JPS5921380Y2 - liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal display device, particularly a twisted alignment type liquid crystal display device in which liquid crystal molecules form a spiral structure between electrode plates.

In a liquid crystal display device, in order to orient the liquid crystal molecules between the electrode plates so that they form a spiral structure, the electrode surface of the electrode plate can be rubbed in a certain direction with a cotton cloth, or the cotton cloth can be coated with polyfluorocarbon or polyfluoroethylene. This can be done by applying and rubbing an alignment agent, by vapor depositing an alignment agent and rubbing it with a cotton cloth, or by diagonally vapor depositing an insulator.

Two electrode plates that have been oriented in this way are placed opposite each other so that their alignment directions intersect at 90°, and when they are sealed and a liquid crystal with positive induction anisotropy is injected into the gap, the liquid crystal molecules forms a helical molecular arrangement between the electrode plates.

At this time, there are two types of twist directions of the liquid crystal molecules.

In other words, as shown in the first diagram, the upper electrode surface is oriented from the bottom vertical direction upward in the Y-axis direction, and the lower electrode surface is oriented from the bottom lateral direction to the right in the X-axis direction. (At this time, the orientation treatment is said to be in the right-handed twist direction.

), the twisting of liquid crystal molecules is such that the molecules in contact with the upper and lower electrode surfaces become molecules 1, 2 or 3, 4, which are oriented with their long axes aligned in the direction of rubbing the electrode surfaces, and the molecules in between are molecules 1, 2, and 3, which are oriented in the direction in which the electrode surfaces are rubbed. When subjected to a force of 2 or 3 or 4 degrees, the entire structure becomes twisted 90 degrees in a spiral shape.

At this time, the direction of twist of the liquid crystal molecules is a left-handed twist orientation A, which is sequentially twisted counterclockwise from molecule 1 at the top to molecule 2 at the bottom, as shown in the second figure, and a left-handed twist orientation A, as shown in the third figure. There exists a right-twist orientation B that is sequentially twisted clockwise from 3 to molecule 4 at the bottom.

As shown in FIG. 4, in one liquid crystal display device 5, there is a region 6 with left-handed twist orientation A, and a region 6 with right-handed twist orientation B.
A region 7 consisting of

These two regions 6 and 7 are both stable when no electric field is applied, and when an electric field is applied, display contrast, rise time, fall time during driving, and response limit frequency are determined between regions 6 and 7. Moreover, due to changes in state due to alternating current electric fields and mechanical forces, irregular display unevenness occurs and the display is difficult to see.

In the present invention, the orientation processing direction of two opposing electrode plates is 90'.
By making the liquid crystal molecules slightly larger, the liquid crystal molecules in the entire display device are brought into a stable state aligned with one of the crack orientations, thereby providing an easy-to-read display device with uniform contrast and response characteristics. be.

First, the configuration of the liquid crystal cell will be explained.

In FIG. 5, reference numeral 8 denotes a polarizing plate on the light source side, under which an electrode plate 9 on the light source side and an electrode plate 10 opposing it are positioned with a predetermined gap provided by a spacer 11. It is filled with nematic liquid crystal 12 having positive dielectric anisotropy.

A polarizing plate 13 is located below it.

Electrodes are formed on opposing surfaces of the electrode plates 9 and 10, and are subjected to a predetermined orientation treatment.

By the way, in order to align the orientation of the liquid crystal 12 to either the left-twisted orientation or the right-twisted orientation, the orientation processing directions of the electrode plates 9 and 10 may be made to intersect at 90'±a ('a )Q).

This is because when the orientation processing directions of the two opposing electrode plates 9 and 10 are made to intersect at 90'±a, the long axis direction of the liquid crystal molecules in contact with the electrode plates 9 and 10 is in the orientation processing direction. This is because the liquid crystal molecules in the intermediate layer are twisted spirally in the direction of easy twisting, that is, in the direction of the 90°-a angle.

For example, as shown in Figure 6, the upper electrode plate 9 is oriented from bottom to top in the direction of arrow 14, and the lower electrode plate 10 is oriented clockwise with respect to the arrow at an opening angle of 90°+a from left to right in direction of arrow 15. When the orientation treatment is performed in the direction (at this time, the twist indicated by the orientation treatment direction is a right-handed twist direction).

), the liquid crystal molecules are oriented uniformly in a left-handed twisted orientation throughout the cell as shown in Figure 7.

Furthermore, even if the twists indicated by the orientation treatment directions are the same right-handed twist direction, as shown in FIG.
When the angle formed by 7) is set to 90°-a, the orientation of the liquid crystal molecules becomes a right-handed orientation uniformly throughout the cell as shown in FIG. 9.

In this way, the orientation treatment direction of the two opposing electrode plates is 90°.
When the liquid crystal molecules are opposed to each other so as to intersect with the angle ±a, the liquid crystal molecules are uniformly aligned in either the left-handed or right-handed twisted orientation.

Therefore, the striped pattern shown in Figure 4, which was a problem when the two electrode plates were crossed at 90° in the alignment direction, completely disappeared, and good results were obtained in both cases during DC drive. It was done.

On the other hand, in the case of AC drive, the rise time, fall time, response limit frequency etc. was different.

The former orientation process was superior in terms of rise time, fall time, response limit frequency, etc., and was stable with no fluctuation in the optimal viewing angle.

In addition, in the case of the latter orientation treatment, a phenomenon occurs in which the right-twisted orientation temporarily transitions to the left-twisted orientation during and for a while after driving due to mechanical force or in a high electric field, and for this reason, it can be seen in a state with good contrast. It was unstable during AC drive, with the obtained angle gradually shifting.

Note that a is preferably implemented within a range of about 20° or less.

Next, in this way, the orientation treatment direction of the two electrode plates is 90'.
If two polarizing plates with parallel or perpendicular light absorption axes are placed between them to sandwich the liquid crystal cell as shown above, the thickness of the liquid crystal cell will not be strictly uniform. In some cases, interference colors become visible, which is unsightly.

Therefore, the directions of the light absorption axes of the two polarizing plates 8 and 13 shown in FIG.

That is, the opening angle of the two polarizing plates 8 and 13 in the light absorption axis direction also deviates slightly from 90°, similar to the opening angle of the two electrode plates 9 and 10 in the orientation process direction.

By doing so, it is possible to eliminate the appearance of interference colors.

According to the invention, by making the direction of orientation of the two electrode plates slightly larger than 90°, the twist direction of the liquid crystal molecules in the entire display cell can be made constant and striped patterns can be eliminated, resulting in improved contrast and It is possible to provide an easy-to-read display device with uniform response characteristics, which is even more excellent in terms of rise time, fall time, response limit frequency during liquid crystal drive, and stability during AC drive.

Furthermore, interference colors can be eliminated by making the direction of the light absorption axis of the polarizing plates arranged to sandwich the liquid crystal display cell correspond to the alignment direction of the electrode plates.

[Brief Description of the Drawings] Fig. 1 is a perspective view illustrating the direction of conventional alignment treatment of opposing electrode plates, and Figs. 2 and 3 are models of two types of twisted alignment states of liquid crystal molecules caused by the above alignment treatment. 4 is a plan view of a liquid crystal display device in which different twisted alignment regions exist, FIG. 5 is a cross-sectional view of the liquid crystal display device, FIG. FIG. 8 is a diagram showing another orientation treatment direction of the present invention, and FIG. 9 is a model diagram of the twisted orientation state of liquid crystal molecules produced by the above treatment. 8... Polarizing plate on the light source side, 9... Electrode plate on the light source side, 10... Electrode plate, 12...
Liquid crystal, 13...Polarizing plate, 14, 15° 16.1
7... Orientation processing direction.

Claims (1)

[Scope of utility model registration request] In a twisted alignment type liquid crystal display device, by making the alignment treatment direction applied to two opposing electrode plates slightly larger than 90', the twist direction of the liquid crystal molecules interposed in the gap between the electrode plates can be adjusted. is set to a twist angle slightly smaller than 90° in the direction opposite to the twist direction indicated by the orientation processing direction, and is driven by applying an AC voltage between the electrode substrates, and the two electrode plates facing each other are driven. A liquid crystal display device characterized in that the light absorption axis direction of the opposing polarizing plate is parallel or perpendicular to the alignment direction of the electrode plate.