JPH03185424A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To expedite the response to electric field impression by providing two sheets of substrates which are held in parallel, a liquid crystal layer which is crimped by the substrates and liquid crystal orientable particles incorporated into the liquid crystal layer. CONSTITUTION:Electrode layers and if necessary, protective films are formed on the inside surfaces of two sheets of the substrates 1 which are held in parallel. The substrate 1 on an observer side is formed transparent. The liquid crystal orientable particles 3 are incorporated into the liquid crystal layer 2 of a nematic phase crimped by the substrates 1. The liquid crystal molecules are respectively oriented with the surfaces of the liquid crystal orientable particles 3 to form the miscelle-like orientated groups. Light scattering is, therefore, generated by the oriented groups in the electric fieldless state and the liquid crystal layer is observed in white. The liquid crystal molecules array in the electric field direction in the liquid crystal layer 2 when the electric field is impressed to the liquid crystal layer 2. The liquid crystal layer is thereby made into the light transparent state and the background color is observed. The liquid crystal molecules are directly influenced in this way by the presence or absence of the impressed voltage, the lower voltage is necessitated and the quick response to the electric field impression is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a liquid crystal display device that performs display by scattering and transmission.

(B) Prior Art Conventionally, there are devices that perform display using a scattering state and a transmitting state. There are nematic dispersion type liquid crystal display devices such as.

In the DSM type, light-scattering domains are generated by ions traveling in the liquid crystal layer in response to an electric field, and in the phase transition type, the phase of the liquid crystal changes from nematic to cholesteric.
Alternatively, it utilizes the fact that the state of scattering and transmission of light changes due to the transition from these to smectic.
In the nematic dispersion type, liquid crystal is divided or dispersed into minute regions, and light scattering in each minute region is removed by an electric field.

(c) Problems to be solved by the invention Among these display modes, the DSM type consumes a lot of power and the liquid crystal deteriorates quickly, and the phase change type requires a high driving voltage and has memory properties. The drive circuit requires a special circuit that has a high withstand voltage and performs complicated control, the manufacturing method for liquid crystal panels in the nematic dispersion type is complicated, and the drive voltage is divided due to the dielectric properties of the polymer skeleton. It has drawbacks such as being large, at several tens of volts and hundreds of volts.

(d) Means for Solving the Problems The present invention has been developed in consideration of the above-mentioned points, and includes liquid crystal alignment particles mixed into a liquid crystal layer sandwiched between substrates, and more preferably the liquid crystal alignment. The specific gravity of the liquid crystal particles is approximately equal to the specific gravity of the liquid crystal.

(e) Effect As a result, when there is no electric field, the liquid crystal molecules are oriented under the control of the liquid crystal alignment particles, so the layer as a whole exhibits a light scattering state, and when an electric field is applied, the liquid crystal molecules align in the direction of the electric field. Therefore, it becomes a light-transmitting state.

(f) Example The present invention will be explained in detail with reference to FIG.

Reference numeral 1 denotes two substrates held in parallel, each having an electrode layer on the inner surface and a protective film if necessary, and at least the substrate on the viewer's side is made of a transparent substrate such as glass. Reference numeral 2 denotes a nematic phase liquid crystal layer held between substrates 1, and liquid crystal alignment particles 3 are mixed in the liquid crystal layer 2. As a result, the liquid crystal molecules are aligned with respect to the surfaces of the liquid crystal alignment particles 3, forming a micelle-like alignment group.

Therefore, as shown in FIG. 1a, in the absence of an electric field, light scattering occurs due to the alignment group, and the liquid crystal layer is observed as white. As shown in the figure, when an electric field is applied to the liquid crystal layer 2, the liquid crystal layer moves in the direction of the electric field (in the example shown, a liquid crystal whose dielectric anisotropy of liquid crystal molecules is positive [Δε〉0] is used, and the liquid crystal layer 2 is moved in the direction parallel to the electric field. )
The liquid crystal molecules are aligned, and this causes the liquid crystal layer to become light-transmissive, allowing the background color to be observed.

When the thickness of the liquid crystal layer 2 is increased, the drive voltage becomes higher and the response characteristics become slower, and when the liquid crystal layer 2 is made thinner, the amount of light scattering decreases. Although the driving voltage depends on the magnitude of the dielectric anisotropy of the liquid crystal layer, it is generally not practical unless it is 40 volts or less, and the response need only be 300 milliseconds or less. Therefore, in order to obtain a predetermined display density, it is sufficient that the thickness is 5 μm or more and 30 μm or less.

The size of the micellar orientation group is 0.5 to avoid wavelength-selective scattering when white light scattering is assumed.
It is desirable that the thickness is μm or more.

However, when the size is several tens of micrometers, for example, the amount of light scattering decreases within the above-mentioned range of thickness of the liquid crystal layer, making it impossible to obtain a high contrast ratio. Generally, the birefringence of nematic liquid crystal is in the range of 0.601 to 0.30 due to requirements such as operating speed and operating voltage, but this value also affects the amount of light scattering.

Therefore, in the range of birefringence mentioned above, the average diameter dm of the alignment group is dm>0.5 with respect to the thickness d of the liquid crystal layer 2.
It is preferable that the range is μm and d/dm>5.0.

On the other hand, the liquid crystal alignment particles 3 move every time an electric field is applied,
It is best to use something that does not settle down during long-term storage. For this purpose, the specific gravity of the liquid crystal alignment particles 3 should be approximately equal to the specific gravity of the liquid crystal (101 to 1.06), such as polyethylene, polystyrene, polypropylene, polybutadiene, polyacrylate, polymethacrylate, nylon, Teflon, etc. Organic polymer fine powder consisting of polyvinylidene fluoride, polyacrylonitrile, epoxy resin, or a specific gravity-adjusted product containing these as main ingredients and adding materials that have affinity for liquid crystal molecules or do not affect liquid crystal, or silica, alumina, An inorganic fine powder such as magnesia coated with the above polymer can be used. Liquid crystal orientation can be imparted to these fine powders by adding polar groups to polymer chains, filling them with long-chain silane coupling agents, or adding chromium complexes. can.

When the amount of dispersion of the liquid crystal alignment particles 3 in the liquid crystal 2 is small, the restraining force on the liquid crystal molecules is small, so the amount of light scattering in the absence of an electric field is small, and when it is large, the transmittance when an electric field is applied decreases and the operation becomes slow. This tendency of properties is common to all of the above-mentioned materials.

ZLI 1565 (manufactured by Merck & Co., Ltd.) is used as a typical nematic liquid crystal, and the material has an adjusted average particle diameter of 2.0 μm.
Grind polystyrene beads in a ball mill, mix this with the liquid crystal, form a container with a sealant (not shown) so that the distance between the substrates is 15 μm, and then inject the liquid crystal mixed with the fine powder. Figure 2 shows the characteristics when a display device was obtained and driven with alternating current. In FIG. 2, the black circles indicate the light transmittance when no electric field is applied, and the open circles indicate the light transmittance when an electric field is applied.

In the characteristics of such a mixture ratio, the contrast is 3 to 1.
In order to ensure the above practical range, liquid crystal alignment particles 3
The mixing ratio (liquid crystal orientation particles/liquid crystal) to the liquid crystal 2 is preferably in the range of 0.1 to 0.5 in terms of weight ratio.

(G) Effects of the Invention As described above, since liquid crystal molecules are directly affected by the presence or absence of applied voltage, the voltage may be low and the response to the applied electric field is fast. When the applied voltage is removed, the orientation is controlled by the dispersed particles, so the response is quick even when the electric field is removed. Since the movement of these liquid crystal molecules responds to an electric field and no current flows, there is extremely little deterioration of the liquid crystal due to driving.

[Brief explanation of drawings]

FIGS. 1a and 1b are schematic diagrams of a liquid crystal display device according to an embodiment of the present invention, and FIG. 2 is a characteristic diagram of liquid crystal alignment particles to be mixed with the liquid crystal of the display device. 1...Substrate, 2...Liquid crystal, 3...Liquid crystal alignment particles.

Claims (2)

[Claims] (1) A liquid crystal display device comprising at least two substrates held in parallel, a liquid crystal layer sandwiched between the substrates, and liquid crystal alignment particles mixed in the liquid crystal layer. (2) The liquid crystal display device according to claim 1, wherein the specific gravity of the liquid crystal alignment particles is approximately equal to the specific gravity of the liquid crystal in the liquid crystal layer.