JPH01217316A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To form a background and a display part in an achromatic color and to execute a black-and-white display by correcting a phase by using a phase plate having double refractiveness with respect to a color determined by the constituting condition of a liquid crystal element. CONSTITUTION:A nematic liquid crystal having a positive dielectric anisotropy to which an optically active substance is added is inserted and pinched between a pair of upper and lower electrode substrates 21, 22 arranged so as to be opposed to each other, and a twisted spiral structure within a range of 180 deg.-270 deg. is formed in its thickness direction. Subsequently, polarization axes 26, 27 or absorption axes of a pair of polarizing plates 24, 25 provided by pinching this spiral structure between them are arranged at a prescribed angle against the liquid crystal molecule array direction of the adjacent electrode substrate. In this case, as for a means forming a color generated in a liquid crystal display element in which the product DELTAn.(d) of thickness (d)(mum) of a liquid crystal layer and a refractive index anisotropy DELTAn of a liquid crystal is within a range of 0.4mum-1.5mum, to roughly an achromatic color, one sheet or more of plastic films having double refractivity are used as a phase plate. In such a way, a background and a display part are not colored, and a black- and-white display can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device, and particularly to a field effect liquid crystal display device that has excellent time division drive characteristics and is capable of black and white display.

[Conventional technology]

FIG. 1 shows a perspective view of a so-called twisted nematic type liquid crystal display element having excellent time-division driving characteristics and used in a conventional liquid crystal display device. As shown in the figure, the picture electrode substrate has a spiral structure twisted in the range of 180 degrees to 270 degrees due to the nematic liquid crystal 3 having positive dielectric anisotropy between the two electrode substrates 1°2. On the outside, the polarizing plates 4 and 5 are arranged with their polarization axes (or absorption axes) 6,
They were arranged so that the included angle between them was in the range of 20 degrees to 70 degrees.

In order to align the liquid crystal molecules between two electrodes so that they form a spiral structure twisted in the range of 180 degrees to 270 degrees, for example, the surface of the electrode substrate in contact with the liquid crystal can be rubbed in one direction with a cloth, etc. This is done by a so-called rubbing method. The rubbing direction at this time, that is, the rubbing directions 8 and 9, is the alignment direction of the liquid crystal molecules. 2 which was oriented in this way
The two electrode substrates 1 and 2 are placed facing each other with a gap such that their respective rubbing directions 8 and 9 intersect with each other in a range of approximately 180 degrees to 270 degrees, and the two electrode substrates 1 and 2 are bonded together using a sealant. However, when a nematic liquid crystal 3 having positive dielectric anisotropy is filled in the gap, the liquid crystal molecules are arranged in a spiral structure rotated in the range of approximately 180 degrees to 270 degrees between the electrode substrates. Polarizing plates 4 and 5 are provided above and below the liquid crystal element configured in this way, and the polarization axes (or absorption axes) 6 and 7 of the liquid crystal molecules adjacent to each electrode substrate are determined from the optimum value of contrast. A size between 0 degrees and 70 degrees clockwise or counterclockwise is required based on the arrangement direction of .

Although FIG. 1 shows a transmission mode in which the backlight 1-10 is arranged, the principle of operation in the reflection mode is substantially the same as that in the transmission mode.

FIG. 2 shows the relationship between applied voltage and brightness of a display using a liquid crystal display having such a structure. The figure shows normal
Two modes, open mode A and normally closed mode B, are shown, and both have the characteristic that the brightness rises steeply with respect to the applied voltage. This characteristic is a factor that enables high time-division driving □ without reducing contrast.

Here, time-division driving will be briefly explained using a dot matrix display as an example. As shown in Figure 3, striped Y electrodes (signal electrodes) 1 are formed on the lower electrode substrate.
2, an X electrode (scanning electrode) 11 is formed on the upper electrode substrate, and characters and the like are displayed by lighting or not lighting the liquid crystal at the intersection of both the X and Y electrodes. In the same figure, n scanning electrodes are Xll X21 ” X n + Xll xz
, ++++++++ X n and repeated line sequential scanning is repeated to perform time division driving. A certain scanning electrode (X in the figure)
When a) is selected, all pixels on that electrode,
Yl, Y2, which are signal electrodes 12; . . . From Yn, a selected or non-selected display signal is simultaneously added according to the signal to be displayed. In this way, depending on the combination of voltage pulses applied to the scanning electrode 11 and the signal electrode 12, lighting or non-lighting at the intersection is selected. The number of scanning electrodes X in this case corresponds to the number of time divisions.

However, the so-called twisted nematic type of liquid crystal display, which has this excellent time-division drive characteristic, is
Although the background color or display color in the blue mode is shown on the 018 chromaticity coordinate in the figure, at least one of the background or the display section is colored, and black and white display cannot be performed.

However, in recent years, demands for improving the image quality of liquid crystal display elements and increasing the amount of displayed information have become stricter, and the required specifications are as follows:
The situation is that there is a shift from black and white display to color display. For this reason, Seiko Epson made the liquid crystal display a two-layer structure, namely, reverse twist, same twist 1-angle, and same Δn.
-d liquid crystal elements are stacked to achieve black and white display.

(Sanetoshi, Ei FBI, Wada: Television Society Technical Report,
] 1. P79, 1987) [Problem to be solved by the invention] In the above-mentioned prior art, in order to realize black and white display, 80-d
It was difficult to manufacture and mass production was low because it required precise matching.

An object of the present invention is to make the background and the display part achromatic to enable black and white display as well as color display.

[Means to solve the problem]

The above purpose is to make the background and display part achromatic by correcting the phase using a phase plate having birefringence for the color determined by the configuration conditions of the liquid crystal element.
A black and white display is achieved.

[Effect]

Rice Terra (liquid crystal element with excellent time-division drive characteristics)
・What is called a nematic type has a color on at least one of the background or display area. A phase plate having birefringence is used to correct the phase of the color attached to at least one of the background and the display section, thereby rendering the background and the display section achromatic. As a result, in a sheathed nematic liquid crystal display device having excellent time-division driving characteristics, where at least one of the background and display part is colored, the background and display part are no longer colored. Black and white display is possible.

〔Example〕

Hereinafter, a liquid crystal display element suitable for carrying out the present invention will be explained using the drawings.

Figure 5 shows the alignment direction of liquid crystal molecules (for example, rubbing direction), the twisting direction of liquid crystal molecules, and the absorption axis (or polarization axis) direction of the polarizing plate when the liquid crystal display element according to the present invention is viewed from above. . FIG. 6 is a perspective view showing their relationship.

The twist direction and twist angle α of the liquid crystal molecules 23 are defined by the rubbing direction 28 of the upper electrode substrate 21, the rubbing direction 29 of the lower electrode substrate 22, and the type and amount of the optically active substance added to the nematic liquid crystal. The maximum value of the twist angle α is limited because the lighting state near the threshold value is an orientation that scatters light, and the upper limit is 270 degrees, and the lower limit is limited by the contrast, and the limit is 180 degrees.

In this embodiment, the twist angle α was set to 2 because the purpose of this embodiment was to provide a liquid crystal element capable of displaying black and white with a sufficiently satisfactory contrast of 1 or more even when the number of scanning lines was 200 or more.
It was set at 60 degrees.

The angle β3 formed between the polarization axis (or absorption axis) 26 of the upper polarizing plate 24 and the polarization axis (or absorption axis) 27 of the lower polarizing plate 25 is determined by considering contrast, brightness, color, etc. when using a phase plate. If not, a range of 0 degrees to 60 degrees is preferred. However, in this example using a phase plate, for example, G1225DU manufactured by Nitto Denko is used as a polarizing plate, and β3 is 20
It was a degree. Also, the angle β1 between the polarization axis (or absorption axis) 26 of the upper polarizing plate 24 and the rubbing direction 28 of the upper electrode substrate 21, the polarization axis (or absorption axis) 27 of the lower polarizing plate 2S and the lower electrode substrate 22, The angle β2 formed by the rubbing direction 29 is preferably in the range of 0 degrees to 60 degrees, considering the last, brightness, color, etc. of the controller 1. In this example, β1
was set to 20 degrees, and β2 was set to 40 degrees.

Further, the liquid crystal display element according to this example has a remarkable Δn−d
It exhibits n-character and is 0.0 in terms of contrast, brightness, and color.
When the condition of 4 μm≦Δn-d≦1.5 μm is satisfied, particularly good characteristics are exhibited; when the thickness is 0.4 μm or less, the transmittance is low, and when the thickness is 1.5 μm or more, the contrast ratio is low and the display characteristics are deteriorated.

Here, the value of Δn has wavelength dependence, and tends to be large on the short wavelength side and small on the long wavelength side. The value of Δn used in this specification was measured at 25° C. using He-Ne laser light (wavelength 6328). In this example, a nematic liquid crystal whose main components are a vinyl enyl liquid crystal and an ester cyclohexane liquid crystal is used, and 0.5% by weight of Merck's 8811 as an optically active substance is added. In addition, in this example, Δn =0.083
The thickness of the liquid crystal layer was 6 μm. Therefore, Δn-d of the liquid crystal element of this example was set to 0.5.

Furthermore, in the configuration of the liquid crystal display element and the polarizing plate as described above, the background and the display section' are colored as described above. A phase plate was installed to make the display color achromatic.

In this embodiment, a so-called parallel alignment liquid crystal element with a twist angle α of 0 degrees was used as a phase plate for making the background color and display color achromatic.

The angle β4 between the rubbing direction 34 of the upper substrate 3 of the parallel-aligned liquid crystal element serving as a phase plate and the polarization axis 26 of the upper polarizing plate 24, and the rubbing direction 35 of the lower substrate 32 and the polarization axis of the lower polarizing plate 25 Considering that the angle β5 formed with 27 is a complementary color to the background color and display color of the liquid crystal display element,
A range of 0 degrees to 60 degrees is desirable.

In this example, β4 is 25 degrees, β5 is 45 degrees, or β4
was set at 65 degrees, and β5 was set at 45 degrees. Further, Δn-d of the parallel alignment liquid crystal element serving as the phase plate was set to 0.36.

In this embodiment, a cold cathode tube is used as the light source 15, but a hot cathode tube or an electroluminescent tube 1- may also be used.

By configuring the liquid crystal element in this manner, the background color and display color can be made achromatic.

In this example, a liquid crystal display element with a twist angle α of 260 degrees was used;
Furthermore, even in a larger range, the background color and display color can be made achromatic.

In this embodiment, a cold cathode tube is used as the light source 15, but a similar achromatic color can be obtained even by using an external light type that uses a reflector without using a light source.

Figure 7 shows the colors of the background and display area in this example.
Shown in E chromaticity coordinates. As shown in the figure, both the background color and the color of the display section are achromatic near the C light source, indicating that the display is black and white.

Further, the contrast ratio, which is the ratio of the luminance during white display and the luminance during black display, is 9:1 at this time.

FIG. 8 shows the structure of a liquid crystal element according to another embodiment suitable for carrying out the present invention. As shown in the figure, instead of the liquid crystal display element with a twist angle α of 260 degrees and Δn-d of 0.5 shown in FIG.
A guest-host type liquid crystal display element with 0.5 is used, and the other configurations are the same as in FIG.

Figure 9 shows the colors of the background and display area in this example.
Shown in E chromaticity coordinates. As shown in the figure, both the background color and the color of the display section are achromatic near the C light source, indicating that the display is black and white.

Further, the contrast ratio, which is the ratio of the luminance during white display and the luminance during black display, is 15:1.

In this example, Δn-d of the liquid crystal display element was set to 0.5.
However, a similar black and white display can be obtained even when a liquid crystal display element with Δn-d of 0.96 to 0.97 is used.

The configuration is similar to that shown in FIGS. 6 and 8, or the liquid crystal element used as a phase plate has a twist angle α of 1-8.
Use one with a temperature of 0 degrees. At this time, β1 is 50 degrees, β2 is 30 degrees, β3 is 20 degrees, β4 is 25 degrees, and β5 is 45 degrees.

From the above, when using a liquid crystal element as a phase plate, it is not necessary to make the twist angle equal to that of the driving liquid crystal element.

Figure 10 shows the display colors on CIE chromaticity coordinates when a liquid crystal display element equipped with an organic color filter is used as the liquid crystal display element in the configuration shown in Figure 8 and driven at a 1'/2'OO duty. It was shown to.

As shown in the figure, each color has high color purity and a wide color range. The organic color filter used in this example was one used in liquid crystal color television receivers.

FIG. 11 shows the structure of a liquid crystal element according to another embodiment suitable for carrying out the present invention. As shown in the figure, a plastic film having birefringence is used instead of the parallel alignment liquid crystal element used as the phase plate shown in FIG. The angle formed by the rubbing axis direction 68 is approximately 90°, and the other configurations are the same.

In FIG. 1-2, the background color and the color of the display section in this configuration are shown on the CJE chromaticity coordinates. As shown in the figure, the color of the background and display section is an achromatic color similar to that of the C light source, allowing black and white display.

Note that it is desirable that the plastic film used as the phase plate has wavelength dependence of transmitted light close to wavelength dependence of transmitted light of liquid crystal. Figure 13 shows the wavelength dependence of transmitted light of a liquid crystal element with a diameter of 8n-d-〇 and 75μm, and Figure 14 shows the wavelength dependence of transmitted light with Δn-d = 0.
．． Figure 15 shows the wavelength dependence of the transmitted light of the polycarbonate film used as a 4.3 μm phase plate.
The wavelength dependence of light transmitted through the film to Peller 1, which has a small effect as a phase plate of =2.53 μm, is shown.

Figure 16 shows Δr1・d of a polycarbonate film and a liquid crystal element with a twist angle of 240°, which enables black and white display.
shows the relationship between The solution of Δn-d that realizes black and white display is not negative, has periodicity, and is 2π・Δn-d/λ±mπ/2
is satisfied and m is an integer, the display becomes black and white. for example,
In a liquid crystal element with a rice 1 angle of 240° and Δn-d = 0.80 μm, Δn-d of the polycarbonate film
is 0238 μm and 0 when the polarizing plate is made of orthogonal Nicols.
．． When it is 85 μm and parallel Nicols, a black and white display is obtained when it is 0.56 μm.

FIG. 17 shows the relationship between Δn-d of the film and the Con1 Hellas 1-ratio when a polycarbonate film was used, which was obtained through an experiment.

Figure 1.8 shows the relationship between Δn-d and transmittance of a polycarbonate film obtained through experiments.

FIG. 19 shows the relationship between Δn-d, contrast ratio, and transmittance of a polycarbonate film obtained through experiments.
1 or higher and a high transmittance of 15% or higher, the 80-d range of the film is preferably from 0.2 μm to 1.2 μm.

The liquid crystal element with 240 melon twist has been explained above, but when the Δn-d range of the liquid crystal element is from 0.4 μm to 1.5 μ'm, the liquid crystal element with a rice angle of 180 degrees to 270 degrees However, it shows similar results.

Similar results were obtained using the above-mentioned polycarbonate film, polyhinyl alcohol, and dorianyl sial-I film as the birefringent plastic film used as the phase plate.

In addition to the method of changing the thickness d of the film and the method of changing Δr by changing the stretching ratio in the film manufacturing process, the adjustment of Δn-d of the film can be done by laminating the film t3. An f method in which −d is varied is also possible.

FIG. 20 shows a film lamination method, but it is also possible to give the film an optical rotation of 360° from Oo by laminating the film 11 with the stretching axis slightly smoothed.

FIG. 21 shows a diagram in which a polarizing plate and a phase plate film are integrated into one structure. By backing the film with the polarizing plate 1, the element structure can be simplified.

Note that the liquid crystal element and the plastic film having birefringence used as the phase plate have a twist angle α of 180 degrees to 2 degrees.
Although the configuration has been described in which the liquid crystal display element in the range of 70 degrees and the upper polarizing plate are arranged, the liquid crystal element used as a phase plate and the plastic film 11 having birefringence are
Similarly, for a configuration arranged between a liquid crystal display element with a twist angle α in the range of 180 degrees to 270 degrees and a lower polarizing plate, the background color and display color can be made achromatic, and black and white display is possible. It will be done.

Furthermore, by printing at least one side of the birefringent plastic film used as a phase plate in red, green, or blue, it can be used as a color filter to display color on a liquid crystal display. is also possible.

As described above, by combining a liquid crystal display element and a member having birefringence, the background or display part can be made achromatic, making black-and-white display possible.

〔Effect of the invention〕

According to the present invention, since the color of the background and the display section can be made achromatic, there is an effect that black and white display is possible.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional twisted nematic type liquid crystal element with excellent time-division drive characteristics, and Figure 2 is a characteristic showing the relationship between applied voltage and brightness of displays using the conventional and present liquid crystal elements. 3 is a configuration diagram of a dot matrix display for explaining time-division driving,
Figure 4 is a diagram showing the background color and display color of a conventional twisted nematic type liquid crystal display element with excellent time-division driving characteristics on CIE chromaticity coordinates, and Figure 5 is a diagram showing the background color and display color of a liquid crystal display element of the present invention. Orientation direction of liquid crystal molecules when viewed from above (
For example, the rubbing direction), the twist direction of liquid crystal molecules, and the absorption axis (or polarization axis) direction of the polarizing plate; FIG. 6 is a perspective view showing the relationship in FIG. 5; FIG. 7 is a liquid crystal display element according to the present invention. FIG. 8 is a diagram showing the configuration of a liquid crystal display element in another embodiment of the present invention, and FIG. 9 is a diagram showing the configuration of the liquid crystal display element in another embodiment of the present invention. The color of the background and display part of the liquid crystal display element in the example was determined by CIE.
The diagram shown on the chromaticity coordinates, Figure 10, shows the CIE color display when using a liquid crystal display element equipped with an organic color filter.
11 is a diagram showing the configuration of a liquid crystal display element in another embodiment of the present invention, and FIG.
A diagram showing the background and display part colors of the liquid crystal display element in the example of the configuration shown in Figure 1 on CIE chromaticity coordinates. A diagram showing the wavelength dependence of transmitted light, Figure 14 is Δn-
d:=0.49 μm A diagram showing the wavelength dependence of transmitted light of a polycarbonate film, FIG. 15 is Δn−d;1.
A diagram showing the wavelength dependence of transmitted light of a 20 μm PET film, Figure 16 is a diagram showing the relationship between Δn-d of the polycarbonate film and Δn-d of the liquid crystal element, and Figure 17 is a diagram showing the relationship between Δn-d of the polycarbonate film and Δn-d of the liquid crystal element. Δn-d of film
FIG. 18 is a diagram showing the relationship between Δn-d and transmittance of polycarbonate film,
Figure 19 is a diagram showing the relationship between Δn-d, contrast ratio, and transmittance of a polycarbonate film, Figure 20 is a diagram showing an example of a film lamination method, and Figure 21 is a diagram showing an example of a film and polarizing plate lamination method. FIG. ], 21, 41.61... Upper electrode substrate of liquid crystal display element, 2, 22, 42.62... Lower electrode substrate of liquid crystal display element, 3, 23, 3. '3, 4. 3, 53, 63...
・Liquid crystal molecules, 4, 24, 44, 64...upper polarizing plate,
5.25, 45.65...lower polarizing plate, 6,26°4
6.66...Polarization axis of upper polarizing plate, 7.27°47.
67... Polarization axis of lower polarizing plate, 8,28°4.8.68
...Rubbing direction of upper electrode substrate of liquid crystal display element, 9,
29,49. '69...Rubbing direction of lower electrode substrate of liquid crystal display element, 10,30°50.70...Backlight j., 11...Scanning electrode, 12...Signal electrode, 3
1. 51... Upper electrode substrate of the liquid crystal element used as a phase plate, 32, 52... Lower electrode substrate of the liquid crystal element used as a phase plate, 34° 54... Rubbing of the upper electrode substrate of the liquid crystal element used as a phase plate Direction, 35.・55
...Rubbing direction of lower electrode substrate of liquid crystal element used as phase plate, 56...Dichroic dye, 71,72.75
...Plastic film with birefringence, 73.
...Plastic film stretching axis, 74...Polarizing plate.

Claims (1)

[Scope of Claims] 1. A nematic liquid crystal having positive dielectric anisotropy and to which an optically active substance is added is sandwiched between a pair of upper and lower electrode substrates arranged oppositely, and 180 degrees in the thickness direction thereof. The polarization axis or absorption axis of a pair of polarizing plates, which form a twisted helical structure within a range of 270 degrees from The product Δn・d of the thickness d (μm) of the liquid crystal layer and the refractive index anisotropy Δn of the liquid crystal is from 0.4 μm to 1.5 μm.
A liquid crystal display element, characterized in that one or more plastic films having birefringence are used as a phase plate to make the color produced in the liquid crystal display element in the range of m to approximately achromatic. 2. In the liquid crystal display element according to claim 1, polycarbonate or polyvinyl alcohol,
Or a liquid crystal display element using a plastic film made of trianyl cyanolate. 3. A liquid crystal display element according to claim 1, characterized in that at least one plastic film is laminated thereon. 4. In the liquid crystal display element according to claim 1, optical rotation is imparted by laminating at least one plastic film having birefringence and shifting the stretching axis of the plastic film. Characteristic liquid crystal display element. 5. In the liquid crystal display element according to claim 1, Δ is an index indicating the birefringence of the plastic film.
A liquid crystal display element in which n.d is in the range of 0.2 μm to 1.2 μm. 6. A liquid crystal display element according to claim 1, characterized in that a polarizing plate is lined with one or more plastic films having birefringence. 7. A liquid crystal display element according to claim 1, characterized in that a color filter is attached to a plastic film used as a phase plate.