JPS62119522A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To enable display of sufficient contrast by coating a silyl isocyanate compd. on a substrate and forming liquid crystal orientation film comprising siliceous material formed by the cleavage reaction between the silyl group and the isocyanate group. CONSTITUTION:Suitable silyl isocyanate compd. is one having Si-NCO bond, for example, tetraisocyanate silane Si(NCO)4, alkyl silyl isocyanate compd. RnSi(NCO)4-n, alkoxysilane isocyanate compd. (RO)nSi(NCO)4-n [in these formulas, R is alkyl, alkenyl, etc.], and condensation products thereof. Coated film of these compds. cause cleavage reaction between the silyl group and the isocyanate group by the hydrolysis or alcoholysis, and reaction products derived from the isocyanate group, etc., are removed from the film in the form of gaseous component, etc., leaving siliceous film finally. By this method, display of sufficient contrast is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] A siliceous film based on a silyl isocyanate compound is used as an alignment film of a nematic-cholesteric phase transition type liquid crystal to improve the bistability of the liquid crystal.

[Industrial application field]

The present invention relates to a liquid crystal display element, and in particular, in a display method that utilizes the voltage-transmittance bistability associated with nematic-cholesteric phase transition caused by an electric field, a substrate with a transparent electrode is used to make the bistability more stable. The present invention relates to the use of siliceous membranes prepared based on silyl isocyanate compounds.

[Conventional technology]

A nematic-cholesteric phase transition type liquid crystal, such as a liquid crystal that is a mixture of a nematic liquid crystal and a liquid crystal with chirality, is sealed in a cell with a thickness of about 9 μm made of two opposing glass substrates with transparent electrodes, and a voltage is applied from the outside. Then, the change in the voltage emitted light transmittance as shown in FIG. 4 is shown. In FIG. 4, at voltage Vd, there are states of H' with a large light transmittance and a state of F with a small light transmittance. 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. 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.

Conventionally, polyimides, silane coupling agents, and the like have been used as liquid crystal alignment films to which the present invention relates.

[Problem that the invention seeks to solve]

However, in general, in state 11' in Fig. 4, if the voltage is maintained at Vd, the transmittance will decrease over time, and eventually the transmittance at the TI' position will be the same as the transmittance at the F position. becomes impossible to display.

Furthermore, in order to maintain the state of H' stably over time, if the applied voltage is set to Vd' which is greater than Vd, F
The light transmittance increases to Fl, resulting in a display with very poor contrast. Therefore, in order to realize this display method, the change in the light transmittance curve is sharp at the threshold voltage shown in Figure 1, and the voltage width (hysteresis width) of the rising curve and the 3'l falling curve is large. This is desirable. This hysteresis width is due to fluctuations in drive voltage due to variations in liquid crystal cell thickness and
Considering the variation in drive elements from the roadside, 2.5V or more is required. Further, the hysteresis width is the margin voltage width required to actually perform a phase change type liquid crystal display, and 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. However, in liquid crystal cells fabricated using glass substrates with transparent electrodes treated with polyimide or silane coupling agents, which are known liquid crystal alignment agents, the hysteresis width is extremely narrow at around 0.5 V. Therefore, it is impossible to perform display with a constant voltage Vd.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art,
In order to perform stable display with good contrast, the liquid crystal alignment film used for the glass substrate with transparent electrodes is provided so as to ensure a wide hysteresis width formed by the applied voltage emitted light transmittance curve.

[Means for solving problems]

As a result of intensive efforts to achieve the above object, the present inventors have discovered that the above object can be achieved by using a siliceous film prepared using a silyl isocyanate compound as a liquid crystal alignment film. completed.

That is, the present invention provides a liquid crystal display element using a nematic-cholesteric phase transition type liquid crystal having a hysteresis effect that enables bistable display, in which a silyl isocyanate compound is coated on a substrate.

A liquid crystal display element characterized in that it has a siliceous film formed by a cleavage reaction between a silyl group and one or more isocyanate groups as a liquid crystal alignment film.

The silyl isocyanate-1 compound is a compound having a 5i-NGO bond, such as tetraisocyanate silane Si (NGO) s, alkyl silyl isocyanate compound R,5l(NCo)4-, alkoxysilane isocyanate. System compounds (RO) ,,St (
NGO) a-7 [In these formulas, R is an alkyl group, an aryl group, an alkenyl group, etc. ], and their condensates are known. In the coating film of these compounds, the silyl group and the isocyanate group are cleaved by hydrolysis or alcoholysis reaction, and the reaction products based on the isocyanate group are removed from the film as gas components and other substances, and finally the silyl group is removed. It is known that a membrane remains. For example, the hydrolysis reaction of 5i-NGO compound is expressed as follows.

According to the present invention, when a siliceous film prepared by applying a silyl isocyanate compound is used as a liquid crystal alignment film, a hysteresis width large enough to enable stable driving can be obtained, and a display with good contrast can be obtained.

A nematic-cholesteric phase transition liquid crystal that has a hysteresis effect that enables bistable display is generally composed of a mixed liquid crystal of nematic liquid crystal and cholesterlink liquid crystal or chiral nematic liquid crystal, but the above hysteresis width varies depending on the composition. However, there are no particular restrictions on the application of the present invention. Typical liquid crystal (composition) is exemplified as follows: [Example] Execution ±1.0OX100X1. IIt anti-5 in Itmm
After cleaning the glass substrate with 0Ω/Ca indium oxide as a transparent electrode,
The coating agent "5IC-033" (acetate ester solution of silyl isocyanate) was applied with a spinner using a spin code (2000 rpm x 60 sec). Thereafter, the glass substrate was dried at room temperature to obtain a siliceous film with a thickness of about 1100 nm, and then a dry cell with a cell thickness of 9 μm was fabricated. This cell is equipped with Nippon Rososh's Nemadisoku liquid crystal 'Nr.
, 2801"87wt% and chiral nematic liquid crystal CB-15 manufactured by BD11, (compound 13 represented by the following formula)
A liquid crystal cell was prepared by injecting a phase change type liquid crystal prepared by mixing wt%.

The hysteresis width of this liquid crystal cell was measured as follows. First, a certain voltage Vd is set and the liquid crystal cell is driven with the drive waveform shown in FIG. 2(A). At this time, the change in light transmittance after writing is measured with respect to time. Next, the voltage V d
Similarly, the change in light transmittance is measured with respect to time by applying a voltage Vd2 slightly higher than +. Thereafter, the voltage is increased sequentially from Vd2 to Vd3, and this is continued until a phase transition from cholesteric phase to nematic phase occurs. Next, Figure 2 (a)
Similar measurements are made using the drive waveform shown in Figure 2, starting from a high voltage that maintains the nematic phase and decreasing the voltage sequentially. FIG. 3 is obtained by plotting the change in light transmittance after a certain period of time has elapsed after writing against each voltage from the graph of the change in light transmittance with respect to time obtained in this way.

Note that the light transmittance at this time is expressed as a voltage using a photocell. In the measurements shown in Figure 3, the writing time was 4. ms
/1ine shows the change in applied voltage emitted light transmittance 10 seconds after writing. As a result of finding the hysteresis width from this graph, the hysteresis width is 3.5V at a drive voltage of 37V.
(The ratio of phantom to the drive voltage is 9.5%), which far exceeds the hysteresis width (2.5V) that can tolerate fluctuations in the drive voltage and drive elements as explained earlier, and the contrast is 1: 5, and the manufactured liquid crystal cell was able to display the entire surface.

Reference Table 1 shows the hysteresis width and contrast when polyimide or a silane coupling agent is used as a liquid crystal aligning agent.

In this comparative example, the voltage hysteresis width was narrow and the contrast I· was poor, so full-screen display was not possible.

〔Effect of the invention〕

According to the present invention, the voltage hysteresis width created by the voltage radiation transmittance curve can be widened, so that a large area liquid crystal display using a phase change type liquid crystal can be displayed stably with good contrast.

[Brief explanation of drawings]

Figure 1 is a graph defining the hysteresis width (Δ), Figure 2 is a diagram showing drive waveforms, Figure 3 is a graph representing actual measurement data of the example, and Figure 4 is a cholesteric-nematic phase transition type liquid crystal. FIG. 2 is a graph showing the relationship between applied voltage and light transmittance.

Claims (1)

[Claims] 1. In a liquid crystal display element using a nematic-cholesteric phase transition type liquid crystal that has a hysteresis effect that enables bistable display, a silyl isocyanate compound is coated on a substrate, and a silyl isocyanate compound is formed by a cleavage reaction between a silyl group and an isocyanate group. 1. A liquid crystal display element comprising a siliceous film as a liquid crystal alignment film.