JP3182925B2 - Liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates, smelling between the pair of electrodes
The present invention relates to a liquid crystal display device that displays an image by enclosing a liquid crystal in a stactic layer and controlling the molecular arrangement of the liquid crystal in the smectic layer .

[0002]

2. Description of the Related Art Conventionally, an antiferroelectric liquid crystal has two stable states (bright state) with respect to application of an electric field and has one stable state when no electric field is applied.
It has three stable states (dark state), and has a high-speed response and a steep threshold and a hysteresis characteristic of light transmittance with respect to a DC voltage as electro-optical characteristics accompanying the switching between the three stable states. It is known (JP-A-2-153322).

When driving a liquid crystal display device using such an antiferroelectric liquid crystal, it is necessary to perform a so-called AC drive in which the polarity of an applied voltage is inverted at a predetermined cycle in order to prevent the liquid crystal from being decomposed. Is also known (Japanese Unexamined Patent Publication No.
173724).

[0004]

However, when such an AC drive is performed, the antiferroelectric liquid crystal has an arrangement of liquid crystal molecules in two stable states (both in a bright state) as the polarity of the applied voltage is inverted. Change. On the other hand, when the liquid crystal panel is viewed from a specific direction, the light transmission characteristics of the liquid crystal panel in the two bright states are different. For this reason, when the liquid crystal panel is AC-driven, there is a problem that a screen flickers (so-called flicker) appears as if the display image pulsates in accordance with the inversion cycle, and the display quality is degraded.

For example, as shown in FIG. 8, when the liquid crystal panel is viewed from a normal z perpendicular to the liquid crystal panel, the displayed image can be viewed well, but the direction of the smectic layer 80 for specifying the initial alignment direction of the liquid crystal molecules. (In the figure, parallel to the x-axis)
Angle (azimuth) φ is about 45 °, 135 °, 22
At 5 ° and 315 °, the normal z perpendicular to the liquid crystal panel
When the liquid crystal panel is viewed from a viewing angle direction in which the angle (inclination angle) θ with respect to is greater than or equal to 30 °, flicker corresponding to the inversion cycle of the AC voltage is sensed.

First, FIG. 9 is a view schematically showing a liquid crystal molecule arrangement when the liquid crystal panel is viewed from the z direction orthogonal to the liquid crystal panel. The optical axis of the birefringent antiferroelectric liquid crystal is in the major axis direction of the liquid crystal molecules. The light transmittance when viewed from the z direction can be represented by the following equation.

I ² = I ₀ ² sin ² (2 · θt) · sin ² (π · Δn · d / λ) where I: transmitted light intensity I ₀ : incident light intensity θt: major axis of liquid crystal molecules Angle formed with polarization axis Δn: Refractive index anisotropy of liquid crystal layer d: Thickness of liquid crystal layer For this reason, if the observation direction deviates from the z-axis, apparent θ
t and Δn change, and the observed transmitted light intensity I changes. Therefore, when the liquid crystal panel is viewed from a fixed direction such as φ = 45 ° or 135 ° as described above, the brightness changes between a bright state due to a positive voltage and a bright state due to a negative voltage, and is sensed as flicker. It will be lost.

The present invention has been made in view of these problems, and has been made to improve the display quality of a liquid crystal display device using a smectic layer liquid crystal by suppressing flicker generated when AC driving is performed. .

[0009]

Means for Solving the Problems] The present invention has been made in order to achieve the above object, a pair of electric disposed opposite to each other
An electrode substrate, and sealed between the pair of electrode substrates, when no electric field is applied.
Stable first stable state, formed when an electric field is applied in one direction
The second stable state formed, and in the direction opposite to the direction of the electric field
Has a third stable state formed when an electric field is applied
Each of the smectic layer liquid crystal and the pair of electrode substrates
A dark state when the liquid crystal is in the first stable state;
Absorbed to be in a bright state in the second and third stable states
First and second polarizers whose axes are set to be orthogonal to each other
Disposed between the pair of electrode substrates and the respective polarization axes.
A liquid crystal display element comprising: first and second phase plates having a stretching axis . In addition, the
The stretching axis of the first phase plate and the stretching axis of the second phase plate are orthogonal to each other.
And the absorption axis of the first polarizer.
And the stretching axis of the first phase plate are parallel to each other, and
The absorption axis of the photon and the stretching axis of the second phase plate are parallel
It is desirable.

[0010]

The applicant of the present application has proposed various configurations of a liquid crystal display device using an antiferroelectric liquid crystal that can reduce the difference in light transmission characteristics between when a positive voltage is applied and when a negative voltage is applied. investigated. As a result, they have found that it is effective to insert a pair of phase plates between the liquid crystal layer and a pair of polarizers provided on both surfaces thereof. Further, it has been found that when each phase plate is inserted such that the stretching axis of the phase plate is parallel to the absorption axis of the adjacent polarizer, a remarkable effect can be obtained.

With such a configuration, the difference in the light transmission characteristics of the liquid crystal display element between when a positive voltage is applied and when a negative voltage is applied, especially when viewed from the specific direction, is reduced. be able to. The reason for this is
It is considered as follows, but the detailed reason is not clear.
That is, it is considered that the inserted phase plate compensates for the change in the apparent refractive index anisotropy (△ n) of the liquid crystal layer and the change in the polarization characteristics (corresponding to θt) depending on the observation direction of the polarizer. It is done.

In the present invention, as described above, the first and second positions
Since the phase plate is provided, the difference in light transmission characteristics between when a positive voltage is applied and when a negative voltage is applied is reduced, and flicker that occurs when AC driving is performed is suppressed.

The retardation value of the phase plate (so-called retardation) depends on the viewing angle dependence of the true birefringence of the antiferroelectric liquid crystal layer, the thickness of the liquid crystal layer, and the polarization characteristics of the polarizer. The optimal value is different. For this reason, in designing the present invention, it is desirable to experimentally determine the optimum value of the retardation, and to select the phase plate in accordance with that.

[0014]

Next, an embodiment of the present invention will be described with reference to the drawings. First, FIG. 1 is a cross-sectional view schematically showing a configuration of a liquid crystal display device of an embodiment. The liquid crystal cell 1 is configured by sealing an antiferroelectric liquid crystal 7 between a pair of transparent electrode substrates 3 and 5. Phase plates 11 and 13 are attached to the surfaces of the transparent electrode substrates 3 and 5, respectively, and polarizers 15 and 17 are attached to the surfaces of the phase plates 11 and 13, respectively.

The liquid crystal cell 1 is manufactured as follows.
That is, first, I.V. is applied to the surfaces of the transparent substrates 3a and 5a made of glass by a method such as vapor deposition or sputtering. T. O.
(Indium tin oxide) or transparent conductive films 3b and 5b made of tin oxide are formed. continue,
The transparent conductive films 3b and 5b are etched in a stripe shape. The direction of the stripe is the same as that of the transparent electrode substrates 3 and 5.
Are set so that the stripes of the transparent conductive films 3b and 5b are orthogonal to each other when they face each other.

On the surfaces of the transparent conductive films 3b and 5b, alignment control layers 3c and 5c for aligning liquid crystal molecules are respectively provided. As the orientation control layers 3c and 5c, a known film such as a film obtained by rubbing a polymer film such as polyimide in one direction or an oblique deposition film of SiO can be used. Note that the alignment control layer may be provided on only one of the transparent electrode substrates 3 and 5.

Subsequently, the transparent electrode substrates 3, 5 are opposed to each other at an interval of 2 μm so that the transparent conductive films 3b, 5b are inside, and the periphery is sealed with an adhesive 19. An antiferroelectric liquid crystal 7 is sealed between them. When enclosing the antiferroelectric liquid crystal 7, the antiferroelectric liquid crystal 7, for example, 4
-(1-trifluoromethylheptoxycarbonylphenyl) -4'-octyloxycarbonylphenyl-4
Heating the carboxylate as an isotropic liquid and injecting it between the two transparent electrode substrates 3 and 5 using capillary action;
Thereafter, the entire liquid crystal panel 1 is gradually cooled at about 1 ° C. per minute,
Cool until it reaches an antiferroelectric liquid crystal phase (SmC _A ^* phase).
In addition, as the antiferroelectric liquid crystal 7,
(1-trifluoromethylnonyloxycarbonylphenyl) -4'-octylbiphenyl-4-carboxylate, 4- (1-trifluoromethyldecyloxycarbonyl) -4'-biphenyl-2-fluoro-4-octylbenzoate, Various antiferroelectric liquid crystals such as 4- (1-methylheptylcarbonylphenyl) -4'-octylbiphenyl-4-carboxylate can be used.

When the phase plates 11 and 13 and the polarizers 15 and 17 are sequentially adhered to the liquid crystal cell 1 thus manufactured, the liquid crystal display element of the present embodiment is completed. 11, 13 absorption axes, and polarizer 15,
The stretching axis 17 is set in the direction shown in FIG. That is, the absorption axis of the polarizer 17 and the stretching axis of the phase plate 13 are
The direction of the smectic layer 80 of the liquid crystal cell 1 (for example, when the alignment control layers 3c and 5c are formed by rubbing treatment,
(Perpendicular to the direction of the rubbing treatment), and the absorption axis of the polarizer 15 and the stretching axis of the phase plate 11 are perpendicular to the direction of the smectic layer 80. Here, the phase plates 11 and 13 are formed by stretching a polymer film such as polycarbonate.

The transparent conductive films 3b and 5b formed in stripes are connected to a well-known driving circuit (not shown) for driving a matrix, and a voltage is applied. Since this type of driving circuit is described in detail in JP-A-56-107216 and JP-A-2-230117, it will not be described in detail here.

In the liquid crystal display device of the present embodiment thus configured, by applying an AC voltage between the transparent conductive films 3b and 5b, the alignment state of the liquid crystal molecules is changed as shown in FIG.
(B) → (a) → (c) → (a) →... For this reason, the light transmittance is improved at the portion where the voltage is applied, and an image can be displayed. Further, the transparent conductive films 3b, 5
When a triangular wave voltage was applied between b and the voltage-transmittance characteristic was confirmed, a sufficient double hysteresis characteristic as shown in FIG. 3 was obtained. That is, the absolute value of the applied voltage is 20 V
When it increases to the vicinity, the relative transmittance of the liquid crystal display element sharply increases and changes from 0% to 100%. Conversely, when the absolute value of the applied voltage decreases to around 0 V, the relative transmittance sharply decreases and changes from 100% to 0%.

Next, the azimuth angle φ defined in FIG.
An experiment was conducted to compare the light transmission characteristics of the liquid crystal display element of the present example in the above two bright states from a direction in which the tilt angle θ and the tilt angle θ were 40 °. In the experiment, "NRF" was used as the phase plates 11 and 13.
-200 "and" NRF-239 "(both trade names: manufactured by Nitto Denko Corporation). In addition, "NRF-20
“0” indicates that the retardation is 200 nm (for example, R = 20
"NFR-239" is R = 23.
9nm product. Further, as the polarizers 15 and 17,
"NPF-G1220DU" (trade name: manufactured by Nitto Denko Corporation) was used. Further, a 3 W electrode tube (trade name “LCD backlight unit TY-BL49”) is used as a light source.
N ": manufactured by Matsushita Electric Industrial Co., Ltd.).

FIG. 4 is a plot of the transmitted light of the liquid crystal display element on a chromaticity diagram. Both the embodiment using "NRF-200" and the embodiment using "NRF-239" have a positive voltage + V (here, 20V) as compared with the conventional liquid crystal display element not using the phase plates 11 and 13. It can be seen that the difference in chromaticity between when the voltage is applied and when the negative voltage −V is applied is extremely small. FIG. 5 shows the phase plate 1 with the phase plate 13 removed.
7 is a plot of the transmitted light of the liquid crystal display element of Comparative Example using only 1 on a chromaticity diagram. In this case, the phase plate 1
A chromaticity difference substantially similar to that of the related art in which 1, 13 is not used occurs between the application of the positive voltage and the application of the negative voltage. When the phase plate 11 is removed and only the phase plate 13 is used, substantially the same result can be obtained. Therefore,
It can be seen that the remarkable effects can be obtained only by providing the phase plates 11 and 13 for each of the polarizers 15 and 17.

Table 1 shows that when the applied voltage is 0, the positive voltage + V
5 shows the measurement results of the luminance and the color difference ΔE of the liquid crystal display element when .DELTA. Is applied and when the negative voltage -V is applied. In Table 1, the phase plates 11, 13
And the phase plates 11 and 13 of "N"
RF-200 "(R = 200 nm), and" NRF-239 "(R = 200 nm) as the phase plates 11 and 13.
239 nm).

[0024]

[Table 1]

Here, the color difference ΔE is calculated as follows based on the chromaticity diagram of FIG. The following color difference calculation method is described in “Color Science Handbook” (edited by the Japan Society of Color Science:
(Published by The University of Tokyo Press). First, the positive voltage + V
Based on the coordinates (x, y) on the chromaticity diagram at the time of application and the luminance Y at that time, variables X and Z are obtained by the following equation. Note that X, Y, and Z are called tristimulus values and are defined in JIS-Z872.
2-1980.

X = X / X + Y + Z y = Y / X + Y + Z Subsequently, based on the tristimulus values X, Y and Z, variables R, G and B are obtained by the following equation. R = 1.1084X + 0.0852Y-0.1454
Z G = −0.0010X + 1.0005Y−0.0004
ZB = -0.0062X + 0.0394Y + 0.8192
Z Subsequently, based on the variables R, G, and B, the variables L, a, and b are obtained by the following equation. L = 25.29G ^1/3 -18.38 a = 106.0 (R ^1/3 -G ^1/3 ) b = 42.34 (G ^1/3 -B ^1/3 ) When negative voltage -V is applied Similarly, the variables L ′,
a 'and b' are obtained. Next, the color difference ΔE is calculated by the following equation, with ΔL = LL ′ Δa = a−a ′ Δb = bb ′. ^{△ E = (△ L) 2} + (△ a) 2 + (△ b) as shown in Table ^2. 1, (R = 200nm), (R = 239n
m) The color difference も when either of the phase plates 11 and 13 is used.
E is significantly smaller than the conventional one. Therefore,
In the liquid crystal display device of the present embodiment, the above direction (φ = 45 °,
(θ = 40 °), it can be seen that flicker when observed can be favorably prevented. Also, a phase plate 1 of (R = 239 nm)
Since the color difference ΔE becomes smaller when 1,13 is used, in the liquid crystal display device of the present embodiment, it is more effective to set the retardation to 239 nm than to set the retardation to 200 nm, so that the flicker preventing effect is more remarkable. It can be seen that it can be obtained.

Subsequently, the liquid crystal display device of the embodiment (R = 23)
The viewing angle dependence of the display contrast at 9 nm) was measured. FIG. 6 shows the measurement results. In FIG. 6, the center of the circle represents the measurement result from the normal z direction, and the contrast viewed from this direction is 100%. The circumferential angle of the broken circle corresponds to the azimuth angle φ, and the radius of the broken circle corresponds to the inclination angle θ. The curve drawn by the solid line has a contrast of 9
It is an iso-contrast line in which the inclination angles θ of 0%, 80%, 70%... Are plotted for all azimuth angles φ. Note that, when converting the contrast into a numerical value, the luminance ratio between the voltage application part and the non-application part measured from each direction is calculated using the normal z
This was done by comparing with the luminance ratio measured from the direction. FIG. 7 is an explanatory diagram showing the viewing angle dependence of the display contrast in a conventional liquid crystal display element that does not use the phase plates 11 and 13. This figure was produced similarly to FIG.

As shown in FIG. 7, in the conventional liquid crystal display device, the azimuth angles are 45 °, 135 °, 225 °, and 31 °.
It can be seen that the contrast is extremely deteriorated at the orientation of 5 °. On the other hand, in the present embodiment, as shown in FIG. 6, the isocontrast line approaches a concentric circle, and the radius of the isocontrast line increases. That is, the liquid crystal display element of this embodiment has a very wide viewing angle.

As described above, in the liquid crystal display element of the present embodiment, the difference in light transmission characteristics between when a positive voltage is applied and when a negative voltage is applied is reduced, and flicker that occurs when AC driving is performed. Can be suppressed. In the above embodiment, a matrix drive type liquid crystal display device has been described.
The present invention can be applied to various liquid crystal display elements such as a multi-plexing drive type.

[0030]

As described above in detail, in the liquid crystal display device of the present invention, a pair of electrode substrates disposed opposite to each other is provided.
And sealed between the pair of electrode substrates, and stable when there is no electric field.
First stable state, formed when an electric field is applied in one direction
A second stable state, and an electric field in a direction opposite to the direction of the electric field.
Smec having a third stable state formed when applied
Tick layer liquid crystal and the pair of electrode substrates
The liquid crystal is in the dark state when the liquid crystal is in the first stable state,
2. The absorption axes are mutually changed so that the state becomes a bright state in the third stable state.
First and second polarizers set to be orthogonal to each other,
A stretching axis disposed between the pair of electrode substrates and the respective polarization axes;
And a first and a second phase plate having the following .

Therefore, according to the present invention, the difference in light transmission characteristics between when a positive voltage is applied and when a negative voltage is applied can be reduced, and flicker that occurs when AC driving is performed can be suppressed. . Therefore, by applying the present invention, a liquid crystal display device having a wide viewing angle and high display quality can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating a configuration of a liquid crystal display device of an example.

FIG. 2 is an explanatory diagram showing a correspondence relationship among an absorption axis, a stretching axis, and a smectic layer direction.

FIG. 3 is an explanatory diagram showing a double hysteresis characteristic of the antiferroelectric liquid crystal layer.

FIG. 4 is a chromaticity diagram showing transmitted light characteristics of the liquid crystal display element of the example.

FIG. 5 is a chromaticity diagram showing transmitted light characteristics of a liquid crystal display element of a comparative example.

FIG. 6 is an explanatory diagram showing the viewing angle dependence of the display contrast of the liquid crystal display element of the example.

FIG. 7 is an explanatory diagram showing the viewing angle dependency of the display contrast of a liquid crystal display element of a comparative example.

FIG. 8 is an explanatory diagram illustrating a problem in a conventional liquid crystal panel.

FIG. 9 is an explanatory diagram illustrating an alignment state of liquid crystal molecules in an antiferroelectric liquid crystal.

[Explanation of symbols]

1: Liquid crystal cell 3b, 5b: Transparent conductive film 3
c, 5c: alignment control layer 7: antiferroelectric liquid crystal 11, 13: phase plate 1
5, 17: polarizer 80: smectic layer

──────────────────────────────────────────────────続 き Continuing on the front page (72) Koji Nakamura, 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Corporation (72) Inventor Yuichiro Yamada 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Denso Corporation (56) References JP-A-4-29219 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/141 G02F 1/13363

Claims (3)

(57) [Claims] 1. A pair of electrode bases disposed opposite to each other
Sealed between the plate and the pair of electrode substrates, stable when no electric field is applied
First stable state, formed when an electric field is applied in one direction
Second stable state, and an electric field in a direction opposite to the direction of the electric field.
Having a third stable state formed when
Liquid crystal and a pair of electrode substrates, respectively.
A dark state when the liquid crystal is in the first stable state,
The absorption axis is set to be in the bright state in the second and third stable states.
First and second polarizers set to be orthogonal to each other;
Stretched between the pair of electrode substrates and the respective polarization axes
A liquid crystal display device comprising: first and second phase plates having axes . 2. The stretching phase of the first phase plate and the second phase
2. The method according to claim 1, wherein a stretching axis of the plate is perpendicular to the drawing axis.
3. The liquid crystal display device according to item 1. 3. An absorption axis of the first polarizer and the first phase.
The stretching axis of the plate is parallel to the absorption axis of the second polarizer.
The stretching axis of the second phase plate is parallel to the second phase plate.
The liquid crystal display device according to claim 1.