JP2640251B2 - 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 a surface-stabilized ferroelectric liquid crystal.
Bistable ferroelectric liquid crystal by ctric liquid crystal) was revealed. This bistable ferroelectric liquid crystal has a structure in which liquid crystal molecules are arranged between a pair of substrates set at a distance small enough to control the formation of a helical arrangement structure of liquid crystal molecules in a chiral smectic phase in a bulk state. This was realized by arranging the vertical molecular layers organized by the 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, color shading during swinging is suppressed,
When yellowish white comes to the display user side in the white state, the contrast in the vertical direction decreases sharply with the maximum near the front, and depending on the viewing angle position derived from the display user's sitting height, etc. There was a problem that the display became low.

Also, when a yellowish white in the white state comes to the display user side, the contrast in the left-right direction is ± near 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 ferroelectric liquid crystal display device in which the display position is set at a viewing angle position 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 upper right to lower left or lower left to upper right, and the first polarized light is applied to a region (I) within 45 ° counterclockwise from the rubbing direction. The transmission axis of the second polarizing plate is disposed in a region (II) within 45 ° counterclockwise from the direction perpendicular to the rubbing direction, and the ferroelectric liquid crystal cell is It is characterized by a mechanism for adjusting the installation angle that stands from the horizontal plane.

In a particularly preferred embodiment of the present invention, from the rubbing direction, the tilt angle theta _a just rotated 45 ° -θ region within _a same counterclockwise from the position of the apparent counterclockwise and region (I), similar to the rubbing direction 45 ° -θ region within _a from the rotational position by the tilt angle theta _a similarly counterclockwise apparent from the counterclockwise direction perpendicular to the area (II) in, and the ferroelectric The smaller angle θ _AP between the transmission axis of the first polarizing plate and the transmission axis of the second polarizing plate of the liquid crystal cell is 45 ° <θ _AP <90 °, and more preferably 75 ° <θ _AP <90 °. It is characterized by being.

[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 upper right to the lower left or from the lower left to the upper right, within a viewing angle of about 30 ° from the front of the panel, the white state changes from yellowish white to blueish white. The rapidly changing area shifts in the oblique direction, thereby suppressing color unevenness when the head is swung.

In addition, counterclockwise with respect to this diagonal rubbing direction, 0
The transmission axis of the first polarizing plate is set in a region (I) of ~ 45 °,
In addition, since the transmission axis of the second polarizing plate is set in an area (II) of 0 to 45 ° counterclockwise with respect to the direction orthogonal to the direction of the oblique rubbing, the white state is always yellowish. Can be controlled so that the white color comes to the display user side.
The contrast within a viewing angle of about 30 ° can be set to a uniform and high value.

Furthermore, by setting the direction of the rubbing and the direction of the transmission axis of the polarizing plate as described above, the contrast with respect to the viewing angle in the up-down direction suddenly decreases from the vicinity of the front as the maximum, but the ferroelectric cell has a problem. Since the setting angle set from the horizontal plane can be adjusted, the display user can adjust the setting angle to a position where the contrast in the vertical direction does not change much.

In addition, by setting the direction of the rubbing 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 in the horizontal viewing angle, that is, a so-called negative / positive state. Although the problem that an inversion region appears appears, as shown in the preferred embodiment described above, the crossing angle θ _AP of the transmission axes of the two polarizing plates is smaller than 90 °, that is, the two polarizing plates are brought into a non-cross Nicol state. By setting, the negative / positive reversal area can be moved to a position of 50 ° or more sufficiently separated from the front.

[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 rubbing direction obliquely, P is the transmission axis of the first polarizing plate (17a in FIG. 3), A is the transmission axis of the second polarizing plate (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.
Transparent electrodes 13a and 13b formed on a and 11b are insulating films formed on the substrates 11a and 11b and the transparent electrodes 12a and 12b, 14a and 14b are alignment films 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), 17b is an analyzer (display side polarizing plate)
It is. This liquid crystal panel 1 has electrodes 12a,
A pair of substrates 11 each having 12b and alignment films 14a, 14b
The ferroelectric liquid crystal cell 10 in which the ferroelectric liquid crystal 15 is sandwiched between a and 11b is arranged on a pair of polarizing plates 17a and 17b. R is the alignment film 14 on the substrates 11a and 11b.
The rubbing directions applied parallel to a and 14b are shown. By rubbing the alignment films 14a and 14b in parallel in this manner, the ferroelectric liquid crystal molecules 15 are aligned in the rubbing direction, and a chevron splay structure as shown in FIG. 4 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 top right to bottom 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 the analyzer 17b is set at a position 7 ° counterclockwise with respect to the rubbing direction R, and the transmission axis direction A of the analyzer 17b is set.
Was set at 12 ° counterclockwise from the direction perpendicular to the rubbing direction.

According to this embodiment, the inclination at which the white state suddenly changes from yellowish white to blueish white shifts in the oblique direction at a viewing angle of about 30 ° from the front of the panel due to oblique rubbing. Color unevenness at the time was suppressed. The colors shown in parentheses in FIG. 5 indicate that, as shown in FIG. 6, each side of the panel 1 can be viewed from within a conical area whose angle with respect to the normal z at the center of the panel is about 30 ° or less. 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 upper right to the lower left, by setting the transmission axis of the polarizing plate substantially counterclockwise, the positive / negative 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-mentioned viewing angle control caused a problem that the contrast with respect to the vertical viewing angle suddenly decreased with the local maximum near the front, but the installation angle of the ferroelectric liquid crystal cell 10 shown in FIG. By using the mechanism 3 that can be used, the display user can adjust the installation angle to a position where the contrast in the vertical direction does not change much.

Further comprising either 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, but a problem arises called negative-positive inversion region appears, theta _AP previously described Here, the negative / positive reversal area was about 50 ° in the crossed Nicols state by making the non-crossed Nicols in which the two states became brighter as 85 °. It was able to improve to a position far enough from the.

[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 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 a rubbing direction, a region (I) and a region (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 view showing the relationship between the rubbing direction and the area (I) and the area (II) in the display device of FIG. 1, and FIG. 6 is an explanatory view showing the appearance of 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 parallel to each other on each of the alignment films in the same direction from the upper right to the lower left or from the lower left to the lower right, and placed opposite to each alignment film with the ferroelectric liquid crystal cell interposed therebetween, The first polarizing plate having a transmission axis set in a region (I) within 45 ° counterclockwise from the rubbing direction and a region (II) within 45 ° counterclockwise 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 tilt angle theta _a just rotated area within well 45 DEG - [theta] _a in the counterclockwise direction from the position of the apparent from the rubbing direction counterclockwise, the region ( II) is the a rubbing direction of the apparent from the perpendicular direction to the counterclockwise tilt angle theta _a just rotated again within 45 ° - [theta] _a counterclockwise from the location area, and said first polarization 2. The ferroelectric liquid crystal display device according to claim 1, wherein the smaller angle θ _AP between the transmission axis of the plate and the transmission axis of the second 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.