JPH01262529A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To increase the degree of black, and also, to make the degree of white satisfactory, and to obtain an ideal black-and-white display by specifying the product of a refractive index anisotropy and layer thickness of a nematic liquid crystal and a pre-tilt angle. CONSTITUTION:The title liquid crystal display device consists of a liquid crystal indicator 12 for executing a positive display of a double refraction type, a driving circuit part 14 and an illuminating part 13, and constituted so that a value of R=DELTAn.d.cos<2>theta related to layer thickness (d) and a refractive index anisotropy DELTAn of a nematic liquid crystal 8 and a pre-tilt angle theta of a liquid crystal molecule enters between 0.3-0.7, and also, an angle theta made by absorption axes (or polarization axes) of each polarizing plate 9, 10 which is stuck to two pieces of substrates 1, 2 goes within a range of 150R-20( deg.)-150R+20( deg.). Also, a correcting means 11 for correcting a spectral transmission spectrum of the upper liquid crystal indicator 12 is provided. In such a way, the degree of black at the time of applying a voltage is improved, the black level is lowered, and the degree of white at the time of applying no voltage is also improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a liquid crystal display device using a birefringence control type liquid crystal display.

(Prior art) There are TN type, DS type, and GH type for liquid crystal display depending on the operation mode.
Although there are many types such as type, DAP type, and thermal writing type, TN type liquid crystal displays are used in most products, including wristwatches, calculators, and measuring instruments. However, with the demand for increased display capacity and larger display area, problems such as lack of contrast and narrow visual range have emerged in TN type liquid crystal displays. Development was expedited.

In recent years, birefringence control type liquid crystal displays such as the SBE (super twisted birefringence effect) type described in Japanese Patent Application Laid-Open No. 60-107020 have been developed as liquid crystal displays that meet these demands. The utensils are attracting attention. The structure of these birefringence-controlled liquid crystal displays includes two transparent substrates each having a transparent electrode formed on at least one side facing each other, and the periphery sealed to form a cell.
A nematic liquid crystal is placed inside the cell. The distance between the opposing substrates is about 3 to 12 μm, and cyclohexane-based, ester-based, phenyl-based, and pyridimine-based liquid crystals are used as the nematic liquid crystal. A chiral agent is added to the nematic liquid crystal, and the molecular axes of the liquid crystal molecules are twisted at an angle of 180° to 360° between the upper and lower substrates. Further, the liquid crystal molecules have a pretilt angle in which the molecular axis is tilted by more than 5° with respect to the plane of the substrate due to the action of an alignment layer on the substrate.

In a SEE type liquid crystal display in which the molecular axis has a twist of 270°, polarizing plates are preferably arranged on the front and rear surfaces outside the substrate, so that the transmission axis of the front polarizing plate is relative to the molecular orientation direction of the front substrate. The best configuration is when the transmission axis of the rear polarizer is approximately 30 degrees clockwise and approximately 30'' counterclockwise or approximately 60' clockwise with respect to the alignment direction of the rear substrate.

Among these, the composition of the composer is displayed in bright yellow when it is not selected,
A black display is obtained in the selected state (yellow mode), and the latter configuration provides a deep blue display in the non-selected state, and becomes transparent in the selected state (blue mode). Also in other birefringent liquid crystal displays, the background color is not achromatic.

On the other hand, a proposal to make the background color achromatic has already been made by the present inventors (filed on February 12, 1988). That is, this is a display that utilizes birefringence, such as an SBE type liquid crystal display, and for example, the layer thickness d (μm) of the nematic liquid crystal, the refractive index anisotropy Δn, and the pretilt angle θ (” )k[[tR=Δn−d −
The first axis of cos2θ falls between 0.3 and 0.7, and the angle e (°) formed by the absorption axis (or polarization axis) of each polarizing plate attached to the two substrates is 150 R- 20(”
) The configuration is such that the range is from 150R+20(') to approximately 150R+20('), and the background and lighting spectra are made close to flat to provide black-and-white display.

(Problem to be Solved by the Invention) However, simply adjusting the absorption axis (or polarization axis) of the polarizing plate by setting Rlfi between 0.3 and 0.7 will not improve the contrast, whiteness, and transmittance. It was extremely difficult to recognize this as a desired value.

In particular, in a transmissive liquid crystal display device that uses a transmissive liquid crystal display and is illuminated from the back, ensuring the contrast of the display will result in a slight coloration, and attempting to maintain whiteness may result in insufficient contrast or a decrease in transmittance. It became.

[Structure of the Invention] (Means for Solving Problem 1) The present invention is a liquid crystal display device consisting of a liquid crystal display that performs birefringent positive display, a drive circuit section, and an illumination section, and in which the layer thickness of nematic liquid crystal is d, R-Δn-d-cos2θ related to refractive index anisotropy Δn and pretilt angle θ of liquid crystal molecules
is between 0.3 and 0.7, and the angle θ formed by the absorption axis (or polarization axis) of each polarizing plate attached to the two substrates is 150 R-20 ('') From 150R
+20 digits). Furthermore, it has a correction means for correcting the spectral transmission spectrum of the above-mentioned liquid crystal display.

Further, the present invention provides the above-mentioned liquid crystal display device, in which negative display is performed instead of positive display, and one of the above-mentioned polarizing plates attached to the two substrates has an absorption axis (or polarization axis) of 9.
It is rotated by 0".

Note that the value of the pretilt angle θ is the average value of the pretilt angles of individual liquid crystal molecules in the entire liquid crystal layer.

Further, a positive display refers to a dark display of black on a bright white background, and a negative display, on the other hand, refers to a white display on a black background.

Furthermore, the definition of angle θ is as follows. In other words, when the liquid crystal molecules rotate to the left (counterclockwise), they move from the absorption axis (or polarization axis) of the front polarizing plate attached to the front panel on the 12 quintillion person's side to the back substrate on the opposite side. clockwise toward the absorption axis (or polarization axis) of the attached back polarizer.
, and when the liquid crystal molecules are clockwise, the direction from the absorption axis (or polarization axis) of the front polarizer to the absorption axis (or polarization axis) of the rear polarizer is the counterclockwise direction. Let it represent the angle formed by .

(Function) The value of R mentioned above is closely related to the displayed color, and according to experiments, for example, if it exceeds 0.7, it will have high spectral reflectance and spectral transmittance at a certain specific wavelength, and if it exceeds 0.7, it will have high spectral reflectance and spectral transmittance, , 3, the difference in spectral reflectance and spectral transmittance when a voltage is applied and when no voltage is applied becomes small, resulting in a decrease in contrast.

Therefore, for positive display, the value of R should be between 0.3 and 0.7, and the above-mentioned angle θ should be set to 150 R-20 (°).
to 150 R + 20 (''), the background color of the transmitted light or reflected light due to the interference phenomenon is made substantially uniform in the visible light region, making it achromatic, and when a selective voltage is applied, the front polarizing plate and the back Experiments have confirmed that it is possible to display black on a white background by combining it with a polarizing plate.Furthermore, it has been confirmed that the spectral transmission spectrum of liquid crystal displays such as color filters, phase plates, and color conversion filters in the light source can be improved. By adding a correction means for correction, the degree of blackness when a voltage is applied is improved, the black level is lowered, and the degree of whiteness when no voltage is applied is also improved.

On the other hand, for negative display, rotate one of the absorption axes (or polarization axes) of the front or rear polarizer by 90' from the position of the polarizer for positive display, and as before, adjust the spectral transmission spectrum of the liquid crystal display. By adding a correction means to correct for this, the background color of transmitted light or reflected light due to interference phenomena is made substantially uniform in the visible light region, making it achromatic, and when a selection voltage is applied, the front polarizing plate and the back polarizing Experiments have confirmed that when combined with a board, it is possible to display white on a black background.

(Example) The details of this invention will be explained below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the present invention. In the same figure, first and second substrates (for example, glass substrates) (
1), the first main surface (1a) of (2).

On the (2a) side, for example, ITO (Indi
Conductive electrode (3) made of (umTin Oxide), (
4) are formed, and the first and second substrates (1), (2
> is each first principal surface (J where 1a> and (2a> face each other):
The distance between the sea urchins and sea urchins is maintained at approximately 5 μm. Also the first and second
The first main surface (1a) of the substrates (1) and (2).

On the (2a) side, alignment layers (5) and (5) made of polyimide, for example, are provided to cover the conductive electrodes (3) and (4), respectively.
6) is formed, and the periphery thereof is sealed with a sealing agent (7) made of, for example, an ultraviolet curing adhesive.

A nematic liquid crystal (8) to which a chiral agent has been added is sandwiched between the first and second substrates (1) and (2), and the molecular axis of the nematic liquid crystal (8) is aligned between the first and second substrates due to the action of the chiral agent. The substrates (1) and (2> have a twist in the range of 180° to 360°, for example, 200° counterclockwise, and the alignment layer (
5>, (6), the first and second substrates (1), (
2>, the pretilt angle θ is greater than 1° and approximately 2°. Further, the refractive index anisotropy Δn of the nematic liquid crystal (8) is about 0.08, and the nematic liquid crystal (8) has a refractive index anisotropy Δn of about 0.08.
) as the product of the refractive index anisotropy Δn, the layer thickness d, and the pretilt angle 0, the value of R=Δn−d−CO52θ is approximately 0.4 between 0.3 and 0.7. And the first substrate (1)
A neutral polarizing plate (9) is placed on the second principal surface (1b) side of the
A neutral polarizing plate (10) and a color filter as a correction means (11) for correcting the spectral transmission spectrum of the liquid crystal display are attached to the second main surface (2b) side of the second substrate (2). has been done. In this way, a desired liquid crystal display (12) that performs positive display is obtained. Here, the polarizing plate (
The arrangement angles of (9) and (10) are as follows: polarizing plate (9),
The polarization axes of (10) are set to be about 15 degrees clockwise and about 75 degrees clockwise with respect to the alignment direction of the first substrate (1), respectively. In addition, polarizing plates (9), (10
) is the angle O formed by the absorption axis (or polarization axis) of 150
It exists in the range of R-20('') to 150R+20(''), for example about 60'.

Further, behind the polarizing plate (10) and the correction means (11) (lower part in the figure), a flat light source consisting of a combination of a light bulb or a fluorescent light and a leading can, or an EL (
An electroluminescent (electroluminescent) lamp is provided to provide uniform illumination over the entire surface of the liquid crystal display (12). Further, on the side surfaces (left and right in the figure) of the second substrate (2), a circuit board (16) on which an electronic component (15) is mounted is mounted as a drive circuit section (14) of the liquid crystal display (12), and a connecting means ( 1
7) Seal the sN voltage on the protrusion of the second substrate (2), for example by a flexible sheet or heat seal! (4) is electrically connected.

FIG. 2 is a diagram showing the relationship between wavelength and spectral transmittance in the absence of the correction means (11) in this embodiment.
In the figure, At represents the time when no voltage is applied, and Bt represents the time when the voltage is applied. As can be seen from the figure, the spectral transmittance of the background color of the transmitted light due to the interference phenomenon approaches flatness and becomes achromatic, and when the selective voltage is applied, the polarizing plate (9), (10
) approaches the spectral transmittance at which they intersect, making it possible to display black on an achromatic background.

FIG. 3 is a diagram showing the relationship between the wavelength and spectral transmittance of the correction means (11). On the other hand, FIG. 4 is a diagram showing the relationship between wavelength and spectral transmittance in this example, in which A represents the time when no voltage is applied, and Bt represents the time when the voltage is applied. Fourth
As can be seen from the figure, the correction means (1) having the characteristics shown in FIG. 3 is added to the liquid crystal display device having the characteristics shown in FIG.
By adding 1), a liquid crystal display device that is more achromatic than the case shown in Figure 2, has sufficiently low transmittance when voltage is applied, and has a high contrast ratio and is suitable for a transmission type can be created.
It will be done.

As a result, it is possible to eliminate variations in visibility evaluation due to differences in the visual sense of the observer, and since the background color and display color are achromatic, the change in the layer thickness d of the nematic liquid crystal (8) Color unevenness is less likely to occur, and color changes from the viewing direction and color changes due to temperature are suppressed. Furthermore, by arranging the color filter behind the polarizing plate (10) together with the correction means (11), color display with good color reproducibility and contrast is possible.

Note that for a liquid crystal display having a structure similar to that of this embodiment, the value of R and the display quality have a relationship as shown in the following table.

(Left below) Table 1 shows 11 configurations similar to the embodiment shown in Figure 1.
Layer thickness d and refractive index anisotropy Δn of nematic liquid crystal (8),
2 is a table showing how the whiteness and brightness of the back color and the contrast 1 to ratio change when the angle O is changed. As can be seen from the table, reducing R to about 0.3 improves the whiteness of the previous day's color, but the contrast ratio decreases and the brightness also becomes darker, making it necessary to illuminate from behind the LCD display. It's coming. On the other hand, when R is increased to about 0.5, the contrast ratio improves although the whiteness deteriorates a little. Moreover, when Rifio exceeds 65, the whiteness of the previous day's color deteriorates, but the brightness becomes brighter. That is, the previous day's color and the spectral transmittance spectrum at the time of voltage application differ depending on the value of R, and the spectral transmittance spectrum that requires the correction means (11) also differs depending on the value of R. The spectrum that requires the correction means (11) is the transmission spectrum of the entire liquid crystal display device from 380 to 78.
The purpose is to make the correction almost uniformly by 0nllll and maintain the necessary transmittance by n.

FIG. 3 is a diagram illustrating the relationship between R and O regarding a liquid crystal display that has the following characteristics and performs a good black and white positive display. In the same figure, the range where good black and white positive display can be achieved is the solid line area centered on the white circle for a given R value, and the three broken lines are 150 R.
It represents the range that satisfies -20('')≦O≦150R+20(°).From the same figure, J: Sea urchin, the value of R is in the range of 0.3 to 0.7, and the angle θ is as above. By defining the inequality within a range that satisfies the inequality, it is possible to obtain a liquid crystal display device that provides good black and white positive display.

Here, when the liquid crystal display performs negative display, the situation is different from when it performs positive display. In this case, the knife having the same configuration as the embodiment shown in FIG. 1 is 150 R-20.
('')≦θ≦150 R+20(') One of the absorption axes (or polarization axes) of the polarizing plates (9) and (11) forming an angle e satisfying R+20(') is further 90' from the original state.
Just rotate it. That is, for example, a polarizing plate (9),
The arrangement angle of (10) is the polarizing plate (9), (10)
The absorption axis (or polarization axis) of is about 15 degrees clockwise and about 16 degrees clockwise with respect to the orientation direction of the first substrate (1), respectively.
δ2 is fixed so that it is 5°. As a result, a liquid crystal display device that provides good black and white negative display can be obtained.

As mentioned above, when performing positive display or negative display, R and the absorption axis (or polarization axis) of polarizing plates (9) and (10)
Although the relationship between the angle θ and the angle θ has been described above, it goes without saying that the corresponding spectrum of the correction means (11) is optimized based on whiteness, contrast, and transmittance.

Up to now, we have explained the case in which a color filter is installed as a correction means (11) in a liquid crystal display device, but the correction means (11) may be provided in a leading conductor layer of an illumination section (13) or in a liquid crystal display device (12). ) first base plate (1) or second base plate (2
) can also be provided. In addition, as a correction means (11), a phase plate such as a resin plate having birefringence is installed between the polarizing plate (9) and the first substrate (1) or between the polarizing plate (10).
and the second substrate (2), or between the first and second substrate (2).
1), (2> Provide a phase plate layer between the first substrate (1)
Alternatively, the spectrum shown in FIG. 2 can be made more uniform by using a substrate having birefringence as the second substrate (2).

[Effect of the invention 1] The present invention is a positive display liquid crystal display device that utilizes interference color due to birefringence, in which the value of R=Δn−d・cos2θ is set between 0.3 and 0.7, and two sheets of Absorption of each polarizing plate attached to the substrate fll! The angle θ formed by l (or polarization axis) is 150R-20('')≦O≦150R+2
0 ('), and further uses a correction means for correcting the spectral transmission spectrum of the liquid crystal display. Further, the present invention is a negative display liquid crystal display device that uses interference color due to birefringence, and has an R value of 0.
Between 3 and 0.7, 150R-20ji) ≦o≦1
50 R+20 (') The absorption axis (or polarization axis) of one of the front and back polarizing plates that forms the satisfying angle e is further rotated by 90', and in addition, as in the case of positive display, the liquid crystal A correction means is used to correct the spectral transmission spectrum of the display.

This combination increases the blackness when voltage is applied (positive display) or when no voltage is applied (negative display), and also improves the whiteness when voltage is applied (negative display) or when no voltage is applied (positive display), making it ideal. A black and white display can be achieved. In particular, a transmissive liquid crystal display device can realize black and white display with sufficient contrast.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of the relationship between wavelength and spectral transmittance in a conventional liquid crystal display, and FIG. 3 is a diagram showing the wavelength of the correction means in this invention. FIG. 1 shows an example of the relationship between wavelength and spectral transmittance, and FIG. 4 shows an example of the relationship between wavelength and spectral transmittance in this invention.
FIG. 5 is a diagram showing an example of the relationship between R and θ in the case of positive display according to the present invention. (1)...First substrate (2)...Second substrate (3), '(4)...Conductive electrode (8)...Nematic liquid crystal (9>, (10)...Polarized light Plate (11)...Correction means (12)...Liquid crystal display (13)...Lighting section (14)...Drive circuit section Agent Patent attorney Noriyuki Chika Yudo Kikuo Takehana Figure 1 Miyocho (7L) Figure 2 Nanicho (71m) Figure 3 Miyoshicho (7!m) Figure 4

Claims (2)

[Claims] (1) First and second electrodes with conductive electrodes formed on the first main surface side
a substrate, the molecular axis being 1 with respect to the plane of the first and second substrates;
has a pretilt angle θ greater than
and a nematic liquid crystal sandwiched between the second substrates with a twist in the range of 180° to 360°, and a polarizing plate adhered to the second main surface side of the first and second substrates, Refractive index anisotropy Δn and layer thickness d(μ
m), and R= as the product of the pretilt angle θ (°)
The value of Δn・d・cos^2θ is between 0.3 and 0.7, and the angle formed by the absorption axis (or polarization axis) of each polarizing plate attached to the first and second substrates is (°) is 150R-2
A liquid crystal display that performs a positive display in the range of 0 (°) to 150R+20 (°), a driving circuit section and an illumination section of this liquid crystal display, and a correction means for correcting the spectral transmission spectrum of the liquid crystal display. A liquid crystal display device comprising: (2) In the liquid crystal display device according to claim 1, negative display is performed instead of positive display, and the absorption axis (or polarization axis) of one of the polarizing plates attached to the first and second substrates is set at 90°. A liquid crystal display device characterized by rotating.