JP3375351B2 - 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 twisted nematic (TN) type liquid crystal display device, and more particularly to a TN type liquid crystal display in which the viewing angle dependence of contrast and color at the time of halftone display is improved. It relates to the device.

[0002]

2. Description of the Related Art In recent years, a TFT-TN type liquid crystal display device has been used as a liquid crystal display device used as a display of a word processor, a personal computer or the like. In this liquid crystal display device, a polarizer normally has its transmission axis on the light incident side of a TN type liquid crystal cell in which a driving thin film transistor (TFT) is arranged for each pixel. The analyzer is arranged parallel to the processing direction, and the analyzer is arranged on the light emitting side of the liquid crystal cell with its transmission axis substantially orthogonal to the transmission axis of the polarizer. Since this conventional liquid crystal display device can be driven by applying a static voltage to each pixel, it has a higher contrast and a relatively wider viewing angle than a simple matrix type liquid crystal display device.

[0003]

However, such a conventional TFT-TN type liquid crystal display device also has a narrower viewing angle than a CRT of a general-purpose display, and the viewing angle (display There is a drawback in that the color change corresponding to the change of the angle of the line of sight with respect to the normal line of the surface, that is, the visual angle dependence of the color change becomes remarkable.

FIG. 21 shows an isocontrast curve in which the applied voltage is V = 0 [V], V = 4.38 [V] in the conventional typical TN type liquid crystal display device. In this figure, the concentric circles are 10 from the inside with respect to the normal direction of the substrate of the liquid crystal display device.
Representing the viewing angle inclined by °, 20 °, 30 °, 40 ° and 50 °, the black square represents contrast 10, white square represents contrast 50, black triangle represents contrast 100, white triangle represents contrast 150, respectively. There is. Further, the arrow R indicates the alignment treatment direction of the light incident side substrate. According to this figure, in the high-contrast viewing angle direction, the angle (hereinafter, referred to as azimuth angle) representing the azimuth of the display surface based on the alignment treatment direction R of the light incident side substrate of the liquid crystal cell is 315 ° downward. The area of high contrast is wide in the horizontal direction with azimuth angles of 225 ° and 45 °, and is obviously wider than the vertical direction with azimuth angles of 135 ° and 315 °. Further, in the vertical direction, the contrast is lower in the lower direction than in the upper direction, and there is no inversion region in the vicinity of the upper direction, but the contrast is the lowest viewing angle direction.

22 (A) to 22 (D), the light transmittance Y
The viewing angle dependence of the Y-V curve showing the relationship between the applied voltage V and the applied voltage V is shown. As shown in FIG. 22A, when the azimuth angle is 315 ° downward and the viewing angle is swung from 0 ° to 50 °, V of the Y-V curve is reduced.
= 2.0 to 4.0 [V], a large bump appears in the area, and the applied voltage area for displaying the intermediate gradation is V = 1.5 to 4.0 [V].
The brightness reversal phenomenon is noticeable when displaying halftones.

On the other hand, as shown in FIG. 22 (B) and FIG. 22 (C), the above-mentioned phenomenon does not occur in the right direction where the azimuth angle on the display surface is 45 ° and the left direction where the azimuth angle is 225 °, but FIG. As shown in D), when the azimuth angle is 135 ° upward and the viewing angle is swung from 0 ° to 50 °, the YV curve gradually approaches a flat line, and there is no difference in brightness between intermediate gradations. Will end up.

Next, the viewing angle dependence of the color change in the conventional TN type liquid crystal display device will be described, but before that, the color difference ΔE *, the lightness index difference ΔL * and the chroma difference ΔC * will be described. The color difference ΔE * means a [distance between colors] based on the [color] at the front view angle when each voltage is applied. The color difference ΔE * is the lightness index difference ΔL * and the chroma difference ΔC.
Depends on * These physical quantities are CIE1976 (L *, u
*, V *) is defined in the color space.

From the normal (X, Y, Z) color space, CIE
The conversion formula to the 1976 (L *, u *, v *) color space is as follows.

[0009]

[Equation 1]

23 (A) to 23 (F) and FIG. 24 (A)
24 (F) and FIGS. 25 (A) to 25 (F) show color difference ΔE *, lightness index difference ΔL *, and chroma difference ΔC * in four directions (azimuth: 135 °, 315 °, 225 °). , 45
6 is a graph showing the viewing angle dependency at each angle of 6 ° for each of 6 levels of applied voltage. In this case, the applied voltage in 6 steps is 0.
V, 1.5V, 2V, 2.5V, 3V, 4V. or,
In these graphs, a quadrangle represents an upward direction, a plus mark represents a downward direction, a circle represents a leftward direction, and a triangle represents a rightward direction.

As is apparent from these graphs, the conventional TFT-TN type liquid crystal display device has a problem that there is a large difference in the [color] with respect to the change of the viewing angle in the halftone display. For these reasons, in the conventional TFT-TN type liquid crystal display device, the viewing angle dependence of the contrast and display color (hereinafter referred to as viewing angle characteristics) is improved, and especially in the case of multi-gradation display, the intermediate gradation is improved. Accurate display is required regardless of the viewing angle.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a liquid crystal display device having excellent viewing angle characteristics and capable of displaying gradation accurately.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pair of electrodes, on each of which they face each other, electrodes which intersect each other and an alignment film which covers the electrodes and is subjected to an alignment treatment in a predetermined direction. A liquid crystal cell formed by enclosing a liquid crystal material between the substrates in a twist orientation of about 90 ° from one substrate to the other substrate; a polarizer disposed on the light incident side of the liquid crystal cell; an analyzer disposed on the light emitting side of the liquid crystal cell, before
The one with the largest refractive index in the plane parallel to the substrate of the liquid crystal cell
Direction of refractive index n _x and the direction orthogonal to this direction in the plane
Refractive index n _Y and the refractive index in the direction orthogonal to these two directions
n _Z and the respective refractive index values are n _Y <n
_The direction in which _Z <n _X is satisfied and the refractive index is the largest is
In parallel with the alignment treatment direction of one of the pair of substrates,
Includes two phase plates arranged on one side of the liquid crystal cell so as to be orthogonal to each other, and the phase plate compensates for a difference in phase difference between light obliquely transmitted through the liquid crystal cell and light vertically transmitted through the liquid crystal cell. It is achieved by a liquid crystal display device characterized by:

[0014]

According to the present invention, the polarizer and the analyzer are arranged outside the TN type liquid crystal cell in which the liquid crystal molecules are twist-aligned at about 90 °, and the polarizer and the analyzer are arranged between the analyzer and the liquid crystal cell. , The slow axis is substantially parallel or substantially orthogonal to the incident side alignment treatment direction of the liquid crystal cell, and the refractive index n _Y in three directions is
Since at least one biaxial phase plate (hereinafter referred to as a biaxial phase plate) in which n _Z and n _X satisfy n _Y <n _Z <n _X is arranged, the biaxial phase plate is used. The difference in the phase difference between the light obliquely transmitted through the liquid crystal cell and the light vertically transmitted is compensated. This allows
The contrast in the viewing angle direction becomes high, the reversal phenomenon of the brightness at the time of displaying the intermediate gradation is suppressed, the color change in the left and right directions is improved, and accurate gradation can be surely displayed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on the embodiments shown in FIGS. (First Embodiment) FIGS. 1 and 2 show a sectional view and an exploded perspective view of a liquid crystal display device as a first embodiment. In this liquid crystal display device, a polarizer 102 is provided on the light incident side of a twisted nematic liquid crystal cell 101, and the liquid crystal cell 101
An analyzer 103 is provided on the light emission side of the, and one biaxial phase plate 104 is provided between the liquid crystal cell 101 and the analyzer 103.

The liquid crystal cell 101 includes one electrode 105, a driving thin film transistor (TFT) 106 arranged in each pixel of the electrode 105, and a lower substrate 108 on which an alignment film 107 covering the electrodes is formed. Of the other electrode 109 which is orthogonal to the electrode 105 of the other electrode and an upper substrate 111 on which an alignment film 110 which covers the other electrode 109 is formed, and the upper and lower substrates 10
A sealing material 112 for joining 8,111 at a predetermined interval and a region surrounded by the upper and lower substrates 108,111 and the sealing material 112 is enclosed, and a ratio d of the gap d and the natural pitch p is set.
The liquid crystal material 113 has a value of / p of about 0.05. The liquid crystal cell 101 is one in which light is incident from below in the drawing, and hereinafter, the lower substrate is referred to as an incident side substrate 108 and the upper substrate is referred to as an emission side substrate 111.

The alignment films 107 and 110 formed on the surfaces of the incident side substrate 108 and the outgoing side substrate 111 facing each other are subjected to an alignment treatment such as rubbing. Incident side substrate 10
As shown in FIG. 2, when the liquid crystal cell 101 is observed from the front (light emission side), the alignment film 107 of the liquid crystal cell 10 of FIG.
The liquid crystal cell 101 is arranged along the longitudinal direction of 1, and the alignment treatment is performed in the direction 107a having an inclination of about 45 ° from the upper left to the lower right of the liquid crystal cell 101. The orientation film 110 of the emitting side substrate 111 is oriented in a direction 110a which is rotated by about 90 ° counterclockwise when viewed from the emitting side with respect to the orientation treatment direction 107a of the incident side orientation film 107 (hereinafter referred to as the incident side orientation treatment direction). Has been applied. By such an alignment treatment, the liquid crystal material 113
Molecules are arranged with a twist of about 90 ° clockwise when viewed from the exit side. In this case, the liquid crystal molecules are aligned with a pretilt angle of about 1 °. The product Δn · d of the gap d of the liquid crystal cell 101 and the refractive index anisotropy Δn is 3
It is in the range of 50 to 550 nm, preferably 380 nm (measurement wavelength: 589 nm).

The transmission axis 102a of the polarizer 102 is the liquid crystal cell 1
It is installed in an arrangement substantially orthogonal to the incident side alignment treatment direction 107a of 01. The analyzer 103 has the transmission axis 103a of the polarizer 102.
Are installed in an arrangement substantially orthogonal to the transmission axis 102a.

The biaxial phase plate 104 is made of polycarbonate and has a refractive index n _{X in the} stretching direction, a refractive index n _Y in the in-plane orthogonal direction,
It has a refractive index in three directions of the thickness direction refractive index n _Z.
The refractive index in the direction satisfies the relationship of n _Y <n _Z <n _X , the stretching direction is the slow axis, and Δn (= n
The value of the product Δn · d of _X− n _Y ) and the thickness d is 300 to 400.
nm range, preferably 365 nm (measurement wavelength: 58
9 nm). The biaxial phase plate 104 is arranged such that the slow axis 104a in the stretching direction is substantially parallel to the incident side alignment treatment direction 107a.

According to the liquid crystal display device of the first embodiment having such a structure, the refractive index in the three directions between the liquid crystal cell 101 and the analyzer 103 satisfies the relationship of n _Y <n _Z <n _X. Biaxial phase plate 1
Since 04 is arranged, the biaxial phase plate 104 corrects the difference in the phase difference between the light obliquely transmitted through the liquid crystal cell 101 and the light vertically transmitted, thereby increasing the contrast in the viewing angle direction and increasing the number of layers. It is possible to suppress the brightness reversal phenomenon during halftone display in gray scale display. As a result, the color change due to the change in the viewing angle in the left-right direction when displaying the intermediate gradation is suppressed,
The viewing angle characteristics are greatly improved, and accurate gradation can be displayed reliably.

Next, a concrete measurement result of the viewing angle characteristic by the TN type liquid crystal display device constructed as described above will be explained in comparison with the conventional one. The liquid crystal display device of the present embodiment is a positive type, in which the transmission axis of the polarizer is orthogonal to the incident side alignment treatment direction of the liquid crystal cell, and the biaxial phase plate is used.
104 is, for example, when the value of Δn · d is 368.8 nm and the thickness d is 64 μm, the stretching direction refractive index n _X is 1.5857, the in-plane orthogonal direction refractive index n _Y is 1.5802, and the thickness direction refractive index n _Z Is 1.
Is 5836, (n _Z -n _Y) and (n _X -n _Z) ratio of 3
The ratio was 4:21 at 4:21. This biaxial phase plate 104 has a benzene ring in the structural formula of polycarbonate, and therefore has a wavelength dependence of Δn · d as shown in FIG.

4 (A) to 4 (F) and 5 (A) to 5
6F and FIGS. 6A to 6F respectively show the viewing angle dependences of the color difference ΔE *, the lightness index difference ΔL *, and the chroma difference ΔC * in the liquid crystal display device of the present example in 6 levels of applied voltage. It is a graph which shows every. Each graph has four directions (up and down, left and right)
5 °, 315 °, 225 °, 45 ° directions) shows changes in color difference ΔE *, lightness index difference ΔL *, and chroma difference ΔC * when the viewing angle θ is changed. 0V, 1.
They are 5V, 2V, 2.5V, 3V and 4V. Further, in these graphs, a quadrangle indicates an upward direction, a plus mark indicates a downward direction, a circle indicates a leftward direction, and a triangle indicates a rightward direction, and respective values when the viewing angle is changed. These visual angle dependences are compared with those of the conventional example shown in FIGS.

In the bright display state in which the applied voltage is 0 V to 1.5 V, the viewing angle dependency of the brightness index difference ΔL * is smaller in the vertical direction than in the conventional example. The viewing angle dependency of the chroma difference ΔC * is smaller in this example than in the conventional example in all directions. Therefore, the viewing angle dependency of the color difference ΔE * is also smaller in this example than in the conventional example in all directions.

In an intermediate gradation display state in which the applied voltage is 1.5 V to 3.0 V, the viewing angle dependency of the chroma difference ΔC * is higher in this example in the horizontal direction (azimuth angles of 225 ° and 45 °). It is smaller than the conventional example. Accordingly, the color difference ΔE *
The viewing angle dependency of is smaller in the present example than in the conventional example in the left-right direction.

As described above, the viewing angle dependence of the color change in the gray scale display in the TN type liquid crystal display device is one biaxial phase plate between the liquid crystal cell and the analyzer as in this example. When properly arranged, it is remarkably improved as compared with the conventional TN type liquid crystal display device. As a result, it is possible to reliably display accurate gradation.

In the first embodiment described above, the transmission axis 2a of the polarizer 102 is orthogonal to the incident side alignment treatment direction 7a of the liquid crystal cell, but the invention is not limited to this. It may be parallel to 7a.

(Second Embodiment) The second embodiment is an example in which one biaxial phase plate is arranged on each of the light incident side and the light emitting side of a TN type liquid crystal cell sandwiched therebetween. In the following embodiments, the same members as those used in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

7 and 8 are a sectional view and an exploded perspective view of a liquid crystal display device as a second embodiment. As shown in FIG. 7, the liquid crystal display device of the present example has a first biaxial phase plate 114 on the light incident side and a second biaxial phase plate 115 on the light emitting side with the liquid crystal cell 101 interposed therebetween. It is arranged. In this case, the slow axis 114a of the first biaxial phase plate 114 is the liquid crystal cell 101.
Of the second biaxial phase plate 115, and the slow axis 115a of the second biaxial phase plate 115 is also the slow axis of the first biaxial phase plate 114.
Both biaxial phase plates 114 and 115 are arranged so as to be parallel to 114a. Further, the polarizer 102 is arranged so that its transmission axis 102a is parallel to the incident side alignment treatment direction 107a, and the analyzer 103 is arranged so that its transmission axis 103a is orthogonal to the transmission axis 102a. Other configurations are the same as those in the first embodiment.

In the liquid crystal display device having such a structure, as in the liquid crystal display device of the first embodiment, two biaxial phase plates 114 are provided for the light passing obliquely through the liquid crystal cell 101 and the light passing vertically. ,
By passing through 115, the difference in phase difference between them is corrected. As a result, the contrast in the viewing angle direction becomes high, the reversal phenomenon of the brightness in the halftone display can be suppressed, and the color change with respect to the change in the viewing angle in the horizontal direction in the halftone display is improved as shown below. The viewing angle characteristics as a display are significantly improved.

FIG. 8 shows isocontrast curves obtained when the applied voltage is V = 0 [V] and V = 4.38 [V] in the liquid crystal display device of this example. Also in this figure, as in FIG. 1, the concentric circles represent the viewing angles tilted from the inside by 10 °, 20 °, 30 °, 40 °, and 50 ° from the normal direction of the substrate of the liquid crystal display device, and the black squares represent Contrast is 10, white squares have a contrast of 50, and black triangles have a contrast of 10.
0 and white triangles indicate a contrast of 150, respectively. As is clear from comparing FIG. 14 with the isocontrast curve of the conventional TN type liquid crystal display device shown in FIG.
The liquid crystal cell 101 of this example has a slightly narrower viewing angle in the left-right direction (direction of azimuth angles of 45 ° and 225 °) than the conventional liquid crystal cell 101.
It becomes wider in the vicinity.

FIGS. 10A to 10D show the viewing angle dependence of the YV curve showing the relationship between the light transmittance Y and the applied voltage V in each direction. FIG. 10A shows a liquid crystal cell 10.
In the downward direction of 1 (direction of azimuth 315 °), the viewing angle is 0 ° ~
22 shows a Y-V curve when shaken at 50 °, where deep valleys are raised and become shallower as compared with FIG. 22A, and the Y value decreases little when no voltage is applied. As shown in FIG. 10D, even when the viewing angle is changed in the upward direction (direction of azimuth angle 135 °) of the liquid crystal cell 101, the Y value changes little when no voltage is applied.

11 (A) to 11 (F) and FIG. 12 (A)
12 (F) and FIGS. 13 (A) to 13 (F), respectively.
Color difference ΔE * and brightness index difference Δ in the liquid crystal display device of this example
6 is a graph showing the viewing angle dependence of L * and the chroma difference ΔC * for each of 6 levels of applied voltage. Here, each graph has four directions of up, down, left, and right (azimuth angle 135 °, 315 °, 2
The changes in the color difference ΔE *, the lightness index difference ΔL *, and the chroma difference ΔC * when the viewing angle θ is changed in the directions of 25 ° and 45 ° are shown, and the applied voltages of 6 levels are 0V, 1.5V, 2V, 2.5
V, 3V and 4V. Further, in these graphs, a quadrangle indicates an upward direction, a plus mark indicates a downward direction, a rhombus indicates a leftward direction, and a triangle indicates a rightward direction. The viewing angle dependence shown in these graphs and FIG.
3 (A) to FIG. 25 (F) will be compared with those of the conventional liquid crystal display device.

In the bright display state in which the applied voltage region is 0.0V to 1.5V, the brightness index difference and the chroma difference are improved in all four directions of up, down, left and right, so that the visual angle dependence of the color difference is different from that of the conventional example. Compared to that, it is greatly suppressed.
By the way, as compared with the viewing angle dependence of the color difference ΔE * in the first embodiment, the viewing angle dependence of the color difference ΔE * in this example in the three directions of the left, right, and bottom excluding the upper direction is more than that of the first embodiment. A little small.

Under an intermediate gradation display state in which the applied voltage region is 1.5 V to 3.0 V, the chroma difference is improved, so that the color difference in the horizontal direction of the liquid crystal cell 101, that is, in the azimuth angles of 225 ° and 45 °. The viewing angle dependency is improved compared to other directions. The viewing angle dependency of the color difference ΔE * in this case is substantially the same as that of the first embodiment.

As described above, according to the liquid crystal display device of the second embodiment, the contrast in the viewing angle direction becomes high, the reversal phenomenon of the brightness under the intermediate gradation display state is suppressed, and the intermediate gradation is obtained. In the display, the color change according to the change of the viewing angle in the left-right direction is suppressed, the viewing angle characteristics are further improved as compared with the first embodiment, and more reliable gradation display is possible.

In the above-mentioned embodiments, etc., Δn · d of the liquid crystal cell is set in the range of 350 to 550 nm, and Δn · d of the biaxial phase plate is set in the range of 300 to 400 nm.
Not limited to this, the Δn · d of the liquid crystal cell should be 350 to 700n.
In the range of m, the biaxial phase plate has Δn · d of 200 to 60.
Even if it is set in the range of 0 nm, the viewing angle characteristics can be improved as in the above-described embodiment.

(Third Embodiment) In the third embodiment, two biaxial phase plates are arranged on the light emitting side of a liquid crystal cell.

14 and 15 are a sectional view and an exploded perspective view of a liquid crystal display device as a third embodiment. In this liquid crystal display device, a polarizer 102 is provided on the incident side of a twisted nematic liquid crystal cell 101, and the liquid crystal cell 10 is provided.
An analyzer 103 is provided on the emission side of 1, and first and second biaxial phase plates 116 and 117 are arranged between the liquid crystal cell 101 and the analyzer 103 in this order from the liquid crystal cell 101 side.

The alignment films 107 and 110 formed on the entrance-side substrate 108 and the exit-side substrate 111 are subjected to an alignment treatment such as rubbing. The alignment film 107 on the incident side substrate 108 is shown in FIG.
When observing the liquid crystal cell 101 from the front (light emission side), the liquid crystal cell 101 is arranged horizontally along the longitudinal direction of the liquid crystal cell 101, and the liquid crystal cell 101 is arranged from the upper left to the lower right. The orientation treatment is applied in the direction 107a having an inclination of about 45 °. The alignment film 110 on the emission side substrate 111 is subjected to the alignment treatment in a direction 110a which is rotated by approximately 90 ° counterclockwise when viewed from the light emission side with respect to the incident side alignment treatment direction 107a. By such an alignment treatment, the molecules of the liquid crystal material 113 are arranged with a twist of about 90 ° clockwise when viewed from the light emitting side. The ratio d / p of the gap d and the natural pitch p of the liquid crystal material 113 is about 0.05, and the pretilt angle of the liquid crystal molecules is about 1 °. In addition, the gap d of the liquid crystal cell 101
The value of the product Δn · d of the refractive index anisotropy Δn is 350 to 70.
In the range of 0 nm, preferably 380 nm (measurement wavelength: 5
89 nm).

The transmission axis 102a of the polarizer 102 is the liquid crystal cell 1
It is arranged so as to be substantially orthogonal to the incident orientation processing direction 107a of 01. The analyzer 103 is arranged so that its transmission axis 103a is substantially orthogonal to the transmission axis 102a of the polarizer 102.

Each of the first and second biaxial phase plates 116 and 117 is made of polycarbonate and has a refractive index n _{x in the} stretching direction, a refractive index n _y in the in-plane orthogonal direction, and a refractive index n _{z in} the thickness direction.
Has a refractive index in one direction, and the refractive index in these three directions is n _Y <n _Z
<N _x is satisfied, the stretching direction is the slow axis, and the product of refractive index anisotropy Δn (= n _x −n _y ) and thickness d is Δn · d in the range of 200 to 600 nm. , Preferably 365n
m (measurement wavelength: 589 nm). The first biaxial phase plate 116 is arranged such that the slow axis 116a in the stretching direction is substantially parallel to the incident side alignment treatment direction 107a, and the second biaxial phase plate 117 has the slow phase. Axis 117a is first
The biaxial phase plate 116 is arranged so as to be substantially orthogonal to the slow axis 116a.

In this embodiment, the liquid crystal cell 101 and the analyzer 103 are used.
Since the first and second biaxial phase plates 116 and 117 satisfying the relationship of n _Y <n _Z <n _X in the three directions are arranged between the two biaxial phase plates, By 116 and 117, the difference in phase difference between the light vertically transmitted through the liquid crystal cell 101 and the light obliquely transmitted is corrected, the inversion phenomenon of the brightness at the time of halftone display is suppressed, and the halftone in the left and right directions is suppressed. The viewing angle dependency of the color change in display is reduced, and the viewing angle characteristics can be significantly improved.

Next, the viewing angle characteristics of such a TN type liquid crystal display device will be described in comparison with the viewing angle characteristics of the conventional liquid crystal display device. The first and second biaxial phase plates 116 and 117 used in the liquid crystal display device of this example have a value of Δn · d of 3
When the thickness d is 6 μm and the thickness d is 64 μm, the drawing direction refractive index n _X is 1.5857, the in-plane orthogonal direction refractive index n _Y is 1.5802, and the thickness direction refractive index n _Z is 1.5836, and (n _Z −n _Y ) And (n _X
The ratio to −n _Z ) is 34:21, which is a ratio of about 6 to 4. The biaxial phase plates 116 and 117 are made of polycarbonate.

FIG. 16 shows isocontrast curves obtained when the applied voltage is V = 0 [V] and V = 4.38 [V] in the liquid crystal display device using the first and second biaxial phase plates 116 and 117 described above. showed that. Also in this figure, the concentric circles are 10 °, 20 °, and 3 ° from the normal direction of the substrate of the liquid crystal display device from the inside, respectively.
Represents viewing angles at 0 °, 40 °, and 50 °, with black squares having a contrast of 10 and white squares having a contrast of 5.
0, the black triangle represents a contrast of 100, and the white triangle represents a contrast of 150. The shape of the isocontrast curve shown in FIG. 16 is close to that of the conventional liquid crystal display device shown in FIG.

17A to 17D show the viewing angle dependence of the YV curve in the liquid crystal display device of this example. FIG. 17
17A shows the liquid crystal cell 101 in the downward direction (the azimuth angle is 315 °), and FIGS. 17B and 17C show the liquid crystal cell 10.
Left, right direction of 1 (direction of azimuth angle 45 °, 225 °)
17D shows the liquid crystal cell 1 in the upward direction (azimuth angle 135
(Y direction), each Y-V curve when the viewing angle is swung from 0 ° to 50 °. 2 (A) to FIG. 17 (D), which are similar YV curves of the conventional liquid crystal display device.
As is clear by comparing 2 (A) to 22 (D), the viewing angle dependences of the YV curves in both are almost the same.

18 (A) to 18 (F) and FIG. 19 (A)
19 (F) and 20 (A) to 20 (F), the color difference ΔE *, the lightness index difference ΔL *, and the lightness index difference ΔL *, respectively, according to the liquid crystal display device of the present example.
4 directions of chroma difference ΔC * up / down / left / right (azimuth: 135 °,
315 °, 225 °, 45 °) is a graph showing each viewing angle dependency for each of 6 levels of applied voltage. In this case, the applied voltage in 6 steps is 0V, 1.5V, 2V, 2.5.
V, 3V and 4V. Further, in these graphs, a quadrangle indicates an upward direction, a plus mark indicates a downward direction, a circle indicates a leftward direction, and a triangle indicates a rightward direction, and respective values when the viewing angle is changed. The viewing angle dependence shown in these graphs and FIG.
3 (A) to FIG. 25 (F) will be compared with those of the conventional liquid crystal display device.

First, in the bright display state in which the applied voltage region is V = 0.0 to 1.5 [V], the viewing angle dependence of the chroma difference by the liquid crystal display device of this example is suppressed to be smaller than that of the conventional example. That is, the viewing angle dependency of the chroma difference in this example is improved as compared with the conventional example. Therefore, the viewing angle dependence of the color difference in the left and right directions of azimuth angles of 225 ° and 45 ° by the liquid crystal display device of this example is also improved as compared with those of the conventional example. Further, in the intermediate gradation display state in which the applied voltage region is V = 1.5 to 3.0 [V], the viewing angle dependency of the chroma difference is also improved, so that the azimuth angles of 225 ° and 45 ° in the left and right directions (especially azimuth angle 2
The viewing angle dependency of the color difference in the left direction (25 °) is improved. Further, in the dark display state in which the applied voltage region is V = 3.0 to 4.0 [V], the viewing angle dependence of the color difference in the upward direction of the azimuth angle of 135 ° is maintained at the same level as in the conventional case.

As described above, in the liquid crystal display device of this example,
The brightness reversal phenomenon during the halftone display is suppressed, and the color change due to the change in the viewing angle in the left and right directions during the halftone display is suppressed to be smaller than that in the conventional example. As a result, the liquid crystal display device of the present example has improved viewing angle characteristics and can accurately display gradation.

In the embodiment described above, the liquid crystal cell 101
And the analyzer 103 between the first and second biaxial phase plates 116 and 117.
However, the present invention is not limited to this, and for example, the first and second biaxial phase plates 116 and 117 may be arranged in this order between the liquid crystal cell 101 and the polarizer 102.

Further, in the above-described embodiment, the polarizer 102 has its transmission axis 102a as the incident side alignment treatment direction 107 of the liquid crystal cell 101.
Although it is arranged almost orthogonal to a, the invention is not limited to this, and the polarizer 102 and the analyzer 103 are rotated by 90 °, and
A transmission axis 102a of the liquid crystal cell 102 has an incident side alignment treatment direction 10 of the liquid crystal cell 101.
It may be arranged so as to be substantially parallel to 7a, and in this case also, the same effect as that of the above-described embodiment can be obtained.

[0051]

As described above in detail, according to the present invention, a polarizer is arranged so that liquid crystal molecules are twisted in a 90-degree orientation between a pair of substrates so as to be sandwiched outside a TN type liquid crystal cell. And the analyzer is placed and the liquid crystal
Refraction on one side of the cell in a plane parallel to the liquid crystal cell substrate
Refractive index n _{X in the} direction with the largest index , this direction and the surface
The refractive index n _Y in the directions orthogonal to each other and
Both have a direction of the refractive index n _Z for each refraction
The two phase plates whose ratio values satisfy n _Y <n _Z <n _X are
The direction of the largest refractive index of the one of the pair of substrates.
Arranged in parallel or orthogonal to the orientation processing direction of one substrate,
These phase plates are configured to compensate for the difference in phase difference between the light obliquely transmitted through the liquid crystal cell and the light vertically transmitted. As a result, the contrast in the viewing angle direction becomes high, the reversal phenomenon of the brightness at the time of halftone display is suppressed, and the viewing angle dependency of the color change in the left and right directions is reduced,
It is possible to significantly improve the viewing angle characteristics and display the gradation accurately.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a liquid crystal display device as a first embodiment of the present invention.

FIG. 2 is an exploded perspective view showing a schematic configuration of the first embodiment.

FIG. 3 is a graph showing the wavelength dependence of Δn · d of the biaxial phase plate.

4A to 4F are graphs showing the viewing angle dependence of the color difference ΔE * for each direction in which the viewing angle is changed by the liquid crystal display device of the first embodiment for each of 6 levels of applied voltage. is there.

5A to 5F are lightness index differences ΔL for respective directions in which the viewing angle is changed by the liquid crystal display device of the first embodiment.
8 is a graph showing the viewing angle dependence of * for each of 6 levels of applied voltage.

6A to 6F are chroma difference ΔC * for each direction in which the viewing angle is changed by the liquid crystal display device of the first embodiment.
3 is a graph showing the viewing angle dependence of the above for each of 6 levels of applied voltage.

FIG. 7 is a sectional view showing a liquid crystal display device as a second embodiment of the present invention.

FIG. 8 is an exploded perspective view showing a schematic configuration of the second embodiment.

FIG. 9 is an isocontrast curve diagram of the liquid crystal display device of the second embodiment.

FIGS. 10A to 10D respectively show characteristics of the light transmittance Y and the applied voltage V at different viewing angles in the liquid crystal display device of the second embodiment for each Y-direction for each viewing angle changing direction. It is a V characteristic view.

11A to 11F are graphs showing the viewing angle dependence of the color difference ΔE * for each direction in which the viewing angle is changed by the liquid crystal display device of the second embodiment, for each of 6 levels of applied voltage. is there.

12 (A) to (F) are lightness index differences Δ for each direction in which the viewing angle is changed by the liquid crystal display device of the second embodiment.
6 is a graph showing the viewing angle dependence of L * for each of 6 levels of applied voltage.

13A to 13F are chroma differences ΔC for respective directions in which the viewing angle is changed by the liquid crystal display device of the second embodiment.
8 is a graph showing the viewing angle dependence of * for each of 6 levels of applied voltage.

FIG. 14 is a sectional view showing a liquid crystal display device as a third embodiment of the present invention.

FIG. 15 is an exploded perspective view showing a schematic configuration of the third embodiment.

FIG. 16 is an isocontrast curve diagram of the liquid crystal display device of the third embodiment.

FIGS. 17A to 17D respectively show Y- characteristics of the light transmittance Y and the applied voltage V for different viewing angles in the liquid crystal display device of the third embodiment for each viewing angle changing direction. It is a V characteristic view.

18A to 18F are graphs showing the viewing angle dependence of the color difference ΔE * for each direction in which the viewing angle is changed by the liquid crystal display device of the third embodiment, for each of 6 levels of applied voltage. is there.

19 (A) to (F) are lightness index differences Δ for each direction in which the viewing angle is changed by the liquid crystal display device of the third embodiment.
6 is a graph showing the viewing angle dependence of L * for each of 6 levels of applied voltage.

20A to 20F are chroma difference ΔC for each direction in which the viewing angle is changed by the liquid crystal display device of the third embodiment.
8 is a graph showing the viewing angle dependence of * for each of 6 levels of applied voltage.

FIG. 21 is an isocontrast curve diagram of a conventional liquid crystal display device.

22A to 22D are Y-V characteristic diagrams showing the characteristics of the light transmittance Y and the applied voltage V for different viewing angles according to the conventional liquid crystal display device for each viewing angle changing direction. is there.

23A to 23F are graphs showing the viewing angle dependence of the color difference ΔE * for each direction in which the viewing angle is changed by the conventional liquid crystal display device, for each of 6 levels of applied voltage.

24A to 24F are graphs showing the viewing angle dependence of the brightness index difference ΔL * for each direction in which the viewing angle is changed by the conventional liquid crystal display device, for each of 6 levels of applied voltage.

25A to 25F are graphs showing the viewing angle dependence of the chroma difference ΔC * for each direction in which the viewing angle is changed by the conventional liquid crystal display device, for each of 6 levels of applied voltage.

[Explanation of symbols]

101 LCD cell 102 Polarizer 103 Analyzer 104,114,115,116,117 Biaxial phase plate 105,109 electrodes 106 thin film transistor 107,110 Alignment film 108 Lower substrate (incident side substrate) 111 Upper substrate (outgoing side substrate) 112 Seal material 113 Liquid crystal material

Claims (2)

(57) [Claims] 1. Between a pair of substrates each having an electrode intersecting with each other and an alignment film covering the electrodes and subjected to an alignment treatment in a predetermined direction on each of the facing surfaces, one substrate to the other A liquid crystal cell formed by enclosing a liquid crystal material twisted at about 90 ° toward the substrate, a polarizer arranged on the light incident side of the liquid crystal cell, and a light emitting side arranged on the light emitting side of the liquid crystal cell. The highest refractive index in the plane parallel to the analyzer and the liquid crystal cell substrate.
Refractive index n _x in the direction and the direction orthogonal to this direction in the plane
Direction refractive index n _Y and refraction in the direction orthogonal to these two directions
Has a refractive index n _Z, and the value of each refractive index is n _Y <
n _Z <n _X is satisfied, and the direction in which the refractive index is the largest is the front
Parallel to the alignment treatment direction of one of the pair of substrates
Or two phase plates arranged on one side of the liquid crystal cell so as to be orthogonal to each other, and a phase difference between the light obliquely transmitted through the liquid crystal cell and the light vertically transmitted by the phase plate. A liquid crystal display device, characterized in that 2. A liquid crystal display device according to claim 1, wherein said two phase plates are disposed between the said analyzer crystal cell.