JP2627311B2 - LCD display - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display which is suitable for high-time-division driving and has a clear display.

B) Conventional technology In recent years, liquid crystal display devices have been commercialized in which liquid crystal molecules are oriented so as to form a helical structure with a screw angle of 180 to 300 degrees, thereby enabling a wide viewing angle with good contrast and a high time-division driving. However, the display color appears to be colored blue or yellow due to the birefringence of the liquid crystal. Therefore, Nikkei Microdevices Magazine n
As described in page o.28 (October 1987), page 84, a liquid crystal display for high time division driving capable of displaying black on a white background has been developed. Of the several methods, the method using a phase compensation panel plate is said to bring the other hues closest to a white background, but is not preferable because two liquid crystal panels are required.

More specifically, in the above-described liquid crystal display in which liquid crystal molecules are greatly twisted, interference colors are observed due to the birefringence of the liquid crystal. This is because light appears in the liquid crystal layer because the light ray is elliptically deflected, so that the same liquid crystal panel as the driving liquid crystal panel is laminated for color erasure for the purpose of twisting the twisted light. ing. However, such a liquid crystal panel is suitable for high time-division driving, so that the display area becomes large, and since the control of the liquid crystal layer is strictly controlled, the yield is low and the cost is high. Further, since the entire display is thick, the display position is shifted due to parallax and the contrast is changed, which is not preferable.

On the other hand, in terms of adjusting the hue on the liquid crystal display, 1 /
The idea of using a four-wavelength plate or a phase plate has been around for a long time, for example, Japanese Patent Application Laid-Open Nos. 50-72645 and 55-600. However, it is practically difficult to achromatically attenuate by circular deflection or a quarter-wave plate, and when using a phase plate, the effect cannot be obtained unless the characteristics of the liquid crystal layer are specified. Interfering colors appeared and it was not practical.

C) Problems to be Solved by the Invention The present invention has been made in view of the above points. In a liquid crystal display in which liquid crystal molecules have a helical structure with a screw angle of 180 to 300 degrees, an optical uniaxial liquid crystal is used. It is an object of the present invention to provide a liquid crystal display in which the display color is achromatic and the contrast is increased by laminating a phase plate for compensating the liquid crystal layer so as to be a layer having a characteristic property, and the display position does not shift or the contrast does not change due to parallax.

D) Means for Solving the Problems The present invention provides a liquid crystal display having a helical structure in which the liquid crystal molecules have a screw angle of 180 to 300 degrees, including a phase plate inserted between a liquid crystal layer and a polarizer. The product of the birefringence anisotropy △ n and the thickness d △ n · d (LC) of the phase plate and the product of the birefringence anisotropy △ n and the thickness d △ n · d (PH) are 0.72 △ n · d ( LC) -0.36 <{n · d (PH) <0.72} n
-The relation of d (LC) -0.16 is satisfied. In particular, the phase plate has optical uniaxiality, the direction of the optical axis and the polarization axis of the polarizer are 40 degrees or more and 50 degrees or less, and the polarization of the polarizer is In this liquid crystal display, the angle between the axis and the orientation direction of the liquid crystal molecules adjacent to the axis is 40 degrees or more and 60 degrees or less.

In the present invention, the liquid crystal layer is homogeneously oriented, has a thickness of 10 μm or less, and has a retardation Δnd (LC) of 0.6 to 0.9.
A nematic liquid crystal layer in which liquid crystal molecules form a spiral structure with a screw angle of 180 to 300 degrees, and a polarizer sandwiching the liquid crystal layer,
It consists of a resinous phase plate inserted between the liquid crystal layer and the polarizer, and the retardation of the phase plate △ nd (PH) is 0.72 △ nd (LC) −0.36 <△ nd (PH) < 0.72 △ n
-A liquid crystal display with an achromatic background by satisfying the relationship of d (LC)-0.16.

(E) Function As a result, the liquid crystal display can perform display with uncolored light rays and black light shielded, so that a display with high display quality as if printed on paper can be performed and the contrast is high. Since this display can be inverted between black and white, both negative display and positive display can be performed.

Since only one liquid crystal panel is used and the phase plate can be manufactured by molding, the productivity is good and the cost is low. Further, since the retardation Δn · d (PH) of the phase plate can be reduced, the phase plate can be configured to have a large area while keeping the optical characteristics constant.

F) Embodiment FIG. 1 is a sectional view of a liquid crystal display according to an embodiment of the present invention.
Reference numeral 1 denotes a substrate formed of a glass plate or the like having a transparent electrode and an alignment film of liquid crystal molecules on its inner surface. The transparent electrodes are arranged so as to be orthogonal to each other on the upper and lower substrates so as to perform a dot matrix display, for example. An orientation treatment is performed so that the molecules are homogeneously oriented. These substrates 1 are adhered in parallel by a sealant to form a container. 2 is the substrate 1
A liquid crystal layer composed of a chiral nematic phase liquid crystal having a positive dielectric anisotropy sandwiched between the liquid crystal layers. The liquid crystal molecules have a helical structure with a screw angle of 180 to 300 degrees, for example, a 240 degree twist nematic. Numeral 3 denotes two polarizers arranged outside the substrate 1 so as to sandwich the liquid crystal layer 2, and the polarization axis is set so as to optimize the contrast peculiar to the display mode as described in the related art. ing. Reference numeral 4 denotes a resin phase plate inserted between the liquid crystal layer 2 and the polarizer 3.

A more specific description will be given, including the respective optical characteristics. The liquid crystal layer 2 should basically have the same conditions as those of the conventional display mode in which the liquid crystal molecules have a large twist angle utilizing birefringence. Optical properties based on the optical properties and the optical rotation caused by the helical structure, it was found that the optical properties were more complicated. When an anisotropic body is sandwiched between orthogonal Nicols, the intensity of light reaching the naked eye through the laminate, that is, the brightness, is expressed by the following equation.

I = I o sin ² (2θ) sin ² {(π / λ) {nd} where I: transmitted light intensity I o: incident light intensity θ: optical axis of the optically uniaxial anisotropic body and one polarization axis Λ: wavelength of light used for observation Δn: refractive index anisotropy of the optically uniaxial anisotropic material d: thickness of the optically uniaxial anisotropic material From the above equation, the change in brightness when observing with monochromatic light depends only on θ. That is, light and dark are repeated four times while rotating the optically uniaxial anisotropic body by 360 degrees. However, when observing with white light or light of a color close thereto, sin ² {(π / λ)}
Since nd｝ changes with the wavelength λ, the transmitted light intensity I has wavelength dependence. In order to obtain the maximum contrast as the optically uniaxially anisotropic body, the polarization axis of the polarizing plate and the optical axis of the optically uniaxially anisotropic body are shifted from each other by 45 degrees, as is well known. However, in the case of the liquid crystal layer, the liquid crystal molecules have a helical structure, so that optical rotation occurs, and the optical axis rotates along the twist, so that the above formula is not satisfied. Therefore, the alignment direction of the liquid crystal molecules that approach the polarization axis of one polarizer
The angle was set to 45 degrees, the other polarizer was rotated, and the spectrum of the transmitted light was examined. As shown in FIG. 2, the transmitted light intensity characteristic corresponding to the above equation in the visible light region was obtained. It was found that there were two angles shown (states 1 and 4 in the figure). At this time, the angle between the polarization axis of the rotated polarizer and the liquid crystal molecule axis close to it is almost 40 to 60 in the same direction as the twist of the liquid crystal molecules with the liquid crystal molecule axis as a base point.
Degrees and 130-150 degrees. Based on this state, as a method of compensating for birefringence in a liquid crystal display, it was considered to adjust the optical characteristics of the phase plate so that the laminate of the liquid crystal layer and the phase plate becomes an optically uniaxial anisotropic body.

According to the empirical formula derived based on this principle, the liquid crystal molecules are
In a liquid crystal display having a helical structure with a screw angle of 180 to 300 degrees, the light transmitted through the liquid crystal layer is represented by I = I cos ² {(π / λ) (0.72 {nd (LC) -a)}. a changes according to the helical structure and tilt angle of the liquid crystal layer, and takes a value of 0.16 <a <0.36. Therefore, the retardation of the phase plate for making the display achromatic, that is, the product of the birefringence anisotropy Δn and the thickness d Δnd · (PH) is 0.72Δnd · (LC) −0.36 <Δn.・ D (PH) <0.72 △ n
When the relationship of d (LC) −0.16 is satisfied, the optical path length of the transmitted light of the liquid crystal display having a spiral structure in which the optically uniaxial anisotropic substance and the liquid crystal molecules have a screw angle of 180 to 300 degrees becomes almost equal.

FIG. 3 shows a region according to such conditions, and FIG. 4 and a typical embodiment are shown below.

Here, α is the angle between the polarization axis (base point) of the polarizer provided with the phase plate and the light distribution direction of the liquid crystal molecules adjacent thereto, and β is the polarization axis (base point) of the polarizer without the phase plate. The angle between adjacent liquid crystal molecules, γ, is the angle between the alignment direction of the polymer of the phase plate (the optical axis direction of the optical uniaxiality) and the polarization axis (base point) of the adjacent polarizer. The lots d and e are unfavorable examples listed for comparison.

Note that the display becomes darker and the contrast becomes lower as Δn · d (LC) becomes smaller. On the other hand, when it becomes larger, the phase wavelength of the birefringent interference color shifts, and eventually higher-order interference occurs. The contrast is good, the color of the interference of the liquid crystal layer is easily compensated, and the phase plate is easily uniaxially stretched. The conditions for the thickness of the liquid crystal layer are 10 μm or less and the product of the birefringence anisotropy Δn and the thickness d Δn.・ 180 with d (LC) in the range of 0.6 to 0.9
The object is a nematic liquid crystal layer having a helical structure having a screw angle of about 300 degrees.

The above-mentioned phase plate 4 is made of polyvinyl butyrol,
A polymer resin plate of polyvinyl alcohol, polyester, cellulose acetate, polypropylene, polycarbonate, or the like can be uniaxially stretched and used as a sheet, or a single sheet or a plurality of sheets can be laminated.

G) Effect of the Invention As described above, the liquid crystal display compensates for the light beam birefringently rotated by the liquid crystal panel as an optically uniaxial anisotropic body, so that the uncolored light beam (this makes the ground color white). ), The display can be performed in black light, which is shielded from light, so that a display with high display quality, such as black printing on white paper, can be performed, and the contrast is high. Since this display can be inverted, a negative display can also be performed. Since only one liquid crystal panel is used and the phase plate can be manufactured by molding, the productivity is good and the cost is low.

Further, since Δn · d (PH) of the phase plate can be reduced, a large area can be formed while keeping the optical characteristics of the phase plate constant. Furthermore, since the entire liquid crystal display can be made thin, there is no shift in display position or change in contrast due to parallax.

[Brief description of the drawings]

1 is a sectional view of a liquid crystal display according to an embodiment of the present invention, FIG. 2 is a characteristic diagram according to the present invention, FIG. 3 is a characteristic diagram relating to birefringence anisotropy of the present invention, and FIG. FIG. 4 is a display characteristic diagram of the liquid crystal display according to the embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Liquid crystal layer, 3 ... Polarizer, 4 ... Phase plate.

Claims (2)

(57) [Claims] 1. A liquid crystal display device comprising: a substrate; and liquid crystal molecules having a positive dielectric anisotropy.
A nematic liquid crystal layer that is homogeneously oriented to form a helical structure with a screw angle of 180 to 300 degrees and is sandwiched between substrates, and a polarizer that has a polarization axis set to sandwich the liquid crystal layer and optimize contrast. And a phase plate inserted between the liquid crystal layer and the polarizer. The product Δn · d (LC) of the birefringence anisotropy Δn of the liquid crystal layer and the thickness d and the birefringence anisotropy Δn of the phase plate
A liquid crystal display characterized in that the product Δn · d (PH) of the thickness d and the thickness d satisfies the following relationship: 0.72Δnd · (LC) −0.36 <Δnd · (PH) <0.72Δnd · (LC) −0.16 . 2. A helix having a helix angle of 180 to 300 degrees, wherein the liquid crystal molecules are homogeneously oriented and have a thickness of 10 μm or less, a product Δn · d (LC) of birefringence anisotropy Δn and thickness d of more than 0.6 and less than 0.9. A nematic liquid crystal layer having a structure, a polarizer sandwiching the liquid crystal layer, and a product Δn · d (PH) of a birefringence anisotropy Δn and a thickness d inserted between the liquid crystal layer and the polarizer is 0.72Δn. A liquid crystal display having an achromatic background with a resin phase plate that satisfies the relationship d (LC) −0.36 <Δn · d (PH) <0.72Δn · d (LC) −0.16.