JPH07301794A - Liquid crystal display - Google Patents

Abstract

(57) [Abstract] [Purpose] Even if a film substrate is used to make it thinner, lighter, and more flexible, the display quality is as good as that of a glass substrate. [Structure] Liquid crystal molecules are twist-aligned in a range of 180 ° to 360 ° from an incident side film substrate 4 toward an emitting side film substrate 7, and a transmission axis 10a of a polarizer 10 disposed on the incident side is subjected to an incident side alignment treatment. 120 ° to direction 3a
˜150 °, and the transmission axis 11a of the analyzer 11 arranged on the emission side is intersected with the incident side alignment treatment direction 3a in the range of 80 ° to 105 °. 5 ° to 3 with respect to the incident side alignment treatment direction 3a
The retardation axes of the film substrates 4 and 7 are intersected with each other at a predetermined angle with respect to the optical axis 12a of the phase plate 12 so that the retardation of the entire liquid crystal display device is exhibited as much as possible. A pair of film substrates 4,
7 and the liquid crystal layer of the liquid crystal cell 1 and the retardation of the phase plate 12 are mutually compensated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a super twisted nematic type liquid crystal display device.

[0002]

2. Description of the Related Art Display devices used in office automation equipment are required to have high-definition display, and therefore have a large number of pixels and high time-division driving. In order to meet such a demand, as a display device such as a personal computer, a liquid crystal display device of a super twisted nematic type (hereinafter referred to as STN type) capable of high time division driving and having a relatively high contrast is used. In this STN type liquid crystal display device, a simple matrix structure having a simple element structure and a simple driving device is widely known. This STN-type liquid crystal display device having a simple matrix structure includes a pair of glass substrates which are arranged to face each other with a predetermined space therebetween, and electrodes which are formed on the facing surfaces of the pair of glass substrates so as to be orthogonal to each other. A liquid crystal cell formed of an alignment film formed on each of the facing surfaces of each glass substrate so as to cover the electrodes and subjected to an alignment treatment in a predetermined direction, and a liquid crystal sealed between the pair of glass substrates so as to be sandwiched between the alignment films is formed. I have it. In this liquid crystal cell, the molecules of the liquid crystal near the alignment film interposed between the alignment films are aligned in a predetermined direction by the regulating force of the alignment film, whereby the liquid crystal molecules are moved from one glass substrate to the other glass substrate in the STN type. In the case of, they are arranged side by side so as to be twisted at 180 ° to 360 °. Then, on the outside of the liquid crystal cell, a pair of polarizing plates is arranged so as to sandwich them,
Between the pair of polarizing plates, a phase plate for compensating for the difference in the phase difference for each wavelength light generated in the liquid crystal cell is arranged. In such a liquid crystal display device, an electric field is applied between opposing electrodes by time-division driving, so that the alignment of twist-aligned liquid crystal molecules is changed, and an optical change accompanying the change of the alignment state of the liquid crystal molecules is caused. Is visualized by a pair of polarizing plates, and the coloration of the display is suppressed by the phase plate to achieve the desired display.

[0003]

However, in such an STN type liquid crystal display device, since the glass substrate is used as the substrate of the liquid crystal cell, it is thick and heavy, which hinders reduction in thickness and weight. In addition, there is a problem that it is difficult to obtain a free shape. So, in the past,
Instead of a glass substrate, it has been studied to use a film substrate that is thin, light, easy to cut, can be formed into a free shape, and can be bent. However, in such a liquid crystal display device, the film substrate itself has a retardation (optical phase difference). Therefore, if the film substrate is simply used, the retardation of the film substrate adversely affects the display and the display quality deteriorates. There is a problem of doing. The present invention has been made in view of the above circumstances, and even if a film substrate is used to achieve thinning, weight reduction, and shape freedom, a liquid crystal capable of ensuring display quality as good as that of a glass substrate. An object is to provide a display device.

[0004]

According to the present invention, in order to achieve the above-mentioned object, electrodes facing each other are formed with an intersecting electrode and an alignment film covering the electrodes and subjected to an alignment treatment in a predetermined direction. A film liquid crystal cell enclosing a liquid crystal for twist alignment between the alignment films of a pair of flexible film substrates, a pair of polarizing plates arranged outside the film liquid crystal cell to sandwich the liquid crystal cell, And a phase plate disposed between the polarizing plates of the liquid crystal, and the molecules of the liquid crystal are directed from one film substrate to the other film substrate.
Twist alignment is performed in the range of 80 ° to 360 °, the transmission axis of one polarizing plate is intersected with the alignment treatment direction of the alignment film of one film substrate in the range of 120 ° to 150 °, and the other polarizing plate is aligned. The transmission axis is 80 ° with respect to the alignment treatment direction.
To intersect with the optical axis of the phase plate in the range of 5 ° to 30 ° with respect to the alignment treatment direction, and the optical axis of the pair of film substrates is predetermined with respect to the optical axis of the phase plate. It is characterized by intersecting at an angle.

[0005]

According to the present invention, the liquid crystal molecules are moved from one film substrate to the other film substrate by 180 ° to 3 °.
Twist alignment in the range of 60 °, the transmission axis of one polarizing plate is intersected with the alignment treatment direction of the alignment film of one film substrate in the range of 120 ° to 150 °, and the transmission axis of the other polarizing plate is 80 ° to 105 ° with respect to the alignment treatment direction
In the range of 5 ° to 30 ° with respect to the alignment treatment direction, and the optical axes of the pair of film substrates intersect with the optical axis of the phase plate at a predetermined angle. By doing so, the pair of film substrates, the phase plate, and the liquid crystal layer mutually compensate each other's retardation (optical retardation), and the development of retardation in the liquid crystal display device as a whole is suppressed as small as possible. As a result, the display quality can be as high as that of the glass substrate even if the film substrates each having the retardation are used.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the liquid crystal display device of the present invention will be described below with reference to FIGS. 1 and 2 are a sectional view and an exploded perspective view of a liquid crystal display device having a simple matrix structure. In these figures, 1 is a film liquid crystal cell. The film liquid crystal cell 1 includes a lower film substrate 4 on which a plurality of strip-shaped electrodes 2 arranged in parallel in a predetermined direction and an alignment film 3 covering these electrodes 2 are formed, and orthogonal to the one electrode 2. The upper film substrate 7 and the upper and lower film substrates 7 and 4 on which the plurality of strip-shaped other electrodes 5 and the alignment film 6 covering the other electrodes 5 are arranged in parallel in the opposite direction. It is sealed in a region surrounded by the sealing material 8 which is bonded at a predetermined interval and the upper / lower film substrates 7 and 4 and the sealing material 8, and has a dielectric constant ratio Δε.
The value of / ε⊥ is 1.90, the value of the elastic constant ratio K3 / K1 is 1.83, the value of K3 / K2 is 2.40, and the value of the ratio d / p of the gap d and the natural pitch p is 0.5. And the liquid crystal 9 of. In this liquid crystal cell 1, light is incident from below in the drawing. Below, the lower film substrate is referred to as the incident side film substrate 4, and the upper film substrate is referred to as the emission side film substrate 7. A polarizer 10 made of a linear polarizing plate is arranged outside the incident side film substrate 4 of the liquid crystal cell 1, and a linear polarizing plate analyzer 1 is placed outside the exit side film substrate 7.
1 is arranged. Moreover, a phase plate 12 is interposed between the liquid crystal cell 1 and the analyzer 11.

An alignment film 3 formed on each of the surfaces of the incident side film substrate 4 and the emitting side film substrate 7, which face each other,
6 is subjected to an alignment treatment such as rubbing. That is, as shown in FIG. 2, the alignment film 3 of the incident-side film substrate 4 has a direction inclined at a predetermined angle from the lower right to the upper left with respect to a horizontal line when the liquid crystal cell 1 is observed from the front. Alignment treatment is applied to 3a. The orientation film 6 of the emission side film substrate 7 with respect to the incidence side film substrate 4 is counterclockwise (hereinafter, referred to as negative or −) with respect to the orientation processing direction 3a of the incidence side film substrate 4 (hereinafter, referred to as the incidence side orientation processing direction). The orientation process is performed in the direction 6a rotated by a predetermined angle θ1. By such an alignment treatment, the molecules of the liquid crystal 9 are aligned with a pretilt angle of about 3 °, and a negative rotation direction of −180 ° to −360 ° from the incident side film substrate 4 toward the emitting side film substrate 7. It is twisted and arranged in the range angle (φ), preferably in the range of −200 ° to −240 °. The product Δnd of the refractive index anisotropy Δn of the liquid crystal layer of the liquid crystal cell 1 and the gap (liquid crystal layer thickness) d.
The value of is set to about 850 nm (measurement wavelength: 589 nm). Each of the film substrates 4 and 7 is made of a synthetic resin such as polyether sulfone (PES), and has a retardation (product Δnd of refractive index anisotropy Δn of the film substrate and thickness d of the film substrate). The exit direction is the same, and the retardation (Δnd) value is 2
It is set to 0 nm or less, preferably 10 nm or less.

The polarizer 10 is arranged so that its transmission axis 10a forms an angle (α) in the range of 120 ° to 150 ° clockwise (hereinafter referred to as positive or +) with respect to the incident side alignment treatment direction 3a. Has been done. The analyzer 11 has its transmission axis 11
a is 80 ° clockwise with respect to the incident side alignment treatment direction 3a
It is arranged so as to form an angle (β) in the range of 105 °. The phase plate 12 has its optical axis (slow axis or fast axis).
12a is 5 ° clockwise with respect to the incident side alignment treatment direction 3a.
It is arranged so as to form an angle (γ) in the range of ˜30 °. The phase plate 12 has a refractive index anisotropy Δn and a thickness d.
The value of the product Δnd with 570 nm (measurement wavelength: 589n
m) is set.

In such an STN type liquid crystal display device,
The molecules of the liquid crystal 9 are twist-aligned in the range of -180 ° to -360 ° from the incident side film substrate 4 toward the emitting side film substrate 7, and the transmission axis 10a of the polarizer 10 is oriented with respect to the incident side alignment treatment direction 3a. The transmission axis 11a of the analyzer 11 is intersected with the incident side alignment treatment direction 3a in the range of 80 ° to 105 °, and the optical axis 12a of the phase plate 12 is aligned with the incidence side. The film substrate 4 is intersected with the processing direction 3a in the range of 5 ° to 30 °.
By setting the value of each Δnd of 7 to 20 nm or less, the retardation of each of the pair of film substrates, the liquid crystal layer of the liquid crystal cell 1, and the phase plate 12 is increased even if each of the film substrates 4 and 7 has a retardation. They compensate each other and the retardation of the liquid crystal display device as a whole is suppressed as small as possible.

Next, in this liquid crystal display device, the twist angle φ of the liquid crystal molecules of the film liquid crystal cell 1 is 240 °, 2
The results of examining three kinds of 20 ° and 200 ° will be described. First of all, the optimum arrangement relationship when the two substrates have no retardation (for example, the same as the glass substrate) is as follows. When the twist angle (φ) is −240 °, the transmission axis 10a of the polarizer 10 is 125 ° (α) and the optical axis 12a of the phase plate 12 is 10 ° (γ) with respect to the incident side alignment treatment direction 3a. ), The transmission axis 11a of the analyzer 11 is arranged to intersect at an angle (β) of 85 °. When the twist angle (φ) is −220 °, the incident side alignment treatment direction 3a
On the other hand, the transmission axis 10a of the polarizer 10 has an angle of 135 ° (α), the optical axis 12a of the phase plate 12 has an angle of 25 ° (γ), and the transmission axis 11a of the analyzer 11 has an angle of 95 ° (β). The layout is such that they intersect at. When the twist angle (φ) is -200 °, the incident side alignment treatment direction 3a
On the other hand, the transmission axis 10a of the polarizer 10 is 145 ° (α), the optical axis 12a of the phase plate 12 is 25 ° (γ), and the transmission axis 11a of the analyzer 11 is 100 ° (β). The layout is such that they intersect at.

Next, in each of such arrangements, the liquid crystal is sandwiched between the film substrates 4 and 7, and the slow axes of the two film substrates 4 and 7 are started in the left-right direction of the liquid crystal display device. The contrast when rotated at every 30 ° was examined. At this time, the state in which the contrast is highest is a state in which the slow axes of the film substrates 4 and 7 do not coincide with the vertical direction and deviate from them, and the state in which the contrast is the lowest is that of the film substrates 4 and 7. It was found that the phase axes coincided with each other in the left-right direction and were small even in the vicinity thereof.

The case where the slow axes of the film substrates 4 and 7 are in the left-right direction and has the smallest contrast, that is, the case where the arrangement of the film substrates 4 and 7 is the most disadvantageous for obtaining high contrast will be described below. At this time, the incident side film substrate 4 and the emitting side film substrate 7 were arranged as follows in the optimum arrangement relationship when the substrate does not have retardation. When the twist angle (φ) is −240 °, the slow axis of the incident side film substrate 4 is −30 ° with respect to the incident side alignment treatment direction 3a.
The exit side film substrate 7 was arranged so that the slow axes intersect at an angle of −30 °. When the twist angle (φ) is −220 °, the slow axis of the incident side film substrate 4 is −20 ° with respect to the incident side alignment treatment direction 3a, and the outgoing side film substrate 7 is present.
Were arranged so that their slow axes intersected at an angle of -20 °.
When the twist angle (φ) is −200 °, the slow axis of the incident side film substrate 4 is −10 with respect to the incident side alignment treatment direction 3a.
It was arranged so that the slow axis of the exit side film substrate 7 intersects at an angle of -10 °.

In FIGS. 3 to 5, the values of Δnd of the film substrates 4 and 7 are 0, 5, 1 in these three types of arrangement relationships.
1/4, 1/8, 1/16, 1 for 0 and 20 nm
The result of examining the front contrast at each duty of / 48 is shown. However, the bias takes an optimum value (√ (N + 1) at 1 / N duty). As is clear from these figures, even when the slow axes of the film substrates 4 and 7 are aligned in the left-right direction, the contrast is not always obtained when the film substrates 4 and 7 have no retardation (when the value of Δnd is 0). It turns out that does not fall. For example, when the value of Δnd is 10 nm or less, there is almost no effect, when the twist angle (φ) is 240 ° or 200 °, it does not decrease, and even at 220 °, the decrease is about 14%, and when the value of Δnd is 20 nm and the duty is low, It can be seen that has little effect on. Further, when the twist angle (φ) becomes smaller, the absolute value of the front contrast decreases, so that it can be seen that the change caused by the duty on the contrast becomes smaller. At this time, the tint is increased by 13% at maximum when the value of Δnd is 10 nm or less. However,
It may decrease when the duty is high.

6 and 7, the twist angle (φ) is 2
The results of examining the transmittance and chromaticity with respect to the applied voltage at the 1/4 duty and the 1/48 duty at 40 ° are shown. As is clear from these figures, since the voltage width between the selection voltage and the non-selection voltage is wide at low duty, the Δnd value of the film substrates 4 and 7 is hardly affected at 0 to 20 nm, but at high duty, Since the voltage width is narrow, it can be seen that the film substrates 4 and 7 are affected when the value of Δnd is 20 nm. For example,
Δ of film substrates 4 and 7 at 1/48 duty
When the value of nd is 0 to 10 nm, FIGS.
As shown in, the contrast ratio is about 158 to 161, while the value of Δnd of the film substrates 4 and 7 is 20.
7 nm, the transmittance (Y) when the non-selection voltage is applied is 27.87% and the transmittance (Y) when the selection voltage is applied is 0.374%. Contrast ratio is 7
It was 4.52, which shows that it was affected.

As described above, in this STN type liquid crystal display device, various characteristics of the retardation and display quality of the film substrates 4 and 7 were evaluated, and as a result, particularly regarding the contrast, the retardation (Δnd of the film substrates 4 and 7 was increased. Value is less than 10 nm, and the retardation (value of Δnd) is 20 nm, the effect is small when the duty is low, which makes it possible to use a thin and light film substrate. Become.

Although the phase plate 12 is interposed between the film liquid crystal cell 1 and the analyzer 11 in the above embodiment, the present invention is not limited to this, and the phase plate 12 is interposed between the film liquid crystal cell 1 and the polarizer 12. 12 may be interposed. Further, in the above embodiment, the case of the transmissive type has been described, but the present invention is not limited to this, and can be applied to the reflective type.

[0017]

As described above, according to the present invention, the molecules of the liquid crystal are twisted in the range of 180 ° to 360 ° from one film substrate to the other film substrate, and one of the polarizing plates is The transmission axis intersects the alignment treatment direction of the alignment film of one film substrate in the range of 120 ° to 150 °, and the transmission axis of the other polarizing plate is in the range of 80 ° to 105 ° with respect to the alignment treatment direction. The optical axis of the phase plate is intersected with the alignment treatment direction in the range of 5 ° to 30 °, and the optical axes of the pair of film substrates are intersected with the optical axis of the phase plate at a predetermined angle. Thereby, the retardation of the pair of film substrates and the liquid crystal layer of the liquid crystal cell and the retardation of the phase plate mutually compensate each other, and the expression of the retardation of the liquid crystal display device as a whole is suppressed as small as possible. Even if a film substrate is used in order to reduce the thickness, reduce the weight, and make the shape more flexible, the display quality can be as high as that of the glass substrate.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a liquid crystal display device to which the present invention is applied.

FIG. 2 is an exploded perspective view of FIG.

FIG. 3 is a diagram showing front contrast (CR) and chroma difference (C *) at each duty with respect to Δnd of the film substrate when the twist angle of liquid crystal molecules is 240 °.

FIG. 4 is a diagram showing front contrast (CR) and chroma difference (C *) at each duty with respect to Δnd of a film substrate when a twist angle of liquid crystal molecules is 220 °.

FIG. 5 is a diagram showing front contrast (CR) and chroma difference (C *) at each duty with respect to Δnd of a film substrate when a twist angle of liquid crystal molecules is 200 °.

6A to 6D show liquid crystal molecules having a twist angle of 24.
Due to the arrangement relationship at 0 °, Δnd of the film substrate is 0,
The figure which shows the transmittance | permeability with respect to the applied voltage when it drives at 1/4 duty in 5, 10, 20 nm, (a)-.
(D) is a chromaticity diagram for each.

7A to 7D show a liquid crystal molecule having a twist angle of 24.
Due to the arrangement relationship at 0 °, Δnd of the film substrate is 0,
The figure which shows the transmittance | permeability with respect to the applied voltage when it drives with 1/48 duty in 5, 10 and 20 nm, (a)-
(D) is a chromaticity diagram for each.

[Explanation of symbols]

 1 Film Liquid Crystal Cell 2, 5 Electrodes 3, 6 Alignment Film 3a Incident Side Orientation Treatment Direction 4 Incident Side Film Substrate 7 Emission Side Film Substrate 9 Liquid Crystal 10 Polarizer 10a Transmission Axis 11 Analyzer 11a Transmission Axis 12 Phase Plate 12a Optical Axis

Claims (4)

[Claims] 1. A pair of flexible film substrates having a pair of flexible film substrates, wherein electrodes facing each other are provided with electrodes intersecting each other and an alignment film covering the electrodes and subjected to an alignment treatment in a predetermined direction. A film liquid crystal cell enclosing a liquid crystal in twist alignment, a pair of polarizing plates arranged outside the film liquid crystal cell, and a phase plate arranged between the pair of polarizing plates, The molecules of the liquid crystal are twisted in the range of 180 ° to 360 ° from the one film substrate to the other film substrate, and the transmission axis of the one polarizing plate is an alignment treatment of the alignment film of the one film substrate. 12 to the direction
It intersects in the range of 0 ° to 150 °, the transmission axis of the other polarizing plate intersects in the range of 80 ° to 105 ° with respect to the alignment treatment direction, and the optical axis of the phase plate extends in the alignment treatment direction. In the liquid crystal display device, the pair of film substrates intersect with each other in a range of 5 ° to 30 °, and the optical axes of the pair of film substrates intersect with the optical axis of the phase plate at a predetermined angle. 2. The product Δnd of the refractive index anisotropy Δn of each film substrate and the thickness d of each film substrate is 20 nm or less in each of the pair of film substrates. And the liquid crystal display device according to 2. 3. The liquid crystal has a product Δnd of refractive index anisotropy Δn and liquid crystal layer thickness d of 850 nm, and the phase plate has a product Δnd of refractive index anisotropy Δn and thickness d. The liquid crystal display device according to claim 1 or 2, wherein the value of is 570 nm. 4. A liquid crystal in which twist alignment is performed between a pair of flexible film substrates in which an electrode is formed on each of opposite surfaces and an alignment film is formed so as to cover the electrodes and which is subjected to an alignment treatment in a predetermined direction. A film liquid crystal cell encapsulating, a pair of polarizing plates arranged outside the film liquid crystal cell so as to sandwich it, and a phase plate arranged between the pair of polarizing plates, wherein the liquid crystal molecule Is twist-oriented from one film substrate to the other film substrate, and in the pair of film substrates, the product Δnd of the refractive index anisotropy Δn of each film substrate and the thickness d of each film substrate is not more than a predetermined value. A liquid crystal display device characterized by the following.