JPH10186355A - Liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display a high quality image by eliminating a phase difference according to a viewing angle generated in a liquid crystal display element, and particularly effectively preventing a coloring phenomenon of a liquid crystal screen occurring as a viewing angle increases. Provided is a liquid crystal display device that can be used. SOLUTION: A liquid crystal display element 1 constituted by enclosing a liquid crystal layer 8 between a pair of electrode substrates 6 and 7 and a pair of polarizers 4 and 5 arranged on both sides of the liquid crystal display element 1 are provided. Have a negative refractive index anisotropy between the main refractive indices n _a and n
_In a liquid crystal display device in which at least one retardation plate 2.3 having no refractive index ellipsoid is interposed in which _c is parallel to the surface and main refractive index n _b is parallel to the normal direction of the surface, the liquid crystal layer 8
The change in the refractive index anisotropy Δn of the liquid crystal material with respect to the wavelength of light in the above is set in a range where coloring of the liquid crystal screen depending on the viewing angle does not occur.

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 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 A liquid crystal display device using a nematic liquid crystal display element has been widely used for a numerical segment type display device such as a clock or a calculator, but recently, a word processor, a notebook personal computer, and a It is also used for LCD televisions.

[0003] A liquid crystal display element generally has a light-transmitting substrate, on which electrode lines and the like are formed to turn on and off pixels. For example, in an active matrix type liquid crystal display device, an active element such as a thin film transistor is formed on the substrate together with the above electrode lines as switching means for selectively driving a pixel electrode for applying a voltage to the liquid crystal. Further, in a liquid crystal display device that performs color display, a color filter layer of red, green, blue, or the like is provided on a substrate.

[0004] As a liquid crystal display system used in the above-mentioned liquid crystal display element, a different system is appropriately selected according to the twist angle of the liquid crystal. For example, an active drive type twisted nematic liquid crystal display method (hereinafter, referred to as a TN method) and a multiplex drive type super twisted nematic liquid crystal display method (hereinafter, referred to as an STN method) are well known.

[0005] In the TN mode, 90 nematic liquid crystal molecules are used.
° Display is performed by orienting in a twisted state and guiding light along the direction of the twist. The STN method utilizes the fact that the transmittance near the threshold of the voltage applied to the liquid crystal changes sharply by expanding the twist angle of the nematic liquid crystal molecules to 90 ° or more.

[0006] In the STN system, since the birefringence effect of liquid crystal is used, a unique color is given to the background of the display screen due to color interference. It is considered that the use of an optical compensator is effective in solving such inconveniences and performing monochrome display by the STN method. Display methods using an optical compensator include a double super twist nematic phase compensation method (hereinafter, referred to as a DSTN method) and a film type phase compensation method in which a film having optical anisotropy is arranged (hereinafter, a film addition type). System).

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

On the other hand, the TN system is roughly classified into a normally black system and a normally white system. In the normally black mode, a pair of polarizing plates are arranged so that their polarization directions are parallel to each other, and black is displayed in a state where no on-voltage is applied to the liquid crystal layer (off state). In the normally white mode, a pair of polarizing plates are arranged so that their polarization directions are orthogonal to each other, and white is displayed in an off state. The normally white method is effective in terms of display contrast, color reproducibility, display angle dependency, and the like.

In the above-mentioned TN liquid crystal display device, the liquid crystal molecules have a refractive index anisotropy Δn, and the liquid crystal molecules are inclined and oriented with respect to the upper and lower substrates. In addition, there is a problem that the contrast of the displayed image changes depending on the viewing direction and the angle of the viewer, and the viewing angle dependency increases.

FIG. 10 schematically shows a cross-sectional structure of the TN liquid crystal display element 31. This state shows a case where a voltage for halftone display is applied and the liquid crystal molecules 32 are slightly rising. In this TN liquid crystal display element 31, the linearly polarized light 35 passing through the normal direction of the surface 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 formed by liquid crystal molecules 32. And the angles at which they intersect are different. Since the liquid crystal molecules 32 have a refractive index anisotropy Δn, the linearly polarized light 35
When the light 37 passes through the liquid crystal molecules 32, normal light and extraordinary light are generated, and are converted into elliptically polarized light in accordance with the phase difference between them, which is a viewing angle dependent source.

Further, inside the actual liquid crystal layer, the liquid crystal molecules 32 are located near the intermediate portion between the substrates 33 and 34 and the substrate 3.
3 and the vicinity of the substrate 34 are different in tilt angle, and the liquid crystal molecules 32 are twisted by 90 ° about the normal direction.

As described above, the linearly polarized lights 35, 36, and 37 passing through the liquid crystal layer receive various birefringence effects depending on their directions and angles, and exhibit complicated viewing angle dependence.

As the above-mentioned viewing angle dependency, specifically, a phenomenon in which a display image is colored at a certain angle or more when the viewing angle is inclined from the normal direction of the display screen to the normal viewing angle direction which is the downward direction of the display screen. (Hereinafter, referred to as “coloring phenomenon”) and a phenomenon in which black and white are reversed (hereinafter, referred to as “reversal phenomenon”).
Further, when the viewing angle is inclined in the opposite viewing angle direction, which is the upper direction of the display screen, the contrast sharply decreases.

Further, in the above liquid crystal display device, there is 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 at a short distance, colors displayed at the upper part and the lower part of the display screen may be different due to the effect of viewing angle dependence. This is because the viewing angle of the entire display screen is increased, which is the same as viewing the display screen from an oblique direction.

In order to improve such viewing angle dependency,
It has been proposed to insert a retardation film (retardation film) as an optical element having optical anisotropy between a liquid crystal display element and one of the polarizing plates (for example, JP-A-55-60).
0, JP-A-56-97318, etc.).

According to this method, light that has been converted from linearly polarized light to elliptically polarized light after passing through liquid crystal molecules having refractive index anisotropy is interposed on one or both sides of a liquid crystal layer having refractive index anisotropy. By allowing the light to pass through the phase difference plate, the change in the phase difference between the normal light and the extraordinary light generated at the viewing angle is compensated, and the light is converted back to linearly polarized light, thereby improving the viewing angle dependency.

As such a retardation plate, one in which one principal refractive index direction of a refractive index ellipsoid is parallel to a normal direction of the surface of the retardation plate is described in, for example, JP-A-5-313159. Have been.

[0018]

However, in today's situation where a liquid crystal display device having a wider viewing angle and a higher display quality is desired, further improvement in viewing angle dependence is required, and the above-mentioned refractive index ellipsoid is required. It is not always sufficient to use a retardation plate in which one principal refractive index direction is made parallel to the normal direction of the surface of the retardation plate, and there is still room for improvement.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a liquid crystal display device having the above-mentioned retardation plate, in which a change in the refractive index anisotropy Δn with respect to the wavelength of a liquid crystal material used for a liquid crystal layer. By setting to the best range,
It is to improve the viewing angle dependency in addition to the compensation effect by the phase difference plate, and particularly to effectively improve the coloring phenomenon.

[0020]

According to a first aspect of the present invention, there is provided a liquid crystal display device comprising a pair of light-transmitting layers each having a transparent electrode layer and an alignment film formed on opposing surfaces. A liquid crystal display element configured by enclosing a liquid crystal layer between substrates, a pair of polarizers disposed on both sides of the liquid crystal display element, and at least one sheet between the liquid crystal display element and the polarizer An interposed retardation plate,
The three main refractive indices n _a , n _b and n _{c of the} index ellipsoid are n _a
= N _c > n _b , and the main refractive indices n _a and n _c
Are parallel to the surface, and a retardation plate whose main refractive index n _b is parallel to the normal direction of the surface, wherein the refractive index anisotropy of the liquid crystal material in the liquid crystal layer sealed in the liquid crystal display element is It is characterized in that the change of the property Δn with respect to the wavelength of light is set in a range in which coloring of the liquid crystal screen depending on the viewing angle does not occur.

According to the above arrangement, the linearly polarized light passes through the birefringent liquid crystal layer, and normal light and extraordinary light are generated.
When converted into elliptically polarized light with these phase differences, the three principal refractive index n _a of the refractive index ellipsoid, n _b, n _c is n _a =
n _c > n _b , and a retardation plate whose main refractive indices n _a and n _c are parallel to the surface and whose main refractive index n _b is parallel to the normal direction of the surface is provided between the liquid crystal layer and the polarizer. , The change in the phase difference between the normal light and the extraordinary light caused by the viewing angle is compensated by the phase difference plate. However, even if such a compensating function alone is required to further improve the viewing angle dependence, it is not always sufficient.

The inventors of the present invention have conducted various studies and 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). And completed the present invention.

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 sealed in the liquid crystal display element.
The change with respect to the wavelength of n light is set in a range in which coloring of the liquid crystal screen depending on the viewing angle does not occur. This allows
It has become possible to further prevent the coloring of the screen.
It should be noted that the contrast change and the inversion phenomenon can be improved as compared with the case where only the compensation function of the retardation plate is used.

The range in which the change in the refractive index anisotropy Δn of the liquid crystal material with respect to the wavelength of light does not cause coloring of the liquid crystal screen depending on the viewing angle is specifically the range described in claim 2.

That is, as described in claim 2, the liquid crystal material in the liquid crystal layer has a refractive index anisotropy Δn (450) for light having a wavelength of 450 nm and a refractive index anisotropy Δn (650) for light having a wavelength of 650 nm. Difference Δn (450) −Δn
(650) is set in a range from 0 to less than 0.0090.

At least within this range, although slightly colored at a viewing angle of 50 ° required for a normal liquid crystal display device, it can be sufficiently used in any direction.

In a liquid crystal display device having a wider viewing angle such as a visual angle of 70 °, it is preferable that the change in the refractive index anisotropy Δn of the liquid crystal material with respect to the wavelength of light is in the range described in claim 3.

That is, as described in claim 3, the liquid crystal material in the liquid crystal layer has a refractive index anisotropy Δn (450) for light having a wavelength of 450 nm and a refractive index anisotropy Δn (650) for light having a wavelength of 650 nm. Difference Δn (450) −Δn
(650) is set in the range of 0 or more and 0.0045 or less.

With this range, a coloring phenomenon can be completely eliminated even when viewed from all directions at a viewing angle of 70 ° required for a liquid crystal display device having a wide viewing angle.

In the liquid crystal display device according to the first and second aspects of the present invention, the liquid crystal material in the liquid crystal layer has a refractive index anisotropy Δn (550) with respect to light having a wavelength of 550 nm. ) Is greater than 0.060 and 0.1.
It is preferable to set it to a range smaller than 120.

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

In this case, the liquid crystal material in the liquid crystal layer has a refractive index anisotropy Δn (550) of the liquid crystal material with respect to light having a wavelength of 550 nm in a range of 0.070 or more and 0.095 or less. By setting to, the phase difference corresponding to the viewing angle generated in the liquid crystal display element can be more effectively eliminated, so that the contrast change, the reversal phenomenon in the left and right direction, and the coloring phenomenon in the liquid crystal display image can be reliably improved. Can be.

According to a sixth aspect of the present invention, in the liquid crystal display device according to the first, second or fourth aspect of the present invention,
In all retardation plates, the main refractive index n _a and the main refractive index n _b
(N _a −n _b ) × d
Is preferably set between 80 nm and 250 nm.

As described above, in all the phase difference plates interposed in the liquid crystal display device, the product (n _a) of the difference between the main refractive index n _a and the main refractive index n _b and the thickness d of the phase difference plate. −n _b ) × d
Is set between 80 nm and 250 nm, the phase difference compensating function of the phase plate provided in the present invention can be reliably obtained.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

The liquid crystal display device according to this embodiment has the structure shown in FIG.
, A liquid crystal display element 1 and a pair of retardation plates 2.
3 and a pair of polarizing plates (polarizers) 4 and 5.

The liquid crystal display element 1 has a structure in which a liquid crystal layer 8 is interposed between electrode substrates 6 and 7 arranged opposite to 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 on 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.

For the sake of simplicity, FIG. 1 shows a configuration for two pixels, but 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. The glass substrate 9 is arranged at a predetermined interval and
The portions 12 are formed so as to be orthogonal to each other when viewed from a direction perpendicular to the substrate surface. A portion where the transparent electrodes 10 and 13 intersect 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 drive circuit (not shown).

The electrode substrates 6 and 7 are adhered to each other with a sealing resin 15.
The liquid crystal layer 8 is sealed in the space formed by the above. Although the details will be described later, the liquid crystal layer 8 of the present liquid crystal display device is configured so that the liquid crystal layer 8 has a combination of the phase difference compensation function of the retardation plates 2 and 3 and the best characteristic. A material whose refractive index anisotropy Δn satisfies a predetermined condition is selected.

In the present liquid crystal display device, a liquid crystal cell 16 is a unit in which the above-mentioned liquid crystal display element 1 is formed with retardation plates 2.3 and polarizing plates (polarizers) 4.5. The alignment films 11 and 14 are rubbed in advance so that the interposed liquid crystal molecules are twisted at about 90 °. FIG.
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 retardation plates 2 and 3 are interposed between the liquid crystal display element 1 and the polarizing plates 4 and 5 disposed on both sides of the liquid crystal display element 1, respectively. The retardation plates 2 and 3 are formed by horizontally aligning and cross-linking discotic liquid crystals on a support made of a transparent organic polymer.

As a support for the retardation plates 2 and 3, triacetyl cellulose (TA) commonly used for a polarizing plate is generally used.
C) is highly reliable and suitable. Otherwise, polycarbonate (PC), polyethylene terephthalate (P
A colorless and transparent organic polymer film excellent in environmental resistance and chemical resistance such as ET) is suitable.

As shown in FIG. 3, the phase difference plates 2 and 3, has a main refractive index n _a · n _b · n _c of three different directions.
Direction of the principal refractive index n _a is, y coordinate and direction coincides among the coordinate axes in the orthogonal coordinate xyz another, the direction of the principal refractive index n _c is match the x-axis and direction. Direction of the principal refractive index n _b is a direction (direction normal to the surface) perpendicular z coordinate axes on the surface corresponding to the screen in the phase difference plates 2 and 3 are identical. That is, in the phase difference plates 2 and 3, there is no inclination of the refractive index ellipsoid.

Each of the retardation plates 2 and 3 has a main refractive index of n _a = n.
It meets the relationship of _c> n _b. Thus, since there is only one optical axis, the retardation plates 2 and 3 have uniaxiality and the refractive index anisotropy becomes negative. Phase difference plate 2/3
Is the first retardation value (n _c −n _a ) × d of n _a
= N _c, which is almost 0 nm. The second retardation value (n _c -n _b) × d is, 80Nm～250nm
Is set to any value within the range By setting the second retardation value (n _c -n _b) × d in this range, it is possible to reliably obtain the compensation function of the phase difference by the phase difference plates 2 and 3. The above n _c -n _a and n _c
−n _b represents the refractive index anisotropy Δn, and d is the retardation plate 2.3
Represents the thickness.

The arrangement of the retardation plates 2 and 3 may be such that even if only one of the retardation plates 2 (3) is arranged on one side, the retardation plates 2 and 3 are arranged on one side. Can also. Further, three or more retardation plates can be used.

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 provided.
Means that the absorption axes AX ₁ and AX ₂ are the alignment films 11.
4 (see FIG. 1) are arranged in parallel with the rubbing directions R ₁ and R ₂ respectively. 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.

The direction D of the main refractive index n _c of the phase difference plate 2
₁ is arranged to be parallel to the rubbing direction R _1, the direction D ₂ of the principal refractive index n _c of the phase difference plate 3 are arranged in parallel to the rubbing direction R _2.

With the arrangement of the phase difference plates 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 and white display is performed when off.

In general, in an optically anisotropic material 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 has a refractive index ellipse. Represented by the body. The refractive index anisotropy Δn has different values depending on from which direction the refractive index ellipsoid is observed.

Next, the above-described liquid crystal layer 8 will be described in detail. As described above, in the liquid crystal layer 8, the liquid crystal material constituting the liquid crystal layer 8 is provided with a refractive index anisotropy so that a combination having a phase difference compensating function of the retardation plates 2 and 3 and the best characteristics are obtained. A liquid crystal material is used in which Δn is set to a predetermined condition, that is, a range in which the change in refractive index anisotropy Δn with respect to the wavelength of light does not cause coloring of the liquid crystal screen depending on the viewing angle.

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

That is, Δn which is the difference between the refractive index anisotropy Δn (450) of the liquid crystal material for light having a wavelength of 450 nm and the refractive index anisotropy Δn (650) for light having a wavelength of 650 nm.
(450) −Δn (650) is in a range of 0 or more and less than 0.0090. More preferably, Δn (45
0) -Δn (650) is in the range of 0 or more and 0.0045 or less.

By using a liquid crystal material designed to satisfy such conditions, the contrast change, inversion phenomenon, coloring caused by the viewing angle of the display screen due to the phase difference compensation function of the phase difference plates 2 and 3 can be achieved. Not only improvement of phenomenon,
The coloring phenomenon on the display screen can be further improved.

In detail, by using a liquid crystal material designed to satisfy the wider range, the color is slightly colored at a viewing angle of 50 ° required for a normal liquid crystal display device, but from any direction. Even if it is seen, it can be made to be sufficiently usable. By satisfying the particularly preferable range, no coloration can be obtained at a viewing angle of 70 ° from any direction. Also, by using a liquid crystal material designed to satisfy the above conditions, the contrast change and the inversion phenomenon can be improved as compared with the case where only the compensation function of the phase difference plates 2 and 3 is used.

More preferably, the conditions of the above-mentioned set range are satisfied and the conditions of the following set range are simultaneously satisfied. In the liquid crystal layer 8 of the present liquid crystal display device, This satisfies the condition of this setting range.

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 in a range larger than 0.060 and smaller than 0.120. More preferably, Δn (550) is set to 0.070 or more and 0.09 or more.
5 or less.

By satisfying these setting conditions, the phase difference compensating function of the phase difference plates 2 and 3 and the change of the refractive index anisotropy Δn of the liquid crystal material with respect to the wavelength are set within the above-mentioned setting range. In addition to the improvement of the viewing angle dependency with the compensation function, the reduction of the contrast ratio in the anti-viewing angle direction and the inversion phenomenon in the left-right direction can be further improved.

FIG. 5 shows a liquid crystal layer 8 in the present liquid crystal display device.
Δn (λ) (wavelength-refractive index anisotropy Δn characteristic) with respect to wavelength (λ) of one liquid crystal material that can be used for (1) 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 for comparison with a dashed line curve b.

As is clear from the comparison between the curves a and b, Δn (λ) with respect to the wavelength (λ) of the liquid crystal material that can be used for the liquid crystal layer 8 of the present liquid crystal display device is the same as that of the conventional liquid crystal. The inclination is gentler than that of the liquid crystal material of the display device, and the display device is slightly flat to the right.

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

As is apparent from a comparison between the curves c and d, Δn (λ) / Δn with respect to the wavelength (λ) of the liquid crystal material that can be used for the liquid crystal layer 8 of the present liquid crystal display device.
(550) also has a gentler slope than the liquid crystal material of the conventional liquid crystal display device.

With such a configuration, in the liquid crystal display device of the present embodiment, the phase difference corresponding to the viewing angle generated in the liquid crystal display element 1 is compensated for by the phase difference plates 2 and 3 together with the compensation function of the liquid crystal layer 8. The compensation function by setting the change of the refractive index anisotropy Δn with respect to the wavelength of the liquid crystal material in a range where coloring of the liquid crystal screen does not occur, thereby improving the contrast change, inversion phenomenon, and coloring phenomenon depending on the viewing angle, thereby achieving high quality. Images can be displayed.

Next, an example according to the present embodiment configured as described above will be described together with a comparative example. (Embodiment 1) In this embodiment, the liquid crystal layer 8 of the liquid crystal cell 16 in the liquid crystal display device of FIG. 1 has a refractive index anisotropy Δn (450) at a wavelength of 450 nm and a refractive index anisotropy Δn (650) at a wavelength of 650 nm. Δn (45)
0) -Δn (650) are 0, 0.0030,
Using a liquid crystal material set to 0.0045, 0.0055, and 0.0070, and setting the cell thickness (the thickness of the liquid crystal layer 8) to 5 μm
5 samples # 1 to # 5 were prepared.

The phase difference plates 2 in samples # 1 to # 5
The above-mentioned first retardation value is obtained by coating a discotic liquid crystal on a transparent support (for example, triacetyl cellulose (TAC), etc.), and aligning and cross-linking the discotic liquid crystal. Is 0 nm,
The one having the above-mentioned second retardation value of 100 nm was used.

As a comparative example with respect 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 prepared except that a liquid crystal material having the above Δn (450) −Δn (650) of 0.0090 was used.

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

[0067]

[Table 1]

For samples # 1 to # 3 of the example,
Even when viewed from all directions with a viewing angle of 70 °, no coloring was observed and good image quality was obtained. In sample # 4, no coloring was observed from any direction at a viewing angle of 50 °, but slight coloring was observed at a viewing angle of 60 ° when viewed from the left and right directions. However, this degree of coloring was sufficiently usable. In sample # 5, slight coloring was observed when viewed from the left and right directions at a viewing angle of 50 °, but this was also of a degree that could withstand use.

On the other hand, in Comparative Sample # 100, even when viewed from the left and right directions even at a viewing angle of 50 °, coloring from yellow to almost unusable was confirmed.

Example 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 three-dimensional light receiving angle, and is arranged at a position at a predetermined distance from the coordinate origin in a direction forming an angle φ (viewing angle) with respect to the z direction perpendicular to the surface 16a. ing.

At the time of measurement, a wavelength of 550 nm is applied to the liquid crystal cell 16 installed in the measurement system from the surface opposite to the surface 16a.
m monochromatic light. Part of the monochromatic light transmitted through the liquid crystal cell 16 enters the light receiving element 21. After the output of the light receiving element 21 is amplified to a predetermined level by the amplifier 22, it is recorded by a recording device 23 such as a waveform memory and a recorder.

In this embodiment, the liquid crystal layer 8 in the liquid crystal cell 16 shown in FIG. 1 has a refractive index anisotropy Δn at a wavelength of 550 nm.
(550) are 0.070, 0.080, 0.
The cell thickness (liquid crystal layer 8
(Thickness of 5 μm) were prepared.

The phase difference plate 2 in samples # 6 to # 8
As 3, the same as the retardation plates 2 and 3 in Example 1 described above, in which discotic liquid crystals were aligned in parallel, was used.

The samples # 6 to # 8 are set in the measuring 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 fixed angle φ. The output level of the light receiving element 21 with respect to was measured.

In the measurement, assuming that the light receiving element 21 is arranged at an angle φ of 50 ° and the y direction is on the upper side of the screen and the x direction is on the left side of the screen, the arrangement position of the light receiving element 21 is assumed. Was changed to the left and right respectively.

FIGS. 8A and 8B show the results. FIG.
(A) and (b) are graphs showing light transmittance (transmittance-liquid crystal applied voltage characteristics) with respect to a voltage applied to samples # 6 to # 8.

FIG. 8 (a) shows the result of measurement from the right side of FIG. 2, and FIG. 8 (b) shows the result of measurement from the left side of FIG.

In FIGS. 8A and 8B, curves L1 and L4 indicated by dashed lines respectively show the liquid crystal layer 8 with Δn (550).
The curves L2 and L5 indicated by the solid lines in the sample # 6 using the liquid crystal material of
50) Sample # 7 using a liquid crystal material of 0.080, and curves L3 and L6 indicated by broken lines show Δn
Sample using liquid crystal material of (550) = 0.095♯
Eight.

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

As in the present embodiment, the measurement was carried out by arranging the light receiving elements 21 at an angle φ of 50 ° and changing the position of the light receiving elements 21 to the left and right.

The results are shown in FIGS. 9A and 9B. FIG.
(A) and (b) are graphs showing light transmittance (transmittance-liquid crystal applied voltage characteristic) with respect to a voltage applied to comparative samples # 101 and # 102.

FIG. 9A shows the result of measurement from the right direction in FIG. 2, and FIG. 9B shows the result of measurement from the left direction in FIG.

In FIGS. 9A and 9B, the curves L10 and L12 indicated by solid lines respectively show the liquid crystal layer 8 with Δn (550)
Comparative sample using liquid crystal material of = 0.060 # 101
The curves L11 and L13 indicated by broken lines correspond to the liquid crystal layer 8
Comparative sample # 102 using a liquid crystal material having Δn (550) of 0.120.

FIG. 8 shows a comparison between the transmittance in the right direction and the voltage applied to the liquid crystal of the samples # 6 to # 8 of this embodiment and the comparative samples # 101 and # 102 of the comparative example.
In (a), it was confirmed that the transmittance decreased to almost zero when the voltage was applied to all of the curves L1, L2, and L3. Also, in FIG. 9A, as the voltage is applied to the curve L10, the transmittance becomes almost zero as in FIG. 8A.
Although it decreases until it becomes close, the reversal phenomenon described above was confirmed for the curve L11.

Similarly, for samples # 6 to # 8 and comparative samples # 101 and # 102, curves L4, L5 and L6 in FIG. 8B and FIG. In the curve L12 of FIG. 9B, as the voltage is applied, the transmittance is all reduced to almost zero, but FIG.
The reversal phenomenon was confirmed only in the curve L13 of (b).

Further, the samples # 6 to # 8 and the comparative samples # 101 and # 102 were visually checked under white light.

For samples # 6 to # 8 of the example,
No coloration was observed from any direction at a viewing angle of 50 °, and the image quality was good. In contrast, the comparative sample # 10
It was confirmed that about 1 · # 102, when viewed from the left and right directions at a viewing angle of 50 °, the color was gradually changed from yellow to yellow.

As described above, as shown in FIGS. 8A and 8B, the liquid crystal layer 8 has a refractive index anisotropy Δn (550) at a wavelength of 550 nm of 0.070, 0.080, and 0.080, respectively.
In the case of using a liquid crystal material set to 0.095, the transmittance decreases sufficiently as the voltage is applied, and the viewing angle increases because no reversal 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 shown in FIGS. 9A and 9B, the liquid crystal layer 8 has the refractive index anisotropy Δn (550) at the wavelength of 550 nm of 0.060 and 0.120, respectively. It can be seen that the viewing angle dependency is not sufficiently improved when the liquid crystal material is used.

Further, 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 of the phase difference plates 2 and 3,
When the second retardation value was within the range of 80 nm to 250 nm, there was basically no change. In addition, it was confirmed that the viewing angle in the horizontal direction (left-right direction) did not increase when the value exceeded the above range.

The comparative samples # 101 and # 10
2, the liquid crystal layer 8 in the liquid crystal cell 16 of FIG. 1 has a refractive index anisotropy Δn at a wavelength of 550 nm.
(550) are 0.065, 0.100,.
Three samples # 9 to # 11 were prepared in the same manner as in the present example except that the liquid crystal material of No. 115 was used, and the light receiving element 21 was formed using the measuring system shown in FIG. The output level of the light receiving element 21 with respect to the voltage applied to the samples # 9 to # 11 when the angle was fixed at a constant angle φ was measured. In addition, visual confirmation was performed under white light.

As a result, the sample # 1 having a refractive index anisotropy Δn (550) at a wavelength of 550 nm of 0.100 was obtained.
0, and the refractive index anisotropy Δn (5
In sample # 11 in which 50) was set to 0.115, the angle φ
When the angle was set to 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 this increase in transmittance was acceptable for use. On the other hand, wavelength 5
The refractive index anisotropy Δn (550) at 50 nm is 0.0
In sample # 9 with 65, there was no problem in the result in the left-right direction.

In the visual inspection, sample # 1
In the case of 0 · # 11, slight coloring was observed from yellow to orange, but it was not a problem. Sample ♯
In No. 9, it was confirmed that it was slightly bluish. However, this degree of bluing was not a problem.

As a supplement, a voltage of about 1 V was applied to sample # 9 and comparative sample # 101.
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 that was unbearable for use was observed. On the other hand, a slight decrease in transmittance was confirmed in sample # 9, but it was of a level that could be used, and there was no problem.

[0095]

As described above, in the liquid crystal display device according to the first aspect of the present invention, a liquid crystal layer is sealed between a pair of light-transmitting substrates each having a transparent electrode layer and an alignment film formed on opposing surfaces. A liquid crystal display device, a pair of polarizers disposed on both sides of the liquid crystal display device, and a retardation plate interposed between the liquid crystal display device and the polarizer. And 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 ,
A liquid crystal display device comprising: a retardation plate whose main refractive indices n _a and n _c are parallel to the surface and whose main refractive index n _b is parallel to the normal direction of the surface. The change in the refractive index anisotropy Δn of the liquid crystal material with respect to the wavelength of light in the above is set in a range in which coloring of the liquid crystal screen depending on the viewing angle does not occur.

According to a second aspect of the present invention, in the liquid crystal display device according to the first aspect, the liquid crystal material in the liquid crystal layer has a refractive index anisotropy Δn (450) with respect to light having a wavelength of 450 nm.
And the refractive index anisotropy Δn (65
0) difference Δn (450) −Δn (650) is set in a range of 0 or more and less than 0.0090.

According to a third aspect of the present invention, in the liquid crystal display device according to the second aspect, the liquid crystal material in the liquid crystal layer has a refractive index anisotropy Δn (450) with respect to light having a wavelength of 450 nm.
And the refractive index anisotropy Δn (65
0) difference Δn (450) −Δn (650) is set in a range of 0 or more and 0.0045 or less.

Thus, in the liquid crystal display device according to the first to third aspects of the present invention, the change in the phase difference of the liquid crystal display element is further improved as compared with the case where only the compensating function is provided by the phase difference plate, and it is particularly dependent on the viewing angle. Since the coloring phenomenon of the liquid crystal screen can be further prevented, the liquid crystal display device including such a phase difference plate and the liquid crystal display element prevents the inversion phenomenon, the decrease in the contrast ratio in the anti-viewing angle direction, and the coloring phenomenon. be able to.

In particular, in the liquid crystal display device according to the second aspect of the present invention, the liquid crystal display device has a liquid crystal display enough to withstand use even when viewed from all directions at a viewing angle of 50 ° required for a normal liquid crystal display device. Coloring of the screen can be suppressed.

Furthermore, in the liquid crystal display device according to the third aspect of the present invention, in a liquid crystal display device having a wider viewing angle such as a viewing angle of 70 °, a state in which the liquid crystal screen is completely free of color when viewed from any direction can be realized.

Therefore, the above configuration has an effect that the quality of the display image of the liquid crystal display device is remarkably improved because the contrast ratio in the black and white display is not affected by the viewing angle direction of the viewer.

In the liquid crystal display device according to the present invention, the liquid crystal material in the liquid crystal layer has a refractive index anisotropy Δ of the liquid crystal material with respect to light having a wavelength of 550 nm.
This is a configuration in which n (550) is set in a range larger than 0.060 and smaller than 0.120.

As a result, the phase difference corresponding to the viewing angle generated in the liquid crystal display element can be eliminated, so that not only the coloring phenomenon depending on the viewing angle but also the contrast change and the reversal phenomenon in the left and right directions on the display screen. Etc. can be further improved.

According to a fifth aspect of the present invention, in the liquid crystal display device according to the fourth aspect, the liquid crystal material in the liquid crystal layer has a refractive index anisotropy Δn (5) with respect to light having a wavelength of 550 nm.
50) is a configuration set in the range of 0.070 or more and 0.095 or less.

As a result, it is possible to further improve the contrast change depending on the viewing angle, the left-right inversion phenomenon, and the like, as compared with the liquid crystal display device according to the fourth aspect of the present invention.

The liquid crystal display device according to the invention of claim 6 is the liquid crystal display device according to claim 1, 2 or 4, wherein the difference between the main refractive index n _a and the main refractive index n _b and the position of all the retardation plates are different. The product (n _a −n _b ) × d with the thickness d of the retardation plate is 2 from 80 nm.
The configuration is set between 50 nm.

As described above, in all the phase difference plates interposed in the liquid crystal display device, the product (n _a) of the difference between the main refractive index n _a and the main refractive index n _b and the thickness d of the phase difference plate. −n _b ) × d
Is set between 80 nm and 250 nm, the function of compensating for the phase difference by the above-described retardation plate of the present invention can be reliably obtained, and the visibility can be reliably improved.

[Brief description of the drawings]

FIG. 1 is an exploded cross-sectional view illustrating 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 phase difference plate in the liquid crystal display device, in which respective parts of the liquid crystal display device are disassembled.

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

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

FIG. 7 is a perspective view showing a measurement system for measuring the viewing angle dependency 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.

FIG. 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. 10 is a schematic diagram showing a twist alignment of liquid crystal molecules in a TN liquid crystal display device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 liquid crystal display element 2.3 retardation plate 4.5 polarizing plate (polarizer) 8 liquid crystal layer 9.1 glass substrate (light-transmitting substrate) 10.13 transparent electrode (transparent electrode layer) 11.14 alignment film

Claims (6)

[Claims] 1. A liquid crystal display device comprising a liquid crystal layer encapsulated between a pair of translucent substrates each having a transparent electrode layer and an alignment film formed on opposing surfaces, and both sides of the liquid crystal display device. And a retardation plate interposed between at least one of the liquid crystal display element and the polarizer, wherein the three main refractive indices n _a and n _{b of the} index ellipsoid are provided. , N _c has a relationship of n _a = n _c > n _b , and a retardation plate in which the main refractive indices n _a and n _c are parallel to the surface and the main refractive index n _b is parallel to the normal direction of the surface. The change in the refractive index anisotropy Δn of the liquid crystal material in the liquid crystal layer enclosed in the liquid crystal display element with respect to the wavelength of light is set in a range in which coloring of the liquid crystal screen depending on the viewing angle does not occur. A liquid crystal display device characterized in that: 2. The method according to claim 1, wherein the liquid crystal material in said liquid crystal layer has a wavelength of 45.
The difference Δn (450) −Δn (650) between the refractive index anisotropy Δn (450) for light of 0 nm and the refractive index anisotropy Δn (650) for light of 650 nm is 0 or more and 0.00 or more.
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is set in a range less than 90. 3. The method according to claim 1, wherein the liquid crystal material in said liquid crystal layer has a wavelength of 45.
The difference Δn (450) −Δn (650) between the refractive index anisotropy Δn (450) for light of 0 nm and the refractive index anisotropy Δn (650) for light of 650 nm is 0 or more and 0.00 or more.
3. The liquid crystal display device according to claim 2, wherein the range is set to 45 or less. 4. A liquid crystal material having a wavelength of 55
The refractive index anisotropy Δn (550) for light of 0 nm is:
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is set in a range larger than 0.060 and smaller than 0.120. 5. The liquid crystal material according to claim 1, wherein
The refractive index anisotropy Δn (550) for light of 0 nm is:
The liquid crystal display device according to claim 4, wherein the liquid crystal display device is set in a range from 0.070 to 0.095. 6. The product (n _a ) of the difference between the main refractive index n _a and the main refractive index n _b and the thickness d of the phase difference plate in all the phase difference plates.
5. The liquid crystal display device according to claim 1, wherein −n _b ) × d is set between 80 nm and 250 nm.