JPH05289097A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal display element of a black-and-white display, which scarcely has visual angle dependency, and also, has a satisfactory electro-optical characteristic such as sharp responsiveness, etc. CONSTITUTION:Between two pieces of substrates 4c, 4d with electrodes 4a, 4b, a positive nematic liquid crystal layer 4e of dielectric anisotropy is inserted and held, and on the surface of a substrate, the element has a tilt orientation in which a liquid crystal molecular major axis of the liquid crystal layer is arrayed in one direction, and on the surface of its upper and lower substrates, a straight line on the direction in which the liquid crystal molecular major axis is arrayed in opposed points is arrayed so as to have each intersecting point between planes having the surface of the upper and the lower substrates, and also, a driving liquid crystal panel in which a liquid crystal is not twisted, and a double refraction anisotropy compensating panel for compensating optically double refraction anisotropy in its plane direction are laminated optically and continuously.

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.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices (hereinafter abbreviated as LCDs) are used in word processors, personal computers,
Widely used for projection TVs, small TVs, etc. Among them, the growth as a display for laptop computers and word processors is remarkable. As a method of configuring an LCD for such an application, there are two methods, a simple matrix method and an active matrix method. Among them, the active matrix method has the features of wide viewing angle, fast response speed, and high contrast, but due to its high price, it has not been generalized in large liquid crystal panels and is currently simple. The matrix method is mainly used.

Of these, the operating mode of the liquid crystal generally widely used as a simple matrix type LCD is T
N (Twisted Nematic) and STN (Super Twisted Nema)
TN), TN is difficult to drive with high duty, STN can drive with high duty, but the response speed is slow, and high pretilt orientation (ideally 5 ° or more is ideal.
(10 ° or more) is required, and a new operation mode is required because the cell gap is strictly controlled.

Therefore, in recent years, a new mode utilizing the birefringence effect using vertical alignment which can respond faster than STN has been actively studied under the names such as VAN (H.HIRAI et. JAPAN DISPLAY '89 P.184). ing. However, with this method, it is difficult to vertically orient the liquid crystal molecules uniformly, and display unevenness is likely to occur.

On the other hand, among LCDs using the same birefringence effect, a homogeneous alignment type LCD having a twist angle of 0 ° is used.
It has been shown that good black-and-white display can be obtained by compensating for interference colors under a polarizing plate arranged in a crossed nicols with the liquid crystal molecules arranged orthogonally to each other (Saito et al., 1990). Spring Response Proceedings 30p-pd-7).
The liquid crystal display element using two homogeneous alignment type LCDs has a clear and steep threshold value, and can be effectively used in the current alignment technology, and has a feature that the response speed is fast. Therefore, it is expected to be applied as a large-area, high-definition liquid crystal display.

However, this homogeneous orientation type L
A liquid crystal display device using two CDs has a problem of viewing angle dependence that the contrast ratio remarkably changes depending on the viewing direction and angle.

The problem of the viewing angle dependence of the contrast ratio is
This is due to the viewing angle dependence of the transmittance in both the state where a voltage is applied to the liquid crystal (white) and the state where no voltage is applied (black).
Of these, regarding the viewing angle dependence of the transmittance when no voltage is applied (black), a vertically aligned nematic liquid crystal panel is used as an optical compensation means so that the birefringence value is constant regardless of the viewing angle. , The homogeneous alignment type LCD
It has been proposed to adopt a configuration in which a liquid crystal display device using two sheets is stacked (Yoshida et al.
k-10). However, this compensating means does not optically compensate the viewing angle dependence of the transmittance in the state (white) in which a voltage is applied to the liquid crystal, and does not sufficiently optically compensate the viewing angle dependence of the liquid crystal display element. There wasn't.

[0008]

As described above, in the conventional structure, since the viewing angle dependence of the contrast ratio is not sufficiently optically compensated, the viewing angle dependence problem that the contrast ratio changes depending on the viewing direction and angle. Was not solved enough.

[0009]

A liquid crystal display device of the present invention comprises a nematic liquid crystal layer having a positive dielectric anisotropy sandwiched between two substrates with electrodes, and liquid crystal molecules of the liquid crystal layer on the surface of the substrate. The major axis has a tilt alignment that aligns in one direction, and on the upper and lower substrate surfaces, straight lines in the direction in which the liquid crystal molecule long axes are aligned at opposing points are mutually aligned between the planes having the upper and lower substrate surfaces. The driving liquid crystal panel, which is arranged so as to have intersecting points, and in which the liquid crystal is not twisted, and the birefringence anisotropy compensation panel for optically compensating the birefringence anisotropy in the plane direction thereof, It is characterized in that they are laminated optically continuously. In addition, a viewing angle dependent compensation panel in which liquid crystal molecules are vertically aligned is superimposed on the driving liquid crystal panel so that the birefringence value when no voltage is applied does not easily change depending on the viewing angle.

Further, as the compensating panel, an optically anisotropic film having a refractive index anisotropy for optically compensating similarly to the compensating panel in which the liquid crystal molecules are vertically aligned is used.

Further, as a compensating panel for optically compensating the birefringence anisotropy in the plane direction, a liquid crystal panel having a liquid crystal molecule arrangement substantially equal to that of the driving liquid crystal panel and having substantially the same optical anisotropy thereof is provided. It is characterized in that the liquid crystal molecule array is overlapped so as to be substantially orthogonal to the liquid crystal molecule array of the driving liquid crystal panel.

As a compensation panel for optically compensating the birefringence anisotropy in the plane direction, an optically anisotropic film having an optical anisotropy substantially equal to that of the driving liquid crystal panel is used. It is characterized in that it is positioned so as to have an optical anisotropy opposite to the optical anisotropy in the plane direction of.

[0013]

The present invention achieves the above object, and the principle and method for achieving the object will be described below.

FIG. 5 illustrates an arrangement of liquid crystal molecules cut along a plane having a liquid crystal molecule long axis alignment direction and a substrate vertical direction of a driving liquid crystal cell of a liquid crystal display device using two homogeneous alignment type LCDs according to a conventional technique. A sectional view is shown. That is, the upper substrate 14c having the electrode 14a and the electrode 14b
3 shows the arrangement of the long axes of the liquid crystal molecules 14e of the liquid crystal layer between the opposite points of the lower substrate 14d having the position. In the figure, (a) shows the molecular arrangement when no voltage is applied, and (b) shows the molecular arrangement when no voltage is applied. As shown in FIG. 5A, the liquid crystal molecules have the same tilt angle α 0 and form a so-called uniform arrangement.
A liquid crystal cell having a twisted molecular arrangement in this state is generally called a homogeneous cell, and when a voltage (for example, 2 v) is applied to this cell, the liquid crystal cell is tilted in the tilt angle α1 direction as shown in FIG. 5B. The molecule tilts. In the conventional example, by utilizing the change in the anisotropy of the refractive index due to the tilt of the liquid crystal molecule,
The brightness of the display is getting.

It is generally known that liquid crystal molecules have different refractive indexes in the major axis direction and the minor axis direction of the liquid crystal molecules.
When light is incident on such liquid crystal molecules, emitted light corresponding to the refractive index anisotropy of the liquid crystal molecules is obtained. When the liquid crystal molecules are arranged uniformly in the thickness direction of the liquid crystal layer as in the homogeneous cell, the absolute amount of retardation as a cell is determined by the refractive index anisotropy (Δn) and the liquid crystal layer thickness. It is determined by the value (Δn · d) multiplied by (d), and this value is called the retardation value R.

FIG. 6 is a diagram showing a coordinate system when considering the viewing angle dependence of these liquid crystal display elements. Generally, a liquid crystal display device using two pieces of the homogeneous alignment type LCD described above is
The absorption axis x of the analyzer and the absorption axis y of the polarizer are arranged in an orientation of ± 45 ° with respect to the alignment direction of the liquid crystal molecule long axis 1 of the driving liquid crystal cell (in parallel to the substrate surface xy). This is to make full use of the birefringence effect.

Now, letting the inclination angle θ of the cell from the vertical direction z in FIG. 6 be the observation angle (Veiwing Angle), the retardation when a voltage is applied to the driving liquid crystal cell of the conventional liquid crystal display element in FIG. 5B. The value changes like Rp in FIG. The reason why the retardation value R thus changes depending on the observation angle θ can be explained by the fact that the apparent length of the long axis of the liquid crystal molecule changes depending on the observation angle.
The same idea can be applied when considering the improvement of the viewing angle dependency as in the present invention.

That is, FIG. 4 is a sectional view for explaining the liquid crystal molecule alignment of the driving liquid crystal cell of the liquid crystal display element of the present invention, which is similar to FIG. As in FIG. 5, (a) shows the case when no voltage is applied,
(B) shows the molecular arrangement when a voltage is applied (for example, 2v). Generally, the tilt angle of the liquid crystal molecules changes with respect to the thickness direction of the liquid crystal layer, and a molecular arrangement in which the tilt directions of the upper half and the lower half of the liquid crystal layer are approximately opposite to each other is called a splay alignment, A liquid crystal display element in the case where liquid crystal molecules are not twisted as shown in FIG. 7A is called a π cell (conventionally, in this π cell, a high voltage is applied and liquid crystals are sufficiently vertically aligned). , And a voltage slightly lower than that voltage, it has been proposed to use as a display element by utilizing a change in birefringence in a so-called bent arrangement, but the operating principle of the present invention is different from this. 4 (a) and (b)
As described above, the principle of operation is to utilize the change in birefringence due to a slight change in the tilt angle of liquid crystal molecules when no voltage is applied and when a low voltage is applied).

As can be seen from FIG. 4 (b), considering the change in retardation value when a voltage is applied as in the conventional liquid crystal display element, the upper half du of the upper substrate 4c side having the electrode 4a of the liquid crystal layer is du. Then, the value is half the retardation value Rp of the conventional liquid crystal display element, and the lower substrate 4d having the electrode 4b is used.
The lower half of the side, dd, shows the opposite change. Therefore, the retardation values Ru and Rd of the upper half and the lower half are as shown in FIG. 7, and the sum of the retardation values Ru and Rd is as shown in FIG. 7 with respect to the observation angle of the driving liquid crystal cell of the liquid crystal display device of the present invention. It changes like Ra.

As described above, by making the molecular arrangement of the driving liquid crystal cell to be a so-called π cell, the change in retardation value is small, and the viewing angle dependence of the retardation value when a voltage is applied becomes smaller than that of the conventional one.

Further, the retardation value when a voltage is applied and when no voltage is applied when a viewing angle dependent compensation panel in which liquid crystal molecules are vertically aligned is used so that the retardation value when no voltage is applied is unlikely to change depending on the observation angle. Considering the viewing angle dependence of the conventional liquid crystal display device, as shown in FIG.
become that way. Here, Rpn is a retardation value without a compensation panel, and Rpc is a retardation value when combined with a compensation panel. For reference, the retardation value Rp when a voltage is applied is shown. Rpnc is a retardation value when no voltage is applied when combined with a compensation panel.

On the other hand, the liquid crystal display device of the present invention has a structure as shown in FIG. Here, Ran is Ra when no voltage is applied, and Ranc is Ra when no voltage is applied in combination with the viewing angle dependent compensation panel.
Indicates a retardation value when voltage is applied, and Ran indicates each retardation value when voltage is applied in combination with a viewing angle dependent compensation panel. Also in the liquid crystal display device of the present invention, the same compensation effect as in the conventional example can be obtained, which is the same as the principle in which the conventional example is optically compensated. In these figures, in the liquid crystal display element of the present invention, the viewing angle dependence of the retardation value when no voltage is applied is more symmetrical than that in the conventional example, because the liquid crystal molecule arrangement is the upper half du of the liquid crystal layer. This is due to the symmetrical shape of the lower half Dd.

As described above, according to the present invention, it is possible to obtain a liquid crystal display device in which the viewing angle dependency of the conventional liquid crystal display device when a voltage is applied is significantly improved.

The compensating panel in which liquid crystal molecules are vertically arrayed so that the above-mentioned retardation value does not easily change depending on the observation angle is an optically anisotropic film (for example, a highly arrayed film having the same array) exhibiting the same effect. Molecular liquid crystal film)
The same effect can be obtained even if replaced with, and as a compensating panel for optically compensating the birefringence anisotropy in the plane direction for compensating the interference color, it has a liquid crystal molecule arrangement almost equal to that of the driving liquid crystal panel, A liquid crystal panel whose optical anisotropy is almost the same, or a liquid crystal panel whose uniform anisotropy is uniform as in the prior art, which is almost the same as that of the driving liquid crystal panel, or an optical anisotropic film which produces a similar effect (for example, a uniaxial film). It is clear that the display color is changed to black and white by using a retardation film having a sex property.

[0025]

EXAMPLES Examples of the liquid crystal display device of the present invention will be described in detail below.

Example 1 In FIG. 1, the upper polarizing plate 1,
The viewing angle dependent compensation panel 2, the birefringence anisotropy compensation panel 3, the driving liquid crystal panel 4, and the lower polarizing plate 5 are arranged on the xy plane of the xyz coordinates and with the z axis as the normal line.

The driving liquid crystal panel 4 is made of transparent glass substrates 4c and 4d on which transparent electrodes 4a and 4b of ITO are adhered.
Are opposed to each other so that the positive nematic liquid crystal layer 4e is sandwiched therebetween.

SE-7210 (Nissan Chemical Co., Ltd.) is used as an alignment film on the upper substrate 4c side to obtain a high pretilt.
(Manufactured by: pretilt angle = about 5 °), and the other lower substrate 4d is provided with an alignment film having a low pretilt as an alignment film Optoma-AL-1051 (manufactured by Nippon Synthetic Rubber Co., Ltd .: pretilt angle = about 1 °). ) Is applied to the upper and lower substrates, and the rubbing alignment treatment is performed with the vector parallel to the left direction as shown in FIG. 3A. (4.1) on the upper substrate side and (4.2) on the lower substrate side.
Then, the cells were formed into cells. As the liquid crystal of the liquid crystal layer, ZLI-3276-100 (manufactured by Merck Japan Co., Ltd.) without a chiral agent was used. A driving liquid crystal panel 4 according to this example was obtained with a liquid crystal layer thickness of 5 μm. A drive power supply 4f is connected to each of the electrodes 4a and 4b of this panel. Here, the reason why the pretilts of the upper and lower substrates are not made equal is to make it difficult to generate reverse when voltage is applied.

The birefringence anisotropy compensating panel 3 has the same cell structure as the driving liquid crystal panel 4, that is, a liquid crystal cell in which a liquid crystal layer 3c is sandwiched between a pair of substrates 3a and 3b.
As shown in (b), in the rubbing direction, (3.
1) On the lower substrate, (3.2) has a structure in which the vector is parallel and the vector is 180 ° opposite to the left-right direction, and is aligned along the x-axis so as to be orthogonal to the rubbing direction of the driving liquid crystal panel 4 as shown in FIG. , The driving liquid crystal cells were stacked so as to be technologically continuously laminated. The compensation panel 3 optically compensates the birefringence anisotropy in the plane direction that compensates the interference color.

Further, as the viewing angle dependence compensating panel 2, a vertical alignment type liquid crystal element having anisotropy opposite to the retardation value of the sum total of the two liquid crystal cells and having the same value is used as the optical axis (2.
The liquid crystal display element 10 of the present invention was obtained by stacking 1) along the z-axis and arranging a pair of polarizing plates 1 and 5 in a crossed Nicol polarizing plate arrangement which was shifted by 45 ° from the xy axes.

FIG. 5 shows the change of the contrast ratio with respect to the observation angle by time-division driving at 1/100 duty, and in the case where the vertical alignment type liquid crystal element is used as a viewing angle dependent compensation panel in this embodiment. The curve CR1 in FIG. 9 is obtained, and even if the observation angle θ is changed to ± 60 ° or more, the contrast ratio does not change significantly, and good viewing angle dependence is obtained.

As a modification of this embodiment, even when the viewing angle compensation panel is not used, as in CRn1 in FIG. 9, a good viewing angle dependence of a contrast ratio of 2: 1 or more is obtained at a viewing angle of ± 60 ° together with the above embodiment. Was obtained.

(Embodiment 2) Embodiment 2 is shown in FIG.
Portions having the same reference numerals as those in FIG.

A driving liquid crystal panel 4 similar to that of Example 1 was prepared in the same cell structure as the driving liquid crystal panel as a compensating panel 30 for optically compensating for birefringence anisotropy in the plane direction for compensating interference colors. The liquid crystal panels were engineered continuously so that the rubbing direction, (3.3) on the upper substrate and (3.4) on the lower substrate were orthogonal to the rubbing directions (4.1) and (4.2) of the driving liquid crystal panel 4. .. Further, a vertical alignment type liquid crystal element having anisotropy opposite to the retardation value of the total sum of the two liquid crystal cells and having the same value is stacked as a viewing angle dependent compensation panel 2 to form a crossed Nicols polarizing plate 1. The liquid crystal display element of this example was obtained with 5 arrangements.

FIG. 10 shows the change of the contrast ratio with respect to the observation angle by time-division driving at 1/100 duty. When the vertical alignment type liquid crystal element of this embodiment is used as the compensation panel 2. Is like CR2 in Figure 10,
As a modified example, CRn2 in FIG. 10 is obtained even when the vertical alignment type liquid crystal element is not used, and both have excellent viewing angle dependence superior to that of the first embodiment.

Comparative Example 1 A conventional liquid crystal panel having the same cell configuration as that of Example 1 except that the rubbing directions of the driving liquid crystal panel in Example 1 are parallel and the vectors are reversed as shown in FIG. 3B. The liquid crystal display element by the technology of was obtained. Example 1
Similarly, when time-division driving was performed at 1/100 duty and the change in contrast ratio with respect to the observation angle was measured, the result was as shown in FIG. Even when a vertically aligned liquid crystal element is used as a viewing angle dependent compensation panel, CR
As shown in p, the contrast ratio is 2: 1 or less at 30 ° or more in the + direction, and when the vertical alignment type liquid crystal element is not used as a compensation panel, it becomes like CRpn ±.
At 20 °, the contrast ratio became 2: 1 or less, and neither good viewing angle dependency was obtained.

Example 3 A retardation film having a retardation value equal to that of a driving liquid crystal cell was used as a compensation panel for optically compensating birefringence anisotropy in the plane direction for compensating interference colors. A liquid crystal display device of the present invention was obtained with the same cell configuration as in Example 2 of FIG. Example 2
Similarly, time division drive is performed at 1/100 duty,
When the change in contrast ratio with respect to the observation angle was measured, almost the same results as in FIG. 10 were obtained.

(Embodiment 4) The same cell configuration as that of Embodiment 2 of FIG. 2 is used except that a vertically aligned polymer liquid crystal film that can obtain the same compensation effect as that of Embodiment 2 is used as a compensating panel depending on the viewing angle. A liquid crystal display device of the present invention was obtained. As in Example 1, time-division driving was performed at a 1/100 duty, and changes in the contrast ratio with respect to the observation angle were measured. As a result, almost the same results as in FIG. 10 were obtained.

[0039]

According to the present invention, it is possible to obtain a black and white liquid crystal display device having extremely small viewing angle dependency and excellent electro-optical characteristics such as steep response.

In the embodiments and the like, only the simple matrix driving is explained, but the same effect can be obtained by using the active matrix driving provided with the switching elements such as TFTs, and the color filter or the like is used. Needless to say, the same effect can be obtained by applying it to the color display.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a liquid crystal display element according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a liquid crystal display element according to another embodiment of the present invention.

3A and 3B are plan views illustrating a substrate rubbing direction of a liquid crystal display device according to an embodiment of the present invention. FIG. 3A is a rubbing direction of a driving liquid crystal panel, and FIG. 3B is a rubbing direction of a birefringence anisotropy compensation panel. Indicates.

FIG. 4 is a diagram illustrating a liquid crystal molecule alignment of the liquid crystal display element of the present invention.

FIG. 5 is a diagram illustrating a liquid crystal molecule alignment of a liquid crystal display element according to a conventional technique.

FIG. 6 is a diagram for defining an observation angle of a liquid crystal display element.

FIG. 7 is a diagram showing changes in retardation value with respect to an observation angle when a voltage is applied to a driving liquid crystal cell of the liquid crystal display device of the present invention and a conventional liquid crystal display device.

FIG. 8 shows changes in retardation value with respect to an observation angle when a voltage is not applied and when a voltage is applied, with and without a compensation panel for compensating the viewing angle dependence of the liquid crystal display device of the present invention. FIG.

FIG. 9 is a curve diagram showing an example of a result of measuring a change in contrast ratio with respect to an observation angle by the liquid crystal display element of the present invention.

FIG. 10 is a curve diagram showing an example of a result of measuring a change in contrast ratio with respect to an observation angle by the liquid crystal display device of the present invention.

FIG. 11 is a diagram showing a change in retardation value with respect to an observation angle when a voltage is applied to a liquid crystal display element according to the related art and a driving liquid crystal cell of the liquid crystal display element according to the related art.

FIG. 12 is a curve diagram showing an example of a result of measuring a change in contrast ratio with respect to an observation angle by a liquid crystal display element according to a conventional technique.

[Explanation of symbols]

1, 5 ... Polarizing plate, 2 ... Viewing angle dependent compensation panel, 3 ... Birefringence anisotropy compensation panel, 4 ... Driving liquid crystal panel, 4a,
4b ... Electrodes, 4c, 4d ... Substrate, 4e ... Liquid crystal layer

Claims (5)

[Claims] 1. A nematic liquid crystal layer having a positive dielectric anisotropy is sandwiched between two substrates with electrodes, and has a tilt alignment in which liquid crystal molecule long axes of the liquid crystal layer are aligned in one direction on the surface of the substrate. That is, on the upper and lower substrate surfaces, straight lines in the direction in which the liquid crystal molecule long axes are arranged at opposing points are arranged so as to have points intersecting each other between the planes having the upper and lower substrate surfaces, and It is characterized in that a driving liquid crystal panel in which liquid crystal is not twisted and a birefringence anisotropy compensation panel for optically compensating the birefringence anisotropy in the plane direction thereof are optically continuously laminated. Liquid crystal display device. 2. A driving-use liquid crystal panel is overlaid with a viewing-angle dependent compensating panel in which liquid crystal molecules are vertically aligned so that the birefringence value of the driving liquid-crystal panel when voltage is not applied does not easily change depending on the viewing angle. Claim 1 characterized by the above.
The liquid crystal display element described. 3. The liquid crystal display device according to claim 2, wherein an optically anisotropic film having a refractive index anisotropy is used as the viewing angle dependent compensation panel. 4. A birefringence anisotropy compensating panel for optically compensating for birefringence anisotropy in a plane direction, which has a liquid crystal molecule alignment substantially equal to that of a driving liquid crystal panel and has substantially the same optical anisotropy. 2. The liquid crystal display device according to claim 1, wherein the panels are stacked so that the liquid crystal molecule arrangement thereof is substantially orthogonal to the liquid crystal molecule arrangement of the driving liquid crystal panel. 5. A birefringence anisotropy compensating panel for optically compensating birefringence anisotropy in the plane direction, which comprises driving an optically anisotropic film having an optical anisotropy substantially equal to that of a driving liquid crystal panel. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is positioned so as to have an optical anisotropy opposite to the optical anisotropy in the plane direction of the liquid crystal panel.