JP2591147B2 - Ferroelectric liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal display device for displaying characters and images,
Particularly, the present invention provides a highly reliable ferroelectric liquid crystal display device.

2. Description of the Related Art A ferroelectric liquid crystal has two stable alignment states when sandwiched between two substrates, and can be transferred from one to the other by applying an electric field. It has a memory effect of maintaining a later alignment state. It also has the characteristic that the response to an electric field is very fast, on the order of microseconds.

Due to these features, ferroelectric liquid crystal is applied to a multiplex drive liquid crystal display device with a large number of scanning lines.
Since the scan selection period is short and the non-selection period can maintain a stable state due to the memory effect, excellent characteristics such as no decrease in contrast can be obtained.

Problems to be Solved by the Invention As described above, a major feature of ferroelectric liquid crystals is the memory effect, which enables multiplex driving of multiple scanning lines. It was found that a change over time occurred. That is, when no electric field is applied to the liquid crystal, the liquid crystal molecules
Is in one of two stable states, and maintains that state due to the memory effect until the next electric field is applied.
In this electric field-free state, the orientation of the liquid crystal changes,
It was found that the display characteristics deteriorated.

FIG. 3 shows the threshold characteristics of the ferroelectric liquid crystal in the initial state.
FIG. 4 shows that at room temperature in a memory state where the transmitted luminous intensity is 0,
This is the characteristic after being left for 00 hours. In each case, the vertical axis indicates the transmitted light intensity at the time of memory. FIG. 5 shows a method of measuring the threshold characteristics. The optical response at the 400th pulse after the write pulse is used as a memory characteristic. The threshold characteristic after leaving for 1000 hours is highly asymmetric due to the difference in polarity, and the memory stability is also deteriorated.

It is thought that these changes in properties are caused by the fact that ions in the liquid crystal move due to the polarization electric field of the ferroelectric liquid crystal molecules to form a space charge polarization field, and the deformation of the liquid crystal layer near the alignment film interface. In addition, since the display quality is remarkably deteriorated due to the change in the threshold characteristic and the deterioration of the memory property, prevention of the change over time is a serious problem in improving the reliability of the ferroelectric liquid crystal display device.

The present invention solves such a problem, and an object of the present invention is to obtain a highly reliable ferroelectric liquid crystal device in which a driving device and an alignment film have a conventional configuration and display quality does not deteriorate due to aging. I do.

Means for Solving the Problems In order to solve the above-mentioned problems, the ferroelectric liquid crystal device of the present invention comprises adding at least one silane coupling agent to a ferroelectric liquid crystal.

Action It is considered that the action of the above means is that the added silane coupling agent improves the orientation of the ferroelectric liquid crystal and prevents a change with time due to being left without an electric field.

Hereinafter, an embodiment of the ferroelectric liquid crystal display device of the present invention will be described with reference to the drawings.

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

A polyvinyl alcohol (PVA117, manufactured by Kuraray Co., Ltd.) film is applied as an alignment film 2 on the surface of the substrate 1 on which the transparent electrode pattern (not shown) is formed, and rubbed in one direction with a nylon cloth, and then an epoxy-based adhesive. Is bonded as a sealing material 5 and a ferroelectric liquid crystal 3 (ZLI-3489 manufactured by Merck) containing 0.5 wt% of γ-glycidoxypropyltrimethoxysilane is sealed between the substrates. As the spacer 4 for determining the thickness of the liquid crystal layer, 2 μm silica beads were used. In an actual use state, a polarizing element is arranged outside the two substrates. FIG. 2 shows the threshold characteristics after leaving at room temperature for about 1000 hours when the transmitted relative luminous intensity is 0. In the figure, a is the one obtained by adding 0.5 wt% of the γ-glycidoxypropyltrimethoxysilane, and b is 0.2
5% by weight is added, and c is the characteristic of the non-added one.
In the case of no additive, the asymmetry of the threshold characteristics was remarkable, but 0.5 wt.
In the case of adding%, there is almost no change and the symmetric and sharp characteristics are maintained. Addition of 0.25 wt% has an improvement effect, but a change in threshold characteristics is observed. Regarding the addition amount, when the amount is small, the effect of improving the characteristics is small, and when the amount is large, the orientation tends to be disordered. For this reason, in this embodiment, 0.5 wt.
%, But the optimum amount varies depending on the added silane coupling agent.

As the silane coupling agent, in addition to the epoxy silane coupling agent, a vinyl silane coupling agent such as vinyltrimethoxysilane, γ- (2-aminoethyl)
Amino-based silane coupling agents such as aminopropyltrimethoxysilane and linear alkyl-based silane coupling agents such as n-decyltrimethoxysilane also had the same effect. The liquid crystal is not limited to ZLI-3489,
In addition, the same effect was obtained when not only polyvinyl alcohol but also a polyimide film, a silane coupling agent, and a protein film were used for the alignment film.

Effect of the Invention As described above, the present invention provides at least one ferroelectric liquid crystal.
By adding the various silane coupling agents, it is possible to obtain a highly reliable ferroelectric liquid crystal display device in which the threshold characteristics do not change with time even when left for a long period of time and the display quality does not deteriorate.

[Brief description of the 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 the ferroelectric liquid crystal display device according to an embodiment of the present invention, and FIGS. FIG. 5 is a diagram showing a threshold characteristic of the ferroelectric liquid crystal display device, and FIG. 5 is an explanatory diagram of a method for measuring the threshold characteristic. 1 .... substrate, 2 .... alignment film, 3 .... ferroelectric liquid crystal (with silane coupling agent added).

Claims (1)

(57) [Claims] 1. A ferroelectric liquid crystal display device comprising at least one silane coupling agent added to a ferroelectric liquid crystal.