JP2003228070A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device wherein the change of contrast, a coloring phenomenon, a reversion phenomenon and the like which are caused depending on a visual angle can be further improved and in particular the coloring phenomenon of a liquid crystal screen depending on the visual angle can be effectively improved. <P>SOLUTION: Optical retardation plates 2 and 3 wherein principal refractive indexes na, nb and nc thereof have a relation of na=nb>nc, the direction of the principal refractive index nb is inclined from the normal direction of the surface of the optical retardation plates clockwise or counterclockwise around the axis of the direction of one of the principal refractive index na or nc nearly parallel to the surface of the optical retardation plate and the direction of the other principal refractive indeed nc or na is inclined from the direction nearly parallel to the surface are disposed between a liquid crystal display element 1 and polarizing plates 4 and 5, respectively. A combination condition of average length of alkyl chains of a liquid crystal material in a liquid crystal layer 8, a changing degree of a normal light refractive index no of the liquid crystal material to the wavelength and a changing degree of an abnormal light refractive index ne of the liquid crystal material to the wavelength is set to be in the range where screen coloring depending on the visual angle is not generated. <P>COPYRIGHT: (C)2003,JPO

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 which a viewing angle of a display screen is improved by combining a liquid crystal display element and a retardation element having optical anisotropy.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display device using a nematic liquid crystal has been widely used for a numerical segment type display device such as a clock and a calculator, but recently, a word processor, a notebook type personal computer, an in-vehicle liquid crystal television, etc. It is also used for.

This liquid crystal display device generally has a pair of translucent substrates which are opposed to each other with a liquid crystal layer interposed therebetween, and electrode wirings for turning on / off pixels are formed on the substrates. Has been formed. For example, in an active matrix liquid crystal display device, pixel electrodes for applying a voltage to liquid crystal are provided in a matrix, and active elements such as field effect transistors are used as switching means for selectively applying a potential to each pixel electrode. Are provided on the substrate together with the electrode wiring. Furthermore, in a liquid crystal display device that performs color display, color filter layers of red, green, blue, etc. are provided on a substrate.

In such a liquid crystal display device, different display systems are appropriately selected and used according to the twist angle of the liquid crystal. Among them, for example, an active drive type twist nematic liquid crystal display system (hereinafter referred to as TN system) and a multiplex drive type super twist nematic liquid crystal display system (hereinafter referred to as STN system) are well known.

In the former TN mode, display is performed by orienting nematic liquid crystal molecules in a 90 ° twisted state between a pair of substrates and guiding light along the twisted direction. The latter STN method utilizes the fact that the light transmittance in the vicinity of the threshold value of the liquid crystal applied voltage sharply changes by making the twist angle of the nematic liquid crystal molecules larger than 90 ° between the pair of substrates.

Among these display systems, the STN system utilizes the birefringence effect of liquid crystal, so that the background of the display screen is colored uniquely due to color interference. Conventionally, it has been considered effective to use an optical compensator in order to prevent such coloring and perform black and white display by the STN method. Display methods using this optical compensator are roughly classified into a double super twisted nematic phase compensation method (hereinafter referred to as DSTN method) and a film type phase compensation method (hereinafter referred to as film addition type method).

The above-mentioned DSTN system includes a display liquid crystal cell and
This display liquid crystal cell has a structure having two layers of liquid crystal cells, that is, a liquid crystal cell twisted and aligned at a twist angle in the opposite direction, and the other film addition type method is to arrange a film having optical anisotropy. It is a structure. From the viewpoints of lightness and low cost, the film addition type method is considered to be effective.

In the above-mentioned STN system, since the black-and-white display characteristics are improved by adopting these phase compensation systems, a color STN liquid crystal display device capable of color display by providing a color filter layer has been realized.

On the other hand, the TN method is roughly classified into a normally black method and a normally white method.

In the former normally black system, a pair of polarizing plates are arranged so as to sandwich the both sides of a liquid crystal display device so that their polarization directions are parallel to each other, and a state in which an on-voltage is not applied to a liquid crystal layer (off state). ) Is a method of displaying black. In the latter normally white method, 1
This is a method of arranging a pair of polarizing plates so that their polarization directions are orthogonal to each other and displaying white in the off state on the liquid crystal layer. Of these, the normally white method is effective from the viewpoints of display contrast, color reproducibility, viewing angle dependence of display, and the like.

By the way, in the above-mentioned TN type liquid crystal display device, since the liquid crystal molecules have the refractive index anisotropy Δn and the liquid crystal molecules are inclined and aligned with respect to the upper and lower substrates, There is a problem in that the contrast of the display image changes depending on the direction and angle at which the observer looks at the display screen, and the viewing angle dependency increases. This problem will be described below.

FIG. 8 schematically shows a cross-sectional structure of a TN type liquid crystal display element 31, showing a state where liquid crystal molecules 32 are slightly raised by application of a halftone display voltage to the liquid crystal layer. There is.

In this liquid crystal display element 31, linearly polarized light 3 passing through in the normal direction of the surfaces of the pair of substrates 33 and 34.
5, and the linearly polarized lights 36 and 37 that pass with an inclination with respect to the normal direction have different angles intersecting with the liquid crystal molecule 32. Here, since the liquid crystal molecule 32 has a refractive index anisotropy Δn, normal light and extraordinary light are generated when each of the linearly polarized light 35, 36, and 37 passes through the liquid crystal molecule 32. Since this is converted into elliptically polarized light, this causes the viewing angle dependence.

Further, inside the actual liquid crystal layer, the tilt angles of the liquid crystal molecules 32 are different between the vicinity of the intermediate portion between the substrates 33 and 34 and the vicinity of the substrates 33 and 34, and the normal direction of the substrate surface. Since the liquid crystal molecules 32 are twisted by 90 ° about the axis, they also cause the viewing angle dependence.

Thus, the linearly polarized light 3 passing through the liquid crystal layer 3
5, 36 and 37 show various viewing angle dependences due to various birefringence effects depending on their directions and angles.

For example, when the viewing angle is inclined from the normal direction of the screen toward the normal viewing angle direction (downward direction of the screen), the phenomenon that the display screen is colored at a certain angle or more (hereinafter, referred to as coloring phenomenon) or black and white is reversed. A phenomenon (hereinafter referred to as a reversal phenomenon) occurs. Further, when the viewing angle is tilted from the screen normal direction to the counter viewing angle direction (upward direction of the screen), the contrast sharply decreases.

Further, the above-mentioned liquid crystal display device has a problem that the viewing angle becomes narrower as the display screen becomes larger. For example, when a large liquid crystal display screen is viewed from a front direction at a short distance, the colors displayed on the upper part and the lower part of the screen may be different due to the viewing angle dependency. This is because as the display screen becomes larger, the viewing angle of the entire screen becomes larger, which is the same as viewing the display screen from an oblique direction.

In order to improve the viewing angle dependency in such a TN system, a retardation film (or retardation film) as an optical element (retardation element) having optical anisotropy is used as a liquid crystal display element and a polarizing plate. A method of arranging between and is proposed.

According to this method, the light that has been converted from linearly polarized light to elliptically polarized light by passing through liquid crystal molecules having refractive index anisotropy is provided with a phase difference provided on one side or both sides of the liquid crystal layer having refractive index anisotropy. Pass the board. This makes it possible to compensate for the phase difference change between the normal light and the extraordinary light that occurs depending on the viewing angle and convert the linearly polarized light again, so that the viewing angle dependency can be improved.

For example, JP-A-5-313159 proposes a method of using a retardation plate in which one main refractive index direction of an index ellipsoid is parallel to the normal line direction of the surface of the retardation plate. Has been done. However, even if this retardation plate is used, there is a limit in improving the inversion phenomenon in the normal viewing angle direction.

Therefore, Japanese Patent Laid-Open No. 6-75116 proposes a method of using a retardation plate in which the main refractive index direction of the index ellipsoid is inclined with respect to the normal line direction of the surface of the retardation plate. Has been done. Here, the following two types of phase difference plates are listed.

One of the three main refractive indices of the refractive index ellipsoid of the phase difference plate is such that the direction of the minimum main refractive index is parallel to the surface of the phase difference plate, and the remaining two main refractive indices. One direction of the refractive index is inclined at an angle of θ with respect to the surface of the retardation plate, and the other direction is inclined at an angle of θ with respect to the normal direction of the surface of the retardation plate. The angle is ≤θ≤70 °.

The other is 3 of the refractive index ellipsoid of the retardation plate.
The two main refractive indices na, nb, and nc are na = nc> nb, and the direction of the main refractive index nb is the normal direction of the surface with the direction of the main refractive index na or nc parallel to the surface of the retardation plate as the axis. From the direction parallel to the surface to the clockwise or counterclockwise direction while tilting clockwise or counterclockwise from the above, and the phase difference in which the refractive index ellipsoid is tilted. It is a plate.

Of these two types of retardation films, the former one can use a uniaxial one and a biaxial one. The latter may use only one such retardation plate, but further uses two retardation plates in combination so that the inclination directions of the respective main refractive indices nb form an angle of 90 ° with each other. You can also

By disposing at least one such retardation film between the liquid crystal display element and the polarizing plate, a change in contrast depending on the viewing angle of the displayed image, a coloring phenomenon and a reversal phenomenon are caused to some extent. Can be improved.

Further, in Japanese Patent Application Laid-Open No. 8-101381, in the liquid crystal display device using the latter of the above-mentioned two types of retardation plates, the wavelength dispersion of the refractive index anisotropy of the retardation plate is reflected by the liquid crystal. There has been proposed a method of improving the viewing angle characteristics of display colors by making the anisotropy smaller than the wavelength dispersion. Further, in JP-A-5-215912, in a liquid crystal display device using a conventional retardation plate in which the refractive index ellipsoid is not tilted, the wavelength dispersion of the refractive index anisotropy of the retardation plate is changed to the refractive index difference of the liquid crystal. A method of improving the viewing angle characteristics by making the wavelength dispersion smaller than that of isotropic dispersion has been proposed.

Here, as a method of adjusting the wavelength dispersion of the retardation plate, there are a method of changing the material of the retardation plate and a method of adjusting the thickness of the retardation plate.

[0028]

Under the circumstances where a liquid crystal display device having a wide viewing angle and a high display quality is desired as in today's day, further improvement of the viewing angle dependency is required, and the above-mentioned Japanese Patent Laid-Open No. It is not always sufficient to use only the retardation plate disclosed in JP-A-6-75116.

On the other hand, in the methods disclosed in JP-A-8-101381 and JP-A-5-215912, the materials usable as the retardation plate are limited,
A retardation plate made of a material having an appropriate wavelength dispersion is not practical. Further, if the thickness of the retardation plate is increased, the phase difference changes due to the change of the optical path length and the change of the refractive index ellipsoid when the viewing angle is tilted, which hinders the expansion of the viewing angle and is not preferable in practice. Furthermore, this method has not yet improved the coloring phenomenon of the display screen when the viewing angle is tilted,
There is still room for improvement.

The present invention has been made to solve the problems of the prior art, and further improves the contrast change, the coloring phenomenon, the reversal phenomenon and the like that occur depending on the viewing angle, and particularly, it depends on the viewing angle. An object of the present invention is to provide a liquid crystal display device capable of effectively improving the coloring phenomenon of a liquid crystal screen.

[0031]

A liquid crystal display device according to the present invention comprises a liquid crystal display element in which a liquid crystal layer is sandwiched between a pair of substrates each having an electrode layer and an alignment film, and both sides of the liquid crystal display element. In a liquid crystal display device having a pair of polarizers sandwiched between and at least one polarizer and at least one retardation element provided between the liquid crystal display elements, three of the refractive index ellipsoids of the retardation elements are provided. Principal refractive indices na, nb and n
c has a relationship of na = nc> nb, and the direction of the main refractive index nb is the normal to the surface with one direction of the main refractive indices na and nc substantially parallel to the surface of the retardation element as an axis. A screen that is tilted clockwise or counterclockwise from the direction and the other direction of the main refractive indices na and nc is tilted clockwise or counterclockwise from the direction substantially parallel to the surface, and is dependent on the viewing angle. The average alkyl chain length of the liquid crystal material in the liquid crystal layer, the degree of change of the normal light refractive index no of the liquid crystal material with respect to the wavelength, and the change of the extraordinary light refractive index ne of the liquid crystal material with respect to the wavelength so that coloring does not occur. The combination condition with the degree is set, and the above-mentioned purpose is achieved by that.

The average alkyl chain (C _m H
The length m of _{2m + 1} −) is set in the range of m <3.40, and the extraordinary refractive index n of the liquid crystal material with respect to light having a wavelength of 450 nm is n.
e (450), the degree of change in the extraordinary light refractive index ne (550) for light with a wavelength of 550 nm and the extraordinary light refractive index ne (650) for light with a wavelength of 650 nm, and a wavelength of 450 nm
Refractive index for normal light no (450), wavelength 550
The degree of change of the normal light refractive index no (550) with respect to the light of wavelength nm and the change degree of the normal light refractive index no (650) with respect to the light of wavelength 650 nm is 1 ≦ (((no (450) -no (550)) / (no
(550) -no (650))) / ((ne (450))
-Ne (550)) / (ne (550) -ne (65
0)))) ≦ −0.422 m + 2.55.

An extraordinary light refractive index ne (450) for light having a wavelength of 450 nm, an extraordinary light refractive index ne (550) for light having a wavelength of 550 nm, and a wavelength of 650 nm of the liquid crystal material.
Of the extraordinary light refractive index ne (650) with respect to the light of
50), the normal light refractive index no for light with a wavelength of 550 nm
(550) and the degree of change of the normal light refractive index no (650) with respect to light having a wavelength of 650 nm are 1 ≦ (((no (450) −no (550)) / (no
(550) -no (650))) / ((ne (450))
-Ne (550)) / (ne (550) -ne (65
0)))) ≦ −0.343 m + 2.26 is preferably set.

The average alkyl chain (C _m H
The length m of _{2m + 1} −) is set in the range of 3.40 ≦ m ≦ 3.90, and the extraordinary light refractive index ne (450) of the liquid crystal material with respect to light having a wavelength of 450 nm and the extraordinary light with respect to light of 550 nm are given. The degree of change of the refractive index ne (550) and the extraordinary light refractive index ne (650) with respect to the light of wavelength 650 nm, and the normal light refractive index no (450) with respect to the light of wavelength 450 nm,
Normal light refractive index no (55
0) and normal light refractive index no for light of wavelength 650 nm
The degree of change of (650) is 0.80 ≦ (((no (450) −no (550)) /
(No (550) -no (650))) / ((ne (4
50) -ne (550)) / (ne (550) -ne
(650)))) ≦ 1.20 may be set.

Extraordinary light refractive index ne (450) for light of wavelength 450 nm, extraordinary light refractive index ne (550) for light of wavelength 550 nm and wavelength 650 nm of the liquid crystal material
Of the extraordinary light refractive index ne (650) with respect to the light of
50), the normal light refractive index no for light with a wavelength of 550 nm
(550) and the degree of change of the normal light refractive index no (650) with respect to light having a wavelength of 650 nm are 0.85 <(((no (450) -no (550)) /
(No (550) -no (650))) / ((ne (4
50) -ne (550)) / (ne (550) -ne
(650)))) <1.15 is preferably set.

The average alkyl chain (C _m H
The length m of _{2m + 1} −) is set in the range of m> 3.90, and the extraordinary refractive index n of the liquid crystal material with respect to light having a wavelength of 450 nm is n.
e (450), the degree of change in the extraordinary light refractive index ne (550) for light with a wavelength of 550 nm and the extraordinary light refractive index ne (650) for light with a wavelength of 650 nm, and a wavelength of 450 nm
Refractive index for normal light no (450), wavelength 550
The degree of change of the normal light refractive index no (550) for the light of wavelength nm and the change degree of the normal light refractive index no (650) for the light of wavelength 650 nm is -0.422m + 2.55≤ (((no (450) -n
o (550)) / (no (550) -no (65
0))) / ((ne (450) -ne (550)) /
(Ne (550) −ne (650)))) ≦ 1 may be set.

Extraordinary light refractive index ne (450) for light of wavelength 450 nm, extraordinary light refractive index ne (550) for light of wavelength 550 nm and wavelength 650 nm of the liquid crystal material
Of the extraordinary light refractive index ne (650) with respect to the light of
50), the normal light refractive index no for light with a wavelength of 550 nm
(550) and the degree of change of the normal light refractive index no (650) with respect to light having a wavelength of 650 nm are −0.343 m + 2.26 ≦ (((no (450) −n
o (550)) / (no (550) -no (65
0))) / ((ne (450) -ne (550)) /
It is preferable that (ne (550) −ne (650)))) ≦ 1 is set.

The refractive index anisotropy Δn (550) of the liquid crystal material with respect to light having a wavelength of 550 nm is preferably set in a range of more than 0.060 and less than 0.120.

The refractive index anisotropy Δn (550) of the liquid crystal material with respect to light having a wavelength of 550 nm is 0.070 or more and 0.0.
It is preferably set in the range of 95 or less.

It is preferable that the inclination angle of the refractive index ellipsoid in the retardation element is set in the range of 15 ° to 75 °.

The product of the difference between the main refractive indices na and nb of the retardation element and the thickness d of the retardation element (na-nb) * d.
Is preferably set in the range of 80 nm to 250 nm.

The background of the completion of the present invention and the operation of the present invention will be described below.

In the present invention, the three main refractive indices na, nb and nc of the refractive index ellipsoid of the retardation element are na = nc.
> Nb, and the direction of the main refractive index nb is clockwise or counterclockwise from the direction normal to the surface with one direction of the main refractive indexes na and nc substantially parallel to the surface of the retardation element as an axis. While tilting clockwise, the other direction of the main refractive indices na and nc tilts clockwise or counterclockwise from the direction substantially parallel to the surface, so that the refractive index ellipsoid of the phase difference element tilts. There is. When the linearly polarized light passes through the liquid crystal layer having birefringence and normal light and extraordinary light are generated, the passing light is changed to elliptically polarized light due to the phase difference between them. The phase difference from the extraordinary light is compensated.

However, such a compensation function of the phase difference plate alone cannot sufficiently satisfy the demand for further improvement of the viewing angle dependency.

Therefore, as a result of repeated studies by the present inventors, in the liquid crystal layer enclosed in the liquid crystal display device, the average alkyl chain length of the liquid crystal material and the normal light refractive index no of the liquid crystal material are no.
Of the liquid crystal material with respect to the wavelength, and the extraordinary refractive index n of the liquid crystal material
The inventors have found that the combination condition of the change degree of e with respect to the wavelength has a particular effect on the coloring of the liquid crystal display screen, and have completed the present invention.

In the liquid crystal display device of the present invention, the average alkyl chain length of the liquid crystal material and the normal light refractive index no of the liquid crystal material are
Of the liquid crystal material with respect to the wavelength, and the extraordinary refractive index n of the liquid crystal material
The combination condition with the degree of change of e with respect to the wavelength is set to a range in which screen coloring depending on the viewing angle does not occur.
This makes it possible to further prevent the screen from being colored, and further, as shown in the embodiments described later, it is possible to further improve the contrast change and the inversion phenomenon as compared with the case where only the compensation function of the retardation film is used. did it.

The relationship between the average alkyl chain length of the liquid crystal material, the degree of change of the normal light refractive index no of the liquid crystal material with respect to the wavelength, and the degree of change of the extraordinary light refractive index ne of the liquid crystal material with respect to the wavelength is specifically as follows. Set to the range of.

(1) Average alkyl chain (C _m H of liquid crystal material)
_When the length m of _{2m + 1} −) is m <3.40, the extraordinary refractive index ne (45
0), the extraordinary refractive index ne for the light of wavelength 550 nm
(550) and the degree of change of the extraordinary light refractive index ne (650) with respect to the light of wavelength 650 nm, the normal light refractive index no (450) with respect to the light of wavelength 450 nm, the normal light refractive index no (550) with respect to the light of wavelength 550 nm, and Wavelength 650
The degree of change of the normal light refractive index no (650) with respect to the light of nm is expressed as 1 ≦ (((no (450) −no (550)) / (no
(550) -no (650))) / ((ne (450))
-Ne (550)) / (ne (550) -ne (65
0)))) ≦ −0.422 m + 2.55.

In this case, as shown in Embodiment 1 to be described later, although a slight coloring occurs at a viewing angle of 50 ° required for a normal liquid crystal display device, it can be sufficiently used from any direction. Display is obtained.

More preferably, 1≤ (((no (450) -no (550)) / (no
(550) -no (650))) / ((ne (450))
-Ne (550)) / (ne (550) -ne (65
0)))) ≤-0.343m + 2.26.

In this case, as shown in Embodiment 1 described later, in a liquid crystal display device having a wider viewing angle of 70 °, a display without any coloring phenomenon can be obtained when viewed from any direction.

(2) Average alkyl chain (C _m H of liquid crystal material)
_When the length m of _{2m + 1} −) is 3.40 ≦ m ≦ 3.90, the extraordinary refractive index ne of the liquid crystal material with respect to light having a wavelength of 450 nm is ne.
(450), the degree of change of the extraordinary light refractive index ne (550) for the light of wavelength 550 nm and the extraordinary light refractive index ne (650) for the light of wavelength 650 nm, and the normal light refractive index no (450) for the light of wavelength 450 nm, Wavelength 550n
Normal light refractive index no (550) and wavelength 6 for m light
The degree of change of the normal light refractive index no (650) with respect to the light of 50 nm is 0.80 ≦ (((no (450) −no (550)) /
(No (550) -no (650))) / ((ne (4
50) -ne (550)) / (ne (550) -ne
(650)))) ≤ 1.20.

In this case, as shown in Embodiment 2 to be described later, although a slight coloring occurs at a viewing angle of 50 ° required for a normal liquid crystal display device, it can be sufficiently used from any direction. Display is obtained.

More preferably, 0.85 <(((no (450) -no (550)) /
(No (550) -no (650))) / ((ne (4
50) -ne (550)) / (ne (550) -ne
(650)))) <1.15.

In this case, as shown in Embodiment 2 described later, in a liquid crystal display device having a wider viewing angle of 70 °, a display without any coloring phenomenon can be obtained when viewed from any direction.

(3) Average alkyl chain (C _m H of liquid crystal material)
_When the length m of _{2m + 1} −) is m> 3.90, the extraordinary light refractive index ne (45
0), the extraordinary refractive index ne for the light of wavelength 550 nm
(550) and the degree of change of the extraordinary light refractive index ne (650) with respect to the light of wavelength 650 nm, the normal light refractive index no (450) with respect to the light of wavelength 450 nm, the normal light refractive index no (550) with respect to the light of wavelength 550 nm, and Wavelength 650
The degree of change of the normal light refractive index no (650) with respect to the light of nm is −0.422m + 2.55 ≦ (((no (450) −n
o (550)) / (no (550) -no (65
0))) / ((ne (450) -ne (550)) /
(Ne (550) −ne (650)))) ≦ 1.

In this case, as shown in Embodiment 3 which will be described later, although a slight coloring occurs at a viewing angle of 50 ° required for a normal liquid crystal display device, it can be sufficiently used from any direction. Display is obtained.

More preferably, -0.343m + 2.26≤ (((no (450) -n
o (550)) / (no (550) -no (65
0))) / ((ne (450) -ne (550)) /
(Ne (550) −ne (650)))) ≦ 1.

In this case, as shown in Embodiment 3 described later, in a liquid crystal display device having a wider viewing angle of 70 °, a display without any coloring phenomenon can be obtained when viewed from any direction.

In the liquid crystal display device of the present invention, the wavelength of 5
Refractive index anisotropy Δn (5
It is preferable to set 50) to a range larger than 0.060 and smaller than 0.120. Wavelength 55 in the visible light range
Refractive index anisotropy Δn (55
0) is 0.060 or less or 0.120 or more,
This is because it has been confirmed that an inversion phenomenon and a decrease in contrast ratio occur depending on the viewing angle direction, as shown in Embodiment 4 described later. By setting the refractive index anisotropy Δn (550) of the liquid crystal material with respect to light having a wavelength of 550 nm in the range of more than 0.060 and less than 0.120, it is possible to eliminate the phase difference according to the viewing angle. Naturally, the coloring phenomenon that occurs depending on the viewing angle on the screen can be further improved with respect to the contrast change, the inversion phenomenon in the horizontal direction, and the like.

Here, by setting the refractive index anisotropy Δn (550) of the liquid crystal material with respect to light having a wavelength of 550 nm in the range of 0.070 or more and 0.095 or less, as shown in Embodiment 4 described later, It is possible to more effectively eliminate the phase difference according to the viewing angle. Therefore, it is possible to reliably improve the coloring phenomenon, the change in contrast, the inversion phenomenon in the left-right direction, and the like that occur depending on the viewing angle on the liquid crystal display screen.

In the liquid crystal display device of the present invention, it is preferable to set the tilt angle of the refractive index ellipsoid in the retardation element within the range of 15 ° to 75 °. By setting the tilt angle of the refractive index ellipsoid of the phase difference element in this way, the phase difference change between the normal light and the extraordinary light generated according to the above-described viewing angle can be changed as shown in Embodiment 4 described later. The phase difference element can surely compensate.

In the liquid crystal display device of the present invention, the product (na−nb) × d of the difference between the main refractive indexes na and nb of the retardation element and the thickness d of the retardation element is 80 nm to 250 nm.
It is preferable to set it in the following range. Thus, the difference between the main refractive indices na and nb of the phase difference element and the thickness d of the phase difference element
By setting the product of and, as shown in Embodiment 4 described later, it is possible to reliably compensate the phase difference change between the normal light and the extraordinary light, which occurs according to the viewing angle, by the phase difference element.

[0064]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a liquid crystal display device which is an embodiment of the present invention. The liquid crystal display device includes a liquid crystal cell 16 including a liquid crystal display element 1, a pair of retardation plates 2 and 3, and a pair of polarizing plates 4 and 5, and a drive circuit 17.

In the liquid crystal display element 1, a liquid crystal layer 8 is sandwiched between a pair of electrode substrates 6 and 7 which are arranged to face each other. In one electrode substrate 6, a transparent electrode 10 made of ITO (indium tin oxide) is formed on the surface of a glass substrate (translucent substrate) 9 serving as a base on the liquid crystal layer 8 side, and an alignment film 11 is formed thereon. Has been formed. On the other electrode substrate 7, a transparent electrode 13 made of ITO is formed on the surface of the glass substrate (translucent substrate) 12 serving as a base on the liquid crystal layer 8 side, and an alignment film 14 is formed thereon.

Both transparent electrodes 10 and 11 are connected to a drive circuit 17. Although FIG. 1 shows a configuration for two pixels for simplification, a strip-shaped transparent electrode 10 having a predetermined width is formed in almost the entire display portion of the liquid crystal display element 1.
13 is formed on the glass substrates 9 and 12, and the transparent electrode 10 on one glass substrate 9 and the transparent electrode 13 on the other glass substrate 10 intersect each other when viewed from a direction perpendicular to the substrate surface (here, (Orthogonal).

The alignment films 11 and 14 have been previously subjected to rubbing treatment so that the liquid crystal molecules in the liquid crystal layer 8 are twisted and aligned by about 90 °. Rubbing direction R1 of alignment film 11 and alignment film 1
As shown in FIG. 2, the rubbing directions R2 of 4 are set in directions orthogonal to each other.

Both electrode substrates 6 and 7 are bonded together by a seal resin 15, and the electrode substrates 6 and 7 and the seal resin 1 are bonded together.
A liquid crystal layer 8 is enclosed in a space surrounded by 5. Although details of the liquid crystal layer 8 will be described later, an alkyl chain of the liquid crystal material in the liquid crystal layer 8 and normal light are used so that the best characteristics can be obtained by combining with the phase difference compensation function of the phase difference plates 2 and 3. The relationship between the degree of change of the refractive index no with respect to wavelength and the degree of change of the extraordinary refractive index ne with respect to wavelength is set within a predetermined range.

The retardation plates 2 and 3 are arranged one each between the liquid crystal display element 1 and the polarizing plates 4 and 5 on both sides thereof. The retardation plates 2 and 3 are obtained by cross-linking a discotic liquid crystal on a support made of a transparent organic polymer by being tilted or hybrid-aligned. As a result, as will be described later, the retardation plates 2 and 3 having the inclined refractive index ellipsoids.
Is obtained.

The support material for the retardation plates 2 and 3 is triacetyl cellulose (TA) which is generally used for polarizing plates.
C) is suitable, and a retardation plate with high reliability can be obtained.
Other materials include polycarbonate (PC),
A colorless and transparent organic polymer film having excellent environment resistance and chemical resistance, such as polyethylene terephthalate (PET), is suitable.

As shown in FIG. 3, the retardation plates 2 and 3 have different main refractive indices na, nb and nc in three directions.

The three main refractive indices na, nb and nc are na
= Nc> nb. In this case, since there is only one optical axis, the retardation plates 2 and 3 are uniaxial, and the refractive index anisotropy is negative.

The direction of the main refractive index na is the orthogonal coordinate axis xyz.
Among these, the direction of the y-axis parallel to the surfaces of the phase difference plates 2 and 3 (parallel to the screen) is matched. The direction of the main refractive index nb is from the direction of the z-axis perpendicular to the surfaces of the phase difference plates 2 and 3 (normal direction of the surface, perpendicular to the screen) to the direction of arrow A with the direction of the main refractive index na as the axis. θ is tilted. The direction of the main refractive index nc is
With the direction of the main refractive index na as the axis, the angle θ is inclined in the direction of arrow B from the direction of the x-axis parallel to the surfaces of the phase difference plates 2 and 3 (parallel to the screen). The inclination angle θ of this index ellipsoid is preferably 15 ° ≦ θ ≦ 75 °. By setting this range, the phase difference compensating function of the phase difference plates 2 and 3 can be surely obtained regardless of whether the tilt direction of the index ellipsoid is clockwise or counterclockwise. Here, the phase difference plates 2, 3
Let D be the direction in which the direction of the main refractive index nb that is inclined in the direction that gives anisotropy to is projected onto the surfaces of the phase difference plates 2 and 3.

The first retardation value of the retardation plates 2 and 3 is the product of the difference between the main refractive indices na and nc (refractive index anisotropy Δn) and the thickness d of the retardation element (nc-na) ×. Although it is represented by d, it is almost 0 nm because na = nc. The second retardation value is the product (na−n) of the difference between the main refractive indices na and nb (refractive index anisotropy Δn) and the thickness d of the retardation element.
It is represented by b) × d, but it is preferably set in the range of 80 nm or more and 250 nm or less. By setting this range, the phase difference compensating function of the phase difference plates 2 and 3 can be surely obtained.

Liquid crystal and retardation film (retardation film)
In such an anisotropic body, the anisotropy of the main refractive indices na, nb, and nc in the three-dimensional direction is represented by a refractive index ellipsoid.
The refractive index anisotropy Δn has different values depending on from which direction the refractive index anisotropic body is observed.

In the liquid crystal display device of this embodiment, the liquid crystal display element 1, the retardation plates 2 and 3, and the polarizing plates 4 and 5 are arranged as shown in FIG.

The polarizing plate 4 is arranged so that its absorption axis AX1 is parallel to the rubbing direction R1 of the above-mentioned alignment film 11, and the polarizing plate 5 has its absorption axis AX2 in the above-mentioned alignment film 14.
Are arranged so as to be parallel to the rubbing direction R2. In this liquid crystal display device, since the rubbing directions R1 and R2 are orthogonal to each other, the absorption axes AX1 and AX2 are also orthogonal to each other.

The phase difference plate 2 is moved in the direction D (D
1) is arranged so as to be parallel to the rubbing direction R1 of the alignment film 11, and the phase difference plate 3 has the direction D (D) shown in FIG.
2) is arranged so as to be parallel to the rubbing direction R2 of the alignment film 14.

The liquid crystal display element 1, the retardation plate 2,
By arranging 3 and the polarizing plates 4 and 5, it is possible to obtain a so-called normally white mode liquid crystal display device which transmits light when turned off without applying an on-voltage to the liquid crystal layer 8 and displays white.

Regarding the arrangement of the phase difference plates 2 and 3,
Only one of the phase difference plates 2 and 3 may be arranged on one side of the liquid crystal display element 1, or both of the phase difference plates 2 and 3 may be arranged on one side of the liquid crystal display element 2 in an overlapping manner. Good. Furthermore, it is also possible to use three or more retardation plates.

Next, the liquid crystal layer 8 will be described in detail.

As described above, in order to obtain the best characteristics in combination with the phase difference compensating function of the phase difference plates 2 and 3, the alkyl chain of the liquid crystal material in the liquid crystal layer 8 and the wavelength of the normal light refractive index no are compared. The relationship between the degree of change and the degree of change of the extraordinary light refractive index ne with respect to the wavelength is set in a range in which coloring depending on the viewing angle does not occur on the display screen.

Specifically, the relationship between the average alkyl chain length of the liquid crystal material, the degree of change of the normal light refractive index no of the liquid crystal material with respect to wavelength, and the degree of change of the extraordinary light refractive index ne of the liquid crystal material with respect to wavelength is as follows: It is set so as to satisfy the condition of at least one of the following setting ranges (1) to (3).

(1) Average alkyl chain (C _m H of liquid crystal material)
_When the length m of _{2m + 1} −) is m <3.40, the extraordinary refractive index ne (45
0), the extraordinary refractive index ne for the light of wavelength 550 nm
(550) and the degree of change of the extraordinary light refractive index ne (650) with respect to the light of wavelength 650 nm, the normal light refractive index no (450) with respect to the light of wavelength 450 nm, the normal light refractive index no (550) with respect to the light of wavelength 550 nm, and Wavelength 650
The degree of change of the normal light refractive index no (650) with respect to the light of nm is expressed as 1 ≦ (((no (450) −no (550)) / (no
(550) -no (650))) / ((ne (450))
-Ne (550)) / (ne (550) -ne (65
0)))) ≦ −0.422 m + 2.55.

More preferably, 1≤ (((no (450) -no (550)) / (no
(550) -no (650))) / ((ne (450))
-Ne (550)) / (ne (550) -ne (65
0)))) ≤-0.343m + 2.26.

(2) Average alkyl chain (C _m H of liquid crystal material)
_When the length m of _{2m + 1} −) is 3.40 ≦ m ≦ 3.90, the extraordinary refractive index ne of the liquid crystal material with respect to light having a wavelength of 450 nm is ne.
(450), the degree of change of the extraordinary light refractive index ne (550) for the light of wavelength 550 nm and the extraordinary light refractive index ne (650) for the light of wavelength 650 nm, and the normal light refractive index no (450) for the light of wavelength 450 nm, Wavelength 550n
Normal light refractive index no (550) and wavelength 6 for m light
The degree of change of the normal light refractive index no (650) with respect to the light of 50 nm is 0.80 ≦ (((no (450) −no (550)) /
(No (550) -no (650))) / ((ne (4
50) -ne (550)) / (ne (550) -ne
(650)))) ≤ 1.20.

More preferably, 0.85 <(((no (450) -no (550)) /
(No (550) -no (650))) / ((ne (4
50) -ne (550)) / (ne (550) -ne
(650)))) <1.15.

(3) Average alkyl chain (C _m H of liquid crystal material)
_When the length m of _{2m + 1} −) is m> 3.90, the extraordinary light refractive index ne (45
0), the extraordinary refractive index ne for the light of wavelength 550 nm
(550) and the degree of change of the extraordinary light refractive index ne (650) with respect to the light of wavelength 650 nm, the normal light refractive index no (450) with respect to the light of wavelength 450 nm, the normal light refractive index no (550) with respect to the light of wavelength 550 nm, and Wavelength 650
The degree of change of the normal light refractive index no (650) with respect to the light of nm is −0.422m + 2.55 ≦ (((no (450) −n
o (550)) / (no (550) -no (65
0))) / ((ne (450) -ne (550)) /
(Ne (550) −ne (650)))) ≦ 1.

More preferably, -0.343m + 2.26≤ (((no (450) -n
o (550)) / (no (550) -no (65
0))) / ((ne (450) -ne (550)) /
(Ne (550) −ne (650)))) ≦ 1.

With this structure, the liquid crystal display device of this embodiment compensates for the phase difference change between the normal light and the extraordinary light which occurs in the liquid crystal display element 1 depending on the viewing angle by the phase difference plates 2 and 3, and at the same time, the liquid crystal display The coloring depending on the viewing angle generated on the screen can be compensated particularly effectively by the liquid crystal material of the liquid crystal layer 8. Therefore, the coloring of the display screen depending on the viewing angle is effectively improved, and at the same time, the contrast change and the reversal phenomenon are also improved, and a high quality image can be obtained.

The liquid crystal display device of the present invention will be described below with reference to more specific embodiments.

(Embodiment 1) In Embodiment 1, in the liquid crystal display device shown in FIG. 1, a material system represented by the following structural formula is blended as a liquid crystal material of the liquid crystal layer 8 to obtain an average alkyl chain for 1 mol. The length _{m of} (C _m H _{2m + 1} −) is m
<3.40, and the extraordinary refractive index ne (450) for the light of wavelength 450 nm, the extraordinary refractive index ne (550) for the light of wavelength 550 nm, and the wavelength 650 nm of the liquid crystal material.
Of the extraordinary light refractive index ne (650) with respect to the light of
50), the normal light refractive index no for light with a wavelength of 550 nm
(550) and the degree of change of the normal light refractive index no (650) with respect to light having a wavelength of 650 nm are 1 ≦ (((no (450) -no (550)) / (no
(550) -no (650))) / ((ne (450))
-Ne (550)) / (ne (550) -ne (65
0)))) ≦≦ −0.422 m + 2.55.

[0094]

[Chemical 1]

Cell thickness of liquid crystal cell 16 (thickness of liquid crystal layer 8)
Was 5 μm, and five liquid crystal display devices (Samples # 11 to # 15) shown in Table 1 below were produced.

As the retardation plates 2 and 3, a discotic liquid crystal is applied to a transparent support (eg, triacetyl cellulose (TAC)), and the discotic liquid crystal is inclined and crosslinked to form a first retarder. The retardation value (nc-na) × d is 0 nm, the second retardation value (na-nb) × d is 100 nm, and the direction of the main refractive index nb shown in FIG. 3 is an arrow from the z-axis direction in the xyz coordinate axes. An index ellipsoid having an inclination angle θ = 20 ° in which the main refractive index nc was inclined about 20 ° in the direction A and the direction of the main refractive index nc was inclined about 20 ° in the direction of the arrow B from the x-axis direction was produced.

For comparison, in the liquid crystal display device shown in the liquid crystal display device of FIG. 1, the liquid crystal material of the liquid crystal layer 8 is 1> (((no (450) -no (550)) / (no
(550) -no (650))) / ((ne (450))
-Ne (550)) / (ne (550) -ne (65
0)))) or (((no (450) -no (55
0)) / (no (550) -no (650))) /
((Ne (450) -ne (550)) / (ne (55
0) -ne (650))))>-0.422m + 2.5
Two liquid crystal display devices (Comparative Samples # 100 and # 101) shown in Table 1 below were produced in the same manner as this embodiment except that the liquid crystal display device set in the range of 5 was used.

Table 1 below shows the results of a visual test under the white light of the samples # 11 to # 15 and the comparative samples # 100 and # 101. In Table 1 below and Tables 2 and 3 of Embodiments 2 and 3 described later, F (no (λ), ne (λ) = (((no (450) −
no (550)) / (no (550) -no (65
0))) / ((ne (450) -ne (550)) /
(Ne (550) -ne (650)))), where ○ is not colored, Δ is colored enough to withstand use, ×
Indicates that there is coloring that cannot be used.

[0099]

[Table 1]

As shown in Table 1 above, the samples # 13 to # 15 of this embodiment were not colored in any direction at a visual angle of 70 °, and good image quality was obtained. Therefore, 1 ≦ (((no (450) -no (550)) / (no
(550) -no (650))) / ((ne (450))
-Ne (550)) / (ne (550) -ne (65
It is understood that particularly excellent characteristics are obtained in the range of 0)))) ≦ −0.343 m + 2.26.

In addition, samples # 11 and # of this embodiment are
With respect to No. 12, no coloring was observed from any direction up to a viewing angle of 50 °, and good image quality was obtained. At a viewing angle of 60 °, some coloration was confirmed when viewed from the left and right directions, but it was coloration that could be used.

On the other hand, with respect to the comparative samples # 100 and # 101, it was confirmed that the samples were colored from yellow to orange at a viewing angle of 50 ° and could not be used even when viewed from the left and right directions.

Further, sample # 11 to sample # of the present embodiment except that a discotic liquid crystal was applied to the transparent supports as the retardation plates 2 and 3 for hybrid alignment.
Similar results were obtained for the liquid crystal display devices manufactured in the same manner as in No. 15 and Comparative Samples # 100 and # 101.

(Embodiment 2) In Embodiment 2, in the liquid crystal display device shown in FIG. 1, a material system represented by the following structural formula is blended as a liquid crystal material of the liquid crystal layer 8 to obtain an average alkyl chain for 1 mol. The length _{m of} (C _m H _{2m + 1} −) is set to 3.40 ≦ m ≦ 3.90, and the wavelength of the liquid crystal material is 450 n.
Extraordinary refractive index ne (450) for m light, wavelength 55
Extraordinary light refractive index ne (550) for 0 nm light and extraordinary light refractive index ne (650) for light having a wavelength of 650 nm
Of the normal light refractive index no (450) for the light of wavelength 450 nm, the normal light refractive index no (550) for the light of wavelength 550 nm and the normal light refractive index no (650) for the light of wavelength 650 nm. 0.80 ≦ (((no (450) −no (550)) /
(No (550) -no (650))) / ((ne (4
50) -ne (550)) / (ne (550) -ne
(650)))) ≦ 1.20 was used.

[0105]

[Chemical 2]

The liquid crystal cell 16 had a cell thickness of 5 μm, and the five liquid crystal display devices (samples # 21 to # 2) shown in Table 2 below were used.
5) was produced.

As the retardation plates 2 and 3, a discotic liquid crystal is applied to a transparent support (eg, triacetyl cellulose (TAC)), and the discotic liquid crystal is inclined and crosslinked to form a first retarder. The retardation value (nc-na) × d is 0 nm, the second retardation value (na-nb) × d is 100 nm, and the direction of the main refractive index nb shown in FIG. 3 is an arrow from the z-axis direction in the xyz coordinate axes. An index ellipsoid having an inclination angle θ = 20 ° in which the main refractive index nc was inclined about 20 ° in the direction A and the direction of the main refractive index nc was inclined about 20 ° in the direction of the arrow B from the x-axis direction was produced.

Furthermore, for comparison, in the liquid crystal display device shown in the liquid crystal display device of FIG. 1, the liquid crystal material of the liquid crystal layer 8 is 0.80> (((no (450) -no (550)) /
(No (550) -no (650))) / ((ne (4
50) -ne (550)) / (ne (550) -ne
((650)))) or (((no (450) -no (5
50)) / (no (550) -no (650))) /
((Ne (450) -ne (550)) / (ne (55
0) -ne (650))))> 1.20, the two liquid crystal display devices (Comparative Samples # 200 and # 200) shown in Table 2 below were prepared in the same manner as in the present embodiment. 201) was produced.

Table 2 below shows the results of a visual test under the white light of the samples # 21 to # 25 and the comparative samples # 200 and # 201.

[0110]

[Table 2]

As shown in Table 2 above, the samples # 22 to # 24 of this embodiment were not colored in any direction at a visual angle of 70 °, and good image quality was obtained. Therefore, 0.85 <(((no (450) -no (550)) /
(No (550) -no (650))) / ((ne (4
50) -ne (550)) / (ne (550) -ne
It is understood that particularly excellent characteristics are obtained in the range of (650)))) <1.15.

In addition, samples # 21 and # of this embodiment are
With respect to No. 25, coloring was not confirmed from any direction up to a viewing angle of 50 °, and good image quality was obtained. At a viewing angle of 60 °, some coloration was confirmed when viewed from the left and right directions, but it was coloration that could be used.

On the other hand, with respect to the comparative samples # 200 and # 201, it was confirmed that even at a viewing angle of 50 °, coloring from yellow to orange was unacceptable when used from the left and right directions.

Further, Samples # 21 to # of the present embodiment were used except that the discotic liquid crystal was applied to the transparent supports as the retardation plates 2 and 3 to perform the hybrid alignment.
Similar results were obtained for the liquid crystal display devices manufactured in the same manner as in No. 25 and Comparative Samples # 200 and # 201.

(Embodiment 3) In Embodiment 3, in the liquid crystal display device shown in FIG. 1, a material system represented by the following structural formula is blended as a liquid crystal material of the liquid crystal layer 8 to obtain an average alkyl chain for 1 mol. The length _{m of} (C _m H _{2m + 1} −) is m
> 3.90, the extraordinary refractive index ne (450) for the light of the wavelength of 450 nm, the extraordinary refractive index ne (550) for the light of the wavelength of 550 nm, and the wavelength of 650 nm of the liquid crystal material.
Of the extraordinary light refractive index ne (650) with respect to the light of
50), the normal light refractive index no for light with a wavelength of 550 nm
(550) and the degree of change of the normal light refractive index no (650) with respect to light having a wavelength of 650 nm are −0.422 m + 2.55 ≦ (((no (450) −n
o (550)) / (no (550) -no (65
0))) / ((ne (450) -ne (550)) /
(Ne (550) −ne (650)))) ≦ 1 was used.

[0116]

[Chemical 3]

The liquid crystal cell 16 had a cell thickness of 5 μm, and five liquid crystal display devices (samples # 31 to # 3) shown in Table 3 below were used.
5) was produced.

As the phase difference plates 2 and 3, a discotic liquid crystal is applied to a transparent support (for example, triacetyl cellulose (TAC)), and the discotic liquid crystal is inclined and crosslinked to form a first retarder. The retardation value (nc-na) × d is 0 nm, the second retardation value (na-nb) × d is 100 nm, and the direction of the main refractive index nb shown in FIG. 3 is an arrow from the z-axis direction in the xyz coordinate axes. An index ellipsoid having an inclination angle θ = 20 ° in which the main refractive index nc was inclined about 20 ° in the direction A and the direction of the main refractive index nc was inclined about 20 ° in the direction of the arrow B from the x-axis direction was produced.

For comparison, in the liquid crystal display device shown in the liquid crystal display device of FIG. 1, the liquid crystal material of the liquid crystal layer 8 is -0.422 m + 2.55> (((no (450) -n
o (550)) / (no (550) -no (65
0))) / ((ne (450) -ne (550)) /
(Ne (550) -ne (650)))) or (((n
o (450) -no (550)) / (no (550)-
no (650))) / ((ne (450) -ne (55)
0)) / (ne (550) -ne (650))))> 1 was used, except that two liquid crystal display devices shown in Table 3 below (comparison) were used in the same manner as this embodiment. Samples # 300 and # 301) were prepared.

Table 3 below shows the results of a visual test under the white light of the samples # 31 to # 35 and the comparative samples # 300 and # 301.

[0121]

[Table 3]

As shown in Table 3, the samples # 33 to # 35 of the present embodiment were not colored in any direction at a visual angle of 70 °, and good image quality was obtained. Therefore, −0.343m + 2.26 ≦ (((no (450) −n
o (550)) / (no (550) -no (65
0))) / ((ne (450) -ne (550)) /
It can be seen that particularly excellent characteristics are obtained in the range of (ne (550) -ne (650))) ≦ 1.

With respect to the sample # 31 of the present embodiment, no coloring was observed from any direction up to a viewing angle of 50 °, and good image quality was obtained. At a viewing angle of 60 °, the coloring was such that it could not be used when viewed from the left and right.

With respect to the sample # 32 of the present embodiment, no coloring was observed from any direction up to a viewing angle of 50 °, and good image quality was obtained. At a viewing angle of 60 °, some coloration was confirmed when viewed from the left and right directions, but it was coloration that could be used.

On the other hand, the comparative samples # 300 and # 301 were confirmed to have a yellow to orange coloration that could not be used even when viewed from the left and right even at a viewing angle of 50 °.

Further, as the retardation plates 2 and 3, samples # 31 to # of the present embodiment are applied except that a discotic liquid crystal is applied to a transparent support for hybrid alignment.
The same results were obtained for the liquid crystal display devices manufactured in the same manner as in No. 35 and Comparative Samples # 300 and # 301.

(Embodiment 4) In Embodiment 4, in the liquid crystal display device shown in FIG. 1, as a liquid crystal material of the liquid crystal layer 8, a refractive index anisotropy Δn (55) for light having a wavelength of 550 nm is used.
0) was set to 0.070, 0.080, and 0.095, and three liquid crystal display devices (samples # 41 to # 43) were produced with the liquid crystal cell 16 having a cell thickness of 5 μm. The average alkyl chain length m and the degree of change in the normal light refractive index no and the degree of change in the extraordinary light refractive index ne of each sample F (n
o (λ) and ne (λ) are as shown in Table 4 below.

[0128]

[Table 4]

As the retardation plates 2 and 3, the same ones as those in the above-described first embodiment in which the discotic liquid crystal is tilted and aligned are used.

Further, for comparison, in the liquid crystal display device shown in the liquid crystal display device of FIG. 1, as the liquid crystal material of the liquid crystal layer 8, the refractive index anisotropy Δn for light having a wavelength of 550 nm is Δn.
Two liquid crystal display devices (comparative samples # 401 and # 402) were produced in the same manner as in the present embodiment except that (550) was set to 0.060 and 0.120.

For the samples # 41 to # 43 and the comparative samples # 401 and # 402, the viewing angle dependence of the liquid crystal display device was measured by using the measurement system including the light receiving element 21, the amplifier 22 and the recording device 23 as shown in FIG. The sex was measured.

In this measurement system, in the liquid crystal cell 16 of the liquid crystal display device, the surface 16a on the glass substrate 9 side has an orthogonal coordinate axis x.
It is installed at the position of the reference plane xy of yz.

The light receiving element 21 is an element capable of receiving light at a fixed stereoscopic light receiving angle, and is arranged at a predetermined distance from the coordinate origin in a direction forming an angle φ (visual angle) with the z direction perpendicular to the surface 16a of the liquid crystal cell 16. It is placed in the position where it was placed.

At the time of measurement, the wavelength of 550 nm from the surface opposite to the surface 16a with respect to the liquid crystal cell 16 installed in the measurement system.
Of monochromatic light. As a result, a part of the monochromatic light transmitted through the liquid crystal cell 16 is incident on the light receiving element 21. Then, the output of the light receiving element 21 is amplified to a predetermined level by the amplifier 22 and then recorded by the recording device 23 including a waveform memory, a recorder and the like.

Sample # 41 of the present embodiment is applied to this measurement system.
~ # 43 and comparative samples # 401 and # 402 were installed, and the relationship between the voltage applied to each liquid crystal display device and the output level of the light receiving element 21 when the light receiving element 21 was fixed at a constant angle φ was measured. .

Here, the x direction is the lower side of the screen, and y
Assuming that the direction is on the left side of the screen, the arrangement position of the light receiving element 21 was changed to the upward direction, the right direction, and the left direction so that the angle φ was 50 °, and the measurement was performed.

The measurement results of samples # 41 to # 43 of this embodiment are shown in FIGS. 6 (a) to 6 (c), and the measurement results of comparative samples # 401 and # 402 are shown in FIG. 7 (a).
~ (C). 6 (a)-(c) and 7 (a)-
FIG. 6C is a graph showing the light transmittance (transmittance-liquid crystal applied voltage characteristic) with respect to the voltage applied to each liquid crystal display device, and FIG. 6A and FIG. 6B and FIG. 7B are results obtained by measuring from the right direction of FIG. 2, and FIG. 6C and FIG. Is the result of measurement from the left direction.

In FIGS. 6 (a) to 6 (c), the curves L1, L4, and L7 indicated by the alternate long and short dash line are Δn (5
50) = 0.070 Sample # 41 using liquid crystal material
And the curves L2, L5, and L8 indicated by solid lines are the liquid crystal layer 8
Shows sample # 42 using a liquid crystal material of Δn (550) = 0.080, and the curves L3, L6, L9 shown by the dotted lines are shown.
Indicates a sample # 43 using a liquid crystal material of Δn (550) = 0.095 for the liquid crystal layer 8. 7A to 7C, curves L10, L12, and L14 shown by solid lines show comparative sample # 401 using a liquid crystal material of Δn (550) = 0.060 for the liquid crystal layer 8, and are shown by dotted lines. Curve L1
1, L13, and L15 are Δn (550) = 0.
A comparative sample # 402 using 120 liquid crystal materials is shown.

Regarding the transmittance in the upward direction-liquid crystal applied voltage characteristic, the samples # 41 to # 43 of this embodiment are shown in FIG.
As shown in L1 to L3 of (a), it was confirmed that the transmittance was sufficiently decreased as the voltage was increased. On the other hand, in the comparative sample # 402, as shown by L11 in FIG. 7A, the transmittance does not decrease sufficiently even when the voltage is increased, and in the comparative sample # 401, the transmittance is indicated by L10 in FIG. 7A. As described above, an inversion phenomenon was observed in which the transmittance once decreased and then increased again as the voltage increased.

Similarly, regarding the transmittance-liquid crystal applied voltage characteristic in the right direction, in the samples # 41 to # 43 of this embodiment, as shown by L4 to L6 in FIG. Accordingly, it was confirmed that the transmittance decreased to almost zero. On the other hand, in comparison sample # 401, FIG.
As shown in L12 of Comparative Sample No. 402, although the transmittance decreases to almost 0 as the voltage increases,
Then, as indicated by L13 in FIG. 7B, a reversal phenomenon was observed in which the transmittance once decreased as the voltage increased and then increased again.

Similarly, regarding the transmittance-liquid crystal applied voltage characteristic in the left direction, in the samples # 41 to # 43 of this embodiment, as shown by L7 to L9 in FIG. Accordingly, it was confirmed that the transmittance decreased to almost zero. On the other hand, in comparative sample # 401, FIG.
As shown by L14 of Comparative Sample # 402, although the transmittance decreases to nearly 0 as the voltage increases,
Then, as indicated by L15 in FIG. 7C, a reversal phenomenon was observed in which the transmittance once decreased as the voltage increased and then increased again.

Further, the samples # 41 to # 43 and the comparative samples # 401 and # 402 were subjected to a visual test under white light.
For 41 to # 43 and comparative sample # 401, coloring was not confirmed from any direction up to a viewing angle of 50 °,
Good image quality was obtained.

On the other hand, with respect to the comparative sample # 402, coloring from yellow to orange was confirmed when viewed from the left and right at a viewing angle of 50 °.

From the above results, as the liquid crystal material of the liquid crystal layer 8, the refractive index anisotropy Δn (55
0) is set to 0.070, 0.080, 0.095 according to the present embodiment (samples # 41 to # 43).
Then, as shown in FIGS. 6A to 6C, when the voltage is applied, the transmittance is sufficiently reduced and the reversal phenomenon is not observed, so that the viewing angle is widened. Since no coloring phenomenon is observed, it can be seen that the display quality of the liquid crystal display device is significantly improved.

On the other hand, as the liquid crystal material of the liquid crystal layer 8, the refractive index anisotropy Δn (55
0) is set to 0.060 and 0.120 (Comparative Samples # 401 and # 402).
As shown in FIGS. 7A to 7C, it can be seen that the viewing angle dependency is not sufficiently improved.

Further, as the retardation plates 2 and 3, sample # 41 to sample # of the present embodiment are applied except that a discotic liquid crystal is applied to a transparent support for hybrid alignment.
Similar results were obtained for the liquid crystal display devices manufactured in the same manner as the sample No. 43 and the comparative samples # 401 and # 402.

As a result of investigating the dependency of the transmittance-liquid crystal applied voltage characteristic on the tilt angle θ by changing the tilt angle θ of the refractive index ellipsoids of the retardation plates 2 and 3, 15 ° ≦ θ ≦ 75.
Within the range of 0 °, basically the same results as described above were obtained regardless of the alignment state of the discotic liquid crystal in the retardation films 2 and 3. On the other hand, it was confirmed that when the tilt angle is less than 15 ° or exceeds 75 °, the viewing angle in the counter-viewing angle direction is not expanded.

As a result of examining the dependence of the transmittance-liquid crystal applied voltage characteristic on the second retardation value by changing the second retardation value (na-nb) × d of the retardation plates 2 and 3. , The second retardation value is 80 nm
Within the range of 250 nm or less, basically the same result as that described above was obtained regardless of the alignment state of the discotic liquid crystal in the retardation films 2 and 3. On the other hand, the second retardation value is less than 80 nm or 2
It was confirmed that when the thickness exceeds 50 nm, the viewing angle in the lateral direction (horizontal direction) is not expanded.

Furthermore, the above comparative samples # 401 and #
In the liquid crystal display device shown in the liquid crystal display device of FIG. 1, based on the result of the visual examination of 402, as the liquid crystal material of the liquid crystal layer 8, the refractive index anisotropy Δn with respect to light having a wavelength of 550 nm
Three liquid crystal display devices (samples # 44 to # 46) were produced in the same manner as in the present embodiment except that those having (550) set to 0.065, 0.100, and 0.115 were used.

These samples # were added to the measurement system shown in FIG.
44 to # 46 are installed and the light receiving element 21 is set to a constant angle φ.
The relationship between the voltage applied to each liquid crystal display device and the output level of the light receiving element 21 was measured in the case of being fixed by, and further, a visual test was performed under white light.

As a result, in the samples # 45 and # 46 of this embodiment in which the refractive index anisotropy Δn (550) with respect to the light having the wavelength of 550 nm is set to 0.100 and 0.115,
When the angle φ = 50 °, a slight increase in transmittance was confirmed when the voltage was increased in the left-right direction. However, the reversal phenomenon did not occur visually, and such an increase in transmittance was acceptable for use. In the upward direction, no problem was obtained. on the other hand,
Refractive index anisotropy Δn (55
0) set to 0.065 in this embodiment sample # 4
In Comparative Example 4, as in Comparative Sample # 401 described above, there was an inversion phenomenon in which the transmittance once decreased and then increased again as the voltage was increased in the upward direction.
Compared with the comparative sample # 401 (L10) shown in (a), the degree of increase in transmittance was small and it was usable. In the left-right direction, no problem was obtained.

Further, in the visual examination, slight coloring from yellow to orange was confirmed for Samples # 45 and # 46 of this embodiment, but the coloring was such that it did not pose a problem. On the other hand, although it was confirmed that Sample # 44 of the present embodiment exhibited a slight bluish tint, the bluish tint was such that it did not pose a problem.

Furthermore, sample # 44 and comparative sample #
The voltage of about 1 V is applied to the liquid crystal cell 401.
The transmittance at the time of white display in the normal direction of the surface of No. 6 was measured. As a result, the comparative sample # 401 showed a decrease in transmittance that was unbearable for use. On the other hand, although it was confirmed that the sample # 44 of the present embodiment had a slight decrease in transmittance, it was to a degree that it could be used.

[0154]

As described above in detail, according to the present invention, the three main refractive indices na, nb and nc of the refractive index ellipsoid.
Has a relationship of na = nc> nb, and the direction of the main refractive index nb is clockwise or counterclockwise from the normal line direction of the surface with one direction of the main refractive indices na and nc substantially parallel to the surface as an axis. By using a retardation plate that is inclined clockwise and the other direction of the main refractive indices na and nc is inclined clockwise or counterclockwise from a direction substantially parallel to the surface, Changes can be compensated. In addition, the average alkyl chain length of the liquid crystal material of the liquid crystal layer, the degree of change of the normal light refractive index no of the liquid crystal material with respect to the wavelength,
By setting the combination condition with the degree of change of the extraordinary light refractive index ne of the liquid crystal material with respect to the wavelength in a range in which screen coloring depending on the viewing angle does not occur, coloring of the liquid crystal display screen depending on the viewing angle can be further prevented. In addition, the reversal phenomenon and the reduction of the contrast ratio in the direction of the opposite viewing angle can be further improved as compared with the case where only the compensation function of the retardation film is used.

Particularly, in the case of the present invention of claim 2, claim 4 or claim 6, at a viewing angle of 50 ° required for an ordinary liquid crystal display device, it can be sufficiently used from all directions. It is possible to suppress the coloring of the liquid crystal display screen to some extent.

Furthermore, claim 3, claim 5, or claim 7
According to the present invention, in a liquid crystal display device having a wider viewing angle of 70 °, it is possible to realize a state in which the liquid crystal display screen has no coloring phenomenon when viewed from any direction.

Therefore, according to the present invention, the contrast ratio in black-and-white display is not influenced by the viewing angle direction of the observer, so that the quality of the display image of the liquid crystal display device can be significantly improved.

According to the present invention of claim 8, a wavelength of 5
By setting the refractive index anisotropy Δn (550) for light of 50 nm to a range larger than 0.060 and smaller than 0.120, it is possible to eliminate the phase difference generated in the liquid crystal display element depending on the viewing angle. Therefore, not only the coloring phenomenon that occurs depending on the viewing angle on the liquid crystal display screen, but also the contrast change and the lateral inversion phenomenon can be further improved.

Further, according to the present invention of claim 9, the refractive index anisotropy Δn (5
By setting 50) in the range of 0.070 or more and 0.095 or less, it is possible to more effectively eliminate the phase difference caused depending on the viewing angle as compared with the case of the present invention according to claim 8. Therefore, it is possible to more surely improve the coloring phenomenon, the change in contrast, the inversion phenomenon in the left-right direction, and the like that occur depending on the viewing angle on the liquid crystal display screen.

According to the tenth aspect of the present invention, by setting the tilt angle of the index ellipsoid in the range of 15 ° or more and 75 ° or less, the phase difference compensating function of the phase difference element can be surely obtained. Therefore, the visibility can be surely improved.

In the eleventh aspect of the present invention, the product (na-nb) × d of the difference between the main refractive indices na and nb of the retardation element and the thickness d of the retardation element is 80 nm or more and 250 n or more.
By setting the range to m or less, the function of compensating for the phase difference by the phase difference element can be surely obtained, so that the visibility can be surely improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a liquid crystal display device which is an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a rubbing direction of an alignment film and a viewing angle direction in the liquid crystal display device of FIG.

3 is a perspective view showing a direction of a main refractive index of a retardation plate in the liquid crystal display device of FIG.

4 is a perspective view showing an optical arrangement of a liquid crystal display element, a polarizing plate and a retardation plate in the liquid crystal display device of FIG.

FIG. 5 is a perspective view showing a measurement system for measuring the viewing angle dependency of the liquid crystal display device of Embodiment 4.

FIG. 6 is a graph showing the transmittance-liquid crystal applied voltage characteristics of the liquid crystal display device of Embodiment 4.

FIG. 7 is a graph showing a transmittance-liquid crystal applied voltage characteristic of a liquid crystal display device of a comparative example.

FIG. 8 is a schematic diagram showing twisted alignment of liquid crystal molecules in a TN liquid crystal display device.

[Explanation of symbols]

1 Liquid crystal display element A few phase plates 4, 5 Polarizer 6, 7 electrode substrate 8 Liquid crystal layer 9, 12 translucent substrate 10, 13 Transparent electrode 11, 14 Alignment film 15 Seal resin 16 Liquid crystal cell 17 Drive circuit

Continued front page    F term (reference) 2H049 BA02 BA06 BA42 BB03 BB49                       BC04 BC22                 2H088 GA02 HA15 HA18 JA05 KA04                       KA05 KA17 KA18 MA07 MA20                 2H091 FA08X FA08Z FA11X FA11Z                       FA12X FA12Z FB02 FC01                       FD08 FD09 FD10 HA07 KA01                       KA10 LA16 LA19 LA30

Claims (8)

[Claims] 1. A liquid crystal display device comprising a liquid crystal layer sandwiched between a pair of substrates each having an electrode layer and an alignment film, a pair of polarizers sandwiching both sides of the liquid crystal display device, and at least one polarizer. And at least one retardation element provided between the liquid crystal display elements, the three main refractive indexes na, n of the refractive index ellipsoids of the retardation elements.
b and nc have a relationship of na = nc> nb, and the direction of the main refractive index nb is the surface with the direction of one of the main refractive indexes na and nc substantially parallel to the surface of the retardation element being the axis. While tilting clockwise or counterclockwise from the normal direction,
The other direction of the principal refractive indices na and nc is inclined clockwise or counterclockwise from the direction substantially parallel to the surface, and the average alkyl chain (C _m H2
The length _{m of m + 1} −) is set in the range of m <3.40,
An extraordinary light refractive index ne (450) for light having a wavelength of 450 nm, an extraordinary light refractive index ne (550) for light having a wavelength of 550 nm, and a degree of change of extraordinary light refractive index ne (650) for light having a wavelength of 650 nm; Wavelength 450n
Normal light refractive index no (450) for m light, wavelength 55
Normal light refractive index no (550) for 0 nm light and normal light refractive index no (650) for 650 nm wavelength light
And the degree of change of 1 ≦ (((no (450) −no (550)) / (no
(550) -no (650))) / ((ne (450))
-Ne (550)) / (ne (550) -ne (65
0)))) ≦ −0.422 m + 2.55 The liquid crystal display device is set in the range. 2. An extraordinary refractive index ne (450) for light having a wavelength of 450 nm, an extraordinary refractive index ne (550) for light having a wavelength of 550 nm, and a wavelength of 650n.
The degree of change of the extraordinary light refractive index ne (650) with respect to m light and the normal light refractive index no (4
50), the normal light refractive index no for light with a wavelength of 550 nm
(550) and the degree of change of the normal light refractive index no (650) with respect to light having a wavelength of 650 nm are 1 ≦ (((no (450) −no (550)) / (no
(550) -no (650))) / ((ne (450))
-Ne (550)) / (ne (550) -ne (65
The liquid crystal display device according to claim 1, wherein 0)))) ≦ -0.343 m + 2.26. 3. A liquid crystal display device comprising a liquid crystal layer sandwiched between a pair of substrates each having an electrode layer and an alignment film, a pair of polarizers sandwiching both sides of the liquid crystal display device, and at least one polarizer. And at least one retardation element provided between the liquid crystal display elements, the three main refractive indexes na, n of the refractive index ellipsoids of the retardation elements.
b and nc have a relationship of na = nc> nb, and the direction of the main refractive index nb is the surface with the direction of one of the main refractive indexes na and nc substantially parallel to the surface of the retardation element being the axis. While tilting clockwise or counterclockwise from the normal direction,
The other direction of the main refractive indices na and nc is tilted clockwise or counterclockwise from the direction substantially parallel to the surface, and the average alkyl chain (C _m H
The length m of _{2m + 1} −) is set in the range of 3.40 ≦ m ≦ 3.90, and the extraordinary refractive index ne (450) of the liquid crystal material with respect to light having a wavelength of 450 nm and the extraordinary refractive index of light with a wavelength of 550 nm. ne (550) and the degree of change of the extraordinary light refractive index ne (650) with respect to light having a wavelength of 650 nm,
Normal light refractive index no (45
0), normal light refractive index no for light with a wavelength of 550 nm
(550) and the degree of change of the normal light refractive index no (650) with respect to light having a wavelength of 650 nm are 0.80 ≦ (((no (450) -no (550)) /
(No (550) -no (650))) / ((ne (4
50) -ne (550)) / (ne (550) -ne
(650)))) Liquid crystal display device set in the range of ≤1.20. 4. An extraordinary light refractive index ne (450) for light having a wavelength of 450 nm, an extraordinary light refractive index ne (550) for light having a wavelength of 550 nm, and a wavelength of 650 n.
The degree of change of the extraordinary light refractive index ne (650) with respect to m light and the normal light refractive index no (4
50), the normal light refractive index no for light with a wavelength of 550 nm
(550) and the degree of change of the normal light refractive index no (650) with respect to light having a wavelength of 650 nm are 0.85 <(((no (450) -no (550)) /
(No (550) -no (650))) / ((ne (4
50) -ne (550)) / (ne (550) -ne
The liquid crystal display device according to claim 3, wherein the range (650)))) is set to <1.15. 5. A liquid crystal display device comprising a liquid crystal layer sandwiched between a pair of substrates each having an electrode layer and an alignment film, a pair of polarizers sandwiching both sides of the liquid crystal display device, and at least one polarizer. And at least one retardation element provided between the liquid crystal display elements, the three main refractive indexes na, n of the refractive index ellipsoids of the retardation elements.
b and nc have a relationship of na = nc> nb, and the direction of the main refractive index nb is the surface with the direction of one of the main refractive indexes na and nc substantially parallel to the surface of the retardation element being the axis. While tilting clockwise or counterclockwise from the normal direction,
The other direction of the main refractive indices na and nc is tilted clockwise or counterclockwise from the direction substantially parallel to the surface, and the average alkyl chain (C _m H
The length m of _{2m + 1} −) is set in the range of m> 3.90, and the extraordinary refractive index ne (450) of the liquid crystal material with respect to the light having a wavelength of 450 nm and the extraordinary refractive index ne (550) with respect to the light of the wavelength of 550 nm. And the degree of change of the extraordinary refractive index ne (650) with respect to light of wavelength 650 nm,
Normal light refractive index no (450) for light of 0 nm, normal light refractive index no (550) for light of wavelength 550 nm, and normal light refractive index no (65 for light of wavelength 650 nm)
The degree of change of 0) is −0.422m + 2.55 ≦ (((no (450) −n
o (550)) / (no (550) -no (65
0))) / ((ne (450) -ne (550)) /
A liquid crystal display device in which (ne (550) -ne (650)))) ≦ 1 is set. 6. An extraordinary light refractive index ne (450) for light of a wavelength of 450 nm, an extraordinary light refractive index ne (550) for light of a wavelength of 550 nm, and a wavelength of 650n of the liquid crystal material.
The degree of change of the extraordinary light refractive index ne (650) with respect to m light and the normal light refractive index no (4
50), the normal light refractive index no for light with a wavelength of 550 nm
(550) and the degree of change of the normal light refractive index no (650) with respect to light having a wavelength of 650 nm are −0.343 m + 2.26 ≦ (((no (450) −n
o (550)) / (no (550) -no (65
0))) / ((ne (450) -ne (550)) /
The liquid crystal display device according to claim 5, wherein (ne (550) -ne (650)))) ≦ 1 is set. 7. The refractive index anisotropy Δn (550) of the liquid crystal material with respect to light having a wavelength of 550 nm is set to a range larger than 0.060 and smaller than 0.120.
7. The liquid crystal display device according to claim 6. 8. The refractive index anisotropy Δn (550) of the liquid crystal material with respect to light having a wavelength of 550 nm is 0.070 or more and 0.
The liquid crystal display device according to claim 7, wherein the liquid crystal display device is set in a range of 095 or less.