JPH04348322A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To offer a practical configuration means to realize a STN mode liquid crystal display element of optical phase plate system which can give pure white-black display and high contrast. CONSTITUTION:A liquid crystal display element 10 is obtd. by laminating a pair of uniaxial optical phase plates 6, 7 on one side of a liquid crystal cell 5 and laminating polarizers 8, 9 on both sides of this laminated body. This liquid crystal display element is disposed between substrates facing to each other. The liquid crystal cell 5 consists of nematic liquid having 200-270 deg. torsional angle theta along the perpendicular direction to the substrate. These members are laminated in a manner that the angle between the center angle of the angle made by the optical axes of these phase plates and the axis of the liquid crystal molecule adjacent to the phase plate 6 ranges from 85 to 95 degree, that the angle between the center angle above defined and the absorption axis (polarization axis) of the polarizer 8 adjacent to the optical phase plate 7 ranges from 40 to 50 degree, and that the angle between the absorption axis (polarization axis) of the polarizer 9 adjacent to the liquid crystal cell 5 and the axis of the liquid crystal molecule adjacent to the polarizer 8 ranges from 40 to 50 degree.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an optical phase plate system STN (super twisted nematic) which uses an optical phase plate for color compensation to obtain good black and white display characteristics.
The present invention relates to a mode liquid crystal display (LCD).

0002

2. Description of the Related Art In general, STN mode LCDs have a so-called steep threshold, which is a section where the transmittance changes sharply when the voltage is changed in the transmittance versus voltage characteristic. Time-division drive display with excellent contrast can be achieved by using sections, but the problem is that the transmitted light is colored because the transmittance of the liquid crystal display element differs depending on the wavelength of the transmitted light. There was a point.

[0003] In order to solve this problem, conventionally, an optically anisotropic polymer film or the like is simultaneously laminated on the liquid crystal cell to prevent the transmitted light from being colored and to provide a pure black and white display. An optical phase plate type STN mode liquid crystal display (LCD) constructed as described above has been proposed in Japanese Patent Application Laid-Open No. 64-519.

0004

[Problems to be Solved by the Invention] However, the means proposed in the above-mentioned Japanese Patent Application Laid-Open No. 64-519 is
This article merely discloses the principles of preventing coloration in TN mode LCDs, but does not provide specific configuration means for realizing STN mode LCDs that can display pure black and white and have high contrast. It has not been made clear.

The present invention has been devised with attention paid to this point, and is an optical phase plate type STN mode liquid crystal display element (optical phase plate type STN mode liquid crystal display element) which is capable of pure black and white display and has high contrast.
The purpose of this study is to provide concrete configuration means for realizing an LCD (LCD).

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a liquid crystal cell, a pair of optical phase plates laminated on one side of the liquid crystal cell, and a pair of optical phase plates laminated on one side of the liquid crystal cell. Optical phase plate system S
The optical characteristics of the liquid crystal cell, optical phase plate, and polarizing plate, their stacking state, and the refractive index anisotropy of the liquid crystal cell and optical phase plate that constitute the TN mode liquid crystal display element (LCD) The value of the product of and its thickness is specified as claimed in claims 1 to 3, respectively.

[0007]

[Operation] Using the optical phase plate type STN mode liquid crystal display element (LCD) configured as described above, and using a liquid crystal cell,
Each optical characteristic of the optical phase plate and the polarizing plate and their lamination state, as well as the value of the product of the refractive index anisotropy and the thickness of the liquid crystal cell and the optical phase plate, are determined as described in claims 1 to 3, respectively. If specified, the transmitted light that passes through the LCD will be transmitted at a nearly uniform rate regardless of its wavelength, making it possible to achieve pure black and white display and to actually obtain an LCD with high contrast. can.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a side view of an optical phase plate type STN mode liquid crystal display (LCD) constructed according to the present invention.

In the figure, 1 is a nematic liquid crystal, 2 is a pair of alignment films laminated on both sides of the nematic liquid crystal 1, 3 is a pair of transparent electrodes laminated on the outside of each alignment film 2, and 4 is each transparent electrode 3. The liquid crystal cell 5 is a pair of glass substrates laminated on the outside of the laminate. 6 and 7 are 2 stacked sequentially on one side of the liquid crystal cell 5.
uniaxial film-like optical phase plates 8 and 9 are uniaxial polarizing plates further laminated on both sides of these laminates,
The entire laminate constitutes an optical phase plate type STN mode liquid crystal display (LCD) 10.

FIG. 2 shows an LCD constructed in this manner.
10 shows the optical axis direction of each component and its optical characteristics.

In the figure, 11 is the upper plate rubbing axis of the liquid crystal cell 5, 12 is the lower plate rubbing axis of the liquid crystal cell 5, 13 is the absorption axis (or polarizing axis) of the upper polarizing plate 8, and 14 is the lower polarizing plate 9. , the absorption axis (or polarization axis) of The angle is taken as the positive direction.

Furthermore, the horizontal axis x and the absorption axis (
θP' is the angle between the horizontal axis x and the absorption axis (polarization axis) 14 of the lower polarizing plate 9, and θP' is the angle between the horizontal axis x and the optical axis of the lower phase plate 6. θR1 is the angle between the horizontal axis Each is determined.

In the LCD 10 having such a configuration, the refractive index anisotropy Δn of the liquid crystal cell 5 is 0.147, and the liquid crystal cell 5
The torsion angle θ is 260 degrees, the refractive index anisotropy Δn1, Δn2 of the pair of optical phase plates 6, 7 and their thicknesses d1, d2
The product of these is 380 nm, the angle θP' between the horizontal axis x and the absorption axis (polarization axis) 14 of the lower polarizing plate 9 is 85 degrees, and the angle between the horizontal axis x and the optical axis of the lower phase plate 6 is 85 degrees. θR1
is 70 degrees, and the angle between the horizontal axis x and the upper phase plate 7 is θR
2 is 30 degrees, no voltage is applied when the gap d of the liquid crystal cell 5 is changed using the angle θP between the horizontal axis x and the absorption axis (polarization axis) 13 of the upper polarizing plate 8 as a parameter. The transmittance in the applied state is as shown in FIG. In this figure, when the angle θP is changed in the range of −15 to +5 degrees, the product Δn·d of the refractive index anisotropy Δn of the liquid crystal cell 5 and its gap d is 0.75 to 0.85. It can be seen that the lowest value of the transmittance of the liquid crystal cell 5 exists in the range of .

FIG. 4 also shows the case where the angle θP' and the angle θR1 are selected to be 85 degrees and 70 degrees as in the case of FIG. 3, and the angle θR2 is varied in the range of 25 to 40 degrees. The angle θP shown in FIG. 3 when no voltage is applied
It shows the transmittance of the liquid crystal cell 5 with respect to . As can be seen from this figure, when the angle θR2 is in the range of 25 to 40 degrees, the angle θP is -10 to +1
The minimum value of the transmittance of the liquid crystal cell 5 exists in the range of 0 degrees.

Furthermore, in FIGS. 5 and 6, instead of selecting the angle θR1 as 70 degrees in FIG.
is selected to be 65 degrees or 75 degrees, and the ranges of the other angles θP' and angle θR2 are selected in the same manner as in the case of FIG. 4. Each shows the transmittance. It can be seen from these figures that the liquid crystal cell 5 has a minimum value of transmittance within a predetermined range of the angle θP.

Based on the measurement results shown in FIGS. 4, 5, and 6, for the predetermined range of the angle θR2, when the transmittance of the liquid crystal cell 5 in the state where no voltage is applied is the minimum, angles θP, θP', θR1, θR2
The relationship between can be approximated by the following equation (1).

{1/2(θR1+θR2)−θP}−{
θP'-1/2(θR1+θR2)+10}+1/2{
(θR1-θR2)-40}≒0...(1) Next, the twist angle θ of the liquid crystal cell 5 is selected to be 240 degrees, and the same measurement as described above is performed, and the predetermined range of the angle θR2 is measured in a state where no voltage is applied. The relationship between the angles θP, θP', θR1, and θR2 when the transmittance of the liquid crystal cell 5 becomes the minimum can be approximated by the following equation (2).

{1/2(θR1+θR2)−θP}−{
θP'-1/2(θR1+θR2)+30}+1/2{
(θR1-θR2)-30}≒0...(2) Generally, when the twist angle of the liquid crystal cell 5 is expressed as θ, the transmittance of the liquid crystal cell 5 in a state where no voltage is applied is calculated from equations (1) and (2). The respective angles θP, θP', θR when are the minimum
The relationship between 1, θR2, and θ is approximated by the following equation (3).

{1/2(θR1+θR2)−θP}−{
θP'-1/2(θR1+θR2)+(270-θ)}
+1/2 {(θR1-θR2)-1/2(θ-180)
}≈0 (3) Since equation (3) is somewhat complicated, in the present invention, angles are defined as shown in FIG. 7 in order to simplify it. That is, the central angle 17 of the angle formed by the optical axes 15 and 16 of the pair of optical phase plates 6 and 7 (the angle indicating the average value of the angles formed by the optical axes 15 and 16) and the absorption axis (or polarization axis) 13
θPR is the angle between the center angle 17 and the absorption axis (or polarization axis) 14 of the lower polarizing plate 9, θLP is the angle between the optical axes 15 and 16 of the pair of optical phase plates 6 and 7; θRL is the angle between the center angle 17 and the upper plate rubbing axis 11; If the twist angle is θ, equation (3) can be rewritten as follows.

{θPR−θRP−(270°−θ)}+
1/2 {θRR-1/2 (θ-180°)}≒0...(4
) Also, among the characteristics shown in FIGS. 4, 5, and 6, the transmittance of the liquid crystal cell 5 in the state where no voltage is applied is the lowest when θP'≒85 degrees and θP as shown in FIG. ≒5 degrees,
When θR1≈70 degrees and θR2≈30 degrees, if these are rewritten using the angles defined in FIG. 7, the following results.

θRL≒90°...(5) θLP≒θPR≒45°...(6) θRR-1/2(θ-180°)≒0...(7) Equation (7)
is a special solution when θLP=θPR=45 degrees in equation (4), so if equations (4) and (6) hold, equation (7) also holds.

Therefore, the condition for minimizing the transmittance in the state where no voltage is applied is when equations (4), (5), and (6) hold true. From a practical point of view, if the transmittance of the liquid crystal cell 5 in a state where no voltage is applied is small enough to withstand use, the formula (4
), Equations (5), and Equations (6) can be rewritten as follows by giving the values shown there a width of plus or minus 5 degrees.

85°≦θRL≦95°…(8) 40°≦
θLP≦50° (9) 40°≦θPR≦50°…(10) −5°≦{θPR−θRP−(270°−θ)}+1/
2 {θRR-1/2 (θ-180°)}≦5°…(11
) Next, in the state of FIG. 3, the angle θP is -20 to +3
The angle θR
2 as a parameter, the characteristics are as shown in FIG. If the same thing is done for the cases where the angle θR1 is 65 degrees and 75 degrees, the characteristics will be as shown in FIGS. 9 and 10.

Now, Δn·d of the liquid crystal cell 5 is (Δn·d
) LC, Δn・d of the optical phase plate 6 as Δn1・d1,
If Δn・d of the optical phase plate 7 is Δn2 ・d2, then
For each angle θR2 shown in FIGS. 8, 9, and 10,
(Δn・d)LC, Δn1 to minimize the transmittance of the liquid crystal cell 5 in a state where no voltage is applied (indicated by a circle in the figure)
・d1, Δn2 ・d2, θPR, θLP, θR
The relationship between R and θ can be approximated by the following equation (12).

(Δn・d)LC−(Δn1・d1+
Δn2・d2)+345nm+270nm・sin
θ+57nm・sin{θRR-1/2(θ-180°
)}-2000nm・sin2 (45°-θPR)=
0...(12) However, (Δn・d)LC, Δn1・d1
, Δn2 ・d2 units are nm, θPR, θLP,
The unit of θRR is degrees.

In equation (12), when the left side is greater than 0, the applied voltage-transmittance characteristic in the liquid crystal cell 5 is as follows:
As shown in FIG. 11, the transmittance of the liquid crystal cell 5 is somewhat high when no voltage is applied, but as the applied voltage is increased, the transmittance temporarily decreases, and then increases as the applied voltage is further increased. It exhibits a characteristic in which the transmittance increases rapidly. From a practical point of view, when driving the liquid crystal in a time-division manner, it is better to reduce the transmittance of the liquid crystal cell 5 by applying an OFF voltage, as shown in FIG. The contrast can be increased by lowering the ratio.

Here, if the transmittance of the liquid crystal cell 5 in a state where no voltage is applied is To, and the minimum value of the transmittance in a state where a voltage is applied is Tmin, θP'=85 degrees, θP=5
T when changing the gap d of the liquid crystal cell 5 when θR1=70 degrees, θR2=30 degrees, and θ=260 degrees
o, Tmin have characteristics as shown in FIG.

According to FIG. 12, the point at which the transmittance of the liquid crystal cell 5 becomes the minimum in the voltage applied state, that is, the point at which the transmittance of the liquid crystal cell 5 becomes the minimum, that is, according to the formula (12)
Tmin remains almost constant until the value of (Δn・d)LC is about 30 nm larger than the point where it satisfies the condition, and as (Δn・d)LC increases beyond this value, Tmin
gradually increases. Therefore, from a practical point of view, when formula (12) satisfies the following range, the transmittance of the liquid crystal cell 5 when the OFF voltage is applied can be made sufficiently low.

-10nm≦(Δn・d)LC-(Δn1
・d1 +Δn2 ・d2 )+345nm+270
nm・sin θ+57nm・sin {θRR−1/2(
θ-180°)}-2000nm・sin2(45°-
θPR)≦50nm...(13) The above explanation is about the conditions for lowering the transmittance of the liquid crystal cell 5 when an OFF voltage is applied, but if the above conditions are met, the liquid crystal cell 5 when an ON voltage is applied is Since the transmittance can be made sufficiently high, it is possible to realize a liquid crystal display element 10 that is bright and has high contrast. Further, by using the liquid crystal display element 10, it is possible to realize a nearly achromatic display both when an ON voltage is applied and when an OFF voltage is applied.

In summary, if a liquid crystal display element 10 that satisfies the following five equations (8) to (12) is used, a bright black and white display with high contrast can be realized.

85°≦θRL≦95°…(8) 40°≦
θLP≦50°…(9) 40°≦θPR≦50°…(10) −5°≦{θPR−θRP−(270°−θ)}+1/
2 {θPR-1/2 (θ-180°)}≦5°…(11
) −10nm≦(Δn・d)LC−(Δn1・d1+
Δn2・d2)+345nm+270nm・sin
θ+57nm・sin{θRR-1/2(θ-180°
)}-2000nm・sin2(45°-θPR)≦5
0nm...(12) However, (Δn・d)LC, Δn1・d1, Δn2
- The unit of d2 is nm, and the unit of θPR, θLP, and θRR is degrees.

[0033]

[Effects of the Invention] As explained above, according to the present invention,
Coloring of the STN mode LCD is compensated by optimizing the optical axis arrangement of the optical phase plates 6, 7 and polarizing plates 8, 9, as well as the Δn・d values of the liquid crystal cell 5 and the optical phase plates 6, 7. Therefore, it is possible to realize an optical phase plate type monochrome display LCD having high contrast.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical phase plate type STN mode liquid crystal display element according to the present invention.

FIG. 2 is an explanatory diagram showing optical axis directions and optical characteristics of each component of the liquid crystal display element.

FIG. 3 is a characteristic diagram showing changes in transmittance of a liquid crystal cell when Δn·d of the cell is changed.

FIG. 4 is a characteristic diagram showing changes in transmittance of a liquid crystal cell when the optical phase plate is arranged in a variable manner.

FIG. 5 is a characteristic diagram showing changes in transmittance of a liquid crystal cell when the optical phase plate is arranged in another variable arrangement.

FIG. 6 is a characteristic diagram showing changes in transmittance of a liquid crystal cell when the optical phase plate is arranged in another variable arrangement.

FIG. 7 is an explanatory diagram showing optical axes and the like in each component of a liquid crystal display element using different definitions.

FIG. 8 is a characteristic diagram showing changes in Δn·d of a liquid crystal cell at which the transmittance of the liquid crystal cell is minimized when the optical phase plate is arranged in a variable manner.

FIG. 9 is a characteristic diagram showing changes in Δn·d of a liquid crystal cell at which the transmittance of the liquid crystal cell is minimized when the optical phase plate is arranged in another variable arrangement.

FIG. 10 is a characteristic diagram showing a change in Δn·d of a liquid crystal cell at which the transmittance of the liquid crystal cell is minimized when the optical phase plate is arranged in another variable arrangement.

[Figure 11] Δn・d of the liquid crystal cell is Δn・d of the optical phase plate.
FIG. 4 is a voltage-transmittance characteristic diagram of the cell when the voltage is larger than a predetermined value.

FIG. 12 is a characteristic diagram showing changes in transmittance To and Tmin when Δn·d of the liquid crystal cell is changed.

[Explanation of symbols]

1 Nematic liquid crystal 2 Alignment film 3 Transparent electrode 4 Glass substrate 5 Liquid crystal cells 6, 7 Optical phase plates 8, 9 Polarizing plate 10 Liquid crystal display element 11 Upper plate rubbing axis 12 Lower plate rubbing axis 13 Absorption axis or polarization of upper polarizing plate 8 Axis 14 Absorption axis or polarization axis 15 of lower polarizing plate 9 Optical axis 16 of lower optical phase plate 6 Optical axis 17 of upper optical phase plate 7 Central angle

Claims (3)

[Claims] 1. A liquid crystal cell comprised of a nematic liquid crystal having a structure twisted by 200 to 270 degrees in the vertical direction of the substrates between opposing substrates, and a pair of uniaxial optical phase plates laminated on one side of the liquid crystal cell. In a liquid crystal display device constructed by further laminating polarizing plates on both sides of these laminates, the angle between the central angle of the optical axes of a pair of optical phase plates and the liquid crystal molecule axis adjacent to the optical phase plates is The angle is 85 to 95
The central angle of the angle between the optical axes of a pair of optical phase plates and the absorption axis (or polarization axis) of the polarizing plate adjacent to the optical phase plate is in the range of 40 to 50 degrees. and characterized in that the angle between the absorption axis (or polarization axis) of the polarizing plate stacked adjacent to the liquid crystal cell and the liquid crystal molecule axis adjacent to the polarizing plate is in the range of 40 to 50 degrees. LCD display element. 2. In the liquid crystal display element according to claim 1, the twist angle of the liquid crystal cell is θ degrees, and the center angle of the angle between the optical axes of the pair of optical phase plates and the polarizing plate laminated adjacent to the optical phase plates. The angle between the absorption axis (or polarization axis) is θPR degrees, and the angle between the center angle of the angle between the optical axes of a pair of optical phase plates and the absorption axis (or polarization axis) of the polarizing plate adjacent to the liquid crystal cell is θR
If the angle formed by the optical axes of the pair of optical phase plates is θRR degrees, -5°≦{θPR−θRP−(270°−θ)}+1/
A liquid crystal display element characterized by satisfying the relationship: 2{θRR-1/2 (θ-180°)}≦+5. 3. In the liquid crystal display element according to claim 2, the product of the refractive index anisotropy Δn of the liquid crystal cell and the thickness d of the liquid crystal layer is (Δn·d)LC, and the refraction of the pair of optical phase plates is Rate anisotropy Δn1, Δn2 and their thicknesses d1, d2
Let the products of the
d1 +Δn2 ・d2 )+345nm+270nm
・Sinθ+57nm・Sinθ{θRR-1/2(θ
-180°)}-2000nm・Sin2(45°-θ
A liquid crystal display element characterized by satisfying the relationship: PR)≦50 nm.