JPH01134335A - Phase transition type liquid crystal display element - Google Patents

Abstract

PURPOSE:To increase the hysteresis width created by a voltage versus transmittance curve so that a large-area liquid crystal display is enabled and the contrast thereof is improved by forming a liquid crystal oriented film contg. a liquid crystal orienting agent expressed by the specific formula on a substrate. CONSTITUTION:The liquid crystal oriented film contg. N-alkoxymethylated polyamide as the liquid crystal orienting agent is provided to a nematic/ cholesteric phase transition type liquid crystal display element exhibiting positive dielectric anisotropy, by which the stable large-area liquid crystal display with the good contrast is enabled. The polyamide expressed by the formula is used as the liquid crystal orienting agent. In the formula, R denotes an alkyl group and (n) denotes 50-500. The hysteresis width created by the voltage versus transmittance curve is increased by forming the film contg. such orienting agent on the substrate and, therefore, the stable large-area liquid crystal display using the phase transition type liquid crystal with good contrast is enabled.

Description

Detailed Description of the Invention [Summary of the Invention] The present invention uses N as a liquid crystal aligning agent in order to solve the conventional problem of a narrow hysteresis width and lack of stable display in a nematic cholesteric phase transition type liquid crystal display element.
- By providing a liquid crystal alignment film containing alkoxymethylated polyamide, a large area liquid crystal display can be stably displayed with good contrast.

[Industrial application field]

The present invention relates to a liquid crystal display element. More particularly, the present invention relates to a liquid crystal display element of the nematic-cholesteric phase transition type, which utilizes voltage-light transmittance bistability associated with nematic-cholesteric phase transition caused by an electric field.

[Prior Art] As is well known, the mainstream of conventional liquid crystal display elements (LCDs) is the twisted nematic (TN) method. However, in this TN type liquid crystal display element, since the rise characteristic of the liquid crystal is not steep, when trying to display a large-sized fake dot matrix, a point that is not displayed (a half-display state up to a non-display point, that is, a crosstalk In addition, with this type of liquid crystal display element, when attempting to display a large capacity, the viewing angle is severely restricted, resulting in an extreme drop in contrast. Although efforts such as multiplex matrixing are being made to compensate for these shortcomings, this TN
The type liquid crystal display device cannot overcome the fatal drawback of large-sized liquid crystal displays, that is, the viewing angle range narrows as the number of scanning lines increases.

Under these circumstances, first of all, in order to overcome the phenomenon of crosstalk in line-sequential scanning, which is inevitable for liquid crystals, and to enable large-capacity display, a large-capacity display with about 500 scanning lines was made possible. A storage type liquid crystal display element was developed, and as a result of several improvements to this type of liquid crystal display element, a phase change type liquid crystal display element, which is also the subject of the present invention, was developed (for example, (See specification of Japanese Patent Application No. 59-00966). This LCD
Although it has the same configuration as a TN type LCD, the driving method, that is, the light control method is different from that of the TN type. As shown in FIG. 1, this LCD generally consists of a liquid crystal 1, glass substrates 2 and 3 with a set of transparent electrodes (ITO) 4 and 5, alignment films 6 and 7, and a spacer 8 that holds them. , the display is configured to be displayed by applying an electric field.

[Problem that the invention seeks to solve]

A typical nematic-cholesteric phase transition type liquid crystal display device that exhibits positive dielectric anisotropy is nematic liquid crystal, which is a mixture of nematic liquid crystal and liquid crystal that has chirality.
A liquid crystal cell is manufactured by sealing a cholesteric phase change type liquid crystal into a cell with a thickness of about 6 μm made of two opposing glass substrates with transparent electrodes, and when a voltage is applied to this cell from the outside, the result is shown in Figure 2. A graph of changes in voltage-induced light transmittance is obtained. As is clear from the graph showing the relationship between applied voltage and light transmittance, in the case of such a liquid crystal display element, at voltage Vd, the light transmittance is large H' and small F.
There are two states: A phase change liquid crystal display is a system that attempts to perform display using this bistable state, and the present invention also relates to this display system as described above. This method does not have the drawbacks of TN liquid crystal, which is currently the mainstream liquid crystal display, such as large capacity display, no flicker, and wide viewing angle because it uses light scattering. However, in general, in the H' state in Figure 2, if the voltage is maintained at Vd, the transmittance will decrease over time, and eventually the transmittance at the H' position will become the same as the transmittance at the F position. They become the same and cannot be displayed. Furthermore, if the applied voltage is set to Vd' which is larger than Vd in order to keep the state of H' stable over time, the light transmittance of F increases to F, resulting in a display with very poor contrast. It ends up. Therefore, in order to realize this display method, it is desirable that the change in the light transmittance curve be sharp at the threshold voltage as shown in Figure 3, and that the voltage width (hysteresis width Δ) of the rising and falling curves be as large as possible. . This hysteresis width (Δ) needs to have a ratio of 7% or more to the drive voltage, taking into consideration variations in drive voltage due to variations in cell thickness of liquid crystal cells and variations in drive elements from the drive circuit side. Also, the hysteresis width (
Δ) is the margin voltage width necessary to actually perform a phase change type liquid crystal display, and it varies greatly depending on not only the liquid crystal material but also the liquid crystal alignment film applied to the surface of the glass substrate. Polyimide and silane coupling agents are known as liquid crystal alignment agents in the prior art, but in liquid crystal cells manufactured using glass substrates with transparent electrodes treated with these agents, the hysteresis width (Δ ) is about 0.5V (the ratio of the hysteresis width to the drive voltage is 4.0%), which is very narrow, making it impossible to perform display with a constant voltage Vd.

[Means for solving problems]

According to the present invention, the above-described problems can be solved by using a liquid crystal aligning agent of the following formula: -(-C112-N -C-+-1 CI□-〇-R (wherein, R represents an alkyl group and n is This problem can be solved by using a polyamide represented by 50 to 500 and applying a film containing this alignment agent on the substrate.

Application of the liquid crystal alignment film onto the substrate can advantageously be achieved by any method. For example, about 2 to 3
% coating solution at a rotational speed of about 1500 to 200 rpm, or by vapor deposition of N-alkoxymethylated nylon.

In carrying out the present invention, the composition of the phase transition type liquid crystal sealed in the liquid crystal cell is not particularly limited, and therefore, detailed description thereof will be omitted in this specification. do. In addition, the present inventors have disclosed the famous nematic liquid crystal and the liquid crystal having chirality (chiral nematic liquid crystal) in the Japanese Patent Application No. 59-00966 and the Japanese Patent Application No. 59-180633 cited above. Some examples are listed.

〔Example〕

Examples of the present invention will be described below to make the effects of the present invention more clear.

After cleaning a glass substrate of 100 x 100 After coating with a solution of nylon using a spin coater, it was dried at 150° C. for 1 hour. After this, a dry cell with a cell thickness of 9 μm was fabricated.

This cell contains 90% nematic liquid crystal manufactured by Nippon Roche.
A liquid crystal cell was prepared by injecting a phase change type liquid crystal prepared by mixing -t% and 10 wt% of a chiral nematic liquid crystal having two chiral centers.

The hysteresis width (Δ) of this liquid crystal cell was measured as follows. First, a certain voltage Vdl is set and the liquid crystal cell is driven with the drive waveform shown in FIG. 4A.

At this time, the change in light transmittance after writing is measured with respect to time. Next, a voltage Vd2 slightly higher than the voltage Vdl is applied, and the change in light transmittance is similarly measured with respect to time. Thereafter, the voltage is increased sequentially from Vd 3 to Vd 4, and this is continued until a phase transition from the cholesteric phase to the nematic phase occurs. Next, similar measurements are made with the drive waveform shown in FIG. 4B while sequentially lowering the voltage from the high voltage that maintains the nematic phase. If the change in light transmittance after a certain period of time after writing is plotted against each voltage from the graph of the change in light transmittance with respect to time obtained in this manner, FIG. 5 is obtained. Note that the light transmittance at this time is expressed as a voltage using a photocell. Fifth
The measurement shown in the figure shows the change in light transmittance of the applied voltage lamp 10 seconds after writing with a writing time of 4 ms/line.

When the hysteresis width (Δ) was determined from the graph in Figure 5, it was found that for N-methoxymethylated nylon as shown in Table 1 below, the ratio of the hysteresis width to the driving voltage was 7.0% or more. Ta. This value means that the above-described fluctuations in drive voltage and variations in drive elements can be tolerated. Furthermore, the contrast was 1:5.

The manufactured liquid crystal cell was able to display a full screen display.

The procedure described in Example 1 above was repeated using polyimide as the liquid crystal aligning agent. As is clear from the results in Table 1 below, the hysteresis width (Δ) was narrow (and the contrast was poor), so the fabricated liquid crystal cell was unable to display a full screen.

The results of repeating the procedure described in Example 1 using a silane coupling agent as a liquid crystal aligning agent are as shown in Table 1 below, and the results of Example 2 (Comparative) Example).

Male - Table 1 N-Methoxymethylated N
1.6v boiling point (1'?1I2)
0.5V silane cuffing agent (Example 3) 0.5
VΔ/Snow 2-13v) -+ 7
) −: A ) 12.3%
1:54.0%
te 34.0%
1:3 [Effects of the present invention] According to the present invention, the hysteresis width created by the voltage lamp light transmittance curve can be widened, so that a large area liquid crystal display using a phase change type liquid crystal can display images stably with good contrast. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an example of a phase change type liquid crystal display element according to the present invention, FIG. 2 is a graph showing the relationship between applied voltage and light transmittance of a phase change type liquid crystal, and FIG. FIG. 4A and FIG. 4B are graphs showing drive waveforms of phase change liquid crystal, respectively. FIG. 5 is a graph showing actual measurement data of an example of the present invention. This is a graph representing 1...Liquid crystal, 2.3...Glass substrate,
4.5...Transparent electrode, 6.7...Alignment film, 8.
··Spacer.

Claims (1)

[Claims] 1. Contains a polyamide represented by the following formula as a liquid crystal aligning agent: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, R represents an alkyl group, and n is 50 to 500) A nematic-cholesteric phase transition type liquid crystal display element having a liquid crystal alignment film. 2. Claim 1 in which the liquid crystal exhibits positive dielectric anisotropy
The liquid crystal display element described in .