JP2923164B2 - Liquid crystal display - Google Patents

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, and suppresses a phenomenon in which contrast changes depending on a human viewing angle due to a three-dimensional refractive index anisotropy of a liquid crystal, thereby improving a viewing angle. It is used for

[0002]

2. Description of the Related Art Liquid crystal display devices using liquid crystal molecules can be made thinner and lighter and are now widely used for display of electronic equipment and the like.

[0003] Now, the optical anisotropic element such as a liquid crystal molecules used in the liquid crystal display device, the refractive indices n _x a 3-dimensional direction as shown in FIG. 6, n _y, the refractive index ellipsoid by n _z Is represented by The birefringence phenomenon is a phenomenon relating to a refractive index difference in a two-dimensional plane when the refractive index ellipsoid is viewed from a specific direction (usually the Z-axis direction). The phase difference of the liquid crystal display device is obtained by observing the refractive index ellipsoid from the Z-axis direction and determining the birefringence Δn = nx−ny at the ellipse where the plane at Z = 0 and the ellipsoid intersect.
Is multiplied by the thickness d of the anisotropic body.
However, when this ellipsoid is observed from another direction, its birefringence (nb-na) changes and its optical path length also changes, so that the phase difference is different from that when viewed from the Z-axis direction. Becomes The liquid crystal molecules have dielectric anisotropy, and the dielectric constant of the liquid crystal molecules is in the long axis direction (X axis direction).
Is higher, a force is generated when an electric field is applied so that the major axis direction of the liquid crystal molecules tends to tilt in the direction of the electric field. A display device is made using this dielectric anisotropy.

[0004] Twisted nematic mode liquid crystal display devices are most widely used because they can produce liquid crystal display devices having characteristics such as low voltage and low power consumption. The twisted nematic mode liquid crystal display device has a configuration in which liquid crystal molecules 35 are interposed between two opposing substrates 31, 32 as shown in FIG. Substrates 31 and 32 are provided with transparent electrodes 31b and 32b and alignment films 31c and 32, respectively, on opposite surfaces of two transparent substrates 31a and 32a such as glass.
c. Liquid crystal molecule 3
5 so that the major axis direction is substantially parallel to the substrate surface and is continuously twisted by 90 ° between the substrates.
The orientation direction 2c is set to the directions of arrows 33 and 34 so as to be perpendicular to each other when viewed from the substrate surface.

The operation principle of the liquid crystal display device will be described with reference to a liquid crystal molecule model as shown in FIG. FIG.
FIG. 3 is a model diagram in which liquid crystal molecules 41 are interposed between 3 and 44, and the major axis direction of the liquid crystal molecules 41 is set to be parallel to an electrode surface. FIG. 7A shows a case where the voltage applied to the circuit is zero, and no electric field is applied to the liquid crystal molecules 41.
The major axis direction is kept parallel to the electrode surface. Next, FIG. 7B shows a case where the voltage applied to the circuit is increased, an electric field is applied to the liquid crystal molecules 41, and the major axis direction of the liquid crystal molecules 41 is inclined to some extent in the direction of the electric field. FIG. 7C shows a case in which the applied voltage of the circuit is further increased. Many electric fields are applied to the liquid crystal molecules 41, and the liquid crystal molecules 41 are inclined such that the major axis direction is almost the same as the electric field direction. . This is because the liquid crystal molecules 41 have dielectric anisotropy and have a higher dielectric constant in the long axis direction. Therefore, the liquid crystal molecules are used for a display device having an optical switching function.

[0006] In a liquid crystal display device, a direction having the best contrast and being most suitable for display is set as a normal viewing angle direction. Hard to do. If the normal viewing angle direction is described by one liquid crystal molecule, it can be said that the direction is on an extension of the major axis direction of the liquid crystal molecule when an operating voltage is applied.

In the liquid crystal display device having the above-described structure, since the liquid crystal molecules have the dielectric anisotropy as well as the refractive index anisotropy, the contrast is changed by tilting the viewing angle obliquely to the display surface. With the phenomenon.

[0008]

SUMMARY OF THE INVENTION In a normally white mode twisted nematic mode liquid crystal display device in which light is transmitted when no voltage is applied and a white display is obtained, a characteristic diagram of transmittance and applied voltage is actually measured. Is shown in FIG. FIG.
As shown by the solid line L1, the transmittance of light decreases as the applied voltage value increases, and the transmittance becomes substantially zero when the voltage is saturated, and the transmittance remains zero even when an applied voltage is further applied. Therefore, the black portion is displayed in black. However,
When the viewing angle is gradually tilted from the vertical upper direction of the display surface beyond the normal viewing angle direction, as shown by a solid line L2, the transmittance decreases as the applied voltage increases, and when the applied voltage exceeds a specific voltage value, the transmittance decreases. A phenomenon occurs in which the transmittance increases again and then gradually decreases again. Therefore, at a specific angle, the black portion of the image looks whitish, which is an inversion phenomenon. In addition, the reversal phenomenon does not occur in other viewing angle directions other than the normal viewing angle direction, but as the viewing angle increases, the contrast ratio between black and white decreases due to the effect of refractive index anisotropy. .

The cause of the reversal phenomenon will be described with reference to a liquid crystal molecule model as shown in FIG. In FIG. 7, observer 4
2 tilts the viewing angle beyond the normal viewing direction of the liquid crystal molecules 41. When the applied voltage is zero as shown in FIG.
The liquid crystal molecules appear elliptical to the observer 42 while remaining parallel to the electrodes. Next, when the applied voltage is gradually increased as shown in FIG. 7B, the liquid crystal molecules 41 are inclined in the direction of the electric field, and there is a moment when the observer 42 looks like a perfect circle. When the voltage is further increased as shown in FIG. 7C, the liquid crystal molecules 41 become almost parallel to the direction of the electric field, and appear to the observer 42 as an ellipse again. As a result, a phenomenon occurs in which the transmittance decreases once and the transmittance increases again. This is a phenomenon that occurs because the refractive index anisotropy of the liquid crystal molecules, that is, the refractive index is changed by tilting the viewing angle.

As described above, in the twisted nematic mode liquid crystal display device, a reversal phenomenon and a decrease in contrast seen in the direction of the normal viewing angle cause a serious obstacle for a viewer.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide a liquid crystal display device having improved viewing angle characteristics and improved display quality.

[0012]

According to the present invention, there is provided a liquid crystal display device having a liquid crystal layer twisted by 90 ° between a pair of transparent substrates, wherein at least one of the liquid crystal display devices is provided with an optical surface. comprising one or a plurality of orientation-treated antiparallel cell so as to have the same direction of orientation to the liquid crystal molecules as a compensation cell, the anti-parallel cell
Orientation of the liquid crystal molecules of the liquid crystal and the antiparallel of the liquid crystal layer.
The liquid crystal molecules on the side of the cell are oriented perpendicular to each other .

[0013]

[0014]

In order to improve the viewing angle characteristic called the inversion phenomenon, it is considered that the refractive index anisotropy of the liquid crystal molecules should be constant regardless of the viewing angle. That is, as the viewing angle is increased from the direction perpendicular to the display surface of the liquid crystal display device, the change in the refractive index in the thickness direction of the liquid crystal display device is compensated for, and the viewing angle at which the inversion phenomenon occurs is increased. The corners need to be improved.

Therefore, in the present invention, an anti-parallel cell is used as an optical compensation cell having the same refractive index anisotropy in order to suppress a change in the refractive index in the thickness direction of the liquid crystal display device. The anti-parallel cell, which is an optical compensation cell, injects liquid crystal molecules and does not have a twisted molecular arrangement in the thickness direction as in a twisted nematic mode liquid crystal display device. I am facing. By tilting the liquid crystal molecules of the anti-parallel cell, not completely parallel to the substrate surface, it is possible to offset and reduce the refractive index anisotropy in the thickness direction. The orientation direction of the anti-parallel cell is perpendicular to the orientation direction of the transparent substrate in contact. By making the orientation direction of the anti-parallel cell perpendicular to the orientation direction of the transparent substrate in contact with the anti-parallel cell, the inversion phenomenon is suppressed as compared with the case where the orientation direction is parallel to the orientation direction, and the viewing angle can be increased.

The orientation direction of the anti-parallel cell is individually suitable because the twist of the liquid crystal and its optical characteristics differ depending on the liquid crystal display device such as twisted nematic (TN), super twisted nematic (STN), double super twisted nematic (DSTN) and the like. The orientation direction is selected.

Further, two antiparallel cells may be used. Particularly, in a twisted nematic liquid crystal display device, the second antiparallel cell is aligned with the orientation direction of the first antiparallel cell in contact with the liquid crystal display element. The direction of cell orientation is vertical. In the liquid crystal display device having this structure, the refractive index anisotropy in the thickness direction in the direction that could not be completely compensated for by the first antiparallel cell can be compensated, so that the inversion phenomenon is less likely to occur and the visual field range is reduced. Wider and the viewing angle characteristics are further improved. In other orientation directions, the optical system is distorted.

As described above, by using the anti-parallel cell of the liquid crystal cell having the three-dimensional refractive index anisotropy, the refractive index anisotropy generated in the thickness direction of the liquid crystal display element can be suppressed.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same reference numerals denote the same components.

FIG. 1 is a partially exploded perspective view showing the structure of a twisted nematic mode liquid crystal display device according to an embodiment of the present invention, which is actually laminated.
It is. The liquid crystal display device has a configuration in which a liquid crystal display element 22 is interposed between a pair of polarizing plates 20 and 23, and an anti-parallel cell 21 which is an optical compensation cell is disposed between the polarizing plate 20 and the liquid crystal display element 22. You. In the liquid crystal display device having the above configuration, light incident from the polarizing plate 23 side passes through the liquid crystal display element 22 and the anti-parallel cell 21 and is emitted from the polarizing plate 20.

Next, the components of the liquid crystal display device will be described. The liquid crystal display element 22 has a thickness of 200 made of ITO (indium tin oxide) on the opposing surfaces of a pair of transparent substrates 1 and 2 made of glass, plastic, or the like.
The transparent electrodes 3 and 4 of 0 ° are patterned so as to intersect in a strip shape, and the alignment films 5 and 6 of a thickness of 600 ° made of a polyimide resin are formed on the surface thereof, and plastic beads or the like for keeping the substrate interval constant. The twisted nematic liquid crystal 8 is sealed with a sealing material 9 made of a UV curable resin.
The twisted nematic liquid crystal layer 8 is formed by using arrows 11 and 12 for the alignment films 5 and 6 using a cloth woven with nylon fibers.
Approximately 90 ° spiral by applying orientation treatment in the direction
The liquid crystal molecules are arranged in a twisted manner. Transparent electrodes 3, 4
May be switched by any driving method such as a segment type, a simple matrix type, and an active matrix type.

The liquid crystal display device of this embodiment performs a so-called normally white display in which white light is transmitted by transmitting light when no voltage is applied. Therefore, the polarizing plates 20 and 23 are arranged such that the arrows 13 and 14 that are the transmission axis directions are the same as the arrows 11 and 12 that are the alignment processing directions of the alignment films 5 and 6, respectively.

In the liquid crystal display device, an anti-parallel cell 21 is disposed between the polarizing plate 20 and the liquid crystal display element 22 as an optical compensation cell. Anti-parallel cell 2
1 will be described with reference to FIG.

Transparent substrates 53a and 54a made of glass or the like
Thickness of 2000 made of ITO etc. on each opposite surface
The transparent electrodes 53b and 54b of {circle around (1)} and the alignment films 53c and 54c of thickness 600 ° made of polyimide resin are laminated. Liquid crystal molecules are sealed between the transparent substrates 53a and 54a by a sealing material 56 made of a UV curable resin. The alignment films 53c and 54c are aligned with the arrow 5 which is the alignment processing direction.
1 and 52 are formed so as to face in parallel,
The alignment of the liquid crystal molecules is uniformly oriented in one direction. The orientation direction 15 of the anti-parallel cell 21 configured as described above,
Numeral 16 is arranged so as to be perpendicular to the arrow 11 which is the orientation direction of the liquid crystal display element 22 on the anti-parallel cell 21 side.

FIG. 4 is a graph showing an applied voltage-transmittance characteristic of the liquid crystal display device. A solid line L1 shows a characteristic curve when the liquid crystal display device provided with the anti-parallel cell is viewed from the upper direction perpendicular to the display surface. The solid line L1 is the same as the result measured in the conventional liquid crystal display device and the liquid crystal display device of this embodiment. In the conventional liquid crystal display device, a solid line L2 shows a characteristic curve when viewed from a position inclined at an angle of 40 ° in a normal viewing angle direction from a direction perpendicular to the display surface. Then, the liquid crystal display device of this embodiment provided with the anti-parallel cell is moved from the upper direction perpendicular to the display surface to the normal viewing angle direction by 40 degrees.
A characteristic curve when viewed from the inclined position is indicated by a solid line L3.

In the conventional example, as shown by the solid line L2, a phenomenon occurs in which the transmittance increases again at a high applied voltage value. However, in the present embodiment, as shown by the solid line L3, the width of the re-rise of the transmittance at a high applied voltage value is suppressed to be smaller than in the conventional case. Therefore, in this embodiment, the occurrence of the inversion phenomenon and the decrease in the contrast ratio are improved. Further, the angle at which the reversal phenomenon occurs is larger than in the related art, and the viewing angle range of the liquid crystal display device 1 is expanded.

As another embodiment of the present invention, the polarizing plate 2
It is also possible to adopt a configuration in which the number of antiparallel cells arranged between 0 and the liquid crystal display element 22 is two. FIG. 2 shows a liquid crystal display device having a configuration in which the number of the anti-parallel cells is two. Although the constitutional requirements for each of the single liquid crystal display devices are the same, two antiparallel cells 21 and 24 are provided between the polarizing plate 20 and the liquid crystal display element 22. The liquid crystal display element 22 is arranged so that the orientation direction is perpendicular to the orientation direction 11 on the anti-parallel cell 21 side of the liquid crystal display element 22. Arrange them vertically. By employing the liquid crystal display device using two anti-parallel cells according to the present embodiment, the reversal phenomenon occurs even when judging only in the normal viewing angle direction as compared with the liquid crystal display device using one anti-parallel cell. It is possible to obtain a viewing angle characteristic which is difficult to balance the right and left. Further, enlargement of the entire viewing angle and reduction in contrast are suppressed, and the inversion phenomenon is less likely to occur.

In this embodiment, the anti-parallel cell is provided on the light emitting side, but may be provided on the light incident side.

Also, a transparent electrode made of ITO is provided in the anti-parallel cell, which can freely change the tilt of the liquid crystal molecules of the anti-parallel cell only by changing the applied voltage. Optimal viewing angle characteristics can be obtained in the display device. The applied voltage at that time may be a fixed voltage or may be synchronized with the applied voltage of the liquid crystal display device. Since the liquid crystal molecules are inclined to some extent with respect to the substrate surface even when no voltage is applied, it has been confirmed that the viewing angle can be improved even in a configuration in which no transparent electrode is provided.

In this embodiment, the liquid crystal display device of the twisted nematic mode has been described. However, since the change in the refractive index in the thickness direction of the liquid crystal display device is suppressed, liquid crystal display devices such as STN and DSTN are used. Is also good.

In this embodiment, the liquid crystal layer is sandwiched between glass substrates as an anti-parallel cell. However, other similar optical films such as a film in which liquid crystal molecules are entangled with a polymer or a liquid crystal film can be used. A similar effect can be obtained by employing a material having properties.

[0032]

In the transmittance-applied voltage characteristic diagram as shown in FIG. 4, the viewing angle of the conventional liquid crystal display device having no anti-parallel cell is inclined from the direction perpendicular to the display surface beyond the normal viewing angle direction. The characteristic curve at this time is shown by a solid line L2. Similarly, a solid line L3 shows a characteristic curve when the viewing angle of the liquid crystal display device of the present embodiment provided with the anti-parallel cell is inclined beyond the normal viewing direction from the vertical direction of the display surface. As can be seen from the characteristic diagram, the solid line L3, which is the characteristic curve of the present embodiment, suppresses a re-increase in transmittance, which is an inversion phenomenon.

As described above, according to the present invention, an anti-parallel cell having liquid crystal molecules having anisotropy of the refractive index in the thickness direction, that is, inclined with respect to the substrate surface and having directionality in a certain direction is provided. By using this, the anisotropy of the refractive index generated in the thickness direction of the liquid crystal display element can be offset. As a result, it is possible to improve the characteristics such that the reversal phenomenon does not easily occur even when the viewing angle is increased. The decrease in the contrast ratio due to the inversion phenomenon in the liquid crystal display element is improved, the contrast ratio in black and white display is improved, and the display quality is improved.

By using two anti-parallel cells and making their orientation directions vertical, the transmittance-applied voltage characteristic diagram does not change, but the anisotropy of the refractive index in the thickness direction in other directions is compensated. Therefore, the reversal phenomenon and the decrease in contrast are suppressed at a wide viewing angle, and the viewing angle is further improved.

[Brief description of the drawings]

FIG. 1 is a perspective view of a liquid crystal display device using one anti-parallel cell according to an embodiment of the present invention.

FIG. 2 is a perspective view of a liquid crystal display device using two anti-parallel cells according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a configuration of an anti-parallel cell.

FIG. 4 is a graph showing an applied voltage-transmittance characteristic of the liquid crystal display device 1.

FIG. 5 is a cross-sectional view illustrating a structure of a liquid crystal display device.

FIG. 6 is a view showing the refractive index anisotropy of liquid crystal molecules (refractive index ellipsoid).

FIG. 7 is a diagram illustrating a model of liquid crystal molecules in a liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 2 Transparent substrate 3, 4 Transparent electrode 5, 6 Alignment film 7 Spacer 8 Liquid crystal layer 9 Sealant 11, 12 Orientation direction of liquid crystal display element 13, 14 Transmission axis of polarizing plate 15, 16 Alignment direction of anti-parallel cell 20 , 23 Polarizer 21 Anti-parallel cell 22 Liquid crystal display

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masato Akutomo 22-22, Nagaike-cho, Abeno-ku, Osaka, Osaka Inside Sharp Corporation (72) Inventor Shigemitsu Mizushima 22-22, Nagaike-cho, Abeno-ku, Osaka, Osaka (56) References JP-A-1-217316 (JP, A) JP-A-1-179912 (JP, A) JP-A-1-105217 (JP, A) (58) Fields studied (Int. Cl. ⁶ , DB name) G02F 1/1335 510

Claims (2)

(57) [Claims] 1. A liquid crystal display device in which a liquid crystal layer twisted by 90 ° is interposed between a pair of transparent substrates, wherein at least one of the liquid crystal display devices has an optical compensation cell in the same direction as liquid crystal molecules on a transparent substrate surface side. Antiparallel cells that have been aligned to give
Or a plurality of the anti-parallel cells.
Orientation direction of the liquid crystal layer and the anti-parallel cell side of the liquid crystal layer.
A liquid crystal display device, wherein the liquid crystal molecules are oriented perpendicular to each other . 2. A plurality of anti-parallel cells are provided.
The orientation of the liquid crystal molecules in the anti-parallel cell
Corresponds to the alignment direction of the liquid crystal molecules of other anti-parallel cells.
2. The liquid according to claim 1, wherein the liquid is vertical.
Crystal display device.