JPH0659240A - Liquid crystal display - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize excellent monochrome display having a memory property in a phase plate type STN-LCD. [Structure] The applied voltage-transmittance characteristic of a liquid crystal cell has a hysteresis, and there is a different state in the rising process and the falling process of the voltage due to the hysteresis. , At the point just before the light incident from the outside of the other polarizing plate enters one polarizing plate,
A liquid crystal display device which is approximately linearly polarized light with respect to light of at least red, green, and blue wavelengths, and whose direction is substantially the same as the absorption axis of one polarizing plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device,
In particular, the present invention relates to a liquid crystal display device that uses a phase plate type STN-LCD and realizes excellent monochrome display with memory characteristics.

[0002]

2. Description of the Related Art As a conventional technique relating to a liquid crystal display device which realizes excellent black and white display using STN type liquid crystal, for example, a technique described in Japanese Patent Laid-Open No. 63-271415 is known. This prior art is a liquid crystal display device having a liquid crystal cell in which a nematic liquid crystal having a twist angle of 120 to 330 degrees is sandwiched between a pair of polarizing plates disposed opposite to each other between a pair of polarizing plates. By inserting two or more uniaxial polymer films having different optical axis directions, a good black and white display is realized.

[0003]

In the above prior art, the time division ability depends on the steepness of the voltage-transmittance characteristic of the liquid crystal.
An object of the present invention is to provide a liquid crystal display device capable of high time division driving by providing a memory property and realizing good monochrome display.

[0004]

According to the present invention, the object is to provide a liquid crystal cell comprising a pair of polarizing plates, a liquid crystal cell sandwiched between them, and a birefringent film for color compensation. This is achieved by using one whose rate characteristic exhibits hysteresis.

[0005]

Due to the above-mentioned hysteresis characteristic, even if the same voltage is applied, there are two voltages in which the alignment state of liquid crystal molecules in the liquid crystal cell is different in the voltage rising process and the voltage falling process. Therefore, if the birefringent film is optimized so that black display can be realized for one orientation state when this voltage is applied, this element can display black display and white display at the above voltage. Two displays are possible.
That is, it has a memory property.

[0006]

Embodiments of the liquid crystal display device according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing the construction of an embodiment of the present invention, in which 11 and 12 are polarizing plates, 20 is a liquid crystal cell, and 31, 32.
Is a birefringent film, and 40 is a light source. FIG. 2 is a diagram showing the relationship between the voltage applied to the liquid crystal cell 20 and the capacitance of the liquid crystal cell 20. The alignment state of liquid crystal molecules in the liquid crystal cell changes depending on the applied voltage. Since liquid crystal has anisotropy in dielectric constant,
The capacity of the liquid crystal cell changes depending on the orientation state. Here, a liquid crystal cell having a twist angle of about 180 ° to 270 °, that is, a super twisted (STN) type liquid crystal is used, and a spontaneous pitch obtained by adding a chiral substance is more than that of a normally used STN type liquid crystal. If the length is also increased, the relationship between the capacitance of the liquid crystal cell and the applied voltage exhibits a hysteresis characteristic as shown in FIG. That is, even if the same voltage V ₀ is applied, different orientation states occur in the voltage rising process and the voltage falling process. Therefore, if the birefringent films 31 and 32 are optimized so that black display can be realized with respect to the orientation state of FIG. 2A, the optical characteristics shown in FIG. 3 can be obtained. That is, it has a memory characteristic that black display and white display can be realized for the same voltage V ₀ . Normally, a voltage of V ₀ is applied to the liquid crystal cell, and if a voltage of 0 V is once applied and then the voltage is returned to the original V ₀ , black display (state a) is obtained. Conversely, if a voltage of, for example, 2V ₀ is once applied and then returned to the original V ₀ , white display is performed (state b). Further, the state once displayed is held as long as V ₀ is applied. By utilizing the above characteristics, a monochrome display having memory characteristics can be realized.

Next, a method of optimizing the birefringent films 31 and 32 and realizing black display in the orientation state of a will be described.

When the alignment state of the liquid crystal molecules is in the state a, the polarization states immediately after passing through the polarizing plate 11 and the liquid crystal cell 20 are red (R), green (G) and blue (B) as shown in FIG. ), The birefringent film 31, 32
If is not used, the polarizing plate 12 cannot be arranged so that the transmittance is 0 for all wavelengths, and the display is colored. Therefore, by utilizing the fact that the polarization state is changed by transmitting through the birefringent film, black display is realized by using the two birefringent films 31 and 32 by the following method.

First, using the birefringent film 31, R,
The polarization states for the G and B wavelengths are converted into elliptically polarized light inscribed in the same rectangle as shown in FIG. If the polarization state immediately after passing through the birefringent film 31 satisfies the condition of FIG. 5, the optical axis 51 of the birefringent film 32 is set in the direction parallel to one side of the rectangle, and the birefringent film 32 is formed.
The polarization state of each wavelength can be made to coincide with the diagonal direction of the rectangle by appropriately selecting the phase difference generated in (1). Therefore, black display can be realized by setting the absorption axis 52 of the polarizing plate 12 in the diagonal direction. In other words, this means that R, G, B immediately after passing through the birefringent film 31.
Birefringent film 3 of the electric field representing the polarized light with respect to the wavelength of
The ratio of the absolute value of the vertical component to the absolute value of the component parallel to the optical axis 51 of the second optical axis 51 is substantially equal to each other, and the diagonal direction of both absolute values is substantially the same as the absorption axis of the polarizing plate 12. . At this time, if the product Δnd of the thickness d of the liquid crystal cell and the refractive index anisotropy Δn of the liquid crystal is set to about 0.5 to 1.0 μm, which is about the same as that of a normal STN liquid crystal, white display is realized in the state of b. it can.

[0011]

As described above, the liquid crystal display device of the present invention is a combination of a liquid crystal cell having hysteresis in voltage-transmittance characteristics and a member having birefringence, and a voltage in a region where hysteresis is generated is applied. By limiting the characteristics of the member having birefringence so that black display can be realized with respect to the liquid crystal cell in which it is present, it is possible to realize a good monochrome display having a memory property.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating a hysteresis characteristic of an example of the present invention.

FIG. 3 is a diagram showing a relationship between an applied voltage and a transmittance according to an example of the present invention.

FIG. 4 is a diagram showing a polarization state immediately after passing through the liquid crystal cell 20 of the example of the invention.

FIG. 5 is a diagram showing a polarization state immediately after passing through the birefringent film 31 of the example of the invention.

[Explanation of symbols]

11, 12 ... Polarizing plate, 20 ... Liquid crystal cell, 31, 32 ... Birefringent film, 51 ... Optical axis of birefringent film 32, 52 ... Absorption axis of polarizing plate 12.

Claims (2)

[Claims] 1. A liquid crystal cell in which liquid crystal is inserted between a pair of substrates having electrodes between a pair of polarizing plates, and at least one member having birefringence, and one polarizing plate having birefringence. In the liquid crystal display device in contact with, the applied voltage-transmittance characteristic of the liquid crystal cell has a hysteresis, and there is a different state in the rising process and the falling process of the voltage due to the hysteresis. In one state, at least immediately before the light incident from the outside of the other polarizing plate enters one polarizing plate, at least red, green,
A liquid crystal display device, which is approximately linearly polarized light with respect to light of a blue wavelength, and whose direction is substantially the same as the absorption axis of one polarizing plate. 2. A liquid crystal cell in which liquid crystal is inserted between a pair of substrates having electrodes between a pair of polarizing plates, and at least one member having birefringence, one polarizing plate having birefringence. In the liquid crystal display device in contact with, the applied voltage-transmittance characteristic of the liquid crystal cell has a hysteresis, and there is a different state in the rising process and the falling process of the voltage due to the hysteresis. In one state, at the point immediately before the light incident from the outside of the other polarizing plate enters the member having the first birefringence, the polarization of the light of at least red, green, and blue wavelengths is changed. The ratio of the absolute value of the perpendicular component to the absolute value of the component parallel to the optical axis of the member having the first birefringence of the electric field represented is almost equal, and the diagonal direction of both absolute values is the absorption of one polarizing plate. Almost coincides with the axis The liquid crystal display device which is a light.