JPH04190325A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To display a high quality image with high contrast and without coloring of a display by disposing two phase plates between a liquid crystal cell and one polarizing plate. CONSTITUTION:A value of retardation of a phase plate 31 on the liquid cell side is such a value that when light which goes out from a liquid crystal cell 10 and transmits the phase plate 31 is disposed on a Poincare sphere to be seen, the wavelength light of a visible light band is distributed in the vicinity along the peripheral edge of a section taken by cutting a Poincare sphere in a plane, and a value of retardation of a phase plate 32 on the polarizing plate side is such a value that when light which transmits the phase plate 31 and then transmits the phase plate 32 is disposed on a Poincare sphere to be seen, the wavelength light of a visible light band is distributed in such a manner as to be concentrated on the vicinity of one point on the equator on the Poincare sphere. Accordingly, light which transmits the liquid cell can be forced to enter the outgoing side polarizing plate as linearly polarized light. Thus, in the off-state, leak of light can be decreased and in the on-state, the light transmissivity can be heightened to heighten the contrast, and further a high quality image can be displayed without coloring of a display.

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 180° to 270°.

[Conventional technology]

A liquid crystal display device consists of 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 thereon, and the molecules of this liquid crystal are arranged in a twisted manner between the two substrates, and a liquid crystal cell placed before and after the liquid crystal cell. The liquid crystal cell is generally a TN cell in which liquid crystal molecules are arranged in a twisted manner at a twist angle of approximately 90''.
type is used.

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 a liquid crystal display device using the TN type liquid crystal cell, the response time of the liquid crystal to the application of a display drive voltage is as fast as about 100a+sec, but when time-divisionally driven at high duty, Due to the problem of extremely low light transmittance and dark display, high-duty, time-divisionally driven liquid crystal display devices are
An STN type liquid crystal cell is used, 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 arrangement with a twist angle of 80° to 270° is used, and the liquid crystal used has a refractive index anisotropy Δn of about 130 ns+.

In addition, the layer thickness (cell gap) d of the liquid crystal layer of this STN type liquid crystal cell is approximately 7 μm, 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 refractive index anisotropy Δn and liquid crystal layer thickness d is about 700 nm to 11000 nm, which is larger than the retardation 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 compared to a liquid crystal display device using a TN type liquid crystal cell, the applied display drive voltage is The response time of the liquid crystal to
It is slow at 0a+sec, the liquid crystal cell polarity is large, and the twist angle of the liquid crystal molecules is large, so the optical rotation of the transmitted light is large (from 1, even if time-division driving is performed at high duty, the light transmittance when ON is You can increase the height to get a brighter display.

[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 incident side and enters the liquid crystal cell becomes elliptically polarized light due to a phase difference between each wavelength light due to the wavelength dependence of the liquid crystal cell, and this elliptically polarized light exits the liquid crystal cell. This is because the light enters the polarizing plate on the output side.
When elliptically polarized light enters the output-side polarizing plate in this way, the polarized light component in the absorption axis direction 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, so this leakage occurs. Due to light, the degree of darkness of the OFF portion that should be black decreases, and the contrast decreases.

In addition, in the conventional liquid crystal display device described above, since elliptically polarized light enters the output side polarizing plate, both when ON and OFF, light of a specific wavelength is absorbed by the output side polarizing plate, or when the output side polarizing plate is Therefore, the light transmitted through the output side polarizing plate becomes colored.

FIG. 11 shows the spectrum of 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. I can't get a good contrast,
Further, 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 reduce liquid crystal molecules to 180'.
Although it uses an STN type liquid crystal cell arranged in a twisted arrangement with a twist angle of ~270°, it reduces light leakage when OFF (light blocking) and has high light transmittance when ON (light transmission). An object of the present invention is to provide a liquid crystal display device capable of displaying high-quality images with high contrast and without display coloring.

[Means to solve the problem]

In the present invention, a liquid crystal is sealed between a pair of transparent substrates each having a transparent electrode and an alignment film formed thereon, and molecules of this liquid crystal are placed between the two substrates at an angle of 18° to 27°.

In a liquid crystal display device comprising a liquid crystal cell arranged in a twisted manner with a twist angle of and among these two phase plates, the retardation value of the first phase plate located on the liquid crystal cell side is determined by the value of the retardation of the light emitted from the liquid crystal cell and transmitted through this first phase plate. When viewed on the Poincaré sphere, the wavelength light in the visible light band is distributed along the peripheral line of the cut plane when the Poincaré sphere is cut in a plane, and the polarizing plate side The retardation value of the second phase plate located at It is characterized in that wavelength light in the visible light band is distributed in a concentrated manner around a point on the equator of the Poincaré sphere.

[For production]

That is, the liquid crystal display device of the present invention has liquid crystal molecules of 180
Light that becomes elliptically polarized light in a liquid crystal cell arranged in a twisted manner with a twist angle of 270° to 270° is corrected to linearly polarized light by two phase plates placed between the liquid crystal cell and one polarizing plate. As mentioned above, the retardation value of the phase plate on the liquid crystal cell side is determined by the visible light band when the light emitted from the liquid crystal cell and transmitted through this first phase plate is placed on the Poincaré sphere. When the Poincaré sphere is cut by a plane, the wavelength light is distributed along the peripheral line of the cut surface in the vicinity thereof, and the value of the retardation of the second phase plate on the polarizing plate side is set to the value of the retardation of the liquid crystal cell. When the light that is emitted, passes through the first phase plate, and then passes through the second phase plate is placed on the Poincare sphere and viewed, the wavelength light in the visible light band is near a point on the equator of the Poincare sphere. If we assume that the value is concentrated and distributed, then the light that passes through the first phase plate and the second phase plate after exiting the liquid crystal cell will have almost no phase difference between each wavelength light in almost the entire visible light band. It becomes linearly polarized light.

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 emitted from the liquid crystal cell passes through the first phase plate and the second phase plate. When the light passes through the phase plate and becomes linearly polarized light, and the light enters from the opposite side, the incident light passes through the second phase plate and the first phase plate, compensating for the wavelength dependence of the liquid crystal cell. The light is polarized and then transmitted through a liquid crystal cell, becoming 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, the OF
There is almost no light leakage when F (light cutoff), and especially when it is ON (light transmission).

Since light of a certain wavelength is not absorbed by the output side polarizing plate, it is possible to reduce light leakage when OFF and also increase light transmittance when ON, increasing contrast. Since light of a specific wavelength is neither absorbed by the output polarizing plate nor transmitted through the output polarizing plate,
High quality images can be displayed without coloring the display.

I will refer to and explain.

FIG. 1 is a sectional view of the liquid crystal display device of this embodiment. This liquid crystal display device has 13 pairs of polarizing plates 21 and 22 arranged on both sides of an STN liquid crystal cell 10, and two phase plates 31 and 32 between the liquid crystal cell 1o and one polarizing plate.
In this embodiment, the phase plates 31.
32 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 this side substrate 11. A liquid crystal 18 is sealed in a gap surrounded by a sealing material 13, and a large number of striped transparent scanning electrodes 14 are arranged parallel to each other on the surface of the incident side substrate (lower substrate in the figure) 11 facing the liquid crystal layer. The scanning electrodes 1 are formed in an array on the surface of the output side substrate 12 facing the liquid crystal layer.
4, a large number of striped transparent signal electrodes 14 are arranged in parallel to each other.

In addition, on the electrode formation surfaces of both substrates 11 and 12, alignment films 16 and 17, whose surfaces are subjected to alignment treatment by rubbing, are formed, respectively, and the molecules of liquid crystal 18 sealed between both substrates 11 and 12 are formed. is 180' to 270'' between the two substrates 11° and 12 due to the alignment regulating force of the alignment films 16 and 17.
Twisted array with a twist angle of . Further, the value of the retardation Δnlo'dlO (the product of the refractive index anisotropy Δn of the liquid crystal and the liquid crystal layer thickness d1o) of this liquid crystal cell 10 is 700n■ to 1000n-, and in this example,
The liquid crystal 18 sealed in the liquid crystal cell 10 has a refractive index anisotropy Δ
n. Use a liquid crystal with a value of 16 on 1 or more, and use this liquid crystal 1
Refractive index anisotropy Δn, of 8. The layer thickness (cell gap) of the liquid crystal layer (cell gap) d+. and set the retardation Δn1°·dl of the liquid crystal cell 10. is set to the above value. In addition,
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 is applied to each scanning electrode 14 or each signal electrode 15, respectively.

It is sufficient to provide green and blue color filters.

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 first phase plate 31 on the liquid crystal cell 10 side is a 174-wavelength phase plate, and the polarizing plate 22
The second phase plate 32 on the side is a 1-wavelength phase plate.

Then, the retardation Δn31·d of the first phase plate 31
, 1 (product of refractive index anisotropy Δn31 and plate thickness d31 of the phase plate) is the retardation Δrl+o of the liquid crystal cell 10
-d+o(Δn1o-d1゜m-700nffl~10
1000n, the liquid crystal cell 10 emits this first light.
When the light transmitted through the phase plate 31 is placed on the Poincare sphere and viewed, the wavelength light in the visible light band is distributed along the peripheral line of the cut plane when the Poincare sphere is cut by a plane. It is said that In this embodiment, the retardation Δn31''dl1 of the first phase plate 31 is 125r+m ~1
It is 50 nm.

Moreover, the retardation Δn3□・d3 of the second phase plate 32
The value of 2 is the retardation Δn+od of the liquid crystal cell 10
l. and the retardation Δn31 of the first phase plate 31.
d3, the liquid crystal cell 10 emits light and the first phase plate 3
When the light that has passed through the second phase plate 32 after passing through the second phase plate 32 is viewed on the Poincare sphere, the wavelength light in the visible light band is concentrated and distributed near one point on the equator of the Poincare sphere. It is considered a value. In this embodiment, the retardation Δn32'd32 of the second phase plate 32 is 400nw ~ 7
00ns.

The first phase plate 31 and the second phase plate 32, the incident-side polarizing plate 21, and the exit-side polarizing plate 22 are arranged with their optical axes aligned in the following directions.

FIG. 2 shows the alignment direction of liquid crystal molecules on both substrates 11 and 12 surfaces of the liquid crystal cell 10 (rubbing direction of alignment films 16 and 17).
, the direction of the fast axes of the phase plates 31 and 32, and the polarizing plate 2
As shown in FIG. 2(a), the direction of the polarization axis (transmission axis or absorption axis) of 22 is shown.
The liquid crystal molecule orientation direction 12a on the output side substrate 12 surface is shifted clockwise by a twist angle (180° to 270°) θ of the liquid crystal molecules with respect to the liquid crystal molecule orientation direction 11a on the input side substrate 11 surface. Liquid crystal molecule orientation direction 1 on substrate 11.12 plane
1a and 12a each intersect at the same angle with respect to the horizontal line Z in the viewing angle direction of the liquid crystal display device. Also,
As shown in FIG. 2(b), the fast axis 31a of the first phase plate 31 on the - side of the liquid crystal cell 10 rotates counterclockwise with respect to the liquid crystal molecule orientation direction 12H on the output side substrate 12 surface of the liquid crystal cell 10. 90 to
The fast axis 31a of the second phase plate 32 on the polarizing plate 22 side is at an angle of 100° to 150° counterclockwise with respect to the liquid crystal molecule alignment direction 12a. It is in the direction that intersects at α2. Furthermore, Figure 2 (C
), (d), the polarization axis 2 of the incident side polarizing plate 21
1a is in a direction that intersects the liquid crystal molecule alignment direction 11a on the incident side substrate 11 surface of the liquid crystal cell 10 at an angle β of 110° to 160° counterclockwise, and the polarizing axis 22a of the output side polarizing plate 22 is The direction intersects the liquid crystal molecule alignment direction 12a on the output side substrate 12 surface of the liquid crystal cell 10 at an angle γ of 70° to 190° counterclockwise. Here, clockwise rotation and counterclockwise rotation both refer to 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 application of an OFF voltage, and the liquid crystal molecules rise and enter the alignment state by application of 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 within the range of the angles β and γ as described above, so that the display of the liquid crystal display device is in a 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° to 270°
Two phase plates 31 and 32 are arranged between the TN liquid crystal cell 10 and the output side polarizing plate 22, and among these two phase plates 31 and 32, the first phase plate 31 on the liquid crystal cell 10 side The value of retardation Δn31・d3+ is determined from the liquid crystal cell 10.
retardation Δn1o−d1o(Δn to−d
+o-700nm to 1000rv), when the light emitted from the liquid crystal cell 10 and transmitted through the first phase plate 31 is arranged on the Poincaré sphere, the wavelength light in the visible light band is
When the Poincaré sphere is cut by a plane, the values distributed along and around the peripheral line of the cut plane (Δn31・d3+=1
25 nm to 150 na+) and the second polarizer on the polarizing plate 22 side.
The value of retardation Δn32・d32 of the phase plate 32 is
When the light that is emitted from the liquid crystal cell 10, passes through the first phase plate 31, and then passes through the second phase plate 32 is placed on the Poincare sphere and viewed, the wavelength light in the visible light band is located on the equator of the Poincare sphere. Values concentrated around one point (Δn, 2・
d 32-40On+g ~700nm), and according to this liquid crystal display device, the liquid crystal molecules are aligned at 180°.
Although it uses an STN type liquid crystal cell arranged in a twisted arrangement with a twist angle of ~270°, it reduces light leakage when OFF (light blocking) and has high light transmittance when ON (light transmission). By doing so, it is possible to display high-quality images with high contrast and without display coloration.

FIG. 3 shows the spectrum of the transmitted light of the liquid crystal display device of the above example, and like this spectrum,
This liquid crystal display device has high transmittance when ON, and also has high transmittance when ON.
The transmittance at F is almost 0, and therefore a high contrast display can be obtained. In addition, in this liquid crystal display device, the transmittance when turned off is almost constant over almost all wavelengths in the visible light band, and the transmittance when turned on is also at a high level over almost all wavelengths in the visible light band. Coloration due to wavelength dependence of the liquid crystal cell 10 does not occur. The spectrum shown in FIG. 3 is based on the liquid crystal molecule twist angle θ and retardation Δn of the liquid crystal cell 10.
to' d 10, θ-220'.

Δn + o - d r o - 750 nm, and the first phase plate 3
The retardation Δn31''d31 of the second phase plate 32 is 130 nm, and the retardation Δn32'd32 of the second phase plate 32 is 57 nm.
5 nm, and this first phase plate 31 and second phase plate 31
The phase plate 32 and the polarizing plate 21.22 are arranged at an axial angle α1.2.2 as shown in FIG. β and γ are respectively α1-α 75°, α2-100°, β-165°, γ-135'
This is the measured value when

The reason why a display with high contrast and no coloration can be obtained is that the elliptically polarized light emitted from the liquid crystal cell 10 is transmitted to
This is because the light is returned to linear polarization by the polarization action of the phase plates 31 and 32.If the retardations Δn31・d3□ and Δn32・d32 of the phase plates 3''1 and 32 are respectively set to the above values, Since the light emitted from the liquid crystal cell 10 and further transmitted through the first phase plate 31 and the second phase plate 32 becomes linearly polarized light with almost no phase difference in almost all wavelengths in the visible light band, the contrast can be increased and the display can be improved. Coloring can also be removed.

Next, the polarization state of light in the liquid crystal display device will be explained using a Poincaré sphere.

FIG. 4 shows the Poincaré sphere, which is generally used as a method of expressing the polarization state. C is the spherical axis of the Poincaré sphere (corresponding to the earth's axis), and E is the equator. Both poles of this Poincaré sphere represent circularly polarized light R, the area on the equator E represents linearly polarized light S, and the other regions represent elliptically polarized light. Note that a point on the equator E with longitude 0'' is linearly polarized light in the direction along the equator E, a point with longitude 90@ is linearly polarized light in the direction along the spherical axis C,
A point at longitude 45° is linearly polarized light in a direction of 45° to a tangent parallel to the equator E passing through this point, and a point at longitude 135° is in a direction 135° to a tangent parallel to the equator E passing through this point. (
This is linearly polarized light in a direction perpendicular to the linearly polarized light at a point at a longitude of 45 degrees. Further, the upper hemisphere represents right-handed polarized light, and the lower hemisphere represents left-handed polarized light. The latitude τ and longitude ψ of the distribution point of each wavelength of elliptically polarized light on the Poincaré sphere are determined by the ellipticity ε of the polarized light and the angle in the long axis direction of the ellipse (angle with respect to the horizontal line Z shown in Figure 2) ξ. There is a relationship as shown below.

This is a diagram of the distribution state of light of each wavelength arranged in a ball with τ-2arc tanε as seen from the upper pole side of the Poincaré sphere. Here, the liquid crystal molecule twist angle θ is 240°, and the retardation Δn1°・dlo is 78°.
It shows the distribution of light emitted from a 0ni liquid crystal cell. As shown in FIG. 5, the light A1 emitted from the liquid crystal cell 10 is
The light of each wavelength is elliptically polarized light that is distributed diagonally across the Poincaré sphere.

On the other hand, the phase plate changes the distribution state of each wavelength light on the Poincare sphere by a straight line passing through the center of the sphere and a certain point on the equator E (
It has the function of rotating the beads around the phase plate (fast axis of the phase plate), and therefore the liquid crystal cell 10 emits light and
The light transmitted through the phase plate 31 has the following polarization state.

FIG. 6 is a diagram showing the distribution state of each wavelength light when the light emitted from the liquid crystal cell 10 and transmitted through the first phase plate 31 is arranged on the Poincare sphere, as seen from the upper pole side of the Poincare sphere. Here, the retardation Δn31·d is used as the first phase plate 31.
A phase plate with 3□ of 137r++g is used, and the first phase plate 31 is connected to a straight line (liquid crystal cell 10 The distribution of each wavelength of light is shown when the light is arranged in a direction of 92.5° with respect to the liquid crystal molecule orientation direction 12a on the emission side substrate 12 surface. In this way, the first phase plate 31
When the phase plate 31 of FIG. From this state, the ball is rotated 137n/λ around the fast axis 31a of the first phase plate 31, that is, the straight line passing through the center of the Poincaré sphere and the point at longitude 62.5' on the equator E, and the visible light band is As shown in FIG. 6, the light of each wavelength is distributed in the vicinity along the peripheral line of the cut plane when the Poincaré sphere is cut along a certain plane.

In addition, FIG. 7 shows that the light that has been emitted from the liquid crystal cell 10, transmitted through the first phase plate 31, and then transmitted through the second phase plate 32 is arranged on the Poincare sphere, and the distribution state of each wavelength light is determined on the Poincare sphere. This is a diagram seen from the upper pole side of the retardation Δn3□・d3□ as the second phase plate 32.
Onw phase plate is used, and the second phase plate 32 is connected so that its fast axis 32a is a straight line passing through the center of the Poincaré sphere and a point at 90° longitude on the equator E (the output side substrate of the liquid crystal cell 10). It shows the distribution of light of each wavelength when arranged in a direction of 120° with respect to the orientation direction 12H of liquid crystal molecules on the 12th plane. When the second phase plate 32 is arranged in this way and the light that has been emitted from the liquid crystal cell 10 and transmitted through the first phase plate 31 is passed through the second phase plate 32, the light is emitted from the liquid crystal cell 10 and passes through the first phase plate 31.
The distribution state of each wavelength light transmitted through the 2° phase plate 32 is further changed from the state shown in FIG.
The gem is 610ni/λ centered on the straight line passing through the point of °.
As shown in FIG.
．． 5° to 52.5°).

Since the area on the equator E of the Poincaré sphere represents linearly polarized light as mentioned above, the equator E of the Poincaré sphere is shown in Figure 7.
Each wavelength of light concentrated and distributed near one point above becomes approximately linearly polarized light.

8 to 10 show the light emitted from the liquid crystal cell 10 and the first light when an OFF voltage is applied to the liquid crystal cell 10.
The latitude τ and longitude ψ of the distribution points of each wavelength light on the Poincaré sphere of the light transmitted through the phase plate 31 and the light transmitted through the second phase plate 32 are shown, and the light emitted from the liquid crystal cell 10 is elliptically polarized light whose wavelengths are distributed along latitudes τ and longitudes ψ as shown in FIG. However, when the light emitted from this liquid crystal cell 10 is passed through the first phase plate 31, this light is polarized by the first phase plate 31, and each wavelength light is
As shown in the figure, the distribution is at latitude τ and longitude ψ. Then, when this light is further passed through the second phase plate 32,
As shown in FIG. 10, the light transmitted through this second phase plate 32 is in the visible light band (450 nm to 650 rv in this case).
The wavelength light is distributed almost on the line of latitude τ-〇°, that is, on the equator E, and the wavelength light of this visible light band is distributed on the longitude ψ (ψ-about 90° in Fig. 10), that is, on the equator E. The distribution will be concentrated near one point above. And the 10th
As shown in the figure, the fact that the latitude τ and longitude ψ of the distribution points of each wavelength light are almost the same means that the phase difference between each wavelength light has almost disappeared. The light transmitted through the two-phase plate 32 is almost linearly polarized light.

Note that the polarization states shown in FIGS. 8 to 10 are obtained by using a liquid crystal cell in which the twist angle of liquid crystal molecules is 240° and the retardation Δnlo'dlo or 780 nm as the liquid crystal cell 10, and the retardation Δn3) as the first phase plate 31.・d3
1 is a phase plate of 140 tv, and the second phase plate 32 is a phase plate with a retardation Δn32·d3□ of 610I.
This is a measured value when an FF voltage is applied.

As described above, according to the liquid crystal display device of the above embodiment, the light transmitted through the liquid crystal cell 10 can be made to enter the output side polarizing plate 22 as linearly polarized light, and the light incident on the output side polarizing plate 22 can be linearly polarized. If it is 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. It is possible to reduce the leakage of light when the light is turned on, and also to increase the light transmittance when the light is turned on, thereby increasing the contrast. Although the image does not pass through the image, it is possible to display a high-quality image 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, since the liquid crystal sealed in the liquid crystal cell 22 is a liquid crystal having a refractive index anisotropy of 160 rv or more, the retardation Δn-d of the liquid crystal cell 1o is set to a predetermined value (Example Tel;! 700 nm). The liquid crystal layer thickness d required to achieve ~101000n can be reduced, and if the liquid crystal layer thickness d of the liquid crystal cell 10 can be reduced in this way, the response time of the liquid crystal to the application of the display drive voltage will be shortened. Therefore, responsiveness can also be improved.

That is, the table below compares the response times of the liquid crystal of a liquid crystal display device using a TN type liquid crystal cell, a liquid crystal display device using a conventional STNTN type liquid crystal cell, and the liquid crystal display device of the above example. There is.

As shown in this table, the liquid crystal response time of the liquid crystal display device of the above example is several times that of a liquid crystal display device with a conventional STNTN type liquid crystal cell, and is almost comparable to the liquid crystal response time of a TN type liquid crystal cell. Therefore, since it uses an STN type liquid crystal cell which has excellent time-division drive performance at high duty, it is possible to operate the liquid crystal at high speed.

Note that in the above embodiment, the side on which the phase plates 31 and 32 are arranged is the light output side, but in the above liquid crystal display device, the side on which the phase plates 31 and 32 are arranged is
．． It is also possible to use the side where 32 is not disposed as the light emitting side, in which case the incident light that has passed through the polarizing plate 22 passes through the second phase plate 32 and the first phase plate 31 and is reflected in the liquid crystal cell 10. The light is polarized in a state that compensates for the wavelength dependence, and then passes through the liquid crystal cell 10 and becomes linearly polarized light due to the wavelength dependence.

〔Effect of the invention〕

The liquid crystal display device of the present invention includes two phase plates arranged between a liquid crystal cell and one polarizing plate, and of the two phase plates, a first phase plate located on the liquid crystal cell side. When looking at the retardation value of the light emitted from the liquid crystal cell and transmitted through this first phase plate by placing it on the Poincare sphere, the wavelength light in the visible light band cuts the Poincare sphere with a plane. At the same time, the retardation value of the second phase plate located on the polarizing plate side is set to the value distributed in the vicinity of the edge line of the cut surface. When the light that has passed through this second phase plate is placed on the Poincare sphere and viewed, it is assumed that the wavelength light is in the visible light band or the value is concentrated near one point on the equator of the Poincare sphere. Therefore, the light transmitted through the liquid crystal cell is
By using the phase plate and the second phase plate, linearly polarized light can be input to the polarizing plate on the output side. Therefore, the liquid crystal molecules can be arranged in a twisted manner at a twist angle of 180° to 270°. Although it uses an E S T N-type liquid crystal cell, it reduces light leakage when OFF (light blocking), and increases light transmittance when ON (light transmission), increasing contrast. Furthermore, high-quality images can be displayed without coloring the display.

[Brief explanation of drawings]

Figures 1 to 10 show an embodiment of the present invention.
Figure 1 is a cross-sectional view of the liquid crystal display device, Figure 2 is a diagram showing the alignment direction of liquid crystal molecules on the side substrate surface of the liquid crystal cell and the direction of the optical axes of the phase plate and polarizing plate, and Figure 3 is a diagram showing the transmission of the liquid crystal display device. A diagram showing the spectrum of light. Figure 4 is a perspective view of the Poincare sphere. Figure 5 is a diagram of the distribution of each wavelength of light when the light emitted from the liquid crystal cell is arranged on the Poincare sphere. Figure 6 is a diagram showing the distribution state of light of each wavelength. Figure 7 shows the distribution state of each wavelength of light when the light emitted from the liquid crystal cell and transmitted through the first phase plate is placed on the Poincaré sphere. Figures 8 to 10 show the distribution state of each wavelength of light when the light that has passed through the second phase plate is placed on the Poincaré sphere, and the output from the liquid crystal cell when an OFF voltage is applied to the liquid crystal cell. FIG. 3 is a diagram showing the latitude and longitude of distribution points of each wavelength light on the Poincaré sphere of the light transmitted through the first phase plate, the light transmitted through the first phase plate, and the light transmitted through the second phase plate. FIG. 11 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,
3]...first phase plate, 32...second phase plate. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 R' Figure 4 Figure 11 Procedural Amendment 1991 6. On the 9th day of the Act, Mr. Wataru Fukasawa, Commissioner of the Japan Patent Office1, Indication of the case, Patent Application No. 2-322023,2, Name of the invention, Liquid crystal display device3, Person making the amendment, Relationship to the case, Patent applicant f144) Casio Computer Co., Ltd.4 , Agent 7, Suzuei Naikoku Patent Office, 3-7-2 Kasumigaseki, Chiyoda-ku, Tokyo Contents of amendment (1) Approximately r 130 nm on page 3, line 18 of the specification.''
I corrected it to `` rO, about 13''. (2) On page 11, lines 5 and 6, “Signal electrode 14
'' is corrected to ``Signal electrode 15J.'' (3) On page 11, line 18 of the same page, the sentence ``R 160 nm or more'' is corrected to ``016 or more.'' (4) In the 6th line of page 21, the phrase ``31 phase plate 31'' is corrected to ``31''. (5) In the 18th line of page 25, the phrase "r 160 nm or more" is corrected to "ro, 16 or more." (5) The table on page 26 of the same is corrected as follows. (4) Figures 9 and 10 of the cylinder in the drawing are corrected as shown in the attached sheet.

Claims (1)

[Scope of Claims] 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 thereon, and molecules of this liquid crystal are arranged in a twisted manner between the two substrates at a twist angle of 180° to 270°. and a pair of polarizing plates disposed before and after the liquid crystal cell, wherein two phase plates are disposed between the liquid crystal cell and one of the polarizing plates, and the two phase plates Among the phase plates, the retardation value of the first phase plate located on the liquid crystal cell side was observed by placing the light that was emitted from the liquid crystal cell and transmitted through this first phase plate on a Poincaré sphere. When the wavelength light in the visible light band is distributed along the peripheral line of the cut plane when the Poincaré sphere is cut by a plane, the retardation of the second phase plate located on the polarizing plate side is When looking at the value of light emitted from the liquid crystal cell, transmitted through the first phase plate, and then transmitted through the second phase plate on a Poincaré sphere, the wavelength light in the visible light band is the Poincaré sphere. A liquid crystal display device characterized in that the values are concentrated and distributed near a point on the equator of a sphere.