Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1997-10-21
2001-11-06
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S123000, C349S124000, C349S125000
Reexamination Certificate
active
06313897
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rubbing treatment apparatus, a rubbing method and an alignment film forming method for rubbing a predetermined film-to-be-treated so as to form an alignment film of a device which uses a liquid crystal, such as a liquid crystal display device which is used as display means for OA (office automation) equipment such as a word processor and a personal computer. Further, the invention relates to a rubbing cloth and a rubbing roller of a rubbing treatment apparatus. Still further, the invention relates to a liquid crystal display device including an alignment film which is formed through a rubbing treatment which is performed by the rubbing treatment apparatus.
2. Description of the Related Art
In recent years, as OA equipment such as word processors and personal computers has become popular, an increasing attention is placed on a liquid crystal display device which is characterized In lightness and a low power consumption, for example.
A liquid crystal display device is formed by interposing a liquid crystal between a pair of substrate members, at least one of which transmits light. The pair of substrate members is obtained by forming a display electrode on a light transmitting substrate and thereafter forming an alignment film on the substrate which contains the electrode. In an STN (super-twisted nematic) liquid crystal display device, for instance, liquid crystal molecules which are present between the substrate members are aligned as they are twisted in the range of 180 degrees or larger, e.g., 210 to 260 degrees, between the substrate members. The alignment film has a function of aligning the liquid crystal molecules in one direction. To provide for this function, a surface of the alignment film is rubbed by a predetermined rubbing treatment apparatus.
In recent years, as not only as note type personal computers but as thin display means as well, liquid crystal display devices which provide a dot matrix display of the STN type have expanded a market, due to an improvement of display characteristics. A demand for an increase in the screen size and finer structures has been mounting, and therefore, it is important to improve an in-screen uniformity of a display quality, an in-screen uniformity of a display quality for a half tone display in particular, and a contrast ratio.
Since a display quality is related to alignment of liquid crystal molecules within liquid crystal layers of a liquid crystal display device, a rubbing method and a rubbing treatment apparatus for forming an alignment film, which determines alignment, are extremely important.
FIG. 13
is a plan view for explaining rubbing treatment, showing a substrate member
92
at a step of forming an alignment film. The substrate member
92
which will be eventually divided into four substrate members is prepared, a thin film which is formed at a surface of the substrate member
92
is rubbed.
The substrate member
92
includes a substrate
93
, external connection terminals
94
, and thin films
96
. On one surface of the substrate
93
which has a rectangular shape, four sets of the external connection terminals
94
are formed. Further, adjacent to the external connection terminals
94
, four rectangular regions
95
are defined. The four edges of each region
95
are parallel to the respective edges of the substrate
93
, and the regions
95
correspond to display areas of the liquid crystal display device. A display electrode is formed inside each region
95
. The thin films
96
of an alignment film material such as a polyimide resin are formed in the regions
95
which cover the display electrodes and an exposed surface of the substrate
93
.
At a step of rubbing treatment, using a rubbing treatment apparatus which will be described later, rubbing treatment is performed on the thin films
96
of the substrate member
92
which has such a structure, thereby obtaining an alignment film. The substrate member
92
as it is after the alignment film is formed is divided so that each divided portion contains each region
95
, whereby the substrate members of the liquid crystal display device are obtained.
The rubbing treatment apparatus for rubbing the thin films
96
of the substrate member
92
comprises a stage for mounting the substrate member
92
, and a rubbing roller
97
. A rubbing cloth is applied on a cylindrical curved surface of the rubbing roller
97
, and the rubbing roller
97
is in a contact with one sur face of the substrate member
92
on t he stage. At this step, rubbing treatment is performed in such a manner that the longitudinal direction of the rubbing roller
97
and a predetermined edge of the substrate member
92
intersect at a relatively large crossing angle.
More specifically, in rubbing, the rubbing roller
97
is rotated in a predetermined rotation direction along a circumferential direction with a central axis of the rubbing roller
97
as a rotation center axis so that the curved surface is rubbed against the substrate member
92
with a predetermined pressure, while moving the rubbing roller
97
and the stage relative to a predetermined direction f or movement
98
. At this step, a contacting edge
98
a where the curved surface of the rubbing roller
97
contacts with the substrate member
92
is expressed by a straight line whose both ends meet the two perpendicular edges of the substrate member
92
, or a straight line whose both ends meet the other two opposite edges of the substrate member
92
. The direction for movement
98
, which is perpendicular to the direction in which the contacting edge
98
a
extends, is a direction which is at a predetermined angle &thgr;7 with one edge of the substrate member
92
. The thin films
96
of the substrate member
92
is entirely rubbed, through the relative motion in the direction for movement
98
. A rubbing axis of the alignment film for the substrate members of the liquid crystal display device which is obtained in this method has the predetermined angle &thgr;7 with one edge of the alignment film.
In the rubbing treatment described above, the angle &thgr;7 is determined with an emphasis on a viewing angle characteristic of the liquid crystal display device. More particularly, with respect to a liquid crystal display device which is used as display means for OA equipment, since a user of the de vice generally sits in front of the liquid crystal display device, an excellent viewing angle characteristic is demanded in a
12
-
6
o'clock direction of the liquid crystal display device.
Thus, when rubbing treatment is performed wit h the angle &thgr;7 of 45 degrees, the length of the contacting edge
98
a
largely changes during a period from the beginning of the rubbing treatment until the end of the rubbing treatment. This largely changes a contacting surface area of the rubbing roller
97
for the contact with the thin films
96
per unit time, i.e., a substrate area of the substrate member
92
which is processed by rubbing per unit time. A frictional stress which is created by the contact of the substrate member
92
and the rubbing roller
97
is approximately in proportion to the substrate area, and therefore, the frictional stress largely changes during the period from the beginning of the rubbing treatment until the end of the rubbing treatment. More precisely, the frictional stress increases as the substrate area which is rubbed increases, since the beginning of the rubbing treatment until the rubbing roller
97
reaches a central portion of the substrate member
92
. Further, after the rubbing roller
97
reaches the central portion of the substrate member
92
until the end of the rubbing treatment, the frictional stress decreases as the substrate area which is rubbed decreases.
When the frictional stress largely changes during the rubbing treatment in this manner, a rotation speed of the rubbing roller
97
which rotates at a predetermined rotation speed changes. That is, the rotation speed of the rubbing roller
97
becomes slow as the
Fujii Keizo
Higuchi Masashi
Murayama Shinichi
Conlin David G.
Dike Bronstein Roberts & Cushman IP Group
Neuner George W.
Ngo Julie
Sharp Kabushiki Kaisha
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