light passes through the liquid crystal layer
257
to be elliptically polarized. The elliptically polarized light is then linearly polarized again through the second polarizing plate
259
, and the linearly polarized light is reflected by the reflector
260
and it passes through the second polarizing plate
259
and the liquid crystal layer
257
again before it exits from the first polarizing plate
258
.
The reflector and the reflection type liquid crystal display device have the following reflection characteristics.
For instance, as illustrated in
FIG. 16
, the incidence angle of an incident light J from a point light source disposed on the reflection film
262
is set to a constant incidence angle of 30 degrees with respect to the normal line relative to the surface of the reflection film
262
, and the reflectivity is measured when a reflection angle &thgr; of reflected light K is changed from zero degree to 60 degrees. The measurement results have revealed that the reflectivity reaches almost a lowest level at a reflection angle of 20 degrees or less and 40 degrees or more at right and left, the peak of the reflectivity being observed at a reflection angle of 30 degrees. This trend has been found to be applicable to the measurements of an entire liquid crystal display device equipped with the reflector as well as to the reflector used alone. It has been discovered that the reflectivity reaches a peak at the reflection angle of 30 degrees, and it drops to almost zero percent at reflection angles of 23 degrees or less and 37 degrees or more.
In general, a reflector having a mirror surface exhibits a reflection characteristic in which extremely higher reflectivity is observed at a particular reflection angle in relation to an incidence angle than that in a reflector having random pits and projections on a surface thereof; it is characterized, however, by an extremely limited range of reflection angles at which high reflectivity is obtained, that is, it provides a limited range of visual field angles.
As described above, the conventional reflector with a reflecting surface equipped with random pits and projections has poor reflection efficiency with consequent low reflectivity as a whole, thus failing to fully meet the needs for a reflector that enables efficient reflection of incident light over a wider range of reflection angle. Accordingly, the reflection type liquid crystal display device employing this type of reflector has been posing a problem in that the visual field angles are limited to a range of about 25 degrees to about 35 degrees and that the brightness of the display surface is not satisfactory. There has been another problem: a reflector is required to provide whiteness as well as brightness; however, this type of conventional reflector is unsatisfactory in the whiteness of the reflecting surface because the light having different wavelengths cannot be reflected evenly in good balance. Further, the reflection characteristics including reflection angle and the intensity of reflected light of this type of reflector are automatically decided by the pits and projections formed at random; hence, they have not been controlled by optical design.
To solve the aforesaid problems, a reflector provided with many stripe grooves extending linearly on a surface thereof has been proposed. This reflector, however, has a limited range of reflection angle although it provides desired brightness at the reflection angles in a certain range in the direction perpendicular to the stripe grooves and it exhibits low reflectivity and an extremely limited range of reflection angles in the directions other than the direction perpendicular to the stripe grooves. Hence, the application of this type of reflector to a liquid crystal display device has not solved the foregoing problem of the limited range of visual field angles and insufficient brightness and whiteness of the display surface especially in the direction parallel to the stripe grooves.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made with a view toward solving the problems described above, and it is an object thereof to provide: a reflector capable of providing high reflection efficiency over a wide range of angles; a method for manufacturing the reflector; and a reflection type liquid crystal display device employing the reflector for the display surface thereof to provide a wider range of visual field angles and a higher level of brightness in any directions.
To these ends, according to one aspect of the present invention, there is provided a reflector wherein: many pits are formed in succession on a surface thereof, the inner surface of each of the pits being formed as a partial sphere; the pits are formed to have depths ranging from 0.1 &mgr;m to 3 &mgr;m at random, adjacent pits being disposed at random at pitches ranging from 5 &mgr;m to 50 &mgr;m; and the tilt angles of the inner surfaces of the pits are set within a range of −18 degrees to +18 degrees.
In the reflector in accordance with the present invention, many pits having the inner surfaces shaped as partial spheres are formed on a surface thereof, and the parameters thereof such as the depths of the pits and the pitches between adjoining pits are set to the ranges given above. By so doing, the tilt angles of the inner surfaces of the pits, namely, the tilt angles in a minute unit area, which are considered to govern the reflection angles of reflected light show a fixed distribution pattern in a certain range of angles. Further, since the inner surfaces of the pits are shaped like partial spheres, such a fixed distribution pattern of tilt angles can be accomplished in any directions rather tha
Kano Mitsuru
Miura Akito
Moriike Tatsuya
Moue Koichi
Ohkita Masao
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Chung David
LandOfFree
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