JPS5817787B2 - liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a display device using a liquid crystal, and more particularly to a novel additive for imparting a homeotropic structure to a nematic liquid crystal.

FIG. 1 shows the general structure of any type of liquid crystal display device.

In the figure, 1 and 2 are glass substrates, and the gap between the substrates 1 and 2 is from several microns to several 1 through an electrically insulating spacer 3.
It is maintained at 0 microns.

The inner surface of the glass substrate 1 is coated with a thin transparent conductive film 4 mainly made of tin oxide or indium oxide, and the inner surface of the glass substrate 2 is coated with a conductive thin film 5 such as a thin transparent film mainly made of tin oxide or indium oxide. Conductive film, metal vapor deposited thin film, or thin transparent conductive film with dielectric mirror,
Alternatively, modified conductive films thereof are provided.

A liquid crystal 6 is interposed between the glass substrates 1 and 2, in other words, between the thin film electrodes 4 and 5.

A voltage is applied to the liquid crystal 6 from an external power supply 7 through the electrodes 4 and 5, and external light 8 is modulated for display.

FIG. 2 shows the relative positional relationship between the glass substrates 1 and 2, the liquid crystal molecules 9, and the additive 10 according to the invention.

By adding this additive, the long axes of liquid crystal molecules are aligned perpendicular to the surfaces of glass substrates 1 and 2, as shown in FIG.

This liquid crystal structure is known as a homeotropic structure.

To check whether the liquid crystal display has a homeotropic structure, place linear polarizing plates 11 and 12 on the front and rear surfaces of the liquid crystal display.
When the polarization directions of these linear polarizers are arranged perpendicularly to each other, it can be determined that the liquid crystal structure in the liquid crystal display device is a homeotropic structure because the incident light 13 hardly reaches the observer 14.

Liquid crystal display methods using homeotropic structures include (1) a method in which dynamic light scattering is caused by ion flow caused by voltage application (dynamic light scattering);

(2) A method (DAP) that modulates light by changing the orientation of molecules by applying a voltage and utilizing the phenomenon of birefringence.

(3) A method in which a voltage is applied to a liquid crystal containing a pleochroic dye, causing the dye molecules to lie down and change the color tone.

etc.

In a liquid crystal display, the advantage of adopting a homeotropic structure is that in method (1), it is useful for improving the transparency when no applied voltage is applied and in areas where there are no electrodes and no voltage can be applied.

In addition, methods (2) and (3) can only be displayed effectively if a homeotropic structure is used.

The present invention provides a homeotropic structure by adding additives to the liquid crystal itself, and the additives used in the present invention are represented by the following general formula, where n=1,2; 17≧m≧ 10°-C-(CH2)m With respect to -CH3, when n=1, it is the para position, and when n=2, it is the meta position.

One or more of these compounds, or in combination with other additives providing a homeotropic structure, are added to the liquid crystal material in an amount of 0.5 to 5 parts by weight.

Even if a large amount is added, a homeotropic structure is obtained, but the upper limit of the temperature range of the liquid crystal state is often lowered.
However, the degree of homeotropic organization would not be more complete and would be impractical.

The liquid crystal used for the additive of the present invention is not limited, and liquid crystals of various types such as Schiff base, azobenzene, azoxybenzene, alkoxybenzoic acid, and benzoic acid phenyl ester can be applied.

Next, an example will be explained.

As a liquid crystal material, a mixture of the following compounds at a weight ratio of 1:1:1 was used, and a light receiver was placed at the observer 14 in Figure 2 to measure the amount of light. Light transmission ratio of liquid crystal with and without additive (light transmission amount of liquid crystal containing additive) The amount of light transmission of liquid crystal without additive was measured, and the results were as shown in the following table.

In this case, the thickness of the liquid crystal layer was 10 microns, and measurements were taken at room temperature (20°C).

A photodiode is used as the receiver, and the measurement area of the liquid crystal layer 1
The distribution of the values of X within a square centimeter area was determined.

In the above table, at m-3, the effect of the additive appears to some extent, but the formation of the homeotropic structure did not reach the majority of the measured area, and was not at a practical level.

When m≧10, the effect of the additive is significant, and the value of X becomes small in most of the measurement area, exhibiting a practical homeotropic structure.

As described above, according to the present invention, it is possible to make a nematic liquid crystal exhibit a homeotropic structure, so that effective display can be performed using this.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view of a liquid crystal display device, and FIG. 2 is a schematic view of an apparatus for determining whether or not liquid crystal exhibits a homeotropic structure.

Claims (1)

[Scope of Claims] 1. A liquid crystal display device comprising a nematic liquid crystal material which is made to exhibit a homeotropic structure by adding a compound represented by the following general formula. -〇-(CH2)m-For CH3, when n = 1, it is the para position, and when n22, it is the meta position.