JPH0593923A - Active matrix type liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide the active matrix type liquid crystal display element having excellent orientability in a high-temp. region. CONSTITUTION:A liquid crystal material having p1>=p2 at T1<=T2 when the sizes of the chiral pitch at T1, T2 temps. are respectively designated as p1, p2 is sealed between two sheets of substrates. The liquid crystal material of 1 to 4C satisfying such conditions has the negative dependency of the chiral pitch thereof on temp. and the torsional force of the liquid crystal material increases with an increase in temp., unlike a comparison example shown by C5, C6 and, therefore, the sufficient orientability is maintained even in the high-temp. region of the active matrix type liquid crystal display element sealed therein with such liquid crystal material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art Usually, a display mode of an active matrix type liquid crystal display element is a TN mode, and liquid crystal molecules are twisted by 90 degrees between two substrates. At this time, 2
The orientations of liquid crystal molecules near the surfaces of the substrates are orthogonal to each other, and the orientations are right twist or left twist from one substrate side to the other substrate side. In the active matrix type liquid crystal display device having such a configuration, a chiral material is added to the liquid crystal material in order to give directionality to the twisting direction of the liquid crystal and prevent the generation of reverse twist alignment. If the addition amount of the chiral material is larger within a practical addition amount range, the orientation becomes better, but the driving voltage also becomes higher. Therefore, the chiral pitch of the liquid crystal material is generally 5 at room temperature.
The addition ratio is adjusted so as to be about 0 μm to 200 μm.

[0003]

However, in the above-mentioned conventional structure, there is a problem that the alignment of the liquid crystal becomes more and more difficult because the surface of the substrate constituting the liquid crystal display element is highly uneven and the pixel density tends to increase. I had.

The right-handed chiral materials currently used are, for example, CB-15 and R-811 manufactured by Merck.
The left-handed chiral material includes, for example, C-15, S-811, CN and the like manufactured by Merck Ltd., and the pitch of each of these chiral materials increases with an increase in temperature. It has the property that the temperature dependence of the pitch is defined as positive), and has the problem that the orientation at high temperatures is reduced.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an active matrix type liquid crystal display device having excellent orientation in a high temperature range.

[0006]

In order to achieve this object, the active matrix type liquid crystal display device of the present invention is such that when the chiral pitch magnitudes at temperatures T1 and T2 are p1 and p2, respectively, T1≤T2. The liquid crystal material satisfying p1 ≧ p2 is sealed between two substrates.

[0007]

In general, the alignment of liquid crystal molecules enclosed between two substrates is determined by the elastic energy of the liquid crystal material, the dielectric energy, the binding energy between the liquid crystal material and the surface of the alignment film, etc. However, in the constitution of the present invention, the temperature dependence of the chiral pitch is negative, and the twisting force of the liquid crystal material increases as the temperature rises. Therefore, sufficient orientation can be maintained even in a high temperature region.

[0008]

EXAMPLE An example of the present invention will be described below. The active matrix type liquid crystal display device (hereinafter abbreviated as liquid crystal display device) used for the measurement was prepared as follows. First, 312,000 pixels (89 μm ×
87 μm) and each pixel is provided with a TFT element, and a color filter substrate having red, blue, and green filters corresponding to each pixel is prepared, and then polyimide coating (for example, Chisso Corporation) is prepared. ) Manufactured by PSI-2101) diluted with N-methylpyrrolidone to 4 wt% is applied to the surfaces of the array substrate and the color filter substrate by spin coating,
It was cured under the curing condition of 200 ° C. for 1 hour. Next, the surfaces of the array substrate and the color filter substrate were rubbed so that the twist angle of the liquid crystal molecules was 90 degrees, and then these substrates were bonded together via 4.0 μm glass fibers to form a liquid crystal cell. .. Twelve such liquid crystal cells were prepared and a liquid crystal material containing a chiral material (ZL manufactured by Merck & Co., Inc.
I-1565) was injected under reduced pressure into each liquid crystal cell to prepare a liquid crystal display element. Each liquid crystal display element [1] to
The structures and addition ratios of the chiral materials C1 to C6 contained in [12] are shown in (Table 1). The liquid crystal display devices [9], [10], [11] and [12] are comparative examples, and the chiral materials S-811 and C-15 (both of which are manufactured by Merck & Co.) A liquid crystal material containing a chiral material) was injected under reduced pressure.

[0009]

[Table 1]

In the present embodiment, each chiral material has a chiral pitch of about 100 μm at room temperature and a chiral pitch of 120.
A chiral material was prepared so that two kinds of liquid crystal display elements for the case of μm could be produced.

FIG. 1 is a diagram showing the temperature dependence of the chiral pitch of a liquid crystal display element according to an embodiment of the present invention. The liquid crystal display element is a liquid crystal material containing 1.0 wt% of each chiral material (a liquid crystal material manufactured by Merck). ZLI-1565) is enclosed. A Kano wedge cell was used for the measurement of the chiral pitch. As shown in FIG. 1, the chiral material is C1 to C.
4 is added to the liquid crystal material (C1 to C4 in FIG. 1).
, The chiral pitch decreases with temperature (the temperature dependence is negative), but the chiral material C5 or C6
In the liquid crystal material to which is added (indicated by C5 and C6 in FIG. 1), the chiral pitch slightly increases with temperature (the temperature dependence is positive).

Next, the results of observing the orientation of the liquid crystal at each temperature of 25 ° C. and 55 ° C. are shown in (Table 2).

[0013]

[Table 2]

The evaluation is based on the probability of occurrence of reverse twist when the temperature of the entire surface of the substrate of the liquid crystal display device is raised above the nematic-isotropic phase transition temperature of the liquid crystal and then lowered to a predetermined temperature at -1 ° C./min. went. It should be noted that the judgment is that when the ratio of the number of pixels in which the reverse twist is generated to the total number of pixels is 100 ppm or less, the orientation is ◯, and the orientation is larger than 100 ppm and 300 pp.
When m or less, Δ, and when more than 300 ppm, x. As a result of the evaluation, as shown in (Table 2), the liquid crystal display element C1 of the present example in which the temperature dependence of the chiral pitch is negative.
C4 to C4 have excellent orientation at high temperature, and their practical value is extremely high.

In this embodiment, four kinds of single compounds were used as the chiral material, but this does not limit the present invention in any way, and even a liquid crystal material whose size of the chiral pitch decreases with an increase in temperature. Just do it. Further, even a chiral material having a property of increasing the size of the chiral pitch with an increase in temperature is suitable if the size of the chiral pitch decreases with the increase of temperature as a result of mixing the chiral material with the liquid crystal material. It goes without saying that it is a material.

[0016]

As described above, according to the present invention, a liquid crystal material containing a material having a negative temperature characteristic of chiral pitch as a chiral material is sealed between two substrates.
It is possible to realize an active matrix type liquid crystal display device having excellent orientation (especially orientation at high temperature).

[Brief description of drawings]

FIG. 1 is a diagram showing the temperature dependence of the chiral pitch of a liquid crystal display element in one embodiment of the present invention.

[Explanation of symbols]

C1 to C4 Liquid crystal materials used in the active matrix type liquid crystal display device in one embodiment of the present invention C5 and C6 Liquid crystal materials for comparison

Claims (1)

[Claims] 1. An active matrix type liquid crystal display in which a liquid crystal material satisfying T1 ≦ T2 and p1 ≧ p2 is enclosed between two substrates, where the chiral pitches at temperatures T1 and T2 are p1 and p2, respectively. element.