JPH0943596A - Reflection type liquid crystal display element and liquid crystal display device formed by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bright reflection type liquid crystal display element with which the polarization state on a reflection plate is circularly polarized light regardless of wavelengths. SOLUTION: This reflection type liquid crystal display element is constituted by laminating a polarizing plate 10, a liquid crystal cell 20, a first double refractive film 30, a second double refractive film 40 and the reflection plate 50. The twist angle of the liquid crystal molecules in the liquid crystal cell is in a range from 220 to 260 deg. and the double refractive anisotropy Δnd of the liquid crystals in range from 600 to 800nm. The angle formed by the transmission axis 11 of the polarizing plate 10 and the optical axis 31 of the first double refractive film 30 is in a range from -10 to 15 deg., the Δnd of the first double refractive film 30 in a range from 330 to 460nm, the angle formed by the transmission axis 11 of the polarizing plate 10 and the optical axis 41 of the second double refractive film 40 in a range from 55 to 95 deg. and the Δnd of the second double refractive film 40 in a range from 220 to 270nm.

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 using a liquid crystal, and more particularly to a reflection type liquid crystal display device which realizes a bright display without using a backlight.

[0002]

2. Description of the Related Art As a conventional technique, Japanese Patent Application Laid-Open No. 2-1895
No. 19 and Japanese Patent Laid-Open No. 6-11711. According to this prior art, polarizing plate / liquid crystal cell / reflector, or polarizing plate / birefringent film / liquid crystal cell /
By using the configuration of the reflector and removing the polarizing plate on the reflector side from a reflective liquid crystal display element or the like using a commonly used STN liquid crystal cell, high brightness can be obtained.

[0003]

However, in the above-mentioned structure of polarizing plate / birefringent film / liquid crystal cell / reflector of the prior art, the birefringent film is circularly polarized on the reflector regardless of wavelength. It has been known that a good black display can be obtained by optimizing the above, but the optimization condition of the birefringent film for that is not clear, and there remains the problem of clarifying this and obtaining the optimum black and white display. ing. Therefore, an object of the present invention is to provide a reflection type liquid crystal display element which can obtain a good black and white display with high reflectance and a liquid crystal display device using the same.

[0004]

The above object is to provide a liquid crystal cell in which liquid crystal is inserted between a pair of substrates having electrodes, one polarizing plate arranged on one side of the liquid crystal cell, and one polarizing plate arranged on the other side. It is composed of a reflection plate and two birefringent films arranged between the liquid crystal cell and the reflection plate, and in the liquid crystal cell, liquid crystal molecules are 220 ° to 260 ° from one substrate to the other substrate. The structure is twisted in the range of, and the refractive index anisotropy Δn of the liquid crystal and the distance d between the substrates are
And a product Δnd of the product is in the range of 600 nm to 800 nm, and an angle formed by the transmission axis of the polarizing plate and the optical axis of the first birefringent film is in the range of −10 ° to 15 °. Δnd of the birefringent film of 1 is in the range of 330 nm to 460 nm,
The angle formed by the transmission axis of the polarizing plate and the optical axis of the second birefringent film is in the range of 55 ° to 95 °, and Δnd of the second birefringent film is in the range of 220 nm to 270 nm. This is achieved by a reflective liquid crystal display device.

Alternatively, the angle between the transmission axis of the polarizing plate and the optical axis of the first birefringent film is in the range of 15 ° to 40 °, and Δnd of the first birefringent film is 130 nm.
To 270 nm, the angle between the transmission axis of the polarizing plate and the optical axis of the second birefringent film is in the range of 130 ° to 180 °, and Δnd of the second birefringent film is Ten
It can be achieved even with a reflective liquid crystal display device in the range of 90 nm to 90 nm.

Further, the angle formed by the transmission axis of the polarizing plate and the optical axis of the first birefringent film is in the range of 50 ° to 105 °, and Δnd of the first birefringent film is 30 nm.
To 140 nm, the angle between the transmission axis of the polarizing plate and the optical axis of the second birefringent film is in the range of 5 ° to 30 °, and Δnd of the second birefringent film is , 19
0 nm to 270 nm, or the angle between the transmission axis of the polarizing plate and the optical axis of the first birefringent film is in the range of 140 ° to 180 °, the first birefringence The Δnd of the film is in the range of 150 nm to 210 nm, and the angle formed by the transmission axis of the polarizing plate and the optical axis of the second birefringent film is in the range of 95 ° to 120 °. A reflective liquid crystal display device in which Δnd of the refractive film is in the range of 200 nm to 260 nm may be used.

On the other hand, a liquid crystal display device which achieves the above object uses two birefringent films, and the characteristics of the two birefringent films are circularly polarized with respect to the wavelengths of the three primary colors of light. The reflective liquid crystal display device according to any one of claims 1 to 4 is specified.

[0008]

According to the above construction, a solution that uses two birefringent films and has a characteristic that the two birefringent films are circularly polarized at least for the wavelengths of the three primary colors of light is obtained. Since the heading can be specified, it is possible to meet the optimum conditions for obtaining good black and white display on the reflector. Therefore, in the liquid crystal display element composed of the above specified two birefringent films and the liquid crystal display device using the same, bright display is realized without using a backlight.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the structure of a liquid crystal display element of one embodiment according to the present invention. In the liquid crystal display element of the example, the polarizing plate 10, the
For example, it has a structure in which an STN type liquid crystal cell 20, a first birefringent film 30, a second birefringent film 40, and a reflection plate 50 are laminated. The illustrated angles φ0, φ1, and φ2 are the angle (φ0) formed by the transmission axis 11 of the polarizing plate 10 and the rubbing axis 21 on the polarizing plate side of the liquid crystal cell 20, respectively, and the transmission axis 11 of the polarizing plate and the first compound axis. It is an angle (φ1) formed by the optical axis 31 of the refractive film and an angle (φ2) formed by the transmission axis 11 of the polarizing plate and the optical axis 41 of the second birefringent film.

A method for realizing optimum black and white display using this configuration will be described below. The above-mentioned problem of circularly polarized light cannot be solved only by using one birefringent film, and therefore, there is used a polarizing plate, a liquid crystal cell, a first birefringent film, and a second birefringent film. , The reflective plate is laminated in this order, and the specification for optimizing the characteristics of the first and second birefringent films is performed as described below.

First, before specifying the characteristics of the first and second birefringent films, the polarization state after passing through the polarizing plate and the liquid crystal cell is measured by changing the voltage. Voltage V determined by driving conditions
Normalized Stokes parameters (S1 _OFF , S2 _OFF , S3 _OFF ), which represent polarization state when _OFF , V _{ON are} applied, (S1 _ON , S2 _ON , S3
_ON ) is used to determine the drive voltage so as to maximize the parameter R calculated by the following equation. R = 1- (S1 _OFF , S1 _ON + S2 _OFF , S2 _ON + S3 _OFF , S3 _ON ) ² (Equation 1) Next, in order to obtain a black display when V _OFF or V _{ON is} applied, 1. Determine the properties of the second birefringent film.

(1) As the first birefringent film, a solution in which the birefringence anisotropy (Δnd) 1 satisfies the following equation for wavelengths λ of red, green and blue is obtained.

Β1 = (2π / λ) · (Δnd) 1 (Equation 2) where β1 = ± α−δ0 ⁽¹⁾ + 2πn1, n1 = (0, 1, 2, ...) And α is , Is given by the following equation.

COSα = − (X · COS2φ ₂₁ ) / (Y · SIN2φ ₂₁ ) (Equation 3) where X = (| E0x ⁽¹⁾ | ² − | E0y ⁽¹⁾ | ² ), Y = 2 | E0x
⁽¹⁾ | ・ | E0y ⁽¹⁾ | E0x ⁽¹⁾ and E0y ⁽¹⁾ are the optics of the first birefringent film of the electric field complex vector corresponding to the light transmitted through the polarizing plate / liquid crystal cell, respectively. Components parallel to the axis, components perpendicular to the axis,
[delta] 0 ⁽¹⁾ is a phase difference E0x ⁽¹⁾ and E0y ^(1). φ ₂₁ is
It is an angle formed by the optical axis of the second birefringent film with respect to the optical axis of the first birefringent film.

(2) As the second birefringent film, a solution in which the birefringence anisotropy (Δnd) 2 satisfies the following equation for the wavelengths λ of red, green and blue is obtained. β2 = (2π / λ) · (Δnd) 2 (Equation 4) where β2 = π / 2−δ1 ⁽²⁾ + πn2 n2 = (0, 1, 2, ...) where δ1 ⁽²⁾ is Polarizer / Liquid crystal cell / Second of electric field complex vector corresponding to light transmitted through first birefringent film
It is the phase difference between the component parallel to the optical axis of the birefringent film and the component perpendicular thereto.

Here, the principle of the present invention will be described using the basic configuration of FIG. Polarizing plate 10, liquid crystal cell 20,
In the case of a reflective LCD including the first birefringent film 30, the second birefringent film 40, and the reflector 50, the normally white mode is effective, and therefore, it is considered that black display is performed when V _{ON is} applied. When black is displayed when V _{ON is} applied, the reflectance when V _{OFF is} applied corresponds to the parameter R given by the formula (1) for the light after passing through the polarizing plate / liquid crystal cell. Therefore, if V _OFF and V _ON are selected so that R becomes the maximum, when the black display is obtained when V _{ON is} applied by optimizing the birefringent film, V
The reflectance is maximum when _{OFF is} applied. In the present invention,
In this way, before optimizing the birefringent film,
Optimal drive conditions can be determined.

Next, the characteristics of the first birefringent film are selected so as to satisfy the formulas (2) and (3) with respect to the light having the wavelengths of red, green and blue when V _{ON is} applied, and If the characteristics of the second birefringent film are selected so as to satisfy the equation (4), the light corresponding to the light of these wavelengths on the reflection plate will be the same circularly polarized light. In other words, the polarization state on the reflection plate becomes circularly polarized light regardless of the wavelength, and good black display is realized. Ideally,
It is desirable that the circularly polarized light be the same for all visible wavelengths, but it can be said that visually good black display can be realized if the conditions are satisfied at the wavelengths of the three primary colors of light, red, green, and blue. . As described above, by adopting the configuration of FIG. 1 and obtaining the solution that satisfies the equations (2, 3, 4) and specifying the characteristics of the birefringent film, the circularly polarized light on the reflection plate is It can be realized and the problems of the prior art can be solved.

Next, an embodiment represented by specific numerical values will be described. As described above, each birefringent film 30, 4
The reflectance of white display when black display is obtained by optimizing 0 corresponds to the parameter R defined by the equation (1). FIG. 2 is a diagram showing the relationship between the applied voltage V _OFF in the OFF state and the parameter R. The twist angle of the liquid crystal cell 20 is 2
40 ° and Δnd are 0.5, 0.6, 0.7 and 0.8. The value of R depends on the angle φ0 formed by the transmission axis 11 of the polarizing plate 10 and the rubbing axis 21 of the liquid crystal cell 20, but usually has the maximum value when φ0 = 45 °, so here, φ0 = 45 °. It is known that there is a relationship of the formula (5) between the voltages V _ON and V _OFF applied in the ON state and the OFF state.

V _ON / V _OFF = √ ((√N + 1) / (√N−1)) (Equation 5) This formula can be realized by driving V at 1 / N duty.
_This is an expression that gives the maximum value of _ON / V _OFF . From this figure, for example, when Δnd of the liquid crystal is 0.6, to maximize R, V
It turns out that _OFF = 2.14 (V).

Next, each birefringent film 30, 40 is optimized. The twist angle of the liquid crystal cell 20 is 240 °, Δnd
An example will be described where is 0.6. First, in the case of the reflective type, since the normally white mode is effective, it is optimized so that black display is realized when V _{ON is} applied. That is, V _ON is obtained by substituting V _OFF = 2.14 (V) into the equation (5). Next, the first birefringent film 30
(Δnd) 1 of is determined from the conditions of the expressions (2) and (3). Here, E0x ⁽¹⁾ , E0y ⁽¹⁾ , and δ0 ⁽¹⁾ are obtained as a parallel component, a vertical component, and a phase difference when V _ON is applied to the liquid crystal cell 20. Of the second birefringent film 40
(Δnd) 2 is determined from the condition of Expression (4). Where δ 1 ⁽²⁾
Is calculated as a phase difference when V _ON is applied to the liquid crystal cell 20.

Δnd satisfying these conditions is obtained with respect to the wavelength λ, and if a birefringent film having an optimum value of Δnd with respect to an arbitrary wavelength is obtained, there are innumerable optimal solutions. However, in general, there are no materials that satisfy an infinite number of optimal solutions, and the wavelength characteristics of Δnd are limited. Therefore, the feature of the present invention is that the wavelength λ is set to be at least the wavelengths of the three primary colors of light, that is, the wavelengths of red, green, and blue.
Considering only 0 nm, 555 nm, and 450 nm, and normally, Δnd of red wavelength is smaller than Δnd of green wavelength, and the ratio is
It is about 0.95, and Δnd of blue wavelength is Δnd of green wavelength.
Considering that the ratio is about 1.2,
It seeks a solution.

When a solution satisfying this condition is selected, it has been found that there is a relationship shown in FIG. 3 among φ1, φ2, (Δnd) 1 and (Δnd) 2. In the figure, (Δnd) 1,
(Δnd) 2 is the solution for the green wavelength of 555 nm. FIG. 3 is a diagram showing solutions of φ1φ2, (Δnd) 1, and (Δnd) 2 for realizing black display in the liquid crystal display element of one embodiment according to the present invention. Figure 3 (a) shows the relationship between φ1 and φ2, and Figure 3 (b) shows φ
The relationship between 1 and (Δnd) 1 and (Δnd) 2 is shown. As shown, one of these obtained solutions is φ1 = 12 °, φ
It can be seen that 2 = 92 °, (Δnd) 1 = 393 nm, and (Δnd) 2 = 252 nm.

FIG. 4 is a diagram showing applied voltage-reflectance characteristics of the liquid crystal display device obtained by the solution of FIG. The reflectance with respect to the applied voltage of one Example of a liquid crystal display element is shown. FIG. 5 is a diagram showing the wavelength dependence of the reflectance of the liquid crystal display element obtained by the solution of FIG. 5A shows the relationship between φ1 and φ2, and FIG. 5B shows the relationship between φ1 and (Δnd) 1 and (Δnd) 2. The wavelength dependence of the reflectance during black display and white display is shown. It can be seen that a good black display is realized.

Similarly, a solution that can be optimized is obtained by setting the twist angle in the range of 220 ° to 260 ° and Δnd in the range of 0.6 to 0.8.
Liquid crystal cells in the range up to were determined. FIG. 6 is a diagram showing general solutions of φ1, φ2, (Δnd) 1, and (Δnd) 2 for realizing black display in the liquid crystal display element of the embodiment according to the present invention. It has been found that when the twist angle and the value of Δnd are in the above ranges, the general optimization solution is classified into the following four patterns regardless of the value of the twist angle and the value of Δnd.

Pattern I: φ1 = -10 ° to 15 °, φ
2 = 55 ° to 95 °, (Δnd) 1 = 330 to 460 nm, (Δnd) 2 = 2
20-270nm Pattern II: φ1 = 15 ° -40 °, φ2 = 130 ° -18
0 °, (Δnd) 1 = 130 to 270 nm, (Δnd) 2 = 10 to 90 nm Pattern III: φ1 = 50 ° to 105 °, φ2 = 5 ° to 30 °
°, (Δnd) 1 = 30 to 140 nm, (Δnd) 2 = 190 to 270 nm Pattern IV: φ1 = 140 ° to 180 °, φ2 = 95 ° to 12
0 °, (Δnd) 1 = 150 to 210nm, (Δnd) 2 = 200 to 260nm

[0026]

According to the present invention, a reflective liquid crystal display which is bright and has a high contrast ratio can be provided. Since it does not require a backlight, it has low power consumption and can be used for a display of a portable information device to significantly improve battery consumption time.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the configuration of a liquid crystal display element of one embodiment according to the present invention.

FIG. 2 is a diagram showing a relationship between an applied voltage V _{OFF in an} OFF state and a parameter R.

FIG. 3 is a diagram showing solutions of φ1, φ2, (Δnd) 1, and (Δnd) 2 for realizing black display in the liquid crystal display element of one embodiment according to the present invention.

4 is a voltage applied to the liquid crystal display device obtained by the solution of FIG.
It is a figure which shows a reflectance characteristic.

5 is a diagram showing the wavelength dependence of the reflectance of the liquid crystal display device obtained by the solution of FIG.

FIG. 6 is a diagram showing general solutions of φ1, φ2, (Δnd) 1, and (Δnd) 2 for realizing black display in the liquid crystal display element of the example according to the present invention.

[Explanation of symbols]

10 ... Polarizing plate, 11 ... Transmission axis, 20 ... Liquid crystal cell, 21 ...
Rubbing shaft, 30 ... First birefringent film, 31, 4
1 ... Optical axis, 40 ... 2nd birefringent film, 50 ... Reflector, 60 ... External light

Front page continuation (72) Inventor Ikuo Hiyama 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Katsumi Kondo 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Yoshiaki Nakamura 3681 Hayano, Mobara-shi, Chiba Hitachi Device Engineering Co., Ltd.

Claims (5)

[Claims] 1. A liquid crystal cell in which a liquid crystal is inserted between a pair of substrates having electrodes, one polarizing plate disposed on one side of the liquid crystal cell, a reflector disposed on the other side, the liquid crystal cell, and It is composed of two birefringent films arranged between the reflection plates, and has a structure in which liquid crystal molecules are twisted in the range of 220 ° to 260 ° from one substrate to the other substrate in the liquid crystal cell. The product Δnd of the refractive index anisotropy Δn of the liquid crystal and the distance d between the substrates is in the range of 600 nm to 800 nm, and the transmission axis of the polarizing plate and the optical axis of the first birefringent film are The angle is −10 ° to 15 °, Δnd of the first birefringent film is in the range of 330 nm to 460 nm, and the transmission axis of the polarizing plate and the second birefringent film are The angle formed by the optical axes is in the range of 55 ° to 95 °, and the second birefringent film is used. Reflection type liquid crystal display device Δnd of, characterized in that in the range of 270nm from 220 nm. 2. A liquid crystal cell in which a liquid crystal is inserted between a pair of substrates having electrodes, one polarizing plate arranged on one side of the liquid crystal cell, a reflecting plate arranged on the other side, the liquid crystal cell, and It is composed of two birefringent films arranged between the reflection plates, and has a structure in which liquid crystal molecules are twisted in the range of 220 ° to 260 ° from one substrate to the other substrate in the liquid crystal cell. The product Δnd of the refractive index anisotropy Δn of the liquid crystal and the distance d between the substrates is in the range of 600 nm to 800 nm, and the transmission axis of the polarizing plate and the optical axis of the first birefringent film are The angle formed is in the range of 15 ° to 40 °, the Δnd of the first birefringent film is in the range of 130 nm to 270 nm, the transmission axis of the polarizing plate and the optics of the second birefringent film. The angle formed by the axes is in the range of 130 ° to 180 °, and the second birefringent film Δnd is, reflection type liquid crystal display device, characterized in that in the range of 10nm to 90 nm. 3. A liquid crystal cell in which a liquid crystal is inserted between a pair of substrates having electrodes, one polarizing plate arranged on one side of the liquid crystal cell, a reflecting plate arranged on the other side, the liquid crystal cell, and It is composed of two birefringent films arranged between the reflection plates, and has a structure in which liquid crystal molecules are twisted in the range of 220 ° to 260 ° from one substrate to the other substrate in the liquid crystal cell. The product Δnd of the refractive index anisotropy Δn of the liquid crystal and the distance d between the substrates is in the range of 600 nm to 800 nm, and the transmission axis of the polarizing plate and the optical axis of the first birefringent film are The angle formed is in the range of 50 ° to 105 °, the Δnd of the first birefringent film is in the range of 30 nm to 140 nm, the transmission axis of the polarizing plate and the optics of the second birefringent film. The angle formed by the axes is in the range of 5 ° to 30 °, and the second
The reflective liquid crystal display device, wherein Δnd of the birefringent film is in the range of 190 nm to 270 nm. 4. A liquid crystal cell in which liquid crystal is inserted between a pair of substrates having electrodes, one polarizing plate disposed on one side of the liquid crystal cell, a reflector disposed on the other side, the liquid crystal cell, and It is composed of two birefringent films arranged between the reflection plates, and has a structure in which liquid crystal molecules are twisted in the range of 220 ° to 260 ° from one substrate to the other substrate in the liquid crystal cell. The product Δnd of the refractive index anisotropy Δn of the liquid crystal and the distance d between the substrates is in the range of 600 nm to 800 nm, and the transmission axis of the polarizing plate and the optical axis of the first birefringent film are The angle formed is in the range of 140 ° to 180 °, the Δnd of the first birefringent film is in the range of 150 nm to 210 nm, the transmission axis of the polarizing plate and the optics of the second birefringent film. The angle formed by the axes is in the range of 95 ° to 120 °, and the second birefringent film Δnd is in the range of 200 nm to 260 nm, which is a reflective liquid crystal display device. 5. Using two birefringent films, and
5. The reflective liquid crystal display device according to claim 1, wherein the characteristics of the two birefringent films are specified so as to be circularly polarized with respect to the wavelengths of the three primary colors of light. A liquid crystal display device characterized by the above.