JPH0721591B2 - Liquid crystal display - Google Patents

Description

TECHNICAL FIELD The present invention relates to a liquid crystal display device capable of high duty dynamic driving.

[Prior Art] FIG. 2 is an exploded perspective view showing a liquid crystal cell structure of a conventional liquid crystal display device. In the figure, reference numeral 1 denotes a liquid crystal layer in which liquid crystal molecules are homogeneously aligned, transparent electrodes 2a and 2b are arranged on both sides, and are sandwiched by glass substrates 3a and 3b from the outside. A drive power source 4 and a switch 5 are connected to the transparent electrodes 2a and 2b, and polarizing plates 6a and 6b are arranged on both sides of the liquid crystal cell formed by the glass substrates 3a and 3b.
The polarization directions A and B of the polarizing plates 6a and 6b are orthogonal to each other.

Polarizer 6a and liquid crystal cell as shown by arrow C in the figure, and further polarizer 6b
The intensity I of the transmitted light that passes through and is emitted is given by I = I ₀ sin ² (πR / λ) from the condition of interference between ordinary light and extraordinary light. However, I ₀ is the intensity of light incident on the liquid crystal cell, λ is its wavelength, and R is an amount indicating the optical path difference between ordinary light and extraordinary light called retardation. This retardation R is represented by R = Δn · d in the state where no voltage is applied in the cell of homogeneous orientation. Here, Δn is a birefringence (ne-no) which is a difference between the extraordinary light refractive index ne and the ordinary light refractive index no, and d is a cell gap.

The transmitted light intensity I has a maximum value I ₀ when R = (m + 1/2) λ, where m is the order of interference, and therefore the wavelength λ is changed to find the condition that the transmitted light intensity I is maximum. The birefringence Δn can be determined from the above equation by measuring the interference order m at the wavelength λ of. That is, in the case of the P-type nematic liquid crystal, when a voltage is applied to the cell and its value is increased, the liquid crystal molecules change their orientation in the direction perpendicular to the glass substrates 3a and 3b. Since the retardation R decreases accordingly, the intensity I of transmitted light changes periodically according to the above equation.

In this way, the polarization direction of the transmitted light incident from one polarizing plate 6a changes when passing through the liquid crystal layer 1, and the ON-OFF state of the liquid crystal cell is determined by the change in the transmitted light intensity.
As a result, the liquid crystal cell can be used as the display means, and the liquid crystal display device functions.

[Problems to be solved by the invention]

However, in the conventional liquid crystal display device as described above, the polarization state of the transmitted light is simply changed by the liquid crystal molecules, and a good threshold characteristic of the applied voltage cannot be obtained, and high duty dynamic driving cannot be performed. However, there is a problem that the orientation means is difficult.

The present invention has been made in view of these problems, and an object thereof is to provide a liquid crystal display device capable of high-duty dynamic driving and having no difficulty in the alignment direction.

[Means for solving problems]

The liquid crystal display device of the present invention is a liquid crystal display device in which polarizing plates are disposed on both sides of a two-layer liquid crystal cell, and the two liquid crystal layers have a substantially same retardation and a positive dielectric anisotropy. It is a homogeneous array containing liquid crystals, and the alignment directions at the boundaries of liquid crystal layers of each other are arranged to be orthogonal to each other, and the polarizing plates disposed on both sides have polarization directions of the polarizing plates that are parallel or orthogonal to each other. It is arranged so that the direction forms an angle of 45 degrees with the alignment direction at the boundary of the liquid crystal layer.

[Action]

The light incident from one of the polarizing plates is birefringent in the first liquid crystal layer and reaches the second liquid crystal layer. At this time, the components of the ordinary ray and the extraordinary ray are reversed from the second liquid crystal layer, the phase shift is canceled and the original polarization state is restored. Then, the ON-OFF state of the display unit is determined according to the polarization directions of the polarizing plates on both sides of the liquid crystal cell.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.
In addition, in this embodiment, each liquid crystal layer has a homogeneous alignment for easy description.

FIG. 1 is an exploded perspective view showing a main part of a liquid crystal display device according to the present invention. In the figure, 11 is a two-layer liquid crystal cell having a first liquid crystal layer 12 and a second liquid crystal layer 13 whose alignment directions are orthogonal to each other, and the respective alignment directions A and B are directions indicated by arrows in the figure. . Although not shown, transparent electrodes and glass substrates are arranged on both sides (front and rear) of the liquid crystal cell 11, and polarizing plates 14 and 15 are arranged on the outer sides thereof. The polarization direction of the polarizing plate 14 on the incident light side forms an angle of 45 degrees with the alignment direction A of the liquid crystal layer 12 on the polarizing plate side. Further, the polarizing plate 15 on the outgoing light side is set to be in a state of parallel Nicols or the crossed Nicols with the polarizing plate 14 on the incident light side. In case of negative display.

Each of the liquid crystal layers of the two-layer liquid crystal cell 11 is a nematic liquid crystal of positive dielectric anisotropy, and the retardations of the two liquid crystal layers are substantially the same, and the first and second liquid crystal layers 12 and 13 are formed.
Are arranged so that the respective orientation directions at the boundaries of form an angle of 90 degrees.

The light that has entered one of the polarizing plates 14 becomes linearly polarized light and enters the first liquid crystal layer 12. At this time, since the polarization direction of the polarizing plate 14 and the alignment direction of the liquid crystal layer 12 are arranged so as not to be equal to each other, when passing through the first liquid crystal layer 12, the polarization state is changed due to birefringence by the liquid crystal. It becomes elliptically polarized light and reaches the second liquid crystal layer 13. Then, from the second layer, the components of the ordinary ray and the extraordinary ray are reversed, so that the phase shift is canceled and the original linearly polarized state (the same direction as the incident light) is obtained. Therefore, when the polarizing plates 14 and 15 are in parallel Nicols, the "bright" state is set, and in the case of crossed Nicols, the "dark" state, that is, OFF state is set.

When a voltage is applied to the homogeneously aligned liquid crystal layer of the conventional example, the birefringence Δn changes and the retardation R fluctuates as the liquid crystal molecules in the liquid crystal layer undergo an array change in response to the voltage. To do. This change in retardation R becomes larger as the tilt angle of the liquid crystal molecules in the center of the liquid crystal layer is smaller, that is, when the applied voltage is lower.

Therefore, the lower the applied voltage is, the larger the change in the retardation R is, which causes the transmitted light intensity to change greatly as described above.

Therefore, when the display is performed using the conventional homogeneously aligned liquid crystal layer, the retardation R is provided even when the voltage is equal to or lower than the threshold value, so that coloring occurs. Further, in order to eliminate this coloring and obtain a good black level, it is necessary to apply a voltage to adjust the retardation R, so the driving is performed by setting the off voltage higher than the threshold voltage.

On the other hand, in the present invention, since the liquid crystal layers 12 and 13 are two layers, the phase shift is canceled as described above in the case of the threshold voltage or less. Therefore, the ON voltage and the OFF voltage can be lowered as compared with the conventional case, and the threshold voltage and the OFF voltage can be made substantially equal.

Therefore, the driving voltage can be lowered as compared with the conventional case, and in this case, the transmitted light intensity changes very sharply with respect to the applied voltage near a specific voltage (threshold voltage in this example).

This change in transmitted light intensity causes the liquid crystal cell 11 to turn on as described above.
The OFF state changes, and the steepness of the change in transmittance (change in brightness) is improved compared to the conventional liquid crystal cell.

In this way, since it has a steep threshold value characteristic with respect to the applied voltage, high duty dynamic driving becomes possible. In addition, homeotropic alignment ECB (electrica
lly controlled birefringence) without the difficulty of alignment means as seen in cells, and with homogeneous type EC
Since the coloring phenomenon seen in the B type cell does not occur, black and white display is also possible.

〔The invention's effect〕

As described above, according to the present invention, the two liquid crystal layers include nematic liquid crystals having a positive dielectric anisotropy, and the liquid crystal layers are arranged so that the alignment directions at the boundaries of the liquid crystal layers are orthogonal to each other. The polarizing plates disposed on both sides of the two-layer liquid crystal cell are arranged such that the polarizing directions of the polarizing plates are parallel or orthogonal and the polarizing directions are not equal to the alignment direction of the liquid crystal layer. Has a sharp threshold characteristic,
High-duty dynamic driving is possible, there is no difficulty in the orientation means, and black-and-white display is possible.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing an embodiment of the present invention, and FIG. 2 is an exploded perspective view showing a conventional example. 11 …… 2-layer type liquid crystal cell 12 …… First liquid crystal layer 13 …… Second liquid crystal layer 14,15 …… Polarizing plate

Claims (1)

[Claims] 1. A liquid crystal display device having polarizing plates disposed on both sides of a two-layer liquid crystal cell, wherein the two liquid crystal layers include nematic liquid crystals having substantially the same retardation and positive dielectric anisotropy. In a homogeneous arrangement, the alignment directions at the boundaries of the liquid crystal layers of each other are arranged to be orthogonal to each other, and the polarizing plates disposed on both sides of the polarizing plate are parallel or orthogonal to each other, and the polarizing directions are A liquid crystal display device, wherein the liquid crystal display device is arranged so as to form an angle of 45 degrees with the alignment direction at the boundary of the liquid crystal layer.