JP2640252B2 - Ferroelectric liquid crystal display - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device using a ferroelectric liquid crystal, and more particularly to a ferroelectric liquid crystal display device in which color unevenness is suppressed.

[Prior art] Clark and Lager Wool, Applied Physics Letter
s Volume 36, Issue 11 (issued June 1, 1980), P.899-901,
U.S. Pat. Nos. 4,367,924 and 4,630,595 describe surface stabilized ferroelectric liquid crystals (Surfaca-stabilized farroelc).
Bistable ferroelectric liquid crystal by tric liquid crystal) was revealed. This bistable ferroelectric liquid crystal arranges liquid crystal molecules between a pair of substrates set at a distance small enough to control the formation of a helical arrangement of liquid crystal molecules in a chiral smectic phase in a bulk state, and This was realized by arranging a vertical molecular layer composed of a plurality of liquid crystal molecules in one direction. Such a chiral smectic liquid crystal is expected to be applied as a display screen.

[Problems to be Solved by the Invention] By the way, in such a ferroelectric liquid crystal display device, when a display screen is rubbed horizontally or vertically, a display user may be obstructed by a viewing angle characteristic caused by an alignment state. When the head is swung right and left, there is a problem that the white state changes color remarkably from yellowish white to bluish white, and the color is felt as shading when the head is swung.

On the other hand, if the rubbing direction is applied diagonally to the display screen, the color unevenness when the head is swung is suppressed, but when the yellowish white in the white state comes to the display user side, the vertical contrast is reduced. There is a problem that the display becomes low in contrast depending on the viewing angle position derived from the sitting height of the display user or the like because the area near the front is maximized and rapidly reduced.

Also, when yellowish white comes to the display user side in the white state, the contrast in the left-right direction is ±± in the vicinity of the front.
At a viewing angle of about 30 °, it is almost uniform and easy to see, but when the viewing angle at the left and right is about 45 ° or more, the so-called negative-positive (NEG / POG) inversion where the black state and the white state are interchanged is observed. This caused a problem that the quality was significantly reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to prevent the above-mentioned problems, in particular, color unevenness when the head is swung, to prevent a decrease in contrast due to a vertical viewing angle position of a display user, and to simultaneously perform a negative / positive reversal in the horizontal direction. The present invention is to provide a strongly fusible liquid crystal display device in which the display position is set at a viewing angle sufficiently distant from the front to improve the display quality of the entire display.

[Means for Solving the Problems] That is, the present invention provides a ferroelectric liquid crystal cell in which a ferroelectric liquid crystal is sandwiched between a pair of polarizing plates and a pair of substrates having an electrode and an alignment film. In the liquid crystal display device, parallel rubbing is performed on the alignment film of each of the substrates obliquely from the lower right to the lower left or from the upper left to the lower right, and a first rubbing is performed in a region (I) within 45 ° clockwise from the rubbing direction. The transmission axis of the polarizing plate is arranged, and the transmission axis of the second polarizing plate is arranged in a region (II) within 45 ° clockwise from the direction perpendicular to the rubbing direction. A feature is provided in which a mechanism for adjusting an installation angle that stands from a horizontal plane is provided.

In a particularly preferred embodiment, the more the rubbing direction, similarly to the 45 ° - [theta] _a within region clockwise (I) from a position rotated by a tilt angle theta _a apparent clockwise, likewise the rubbing direction of the present invention the same to an area within 45 ° - [theta] _a clockwise region and (II) from the position rotated by a tilt angle theta _a apparent clockwise from the vertical direction, and, first of the ferroelectric liquid crystal cell The smaller angle θ _AP between the transmission axis of the polarizing plate and the transmission axis of the second polarizing plate
45 ° <θ _AP <90 °, more preferably 75 ° <θ _AP <90 °.

[Action] FIG. 2 shows the relationship between the area (I), the area (II) and the rubbing direction. In the figure, R represents the rubbing direction, R _N is a direction orthogonal to the rubbing, (I) the region (I), a (II) the region (II).

According to the present invention, since the rubbing is performed diagonally from the lower right to the upper left and from the upper left to the lower right, the white state is within a viewing angle of about 30 ° from the front of the panel, and the white state changes from yellowish white to blueish white. The region that rapidly changes to the right shifts in the oblique direction, thereby suppressing color unevenness when the head is swung.

In addition, 0-clockwise with respect to the diagonal rubbing direction.
The transmission axis of the first polarizing plate is set in a region (I) of 45 °, and the second polarization is set in a region (II) of 0 to 45 ° clockwise with respect to a direction orthogonal to the direction of the oblique rubbing. Because the transmission axis of the plate is set, the white state can always be controlled so that the yellowish white comes to the display user side, and the viewing angle within ± 30 ° around the front and left and right, which is important for the display user. The contrast can be set to a uniform and high value.

Further, by setting the direction of the rubbing and the direction of the transmission axis of the polarizing plate as described above, there is a problem that the contrast with respect to the vertical viewing angle sharply decreases with the maximum near the front, and the horizontal plane of the ferroelectric cell is reduced. Since the installation angle can be adjusted, the display user can adjust the installation angle to a position where the contrast in the vertical direction does not change much.

By setting the rubbing direction and the direction of the transmission axis of the polarizing plate as described above, the black state and the white state are switched at about 45 ° or more from the front with respect to the viewing angle in the left-right direction, so-called negative. Although the problem that a positive inversion region appears appears, as shown in the preferred embodiment described above, the crossing angle θ _AP between the transmission axes of the two polarizing plates is made smaller than 90 °, that is, the two polarizing plates are connected to a non-crossed Nicols. By setting the state, the negative / positive reversal area can be moved to the front or to a position 50 ° or more which is sufficiently separated.

[Effects of the Invention] As described above, according to the present invention, it is possible to realize a ferroelectric liquid crystal display device which prevents color unevenness when swinging and has excellent contrast and viewing angle characteristics.

Example An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows an appearance of a ferroelectric liquid crystal display device according to one embodiment of the present invention, and FIG. 3 shows a sectional structure of the liquid crystal panel of FIG. Referring to FIG. 1, reference numeral 1 denotes a liquid crystal panel,
Denotes an operating device, for example, a keyboard, and 3 denotes a ferroelectric liquid crystal cell.
This is an installation angle adjustment mechanism for adjusting the installation angle with respect to the horizontal direction of FIG. 10 (FIG. 3). On the back side of the liquid crystal panel 1, a backlight (not shown) for illuminating the liquid crystal panel 1 from behind is provided. R is the oblique rubbing direction, P is the transmission axis of the first polarizer (17a in FIG. 3), A is the transmission axis of the second polarizer (17b in FIG. 3), H is the horizontal direction, θ _DP is the installation angle of the liquid crystal cell 10.

Referring to FIG. 3, 11a and 11b are substrates, and 12a and 12b are substrates 11.
a, transparent electrodes formed on 11b, 13a, 13b are substrates 11a, 11b
And an insulating film formed on the transparent electrodes 12a and 12b, 14a and 14b
Is an alignment film formed on the insulating films 13a and 13b, 15 is a ferroelectric liquid crystal (FLC), 16 is a bead spacer, 17a is a polarizer (backlight-side polarizing plate), and 17b is an analyzer (display-side Polarizing plate). This liquid crystal panel 1 has electrodes as shown in the figure.
A ferroelectric liquid crystal cell 10 in which a ferroelectric liquid crystal 15 is sandwiched between a pair of substrates 11a and 11b having 12a, 12b and alignment films 14a, 14b, respectively, is disposed between a pair of polarizing plates 17a, 17b. It consists of. R is the alignment film on the substrates 11a and 11b
The direction of the rubbing applied in parallel to 14a and 14b is shown. By rubbing the alignment films 14a and 14b in parallel in this manner, the ferroelectric liquid crystal 15 is aligned in the rubbing direction, and a chevron splay structure as shown in FIG. 14 is formed.

In this embodiment, parallel rubbing is applied to the alignment films 14a and 14b of the liquid crystal panel 1 in FIG. 1 with respect to the vertical direction of the panel frame 6 as shown in FIGS. 1, 2 and 5. It was applied diagonally from the lower right to the upper left in a 45 ゜ direction. At this time, the liquid crystal used was a liquid crystal mixture of pyrimidine, tilt angle theta _a apparent was 7 °. The apparent tilt angle θ _a is the average molecular axis direction θ _PO when the positive polarity pulse is applied to the liquid crystal and then released, and the average molecular axis direction θ _NO when the negative polarity pulse is applied and then released. (Θ _PO −θ _NO ) / 2, which usually coincides with the rubbing direction.

In this embodiment, as shown in FIG.
The transmission axis direction P of 17a is set at a position of 7 ° clockwise with respect to the rubbing direction R, and the transmission axis direction A of the analyzer 17b is
It was set at 12 ° clockwise from the direction perpendicular to the rubbing direction.

According to this embodiment, at a viewing angle of about 30 ° from the front of the panel due to diagonal rubbing, a region where the white state rapidly changes from yellowish white to blueish white shifts obliquely, so Color unevenness at the time was suppressed. As shown in FIG. 6, the colors shown in parentheses in FIG. 5 indicate that the panel 1 can be viewed from various directions within a conical area having an angle of about 30 ° or less with respect to a normal z at the center of the panel. This is a conceptual illustration of the color of the white state in each direction at this time.

In this embodiment, as described above, for the oblique rubbing from the lower right to the lower left, by setting the transmission axis of the polarizing plate substantially clockwise, the sign of the spontaneous polarization Ps and the chevron spray structure are reduced. Ferroelectric liquid crystal (FL
C) Regardless of the twist direction at the upper and lower interfaces of molecules,
The white state can be controlled so that yellowish white comes to the display user side.

By such control, first, the contrast within a viewing angle of about ± 30 ° near the front, which is important for the display user, is controlled to a uniform and high contrast value.

On the other hand, the above-described viewing angle control causes a problem that the contrast with respect to the viewing angle in the vertical direction decreases sharply with the vicinity of the front being maximized, but the ferroelectric liquid crystal cell 10 shown in FIG.
By using the mechanism 3 that can adjust the installation angle that stands from the horizontal plane, the display user can adjust the installation angle to a position where the contrast in the vertical direction does not change much.

Although further problem that negative-positive inversion region in place put the black state and the white state at the front right and left directions of the viewing angle of more than about 45 degrees depending on the viewing angle control described above appears occurs, where the theta _AP previously described Because the two states become non-crossed Nicols in the direction in which both become brighter at 85 °, the negative / positive reversal area was about 50 ° in the crossed Nicols state, but to a position sufficiently away from the front at about 70 ° And could be improved.

[Modifications] The present invention is not limited to the above-described embodiments, and can be appropriately modified and implemented. For example, in the above description, the polarizer 17a is described as the first polarizing plate and the analyzer 17b is described as the second polarizing plate with respect to the direction of the transmission axis of the polarizing plate with respect to the rubbing direction. Alternatively, the polarizer 17a may be a second polarizing plate. Further, in the above-described embodiment, the liquid crystal panel 1 may be used by rotating it by 180 °.

[Brief description of the drawings]

FIG. 1 is an external view of a ferroelectric liquid crystal display device according to one embodiment of the present invention, and FIG. 2 is an explanatory diagram showing a relationship between a rubbing direction and regions (I) and (II) in the present invention. FIG. 3 is an explanatory view of a cross-sectional structure of the liquid crystal panel in FIG. 1, FIG. 4 is an explanatory view of a crystal structure in the liquid crystal cell of FIG. 3, and FIG. FIG. 6 is an explanatory diagram showing a relationship between the region (I) and the region (II), and FIG. 6 is an explanatory diagram showing a state of observing the color of the liquid crystal panel. 1: Liquid crystal panel 3: Cell installation angle adjustment mechanism 10: Ferroelectric liquid crystal cell 11a, 11b: Substrate 12a, 12b: Transparent electrode 14a, 14b: Alignment film 15: Ferroelectric liquid crystal 17a: Polarizer (first polarized light) 17b: Analyzer (second polarizing plate) R: Rubbing direction P: Transmission angle of first polarizing plate A: Transmission angle of second polarizing plate θ _DP : Cell installation angle (I): Area (I) ) (II): Area (II)

Claims (3)

(57) [Claims] 1. A ferroelectric liquid crystal cell in which a ferroelectric liquid crystal is sandwiched between a pair of substrates having electrodes and an alignment film,
Rubbing that is parallel to each other is performed on each of the alignment films obliquely in the same direction from the lower right to the upper left or from the upper left to the lower right, and is arranged to face each alignment film with the ferroelectric liquid crystal cell interposed therebetween. A first deflection plate having a transmission axis set in a region (I) within 45 ° clockwise from the rubbing direction and a region (II) within 45 ° clockwise from a direction perpendicular to the rubbing direction. A ferroelectric liquid crystal display device comprising: a second polarizing plate having a transmission axis set; and a mechanism for adjusting an installation angle at which the ferroelectric liquid crystal cell stands from a horizontal plane. Wherein said region (I) is a region also within 45 ° - [theta] _a clockwise from the tilt angle theta _a just rotated position apparent from the clockwise the rubbing direction, the region (II) There is an area also in the 45 ° - [theta] _a clockwise from the position rotated by a tilt angle theta _a apparent clockwise from the direction perpendicular to the rubbing direction and the transmission axis of the first polarizer When ferroelectric liquid crystal display device according to claim 1, wherein the second angle theta _AP of smaller angle of the transmission axis of the polarizing plate is 45 ° <θ _AP <90 °. 3. The small angle θ _AP between the transmission axis of the first polarizing plate and the transmission axis of the second polarizing plate is 75 ° <θ _AP <90 °. Item 3. A ferroelectric liquid crystal display device according to item 2.