JPH02201422A - Electrooptical element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electro-optical element such as a super twisted nematic liquid crystal display device.

[Conventional technology]

Conventional super twisted nematic liquid crystal display devices, for example as disclosed in Japanese Patent Application Laid-Open No. 60-50511, have a twist angle of liquid crystal molecules of 180 degrees or more, and an optical anisotropy Δ of the liquid crystal.
The product Δn・d of n and liquid crystal layer thickness d is from 0.7 μm to 1.1
It was μm.

(Problem to be Solved by the Invention) Therefore, coloration occurs due to birefringence, but when time-division driving is performed, the color becomes yellow when a non-selective voltage is applied, blue when a selective voltage is applied, and the color shown in Figure 8 when an intermediate voltage is applied. As shown in the degree diagram (CIE standard chromaticity diagram), the range ranged from yellow through a slightly bluish-green to blue, and it was not possible to obtain other colors.Therefore, in addition to the selection voltage and the non-selection voltage, there was a range between the selection voltage and the non-selection voltage. Sufficient multicolor display could not be achieved with gradation display driving by applying voltage.

Furthermore, there are devices equipped with color filters for multicolor display, but they require three pixels for the three primary colors R, G-B, and are very troublesome to manufacture.

The present invention has been proposed in view of the above-mentioned problems, and can easily perform multi-color display by gradation display driving, and can also be time-divisionally driven at a low duty ratio of, for example, 1/100 or less. It is an object of the present invention to provide an electro-optical element that can obtain sufficient contrast even in various cases.

A further object of the present invention is to provide an electro-optical element that can change the color purity of multicolor display and enable full color display including black and white display.

[Means for Solving the Problems] In order to achieve the above object, the electro-optical element of the present invention has the following configuration. That is, a first liquid crystal cell having a twisted oriented nematic liquid crystal sandwiched between a pair of electrode substrates placed opposite to each other, and a pair of polarizing plates placed on both sides of the first liquid crystal cell. In an electro-optical element having a twist angle of the nematic liquid crystal in a range of 180 degrees to 360 degrees, an optical anisotropy Δn of the nematic liquid crystal and a liquid crystal layer thickness d (μm) of the nematic liquid crystal.
and a product Δn-d of 1.1 μm or more, and has means for selecting three or more voltages to be applied between the pair of electrode substrates, and is arranged facing each other between the pair of polarizing plates. The liquid crystal cell is characterized in that a second liquid crystal cell is interposed between a pair of electrode substrates and a nematic liquid crystal that is substantially vertically aligned.

〔Example〕

Hereinafter, the present invention will be specifically explained based on embodiments shown in the drawings.

FIG. 1 is a cross-sectional view of a schematic configuration of a liquid crystal display device as an electro-optical element showing one embodiment of the present invention.

In the figure, 1 is a lower polarizing plate, 2 is an upper polarizing plate, and 10 is a first liquid crystal cell disposed between both polarizing plates 1 and 2.

The first liquid crystal cell 10 has a nematic liquid crystal 13 sandwiched between a lower electrode substrate 11 having an electrode 11a on the upper surface and an upper electrode substrate 12 having an electrode 12a on the lower surface. The nematic liquid crystal 13 is twisted and oriented by subjecting the upper and lower electrode substrates 11 and 12 in contact with it to a rubbing treatment or the like.

Reference numeral 14 denotes a spacer interposed at the periphery between the picture electrode substrates 11 and 12, and the spacer 14 holds the nematic liquid crystal 13 between the picture electrode substrates 11 and 12, and also holds the nematic liquid crystal 13 between the picture electrode substrates 11 and 12. 12, that is, the liquid crystal layer thickness is kept constant.

Note that a distance maintaining member such as glass fiber or glass poles may be scattered between the substrates 11 and 12.

In the figure, 3 is a drive circuit for the first liquid crystal cell 10 connected to the electrodes 11a and 12a. In this example, a time division drive circuit is used, and the voltage selected as the voltage to be applied between the picture electrode substrates is In addition to the voltage and the non-selected voltage, three or more voltages such as an intermediate voltage thereof can be selected to perform gradation display driving.

A second liquid crystal cell 20 is provided between the first liquid crystal cell 10 and the upper polarizing plate 2, and includes a lower electrode substrate 21 having an electrode 21a on the upper surface, and an upper electrode substrate 21 having an electrode 22a on the lower surface. 22, a vertically aligned nematic liquid crystal 2
3 is sandwiched between them.

The liquid crystal 23 is vertically aligned by subjecting the upper and lower electrode substrates 21 and 22 to alignment treatment using a titanium-based alignment agent or the like. 24 is a spacer, 4 is the above electrode 21a, 22
This is a drive circuit for the second liquid crystal cell 20 connected to a, and in this example, except for specific example 4, a static drive circuit is used, and any voltage can be applied to the electrodes 21a and 22a.

FIG. 2 is an explanatory diagram showing the relationship between the molecular axes of liquid crystal molecules close to the electrode substrate and the absorption axis of the polarizing plate in the liquid crystal display device of FIG. 1. Note that in the present invention, the means for aligning the liquid crystal molecules in the first liquid crystal cell 10 is not limited to rubbing treatment, but for convenience of explanation, the alignment direction of the long axis of the liquid crystal molecules near the electrode substrate is This will be explained as a rubbing direction. The same applies to the embodiments described later.

In the figure, R11 and R12 are the rubbing directions of the lower electrode substrate 11 and upper electrode substrate 12 of the first liquid crystal cell 10, respectively, and T is the rubbing direction of the liquid crystal molecules in the first liquid crystal cell 10 from above in the first figure. The downward twist direction and angle, Pl.
P2 is the direction of the absorption axis (polarization axis) of the lower polarizing plate 1 and the upper polarizing plate 2, respectively, and θ1 is the direction of the absorption axis P1 of the lower polarizing plate 1 and the lower electrode substrate 11 of the first liquid crystal cell 10. An angle θ2 between the rubbing direction R11 and the absorption axis direction P2 of the upper polarizing plate 2 and the upper electrode substrate 1 of the first liquid crystal cell 10
2 and the rubbing direction R12.

In the above configuration, the upper electrode substrate and the lower electrode substrate are arranged to face each other so that the twist angle T of the liquid crystal molecules of the first liquid crystal cell 10 is in the range of 180 degrees to 360 degrees. In this case, the twist direction and angle T of the liquid crystal molecules are defined by the rubbing direction R11φR12 and the type and amount of the optically active substance added to the nematic liquid crystal 13. Also, the angles θ1 and θ2 between the rubbing direction and the absorption axis of the polarizing plate are:
Preferably, the angle is in the range of 15 degrees to 75 degrees. Further, the product Δnφd of the optical anisotropy Δn of the liquid crystal and the liquid crystal layer thickness d (μm) is set to be 1.1 μm or more.

In the above configuration, by changing the voltage applied to the pair of electrode substrates 11 and 12, the retardation of the liquid crystal layer changes and becomes smaller. As this retardation changes, the color of transmitted light changes. Therefore, in order to increase this color change, it is sufficient to increase the change in retardation, and it is necessary to increase the initial Δnod. Therefore, we discovered that in order to obtain multicolor display, it is best for the initial Δn-d to be 1.1 μm or more, and by doing so, sufficient multicolor display can be easily achieved by driving the gradation display. It is something that can be done. Note that there is no particular upper limit to the value of Δnod, and multicolor display is possible no matter how large it is.

However, at present, Δn is at most 0.2, and considering response speed and the like, Δn-d is preferably 2.0 or less.

Furthermore, time-division driving is required to increase the display capacity, but with the above configuration, sufficient contrast can be obtained even in low duty ratio driving of, for example, 1/100 or less.

Furthermore, the present invention actively utilizes the birefringence of liquid crystals, and it is necessary that the orientation direction and the direction of the absorption axis (polarization axis) of the polarizing plate are misaligned. When the angles θ1 and θ2 between the direction and the direction of the absorption axis are in the range of 15 degrees to 75 degrees as described above, a multicolor display with high contrast and good color purity can be obtained.

Further, by means of an electrical signal from the drive circuit 4 connected to the second liquid crystal cell 20, the color tone that can be displayed by the display device can be changed, and a black and white display can also be obtained. In other words, full color display is possible.

Hereinafter, specific examples based on the above embodiments will be described.

Specific Example 1 A PCH liquid crystal to which a tolan liquid crystal is added is used as the liquid crystal 13 of the first liquid crystal cell 10 in the above embodiment (Figs. 1 and 2), and the optical anisotropy Δn is 0°18, and the liquid crystal layer thickness is d to 8
μm, and Δnod was 1.44. In addition, the twist angle T1 of the liquid crystal molecules of the first liquid crystal cell 10 is shifted 22 to the left.
The angles θ1 and θ2 were each 45 degrees. The liquid crystal 23 of the second liquid crystal cell 20 has negative dielectric anisotropy.

The drive circuit (time division drive circuit) 3 of the first liquid crystal cell 10 performed four-gradation display drive at a duty ratio of 1/100.

At this time, four colors were displayed, as shown in the chromaticity diagram of FIG. In other words, there are four colors: blue-green, blue-violet, red, and yellow. Next, in the drive circuit 4 of the second liquid crystal cell 20, the effective voltage 1
When 0V is applied, as shown in FIG.
The color tone was the same as when an effective voltage of 2.4 V) was applied. Point A was black with a slight bluish tinge, and point B was white with a slight yellowish tinge, resulting in a nearly black and white display. The contrast ratio at this time is 1:
It was 8.

Concrete Example 2 In Concrete Example 1 above, the twist angle T1 of the liquid crystal molecules of the first liquid crystal cell 10 was changed to 230 degrees to the left, and the other configurations were the same as Concrete Example 2.

Then, the drive circuit 3 of the first cell 10 has a duty ratio of 1.
8 gradation display driving was performed at /200. FIG. 5 shows the color tones at this time, and as is clear from the figure, all eight gradations displayed different tones. Further, the driving circuit 4 of the second liquid crystal cell 20 applies an effective voltage of 10 to the second liquid crystal cell 20.
When V was applied, as shown in FIG. 6, point A had the color tone when the non-selection voltage (effective voltage 2.28 V) was applied, and point B had the color tone when the selection voltage (effective voltage 2.44 V) was applied. Point A was black with a slight bluish tinge, and point B was white with a yellowish tinge, resulting in a nearly black and white display. The contrast ratio at this time was 1:13.

Specific Example 3 In the above specific example 2, the effective voltage applied to the second liquid crystal cell 20 by the drive circuit 4 of the second liquid crystal cell 20 was changed from Ov to IOV. As a result, the green (x, y)-(0,197,0,386) shown in FIG. 6 became blue, red, and black as shown in FIG. 7. Also, the sixth
The other colors shown in the figure could also be changed to white by changing the effective voltage of the drive circuit 4 of the second cell 20 from OV to 10V.

Concrete Example 4 In Concrete Example 3, the electrode pattern of the second liquid crystal cell 20 is made the same as that of the first liquid crystal cell 10, and the electrode pattern of the first liquid crystal cell is overlapped with the electrode pattern of the first liquid crystal cell when viewed from the vertical direction. Duty ratio 1/200 and 8-gradation display driving were performed.

Then, the colors shown in FIG. 5 were modulated as in Example 3, and a full color display was obtained.

Concrete Example 5 In Concrete Example 3, the twist angle T1 of the liquid crystal molecules of the first liquid crystal cell 10 is changed to 330 degrees to the left, and the drive circuit 3 of the first liquid crystal cell 10 produces 8 gray levels with a duty ratio of 1/200. The display was driven. As a result, the viewing angle was wider than that of Example 3.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to easily perform multicolor display by gradation display, and moreover, in the case of time-division driving, multicolor display with good contrast even at a low duty ratio of 1/100 or less Furthermore, full-color display can be obtained, and there are advantages such as being able to provide an electro-optical element that can perform color display much more easily and at a lower cost than the conventional device using color filters.

Figures 4, 5, 6, and 7 are chromaticity diagrams showing color tones displayed by specific examples based on the above embodiments, and Figure 8 shows color tones that can be displayed by a conventional liquid crystal display device. It is a chromaticity diagram showing.

1.2...Polarizing plate 10...First liquid crystal cell 11...Φ12 is the electrode substrate 13...LCD 20...Second liquid crystal cell 21.22・Electrode substrate 23...Liquid crystal.

that's all

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a schematic configuration of a liquid crystal display device as an electro-optical element showing an embodiment of the present invention, and FIG. 2 is an explanation showing the relationship between the absorption axis of the polarizing plate and the rubbing direction, etc. in the liquid crystal display device. Figure, Figure 3 / Applicant Seiko Epson Co., Ltd. Agent Patent Attorney Kizobe Suzuki (and 1 other person) 2a Figure 5ffl Figure 6 Figure 6 Figure 4 Figure 7 Cause 8

Claims (2)

[Claims] (1) A first liquid crystal cell formed by sandwiching twisted oriented nematic liquid crystal between a pair of electrode substrates placed opposite each other, and a pair of polarizing plates placed on both sides of the first liquid crystal cell. and the twist angle of the nematic liquid crystal is 180
In the electro-optical element, the product Δn·d of the optical anisotropy Δn of the nematic liquid crystal and the liquid crystal layer thickness d (μm) of the nematic liquid crystal is 1.1 μm or more, and The voltage applied between the electrodes and substrates is 3
A second liquid crystal cell is interposed between the pair of polarizing plates and includes a nematic liquid crystal aligned almost vertically between a pair of electrode substrates disposed opposite to each other. An electro-optical element characterized by: (2) The means for selecting three or more values of the voltage to be applied between the pair of electrode substrates of the first liquid crystal cell is a time division drive circuit capable of applying an intermediate voltage in addition to the selection voltage and the non-selection voltage. The electro-optical element according to claim 1, characterized in that: