JPH0444006A - Liquid crystal display device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device using a liquid crystal cell in which liquid crystal molecules are arranged in a twisted manner at a twist angle of 1800 to 2600.

[Conventional technology]

A liquid crystal display device includes a liquid crystal cell in which liquid crystal is sealed between a pair of transparent substrates each having a transparent electrode and an alignment film formed on one surface, and the molecules of this liquid crystal are arranged in a twisted manner between the two substrates.
It consists of a pair of polarizing plates arranged on both sides of this liquid crystal cell, and the liquid crystal cell is generally of the TN type in which liquid crystal molecules are arranged in a twisted manner at a twist angle of approximately 90°. .

Incidentally, in recent years, liquid crystal display devices that display television images, etc. have been increasing the number of pixels in order to achieve larger screens and higher resolutions, and as a result, they have become time-divisionally driven with high duty. ing.

However, in the liquid crystal display device using the TN type liquid crystal cell, the response time of the liquid crystal to the application of the display drive voltage is as fast as about 100 m5ec, but when time-division driving is performed at high duty, Because the problem is that the light transmittance is extremely reduced and the display becomes dark,
BACKGROUND ART A liquid crystal display device driven in a time-division manner at a high duty cycle uses an STN type liquid crystal cell in which liquid crystal molecules are arranged in a twisted manner at a twist angle larger than that of a TN type liquid crystal cell.

This STN type liquid crystal cell generally has one liquid crystal molecule.
A liquid crystal arranged in a twisted manner with a twist angle of 80° to 260° is used, and the liquid crystal used has a refractive index anisotropy Δn of about 0.1'31 m. In addition, the layer thickness (cell gap) d of the liquid crystal layer of this STN type liquid crystal cell is approximately 7 mm, which is larger than the liquid crystal layer thickness of the TN type liquid crystal cell, and the retardation Δn-d (liquid crystal The value of the product of the refractive index anisotropy Δn and the liquid crystal layer thickness d is about 0.9 μm, which is larger than the thickness of a TN type liquid crystal cell.

In a liquid crystal display device using this STN type liquid crystal cell, the liquid crystal layer thickness of the liquid crystal cell is larger than the liquid crystal layer thickness of a TN type liquid crystal cell, so the display drive voltage applied is lower than that of a liquid crystal display device using a TN type liquid crystal cell. The response time of the liquid crystal to
Although it is slow at 0a+sec, the retardation of the liquid crystal cell is large, and the twist angle of the liquid crystal molecules is large, so the optical rotation of the transmitted light is also large, so even with high duty and time division driving, the light transmission when ON (light transmission) is low. A brighter display can be obtained by increasing the ratio.

[Problem to be solved by the invention]

However, although liquid crystal display devices using conventional STN type liquid crystal cells can provide bright displays, a certain amount of light still passes through even at 0FF (light cutoff), so the contrast
The brightness ratio between the ON part and the OFF part is poor, and since the retardation and optical rotation of the liquid crystal cell are large, the wavelength dependence of the retardation and optical rotation is large, resulting in coloring of the display.

This is because the light that is linearly polarized by the polarizing plate on the input side and enters the liquid crystal cell becomes elliptically polarized light due to the wavelength dependence of the liquid crystal cell, causing a phase difference in each wavelength light. When elliptically polarized light enters the output polarizing plate in this way, the polarized light component in the direction of the absorption axis of this polarizing plate does not pass through the polarizing plate, but the polarized light component perpendicular to the absorption axis direction passes through the polarizing plate. This leaked light reduces the degree of darkness in the OFF part, which should be black.
Contrast is reduced. In addition, in the conventional liquid crystal display device described above, since the elliptically polarized light enters the polarizing plate on the output side, the ON
Even when the output side is off, light of a specific wavelength is absorbed by the output side polarizing plate or transmitted through the output side polarizing plate, so that the light transmitted through the output side polarizing plate is colored.

Figure 8 shows the spectrum of the transmitted light of a conventional liquid crystal display device.As shown in this spectrum, the difference in transmittance between the ON and OFF states of the conventional liquid crystal display device is small, and therefore the transmittance is sufficient. Moreover, since the transmittance of each wavelength light is not equal both when ON and OFF, the display is colored by the color of the wavelength light with high transmittance. Note that the coloring of this display is yellowish or blueish, and therefore conventional display devices are called yellow mode or blue mode.

The present invention has been made in view of the above circumstances, and its purpose is to adjust liquid crystal molecules from 180° to 180°.
Although it uses an STN type liquid crystal cell arranged in a twisted arrangement with a twist angle of 260°, it reduces light leakage when OFF (light blocking), and also reduces light leakage when ON (light transmission).
To provide a liquid crystal display device capable of displaying high-quality images by increasing light transmittance and contrast, and eliminating coloring of the display.

[Means to solve the problem]

The present invention provides a liquid crystal cell in which a liquid crystal is sealed between a pair of transparent substrates each having a transparent electrode and an alignment film formed on one surface, and molecules of this liquid crystal are arranged in a twisted manner between the two substrates at a twist angle of 180° to 260°. , a liquid crystal display device including a pair of polarizing plates placed on both sides of the liquid crystal cell,
Two phase plates are arranged between the liquid crystal cell and one polarizing plate, and of the two phase plates, the phase plate on the liquid crystal cell side is a ]/1 wavelength phase plate, and the phase plate on the polarizing plate side is The phase plate of 1/
In addition to using a single wavelength phase plate, the retardation of the liquid crystal cell is 0.7 to 1.0 μm, and the retardation of the wavelength phase plate to 1 on the liquid crystal cell side is 500 nm to 600n+n.
/4, the retardation of the wavelength phase plate to 1 on the polarizing plate side is 4
00 nm to 700 nm.

The liquid crystal sealed in the liquid crystal cell has a refractive index anisotropy or 0. I[I7a or higher liquid crystal is preferable.

[Effect]

That is, the liquid crystal display device of the present invention has liquid crystal molecules of 180
Elliptically polarized light transmitted through a liquid crystal cell twisted at a twist angle of 260° to 260° is returned to linearly polarized light by two phase plates placed between the liquid crystal cell and one polarizing plate. As described above, the phase plate on the liquid crystal cell side is a 1/1 wavelength phase plate, the phase plate on the polarizing plate side is a 1/1 wavelength phase plate, and the liquid crystal cell and the 1/1 wavelength phase plate and the 1/1 wavelength phase plate are If the retardation of each 1-wavelength phase plate is set as above, the liquid crystal cell and 1/
The polarization amplitude in the X-axis direction and the polarization amplitude in the Y-axis direction of the light transmitted through both the four-wavelength phase plate are approximately constant over almost the entire visible light region, and furthermore, the polarization amplitude in the X-axis direction and the polarization amplitude in the Y-axis direction of the light transmitted through both the four-wavelength phase plate and the liquid crystal cell are approximately constant over almost the entire visible light region.
The light transmitted through the 4-wavelength phase plate and the 1/1-wavelength phase plate becomes linearly polarized light with almost no phase difference between each wavelength light in almost the entire visible light region. Note that this effect is the same when light is incident from any direction; when light is incident from the liquid crystal cell side, the elliptically polarized light transmitted through the liquid crystal cell changes to 1 wavelength phase plate and 1/1 When the light passes through the wavelength phase plate and becomes linearly polarized light, and the light enters from the opposite side, the incident light passes through the 1/1 wavelength phase plate and the 1/4 wavelength phase plate to compensate for the wavelength dependence of the liquid crystal cell. After that, it is transmitted through a liquid crystal cell and becomes linearly polarized light due to its wavelength dependence. Therefore, according to the present invention, the light that has passed through the liquid crystal cell can be made to enter the output side polarizing plate as linearly polarized light, and if the light that is incident on the output side polarizing plate is linearly polarized, it is 0FF (light blocking). Light leakage when turned on is almost eliminated, and light of a specific wavelength is not absorbed by the output side polarizing plate when turned on (light transmission), which reduces light leakage when turned off and reduces light transmission when turned on. It is possible to increase the contrast by increasing the ratio, and since the light of a specific wavelength is not absorbed by the polarizing plate on the output side or transmitted through the polarizing plate on the output side, high quality can be achieved without coloring the display. images can be displayed.

Further, in this liquid crystal display device, it is preferable that the liquid crystal sealed in the liquid crystal cell be a liquid crystal having a refractive index anisotropy of 0.1B7z+n or more, and if the refractive index anisotropy of the liquid crystal is increased in this way, Since it is possible to reduce the thickness of the liquid crystal layer required to make the liquid crystal cell thickness the above value (07 to 1.On), the response time of the liquid crystal to the application of the display drive voltage can be shortened. Responsiveness can also be improved.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 7.

FIG. 1 is a sectional view of the liquid crystal display device of this embodiment. In this liquid crystal display device, a pair of polarizing plates 21 and 22 are arranged on both sides of an STN type liquid crystal cell 10, and two phase plates 31 and 32 are arranged between the liquid crystal cell 10 and one polarizing plate. In this embodiment, the phase plate 31.3
2 is disposed between the liquid crystal cell 10 and the output side polarizing plate (the upper polarizing plate in the figure) 22.

The liquid crystal cell 10 includes a pair of transparent substrates 1 made of glass.
1.12 is bonded via a frame-shaped sealing material 13, and a liquid crystal 18 is sealed in the gap surrounded by the sealing material 13 between the side substrates 11.12. ) A large number of striped transparent scanning electrodes 14 are arranged parallel to each other on the surface facing the liquid crystal layer 11.
The scanning electrode 14 is provided on the surface of the emission side substrate 12 facing the liquid crystal layer.
A large number of striped transparent signal electrodes 14 are arranged in parallel to each other and perpendicular to each other.

Furthermore, on the electrode formation surfaces of the side substrates 11 and 12, alignment films 16 and 17 whose surfaces are subjected to an alignment treatment by rubbing are formed, respectively, and the liquid crystal 18 sealed between the two prefecture plates 11 and 12 is Due to the alignment regulating force of the alignment films 16°1 and 7, the side substrates 11 and 12 are twisted at a twist angle of 180° to 260°. Further, the value of retardation Δnod (product of refractive index anisotropy Δn of liquid crystal and liquid crystal layer thickness d) of this liquid crystal cell 10 is 0.71 to 1.0.
-, and in this example, the value of the refractive index anisotropy Δn of the liquid crystal 18 sealed in the liquid crystal cell 10 is 0. Using a liquid crystal of L6 or higher, the layer thickness (cell gap) d of the liquid crystal layer is set according to the refractive index anisotropy Δn of this liquid crystal 18, and the retardation Δn-d of the liquid crystal cell 10 is set to the above value (0 ,7-~
1.1bzu+). Note that this liquid crystal cell 10
may display a black-and-white monochrome image or a full-color image. When displaying a full-color image on the liquid crystal cell 10, red, It is sufficient to provide green and blue color filters.

1] On the other hand, among the two phase plates 31 and 32 arranged between the liquid crystal cell 10 and the output side polarizing plate 22, the phase plate on the liquid crystal cell 10 side is a 1/4 wavelength phase plate, and the polarizing plate The phase plate 32 on the 22 side is a 1/4 wavelength phase plate, and the phase plate 32 on the liquid crystal cell side 1
- Retardation Δnod of 1/1 wavelength phase plate 31 of 0
(The product of the refractive index anisotropy Δn of the phase plate and the plate thickness d) is 500
nm to 1/4 of 600 nm, and 1/4 on the polarizing plate 22 side.
The retardation Δn-d of the I-wavelength phase plate 32 is 400n
m ~700 nm.

The 1/4 wavelength phase plate 31, the 1/4 wavelength phase plate 32, and the polarizing plates 21, 22 on the incident side and the output side are arranged with their axial directions aligned in the following directions. .

FIG. 2 shows the liquid crystal molecule alignment direction (rubbing direction of the alignment films 16 and 17) on both the plates 1'l and 12 of the liquid crystal cell 10, the fast axis direction of the phase plates 31 and 32, and the polarizing plate. 2
As shown in FIG. 2(a), the liquid crystal molecule orientation 12a on the output side substrate 12 of the liquid crystal cell 10 is on the incident side. The liquid crystal molecule orientation 11a on the side substrates 11 and 12 is shifted clockwise by the twist angle (180° to 260°) θ of the liquid crystal molecules with respect to the liquid crystal molecule orientation 11a on the substrate 11 surface.

Each of the lines 12a intersects the horizontal line in the viewing angle direction of the liquid crystal display device at the same angle. Also, Figure 2 (
As shown in b), the fast axis direction 34a of the ]/4 wavelength phase plate 31 on the liquid crystal cell 10 side is at an angle of 90° to 100′ counterclockwise with respect to the liquid crystal molecule orientation 12a on the output side substrate 12 surface. The fast axis direction 31a of the l-c phase plate 32 on the polarizing plate 22 side is in the direction intersecting at an angle α2 of 100° to 150° counterclockwise with respect to the liquid crystal molecule alignment 12a. be. Further, as shown in FIGS. 2(C) and 2(d), the polarization axis direction 21a of the incident side polarizing plate 21 is rotated 1 counterclockwise with respect to the liquid crystal molecule orientation 11a on the incident/incident side substrate 11 surface.
The directions intersect at an angle β of 10° to 160°, and the polarization axis direction 22a of the output side polarizing plate 22 is 70° to 1 counterclockwise with respect to the liquid crystal molecule orientation 1.2a on the output side substrate 12 surface.
! JO'' at an angle γ.Here, clockwise and counterclockwise are both directions when viewed from the light output side.

In the liquid crystal display device of this example, light is blocked when the liquid crystal molecules of the liquid crystal cell 10 enter the initial alignment state by applying an OFF voltage, and the liquid crystal molecules rise to the alignment state by applying an ON voltage. It is a so-called negative mode display type in which light sometimes passes through, and the polarizing plate 2 on the incident side
1 and the polarization axis direction 22a of the output side polarizing plate 22 are set to angles within the range of the angles β and γ such that the display of the liquid crystal display device is in negative mode.

That is, the liquid crystal display device of this example has a liquid crystal molecule of 1
S twisted array with twist angle of 80°~260'
Two phase plates 31 and 32 are arranged between the TN liquid crystal cell 10 and the output side polarizing plate 22, and these two phase plates 31
．． 32, the phase plate 31 on the liquid crystal cell 10 side is a 174-wavelength phase plate, the phase plate 32 on the polarizing plate 22 side is a 1/1 wavelength phase plate, and the retardation Δn-d of the liquid crystal cell 10 is 0.7ρ. ~1.0 dust, 17 on the liquid crystal cell 10 side
The retardation Δn-d of the 4-wavelength phase plate 3 is 500n.
m ~ 1/4 of 600 nm, the retardation Δn-d of the wavelength phase plate 32 to 1 on the polarizing plate 22 side is 400 nm -7
According to this liquid crystal display device, since it uses an STN type liquid crystal cell in which liquid crystal molecules are arranged in a twisted manner at a twist angle of 180° to 260°, the It is possible to reduce light leakage, increase light transmittance when ON (light transmission), increase contrast, and display a high-quality image without coloring the display.

FIG. 3 shows the spectrum of transmitted light of the liquid crystal display device of the above example. As shown in this spectrum, this liquid crystal display device has a high transmittance when it is turned on, and when it is turned off.
The transmittance at this time is almost 0, and therefore a high contrast display can be obtained. In addition, in this liquid crystal display device, the transmittance when OFF is almost constant over almost all wavelengths in the visible light region, and the transmittance when ON is also at a high level over almost all wavelengths in the visible light region.
Coloring due to the wavelength dependence of the liquid crystal cell 10 does not occur in the display. The spectrum shown in FIG. 3 is based on the liquid crystal molecule twist angle θ and retardation Δn−d of the liquid crystal cell 10.
θ=220°, Δn-d=0.75 μm, ]/
The retardation Δn-d of the one-wavelength phase plate 31 is 520/
, 4 nm, ]-/1 wavelength phase plate 32 has a retardation Δn-d of 575 nm, and these quarter wavelength phase plate 31, I/1 wavelength phase plate 32, and polarizing plate 21
．． 22 to the axial angle α1.2.2 shown in FIG. β, γ
α1=75゜α (12=100", β-165', 7
This is the measured value when the angle is −135°.

The reason why it is possible to obtain a display with high contrast and no coloring is that the elliptically polarized light transmitted through the liquid crystal cell 10 is transferred to
phase plate 31. This is because the phase plate 31 on the liquid crystal cell 10 side is 1) a 4-wavelength phase plate, and the phase plate 32 on the polarizing plate 22 side is 1) 4-wavelength phase plate.
In addition to the wavelength phase plate, the liquid crystal cell ]0 and ]/44
If the retardation Δn-d of each of the wavelength phase plate 31 and the 1/1 wavelength phase plate 32 is set as described above, the light will pass through the liquid crystal cell 10 and will further pass through the 1/4 wavelength phase plate 31 and 1.71 wavelength. Since the light transmitted through the phase plate 32 becomes linearly polarized light with almost no phase difference in almost all wavelengths in the visible light region, it is possible to increase the contrast and eliminate coloring of the display.

Next, the operation of the 1/1 wavelength phase plate 31 and the 1/1 wavelength phase plate 32 will be explained.

FIG. 4 is a polarization vector diagram of the liquid crystal cell 10, and the polarization vector E varies depending on the wavelength dependence of the liquid crystal cell.
The linearly polarized light that has passed through the incident-side polarizing plate 21 and entered the liquid crystal cell 10 becomes elliptically polarized light corresponding to the locus E' of the polarization vector E.

This polarization vector E can be considered separately into a component force EX in the X-axis direction and a component force EY in the Y-axis direction. It is expressed as

EX = axcos (ω is 10Δ) Ey = aycos ωt ax Polarization amplitude in the HX-axis direction ay Polarization amplitude in the HY-axis direction ω; Angular frequency Δ; Phase of EX as seen from EY Also, the magnitude of polarization due to the polarization vector E is This is called dichroism, and the magnitude of this polarized light is expressed as tanv.

This tanlI' is determined by the ratio of the polarization amplitude aX in the X-axis direction and the polarization amplitude ay in the Y-axis direction.

FIG. 5 shows the polarization state of light transmitted through the liquid crystal cell 10 when an OFF voltage is applied, and FIG. b) shows the polarization magnitude janlF and the phase (phase difference of EX as seen from Ey) Δ of each wavelength light.

As shown in FIGS. 5(a) and (b), the liquid crystal cell]
For the elliptically polarized light that has passed through 0, the polarization amplitude aX+aY of each wavelength light in the X-axis direction and Y-axis direction changes greatly, and 1r also changes, and the phase Δ of each wavelength light also changes depending on the wavelength. This is light with a large phase difference that changes greatly.

However, when the light emitted from the liquid crystal cell 1o is passed through the 1/4 wavelength phase plate 31, this light is polarized due to the wavelength dependence of the 1/1 wavelength phase plate, and the light is polarized in the X-axis direction and Y-axis direction of each wavelength light. The polarized light amplitudes ax and aY in the directions are almost constant.

Figure 6 shows the liquid crystal cell when OFF voltage is applied] 0 and 1
/1-wavelength phase plate 31. Figure (a) shows the polarization amplitude aX + aY of each wavelength light in the X-axis direction and Y-axis direction, and Figure (b) shows the force and phase Δ of each wavelength of light. This figure 6 (a), (b)
), when the light transmitted through the liquid crystal cell 10 is passed through the 1/4 wavelength phase plate 31, the light transmitted through this 1/4 wavelength phase plate 31 has a polarization amplitude aX in the X-axis direction and a polarization amplitude aX in the Y-axis direction. The polarization amplitude ay becomes substantially constant over almost the entire visible light region, and the polarization amplitude ay also becomes substantially constant, and the wavelength at which the phase Δ changes significantly also shifts to the lower wavelength side.

Furthermore, the light that has passed through this 1/1 wavelength phase plate 31 is light that has a phase difference between each wavelength light, but this light is further passed through the I/1 wavelength phase plate 32 of a wavelength near which the phase difference is close to zero. When the light passes through the 1/] wavelength phase plate 32, the light becomes linearly polarized light with almost no phase difference between the respective wavelength lights.

Figure 7 shows liquid crystal cells 10 and 1 when OFF voltage is applied.
Figure (a) shows the polarization state of the light transmitted through the /1 wavelength phase plate 31 and the 1/1 wavelength phase plate 32. Figure (a) shows the polarization amplitude aX + aY of each wavelength light in the X-axis direction and the Y-axis direction. Figure (b) shows the phase Δ of each wavelength light. As shown in FIGS. 7(a) and 7(b), the light transmitted through the liquid crystal cell 10 and further transmitted through the 1/4 wavelength phase plate 31 is
When passed through the wavelength phase plate 32, the light transmitted through this l/1 wavelength phase plate 32 has a polarization amplitude aX in the X-axis direction and the Y-axis direction.
There is almost no change from +ay, but the phase of each wavelength light △
is almost constant over almost the entire visible light region, and therefore, this light becomes linearly polarized light with almost no phase difference between the wavelengths of light.

Note that the polarization states shown in FIGS. 5 to 7 are for liquid crystal cells]
A liquid crystal cell with a twist angle of liquid crystal molecules of 2400 and a liquid crystal layer thickness d or 3.5 μm is used as 0, a 570/4 nm wavelength phase plate 1 as the wavelength phase plate 31, and a 174 wavelength phase plate 31 as the wavelength phase plate 32. Using a 620 nm wavelength phase plate with a phase Δ of the emitted light near zero, the liquid crystal cell]0 electrode 14. ] -5+1O, 11iV OFF voltage is applied.

In this way, according to the liquid crystal display device of the above embodiment, the light that has passed through the liquid crystal cell]0 can be made to enter the output side polarizing plate 22 as linearly polarized light, and the light that is incident on the output side polarizing plate 22 can be If it is linearly polarized light, there will be almost no light leakage when it is OFF, and light of a specific wavelength will not be absorbed by the polarizing plate on the output side when it is ON, so the spectrum will be as shown in Figure 3. , it is possible to reduce the leakage of light when OFF and also increase the light transmittance when ON, thereby increasing the contrast. In addition, light of a specific wavelength can be absorbed by the output side polarizing plate 22 or the output side polarized light can be Since the light does not pass through the plate 22, a high quality image can be displayed without coloring the display. This is true not only for liquid crystal display devices that display black and white monochrome images, but also for liquid crystal display devices that display full-color images. It does not take on the color of
Also colored red with a color filter.

There is no possibility that the green or blue display will take on other colors and cause color shift.

Moreover, in the above embodiment, the liquid crystal sealed in the liquid crystal cell 22 has a refractive index anisotropy of 0. Since the liquid crystal is larger than l [i, ci, it is possible to reduce the liquid crystal layer thickness d required to make the retardation Δn-d of the liquid crystal cell 1o the above value (0.71# to 1.C1gm). If the liquid crystal layer thickness d of the liquid crystal cell [0] can be reduced in this way, the response time (response) of the liquid crystal to the application of the display drive voltage will be shortened, and the responsiveness can also be improved.

In other words, the table below compares the liquid crystal response times of a liquid crystal display device using a TN type liquid crystal cell, a liquid crystal display device using a conventional STN type liquid crystal cell, and the liquid crystal display device of the above example. It shows.

As shown in this table, the liquid crystal display device of the above example has a liquid crystal response time several times that of a liquid crystal display device using a conventional STN type liquid crystal cell, which is almost comparable to the liquid crystal response time of a TN type liquid crystal cell. Therefore, the liquid crystal can be operated at high speed even though it uses an STN type liquid crystal cell which has excellent time-division drive performance at high duty.

In the above embodiment, the side on which the phase plates 31 and 32 are arranged is the light incident side, or the liquid crystal display device is
．． It is also possible to use the side on which 32 is not arranged as the light incidence side, in which case the incident light will pass through the 1/1 wavelength phase plate 3.
2 and ]/1 wavelength through the phase plate 31 and the liquid crystal cell 10
The light is polarized in a state that compensates for the wavelength dependence of the light, and then is transmitted through the liquid crystal cell 10 and becomes linearly polarized light due to the wavelength dependence.

〔Effect of the invention〕

In the liquid crystal display device of the present invention, two phase plates are arranged between a liquid crystal cell and one polarizing plate, and of these two phase plates, the phase plate on the liquid crystal cell side has a wavelength of 1/4. The phase plate on the polarizing plate side is a 1/1 wavelength phase plate, and the retardation of the liquid crystal cell is set to 0.7 μm to 1.0 μm.
1 Set the retardation of the 1/4 wavelength phase plate on the liquid crystal cell side to 5.
Since the retardation of the wavelength phase plate is set to 400 nm to 700 nm, the light transmitted through the liquid crystal cell is
The 1-wavelength phase plate and the 1/1-wavelength phase plate allow linearly polarized light to be incident on the output side polarizing plate. Therefore, the STN type liquid crystal cell has liquid crystal molecules arranged in a twisted manner at a twist angle of 180° to 260°. However, it reduces light leakage when OFF (light blocking), increases light transmittance when ON (light transmission), increases contrast, and eliminates coloring of the display. High quality images can be displayed.

In addition, in this liquid crystal display device, if the liquid crystal sealed in the liquid crystal cell is a liquid crystal with a refractive index anisotropy of 0.1 B, cm or more, the retardation of the liquid crystal cell is set to the above value (0,
Since it is possible to reduce the thickness of the liquid crystal layer necessary to achieve a display voltage of 7 to 1.0, it is possible to shorten the response time of the liquid crystal to the application of the display drive voltage and improve responsiveness.

[Brief explanation of the drawing]

1 to 7 show an embodiment of the present invention, in which FIG. 1 is a cross-sectional view of a liquid crystal display device, and FIG. 2 shows the orientation direction of liquid crystal molecules and the phase plate on both sides of the liquid crystal cell. Figure 3 is a diagram showing the spectrum of transmitted light of the liquid crystal display device, Figure 4 is a polarization vector diagram of the liquid crystal cell, and Figure 5 is the OFF voltage. Figure 6 shows the polarization state of light transmitted through the liquid crystal cell when the voltage is applied.
Figure 7 shows the polarization state of light transmitted through the liquid crystal cell and the 1/1 wavelength phase plate when the F voltage is applied. FIG. 3 is a diagram showing the polarization state of light transmitted through the . FIG. 8 is a diagram showing the spectrum of transmitted light of a liquid crystal display device using a conventional STN type liquid crystal cell. 10...Liquid crystal cell, 11.12...Transparent substrate, 14
...Scanning electrode, 15...Signal electrode, 16.17...
・Alignment film, 18...Liquid crystal, 21.22...Polarizing plate,
31...1/1 wavelength phase plate, 32...1/1 wavelength phase plate. Applicant's agent Patent attorney Takehiko Suzue 22nd

Claims (2)

[Claims] (1) A liquid crystal cell in which a liquid crystal is sealed between a pair of transparent substrates each having a transparent electrode and an alignment film formed on one surface, and the molecules of this liquid crystal are arranged in a twisted manner between the two substrates at a twist angle of 180° to 260°; In a liquid crystal display device including a pair of polarizing plates arranged on both sides of the liquid crystal cell, two phase plates are arranged between the liquid crystal cell and one polarizing plate, and the two phase plates are arranged between the liquid crystal cell and one polarizing plate. Among the plates, the phase plate on the liquid crystal cell side is a 1/4 wavelength phase plate, and the phase plate on the polarizing plate side is a 1/1 wavelength phase plate, and the retardation of the liquid crystal cell is 0.7 μm to 1.0 μm. Set the retardation of the 1/4 wavelength phase plate on the liquid crystal cell side to 500 nm to 600 nm.
/4, A liquid crystal display device characterized in that the retardation of the 1/1 wavelength phase plate on the polarizing plate side is 400 nm to 700 nm. (2) The liquid crystal sealed in the liquid crystal cell has a refractive index anisotropy of 0.
The liquid crystal display device according to claim 1, characterized in that the liquid crystal is 16 μm or more.