Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-08-23
2004-03-16
Nguyen, Dung (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S155000
Reexamination Certificate
active
06707525
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device used as a display screen of a portable personal computer or the like.
2. Description of the Related Art
Conventionally, a color liquid crystal display (LCD) panel has been known as a display device of a portable personal computer or the like.
The color LCD panel is manufactured by, for example, sandwiching a liquid crystal between a TFT (thin film transistor) array substrate and a color filter array substrate. A color LCD module produced by attaching peripheral members such as a driver LSI and a light unit to the panel for modularization is integrated within a main body cover of the portable personal computer and thereby used as a display screen.
The portable personal computer in which the color LCD panel is mounted can be freely carried and used because of its portability. Thus, even when a vibration is imparted to the computer during carriage of the computer or the like, the panel is required to maintain its display quality. Accordingly, a vibration is imparted to the color LCD panel as a quality test to secure the reliability of LCD panel before shipment.
FIGS. 1A and 1B
show the configuration of a conventional color LCD panel and
FIG. 1A
is a sectional view thereof, and
FIG. 1B
is a sectional view thereof for explaining an abnormal alignment. As shown in
FIG. 1A
, the conventional color LCD panel
1
includes: a TFT array substrate
2
; a color filter array substrate
3
; and a liquid crystal layer
4
sandwiched between both the substrates
2
and
3
.
Alignment films
5
are respectively formed on surfaces of the TFT array substrate
2
and the color filter array substrate
3
, the surfaces being disposed opposite each other. The liquid crystal layer
4
surrounded by a sealant
106
that covers a sealing spacer
6
is formed between the TFT array substrate
2
and the color filter array substrate
3
. A gap formed between both substrates
2
and
3
(cell gap) and representing a thickness of the liquid crystal layer
4
is adjusted by a plurality of spacers
7
located therebetween.
The spacers
7
consist of particles having a spherical shape, a columnar shape or the like. Generally, a LCD panel employs spherical shaped particles having diameters characterized by a standard deviation of 3% to 5% of average particle size. Thus, a pressure applied to the spacers varies depending on different diameters of the respective spacers
7
while causing a variation in an amount of deformation of the respective spacers
7
.
In other words, after completion of assembly of cell, the spacers
7
are in a compressed state and the spacer
7
having a small diameter is rarely deformed, and the spacer
107
having a large diameter is deformed to a large extent (FIG.
1
B).
In this state, when a vibration is imparted to the color LCD panel
1
, the small spacer
7
moves within the panel (see arrows in FIG.
1
B). Even when the spacer
7
having an average diameter and deformed to a small extent moves, it moves causing small friction with the alignment films and therefore, never causes change of alignment in the alignment films.
However, particularly in the case where the spacer
107
having a large diameter moves within a large panel, imparting large pressure to the TFT array substrate
2
and the color filter array substrate
3
deforms the panel to thereby move the spacers. Thus, the friction between the moved spacers and the surfaces of both substrates
2
and
3
damages the alignment films
5
.
As a result, the alignment films
5
is again aligned along the direction in which the spacer moves, thereby producing a bright point as a lighting point on a display screen. The bright point occurs more easily in proportion to the size of a screen. It would appear that in proportion to the size of a screen, the deformation of the panel is enhanced to partially impart large force to the panel. Hereinafter, the bright point thus generated is called a vibration bright point.
FIG. 2
is an explanatory view showing a bright point produced by the abnormal alignment observed in the color LCD panel shown in FIG.
1
B. As shown in
FIG. 2
, a pixel is defined by drain wirings
108
and gate wirings
208
and driven by a TFT
9
. When the spacer
107
having a large particle size moves within such a pixel to cause an abnormal alignment that changes the alignment of the alignment films
5
, a region to be displayed normally becomes an abnormal region corresponding to a bright point.
Thus, when the abnormal region corresponding to the bright point is visually recognized on an image, a display contrast of the image is lowered (see JP 09-127515 A).
In order to prevent a vibration bright point from occurrence in a vibration test that is conducted before shipment of an LCD panel, it is necessary to make a particle size distribution of particles within a predetermined range of values so as not to include a spacer having a large particle size.
With respect to the particle size distribution of particles, in a period during which the size of a screen of portable personal computer or the like has been small as observed when a conventional portable personal computer was prevalently used, an LCD panel is also small in size and deformation of the LCD panel due to vibration itself is small, whereby a bright point rarely occurs. Even when a standard deviation of a particle size distribution of particles is of 3% to 5% of average particle size, vibration imparted to the LCD panel is suppressed small.
Recently, the portable personal computer having a large screen size (for example, 14.1-inch type in a notebook personal computer) has been prevalently used making the size of an LCD panel enlarged and therefore, a particle size distribution of particles observed in the conventional LCD panel becomes impermissible in terms of prevention of failure due to occurrence of bright point, thereby causing necessity of making a particle size distribution of particles not greater than 3% of average particle size.
In other words, since the LCD panel enlarged in size has a structure in which an interval between points to support the panel increases, the LCD panel is deformed to a larger extent when external force is imparted thereto, so that the LCD panel partially receives large force (not less than 10 times the external force in some cases).
Such a phenomenon largely affects a LCD panel when the panel is assembled by a front mounting method as one of assembly methods for an LCD panel. That is, when using the front mounting method, as compared with other mounting methods, an interval between points to support the panel is large and the panel itself is not secured to a case by screws, increasing the allowance between the case and the LCD panel. Accordingly, when force is locally imparted to the panel, the spacers within the LCD panel are forcibly moved, causing a bright point due to the realignment of alignment films.
Also, up to now, although a generally used resin spacer has been formed by a suspension polymerization method (the method is widely used in a polymer synthesis technique, in which a liquid organic solvent is dropped into a solvent such as water and after the organic solvent becomes a colloid state as milk, the resultant solvent is heated to obtain particles having the same size as that of the organic solvent during operation for dropping the organic solvent. The drawbacks of the method are that a variation in an amount of organic solvent becomes large during operation for dropping the organic solvent, so that the variation in sizes of the obtained particles becomes large), when a spacer is formed by the suspension polymerization method, a size distribution of particles becomes widely spread and therefore, an operation for classifying particles into some groups of particles based on a target particle size has been necessary. (The classifying operation is performed as follows: mix a powder into a solvent (such as water or an organic solvent,
NEC LCD Technologies Ltd.
Nguyen Dung
Young & Thompson
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