JPH11264976A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display element with excellent visual angle characteristics by using a specified high polymer film as a visual angle compensation plate. SOLUTION: This liquid crystal display cell is constituted of an upper side polarizing plate 1, the high polymer film 2, a liquid crystal cell 3, a lower side polarizing plate 5, the upper substrate 6 of the liquid crystal cell, a lower substrate 7, a transparent electrode 8 and nematic liquid crystal 9. That is, it is provided with the liquid crystal cell 3 composed by clamping the liquid crystal 9 between a pair of the substrates 6 and 7, at least one high polymer film 2 for which an optical axis is inclined to the normal direction of the surface of the high polymer film 2 and the polarizing plates 1 and 5. Then, at the time of defining the refractive index of the normal direction of the high polymer film 2 as nz, the refractive indexes of two directions orthogonal to the normal direction as nx and ny and a film thickness as (d), the sum of the value of (nz-xz)×Xd of the high polymer film 2 is the same as or smaller than the value of Δn×d of the liquid crystal. In such a manner, by using the high polymer film 2 as the visual angle compensation plate, the liquid crystal display element with the excellent visual angle characteristics is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art With the advancement of technology over the past several years, large-sized displays such as 14 to 17 inches have been produced for an active matrix type liquid crystal display device having TFTs and MIM devices for each pixel. T
Application to V is expected.

However, as the size of the screen increases, dissatisfaction with the display performance, particularly the viewing angle characteristics, also increases. The cause is mainly in the liquid crystal display mode itself called twisted nematic (hereinafter referred to as TN) adopted in the conventional liquid crystal display element.

As shown in FIG. 14, a conventional TN type liquid crystal display element has an upper polarizer 1, a liquid crystal cell 3, a lower polarizer 5,
The liquid crystal cell includes an upper substrate 6, a lower substrate 7, a transparent electrode 8, and a nematic liquid crystal 9. As shown in FIG. 9, the relationship between the respective axes is 11 for the direction of the polarization axis of the upper polarizing plate 1 (hereinafter, the polarization axis indicates the transmission axis) and 12 for the orientation of the liquid crystal of the upper substrate 6 of the liquid crystal cell. The liquid crystal alignment direction of the lower substrate 7 of the liquid crystal cell is 13, the polarization axis direction of the lower polarizing plate 5 is 14, and 11 is 1.
The angle formed between 2 and 21 is 21 and the angle formed between 13 and 14 by the twist angle of the nematic liquid crystal 9 determined from 12 and 13 is 23.
Then, the angles 21 and 23 are set to about 0 degrees, respectively, and the angle 22 is set to about 90 degrees.

At this time, the conventional TN type liquid crystal display device is shown in FIG.
The voltage transmittance characteristics as shown in FIG.

[0006]

However, the conventional TN type liquid crystal display device having the above configuration has a problem that the viewing angle range in which the display can be recognized well is narrow. FIG. 15 shows the viewing angle characteristics when the conventional TN type liquid crystal display element is driven with an applied state of 5 volts turned on and an applied state of 1 volt is turned off. Here, the center of the figure is the substrate normal direction, and the six concentric circles surrounding the center are, in order from the inside, the inclination angles of 10 degrees, 20 degrees, 30 degrees, 40 degrees, and 50 degrees from the normal direction.
Degrees and directions of 60 degrees. 41, 42, 4
3, 44, 45, and 46 each have a contrast ratio of 1:
1, 1: 3, 1:10, 1:30, 1: 100, 1: 3
00 is an isocontrast curve. Thus, the conventional T
The characteristics of the N-type liquid crystal greatly change depending on the viewing angle.
Although it cannot be read from this figure, when viewed from above, a troublesome phenomenon of inversion occurs. The reversal phenomenon is a phenomenon in which the transmittance becomes darker and then becomes brighter again with a rise in voltage, so that when a halftone is displayed, a portion that should be displayed darker becomes brighter.

An object of the present invention is to provide a liquid crystal display element having excellent viewing angle characteristics by using a polymer film as a viewing angle compensating plate.

[0008]

A liquid crystal display device according to the present invention comprises a liquid crystal cell having a liquid crystal sandwiched between a pair of substrates;
In a liquid crystal display device having at least one polymer film whose optical axis is inclined with respect to the normal direction of the polymer film surface and a polarizing plate, the refractive index of the polymer film in the normal direction is adjusted. nz, the refractive index in two directions perpendicular to the normal direction is nx, ny, and the film thickness is d, and the sum of the values of (nx−nz) × d of the polymer film is Δnx of the liquid crystal. It is characterized in that it is equal to or smaller than the value of d.

[0009] The liquid crystal of the liquid crystal cell preferably has a twist angle of about 90 degrees.

The transmission axes of the polarizing plates are adjacent to each other.
Alternatively, the liquid crystal cell substrate is disposed so as to be perpendicular to the alignment processing direction of the liquid crystal cell substrate adjacent to the polymer film.

Further, the liquid crystal of the liquid crystal cell has a twist angle of about 0 degrees.

Further, the liquid crystal display element performs a bright display when no voltage is applied and a dark display when a voltage is applied.

Further, the liquid crystal has a pretilt angle of 5 degrees or more.

Further, the anchoring energy between at least one substrate of the liquid crystal cell and the liquid crystal is 1 × 10 ^-4.
J / m ² or less.

Further, when the liquid crystal cell is driven, the effective voltage at the time of ON is set to be four times or more the threshold voltage of the liquid crystal cell.

Further, the present invention is characterized in that the wavelength dispersion value ν of Δn of the polymer film is smaller than that of the liquid crystal.

[0017]

(Embodiment 1) A liquid crystal display device according to Embodiment 1 of the present invention comprises an upper polarizer 1, a polymer film 2, a liquid crystal cell 3, a lower polarizer 5 as shown in FIG. , An upper substrate 6, a lower substrate 7, a transparent electrode 8, and a nematic liquid crystal 9 of a liquid crystal cell. As shown in FIG. 2, the relationship between the respective axes is 11 in the direction of the polarization axis (absorption axis) of the upper polarizing plate 1.
The angle at which the liquid crystal alignment direction of the upper substrate 6 of the liquid crystal cell is 12, the liquid crystal alignment direction of the lower substrate 7 of the liquid crystal cell is 13, and the polarization axis direction of the lower polarizer 5 is 14 and 11 is 12, 12 and 13
Assuming that the twist angle of the nematic liquid crystal 9 determined from the above is 22, and the angle between 14 and 13 is 23, the angles 21 and 23 are respectively set to 90 degrees, and the angle 22 is also set to 90 degrees.

The nematic liquid crystal 9 includes a liquid crystal ZLI-4393 manufactured by Merck and a chiral dopant C manufactured by BDH.
B-15 was used by adding 0.1 wt%. ZLI-43
Since 93 has a birefringence Δn of 0.0851 and a cell gap d of 4.7 μm, Δn × d is 0.40 μm. The liquid crystal uses a polyimide alignment film and has a pretilt angle of 1
The homogeneous orientation was performed at a temperature of not more than the degree. On the other hand, the polymer film 2 is a negative optical anisotropic body made of polycarbonate and has a refractive index ellipsoid as schematically shown in FIG. That n _z normal direction of the refractive index of the film plane 32, a 2 the refractive index in the direction orthogonal to each other in vertical to n _x, When n _y, n
having stones-like shape having a relationship of _z <n _x = n _y. Film used _{herein, n x = 1.588, n y} = 1.58
8, n _z = 1.585, a film thickness _{d = 100μm, (n x -n} z) × d = 0.3μm and, in the liquid crystal cell △ n
Xd was set slightly smaller.

FIG. 4 shows the voltage transmittance characteristics of the liquid crystal display device according to the first embodiment of the present invention prepared as described above. White when no voltage is applied, black when voltage is applied,
It is a so-called normally white display. The threshold voltage defined by the voltage at which the transmittance has changed by 10% is 1.
45 volts.

FIG. 5 shows the viewing angle characteristics when the liquid crystal cell is driven with an applied voltage of 7 volts turned on and an applied voltage of 1 volt is turned off. If only contrast is to be obtained, it is sufficient to apply 5 volts, but by applying 7 volts, the liquid crystal rises almost perpendicularly to the substrate, and the viewing angle compensation by the polymer film becomes more effective. Comparing this viewing angle characteristic with the viewing angle characteristic of the conventional TN type liquid crystal shown in FIG. 15, it can be seen that the isocontrast curve 44 of 1:30 spreads more than ± 20 degrees to the left and right. The vertical direction also shows well-balanced characteristics without being too narrow as in the prior art. Further, although it cannot be read from this figure, the inversion of the halftone is less likely to occur.

(Embodiment 2) The cell configuration and axial relationship of Embodiment 2 are the same as those of Embodiment 1 shown in FIGS. 1 and 2, except that the pretilt angle of the liquid crystal molecules is set to 10 degrees. different. As the pre-tilt angle increases, the threshold voltage is reduced to 0.1.
Even when the voltage was lowered by 3 volts and the ON applied voltage was set to 6 volts, a wide viewing angle equivalent to that of Example 1 was obtained.

Conventionally, the pretilt angle of the TN type liquid crystal is 5 degrees or less, but when a viewing angle compensating plate is provided, it is advantageous to set a large pretilt angle in that the viewing angle is widened.

(Embodiment 3) The cell configuration and axial relationship of Embodiment 3 are the same as those of Embodiment 1 shown in FIGS. 1 and 2, except that an obliquely deposited SiO film is used as an alignment film. Are different.
Thus, the anchoring energy between the liquid crystal molecules and the alignment film became about 4 × 10 ⁻⁵ J / m ² . This is an extremely small value compared to a value of 1 × 10 ⁻³ J / m ² or more when ordinary polyimide or polyvinyl alcohol is used as the alignment film. The liquid crystal molecules in the vicinity of the substrate usually do not move unless a considerably high voltage is applied, but start moving with only a few volts when the anchoring energy is about 4 × 10 ⁻⁵ J / m ² . Therefore, in the first embodiment, the on-applied voltage is set to 7 volts, but in the third embodiment, an equivalent wide viewing angle can be obtained with only 5.5 volts. Other known methods for reducing the anchoring energy include using an LB film as an alignment film, or directly rubbing the surface of the transparent electrode. These methods also have an effect corresponding to the anchoring energy.

(Embodiment 4) The cell configuration, axial relationship, etc. of Embodiment 4 are the same as those of Embodiment 1 shown in FIGS. 1 and 2, but a refractive index ellipse having a shape as shown in FIG. The difference is that a shape shown in FIG. 6 is used instead of the body.
It is still negative optical anisotropic body made of polycarbonate, but the relationship of n _z <n _x = n _y are the same, the optical axis is inclined 5 degrees from the normal direction of the film plane 32, when voltage is applied Are almost parallel to the average direction of the liquid crystal directors of the liquid crystal cell. Since the liquid crystal of the liquid crystal cell does not completely rise at a voltage of about four times the threshold voltage, if the refractive index ellipsoid of the polymer film is tilted in accordance with the liquid crystal, a more complete viewing angle is obtained. Can compensate.

In addition to the method of inclining the refractive index ellipsoid 31 with respect to the film surface 32 as shown in FIG. 6, the film of FIG. 3 may be inclined with respect to the liquid crystal cell substrate. In a direct view type display, such an arrangement is difficult due to space limitations, but is an effective means in a projection type display.

(Embodiment 5) As shown in FIG. 7, the liquid crystal display device in Embodiment 5 of the present invention comprises an upper polarizing plate 1, a polymer film 2, a liquid crystal cell 3, a polymer film 4, a lower polarizing plate. 5, liquid crystal cell upper substrate 6, lower substrate 7, transparent electrode 8,
It is composed of a nematic liquid crystal 9. In addition, the relation of each axis,
Various conditions of the liquid crystal cell are the same as those of the first embodiment shown in FIG.

[0027] In Example 5, was used two upper and lower polymer film, either with negative optical anisotropy of the _{polycarbonate, n x = 1.588, n y} = 1.588,
n _z = 1.585, a film thickness d = 50μm, (n _x -
The sum of _nz ) × d is 0.3 μm.

The voltage transmittance characteristic of this liquid crystal display element is also the same as that of the first embodiment shown in FIG. FIG. 8 shows the viewing angle characteristics when the liquid crystal cell was driven with an applied state of 7 volts turned on, and an applied state of 1 volt as an off state.
Shown in By using two upper and lower polymer films, a wider and symmetrical viewing angle characteristic is obtained than in Example 1 using only one polymer film.

(Embodiment 6) The cell configuration and axial relationship of Embodiment 6 are the same as those of Embodiment 1 shown in FIGS. 1 and 2, except that polyvinyl alcohol is used for the polymer film 2. . Polyvinyl alcohol has a smaller wavelength dispersion of birefringence Δn than the polycarbonate used in Example 1. Here, the chromatic dispersion value ν of △ n is defined as ν≡ △ n (460 nm) / △ n (590 nm) using △ n for light having a wavelength of 460 nm and △ n for light having a wavelength of 590 nm. The ν value of polyvinyl alcohol is 1.005, and the ν value of polycarbonate is 1.095. The viewing angle characteristics when using polyvinyl alcohol, when drawn with an equal contrast curve,
It is almost the same as the case of the first embodiment shown in FIG. 5, but is more excellent in that yellow coloring due to the viewing angle is reduced. Although the ν value of the liquid crystal ZLI-4393 is 1.085, the use of a polymer having a smaller wavelength dispersion value than that of the liquid crystal has the effect of reducing coloring due to the viewing angle.

(Embodiment 7) FIG.
Is the same as that of the first embodiment, but only the axial relationship is different. As shown in FIG. 9, the relationship between the axes in Example 7 is 11 for the polarization axis (absorption axis) of the upper polarizing plate 1, 12 for the liquid crystal alignment direction of the upper substrate 6 of the liquid crystal cell, and 7 for the lower substrate 7 of the liquid crystal cell. Of the liquid crystal alignment direction of 13 and the polarization axis direction of the lower polarizing plate 5 to 14, 1
Assuming that the angle between 1 and 12 is 21, the twist angle of the nematic liquid crystal 9 is 22 and the angle between 14 and 13 is 23, the angles 21 and 23 become 0 degree and the angle 22 becomes 90 degrees, respectively.
Set to degree.

The voltage transmittance characteristic of this liquid crystal display element is also the same as that of the first embodiment shown in FIG. FIG. 1 shows the viewing angle characteristics when the liquid crystal cell was driven with an applied voltage of 7 volts turned on and an applied voltage of 1 volt was turned off.
0 is shown. By making the axial direction of the polarizing plate parallel to the alignment processing direction of the adjacent liquid crystal cell substrate, the viewing angle characteristics in Example 1 which was set perpendicularly became slightly narrower. However, a viewing angle characteristic wider than the conventional viewing angle characteristic of FIG. 15 is still obtained.

(Embodiment 8) FIG.
7 except that the upper and lower polarizers are arranged in parallel. With this arrangement, a so-called normally black display is obtained, which is black when no voltage is applied and white when a voltage is applied. Although such an arrangement has an effect of expanding the viewing angle, it is not as great as in the case of the normally white display. This is because the viewing angle compensating plate used in the present invention compensates for the state in which the liquid crystal rises when a high voltage is applied. Therefore, when the voltage is applied, black is easier to obtain high contrast in a wide viewing angle range. .

(Embodiment 9) The cell configuration and axial relationship of Embodiment 9 are the same as those of Embodiment 1 shown in FIGS. 1 and 2, and the voltage transmittance characteristics are the same as those of FIG. Is that the state where 5 volts is applied to the ON state is turned on. FIG. 11 shows viewing angle characteristics at this time. In the ON state of the first embodiment, 7 volts was applied. However, by lowering this voltage, the viewing angle characteristics of the first embodiment in FIG. 5 became slightly narrower. However, a viewing angle characteristic wider than the viewing angle characteristic of the related art shown in FIG. 15 is still obtained, and there is an effect of expanding the viewing angle without applying a high voltage. Incidentally, it is set to a small value of (n _x -n _z) × d of the polymer film when the high voltage is not applied is desired.

(Embodiment 10) The cell configuration and axial relationship of Embodiment 10 are the same as those of Embodiment 1 shown in FIGS.
0.5μm The values of (n _x -n _z) × d of the polymer film
And a point set larger than Δn × d of the liquid crystal.
Even with this configuration, the viewing angle characteristics are improved, but the effect is small. (N _x -n _z) × d value of the polymer film is most desirable to set △ n × d of the liquid crystal equal to or slightly smaller, set to at least twice the liquid crystal of △ n × d value That doesn't make sense.

(Embodiment 11) In the above embodiment,
Although a TN type liquid crystal display element has been described as an example, the present invention is not limited to a TN type liquid crystal, but can be applied to many other liquid crystal display elements using a nematic liquid crystal having a positive dielectric anisotropy. And the well-known EC
Similar effects can be obtained with a B-type liquid crystal or an STN-type liquid crystal. In the eleventh embodiment, an example of an ECB type liquid crystal will be described.

The cell configuration of the eleventh embodiment is the same as that of the fifth embodiment shown in FIG. As shown in FIG. 12, the relationship between the axes is 11 for the polarization axis (absorption axis) of the upper polarizer 1, 12 for the liquid crystal alignment direction of the upper substrate 6 of the liquid crystal cell, and 12 for the liquid crystal alignment direction of the lower substrate 7 of the liquid crystal cell. 13, the polarization axis direction of the lower polarizer 5 is 14, and the angle between 11 and 12 is 21, and the twist angle of the nematic liquid crystal 9 determined by 12 and 13 is 22, and 1 is 1.
Assuming that the angle formed by 3 is 23, the angles 21 and 23 are respectively set to 45 degrees to the right, and the angle 22 is set to 0 degrees.

The nematic liquid crystal 9 was injected into a cell having a cell gap d of 3.2 μm using a liquid crystal ZLI-4393 manufactured by Merck without adding a chiral dopant. △
n × d becomes 0.27 μm. The polymer film 2 sheets as in Example _{5, n x = 1.588, n} y = 1.58
8, n _z = 1.585 using polycarbonate film, but any film thickness d = 45μm, (n _x -
_nz ) × d = 0.24 μm.

FIG. 13 shows the viewing angle characteristics when the liquid crystal cell was driven with 15 volts applied to the on state and 1 volt applied to the liquid crystal cell in the off state. Thus EC
Even when a B-type liquid crystal is used, a wide viewing angle characteristic equal to or higher than that of a TN-type liquid crystal can be obtained. In the case of ECB-type liquid crystal, since in order to obtain a high contrast is required higher voltage than TN liquid crystal, in order to compensate for residual retardation, without equal n _x and n _y of the polymer film _{(n x -n y) × d} = small retardation or leave about 0.01 [mu] m, or when the film as little mentioned in embodiment 4 arranged inclined with respect to the cell substrate, a relatively low voltage But I can get contrast.

[0039]

As described above, according to the present invention, a liquid crystal display device having excellent viewing angle characteristics can be provided by using a polymer film as a viewing angle compensating plate.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display device according to Examples 1 to 4 and 6 to 10 of the present invention.

FIG. 2 is a relationship diagram of each axis of a liquid crystal display element in Examples 1 to 6, 9, and 10 of the present invention.

FIG. 3 is a schematic view of a refractive index ellipsoid of a polymer film for performing viewing angle compensation used in Examples 1 to 3 and 5 to 11 of the present invention.

FIG. 4 is a diagram showing voltage transmittance characteristics of Examples 1, 5 to 7, 9, and 10 of the present invention and a conventional liquid crystal display element.

FIG. 5 is a diagram illustrating viewing angle characteristics of the liquid crystal display element according to the first embodiment of the present invention.

FIG. 6 is a schematic view of a refractive index ellipsoid of a polymer film for performing viewing angle compensation used in Example 4 of the present invention.

FIG. 7 is a sectional view of a liquid crystal display device according to Examples 5 and 11 of the present invention.

FIG. 8 is a diagram showing viewing angle characteristics of a liquid crystal display element in Example 5 of the present invention.

FIG. 9 is a relationship diagram of each axis of a seventh embodiment of the present invention and a conventional liquid crystal display element.

FIG. 10 shows a liquid crystal display device according to a seventh embodiment of the present invention.
It is a figure showing a viewing angle characteristic.

FIG. 11 shows a liquid crystal display device according to a ninth embodiment of the present invention.
It is a figure showing a viewing angle characteristic.

FIG. 12 is a relationship diagram of each axis of a liquid crystal display element in Example 11 of the present invention.

FIG. 13 is a diagram showing viewing angle characteristics of a liquid crystal display element in Example 11 of the present invention.

FIG. 14 is a sectional view of a conventional TN type liquid crystal display device.

FIG. 15 is a view showing viewing angle characteristics of a conventional TN type liquid crystal display element.

[Explanation of symbols]

 Reference Signs List 1 upper polarizing plate 2 polymer film 3 liquid crystal cell 4 polymer film 5 lower polarizing plate 6 upper substrate of liquid crystal cell 3 lower substrate of liquid crystal cell 3 transparent electrode 9 nematic liquid crystal having positive dielectric anisotropy 11 upper side Polarization axis direction of polarizing plate 1 12 Liquid crystal alignment direction of upper substrate 6 of liquid crystal cell 13 Liquid crystal alignment direction of lower substrate 7 of liquid crystal cell 14 Polarization axis direction of lower polarizing plate 5 21 Angle between 11 and 12 22 Nematic liquid crystal 9 Angle of 14 23 to 13 31 refractive index ellipsoid of polymer film 32 film surface of polymer film 41 isocontrast curve with contrast ratio 1: 1 42 isocontrast curve with contrast ratio 1: 3 43 contrast ratio 1 : 10 iso-contrast curve 44 iso-contrast curve of 1:30 contrast ratio 45 iso-contrast curve of 1: 100 contrast ratio Trust curve 46 contrast ratio of 1: 300 iso-contrast curve of

Claims (4)

[Claims] 1. A liquid crystal cell having a liquid crystal sandwiched between a pair of substrates, at least one polymer film having an optical axis inclined with respect to a normal direction of a polymer film surface, and a polarizing plate. In the liquid crystal display device, when the refractive index in the normal direction of the polymer film is nz, the refractive index in two directions perpendicular to the normal direction is nx, ny, and the film thickness is d,
The sum of the values of (nx−nz) × d of the polymer film is
A liquid crystal display device characterized in that it is equal to or smaller than the value of Δn × d of the liquid crystal. 2. The liquid crystal display device according to claim 1, wherein the twist angle of the liquid crystal is about 90 degrees. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal display device performs a bright display when no voltage is applied and a dark display when a voltage is applied. 4. The liquid crystal display device according to claim 1, wherein said polymer film is disposed with said liquid crystal cell interposed therebetween.