JPH07100789B2 - Liquid crystal display element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal display device, and more particularly to a field effect liquid crystal display device having excellent time division characteristics.

[Conventional technology]

In order to provide a liquid crystal display device having good image quality even when the number of time divisions is 100 or more, the present inventor previously proposed a new liquid crystal cell structure in which a specific twist angle and a polarization axis direction of a polarizing plate are combined (JP JP-A-60-50511, Japanese Patent Application No. 60-50454, Japanese Patent Application No. 60-70950), and liquid crystal materials suitable for this cell structure have been proposed by the present inventors (Japanese Patent Application No. 60-2828).
No. 04). However, as described below, this liquid crystal material has an excellent voltage rising characteristic (γ characteristic), but when the twist angle is increased, domains are generated, and there is a constraint that the twist angle cannot be increased (220 degrees or more). .

[Problems to be solved by the invention]

As described above, when the twist angle is large (220 ° to 270 °), the conventional material has a problem that domains are generated and the twist angle cannot be increased. An object of the present invention is to provide a high contrast liquid crystal display device by improving the liquid crystal material, thereby eliminating the constraint on the twist angle.

[Means for solving problems]

The problem above is that the twist angle of the twisted structure of liquid crystal molecules is 20
As a value within the range of 0 ° to 270 °, as a liquid crystal material, It is solved by using a substance containing 5 to 60% by weight of the substance represented by

[Action]

Even if the twist angle of the twist is expanded to increase the contrast ratio, the addition of the above substances does not generate domains, so that high quality display can be obtained even during high time division driving.

〔Example〕

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

Twist angle of 160 ° to 200 ° (JP-A-60-50511),
By setting the angle between 200 ° -260 ° (Japanese Patent Application No. 60-50454) and 140 ° -250 ° (Japanese Patent Application No. 60-70950), the contrast is several times that of the conventional 90 ° twist structure. I found that I could improve.

FIG. 1 shows the relationship between the twist angle and the contrast.
The data when driving at 1/100 duty is shown, but the contrast was about 2 in the conventional 90 degree twist, but the contrast rises to 9 at a twist angle of 180 ° and 15 at a twist angle of 270 degrees. I understand.

Therefore, there is a great demand for a larger twist angle. There are the following two methods for increasing the twist angle.

(1) By selecting a liquid crystal material, a material having a large margin of d / p (p: peculiar pitch of liquid crystal material, d: cell thickness) in relation to the twist angle is selected.

(2) Increase the tilt angle of the interface that aligns the liquid crystal (5 ° to 30 °).

There are two methods described above. The present invention intends to widen the d / p margin and increase the contrast by selecting the liquid crystal material (1). The interface used for this liquid crystal has a tilt angle of 5 ° or less.

Next, the liquid crystal material and the d / p margin will be described. The relationship is shown in FIG. In order to operate in a region where the twist angle is large, it is necessary to put an appropriate amount of chiral liquid crystal in the liquid crystal material and twist it to a required twist angle so that the liquid crystal material normally twists. For this reason, the boundary between the value of the ratio d / p with the pitch (p) of the liquid crystal material and the normal region when the gap (d) is constant increases with the twist angle. On the other hand, if the pitch (p) is made too small, it becomes larger than the desired twist angle (overtwist), resulting in a non-operating region. The area sandwiched between this under-twist and over-twist is the normal twist area.However, this normal twist area is not the normal operation area but d / p
It has been clarified that the domain generation region becomes larger as the angle becomes larger and the twist angle becomes larger.

As a result of examining various liquid crystal materials, the present inventors have found that the range of this normal region varies depending on the type of liquid crystal material, as shown in FIG.

Materials that show normal areas of A ₁ BC and A ₂ BC are ECH It is a region indicated by a material containing, and in this material system, the twist angle is limited to about 230 degrees, and it is considered that there is a problem above that. On the other hand, materials showing normal regions of A ₃ BC and A ₄ BC are according to the present invention. It is a material-based material containing. With this material system, it is possible to twist up to a twist angle of 270 degrees, as is apparent from the figure.

In order to quantitatively show the d / p tolerance of each material, the d / p width of the normal region when the twist is 250 degrees is used. A
_This means that the material containing the ECH system in the ₁ BC and A ₂ BC regions has a d / p margin of 0, the material of A ₃ BC has a margin of 0.05, and the material of A ₄ BC has a margin of d / p of 0.13.

Structural formula used in the present invention The material is a pyrimidine-based material, but has the following liquid crystal phase transition temperature.

Examples will be shown below. Examples are the composition of liquid crystal material and T
_{Shows the NI} point, voltage, d / p tolerance, and contrast (at 1/100 duty, 250 ° twist).

Example 1 T _NI = 98 ° C Threshold voltage (90%, 10 °) = 2.4V d / p = 0.10 Contrast = 13 Example 2 T _NI = 65 ° C. Threshold voltage (90%, 10 °) = 1.8V d / p = 0.15 Contrast = 10 Example 3 T _NI = 100 ° C. Threshold voltage (90%, 10 °) = 2.5V d / p tolerance = 0.12 Contrast = 12 Example 4 T _NI = 95 ° C. Threshold voltage (90%, 10 °) = 2.3V d / p tolerance = 0.17 Contrast = 9 The above examples have been described. Looking at this data, we find that there is an inverse relationship between contrast and d / p tolerance. It's not clear yet if this is essential, but this By using a pyrimidine-based material having a structure, a liquid crystal display element having a larger twist angle can be manufactured. This makes it possible to obtain a high-contrast display structure.

〔The invention's effect〕

According to the present invention, the domain phenomenon does not occur even if the twist angle is expanded, so that the twist angle can be expanded and a high contrast display can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between twist angle and contrast, and FIG. 2 is a graph showing the relationship between gap-pitch ratio (d / p) and twist angle generated by domains.

 ─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-60-50511 (JP, A) JP-A-61-210324 (JP, A) JP-A-59-199786 (JP, A) JP-A-60- 184587 (JP, A) Okano / Kobayashi, LCD / Basic, published July 15, 1985, Baifukan, page 198

Claims (1)

[Claims] 1. A nematic liquid crystal having a positive dielectric anisotropy and added with an optical rotatory substance is between a pair of upper and lower electrode substrates opposed to each other and on the electrode substrate for orienting the liquid crystal. A liquid crystal display element in which a pair of upper and lower electrode substrates that are processed so that the tilt angle of the liquid crystal interface is 5 degrees or less is enclosed, and a spiral structure in which liquid crystal molecules are twisted by 200 to 270 degrees in the thickness direction is formed. A liquid crystal display device characterized in that the nematic liquid crystal contains 5 to 60% by weight of a substance having the following structure.