JPH09160021A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display element of a twisted nematic type which may be driven with a low voltage. SOLUTION: The element used in this device is formed of a TN type liquid crystal display element having a light diffusion plate having a phase difference dΔn of >=0.50μm or a TN type liquid crystal display element laminated with a twisted phase difference film or uniaxial phase difference film or a TN type liquid crystal display element having 92 to 100 deg. twist angle of liquid crystals 28, >=80μm chiral pitch of the liquid crystals 28 and <=3 deg. pretilt angle of the liquid crystals 28. The low-voltage liquid crystal display element which may be driven with 3V is then attained while a liquid crystal material having a high NI point and low viscosity is used.

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 with low power consumption. More specifically, the present invention relates to a liquid crystal display device having a small drive voltage amplitude.

[0002]

2. Description of the Related Art Liquid crystal display devices are thin, lightweight, and low power consumption display devices, and are widely used in image display devices such as televisions and videos and OA equipment such as word processors and personal computers.

Particularly, recently, there has been a strong demand for lower power consumption for portable notebook personal computers, video cameras, PHS, PDA applications.

The reduction in power consumption, coupled with the development of low-voltage drive ICs, leads to cost reduction, EMI reduction, and device miniaturization, and various measures have been studied.

The methods for reducing power consumption include (a) improving the efficiency of the backlight (improving the lamp efficiency or light guiding property) and (b) improving the panel transmittance (light transmittance of the polarizing plate / color filter). Improvement, improvement of pixel aperture ratio, etc.), (c) lower power consumption by improving drive / circuit system, and (d) reduction of drive voltage amplitude by improving panel optical design and liquid crystal material.

As the improvement effect, the effect of improving the efficiency of the backlight and the improvement of the driving / circuit system are great, but it is also indispensable to reduce the liquid crystal layer drive voltage amplitude from the viewpoint of cost reduction and EMI reduction.

As a method of reducing the drive voltage amplitude,
Generally, lowering the threshold voltage of the liquid crystal material is an effective method and various liquid crystal materials have been proposed. However, since the dielectric constant anisotropy Δε increases and the liquid crystal viscosity increases, it is necessary to keep the NI point of the liquid crystal phase high. It is not easy to achieve high-speed response while keeping it as it is.

On the other hand, it is known that as the twist angle of the liquid crystal layer is increased, the voltage-transmittance characteristic of the liquid crystal panel becomes steeper and the drive voltage amplitude is reduced, but it is easy to secure a sufficient contrast. is not.

Further, by using a polymer material or a material system in which fine particles are dispersed in the liquid crystal layer, the voltage
An attempt to make the transmittance characteristic steep (for example, Japanese Patent Laid-Open No. 7-56
145) has also been done, but there are reliability issues.

[0010]

As described above, with respect to the method of reducing the driving voltage amplitude of the liquid crystal display element, a plurality of approaches are conducted in parallel, including the method of using the liquid crystal-polymer composite. However, a method that has a large effect and does not impair image quality and panel reliability has not been proposed yet.

It is an object of the present invention to provide a liquid crystal display device which uses a liquid crystal material having a high threshold voltage, can be driven at a low voltage, and has a high panel reliability.

[0012]

A twisted nematic (hereinafter referred to as TN) liquid crystal display element having a liquid crystal layer sandwiched between two translucent substrates each having a transparent electrode on the inner surface thereof. Product of the layer thickness d and the refractive index anisotropy Δn dΔ
A liquid crystal display device having n of 0.50 μm or more and including at least one light diffusion plate on the viewer side of the liquid crystal display device, or a liquid crystal display device including a TN type liquid crystal display device and a retardation film, The principal axis azimuth of the surface layer on one side of the retardation film and the principal axis azimuth of the surface layer on the other side are arranged orthogonally, and the principal axis azimuth is liquid crystal from one side to the other side. It is continuously twisted in a direction opposite to the twisting direction of the layer, the principal axis azimuth is substantially parallel to the film surface in the retardation film surface layer, and is substantially perpendicular to the film surface in the retardation film central portion. ,
A liquid crystal display device is used in which the liquid crystal molecule orientation directions of the adjacent liquid crystal display elements and the principal axis directions of the retardation film are orthogonal to each other.

Further, in a liquid crystal display device including a TN type liquid crystal display device and a uniaxial retardation film, the principal axis direction of the uniaxial retardation film is 1 ° to 10 ° with respect to the normal line of the uniaxial retardation film. A liquid crystal display device characterized by being inclined by 90 ° and being orthogonal to the main viewing angle azimuth of the liquid crystal display element, or a twist angle of liquid crystal of 92 ° to 100 °,
A TN type liquid crystal display device in which the chiral pitch of the liquid crystal is 80 μm or more and the pretilt angle of the liquid crystal is 3 ° or less is used.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The voltage-transmittance characteristic of a TN type liquid crystal display device largely depends on the phase difference dΔn of the liquid crystal layer. FIG. 1 shows voltage-transmittance characteristics of liquid crystal display devices having different phase differences.

Since the voltage at which the liquid crystal layer starts to move when a voltage is applied (the so-called Fredericks threshold voltage) is almost the same, if the transmittance of the display element is standardized, the larger the phase difference of the liquid crystal layer when no voltage is applied, the greater the phase difference. The more apparently the voltage-transmittance characteristic becomes steeper.

The first invention utilizes this effect. However, it is generally known that when the phase difference of the liquid crystal layer becomes large, the viewing angle characteristics of the display element deteriorate. On the other hand, the present invention eliminates the viewing angle dependence of the liquid crystal display element by disposing a diffusion plate on the side of the emitted light.

A second aspect of the invention is intended to make the transmittance change steep on the high voltage side in the voltage-transmittance characteristic. When the applied voltage is between the optical threshold voltage and the optical saturation voltage, the transmissivity of the display element also changes according to the applied voltage, but when the applied voltage exceeds the optical saturation voltage, the applied voltage The change in transmissivity of the display element with respect to is sharply reduced (see FIG. 1).

It is considered that this is because the liquid crystal layer in the vicinity of the surface of the alignment film cannot sufficiently dissolve its twisted structure due to the constraint of the alignment film.

According to the present invention, the residual retardation of the liquid crystal display element in the black display region is compensated by the twisted retardation film to reduce the rounding of the voltage-transmittance characteristic in the high voltage region. is there.

The residual retardation can be compensated by using a retardation film whose twist direction is opposite to the molecular orientation state of the liquid crystal layer when a high voltage is applied.

The third aspect of the present invention is such that the residual retardation is compensated by a uniaxial film.

On the other hand, it is known that the steepness of the voltage-transmittance characteristic of the liquid crystal display element can be increased by increasing the liquid crystal twist angle, but the liquid crystal is drastically reduced due to problems such as reduction in contrast and coloring. It is impossible to increase the twist angle.

The fourth invention is a combination of the steepness of the voltage-transmittance characteristic due to the increase of the twist angle of the liquid crystal and the steepness due to the reduction of the threshold voltage in driving the liquid crystal display element.

An increase in the chiral pitch or a decrease in the pretilt angle causes steepening in a high voltage region and a low voltage region, respectively, and both of them lead to a reduction in drive voltage amplitude.

Embodiments will be described in detail below with reference to the drawings. In the following examples, the drive voltage amplitude ΔV is a voltage-transmittance curve in which the maximum light transmittance is 100% and the minimum light transmittance is 0%. It was defined as a value obtained by subtracting the driving voltage V99 of 99%.

In the present embodiment, for the convenience of the experiment, ΔV evaluation was carried out in an evaluation cell in which liquid crystal was sandwiched between two glass substrates having transparent electrodes, but sufficient contrast was obtained in an active matrix type liquid crystal display device. In order to
Considering the driving voltage tolerance such as C output variation, ΔV <2.0V in the evaluation cell is desirable.

(Embodiment 1) FIG. 2 is a constitutional view of a first liquid crystal display element of the present invention. On the two glass substrates 22 and 26 having transparent electrodes, a polyimide alignment film paint AL-1057 (4.0 wt.%, Γ-butyrolactone solution) manufactured by Nippon Synthetic Rubber Co., Ltd. was applied by spin coating, 200
It was cured under the curing condition of 30 ° C. for 30 minutes.

After that, as shown in FIG. 3, the rubbing 32 with the twist angle ω = 90 ° so that the main viewing angle direction is located below the panel,
After applying 34, the two glass substrates 22 and 26 subjected to the rubbing treatment were attached at various intervals using a glass spacer 24, Micropearl (manufactured by Sekisui Fine Chemical Co., Ltd.).

Next, 0.25 wt.% Of cholesteryl nonanoate was added as a chiral material. % Liquid crystal MLC9000-100 / MLC9100-000 equivalent mixture (NI point = 91 ° C., Δn = 0.0995) was injected between glass substrates using a vacuum injection method, and the liquid crystal layer thicknesses were different. Various liquid crystal panels 29 were created.

After that, as shown in FIG.
27 is a liquid crystal panel 29 so that the polarization axes thereof are orthogonal to each other.
And the light diffusing plate 20 on the polarizing plate 21 on the observer side.
Liquid crystal display elements A having different liquid crystal layer thicknesses d.
~ E was created.

Next, the voltage-transmittance characteristic of the liquid crystal display device of the present invention was measured by applying a 30 Hz rectangular wave according to a conventional method.

Table 1 shows the phase difference dΔn, threshold voltage, saturation voltage, and drive voltage amplitude ΔV of each liquid crystal display element at 20 ° C.

[0033]

[Table 1]

As is clear from Table 1, the liquid crystal display devices D and E of the present invention can be driven at a low voltage without increasing the dielectric anisotropy Δε of the liquid crystal material, and have a high NI point.
A liquid crystal material having a low viscosity can be used, and its practical value is extremely high.

Further, in the present invention, since the light diffusing plate is arranged on the viewer side, excellent viewing angle characteristics were observed despite the high dΔn.

The driving voltage amplitude decreases as dΔn increases, but the brightness of the liquid crystal display element decreases greatly when the phase difference dΔn exceeds 0.6 μm. 6 μm is preferable.

In the present embodiment, a simple matrix type liquid crystal display element is used for convenience of measurement, but it goes without saying that an active matrix type liquid crystal display element having a large number of active elements arranged on a substrate may be used.

Further, a light guide plate such as a prism sheet may be provided on the incident light side so that the light is vertically incident on the liquid crystal panel.

(Embodiment 2) FIG. 4 is a constitutional view of a second liquid crystal display element of the present invention. On two glass substrates 42 and 46 having transparent electrodes, a coating composition for polyimide alignment film AL-1057 (4.0 wt.%, Γ-butyrolactone solution) manufactured by Japan Synthetic Rubber Co., Ltd. was applied by spin coating, 200
It was cured under the curing condition of 30 ° C. for 30 minutes.

After that, as shown in FIG. 5, rubbing was performed at a twist angle of ω = 90 ° so that the main viewing angle direction was on the lower side of the panel, and then the two glass substrates 4 subjected to this rubbing treatment.
2, 46 were attached to each other at intervals of 5 μm using a glass spacer 44, Micropearl (manufactured by Sekisui Fine Chemical Co., Ltd.).

Next, 0.26 wt.% Of cholesteryl nonanoate was added as a left-handed chiral material. % Liquid crystal MT-5076LA manufactured by Chisso Corporation (NI point = 92 ° C., Δ
n = 0.083) was injected between the glass substrates by using a vacuum injection method to form a liquid crystal panel 49.

Then, as shown in FIG. 5, the retardation film 41 is arranged so that the principal axis of the adjacent retardation film and the rubbing direction (easy alignment axis) of the liquid crystal panel are orthogonal to each other, and the polarizing plate 40, A liquid crystal display element F was prepared by bonding 47 to a liquid crystal panel 49 so that their polarization axes were orthogonal to each other.

In the retardation film 41, the principal axis direction on one surface of the film and the principal axis direction on the other surface make an angle of 90 °, and this axis azimuth is from one surface to the other surface. It is twisted 90 degrees to the right continuously,
The main axis at the center of the film is almost perpendicular to the film surface. In addition, the retardation of the film has a wavelength of 545
It was 60 nm for nm light.

Next, the threshold voltage, the saturation voltage, and the drive voltage amplitude were measured by the same method as in Example 1. The threshold voltage was 1.24 V, the saturation voltage was 2.15 V, and the drive voltage amplitude ΔV was 1. It was 0.85V.

On the other hand, as a comparative example, a liquid crystal display element G was prepared in exactly the same manner as in Example 2 except that the retardation film was not included. When the threshold voltage, the saturation voltage, and the drive voltage amplitude were measured by the same method as in Example 1, the threshold voltage was 1.33 V, the saturation voltage was 2.40 V, and the drive voltage amplitude ΔV.
Was 2.20V.

The retardation film 41 used in the liquid crystal display element F of the present invention has a function of compensating for the residual retardation in the liquid crystal panel 49 when a voltage is applied, and has a voltage-transmittance characteristic of the liquid crystal panel 49. It has a sharpening effect.

The liquid crystal display device of the present invention is capable of being driven by 3V while using a liquid crystal material having a relatively high threshold voltage, and a liquid crystal material having a high NI point can be used, and its practical value. Is big.

In the retardation film used in Example 2, a mixture of a polymer liquid crystal and a photocurable resin is sandwiched between translucent substrates and photocured while being aligned under a high temperature and a high electric field. Created by

(Embodiment 3) FIG. 6 is a constitutional view of a third liquid crystal display element of the present invention. On two glass substrates 62 and 66 having transparent electrodes, a polyimide alignment film paint AL-1057 (4.0 wt.%, Γ-butyrolactone solution) manufactured by Nippon Synthetic Rubber Co., Ltd. was applied by spin coating, 200
It was cured under the curing condition of 30 ° C. for 30 minutes.

After that, as shown in FIG. 7, rubbing is performed at a twist angle of ω = 90 ° so that the main viewing angle direction is below the panel, and then the two glass substrates 6 subjected to this rubbing treatment
2, 66 were attached at intervals of 5 μm using a glass spacer 64, Micropearl (manufactured by Sekisui Fine Chemical Co., Ltd.).

Next, 0.25 wt.% Of cholesteryl nonanoate was added as a chiral material. % Liquid crystal MT-5076LA manufactured by Chisso Corporation (NI point = 92 ° C., Δn = 0.0
83) is injected between the glass substrates using a vacuum injection method,
A liquid crystal panel 69 was created.

Thereafter, as shown in FIG. 7, the retardation film 61 is arranged so that the principal axis of the retardation film and the principal viewing angle direction of the liquid crystal panel are orthogonal to each other, and further the polarizing plate 6
A liquid crystal display element H was prepared by bonding 0 and 67 to the liquid crystal panel 69 so that their polarization axes were orthogonal to each other.

The principal axis azimuth of the retardation film 61 is inclined by 3 ° with respect to the film normal, and the retardation thereof has a wavelength of 5
It was 45 nm for 45 nm light.

Next, the threshold voltage, the saturation voltage, and the drive voltage amplitude were measured by the same method as in Example 1. The threshold voltage was 1.28 V, the saturation voltage was 2.17 V, and the drive voltage amplitude ΔV was 1. It was 0.90V.

The retardation film 61 used in the liquid crystal display element H of the present invention has a function of compensating for the residual retardation in the liquid crystal panel 69 when a voltage is applied, and has a voltage-transmittance characteristic of the liquid crystal panel 69. It has a sharpening effect.

The principal axis azimuth of the retardation film used in this example has an inclination of 3 ° with respect to the normal to the retardation film, but an angle of 1 ° to 10 ° is suitable. That is, when the angle is less than 1 °, no effect is recognized, and when the angle exceeds 10 °, the contrast is deteriorated and the image quality is deteriorated due to coloring.

The liquid crystal display device of the present invention is capable of driving 3V while using a liquid crystal material having a relatively high threshold voltage, and a liquid crystal material having a high NI point can be used, and its practical value is large.

In the retardation film used in Example 3, a mixture of a polymer liquid crystal and a photocurable resin is sandwiched between translucent substrates and photocured while being aligned at a high temperature and a high electric field. Created by

(Embodiment 4) FIG. 8 is a block diagram of a liquid crystal display device according to a fourth invention of the present invention. The liquid crystal panel 89 was created by the following method, as in the first embodiment. Various alignment film coating materials were applied onto two glass substrates 82 and 86 having transparent electrodes by a spin coating method, and cured at 200 ° C. for 30 minutes.

Then, as shown in FIG. 9, the rubbing 92 is performed with the twist angle ω = 92 degrees so that the main viewing angle direction is below the panel.
After performing 94, the two glass substrates 82 and 86 subjected to the rubbing treatment are subjected to 5 by using a glass spacer 84, Micropearl (manufactured by Sekisui Fine Chemical Co., Ltd.).
The pieces were attached at an interval of μm.

Next, liquid crystal MLC9000-000 manufactured by Merck & Co., Inc. in which the addition ratio of the chiral material cholesteryl nonanoate is changed and the chiral pitch is changed is injected between the glass substrates by using a vacuum injection method to form a liquid crystal panel 89. did.

After that, as shown in FIG.
87 is a liquid crystal panel 89 so that their polarization axes are orthogonal to each other.
Liquid crystal display elements I to X were prepared by pasting before and after.

Table 2 shows the relationship between the pretilt angles of the prepared liquid crystal display devices I to X and the chiral pitch of the injected liquid crystal.

[0064]

[Table 2]

Next, the driving voltage amplitude ΔV of each liquid crystal display element was measured by the same method as in Example 1. The results (Table 3)
Shown in

[0066]

[Table 3]

As is clear from Table 3, the liquid crystal display device of the present invention having a pretilt angle of 3 ° or less and a chiral pitch of 80 μm or more has a driving voltage amplitude ΔV of 2.0.
Since it is V or less, it is extremely useful for realizing a low power consumption liquid crystal display device.

(Embodiment 5) Similar to Embodiment 4, liquid crystal panels having different twist angles of liquid crystal were prepared by the following method. The panel structure is the same as in FIG. First, on two glass substrates 82 and 86 having transparent electrodes, Nissan Chemical Industries, Ltd.
Manufactured polyimide alignment film paint RN-707 (4.0 wt.
%, NMP solution) by spin coating
It was cured under the curing condition of 30 ° C. for 30 minutes.

After that, after rubbing at various liquid crystal twist angles ω so that the main viewing angle direction is on the lower side of the panel, the two glass substrates 82 and 86 subjected to the rubbing treatment are
The glass spacers 84, Micropearl (manufactured by Sekisui Fine Chemical Co., Ltd.), were used to bond them at intervals of 5 μm.

Next, liquid crystal MT-5071L manufactured by Chisso Corp. was prepared by using cholesteryl nonanoate as a left-handed chiral material and adjusting the chiral pitch to 90 μm.
A was injected between the glass substrates by using a vacuum injection method to form a liquid crystal panel 89.

After that, as shown in FIG. 9, the polarizing plates 81 and 87 are arranged on the liquid crystal panel 89 so that their polarization axes are orthogonal to each other.
Liquid crystal display elements α, β and γ were prepared by pasting before and after.

After that, the threshold voltage, the saturation voltage and the driving voltage amplitude were measured by the same method as in Example 1. The results are shown in (Table 4).

[0073]

[Table 4]

The pretilt angle of the liquid crystal material was measured by a separately prepared homogeneous liquid crystal cell and found to be 3 °.

As is clear from Examples 4 and 5, the liquid crystal display device of the present invention provides a liquid crystal display device having a small drive voltage amplitude, and its practical value is great.

When the pretilt angle is 3 ° or less, the chiral pitch exceeds 120 μm, or the liquid crystal twist angle is 100.
If it exceeds 0, reverse twist domains are likely to occur, which is not practical.

[0077]

The liquid crystal display device of the present invention provides a liquid crystal display device which can be driven at 3V even though a liquid crystal material having a relatively high threshold voltage is used, and a liquid crystal material having a high NI point and a low viscosity is used. It is possible to provide a low-voltage liquid crystal display device that has been used.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a relationship between a voltage-transmittance characteristic and a phase difference dΔn in a TN type liquid crystal display element.

FIG. 2 is a diagram showing a first configuration example of the liquid crystal display element of the present invention.

FIG. 3 is a diagram for explaining a relationship between a polarization axis of a polarizing plate and a rubbing direction of an alignment film in a liquid crystal display device of the present invention.

FIG. 4 is a diagram showing a second configuration example of the liquid crystal display element of the present invention.

FIG. 5 is a diagram for explaining a relationship among a polarization axis of a polarizing plate, a rubbing direction of an alignment film, and a principal axis direction of a retardation film in a liquid crystal display device of the present invention.

FIG. 6 is a diagram showing a third configuration example of the liquid crystal display element of the present invention.

FIG. 7 is a diagram for explaining a relationship among a polarization axis of a polarizing plate, a rubbing direction of an alignment film, and a main axis direction of a retardation film in a liquid crystal display device of the present invention.

FIG. 8 is a diagram showing a fourth configuration example of the liquid crystal display element of the present invention.

FIG. 9 is a diagram for explaining the relationship between the polarization axis of the polarizing plate and the rubbing direction of the alignment film in the liquid crystal display device of the present invention.

[Explanation of symbols]

10 voltage-transmittance characteristic when dΔn = 0.58 μm 11 voltage-transmittance characteristic when dΔn = 0.47 μm 12 drive voltage amplitude of a liquid crystal display element when dΔn = 0.58 μm 13 dΔn = 0.47 μm liquid crystal Display element drive voltage amplitude 20 Light diffusion plate 21, 27, 40, 47, 60, 67, 81, 87 Polarizing plate 22, 26, 42, 46, 62, 66, 82, 86 Glass substrate 23, 25, 43, 45, 63, 65, 83, 85 Alignment film 24, 44, 64, 84 Spacer 28, 48, 68, 88 Liquid crystal 29, 49, 69, 89 Liquid crystal panel 31, 51, 71, 91 Polarization axis of upper substrate polarizing plate Direction 32, 52, 72, 92 Upper substrate rubbing direction 33, 53, 73, 93 Lower substrate polarizing plate polarization direction 34, 54, 74, 94 Lower substrate rubbing direction 35, 55 , 75, 95 Liquid crystal twist angle 41, 61 Retardation film 56, 57, 77 Main axis direction of retardation film 76 Main viewing angle direction

Claims (4)

[Claims] 1. A twisted nematic liquid crystal display device comprising a liquid crystal layer sandwiched between two translucent substrates each having a transparent electrode on its inner surface, wherein a layer thickness d of the liquid crystal layer and a refractive index anisotropy Δn.
And a product dΔn of 0.50 μm or more, and at least one light diffusion plate is provided on the viewer side of the liquid crystal display device. 2. A liquid crystal display device including a twisted nematic liquid crystal display device and a retardation film, wherein a principal axis direction of a surface layer on one side of the retardation film and a principal axis direction of a surface layer on the other side are arranged orthogonally. The main axis azimuth is continuously twisted in a direction opposite to the twist direction of the liquid crystal layer from one side to the other side, and the main axis azimuth is on the film surface in the retardation film surface layer. It is substantially parallel, in the central portion of the retardation film is substantially perpendicular to the film surface,
A liquid crystal display device, wherein liquid crystal molecule orientation directions of the adjacent liquid crystal display elements and main axis directions of the retardation film are orthogonal to each other. 3. A liquid crystal display device including a twisted nematic liquid crystal display device and a uniaxial retardation film, wherein the azimuth of the uniaxial retardation film has a principal axis azimuth of 1 ° to the normal to the uniaxial retardation film. A liquid crystal display device, wherein the liquid crystal display device is tilted by 10 ° and is orthogonal to the main viewing angle direction of the liquid crystal display element. 4. A liquid crystal display device including a twisted nematic liquid crystal display element in which the twist angle of the liquid crystal is 92 ° to 100 °, the chiral pitch of the liquid crystal is 80 μm or more, and the pretilt angle of the liquid crystal is 3 ° or less.