JP2947801B2 - Nematic liquid crystal display device with twisted helical structure - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a field effect liquid crystal display device having excellent time-division driving characteristics and capable of displaying black and white.

[Conventional technology]

FIG. 2 shows a structure of a liquid crystal display device having excellent time division driving characteristics used in a conventional liquid crystal display device.
As shown in FIG. 2, a nematic liquid crystal 3 having a positive dielectric anisotropy (abbreviated to a molecular orientation state) is sealed between two electrode substrates 1 and 2. As shown, the liquid crystal molecules have a twisted helical structure exceeding 90 ° between the substrates, preferably in the range of 180 ° to 270 °. Further, polarizing plates 11 and 5 are arranged outside the electrode substrates 1 and 2 so that their polarization axes (or absorption axes) are at an appropriate angle. This angle is usually in the range of 20 ° to 70 °.

The liquid crystal display device with the above structure is described in USP 4,443,065 and a paper by Tei Jiyo Shiehua (SID Digest, 1985).
p.120-123, “24 × 80 character LCD Panel Using the
Supertwistad Birefringence Effect "].

In order to align liquid crystal molecules between two electrodes so as to form a helical structure twisted in the range of 180 to 270 degrees,
For example, the surface of the electrode substrate in contact with the liquid crystal is rubbed in one direction with a cloth or the like, that is, a so-called rubbing method.
The rubbing direction, that is, the rubbing directions 8, 9 at this time is the alignment direction of the liquid crystal molecules. The two electrode substrates 1 and 2 thus oriented are opposed to each other with a gap so that the respective rubbing directions 8 and 9 cross each other in a range of approximately 180 to 270 degrees. When the substrates 1 and 2 are adhered with a sealant and the gap is filled with a nematic liquid crystal 3 having a positive dielectric anisotropy, the liquid crystal molecules are almost 180 degrees between the electrode substrates.
The molecular arrangement is a spiral structure that rotates from 270 degrees to 270 degrees. Polarizing plates 11 and 5 are provided above and below the liquid crystal element thus configured, and the polarization axes (or absorption axes) 6 and 7 of the liquid crystal molecules adjacent to each electrode substrate are adjusted based on the optimum value of contrast. In the clockwise or counterclockwise direction, a size in the range of 0 to 70 degrees is required based on the arrangement direction of.

FIG. 2 shows the transmission mode in which the backlight 10 is arranged. However, the operation principle of the reflection mode provided with a reflector instead of the backlight 10 is substantially the same as that of the transmission mode.

FIG. 3 shows the relationship between the applied voltage and the luminance of a display using a liquid crystal element having such a structure. In the same figure, two of normally open mode A and normally closed mode B are shown.
Although the two modes are shown, each has a characteristic that the luminance rises sharply with respect to the applied voltage. This characteristic is a factor that enables high time-division driving without lowering contrast.

Here, the time division driving will be briefly described by taking a dot matrix display as an example. As shown in FIG. 4, stripe-shaped Y electrodes (signal electrodes) are formed on the lower electrode substrate.
An X electrode (scanning electrode) 11 is formed on the upper electrode plate, and characters and the like are displayed by turning on or off the liquid crystal at the intersection of the X and Y electrodes. In the figure, n scanning electrodes are
_{X 1, X 2, ...... X} n, X 1, X 2, performs time-division driving Repeat ...... X _n and repeated line sequential scanning. When the selected (X ₃ in the figure) a certain scanning electrode, to all the pixels on the electrodes, Y ₁ is a signal electrode 12, Y _2, ...... Y _n from the selection or non-accordance with the signal to be displayed The selected display signal is added at the same time. As described above, lighting or non-lighting of the intersection is selected by the combination of the voltage pulses applied to the scanning electrode 11 and the signal electrode 12.
The number of scan electrodes X in this case corresponds to the number of time divisions.

However, the liquid crystal display element of super twisted nematic type having the excellent time-division driving characteristic has a background color and a display color shown on the CIE chromaticity coordinates in FIG. At least one of the parts was colored and black-and-white display was not possible.

However, in recent years, demands for improving the image quality of liquid crystal display elements and increasing the amount of display information have become severe, and the required specifications are shifting to monochrome display and further to color display. The situation has not been reached.

[Problems to be solved by the invention]

In the above-mentioned prior art, no consideration was given to making the background and the display unit white and black, and there was a limit in terms of display quality. In addition, since at least one of the background and the display unit is colored, it is impossible with this conventional technique to make a color in combination with a color filter.

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the coloring of the background and the display unit so as to be close to an achromatic color, thereby enabling monochrome display and color display.

[Means for solving the problem]

According to the liquid crystal display device of the present invention, a pair of substrates having a plurality of electrodes on opposing surfaces, a twisted nematic liquid crystal layer having a twist angle of 180 degrees or more and 270 degrees or less sandwiched between the pair of substrates, and a pair of substrates The liquid crystal device includes a pair of polarizing plates interposed therebetween, a phase plate disposed between the pair of polarizing plates, and a light source for irradiating the liquid crystal layer with light.

The value of Δn · d, which is the product of the value of the refractive index anisotropy Δn of the liquid crystal layer and the value of the thickness d of the liquid crystal layer, is 0.6 to 0.97, and the polarization axis direction of the pair of polarizers is the direction of the liquid crystal molecules of the liquid crystal layer. Are set at a predetermined angle from the arrangement direction. Further, a phase plate having birefringence and having no light-emitting property is used as a phase plate, and a three-wavelength cold cathode tube is used as a light source.

[Action]

In a liquid crystal display element called a super twisted nematic type, at least one of a background and a display portion is colored. By correcting the phase of at least one of the colored light of the background and the display using a phase plate having birefringence, the coloring of the background and the display is reduced, and the color approaches an achromatic color. As a result, in the conventional super twisted nematic liquid crystal display device in which at least one of the background and the display section is colored, the background and the display section are less colored. , Black and white display becomes possible. Other objects and other features of the present invention will become apparent from the following description of embodiments.

〔Example〕

Hereinafter, a liquid crystal display device suitable for carrying out the present invention will be described in detail with reference to the drawings.

FIG. 6 shows the arrangement direction (for example, rubbing direction) of liquid crystal molecules, the twist direction of liquid crystal molecules, and the absorption axis (or polarization axis) of a polarizing plate when the liquid crystal display device according to the present invention is viewed from above.
Indicates the direction. FIG. 7 is a perspective view showing the relationship.

The twist direction and twist angle α of the liquid crystal molecules 23 are determined by the rubbing direction 28 of the upper electrode substrate 21 and the rubbing direction of the lower electrode substrate 22.
29 and the type and amount of the light-emitting substance added to the nematic liquid crystal. The torsion angle α exceeds 90 ° and is 18
0 ° to 270 ° is desirable.

In the present embodiment, even if the number of scanning lines is 200 or more, the object was to provide a liquid crystal element capable of performing black and white display in which the contrast was sufficiently satisfied.
Degree.

The angle β between the polarization axis (or absorption axis) 26 of the upper polarizer 24 and the polarization axis (or absorption axis) 27 of the lower polarizer 25
_In consideration of contrast, brightness, color, and the like, ₃ is preferably in the range of 0 to 60 degrees when no phase plate is used.
However, in this example using a phase plate, for example, G1225DU manufactured by Nitto Denko was used as the polarizing plate, and β ₃ was set to 20 degrees. Further, an angle β ₁ formed 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 and the polarization axis (or absorption axis) 27 of the lower polarizing plate 25 and the lower electrode substrate twenty two
The angle β ₂ between the rubbing direction 29 and the rubbing direction 29 is preferably in the range of 0 to 60 degrees in consideration of contrast, brightness, color, and the like. 20 degrees beta ₁ in this embodiment, the beta ₂ and 40 degrees.

Here, the value of Δn of the liquid crystal of the liquid crystal display element has wavelength dependence, and tends to be large on the short wavelength side and small on the long wavelength side. In general, this wavelength dependence becomes more remarkable as the value of Δn of the liquid crystal increases. The value of Δn used in the present specification is measured at 25 ° C. using He-Ne laser light (wavelength: 6328 °). In this embodiment, a nematic liquid crystal containing biphenyl-based liquid crystal and estercyclohexane-based liquid crystal as main components, to which 0.5% by weight of S811 manufactured by Merck is added as a light-transmitting substance. In this embodiment, a liquid crystal of Δn = 0.083 is used, and the thickness of the liquid crystal layer is 6
μm. Therefore, the Δn ·
d was set to 0.5 μm.

Further, in the configuration of the liquid crystal display element and the polarizing plate as described above, the background and the display portion are colored as described above, and thus, in the present invention, the background color and the display are provided between the liquid crystal display element and the upper polarizing plate 24. A phase plate for achromatic color was arranged.

As a phase plate for bringing the background color and the display color closer to an achromatic color, the twist angle α between the two glass substrates 31 and 32 is 0.
A device in which liquid crystal 33 having a so-called parallel orientation was sealed was used.

Generally, the rubbing direction 34 of the upper substrate 31 of the parallel alignment liquid crystal element as the phase plate and the polarization axis 26
The angle beta ₅ with the polarization axis 27 of the rubbing direction 35 and the lower polarizing plate 25 of the angle beta ₄ and the lower substrate 32, considering that make complementary background color and the display color of the liquid crystal display device , 0
A range of degrees to 60 degrees is desirable.

In this embodiment, β ₄ is 25 degrees, β ₅ is 45 degrees or β ₄ is 65 degrees.
Every time, was the β ₅ to 45 degrees. Further, Δn · d of the parallel alignment liquid crystal element as this phase plate was set to 0.36.

In this embodiment, a cold cathode tube is used as the light source 30 for the backlight. The cold-cathode tube is a three-wavelength light source, and the emission color can be relatively freely selected by selecting the phosphor. Also,
It has advantages such as low power consumption, small heat generation and long life.
The three-wavelength light source can adjust the peak values of the blue, green, and red emission energies according to the purpose.

With such a liquid crystal element configuration, the background color and the display color can be made almost achromatic. In the present embodiment, a liquid crystal display element having a twist angle α of 260 degrees was used.
Similarly, when the torsion angle α is in the range of 180 ° to 270 ° and further, the background color and the display color can be made almost achromatic.

FIG. 8 shows the colors of the background and the display unit according to the present embodiment.
Shown in E chromaticity coordinates. As shown in the figure, both the background color and the color of the display section are near achromatic near the C light source, indicating that the display is black and white. At this time, the contrast ratio, which is the ratio between the luminance in white display and the luminance in black display, is 9: 1.

FIG. 9 shows a configuration of a liquid crystal element according to another embodiment suitable for carrying out the present invention. As shown in FIG. 7, instead of the liquid crystal display element having a twist angle α of 260 degrees and a Δn · d of 0.5 shown in FIG. 7, a twist angle α of 260 degrees and a Δn · d of 0.5 A guest-host type liquid crystal display device to which a weight percent of black dichroic dye is added is used, and other configurations are the same as those in FIG.

FIG. 10 shows the colors of the background and the display unit according to the present embodiment.
Shown in E chromaticity coordinates. As shown in the figure, both the background color and the color of the display section are almost achromatic near the X light source, and the black and white display is superior to the embodiment shown in FIG. I'm squeezed. At this time, the contrast ratio, which is the ratio between the luminance in white display and the luminance in black display, is 15: 1.

In the above two embodiments, Δn of the liquid crystal display element is
Although the value is set to 0.5, the same monochrome display can be obtained even when a liquid crystal display element having Δn · d of 0.6 to 0.97 is used.

The structure is the same as that shown in FIGS. 6 and 8, except that the liquid crystal element used as the phase plate has a twist angle α of 180 °.
Use the first one. At this time, β ₁ is 50 degrees and β ₂ is 30
Degrees, β ₃ is 20 degrees, β ₄ is 25 degrees, and β ₅ is 45 degrees.

FIG. 13 shows a preferred relationship between the torsion angle (θ ₂ ) of the correction liquid crystal element used as the phase plate and Δn · d of the correction liquid crystal element.

FIG. 11 shows the configuration shown in FIG. 9, in which a liquid crystal display element having an organic or inorganic color filter is used as the liquid crystal display element, and the display color when driven at 1/200 duty is displayed on the CIE chromaticity coordinates. Indicated.

As shown in the figure, it can be seen that each color has high color purity and a wide color specification range. The organic or inorganic color filters used in this example were those used in liquid crystal color television receivers.

FIG. 1 shows the configuration of a liquid crystal device according to another embodiment suitable for carrying out the present invention. As shown in FIG.
A birefringent film 71 is used instead of the parallel alignment liquid crystal element used as the phase plate shown in the figure, and the other configuration is the same.

The display element composed of the rubbing directions 68 and 69 of the alignment films provided on the upper electrode substrate 61 and the lower electrode substrate 62 and the liquid crystal 63 has the same twist angle as that shown in FIG.
260 °, Δn = 0.083, and the thickness of the liquid crystal layer was 6 μm. Polarizing plates 64 and 65 are provided above and below the liquid crystal display element, and the relationship between their polarizing axes (or absorption axes) 66 and 67 and the rubbing direction is the same as that shown in FIG. Further, a backlight 70 was provided on the lower polarizing plate 65 side. This backlight is also a three-wave cold-cathode tube. In a super twisted nematic liquid crystal device having such a configuration, a film 71 having birefringence is provided between the upper polarizing plate 64 and the display device, and the phase correction is performed by the film 71. Is the law.

Fig. 12 shows the background color and display color
It is shown on the E chromaticity coordinates. As shown in the figure,
The colors of the background and the display section are almost achromatic near the C light source, and black and white display is possible.

The film 71 used in this example is a film obtained by uniaxially stretching a polycarbonate film to give birefringence.The product of the birefringence Δn and the thickness d is such that the twist angle of the liquid crystal element is 240 °. , Δn · d is 0.8 μm, 0.4 μm
m, twist angle of liquid crystal element is 240 °, Δn · d is 1.2μ
m, the angle between the upper rubbing axis 68 and the film stretching axis (that is, the optical main axis) is about 90 degrees, and depending on the element conditions of the liquid crystal display element,
It has been found that the best value should be selected.

When the twist angle of the liquid crystal display element is 240 °, preferable combinations of Δnd of the liquid crystal layer and Δnd of the film used as the phase plate are shown in Table 1 and FIG.

Further, in order to select the optimum Δn · d, various transparent materials such as polyvinyl alcohol and trianyl cyanolate may be used as the film material.

Further, it is apparent that a plurality of films may be stacked in order to obtain the optimum value of Δn · d.

In addition, a parallel alignment liquid crystal element used as a phase plate and a plastic film having birefringence were twisted at a twist angle α of 180.
Although the configuration arranged between the liquid crystal display element in the range of ° to 270 ° and the upper polarizing plate has been described, the parallel alignment liquid crystal display element used as the phase plate and the plastic film having birefringence have a twist angle α of 180 °. Also, in the configuration arranged between the liquid crystal display element and the lower polarizing plate in the range of from 270 ° to 270 °, the background color and the display color can be made achromatic, and a monochrome display can be obtained.

As described above, by combining the liquid crystal display element with the member having birefringence for the color of the background or the display section, the color of the background and the display section can be made close to achromatic, thereby enabling monochrome display. Furthermore, since black-and-white display has become possible, the color filter of the three primary colors is arranged in a mosaic form by a generally known colorization method, so that a display device using a super-twisted nematic display element can be used. It is possible to realize colorization.

Further, it has been experimentally found that the liquid crystal material is used as the phase plate and the film is used as the phase plate, and the latter has a high transmissivity.

〔The invention's effect〕

According to the present invention, since the colors of the background and the display unit can be made close to achromatic colors, there is an effect that black-and-white display and further color display can be performed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a liquid crystal display device according to the present invention, FIG. 2 is a configuration diagram of a conventional super twisted nematic type liquid crystal device, and FIG. 3 is a diagram of a display using the conventional and the present invention. Characteristic diagram showing the relationship between applied voltage and luminance,
FIG. 4 is an electrode configuration diagram of a dot matrix display for explaining time-division driving, and FIG. 5 is a CIE chromaticity coordinate diagram showing the background color and display color of a conventional super-twisted nematic liquid crystal display device. FIG. 6 is a view showing the alignment direction (for example, rubbing direction) of liquid crystal molecules, the twist direction of liquid crystal molecules, and the absorption axis (or polarization axis) direction of a polarizing plate when the liquid crystal display device of the present invention is viewed from above. FIG. 7 shows the sixth
FIG. 8 is a CIE chromaticity coordinate diagram of the background of the liquid crystal display device and the color of the display unit in the present invention, and FIG. 9 is a configuration diagram of the liquid crystal display device in another embodiment of the present invention. ,
FIG. 10 is a CIE chromaticity coordinate diagram of the background of the liquid crystal display device and the color of the display unit in the embodiment having the configuration shown in FIG. 9, and FIG. 11 is a display using a liquid crystal display device having an organic color filter. The color is a CIE chromaticity coordinate diagram.
FIG. 13 shows the relationship between the twist angle of the correction liquid crystal element used as a phase plate and Δn · d, and FIG. 13 shows the relationship between Δn · d of the film used as the phase plate. FIG. 4 is a diagram illustrating a relationship between Δn · d of a liquid crystal element. 1,21,41,61: Upper electrode substrate of liquid crystal display element, 2,22,42,62
… Lower electrode substrate of liquid crystal display element, 3,23,33,43,53,63… Liquid crystal molecules, 4,24,44,64… Upper polarizing plate, 5,25,45,65… Lower polarizing plate, 6,26,46,66… Polarization axis of upper polarizer, 7,27,47,67…
Polarization axis of lower polarizing plate, 8, 28, 48, 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, 11: scanning electrode, 12: signal electrode, 31, 51: upper electrode substrate of liquid crystal element used as phase plate, 32, 52: lower electrode substrate of liquid crystal element used as phase plate, 34, 54: Rubbing direction of upper electrode substrate of liquid crystal element used as phase plate, 3
5, 55: rubbing direction of lower electrode substrate of liquid crystal element used as phase plate; 56: dichroic dye; 71: plastic film having birefringence.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Junichi Square 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd.Hitachi Research Laboratory, Ltd. (72) Keiji Nagae 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. In-house (72) Inventor Hideaki Kawakami 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd.Hitachi Research Laboratories Co., Ltd. Yasuhiko Shinto 3300 Hayano, Mobara City, Chiba Prefecture Inside the Mobara Plant, Hitachi, Ltd. (56) References JP-A-64-519 (JP, A) JP-A-63-151924 (JP, A) JP-A 1-179912 (JP, A) JP-A-60-26322 (JP, A) European publication 246842 (EP, A1) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02F 1/13-1/141

Claims (5)

(57) [Claims] 1. A pair of substrates having a plurality of electrodes on opposing surfaces, a twisted nematic liquid crystal layer sandwiched between the pair of substrates and having a twist angle of 180 ° or more and 270 ° or less, and disposed between the pair of substrates. A pair of polarizing plates, a phase plate disposed between the pair of polarizing plates, a color filter formed on one of the pair of substrates, and a light source for irradiating the liquid crystal layer with light. A liquid crystal display device, wherein a value of Δn · d which is a product of a value of a refractive index anisotropy Δn of the liquid crystal layer and a value of a thickness d of the liquid crystal layer is 0.6 μm to 0.97 μm.
The polarization axis direction of the pair of polarizing plates is set to be shifted by a predetermined angle from the alignment direction of the liquid crystal molecules of the liquid crystal layer, and a phase plate having birefringence and having no light-emitting property is used as the phase plate. A color liquid crystal display device using a three-wavelength cold cathode tube as the light source. 2. A color liquid crystal display device according to claim 1, wherein a film is used as said phase plate. 3. A color liquid crystal display device according to claim 2, wherein said film is a uniaxially stretched film. 4. A color liquid crystal display device according to claim 2, wherein a plurality of said films are used. 5. A color liquid crystal display device according to claim 1, wherein said phase plate is a liquid crystal layer of parallel alignment.