JPS62506B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a so-called twisted nematic material in which the helical axis is perpendicular to the two substrates and the long axis of the liquid crystal molecules is twisted substantially by 90 degrees between the substrates. The present invention relates to a multilayer twisted nematic liquid crystal display device in which liquid crystal display cells each having a liquid crystal inserted therein are multilayered.

Twisted nematic liquid crystal display devices exhibit strong anisotropy, that is, visual dependence, in display contrast when an effective voltage is applied within three times the threshold voltage for optical effects when driving the liquid crystal. known (Funada, Ueda, Wada, Mito; Applied Physics, 44 , 866, 1975). This visual dependence is determined by the twist direction (chirality) of the liquid crystal molecules and the slight tilt direction (tilt angle) of the liquid crystal molecules with respect to the substrate surface. Therefore, within the same liquid crystal cell, all liquid crystal molecules are aligned with the same chirality and tail angle, and the best contrast region resulting from this alignment is most often aligned with the direction in which the liquid crystal cell is observed. It is being This is important in manufacturing a twisted nematic liquid crystal display device in order to obtain a high quality display (Japanese Patent Laid-Open No. 51-4996).

The liquid crystal cell of the twisted nematic liquid crystal display device as described above is multilayered, and an electrode structure is configured to partially apply an electric field to each liquid crystal layer.
A multilayer twisted nematic liquid crystal display device comprising a drive circuit for applying a set voltage to each electrode has already been proposed in ``Japanese Patent Laid-Open No. 50-794''. This type of multilayer twisted nematic liquid crystal display device has the following features compared to a single layer device.

[1] Display designs can be diversified.

[2] Electro-optical logic circuits can be formed.

[3] When displaying by multiplex driving, the number of picture elements can be increased by the number of layers if the voltage application time (duty factor) applied to each picture element is kept constant.

However, on the other hand, there is a problem in that the display quality deteriorates due to the multilayer structure, which has been a major obstacle to practical use as a display device.

In view of the above-mentioned drawbacks, the present invention makes full use of technical means to provide a novel and useful display characterized by a liquid crystal molecule orientation direction that does not cause deterioration of display function even when a twisted nematic liquid crystal display cell is made into multiple layers. The purpose is to provide a device.

FIG. 1 is a sectional view showing the structure of a liquid crystal display device in which a twisted nematic liquid crystal cell has a two-layer structure.

Three transparent substrates 1a, 1b made of glass etc.
1c are arranged facing each other, and each transparent substrate 1a, 1
A nematic liquid crystal layer (or a cholesteric liquid crystal layer with a long pitch) 2a,
2b is interposed. Further, in order to apply a driving voltage to the liquid crystal layers 2a, 2b, transparent electrodes 3a, 3b, 3c, 3d made of In ₂ O ₃ etc. are connected to the transparent substrates 1a, 1
Transparent electrodes 3a and 3 are deposited on top of b and 1c.
b is connected to a voltage source 4a to drive the liquid crystal layer 2a, and transparent electrodes 3c and 3d are connected to a voltage source 4b to drive the liquid crystal layer 2b. Transparent electrodes 3a, 3
On the surfaces of b, 3c, 3d and the transparent substrates 1a, 1b, 1c facing the liquid crystal, there is an alignment layer which has been subjected to preferential alignment treatment to determine the molecular alignment of the liquid crystal by a rubbing method, an oblique evaporation method, etc. 5a, 5b, 5c, 5d
is covered. The peripheral edges of the transparent substrates 1a, 1b, 1c are sealed with sealing materials 6a, 6b made of epoxy resin, fritted glass, etc., thereby forming a liquid crystal cell. Linear polarizing filters 7a, 7b made of yaws or polyenes are provided on the outer surfaces of the transparent substrates 1a and 1c, and a scattering/reflecting plate 8 is arranged on the back side of the liquid crystal cell. The polarizing filters 7a and 7b visualize the display based on the orientation change of liquid crystal molecules. Transparent electrodes 3a, 3
By applying voltages to b, 3c, and 3d, a display is performed to the observer 9 through the optical effect based on the orientation change of the liquid crystal layers 2a, 2b.

FIGS. 2A, B, C, D, and E are explanatory diagrams showing the alignment directions of liquid crystal molecules on the alignment layers 5a, 5b, 5c, and 5d surfaces of the liquid crystal display device shown in FIG. 1 and in the entire liquid crystal cell. be. 2A and 2B show the alignment state of the liquid crystal layer 2a, FIG. 2A corresponds to the alignment state on the alignment layer 5a, and FIG. 2B corresponds to the alignment state on the alignment layer 5b. Also, the twist direction is a left-handed thread system. FIGS. 2C and 2D show the alignment state of the liquid crystal layer 2b, and FIG.
corresponds to the orientation state on the orientation layer 5c, and FIG. 2D corresponds to the orientation state on the orientation layer 5d. The twist direction is also a left-handed screw system. In addition, 〓 ² ₂ , 〓 ² ₁ , 〓 in the figure
¹ ₂ , 〓 ¹ ₁ is a vector indicating the alignment direction of liquid crystal molecules. FIG. 3 is an explanatory diagram showing the tilt angle of the liquid crystal layers 2a and 2b. As defined in FIG. 3, the liquid crystal layers 2a, 2b are transparent substrates 3a, 3b,
This direction has a tilt angle Δθ with respect to 3c and 3d.

When the liquid crystal layers 2a and 2b are set in the alignment state shown in FIG. When an electric field is applied to the display surface, a uniform display contrast is not provided, resulting in a decrease in display quality. That is, as shown in FIG. 2E, the areas with good contrast for display are the dotted line area 10 for the liquid crystal layer 2a and the diagonal line area 11 for the liquid crystal layer 2b, so each liquid crystal layer 2a, 2b The area with good contrast will no longer match the contrast, which will cause problems in display.

The present invention is to set the alignment state of a liquid crystal layer periodically and similarly with respect to a helical axis, and will be described in detail below according to an embodiment with reference to the drawings.

FIGS. 4A, B, C, D, and E are explanatory diagrams showing the orientation directions of liquid crystal molecules in a two-layer structure liquid crystal cell that is one embodiment of the present invention.

The structure of the liquid crystal cell is the same as that shown in FIG.
Soda glass having a thickness of about 3 mm, transparent electrodes 3a, 3b, 3c, and 3d patterned by etching or the like in accordance with the display are made of In ₂ O ₃ , and alignment layers 5a, 5b, 5c, and 5d are made of SiO _{2 .} It is formed into a thin film by electron beam evaporation and then rubbed in a certain direction with cloth or the like. Liquid crystal layers 2a, 2b
is a biphenyl liquid crystal with a layer thickness of approximately 7 μm and containing a very small amount of cholesteryl nonanoate.
Adopts ROTN403 (manufactured by Roche). The sealing materials 6a, 6b are made of epoxy resin used for screen printing, etc., and the polarizing filters 7a, 7b are L-83-18 type manufactured by Sanritsu Electric. Further, the scattering reflector plate 8 is made of a sandblasted aluminum plate. The alignment direction of the liquid crystal layer 2a is a direction having 〓 ² ₂ on the alignment layer 5a and 〓 ² ₁ on the alignment layer 5b as shown in FIGS. 4A and 4B, and the orientation direction of the liquid crystal layer 2b is As shown in FIGS. 4C and 4D, the direction 〓 ² ₁ on the orientation layer 5c and the direction 〓 ¹ ₁ on the orientation layer 5d are assumed.
The tail angle Δθ is set in a range of about 2 to 3 degrees.

With the above configuration, the area with good contrast for display is the shaded area 1 shown in FIG. 4E.
2, and the liquid crystal layers 2a and 2b in each liquid crystal cell
The good contrast regions of both coincide in the same 1/4 quadrant determined by the orientation direction.

Incidentally, the constituent materials of the liquid crystal cell are not limited to those in the above embodiments, and the multilayer structure can also have three or more layers.

As explained in detail above, in a multilayer liquid crystal display device in which twisted nematic liquid crystal cells are multilayered, the display function can be increased by making the orientation direction of liquid crystal molecules in each liquid crystal layer periodic and similar. , good display quality is maintained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a two-layer liquid crystal display device. FIGS. 2A, B, C, D, and E are explanatory diagrams showing the alignment directions of liquid crystal molecules for explaining the present invention. FIG. 3 is an explanatory diagram for defining a vector 〓 indicating the alignment direction of liquid crystal molecules. Figure 4 A, B,
C, D, and E are explanatory views of liquid crystal molecule alignment directions showing one embodiment of the present invention. 1a, 1b, 1c...transparent substrate, 2a, 2b...
...Liquid crystal layer, 3a, 3b, 3c, 3d...Transparent electrode, 5a, 5b...Alignment layer, 7a, 7b...Polarizing filter.

Claims (1)

[Claims] 1. At least three cell substrates each having an alignment layer that determines the alignment direction (orientation) of liquid crystal molecules are laminated,
In a multilayer liquid crystal display device in which a twisted nematic alignment liquid crystal layer in which the long axis of the liquid crystal molecules is substantially twisted by 90 degrees is interposed between each cell substrate gap, the front and back surfaces of the central cell substrate arranged in the center are The alignment directions of the alignment layers formed on both surfaces are orthogonal to each other, and between the central cell substrate and two opposing cell substrates disposed facing the central cell substrate in both front and back directions, the alignment layers of both of the opposing cell substrates are and the alignment direction of the alignment layer located on the back side of the facing position of the central cell substrate are made to match, so that the twist directions of the liquid crystal layers layered in the front and back directions of the central cell substrate are made the same. Features of multilayer liquid crystal display device.