JP2667716B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial application field> The present invention relates to a liquid crystal display device in which color compensation is performed in a super twist type liquid crystal.

<Conventional technology> Generally, STN-LCD (super twist type liquid crystal display device)
Is colored yellow-green or blue, but by using a color correction plate, a bright and clear white / black display can be obtained. As a result, display products are improved and can be used for OA equipment such as word processors and computers.

In the two-layer type STN-LCD to which such color compensation has been applied, coloring generated in the first layer (driving cell) is color-corrected in the second layer (optical compensation cell) to be achromatic. This structure requires two liquid crystal cells as compared with the single-layer STN-LCD, and thus has a problem that the thickness of the display device is increased and the weight is increased.

On the other hand, in the retardation plate type STN-LCD, it is known that a retardation plate is provided on the front surface of the liquid crystal cell, and one is provided on each of the front surface and the back surface of the liquid crystal cell. Layer type STN-L
There is a problem that a sufficient display quality cannot be obtained, for example, the contrast is inferior to that of a CD (JP-A-64-519).
No.).

<Problems to be Solved by the Invention> Japanese Patent Application Laid-Open No. 64-519 discloses that a retardation plate is provided on the front and back surfaces of an STN liquid crystal panel. The sum of the retardation values is about 0.6
μm (600 nm), and there is no mention of the respective values. Further, even when a 300 nm retardation plate was provided in the system described in Example 21, good white / black display was not obtained.

The present invention solves the problems of the above-mentioned method, can be made thinner and lighter than the two-layer STN-LCD, and can be compared with the conventional retardation plate STN-LCD. It is intended to provide a liquid crystal display device capable of obtaining clear white / black display.

<Means for Solving the Problems> In a liquid crystal display device including a super twist type liquid crystal display cell in which a liquid crystal is interposed between an upper substrate and a lower substrate, an upper polarizing plate, a first retardation plate, and a super twist Type liquid crystal display cell-second retardation plate-lower polarizing plate are laminated in this order, the retardation values of the first retardation plate and the second retardation plate are equal, and liquid crystal molecule alignment of the upper substrate is performed. axis and the first angle theta ₂ of the the angle theta ₁ of the phase difference plate and the liquid crystal molecular orientation axis of the lower substrate second retardation plate theta ₁
+ Θ ₂ = 180 °, and the effective retardation Re obtained by the sum of the first retardation plate and the second retardation plate
2. The retardation Re1 of the first and second retardation plates and the angle θ between the optical axes of the first and second retardation plates satisfy Re2 = 2Re1cos θ. Features.

<Operation> As described above, since the retardation plates having the same retardation value made of a uniaxial polymer film and the like are disposed symmetrically on the front and back surfaces of the STN liquid crystal panel, the wavelength is longer than when disposed on one side. Dispersion can be approximated to an ideal one.As a result, the retardation plate is compensated over the entire wavelength range, and the azimuthal angle of the output elliptically polarized light is uniform, so that achromatic and high contrast can be achieved simultaneously by optimal setting of the analyzer. Can be achieved.

<Examples> As a result of various studies, in order to increase the transmittance in the ON state and suppress the transmittance in the OFF state, the retardation value of the retardation plate should be within the range of 330 nm to 420 nm and the same. It has been found that it is optimal to symmetrically dispose the one having the value of 前面 on the front and the back. Furthermore, we have found a rule that approximates these setting conditions from the retardation value of the STN liquid crystal panel.

To maintain the brightness of the display as a liquid crystal display device,
It is necessary to consider the retardation value of the retarder to be provided. Fig. 10 (L value = 100 is white, L value =
0 is displayed as black), the sum of the retardation values of the two retardation plates is 2Re (n
m) is 660 nm to 1000 nm (the value indicated by the dotted line in FIG. 10), that is, the retardation value of one retardation plate is
We have found that a range of 330 nm to 500 nm has sufficient brightness. Therefore, the range where the retardation value of the retardation plate is in the range of 330 nm to 420 nm is the optimum condition included in the above conditions.

At this time, the retardation value Re of one retardation plate
1 and the angle θ between the optical axes of the first and second retardation plates can be roughly estimated based on the retardation value d · Δn = Re (panel) of the STN liquid crystal panel by the method described below. .

FIG. 11 shows the retardation value d · Δn of the liquid crystal panel.
And the relationship between the retardation value Re1 of the retardation plate to be used and the above-mentioned are indicated by ○, an experimental value when the twist angle is 240 degrees, Δ is an experimental value when the twist angle is 210 degrees, □ Is the experimental value when the twist angle is 180 degrees,
The correlation is shown at the slope of the oblique line. The approximate value Re1 of the retardation of the retardation plate to be used can be selected from the relationship (shaded area) shown in FIG.

FIG. 12 is an actual measurement diagram showing the relationship between the spectral transmittance of the STN liquid crystal panel and the phase difference plate in one embodiment, and is a measured value in a parallel Nicol state.

In general, an equation representing transmitted light intensity when a birefringent body is placed between parallel Nicols is T = sin2γ × cos ² (πR / λ). Here, the angle γ is the angle between the optical axis and the polarization axis, and R is the retardation value. sin2γ ≠ 0, that is, 2γ ≠ 0, π
In the case of, the maximum value of the transmitted light is cos ² (πR / λ) = 1, that is,
(ΠR / λ) = nπ, that is, when n = 1, it is obtained when R = λ. This indicates that the retardation value of the birefringent body is expressed as the wavelength λ at which the maximum value of transmitted light is given. On the other hand, the minimum value of transmitted light is cos ² (πR / λ) = 0, that is,
(ΠR / λ) = π / 2 + nπ, that is, obtained when R = 3λ / 2 (n = 1). Therefore, the birefringent body having a retardation value of 3R / 2 sounds in an inverted relationship with the birefringent body having a retardation value of R, which shows the maximum and minimum values of transmitted light.

12, reference numeral 131 denotes a spectral transmittance curve of the STN liquid crystal panel, 132 denotes a spectral transmittance curve when the first and second retardation plates are overlapped at an angle θ formed by the optical axis, and 133 denotes an STN liquid crystal panel. 4 shows a spectral transmittance curve when a retardation plate and a retardation plate are almost optimally arranged. Curve 131 has a first minimum at approximately 480 nm and is approximately
The maximum value is shown at 595 nm. On the other hand, curve 132 is almost 590n
The minimum value is at m and the maximum value is at approximately 885 nm (not shown). These maximum values correspond to the effective retardation value Re2 of the retardation plate and the retardation value Re (panel) of the STN liquid crystal panel.
When a flat and low transmittance is obtained as shown in the spectral transmittance curve of, there is a relationship between Re2 and Re (panel) in which the maximum and minimum transmittance wavelengths are reversed. Therefore, as described above, Re (panel) × 3/2 = nRe2 (n = 1
Or 2) is obtained.

Therefore, the retardation value of the STN liquid crystal panel Re2 (pa
nel), an effective retardation value Re2 obtained by the sum of the first and second retardation plates can be determined.

In the example shown in FIG. 12, the retardation value Re (panel) of the liquid crystal panel is 595 nm from the maximum value of the spectral transmittance curve, and the effective retardation value Re2 = 8 when two retardation plates are stacked.
It is 85 nm. On the other hand, the above-mentioned relational expression Re (panel)
× 3/2 = 595n when calculated from n · Re2 (n = 1 or 2)
m × 3/2 = 892.5 nm, and the value when n = 1 and the effective value of 885 nm are approximate values.

On the other hand, FIG. 13 is a view showing the relationship between the angle θ formed by the optical axes of the first and second retardation plates and the effective retardation value formed by the first and second retardation plates. In FIG.
The solid line indicated by a circle is an actual measurement value, and the dotted line indicated by a cross is a theoretical value when Re1cosθ + Re1cosθ = 2Re1cosθ. It turns out that the measured value and this theoretical value are in good agreement. Accordingly, since the effective retardation value Re2 obtained by the sum of the first and second retardation plates and the retardation value Re1 of each retardation plate are obtained as described above, the first and second retardation values are obtained. The angle θ between the optical axes of the retarder is Re
Θ can be roughly calculated from 2 = 2Re1cos θ. After all, ST
N LCD panel twist angle, retardation value d
Once Δn = Re (panel) is determined, the approximate value of the retardation value Re1 of the retardation plate used and the angle θ formed by the optical axes of the first and second retardation plates can be obtained.

Under the conditions set in this manner, in the OFF state, light of three wavelengths of RGB is emitted from the front retardation plate as elongated elliptically polarized light (pseudo linearly polarized light) having a uniform azimuth, and is turned on.
In this state, light of three wavelengths of RGB is emitted from the front retardation plate as elliptically polarized light (quasi-circularly polarized light) having a relatively large azimuth angle and a relatively large elliptical ratio, so that the analyzer arrangement can be optimized. High contrast can be obtained while color compensation can be performed.

However, in detail, since the optical rotation dispersion due to the super-twisted liquid crystal layer is added, the retardation value of the retardation plate and the angle θ formed by the optical axes of the first and second retardation plates are
Requires some adjustment from the above estimates, but is generally effective as an optimization technique.

Hereinafter, the operation of the present structure will be described based on the optical principle based on the wavelength dispersion (hereinafter simply referred to as wavelength dispersion) of the retardation value of the phase difference plate and the STN liquid crystal panel and the phase reduction effect of the phase difference.

First, regarding the retardation plate, the relationship between the optical axes and the wavelength dispersion will be described. The retardation plate for compensating for the retardation of the STN liquid crystal panel is made of polycarbonate, polyvinyl alcohol, or the like, and has a specific retardation (retardation) due to stretching during manufacturing. In terms of crystal optics, it has properties similar to a uniaxial crystal. The optical axes of the phase difference plate are fast axis (F axis or X'axis) in the direction in which the light wave having the maximum velocity of the incident light vibrates, and slow axis in the direction in which the light wave having the minimum velocity vibrates ( (S-axis or Z'-axis), there are two cases of the relationship between the respective optical axes as shown in FIGS. 15 (a) and 15 (b). For example, polycarbonate is the same as (a), and polymethyl methacrylate is (b)
Is a negative sign. In any case, if the fast axis and the slow axis are known, they can be handled in the same manner.

On the other hand, regarding the chromatic dispersion, we obtained the phase difference with respect to the angular wavelength from the analysis of the elliptically polarized light obtained by causing the direct polarization of the monochromatic light to actually enter the retardation plate. FIG. 16 shows an example of the chromatic dispersion thus obtained.

Next, regarding the optical axis relationship of the STN liquid crystal panel, the minor axis direction of the liquid crystal molecule can be taken as the F axis and the major axis direction can be taken as the S axis due to the optical properties of the liquid crystal molecules. As a result, the alignment of liquid crystal molecules is regulated, which is considered as shown in FIG. In FIG. 17, P1 is the liquid crystal molecule alignment axis of the upper substrate, P2 is the liquid crystal molecule alignment axis of the lower substrate, P7 is the F axis of the upper substrate, P8 is the S axis of the upper substrate, and P10 is the S axis of the lower substrate. .

On the other hand, as for the chromatic dispersion, the chromatic dispersion of Δn of the liquid crystal material itself and the optical rotation dispersion by the supertwisted liquid crystal layer are added, and it is not possible to simply obtain the chromatic dispersion from the analysis of the outgoing elliptically polarized light. Therefore, we calculated the wavelength dispersion of the retardation value using a homogeneously aligned liquid crystal panel.
It can be measured in the same way as a retardation plate without optical rotation dispersion), STN
The optical dispersion in the liquid crystal panel was obtained, and the wavelength dispersion of the STN liquid crystal panel was approximately obtained as a synthesis with this.
However, in this measurement, the azimuthal angle of the outgoing elliptically polarized light when linearly polarized monochromatic light was incident parallel to the liquid crystal molecule orientation direction (that is, the S axis) of the incident side substrate of the STN liquid crystal panel was determined as the optical rotation angle.

FIG. 18 shows the result of actually applying the OFF voltage and the ON voltage to the STN liquid crystal panel and calculating the wavelength dispersion at that time. ST
The N liquid crystal panel appears colored because the emitted light before entering the analyzer is elliptically polarized light having different azimuth angles at each wavelength due to the characteristics shown in FIG. Therefore, in order to eliminate this coloring, the phase difference may be reduced to return to linearly polarized light, or to elliptically polarized light having a uniform azimuth angle.

As shown in FIG. 17, the F-axis and the S-axis of the STN liquid crystal panel are on the upper and lower substrates, respectively. Therefore, disposing the retardation plate so that the phase difference is reduced means that the STN liquid crystal panel is Is to dispose a retardation plate so that the F axis or the S axis is orthogonal to the front surface and the rear surface with respect to. That is, a plan view showing an embodiment of the present invention to be described later was defined theta ₂ and in FIG. 2 theta ₂ to is to say to 90 °, this time, the first phase difference plate and the second position If the retardations of the retardation plates are made equal, the relational expression Re2 = 2Re1cosθ derived from FIG. 13 can be used, the optical design can be facilitated, and the production efficiency can be improved.

Note that the phase reduction effect is not necessarily required to be arranged orthogonally, and the phase reduction effect can be obtained if the crossing angle exceeds 45 degrees. However, in the present invention, the first and second retardation plates are
Since it is placed symmetrically with respect to the liquid crystal panel, θ
There is a relationship of ₁ + θ ₃ = 180 degrees.

By the way, the state of the emitted light for obtaining a monochrome display is ideally such that the phase difference is 0 when in the OFF state (when a non-selected waveform is applied).
Alternatively, when the phase difference is mπ (m is an integer) and the ON state (when the selected waveform is applied), the phase difference may be (2m−1) × π / 2 (m is an integer). The outgoing light becomes linearly polarized light when the phase difference is 0 or mπ, while the phase difference plate becomes elliptically polarized light with the maximum ellipticity when the phase difference is (2m−1) × π / 2. The chromatic dispersion in such an ideal state is as shown in FIG.

Therefore, by combining the chromatic dispersion of the STN liquid crystal panel (FIG. 18) and the chromatic dispersion of the retardation plate (FIG. 16),
A perfect black and white display can be obtained by matching the ideal chromatic dispersion shown in FIG.

FIG. 20 shows the wavelength dispersion of the emitted light when the present invention is implemented, and the phase reduction between the retardation plate and the STN liquid crystal panel is one.
Times (the curve in the figure) and two times (the figure,
Curve), when the phase reduction effect is performed twice,
It can be seen that the wavelength dispersion shown in Fig. 19 approaches. This shows that arranging the retardation plates before and after the STN liquid crystal panel, which is a feature of the present invention, makes it possible to approximate the chromatic dispersion more ideally than when the retardation plates are arranged on one side. As a result, the phase difference is compensated over the entire wavelength range, and the azimuths of the outgoing elliptically polarized light are uniform, so that achromatic and high contrast can be achieved simultaneously by optimizing the analyzer settings. (Specific examples in FIGS. 3 and 4 showing the outgoing elliptically polarized light state in Example 1 described later.) Further, from this, a plurality of retardation plates provided on the front and back surfaces of the STN liquid crystal panel are provided. It is possible to approximate the chromatic dispersion to more ideal chromatic dispersion also by stacking the sheets. It is needless to say that the above-described optimization method is effective also in the case of this multi-layered structure.

An embodiment of the present invention will be described with reference to FIG. 1 and FIG.

FIG. 1 is an explanatory view showing the structure of an embodiment of the present invention described below, wherein 1 is an upper polarizing plate, 2 is a first retardation plate,
Denotes an STN liquid crystal panel, 4 denotes a second retardation plate, and 5 denotes a lower polarizing plate. Upper polarizer 1 has a single transmittance of 42% and a degree of polarization of 99.9.
Using a 9% neutral gray type polarizing plate,
The retardation plate 2 is made of a uniaxial polymer film (polycarbonate) and has a thickness of 50 μm and a retardation value of 330 nm.
The STN liquid crystal panel 3 is filled with an LC material to which a levorotatory chiral dopant is added, and has a twist angle of 210 ° and 240 °, d · Δn (d is the liquid crystal layer thickness, Δn is the refractive index anisotropy). Value) = 0.82 μm to 0.92 μm. The second retardation plate 4 has the same retardation value as the first retardation plate 2 disposed on the front side, and the lower polarizing plate 5 has the same retardation value as the upper polarizing plate 1. A transmission type liquid crystal display device was prepared by stacking layers.

The positional relationship of the arrangement in stacking the respective constituent members in this case will be described with reference to FIG. Among the arrows shown in FIG. 2, P1 is the liquid crystal molecule orientation axis of the upper substrate constituting the STN liquid crystal panel 3, P2 is the liquid crystal molecule orientation axis of the lower substrate,
P3 is the absorption axis of the upper polarizing plate 1, P4 is the absorption axis of the lower polarizing plate 5, P5 is the optical axis (S axis) of the first retardation plate 2, and P6 is the second axis.
The optical axis of the retardation plate 4 (S axis), theta ₁ is an angle of the liquid crystal molecular orientation axis P1 (S-axis) and the first retardation plate optical axis P5 of the upper substrate, theta ₂ is the liquid crystal molecules of the lower substrate The angle between the alignment axis P2 (S axis) and the optical axis P6 of the second retardation plate, α is the angle between the liquid crystal molecule alignment axis P2 of the lower substrate and the absorption axis P4 of the lower polarizer, and β is the liquid crystal of the upper substrate. The angle between the molecular orientation axis P1 and the absorption axis P3 of the upper polarizer, and φ represents the liquid crystal twist angle. In the present invention, since the first retardation plate 2 and the second retardation plate 4 are arranged symmetrically, the condition is θ ₁ + θ ₂ = 180 ° (constant).

Example 1 A retardation value of 4 was used for the first and second retardation plates 2 and 4.
The d · Δn of the STN liquid crystal panel 3 is 0.9 nm.
Use a 2μm, twist angle of 240 degrees. θ ₁ = 80
構成, θ ₂ = 100 °, α = 40 °, β = 50 °.

FIG. 3 shows an outgoing polarized light state passing through the first retardation plate 2 in the OFF state, and FIG. 4 shows an outgoing polarized light state passing through the first retardation plate 2 in the ON state.

In FIG. 3, 31 is light having a wavelength of λ = 450 nm, and 32 is λ
The light having a wavelength of 550 nm and the light having a wavelength of 650 nm are 33, and the principal axis direction of the elliptically polarized light substantially coincides with the absorption axis P3 of the upper polarizing plate 1 (black state). In FIG. 4, the principal axes 41, 42, and 43 are elliptically polarized light of wavelengths λ = 450 nm, 550 nm, and 650 nm, respectively, in the direction orthogonal to the absorption axis P3, as in FIG. Is obtained (white state).

In the result evaluated under the driving condition of 1 / 200D.1 / 13B, it is OFF.
A contrast ratio of 120: 1 is obtained with a transmittance of 0.2% and an ON transmittance of 24.1%.

Example 2 A retardation value of 3 was used as the first and second retardation plates 2 and 4.
D · Δn of STN liquid crystal panel 3 is 0.86
Use the one with μm and twist angle of 240 degrees. θ ₁ = 75
構成, θ ₂ = 105 °, α = 45 °, and β45 ° were set and disposed.

FIG. 5 shows an outgoing polarization state passing through the first retardation plate 2 in the OFF state, and FIG. 6 shows an outgoing polarization state passing through the first retardation plate 2 in the ON state.

In FIG. 5, 51 is light having a wavelength of λ = 450 nm, and 52 is λ = 5.
Light having a wavelength of 50 nm, 53 is light having a wavelength of λ = 650 nm, and the principal axis direction of elliptically polarized light is substantially coincident with the absorption axis P3 of the upper polarizing plate 1 (black state). 6, reference numerals 61, 62, and 63 denote elliptical polarization states of light having wavelengths of λ = 450 nm, 550 nm, and 650 nm, respectively, substantially in the direction orthogonal to the absorption axis P3, as in FIG. Since the ratio is high, achromatic and high transmittance can be obtained (white state). A spectral characteristic diagram of this emitted light is shown in FIG. In the figure, 71 is ON, 72 is no voltage applied, and 73 is OFF
Indicates the status. FIG. 7 shows a high ON-state transmittance, a low OFF-state transmittance, and flat spectral characteristics.

In the result evaluated under the driving condition of 1 / 200D.1 / 13B, it is OFF.
A contrast ratio of 37: 1 is obtained with a transmittance of 0.5% and an ON transmittance of 18.6%.

Example 3 A retardation value of 3 was used for the first and second retardation plates 2 and 4.
Using a 50 nm one, the d · Δn of the STN liquid crystal panel 3d is 0.8
Use a 2μm, twist angle of 240 degrees. θ ₁ = 75
構成, θ ₂ = 105 °, α = 45 °, β = 45 °.

FIG. 8 shows an outgoing polarization state passing through the first retardation plate 2 in the OFF state, and FIG. 9 shows an outgoing polarization state passing through the first retardation plate 2 in the ON state. 8, 81 is λ = 450n
light of wavelength m, 82 is light of wavelength λ = 550 nm, 83 is λ = 650 n
The main axis direction of the elliptically polarized light substantially coincides with the absorption axis P3 of the upper polarizing plate 1 at a wavelength of m (black state). 9, 91, 92 and 93 are the same as 81, 82 and 83 in FIG.
= 450 nm, 550 nm, and 650 nm wavelengths of light are in an elliptically polarized state, with their main axes approaching in a direction orthogonal to the absorption axis P3, and achromatic and high transmittance can be obtained. (White state).

In the result evaluated under the driving condition of 1 / 200D.1 / 13B, it is OFF.
A contrast ratio of 24: 1 is obtained with a transmittance of 0.6% and an ON transmittance of 14.4%.

Example 4 A retardation value of 3 was used as the first and second retardation plates 2 and 4.
D · Δn of STN liquid crystal panel 3 is 0.9 nm.
Use 1μm, twist angle 210 degrees. θ ₁ = 90
構成, θ ₂ = 90 °, α = 30 °, β = 60 °.

In the result evaluated under the driving condition of 1 / 200D.1 / 13B, it is OFF.
A contrast ratio of 24: 1 is obtained with a transmittance of 0.5% and an ON transmittance of 12.1%.

Example 5 A retardation value of 3 was used as the first and second retardation plates 2 and 4.
D · Δn of STN liquid crystal panel 3 is 0.8 nm
Use the one with 3μm and twist angle of 210 degrees. θ ₁ = 90
構成, θ ₂ = 90 °, α = 30 °, β = 60 °. As a result of evaluation under the driving conditions of 1 / 200D.1 / 13B, a contrast ratio of 18: 1 was obtained at an OFF transmittance of 0.6% and an ON transmittance of 11.0%.

For comparison, a conventional example of JP-A-64-519, Example 21
FIG. 14 shows a spectral characteristic diagram of. In the figure, 101 indicates an ON state, 102 indicates no voltage, and 103 indicates an OFF state. Since the transmittance in the OFF state is high, the transmittance in the ON state is low, and the spectral characteristics are not flat, a good white / black state cannot be obtained. Also, as a result of evaluating the contrast ratio, only about 4: 1 can be obtained.

Next, a comparison of the contrast ratio between the liquid crystal panels shown in Comparative Examples (1) and (2) in the following table and each of the above Examples is shown.

<Effects of the Invention> As described above, according to the present invention, a thinner and lighter weight than the two-layer STN-LCD can be obtained, and a high contrast ratio can be obtained. In addition, the conventional retardation plate system STN (Japanese Patent Laid-Open No. 64-519
Compared with Example 21), the retardation plates of the present invention having the same retardation value are disposed symmetrically on the front surface and the rear surface (θ _1).
+ Θ ₂ = 180 °), a clear white / black display with higher contrast can be obtained. In addition, two-layer type STN-L
In order to obtain a high contrast of CD or more and a clear white / black display having a high transmittance when ON, the retardation value of the retardation plate is particularly as shown in Examples 1 to 5. Of 330 nm to 500 nm, more preferably 330 nm to 420 nm
It is preferable to use

[Brief description of the drawings]

FIG. 1 is a structural explanatory drawing of a liquid crystal display device for explaining an embodiment of the present invention, FIG. 2 is a plan view showing a positional relationship of the embodiment, and FIG. FIG. 4 is a diagram illustrating an output polarization state after passing through the phase difference plate, FIG. 4 is a diagram illustrating an output polarization state after passing through the first phase difference plate in the ON state of the first embodiment,
FIG. 5 is a diagram showing an output polarization state after passing through the first phase difference plate in the OFF state according to the second embodiment. FIG. 6 is a view showing an output polarization state after passing through the first phase difference plate in the ON state according to the second embodiment. Showing the seventh
FIG. 8 is a diagram showing ON-OFF spectral characteristics of the second embodiment, FIG. 8 is a diagram showing an outgoing polarization state passing through the first retardation plate in the OFF state of the third embodiment, and FIG. 9 is a third embodiment. FIG. 10 is a diagram showing the state of polarized light emitted through the first retardation plate in the ON state of FIG. 10. FIG. 10 shows the retardation value and the brightness (L value) when two retardation plates having the same retardation value are stacked. Fig. 11 shows the relationship between the retardation value d ·
FIG. 12 is a diagram showing the relationship between Δn and the retardation value Re2 of the retardation plate used, FIG. 12 is a diagram showing the relationship between the STN liquid crystal panel and the spectral transmittance of the retardation plate, and FIG. FIG. 14 is a diagram showing the relationship between the angle θ formed by the optical axes of the two phase difference plates and the effective retardation value formed by the first and second phase difference plates.
FIG. 15 shows the spectral characteristics of the conventional device, FIG. 15 shows the relationship between the optical axes of the phase difference plate, FIG. 16 shows the wavelength dispersion of the phase difference plate, and FIG. 17 shows the optical characteristics of the STN liquid crystal panel. FIG. 18 is a diagram showing the relationship between the axes, FIG. 18 is a diagram showing the wavelength dispersion of the STN liquid crystal panel, and FIG.
The figure shows the ideal chromatic dispersion, and FIG. 20 shows the retardation plate and ST
FIG. 9 is a view showing a phase reduction effect when N liquid crystal panels are combined. 1: Upper deflector, 2: First retarder, 3: STN liquid crystal cell, 4: Second retarder, 5: Lower deflector.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Hiroshi Kuwagaki, Inventor 22-22, Nagaikecho, Abeno-ku, Osaka, Osaka Inside Sharp Corporation (72) Inventor Toshimichi Katsube 22-22, Nagaikecho, Abeno-ku, Osaka, Osaka Sharp shares In-company (56) References JP-A-64-519 (JP, A)

Claims (1)

(57) [Claims] 1. A liquid crystal display device comprising a super twist type liquid crystal display cell having a liquid crystal interposed between an upper substrate and a lower substrate, comprising: an upper polarizing plate, a first retardation plate, and a super twist type liquid crystal display cell. -Second retardation plate-Layered in the order of the lower polarizing plate, the retardation values of the first retardation plate and the second retardation plate are equal, and the liquid crystal molecule alignment axis of the upper substrate and the first retardation plate are the same. The angle θ ₁ formed by the _first phase difference plate and the angle θ ₂ formed by the liquid crystal molecule alignment axis of the lower substrate and the second phase difference plate are set as θ ₁ + θ ₂ = 180 °, and the first phase difference is Retardation Re2, the retardation Re1 of the first retardation plate and the second retardation plate obtained by the sum of the first retardation plate and the second retardation plate, and the second retardation difference between the first retardation plate and the second retardation plate A liquid crystal display device characterized in that the angle θ formed by the optical axis of the plate satisfies Re2 = 2Re1cosθ.