JP2003315832A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that display is made dark because of large light absorption loss by a polarizing plate in a TN mode display or an STN mode display provided with the polarizing plate and utilizing optical rotatory power and double refraction of a liquid crystal. <P>SOLUTION: The order parameter of dye molecules in the liquid crystal and durability to light, heat, electricity and the like can be enhanced by applying the liquid crystal containing a clathrate compound including the dye molecules to a guest-host mode. Thereby, a guest-host type liquid crystal display element having high luminosity, high contrast and high reliability can be realized. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device capable of realizing high brightness, high contrast ratio and high reliability. The liquid crystal display element of the present invention is a reflective display,
The present invention can be applied to a liquid crystal display device to which general light modulation is applied, such as a transmissive display, a spatial light modulator, an optical switching device for communication, an optical shutter, a lighting device, and a light control glass.

[0002]

2. Description of the Related Art At present, as a display method in a general flat panel display, particularly a liquid crystal display mounted on a portable information terminal device, a TN (Twisted Nematic) mode or STN utilizing birefringence and optical rotatory power of liquid crystal (Super-Twisted Nemat
ic) mode and the like using a polarizing plate is used.

On the other hand, in addition to the above, a polarizing plate represented by a guest-host (GH) system in which dichroic dye molecules are added to liquid crystal, a dynamic scattering mode, a phase transition mode, and a polymer dispersion mode. A transmission / scattering method that does not use is proposed. In these methods, since there is no light loss due to the polarizing plate, brighter display is possible compared to the former.

[0004]

The TN and STN modes utilize the optical rotatory power and birefringence of liquid crystal, and it is necessary to use a polarizing plate. The absorption loss of light in the polarizing plate is about 60%
As a result, the display becomes dark.

Further, in the GH system, when a p-type dye molecule is used, the light absorption of the dichroic dye molecule is maximum when the polarization direction of light is parallel to the long axis of the molecule, and the light traveling direction. It is the minimum when and the long axes of the molecules are parallel. Therefore, the display color of the liquid crystal display element using the commonly used parallel alignment is a binary state when no electric field is applied and a colorless state when an electric field is applied. Here, in order to increase brightness and contrast ratio without using a polarizing plate, a method of forming a GH liquid crystal layer into a multilayer structure and a method of utilizing a phase transition mode of cholesteric liquid crystal are generally known. However, it is difficult to achieve sufficient brightness and contrast at the same time because the order parameter of the dichroic dye molecule itself in the liquid crystal (parallelism of the dye molecule absorption axis to the orientation direction of the host liquid crystal molecule) is low. There is also a problem in the stability of the dye molecule itself against external stimuli such as light, heat, and electricity.

On the other hand, in the method utilizing light scattering,
In general, a black light absorber is provided behind the reflective liquid crystal display element to realize black display when the liquid crystal layer is in a transparent state and white display by back light scattering when the liquid crystal layer is in a scattering state. In the dynamic scattering mode and the phase transition mode, reliability, response speed, driving voltage, etc. are not practical, and therefore the polymer dispersion mode is currently widely studied. In the polymer dispersion mode, the refractive index of the apparent liquid crystal with respect to the polymer is changed depending on the presence or absence of an electric field, and the scattering state and the transparent state are switched to enable image display.

However, the refractive index of an organic material such as liquid crystal or polymer is generally limited within a narrow range, and even if it is large, the ratio is about 1.2, so that the backward light scattering rate of the light scattering type liquid crystal display element is large. Can't get low enough brightness. Therefore, it is necessary to increase the cell thickness to obtain a high back light scattering rate, but in that case, the driving voltage becomes very high, which is not realistic.

As described above, a liquid crystal display device which realizes high brightness and high contrast has not been realized yet, and in particular, in a portable display terminal which is often used outdoors, due to power consumption and strong external light restrictions, reflection occurs. There is a strong demand for a liquid crystal display device that realizes high brightness and high contrast in a mold. Furthermore,
It is said that TV can be viewed on a mobile terminal in the near future, and a demand for a liquid crystal display device having such characteristics will be stronger.

[0009]

The liquid crystal display device of the present invention has been made to solve the above-mentioned problems. In particular, a reflective display having high brightness, high contrast ratio and high reliability, which does not use a polarizing plate, is provided. It is intended to be provided.

Thus, according to the present invention, there is provided a liquid crystal display device characterized in that a liquid crystal containing an inclusion compound containing dye molecules is sandwiched between two substrates.
This improves the order parameter of the dye molecules in the liquid crystal (parallelism of the dye molecule absorption axis with respect to the orientation direction of the host liquid crystal molecules) and the durability against external stimuli such as light, heat, and electricity. It is possible to realize a GH type liquid crystal display element with high contrast and high reliability.

Furthermore, according to the present invention, a liquid crystal containing an inclusion compound encapsulating a dye molecule is sandwiched between two substrates, and the inclusion compound has liquid crystallinity. A liquid crystal display device is provided. This allows the clathrate compound to be treated as a liquid crystal. Furthermore, it becomes possible to improve the dichroic ratio with a small amount of the inclusion compound.

The dye molecule is preferably a dichroic dye molecule. The dichroic dye molecule is originally used in a GH type liquid crystal display element, and by incorporating this into an inclusion compound, a higher order parameter is realized, and a GH type liquid crystal display with high brightness, high contrast and high reliability. It becomes possible to realize the device.

Further, the inclusion compound is preferably a tube-shaped compound or a necklace-shaped polyrotaxane. As a result, it becomes possible to more effectively realize a GH type liquid crystal display device having high brightness, high contrast and high reliability, as compared with the case where one cyclic molecule is included.

The tube-shaped compound or necklace-shaped polyrotaxane may be cyclodextrin, crown ether, calixarene, cyclophane,
Or at least one of these derivatives or carbon
It is preferably produced based on the type. Generally, carbon nanotubes are famous for forming tubes at the molecular level, but tubes and polyrotaxanes can be formed using cyclodextrins, crown ethers, calixarenes, cyclophanes, or their derivatives.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Inclusion Compound The inclusion compound is not particularly limited as long as it can encapsulate a dye molecule. For example, cyclodextrin, crown ether, calixarene, cyclophane, or a derivative thereof, or a tubular compound or a necklace-shaped polyrotaxane produced by using at least one kind of carbon as a raw material may be mentioned.

Here, as an example, a case where cyclodextrin is used as a raw material for an inclusion compound will be examined. Cyclodextrins are also called cyclic oligosaccharides, and α-glucopyranose groups are cyclically linked by α-1,4-glycosidic bonds, and depending on the number of pyranose groups,
α (6 pieces, cyclohexaamylose, pore size = 0.45
nm), β (7, cycloheptaamylose, pore size =
0.70 nm), γ (8, cyclooctaamylose,
(Pore size = 0.85 nm), δ (9, cyclononaamylose) is attached.

Three-dimensionally, it is a trapezoidal-cylindrical cylindrical shape, the inside of which is hydrophobic and the outside of which is hydrophilic, so that inside it is a hydrophobic molecule (or a hydrophobic group of a size that can be incorporated into a ring). It is known to form a clathrate compound by incorporating a molecule having Utilizing this property, cyclodextrins are widely used as unstable substances, fragrances, stabilizers for agricultural chemicals, and the like.

As shown in FIG. 1, cyclodextrin 1
It is known that when 01 and the linear polymer 102 are mixed, the cyclodextrin clathrates the linear polymer having a flexible degree of freedom to form a complex called a molecular necklace 103 in a solution in a self-organizing manner. There is. In this state, both ends of the linear polymer are blocked with bulky substituents to obtain polyrotaxane 104. Next, in the polyrotaxane, adjacent cyclodextrins are chemically crosslinked, and the substituents at both ends of the linear polymer are removed in a strong alkaline solution to obtain the molecular nanotube 105 that removes the linear polymer (Harada). Mitsu, Kogaku, 44, P390 (1995)).

Next, as shown in FIG. 2, the molecular nanotubes 201 and the dye molecules 202 are mixed to obtain the molecular nanotubes 203 in which the dye molecules are included. Since a nanotube is a rigid molecule, even a polymer having a very large internal degree of freedom loses its degree of freedom when it is included, and is stabilized by the interaction energy with the tube. Due to the rigidity of such a dye molecule inclusion compound, the order parameter in or as a liquid crystal is improved.

Further, when the dye molecule inclusion compound alone exhibits liquid crystallinity, the characteristics are further improved. This is because one of the reasons why the dye molecule addition concentration is set to be relatively low in the above-described examples is that the dye molecules are deposited in a large amount because the solubility of the dye molecules in the liquid crystal is low. . Therefore, since the dye molecule inclusion compound that originally exhibits liquid crystallinity is difficult to separate in the liquid crystal, the addition concentration can be increased. Further, if the temperature range exhibiting liquid crystallinity is wide, it becomes possible to control light by the dye molecule clathrate compound alone. As the dye molecules to be clathrated, it is assumed that a material having absorption in the visible region such as an azo dichroic dye molecule and an anthraquinone dichroic dye molecule is included, but is not limited to this. Not necessarily. The compounding ratio of the dye molecule clathrate compound to the liquid crystal can be appropriately set according to the type and the characteristics of the liquid crystal display device, and for example, 0.5 in the liquid crystal layer.
It can be used in the range of 5.0 wt%.

Liquid crystal molecule The liquid crystal molecule usable in the present invention is not particularly limited, and any known liquid crystal molecule can be used.
Specifically, nematic, cholesteric, smectic liquid crystal and disk-shaped molecular structures using azoxy, Schiff base, biphenyl, benzoate, cyclohexane, heterocyclic compound, tolan, cyclohexylethane are used. There is a discotic liquid crystal. -Driving method Hereinafter, a driving method suitable for the liquid crystal display device of the present invention will be described.

(GH mode) The guest-host (GH) mode is a display mode utilizing the anisotropy of the absorption coefficient of the dichroic dye molecule added to the liquid crystal. If a rod-shaped structure is used as the dichroic dye molecule, the dye molecule arranged in parallel with the liquid crystal molecule can be orientation-changed by the electric field by adding it to the liquid crystal. That is, it is possible to switch between coloring and non-coloring by applying a voltage. When rod-shaped dye molecules are added to the liquid crystal, the dye molecules try to align in parallel with the liquid crystal molecules. However, as shown in FIG. 3, the molecular axis 302 of the dye molecule is the liquid crystal director (average orientation direction) 301. Oriented out of alignment.
When this shift angle is α, the degree of orientational order S of the dye molecules can be expressed as the average of cos ² α as shown in Equation 1.

[0023]

[Equation 1]

Where β is the transition moment 3 of the dye molecule.
03 is the angle formed by the molecular axis 302 of the dye molecule, and φ is the angle formed by the director 301 and the polarization direction 304 of the incident light. Then the absorbance A is

[0025]

[Equation 2]

It is represented by Here, K _M is a coefficient related to the magnitude of the transition moment, c is the dye molecule concentration, and d is the thickness of the liquid crystal cell. The dichroic dye molecule usually has an absorption axis almost parallel to the molecular axis, absorbs a polarized component parallel to the molecular axis, and hardly absorbs a perpendicular component. Such dye molecules are called p-type dye molecules. Here, in the GH mode, assuming that the absorption axis of the dye molecule is arranged completely parallel to the director, the absorption coefficient A _{// in the} director direction and the absorption coefficient A ⊥ in the direction perpendicular to the director are given by Equations 3 and 4.

[0027]

[Equation 3]

[0028]

[Equation 4]

It can be expressed as However, the direction of the transition moment was assumed to be completely parallel to the molecular axis. From these ratios, the dichroic ratio D _P can be obtained as follows.

[0030]

[Equation 5]

The effect of the present invention will be verified based on the above calculation formula. -Heilmeier type GH mode The basic operation of the Heilmeier type GH liquid crystal cell shown in FIG. 4 will be described. In this cell, a dye molecule 403 and a liquid crystal molecule 402 are sandwiched between two transparent substrates 405 having transparent electrodes 404, and each molecule is uniaxially arranged in a direction parallel to the substrate in the voltage-off state of (a). (This orientation is obtained by rubbing the substrates on both sides in parallel or antiparallel directions). If the polarization axis of the polarizing plate 401 is aligned with the director direction in this state, the transmitted light is effectively colored. On the other hand, in the voltage-on state of (b), since both liquid crystal molecules and dye molecules are arranged perpendicularly to the substrate, light is transmitted while remaining colorless (the right side of FIG. 4 schematically shows the wavelength dependence of absorbance).

GH mode using quarter wave plate The basic operation of the GH reflective liquid crystal cell using the quarter wave plate shown in FIG. 5 will be described. In this cell, the transparent electrode 5
The dye molecules 502 and the liquid crystal molecules 501 are sandwiched between two transparent substrates 504 provided with 03, and each molecule is uniaxially arranged in the direction parallel to the substrates in the voltage-off state of (a). In this cell, two incident polarization components orthogonal to each other are
The polarization direction is rotated by 90 ° on the return path by the wave plate 505 and the reflection plate 506. As a result, in the off state, each polarized component is absorbed in either the incident or reflected optical path. On the other hand, in the voltage-on state of (b), since the liquid crystal molecules and the dye molecules are arranged perpendicularly to the substrate, light is reflected while remaining colorless.

.PC (Phase Change) -G
H Mode The basic operation of the PC-GH reflective liquid crystal cell shown in FIG. 6 will be described. In this cell, dye molecules 602 and liquid crystal molecules 601 are provided on two transparent substrates 604 having transparent electrodes 603.
Are sandwiched, and a reflection plate 605 is arranged on the back surface.
The liquid crystal used here is cholesteric liquid crystal, and has a helical structure with the substrate vertical direction as an axis. In this cell, when the applied voltage is increased, a two-step change of (a) → (b) → (c) is shown (V _CN is a cholesteric nematic phase transition voltage). That is, this cell is (a) →
The absorbance changes in two steps, such that the absorbance decreases in the order of (b) → (c).

STN (Super Twisted)
Nematic) -GH mode The basic operation of the STN-GH reflective liquid crystal cell shown in FIG. 7 will be described. In this cell, dye molecules 702 and liquid crystal molecules 70 are formed on two transparent substrates 704 having transparent electrodes 703.
1 is sandwiched, and a reflection plate 705 is arranged on the back surface. The liquid crystal used here is a nematic liquid crystal or a cholesteric liquid crystal, but as compared with the liquid crystal used in the PC-GH mode, since the helical pitch is sufficiently long, the two-step change due to the applied voltage does not occur, and the liquid crystal molecule is generally The same operation as the TN liquid crystal is performed. That is, each molecule is arranged in a state of being twisted in a direction parallel to the substrate in the voltage-off state of (a) (the upper and lower substrates are rubbed at an angle corresponding to the spiral pitch), and the reflected light is colored. On the other hand, in the voltage-on state of (b), since the liquid crystal molecules and the dye molecules are arranged perpendicularly to the substrate, light is reflected while remaining colorless.

Two-layer type-GH mode The basic operation of the two-layer type-GH reflective liquid crystal cell shown in FIG. 8 will be described. This cell does not use a polarizing plate Heilm
It has a structure in which two layers of eier type GH liquid crystal cells are laminated, and the liquid crystal axes in the voltage-off state (a) of both layers are orthogonal to each other. That is, a dye molecule 802 and a liquid crystal molecule 801 are sandwiched between three transparent substrates 804 provided with a transparent electrode 803 or a reflective electrode 805 in two layers on both sides of a central transparent substrate. The molecules in each layer are uniaxially arranged in the direction parallel to the substrate in the voltage-off state (a). In this state, if the liquid crystal molecular axes of the two layers are made orthogonal to each other, the transmitted light is effectively colored. On the contrary, in the voltage-on state of (b), since the liquid crystal molecules and the dye molecules are arranged perpendicularly to the substrate, light is transmitted while remaining colorless. The substrate, the transparent electrode, the reflective electrode, the polarizing plate, the quarter-wave plate, the reflective plate, and the like, which compose the liquid crystal display device of the present invention, are not particularly limited, and a known structure in the field can be adopted. . Further, it may include other components necessary for the liquid crystal display device.

[0036]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to the examples.

Example 1 In the PC-GH mode, a dye molecule inclusion compound was used in place of the conventional rod-shaped dye molecule (fixed dye molecule concentration). The specifications of the PC-GH reflective liquid crystal cell shown in Table 1 were used. On the other hand, the case of applying the dye molecule inclusion compound was simulated.

[0038]

[Table 1]

The dependence of the reflectance R on the order parameter S is shown in Table 2 and FIG. The reflectance is a value at a wavelength of 550 nm.

[0040]

[Table 2]

At present, when the order parameter is 0.75, the reflectance in the bright state is 68.1% and the contrast (C
R) 5.18. On the other hand, by applying the dye molecule inclusion compound, the order parameter is 0.9.
When it is increased to, the reflectance in the bright state is improved to 85.8% and the CR is improved to 7.91. Of course, if the order parameter is further increased, CR is further improved. Further, a further effect can be expected by using a two-layer structure as shown in FIG. Further, since the dye molecules are protected by the inclusion compound against external stimuli such as light, heat and electricity, the reliability is also improved.

(Example 2) In the PC-GH mode, when a dye molecule inclusion compound is used instead of the conventional rod-shaped dye molecule (dye molecule concentration variable), with the same liquid crystal cell specifications as in Example 1, the dye molecule concentration is changed. Was simulated to apply the dye molecule inclusion compound. The dependence of the reflectance R on the order parameter S is shown in Table 3 and FIG. The reflectance is a value at a wavelength of 550 nm.

[0043]

[Table 3]

When the order parameter is increased to 0.9 by applying the dye molecule inclusion compound, the reflectance in the bright state is 70 when the dye molecule concentration (q) is 1.4 wt%.
%, CR> 80 will be achieved. Of course, if the order parameter is further increased, CR is further improved.

Further, the dye molecule is irradiated with light by the inclusion compound,
Reliability is also improved because it is protected against external stimuli such as heat and electricity.

(Example 3) In the STN-GH mode, when a dye molecule clathrate compound is used instead of the conventional rod-shaped dye molecule 1 (fixed dye molecule concentration) In contrast to STN-GH reflective liquid crystal cell, dye molecule The case where a clathrate was applied was simulated. A commercially available nematic liquid crystal was used as the liquid crystal, and chiral was adjusted and added so that the helical pitch was 7.2 μm. The cell gap d is 4.5 μm, and the liquid crystal twist angle (twist angle between the upper and lower substrates) is 225 °. The same dye molecules as in Examples 1 and 2 were used, and the addition amount was 1.0 wt%.
And The calculation here is LC of Shintech.
D Master was used. The results are shown in Table 4. The reflectance is a value at a wavelength of 550 nm.

[0047]

[Table 4]

At present, when the order parameter is 0.74, the reflectance in the bright state is 44% and the CR is 3.9. On the other hand, when the order parameter is increased to 0.9 by applying the dye molecule inclusion compound, the reflectance in the bright state is improved to 54% and the CR is improved to 4.9. Of course, if the order parameter is further increased, CR is further improved. Furthermore, the dye molecules are lighted by the inclusion compound,
Reliability is also improved because it is protected against external stimuli such as heat and electricity.

Example 4 A case was simulated in the same manner as in Example 1 except that a dye molecule inclusion compound having liquid crystallinity was used. As a result, it can be seen that the characteristics are further improved. This is because one of the reasons that the dye molecule addition concentration is set to be relatively low in the above-mentioned Example 1 is that if a large amount of dye molecules is added, precipitation occurs. Therefore,
Since the dye molecule inclusion compound that originally exhibits liquid crystallinity is difficult to separate in the liquid crystal, the addition concentration can be increased. Further, if the temperature range exhibiting liquid crystallinity is wide, it becomes possible to control light by the dye molecule clathrate compound alone.

[0050]

FIG. 11 is a schematic view showing an example of the present invention. Here, liquid crystal molecules 1101 and molecular nanotubes 1102 including rod-shaped dye molecules 1106 are sandwiched between two transparent substrates 1104 having transparent electrodes 1103, and a reflection plate 1105 is arranged on the back surface. As described above, various arrangements of liquid crystal can be applied. By applying an inclusion compound containing a dye molecule to the guest-host mode of a liquid crystal, it is possible to improve the order parameter of the dye molecule in the liquid crystal and the durability against external stimuli such as light, heat, and electricity. It is possible to realize a guest-host type liquid crystal display device having high brightness, high contrast and high reliability.

[Brief description of drawings]

FIG. 1 is a schematic view showing a method for producing a molecular nanotube.

FIG. 2 is a schematic diagram of a dye molecule inclusion molecule nanotube.

FIG. 3 is a schematic diagram showing the arrangement of dye molecules.

FIG. 4 is a schematic view showing the operating principle of a Heilmeier type GH liquid crystal cell.

FIG. 5 is a schematic view showing the operating principle of a reflective GH liquid crystal cell using a quarter-wave plate.

FIG. 6 is a schematic view showing the operating principle of a PC-reflection type GH liquid crystal cell.

FIG. 7 is a schematic diagram showing the operating principle of an STN-reflection type GH liquid crystal cell.

FIG. 8 is a schematic diagram showing the operating principle of a two-layer reflective-GH cell.

FIG. 9 is a diagram showing the order parameter S dependency of the reflectance R in Example 1.

FIG. 10 is a diagram showing the order parameter S dependency of the reflectance R in Example 2.

FIG. 11 is a schematic view showing an example of the present invention.

[Explanation of symbols]

101 cyclodextrin 102 linear polymer 103 molecular necklace 104 polyrotaxane 105, 201 molecular nanotube 202, 403, 502, 602, 702, 802 dye molecule 203, 1102 molecular nanotube encapsulating dye molecule 301 director 302 molecular axis of dye molecule 303 Transition Moment 304 Polarization Direction of Incident Light 401 Polarizing Plates 402, 501, 601, 701, 801, 1101
Liquid crystal molecules 404, 503, 603, 703, 803, 1103
Transparent electrodes 405, 504, 604, 704, 804, 1104
Transparent substrate 505 1/4 wavelength plate 506, 605, 705, 805, 1105 Reflector 1106 Rod-shaped dye molecule

Claims (5)

[Claims] 1. A liquid crystal display device characterized in that a liquid crystal containing an inclusion compound containing dye molecules is sandwiched between two substrates. 2. A liquid crystal display device characterized in that a liquid crystal containing an inclusion compound encapsulating a dye molecule is sandwiched between two substrates, and the inclusion compound has liquid crystallinity. 3. The liquid crystal display device according to claim 1, wherein the dye molecule is a dichroic dye molecule. 4. The liquid crystal display device according to claim 1, wherein the inclusion compound is a tube-shaped compound or a necklace-shaped polyrotaxane. 5. The tube-shaped compound or necklace-shaped polyrotaxane prepared by using at least one of cyclodextrin, crown ether, calixarene, cyclophane, or a derivative thereof, or carbon as a raw material. The liquid crystal display element according to claim 4, wherein