JP3452743B2 - 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 device, and more particularly to a liquid crystal display device which improves the viewing angle dependence of a display screen by combining a liquid crystal display element with a retardation plate.

[0002]

2. Description of the Related Art Conventionally, liquid crystal display devices using nematic liquid crystal display elements have been widely used for numerical segment type display devices such as watches and calculators. It is also used in LCD TVs.

A liquid crystal display element generally has a translucent substrate on which electrode lines and the like for turning on and off pixels are formed. For example, in an active matrix type liquid crystal display device, active elements such as thin film transistors are formed on the above substrate together with the above electrode lines as switching means for selectively driving a pixel electrode for applying a voltage to liquid crystal. Furthermore, in a liquid crystal display device that performs color display, color filter layers of red, green, blue, etc. are provided on a substrate.

As a liquid crystal display system used for the above liquid crystal display device, a different system is appropriately selected according to the twist angle of the liquid crystal. For example, active drive type twisted nematic liquid crystal display system (hereinafter referred to as TN system) and multiplex drive type super twisted nematic liquid crystal display system (hereinafter referred to as STN system) are well known.

The TN system uses 90 nematic liquid crystal molecules.
Display is performed by orienting in a twisted state and guiding light along the twisting direction. The STN method utilizes the fact that the transmittance near the threshold of the liquid crystal applied voltage changes sharply by enlarging the twist angle of the nematic liquid crystal molecules to 90 ° or more.

Since the STN method utilizes the birefringence effect of liquid crystal, a background color of the display screen is given a color due to color interference. It is considered effective to use an optical compensator in order to eliminate such inconvenience and perform black and white display by the STN method. Display methods using an optical compensator include a double super twisted nematic phase compensation method (hereinafter referred to as DSTN method) and a film type phase compensation method in which a film having optical anisotropy is arranged (hereinafter referred to as film addition type). The method is called).

The DSTN method uses a two-layer structure having a display liquid crystal cell and a liquid crystal cell which is twisted and oriented at a twist angle opposite to that of the display liquid crystal cell. The film addition type system uses a structure in which a film having optical anisotropy is arranged. From the viewpoint of light weight and low cost,
The film addition type method is considered to be effective. Since the black-and-white display characteristic is improved by adopting such a phase compensation method, a color STN liquid crystal display device is realized in which a color filter layer is provided in an STN display device to enable color display.

On the other hand, the TN method is roughly classified into a normally black method and a normally white method. In the normally black method, a pair of polarizing plates are arranged such that their polarization directions are parallel to each other, and black is displayed in a state where an on-voltage is not applied to the liquid crystal layer (off state). In the normally white method, a pair of polarizing plates are arranged so that their polarization directions are orthogonal to each other, and white is displayed in the off state. The normally white method is effective in terms of display contrast, color reproducibility, and viewing angle dependence of display.

By the way, in the above TN liquid crystal display device, the refractive index anisotropy Δn exists in the liquid crystal molecules, and the liquid crystal molecules are oriented with an inclination with respect to the two opposing substrates. Therefore, there is a problem in that the contrast of the displayed image changes depending on the viewing direction and angle of the viewer, and the viewing angle dependency increases.

FIG. 10 schematically shows a sectional structure of the TN liquid crystal display element 31. This state shows the case where the voltage for halftone display is applied and the liquid crystal molecules 32 are slightly raised. In the TN liquid crystal display element 31, the linearly polarized light 35 passing through the normal direction of the surfaces of the pair of substrates 33 and 34, and the linearly polarized light 36 and 37 passing with an inclination with respect to the normal direction are the liquid crystal molecules 32. The angle that intersects with is different. Since the liquid crystal molecule 32 has a refractive index anisotropy Δn, linearly polarized light 35/36 in each direction.
When 37 passes through the liquid crystal molecule 32, normal light and extraordinary light are generated, and are converted into elliptically polarized light according to the phase difference between them, which becomes a source of view angle dependence.

Furthermore, inside the actual liquid crystal layer, the liquid crystal molecules 32 are formed near the intermediate portion between the substrate 33 and the substrate 34 and the substrate 3.
3 or the vicinity of the substrate 34 has a different tilt angle, and the liquid crystal molecules 32 are twisted by 90 ° about the normal direction.

From the above, the linearly polarized light 35, 36, 37 passing through the liquid crystal layer is subjected to various birefringence effects depending on its direction and angle, and exhibits a complicated viewing angle dependency.

As the above-mentioned viewing angle dependence, specifically, a phenomenon in which a display image is colored at a certain angle or more when the viewing angle is inclined from the screen normal direction to the normal viewing angle direction which is the lower direction of the screen (hereinafter, A "coloring phenomenon") and a phenomenon of black and white reversal (hereinafter referred to as "reversal phenomenon") occur. Further, when the viewing angle is tilted in the anti-viewing angle direction which is the upper direction of the screen, the contrast sharply decreases.

Further, the above liquid crystal display device has a problem that the viewing angle becomes narrower as the display screen becomes larger. When a large liquid crystal display screen is viewed from the front direction at a short distance, the colors displayed on the upper and lower parts of the screen may be different due to the effect of viewing angle dependence. This is because the viewing angle for viewing the entire screen becomes large, which is the same as viewing the display screen from a more oblique direction.

In order to improve such viewing angle dependence,
It has been proposed to insert a retardation plate (retardation film) as an optical element having optical anisotropy between a liquid crystal display element and one polarizing plate (for example, JP-A-55-60).
No. 0, JP-A-56-97318, etc.).

According to this method, light converted from linearly polarized light to elliptically polarized light because it has passed through liquid crystal molecules having refractive index anisotropy is placed on one side or both sides of a liquid crystal layer having refractive index anisotropy. By passing through the retardation plate, the phase difference change between the normal light and the extraordinary light occurring at the viewing angle is compensated and reconverted into the linearly polarized light, and the viewing angle dependency can be improved.

As such a retardation plate, one in which one main refractive index direction of the refractive index ellipsoid is parallel to the normal direction of the surface of the retardation plate is described in, for example, JP-A-5-313159. Has been done. However, even if this phase difference plate is used, there is a limit in improving the inversion phenomenon in the normal viewing angle direction.

Therefore, in Japanese Patent Laid-Open No. 6-75116, a method using a retardation plate in which the main refractive index direction of the index ellipsoid is inclined with respect to the normal direction of the surface of the retardation plate is used. Is proposed. In this method, the following two types of retardation plates are used.

One of the three main refractive indices of the refractive index ellipsoid is that the direction of the minimum main refractive index is parallel to the surface, and the remaining two main refractive indices have a phase difference in one direction. The surface of the plate is inclined at an angle of θ, and the other direction is also inclined at an angle of θ with respect to the normal direction of the surface of the retardation plate, and the value of θ is 20 ° ≦ θ ≦ 70. It is a retardation plate that satisfies °.

The other is that the three main refractive indices n _a , n _b and n _c of the index ellipsoid have a relationship of n _a <n _c <n _b , and the main refractive index n _a within the surface or With the direction of n _c as an axis, the direction of the main refractive index n _b parallel to the normal direction of the surface and the direction of the main refractive index n _c or n _a in the surface are clockwise.
Alternatively, it is a retardation plate whose refractive index anisotropy is represented by a refractive index ellipsoid which is tilted by tilting counterclockwise.

Regarding the above-mentioned two types of retardation plates, the former may be a uniaxial one or a biaxial one. In the latter case, not only one retardation plate is used, but two retardation plates are combined to obtain each main refractive index n _b.
It is possible to use those in which the inclination directions of are set to form an angle of 90 ° with each other.

In a liquid crystal display device constructed by interposing at least one such retardation film between a liquid crystal display element and a polarizing plate, a contrast change and a coloring phenomenon which occur depending on a viewing angle of a display image. The inversion phenomenon can be improved to some extent.

[0023]

However, under the circumstances where a liquid crystal display device having a wider viewing angle and a higher display quality is desired today, further improvement of the viewing angle dependency is required, and the above-mentioned JP-A-6- When the retardation plate disclosed in Japanese Patent No. 75116 is used, it cannot be said that the retardation plate is sufficient, and there is still room for improvement.

The present invention has been made in view of the above problems, and an object thereof is to obtain a refractive index anisotropy Δn with respect to a wavelength of a liquid crystal material used for a liquid crystal layer in a liquid crystal display device in which the above retardation film is interposed. By setting the change in the optimum range, it is to further improve the viewing angle dependency in addition to the compensation effect of the retardation plate, and particularly to effectively improve the coloring phenomenon.

[0025]

A liquid crystal display device according to the present invention is constituted by enclosing a liquid crystal layer between a pair of translucent substrates each having a transparent electrode layer and an alignment film formed on opposing surfaces. A liquid crystal display element, a pair of polarizers disposed on both sides of the liquid crystal display element, and at least one retardation plate interposed between the liquid crystal display element and the polarizer. Elliptic three principal refractive indices n _a , n
_b and n _c have a relationship of n _a <n _b <n _{c, and} the principal refractive index n _b parallel to the surface normal direction with the direction of the principal refractive index n _a or n _{c in} the surface as an axis A liquid crystal display provided with a retardation plate in which the refractive index ellipsoid is tilted by tilting the direction and the direction of the main refractive index n _a or n _c in the surface clockwise or counterclockwise. The device is characterized in that the following measures are taken in order to solve the above problems.

That is, the liquid crystal material in the liquid crystal layer
Of the refractive index anisotropy Δn (4
50) and refractive index anisotropy Δn with respect to light having a wavelength of 650 nm
The difference Δn (450) −Δn (650) of (650) is
It is set in the range of 0.0070 to 0.0250 .

In the above structure, when the linearly polarized light passes through the liquid crystal layer having birefringence, normal light and extraordinary light are generated and converted into elliptically polarized light according to the phase difference between them, the main refractive index n _a , n _b , and n _c have a relationship of n _a <n _b <n _c , and the minor axis of the index ellipsoid including the main index n _b is tilted with respect to the normal direction of the surface of the retardation plate. The retardation plate is interposed between the liquid crystal layer and the polarizer. According to this, the phase difference change between the normal light and the abnormal light that occurs depending on the viewing angle is compensated by the phase difference plate. However, such a compensation function alone is not always sufficient under the situation where further improvement in viewing angle dependency is required.

Therefore, as a result of repeated studies, the inventors of the present invention have found that the change in the refractive index anisotropy Δn of the liquid crystal material in the liquid crystal layer with respect to the wavelength of light particularly affects the coloring of the liquid crystal screen (display screen). The present invention has been completed and the present invention has been completed.

In the liquid crystal display device of the present invention, the refractive index anisotropy Δ of the liquid crystal material in the liquid crystal layer enclosed in the liquid crystal display element is
The change of n with respect to the wavelength of light is set within the above range. This makes it possible to prevent the screen from being colored further. It should be noted that the contrast change and the reversal phenomenon could be improved as compared with the case where only the compensation function of the retardation plate was used.

[0030]

[0031]

By setting the above difference at least within this range, a viewing angle of 50 ° required in a normal liquid crystal display device is obtained.
In the above, although there is some coloring, it is possible to obtain display characteristics that can be sufficiently used in any direction.

[0033]

A wider field of view, such as a viewing angle of 70 °
In the corner liquid crystal display device, the liquid crystal material in the liquid crystal layer has a refractive index anisotropy Δn (4
50) and refractive index anisotropy Δn with respect to light having a wavelength of 650 nm
The difference Δn (450) −Δn (650) of (650) is
It is set in the range of 0.0200 to 0.0250.

Within this range, it is possible to realize a display without any coloring phenomenon at any viewing angle of 70 ° required in a liquid crystal display device having a wide viewing angle even when viewed from any direction.

In the liquid crystal display device of the present invention described above, the refractive index anisotropy Δn (550) of the liquid crystal material in the liquid crystal layer with respect to light having a wavelength of 550 nm is 0.060.
It is preferable to set it in a range larger than 0.120.

This is the refractive index anisotropy Δn of the liquid crystal material with respect to light having a wavelength of 550 nm, which is the central region of the visible light region.
This is because it was confirmed that when (550) is 0.060 or less or 0.120 or more, an inversion phenomenon and a decrease in contrast ratio occur depending on the viewing angle direction. Therefore, the refractive index anisotropy Δn of the liquid crystal material with respect to light having a wavelength of 550 nm
By setting (550) in the range larger than 0.060 and smaller than 0.120, the phase difference corresponding to the viewing angle generated in the liquid crystal display element can be eliminated. Therefore, not only the coloring phenomenon that occurs depending on the viewing angle on the display screen, but also the contrast change, the inversion phenomenon in the horizontal direction, and the like can be further improved.

In this case, further, the refractive index anisotropy Δn of the liquid crystal material in the liquid crystal layer with respect to light having a wavelength of 550 nm.
By setting (550) in the range of 0.070 or more and 0.095 or less, the phase difference generated in the liquid crystal display element depending on the viewing angle can be more effectively eliminated. therefore,
It is possible to surely improve the contrast change, the lateral inversion phenomenon, and the coloring phenomenon in the liquid crystal display image.

In the above-mentioned liquid crystal display device of the present invention, it is preferable that the tilt angle of the refractive index ellipsoid is set between 15 ° and 75 ° in all the retardation plates.

As described above, by setting the inclination angle of the index ellipsoid in all the retardation plates interposed in the liquid crystal display device between 15 ° and 75 °, the retardation of the retardation plate described above is reduced. The compensation function can be surely obtained.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIGS. 1 to 9.

The liquid crystal display device according to this embodiment is shown in FIG.
As shown in, the liquid crystal display element 1 and the pair of retardation plates 2
3 and a pair of polarizing plates (polarizers) 4.5.

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

Although FIG. 1 shows a structure for two pixels for simplification, in the entire liquid crystal display element 1, strip-shaped transparent electrodes 10 and 13 having a predetermined width are provided on the glass substrates 9 and 12, respectively. Glass substrates 9 arranged at a predetermined interval
The areas 12 are formed so as to be orthogonal to each other when viewed from the direction perpendicular to the substrate surface. The intersection of both transparent electrodes 10 and 13 corresponds to a pixel for displaying, and these pixels are arranged in a matrix in the entire liquid crystal display device. A voltage based on display data is applied to the transparent electrodes 10 and 13 by a driving circuit (not shown).

The electrode substrates 6 and 7 are bonded together with a seal resin 15, and the electrode substrates 6 and 7 and the seal resin 15 are attached.
The liquid crystal layer 8 is enclosed in the space formed by Although the details will be described later, the liquid crystal layer 8 in the present liquid crystal display device is a liquid crystal forming the liquid crystal layer 8 so that the liquid crystal layer 8 is a combination having a phase difference compensation function by the retardation plates 2 and 3 and the best characteristics. A material is selected so that its refractive index anisotropy Δn satisfies a predetermined condition.

In the present liquid crystal display device, the liquid crystal cell 16 is a unit in which the liquid crystal display element 1 is provided with the retardation plates 2.3 and the polarizing plates (polarizers) 4.5. The alignment films 11 and 14 are preliminarily subjected to a rubbing treatment so that the intervening liquid crystal molecules are twisted and aligned at about 90 °. Figure 2
As shown in, the rubbing direction R ₁ of the alignment film 11, and the rubbing direction R ₂ of the alignment film 14 is set in a direction perpendicular to each other.

The phase difference plates 2 and 3 are interposed between the liquid crystal display element 1 and the polarizing plate 4 so as to overlap each other. Phase difference plate 2.3
Is formed by a liquid crystal polymer having a positive refractive index anisotropy being tilt-aligned or hybrid-aligned and crosslinked on a support made of a transparent organic polymer. As a result, the refractive index ellipsoid described later in the phase difference plates 2 and 3 becomes
The phase difference plates 2 and 3 are formed so as to be inclined.

As a support for the retardation plates 2 and 3, triacetyl cellulose (TA
C) has high reliability and is suitable. Other than that, polycarbonate (PC), polyethylene terephthalate (P
A colorless and transparent organic polymer film having excellent environmental resistance and chemical resistance such as ET) is suitable.

As shown in FIG. 3, the retardation plates 2 and 3 have principal refractive indices n _a , n _b and n _c in three different directions.
The direction of the main refractive index n _a coincides with the y coordinate axis of the coordinate axes in the Cartesian coordinates xyz. The direction of the main refractive index n _b is inclined in the direction of arrow A with respect to the z coordinate axis (the normal direction of the surface) perpendicular to the surface corresponding to the screen in the phase difference plates 2 and 3.

The retardation plates 2 and 3 have principal refractive indices of n _a <n.
The relationship of _b <n _c is satisfied. As a result, since there are two optical axes, the retardation films 2 and 3 have biaxiality, and the refractive index anisotropy becomes positive. The first retardation value of the phase difference plate _{2 · 3 (n c -n a} ) × d is 220n
m, the second retardation value (n _c −n _b ) × d
Is 35 nm. The above n _c -n _a and n _c -
n _b represents the refractive index anisotropy Δn, and d represents the thickness of the retardation films 2 and 3.

The angle θ at which the main refractive index n _{b of} the phase difference plates 2 and 3 is tilted, that is, the tilt angle θ of the index ellipsoid is
It is set to an arbitrary value within the range of 15 ° ≦ θ ≦ 75 °.
By setting the tilt angle θ within such a 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. You can

Regarding the disposition of the retardation plates 2 and 3, it is possible to dispose only one of the retardation plates 2 (3) on one side. Furthermore, it is also possible to use three or more retardation plates.

Then, as shown in FIG. 4, in the present liquid crystal display device, the polarizing plates 4 and 5 in the liquid crystal display element 1 are arranged.
Has an absorption axis AX ₁ · AX ₂ of the above-mentioned alignment film 11 · 1.
4 (see FIG. 1) are arranged so as to be parallel to the rubbing directions R ₁ and R ₂ . In the present liquid crystal display device, since the rubbing directions R ₁ and R ₂ are orthogonal to each other, the absorption axes AX ₁ and AX ₂ are also orthogonal to each other.

Here, as shown in FIG. 3, the phase difference plate 2
The direction in which the principal refractive index n _b inclined to the direction that gives anisotropy to 3 is projected on the surface of the retardation films 2 and 3 is defined as D. As shown in FIG. 4, the phase difference plate 3 is arranged so that the direction D (direction D ₂ ) is parallel to the rubbing direction R ₁ ,
The retardation plate 2 is arranged so that the direction D (direction D ₁ ) is parallel to the rubbing direction R ₂ .

With the arrangement of the retardation films 2 and 3 and the polarizing plates 4 and 5 as described above, the present liquid crystal display device performs so-called normally white display in which light is transmitted to display white when it is off.

Generally, in an optically anisotropic body such as a liquid crystal or a retardation film (retardation film), the anisotropy of the main refractive index n _a · n _c · n _{b in} the three-dimensional direction as described above is an ellipsoidal refractive index. Represented by the body. The refractive index anisotropy Δn has a different value depending on the direction in which this refractive index ellipsoid is observed.

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

As described above, in the liquid crystal layer 8, as the liquid crystal material forming the liquid crystal layer 8, the refraction is performed so that the combination has the best function and the function of compensating for the phase difference by the phase difference plates 2 and 3. A liquid crystal material whose index anisotropy Δn satisfies a predetermined condition is used. The predetermined condition is that the change in the refractive index anisotropy Δn with respect to the wavelength of light is set in a range in which the liquid crystal screen is not colored depending on the viewing angle.

Specifically, a liquid crystal material designed to satisfy the conditions of the following setting range is injected.

That is, Δn, which is the difference between the refractive index anisotropy Δn (450) of the liquid crystal material with respect to light having a wavelength of 450 nm and the refractive index anisotropy Δn (650) with respect to light of a wavelength of 650 nm.
(450) −Δn (650) is 0.0070 or more and 0.
The range is set to 0250 or less. More preferred
Is Δn (450) −Δn (650) is 0.0
It must be set in the range from 090 to 0.0250.
And more preferably Δn (450) −Δn above.
(650) means that the range is set to 0.0200 or more and 0.0250 or less .

By using a liquid crystal material designed to satisfy such conditions, the contrast change, the reversal phenomenon, and the coloring that occur depending on the viewing angle of the display screen due to the phase difference compensating function of the phase difference plates 2 and 3. Not only the improvement of the phenomenon,
It is possible to further improve the coloring phenomenon of the display screen.

Specifically, by using a liquid crystal material designed to satisfy at least one value within the above wide range, the viewing angle 50 required in a normal liquid crystal display device is increased.
Although there is some coloring at °, it can be sufficiently used in any direction.

Within the above range, it is considered to be preferable.
By satisfying at least one value in 囲内, viewing angle 60 °
Although it has some coloring, it is enough from any direction
It can withstand use. And, in particular, above
By satisfying at least one value within the more preferable range, it is possible to obtain no coloring at any viewing angle of 70 ° from any direction.

Further, by using the liquid crystal material designed to satisfy this range, the contrast change and the reversal phenomenon are also improved as compared with the case where only the compensation function of the phase difference plates 2 and 3 is used.

Further, in the present liquid crystal display device, it is preferable that the above conditions are satisfied and the following conditions are simultaneously satisfied. In this case, the liquid crystal layer 8
This condition is met in.

That is, 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. More preferably, the Δn (550) is set in the range of 0.070 to 0.095.

By satisfying such conditions as well, the compensating function due to the phase difference by the retardation plates 2 and 3 and the viewing angle dependence due to the compensating function based on the condition of the range of the difference in the refractive index anisotropy Δn can be obtained. In addition to the improvement, it is possible to further reduce the contrast ratio in the counter-viewing angle direction and the inversion phenomenon in the left-right direction.

FIG. 5 shows the liquid crystal layer 8 in the present liquid crystal display device.
Δn (λ) (wavelength-refractive index anisotropy Δn characteristic) of one liquid crystal material that can be used for the above is shown by a solid curve a. In FIG. 5, Δn (λ) with respect to the wavelength (λ) of one liquid crystal material used for the liquid crystal layer in the conventional liquid crystal display device is shown by a dashed line curve b for comparison.

Comparing the curves a and b, the gradient of the wavelength-refractive index anisotropy Δn characteristic in the present liquid crystal display device is found to be the gradient of the wavelength-refractive index anisotropy Δn characteristic in the conventional liquid crystal display device. You can see that it is larger than.

Further, in FIG. 6, Δn (λ) / Δn (550) with respect to the wavelength (λ) of another liquid crystal material that can be used for the liquid crystal layer 8 in the present liquid crystal display device is shown by a solid curve c. Shown in. In FIG. 6, for comparison, Δn (λ) / Δn (55) with respect to the wavelength (λ) of another liquid crystal material used for the liquid crystal layer in the conventional liquid crystal display device.
0) is shown by a dashed line curve d.

Comparing the curves c and d, the gradient of the change of Δn (λ) / Δn (550) in the present liquid crystal display device is also
It can be seen that the gradient of the change of Δn (λ) / Δn (550) in the conventional liquid crystal display device is larger.

In the liquid crystal display device of the present embodiment configured as described above, the phase difference generated in the liquid crystal display element 1 according to the viewing angle is compensated by the phase difference plates 2 and 3, and the liquid crystal material in the liquid crystal layer 8 is used. It has a compensation function based on the fact that the change in the refractive index anisotropy Δn with respect to the wavelength of the transmitted light is set in a range where coloring of the liquid crystal screen does not occur. Thereby, the contrast change, the reversal phenomenon, and the coloring phenomenon depending on the viewing angle are improved, and a high quality image can be displayed.

Next, an example according to the present embodiment configured as described above will be described together with a comparative example. Example 1 In this example, in the liquid crystal layer 8 of the liquid crystal cell 16 in the liquid crystal display device of FIG. 1, the refractive index anisotropy Δn (450) at a wavelength of 450 nm and the refractive index anisotropy Δn (650 at a wavelength of 650 nm are used. ) And Δn (45
0) -Δn (650) are 0.0070, 0.
0090, 0.0120, 0.0200, 0.0250
5 samples # 1 to # in which the cell thickness (thickness of the liquid crystal layer 8) is set to 5 μm using the liquid crystal material set to
5 was used.

Phase difference plate 2 in samples # 1 to # 5
3 is formed by applying a liquid crystal polymer having a positive refractive index anisotropy to a transparent support (for example, triacetyl cellulose (TAC)), tilting and aligning the liquid crystal polymer, and crosslinking the liquid crystal polymer. The first retardation value is 22
0 nm, the second retardation value described above is 35 nm, and the direction of the main refractive index n _b is inclined so as to be approximately 20 ° in the direction indicated by arrow A with respect to the z-axis direction in the xyz-axis coordinates. Is used in which the direction of the main refractive index n _c forms an angle of about 20 ° with respect to the x-axis in the direction indicated by arrow B (that is, the tilt angle θ of the index ellipsoid θ = 20 °). .

As a comparative example to this embodiment, the liquid crystal layer 8 of the liquid crystal cell 16 in the liquid crystal display device of FIG.
A comparative sample # 100 similar to that of this example was used except that the liquid crystal material having Δn (450) −Δn (650) of 0.0045 was used.

Table 1 shows the results of the visual test under the white light for the above samples # 1 to # 5 and the comparative sample # 100.

[0077]

[Table 1]

For samples # 4 and # 5 of the example, no coloration was confirmed and good image quality was obtained even when viewed from all directions with a visual angle of 70 °. In sample # 3, even when viewed from all directions up to a viewing angle of 60 °, coloring was not confirmed and good image quality was obtained. In sample # 2, coloring was not confirmed even when viewed from all directions up to a viewing angle of 50 °, and good image quality was obtained. In sample # 1, coloring was confirmed when viewed from the left and right at a viewing angle of 50 °, but the coloring was sufficient to withstand use.

On the other hand, in the comparative sample # 100, even when the viewing angle is 50 °, when viewed from the left and right directions,
It was confirmed that the coloration was from yellow to dark enough to withstand use. Further, as the retardation plates 2 and 3, a liquid crystal polymer having a positive refractive index anisotropy is hybrid-aligned on a transparent support, and the same result as above was obtained.

(Embodiment 2) Here, as shown in FIG. 7, the viewing angle dependence of the liquid crystal display device was measured using a measurement system including a light receiving element 21, an amplifier 22 and a recording device 23. The liquid crystal cell 16 of the liquid crystal display device is installed such that the surface 16a on the glass substrate 9 side is located on the reference plane xy of the orthogonal coordinates xyz. The light-receiving element 21 is an element capable of receiving light at a fixed stereoscopic light-receiving angle, and is arranged at a position at a predetermined distance from the coordinate origin in a direction forming an angle φ (visual angle) with respect to the z direction perpendicular to the surface 16a. ing.

At the time of measurement, with respect to the liquid crystal cell 16 installed in this measurement system, a wavelength of 550 n was measured from the surface opposite to the surface 16a.
Irradiate m monochromatic light. A part of the monochromatic light transmitted through the liquid crystal cell 16 enters the light receiving element 21. 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 such as a waveform memory or a recorder.

In this embodiment, the liquid crystal layer 16 in the liquid crystal cell 16 shown in FIG. 1 has a refractive index anisotropy Δn at a wavelength of 550 nm.
(550) is 0.070, 0.080, 0.
Using the liquid crystal material set to 095, the cell thickness (the liquid crystal layer 8
Samples # 6 whose thickness) is set to 5 μm
~ # 8 was used.

Phase difference plate 2 in samples # 6 to # 8
As 3, the same retardation plates 2 and 3 as those in the above-described Example 1 in which the liquid crystal polymer having a positive refractive index anisotropy was tilt-aligned were used.

Such samples # 6 to # 8 are installed in the measurement system shown in FIG. 7, and the voltage applied to the samples # 6 to # 8 when the light receiving element 21 is fixed at a constant angle φ. The output level of the light receiving element 21 was measured.

The measurement is performed by arranging the light receiving element 21 so that the angle φ is 50 °, and assuming that the y direction is the upper side of the screen and the x direction is the left side of the screen, the position where the light receiving element 21 is arranged. It was done by fixing it upwards.

The results are shown in the graph of FIG. 8 showing the light transmittance (transmittance-liquid crystal applied voltage characteristic) with respect to the voltage applied to the samples # 6 to # 8. In FIG. 8, the curved line L1 indicated by the alternate long and short dash line is the characteristic of the sample # 6, the curved line L2 indicated by the solid line is the characteristic of the sample # 7, and the curved line L3 indicated by the broken line is the characteristic of the sample # 8.

As a comparative example to the example, the liquid crystal layer 8 in the liquid crystal cell 16 of FIG. 1 has a refractive index anisotropy Δn (550) of 0.060 at a wavelength of 550 nm, respectively.
Two comparative samples # 101 and # 102 similar to those of the example except that the liquid crystal material set to 0.120 was used were prepared. Further, by using the measurement system shown in FIG. 7, the light-receiving element 21 with respect to the applied voltage to the comparative samples # 101 and # 102 when the light-receiving element 21 is fixed at a constant angle φ by the same method as in the present embodiment. The output level was measured.

The measurement was carried out by arranging the light receiving element 21 at an angle φ of 50 ° and fixing the arrangement position of the light receiving element 21 in the same manner as in the present embodiment.

The results are shown in comparison samples # 101 and # 1.
The graph of FIG. 9 showing the light transmittance (transmittance-liquid crystal applied voltage characteristic) with respect to the voltage applied to No. 02. Figure 9
In, the curve L10 indicated by the solid line is the comparative sample # 10.
Curve L11 indicated by a broken line is the characteristic of the comparative sample # 102.

The samples # 6 to # 8 of this example and the comparative samples # 101 and # 102 of the comparative example were compared in the following manner with respect to the transmittance-liquid crystal applied voltage characteristic in the upward direction.
As shown by L1, L2, and L3 in FIG.
It was confirmed that the transmittances of # 8 to # 8 were sufficiently lowered as the applied voltage was increased. On the other hand, L11 in FIG.
As shown in, in the case of the comparative sample # 102, the transmittance is not sufficiently decreased even when the applied voltage is increased. Further, as indicated by L10 in FIG.
In the case of 1, an inversion phenomenon was confirmed in which the transmittance once decreased and then increased again as the applied voltage increased.

Regarding samples # 6 to # 8 of the embodiment,
With respect to a viewing angle of 50 °, coloring was not confirmed from any direction and good image quality was obtained. On the other hand, comparative sample # 1
With respect to 01. # 102, it was confirmed that the coloring from yellow to a gradual color was observed in the left-right direction at a viewing angle of 50 °.

As described above, the liquid crystal layer 8 has a wavelength of 550 nm.
The refractive index anisotropy Δn (550) in each of the above is 0.
In the case of using the liquid crystal material set to 070, 0.080, 0.095, the transmittance is sufficiently reduced when the applied voltage is high, and the inversion phenomenon is not observed, based on the characteristics shown in FIG. It is clear that the viewing angle is expanded. Further, in this case, it can be seen that there is no coloring phenomenon and the display quality of the liquid crystal display device is significantly improved.

On the other hand, the liquid crystal layer 8 has a wavelength of 550 nm.
The refractive index anisotropy Δn (550) in each of the above is 0.
When the liquid crystal material set to 060 and 0.120 is used, it can be seen that the viewing angle dependency is not sufficiently improved based on the characteristics shown in FIG.

As the retardation plates 2 and 3, the samples # 6 to # 8 and the comparative samples # 101 and # 8 were used, except that a liquid crystal polymer having a positive refractive index anisotropy was hybrid-aligned on a transparent support. Similar results were obtained for samples and comparative samples similar to 102.

Further, the dependency of the transmittance-liquid crystal applied voltage characteristic on the inclination angle θ was examined by changing the inclination angle θ of the refractive index ellipsoids of the retardation films 2 and 3. As a result, 15
If θ changes within the range of θ ≦ θ ≦ 75 °, the phase difference plate 2
The dependency basically did not change regardless of the alignment state of the liquid crystal polymer in 3. In addition, it was confirmed that the viewing angle in the opposite viewing angle direction did not widen when the range was exceeded.

Further, the above-mentioned comparative samples # 101 and # 10
Based on the result of the visual inspection of No. 2, the liquid crystal layer 8 in the liquid crystal cell 16 of FIG.
(550) is 0.065, 0.100, 0.
Three samples # 9 to # 11 similar to this example except that the liquid crystal material 115 was used were prepared as the samples of this example. With respect to these samples # 9 to # 11 as well, the output level of the light receiving element 21 with respect to the applied voltage to each was measured using the measurement system shown in FIG. In addition, visual confirmation was performed under white light.

As a result, in samples # 10 and # 11,
When the angle φ was 50 °, good transmittance was obtained in the upward direction. On the other hand, in the sample # 9, the transmittance in the upward direction is increased as the voltage is increased.
Similar to No. 01, it shows a characteristic that it rises once after reaching the minimum value (see FIG. 9).
Less than 101. Therefore, according to the sample # 9, although the transmittance as good as that of the samples # 10 and # 11 cannot be obtained, it is possible to obtain the transmittance that can be used.

In the visual inspection, sample #
In 10 · # 11, slight coloring from yellow to deep color was confirmed, but the coloring was not a problem. It was confirmed that Sample # 9 exhibited a slight bluish tint. However, this level of blueness was not a problem.

As a supplement, a voltage of about 1 V was applied to Sample # 9 and Comparative Sample # 101, and the transmittance of the surface of the liquid crystal cell 16 during white display in the normal direction was measured. As a result, in Comparative Sample # 101, a decrease in the transmittance was found that it could not be used, but in Sample # 101
In No. 9, the transmittance was low enough to withstand use.

[0100]

As described above, in the liquid crystal display device according to the present invention, the liquid crystal layer is enclosed between the pair of translucent substrates each having the transparent electrode layer and the alignment film formed on the opposite surfaces. A liquid crystal display element, a pair of polarizers arranged on both sides of the liquid crystal display element, and at least one retardation plate interposed between the liquid crystal display element and the polarizer. The three principal indices n _a , n of the index ellipsoid
_b and n _c have a relationship of n _a <n _b <n _{c, and} the principal refractive index n _b parallel to the surface normal direction with the direction of the principal refractive index n _a or n _{c in} the surface as an axis A liquid crystal display provided with a retardation plate in which the refractive index ellipsoid is tilted by tilting the direction and the direction of the main refractive index n _a or n _c in the surface clockwise or counterclockwise. The device has the following features. That is, in the liquid crystal layer
Anisotropy of refractive index of liquid crystal material with respect to light having a wavelength of 450 nm
Difference in refractive index for Δn (450) and light with wavelength of 650 nm
Difference in the tropism Δn (650) Δn (450) −Δn (65
0) is set in the range of 0.0070 or more and 0.0250 or less .

[0101]

Alternatively, the refractive index anisotropy Δn (450) of light having a wavelength of 450 nm and the refractive index anisotropy Δn (65 of light having a wavelength of 650 nm of the liquid crystal material in the liquid crystal layer.
0) difference Δn (450) −Δn (650) is 0.02.
It is set in the range of 00 to 0.0250.

As a result, in the liquid crystal display device according to the present invention, the change in retardation of the liquid crystal display element is further improved as compared with the case where only the compensation function of the retardation plate is used. In particular, coloring of the liquid crystal screen depending on the viewing angle can be further suppressed. Therefore, the liquid crystal display device including such a retardation film and the liquid crystal display element can suppress the reversal phenomenon, the decrease in the contrast ratio in the anti-viewing angle direction, and the coloring phenomenon.

In particular, Δn (450) -Δn (650)
However, the liquid crystal display device set in the range of 0.0070 or more and 0.0250 or less can be sufficiently used even when viewed from any direction at a viewing angle of 50 ° required in a normal liquid crystal display device. It is possible to suppress coloring of the liquid crystal screen to an extent that it can withstand.

Further, Δn (450) -Δn (650)
Is set in the range of 0.0200 to 0.0250
In the liquid crystal display device that is used, a viewing angle of 70 ° is supported,
Furthermore, in a liquid crystal display device having a wide viewing angle, it is possible to realize a state in which the liquid crystal screen is not colored at all when viewed from any direction.

As described above, since the contrast ratio in black and white display is not influenced by the viewing angle direction of the viewer, the above-described structure has the effect of significantly improving the quality of the display image on the liquid crystal display device.

Further, in the liquid crystal display device according to the above-mentioned invention, the wavelength of the liquid crystal material in the liquid crystal layer is 550 nm.
Refractive index anisotropy Δn (550) with respect to light is 0.06
It is preferably set to a range larger than 0 and smaller than 0.120.

As a result, the phase difference generated in the liquid crystal display element according to the viewing angle is eliminated. Therefore, not only the coloring phenomenon that occurs depending on the viewing angle on the display screen, but also the contrast change, the inversion phenomenon in the horizontal direction, and the like can be further improved.

In this case, further, the refractive index anisotropy Δn of the liquid crystal material in the liquid crystal layer with respect to light having a wavelength of 550 nm.
(550) is preferably set in the range of 0.070 to 0.095 .

As a result, it is possible to further improve the change in contrast, the inversion phenomenon in the left-right direction, and the like that occur depending on the viewing angle.

Further, in the above-described liquid crystal display device according to the present invention, it is preferable that the tilt angles of the refractive index ellipsoids in all the retardation plates are set between 15 ° and 75 °.

As described above, in all the retardation plates interposed in the liquid crystal display device, the tilt angle of the index ellipsoid is 15 °.
It is possible to ensure the function of compensating for the phase difference by the above-mentioned retardation plate provided by the present invention by setting the angle between 1 and 75 °. As a result, the visibility can be surely improved.

[Brief description of drawings]

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

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

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

FIG. 4 is a perspective view showing an optical arrangement of a polarizing plate and a retardation plate in the liquid crystal display device by disassembling each part of the liquid crystal display device.

FIG. 5 is a graph showing the refractive index anisotropy Δn of one liquid crystal material used in the liquid crystal layer of the liquid crystal display device with respect to wavelength.

FIG. 6 is a graph showing Δn (λ) / Δn (550) with respect to wavelength of one liquid crystal material used for the liquid crystal layer of the liquid crystal display device.

FIG. 7 is a perspective view showing a measuring system for measuring the viewing angle dependence of the liquid crystal display device.

FIG. 8 is a graph showing transmittance-liquid crystal applied voltage characteristics of the liquid crystal display device in Example 1.

9 is a graph showing transmittance-liquid crystal applied voltage characteristics of a liquid crystal display device of a comparative example with respect to Example 1. FIG.

FIG. 10 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 2.3 Phase plate 4.5 Polarizing plate (polarizer) 8 Liquid crystal layer 9 ・ 12 Glass substrate (translucent substrate) 10 ・ 13 Transparent electrode (transparent electrode layer) 11.14 Alignment film

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02F 1/13-1/141

Claims (6)

(57) [Claims] 1. A liquid crystal display device constituted by enclosing a liquid crystal layer between a pair of translucent substrates each having a transparent electrode layer and an alignment film formed on opposite surfaces, and both sides of the liquid crystal display device. And a pair of polarizers arranged in a pair, and at least one retardation plate interposed between the liquid crystal display element and the polarizer, the three main refractive indices n _a and n _{b of the} index ellipsoid. , N _c have a relationship of n _a <n _b <n _c , and the direction of the main refractive index n _b parallel to the normal direction of the surface with the direction of the main refractive index n _a or n _{c in} the surface as an axis. When,
By the direction of the principal refractive index n _c or n _a in the surface is inclined clockwise or counterclockwise, in the liquid crystal display device that includes a retardation plate in which the refractive index ellipsoid is inclined, The liquid crystal material in the liquid crystal layer has a wavelength of 450 nm.
Of refractive index anisotropy Δn (450) and wavelength of 650 nm
Difference in refractive index anisotropy Δn (650) with respect to light Δn (45
0) -Δn (650) is 0.0070 or more and 0.025
A liquid crystal display device characterized by being set in a range of 0 or less . 2. A wavelength of 45 of the liquid crystal material in the liquid crystal layer.
The difference Δn (450) −Δn (650) between the refractive index anisotropy Δn (450) for 0 nm light and the refractive index anisotropy Δn (650) for wavelength 650 nm is 0.0200 or more.
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is set in a range of 0.0250 or less . 3. The wavelength 55 of the liquid crystal material in the liquid crystal layer.
The refractive index anisotropy Δn (550) for 0 nm light is
Set to a range greater than 0.060 and less than 0.120
The liquid crystal display device according to claim 1 , wherein the liquid crystal display device is provided. 4. The wavelength 55 of the liquid crystal material in the liquid crystal layer.
The refractive index anisotropy Δn (550) for 0 nm light is
It is set in the range of 0.070 to 0.095
The liquid crystal display device according to claim 3 , wherein the liquid crystal display device is a liquid crystal display device. 5. An index ellipsoid of all retardation plates.
Check that the tilt angle is set between 15 ° and 75 °
The liquid crystal display device according to claim 1 , wherein the liquid crystal display device is a liquid crystal display device. 6. The liquid crystal layer is twisted and aligned at about 90 °.
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a liquid crystal display device.