JPH02264220A - Ferroelectric liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the change in threshold preferably with age and the deterioration in display quality by a long-term resting by adding at least one kind of silane coupling agent to a ferroelectric liquid crystal. CONSTITUTION:At least one kind of the silane coupling agent is added to the ferroelectric liquid crystal. Namely, polyvinyl alcohol films are applied as oriented films 2 on the surfaces of substrates 1 formed with transparent electrode patterns and after the films are rubbed in one direction by a nylon fabric, the substrates 1 are joined by an epoxy adhesive agent as a sealing material 5. The ferroelectric liquid crystal 3 added with, for example, r-glycidepropyl trimethoxysilane is sealed between the substrates 1. The high-reliability ferroelectric liquid crystal device which is free from the deterioration in the display quality by the change with age is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a liquid crystal display device for displaying characters and images, and in particular provides a highly reliable ferroelectric liquid crystal display device.

Conventional technology: When a ferroelectric liquid crystal is sandwiched between two substrates,
It has two stable orientation states, can be transferred from one to the other by applying an electric field, and has a memory effect of maintaining the orientation state after the transition even after the electric field is removed. Another feature is that the response to electric fields is extremely fast, on the order of microseconds.

Due to these characteristics, when ferroelectric liquid crystals are applied to multiplex-driven liquid crystal display devices with a large number of scanning lines, the scanning selection period is short and the non-selection period can maintain a stable state due to the memory effect, so there is no reduction in contrast. Excellent properties such as no

Problems to be Solved by the Invention As mentioned above, a major feature of ferroelectric liquid crystals is their memory effect, which enables multiplex driving of multiple scanning lines. It was found that changes occur over time. In other words, when no electric field is applied to the liquid crystal, the liquid crystal molecules are in one of two stable states and maintain that state due to the memory effect until the next electric field is applied. It was found that the alignment of liquid crystals changes in this state, resulting in deterioration of display characteristics.

Figure 3 shows the threshold characteristics of the ferroelectric liquid crystal in its initial state, and Figure 4 shows the threshold characteristics of the ferroelectric liquid crystal in the initial state.
These are the characteristics after being left for 00 hours. In both cases, the vertical axis is the transmitted light intensity during memory.

FIG. 5 shows a method for measuring threshold characteristics. The optical response of the 400th pulse after the write pulse is taken as the memory characteristic. 1
The threshold characteristics after being left for 000 hours were significantly asymmetrical due to the difference in polarity, and the memory stability was also degraded.

These changes in properties are thought to be caused by ions in the liquid crystal moving due to the polarization electric field of ferroelectric liquid crystal molecules and forming a space charge polarization field, and deformation of the liquid crystal layer near the alignment film interface. Since display quality is significantly degraded due to changes in threshold characteristics and deterioration of memory properties, prevention of changes over time has become an important issue in improving the reliability of ferroelectric liquid crystal display devices.

The present invention is intended to solve these problems, and aims to provide a highly reliable ferroelectric liquid crystal device that does not deteriorate display quality due to changes over time, while maintaining the conventional configuration of the drive device and alignment film. do.

Means for Solving the Problems In order to solve the above-mentioned problems, the ferroelectric liquid crystal device of the present invention adds a small amount (at least one kind of silane coupling agent) to the ferroelectric liquid crystal.

Effect The effect of the above-mentioned means is considered to be that the added silane coupling agent improves the alignment of the ferroelectric liquid crystal and prevents deterioration over time due to being left in the absence of an electric field.

An embodiment of the ferroelectric liquid crystal display device of the present invention will be described below with reference to the drawings.

Embodiment FIG. 1 is a sectional view of an embodiment of a ferroelectric liquid crystal display device of the present invention.

A polyvinyl alcohol (PVA117 manufactured by Kuraray ■) film is applied as an alignment film 2 to the surface of the substrate 1 on which a transparent electrode pattern (not shown) is formed, and after rubbing in one direction with a nylon cloth, an epoxy adhesive is sealed. The substrates were bonded together as a material 5, and a ferroelectric liquid crystal 3 (ZLI-3489 manufactured by Merck) to which 0.5 wt% of γ-glycidoxypropyltrimethoxysilane was added was sealed between the substrates. Silica beads of 2 μm were used as spacers 4 that determine the thickness of the liquid crystal layer. In actual use, a polarizing element is placed on the outside of the two substrates. FIG. 2 shows the threshold characteristics after being left at room temperature for about 1000 hours in a state where the transmitted relative luminous intensity is O. In the same figure, a represents 0.5 wt% of the γ-glycidoxyprobyltrimethoxysilane.
Characteristics of the additives, b are those with 0.25 wt% added, and C are those with no additives. The threshold characteristics of the additive-free product are markedly asymmetrical, but the one with 0.5 wt% addition has almost no change (symmetrical and steep characteristics are maintained. Also, there is an improvement effect with the addition of 0.25 wt%). However, changes in threshold characteristics are observed.

Regarding the amount added, when the amount is small, the effect of improving properties is small, and when the amount is large, the orientation tends to be disordered.

Therefore, in this example, Q was set to 5 wt%, but
The optimum amount varies depending on the silane coupling agent added.

In addition to the epoxy-based silane coupling agents mentioned above, the silane coupling agents include vinyl-based silane coupling agents such as vinyltrimethoxysilane, amino-based silane coupling agents such as γ(2-aminoethyl)aminopropyltrimethoxysilane, n Straight chain alkyl silane coupling agents such as decyltrimethoxysilane had similar effects. Note that the liquid crystal is not limited to ZLI-3489 (
Moreover, regarding the alignment film, not only polyvinyl alcohol was used, but also a similar effect was obtained when a polyimide film, a silane coupling agent, or a protein film was used.

Effects of the Invention As described above, the present invention has the advantage that by adding at least one type of silane coupling agent to a ferroelectric liquid crystal, there is no change in threshold characteristics over time (no deterioration in display quality) even when left for a long period of time. It is possible to obtain a highly reliable ferroelectric liquid crystal display device free of oxidation.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a ferroelectric liquid crystal display device according to an embodiment of the present invention, FIG. 2 is a threshold characteristic diagram of a ferroelectric liquid crystal display device according to an embodiment of the present invention, and FIGS. 3 and 4 5 is a threshold characteristic diagram of a ferroelectric liquid crystal display device, and FIG. 5 is an explanatory diagram of a threshold characteristic measuring method. 1...Substrate, 2...Alignment film, 3...
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Claims (1)

[Claims] A ferroelectric liquid crystal display device characterized in that at least one kind of silane coupling agent is added to a ferroelectric liquid crystal.