JP2783801B2 - LCD display - Google Patents

Description

The present invention relates to a so-called positive display large torsion angle white mode field effect type liquid crystal display. (B) Conventional technology In recent years, as a liquid crystal display having a high contrast and a wide viewing angle in high time division driving, an electric field effect type in which the twist angle of liquid crystal molecules is large as shown in JP-A-59-20409. Has been developed and commercialized. However, since this display mode utilizes the birefringence of liquid crystal, interference colors appear, and panel selection has been performed based on the color of the observer's preference, that is, the preference rather than the characteristics such as visibility and contrast. . Accordingly, a high time-division liquid crystal display with a display color that does not cause much problem of taste, that is, a black-and-white display close to printing has been developed as described in Nikkei Micro Devices Magazine, August 1987, p. We call it white mode. However, although the contrast measured physically is higher in the white mode than in the previous mode, the contrast from the viewpoint of visibility is the so-called color contrast (contrast based on the hue difference, saturation difference, and brightness difference of the color scheme). ) Is added, and the display contrast in the white mode is evaluated to be low. (C) Problems to be Solved by the Invention In view of the above points, the present invention effectively shields light leakage between display dots by focusing on birefringence due to a large twist angle of liquid crystal molecules. Thus, a liquid crystal display device having improved display contrast is provided. (D) Means for Solving the Problems The present invention provides a white mode having a large torsion angle as described above.
It has a helical structure with a torsion angle of 0 to 270 degrees and an a · Δn value of 0.
The background color is lightened by sandwiching a nematic liquid crystal of 40 to 0.70 with two polarizers whose polarization axes are at 60 to 90 degrees to each other, and at least one of the polarization axes and the adjacent liquid crystal alignment direction is at about 45 degrees. In a liquid crystal display device of light blue or beige color, a grid-like light-shielding film for forming corners of display dots (pixels) is provided on one effective display surface of a substrate for holding liquid crystal, and is more preferable. Is to make the thickness of the film thicker than that of the electrode so as to reduce the thickness of the liquid crystal layer under the film. (E) Function The light transmission amount of the entire display (hereinafter referred to as luminance)
However, the luminance ratio between the lit portion and the non-lit portion increases, and the actual display contrast increases. Hereinafter, this principle will be described in detail in embodiments. FIG. 1 is a sectional view of a liquid crystal display according to an embodiment of the present invention.
(1) and (2) are substrates using a glass plate or the like, and stripe-shaped electrodes (band-shaped electrodes) made of a transparent electrode or the like that are orthogonal to each other on the upper and lower surfaces for performing dot matrix display.
(11)... (21) (21), and alignment films (12) and (22) each having a surface subjected to a liquid crystal alignment treatment on each inner surface. A container for storing is formed. In addition, the stripe electrode (2
1) A grid-like light-shielding film (23) is provided between (21) ..., for example, by dispersing a black dye or pigment in a polymer material or dyeing gelatin or the like to black. Provide. The lattice-shaped coating (23) has a square opening formed by upper and lower striped electrodes (11) (11) ... (21) (2)
1) corresponding to the overlapping portion of the display dots, that is, the display dots (pixels), and the covering (23) is provided only in the area where the display dots exist, particularly in the effective display surface (Av). This is because if a coating is provided so as to extend to the surroundings, not only does the display become dark and does not lead to an improvement in contrast, but also when the display dots located in the periphery are lit, the black frame located outside the dots and the display are connected to improve the display quality. This is because it is not preferable because it lowers. (4) is a nematic liquid crystal sandwiched between the substrates (1) and (2). The liquid crystal molecules have a helical structure having a twist angle of 200 to 270 degrees, the refractive index anisotropy Δn and the liquid crystal layer. thickness a a · [Delta] n value which is the product of the (shown as t _LC in the sense that the thickness of the particular display dot region in FIG. 1) is 0.40
It has been chosen to be ~ 0.70. (5) and (5) are polarizers arranged outside the substrates (1) and (2) so as to sandwich the nematic liquid crystal (4). The polarizers (5) and (5) have a polarization axis of 60 to 90 mutually. The alignment film (12 or 12) which is arranged so as to intersect at a certain degree and which is closest to the polarization axis of one of the polarizers (5).
It is configured so that it intersects with the orientation direction 22) at approximately 45 degrees.
With this configuration, it is possible to configure a so-called white mode in which the background color is a light color system (saturation and brightness are low) and the hue is light blue or beige. FIG. 2 shows the display characteristics when such a liquid crystal display is illuminated by the surface illumination means (6). This characteristic is at 1/200 duty drive, and curves Sa and NSa are the voltage dependence of the selection bias and non-selection bias according to the present invention, and curve Sb
NSb shows the voltage dependence of the selection bias and the non-selection bias in the conventional white mode without the light-shielding film (23), respectively. When the drive voltage is set to, for example, VD in the figure in the high time-division matrix display, the display contrasts Ka and Kb are respectively displayed by the ratio of the selected luminance and the unselected luminance in the drive voltage VD, that is, Wa / Ba and Wb / Bb. Is done. Although the voltage dependence of the luminance is shifted to a darker side in the present invention as compared with the related art, the shift amount of the non-selection luminance and the shift amount of the selection luminance are substantially equal or the former is small and the selection of the contrast expression is small in the driving voltage VD. The contrast is improved because the luminance comes to the denominator. For example, if one display dot is 0.3 × 0.3 mm and a light-shielding film width of 0.03 mm is provided, the contrast is increased by 17%. The improvement of the contrast depends on the aperture ratio of one display dot, but at the same time, is attributed to the light leakage of the lit display dot due to the light-shielding coating. Therefore, the negative display (the brightness is increased by increasing the driving voltage) In the case of (1), the effect is small, and a remarkable effect is obtained at the time of the positive display as in the above-described example. Such an effect was somewhat observed even in a so-called 90 ° twisted nematic, which has a small twist angle and uses only the light-emitting properties of liquid crystal. However, unlike the case of using the light-imparting property, the effect is small if the corners of the display dots are cut off by the light interference due to the liquid crystal birefringence due to the large twist angle. More specifically, in twisted nematic, the light-emitting property of liquid crystal acts in a direction substantially perpendicular to the substrate surface, so that a stripe-shaped light-shielding film is provided between each electrode, and the display dots projected as a display device are provided. The effect of the effect was small because the luminance of the matrix was relatively low, and it was difficult to balance the luminance of the entire display surface. In the present invention, when the stripe-shaped light-shielding films are provided on the upper and lower substrates, the nematic liquid crystal sandwiched between the light-shielding films has a birefringent property, and the effect of preventing light leakage between display dots is reduced by light interference. Therefore, a light-shielding film should be provided in a grid pattern on only one of the substrates. The higher the light-shielding property of the film, the better, but even if the saturation luminance ST is reduced by 10% or more, the display contrast changes visually. Recognize. It is preferable that the photoelectric effect does not occur below the light-shielding film. In the white mode, the consistency of the alignment direction of the helical twist angle of the nematic liquid crystal with respect to the natural pitch is used by shifting it by 10 to 40% from the theoretical value (for example, by setting d / Po to 0.75 for 270 degree twist), If the value is further shifted by 10%, the effect of the light-shielding film becomes more remarkable. Substrate, for example, so that the thickness t _LC in the display dot regions of the nematic liquid crystal to selected values of 4～7Myuemu (1) when keeping the parallelism of (2), stripe electrodes (21) (21) When a light-shielding film (23) is provided at a thickness of, for example, 1.0 μm so as to have a thickness of 1.8 to 2.5 times the thickness of..., The voltage dependence of the luminance is not simply shifted to the dark side, but to Wb− Wa showed a tendency to spread, and the viewing angle dependency was improved. In other words, the viewing angle of high-contrast display was widened. (G) Effects of the Invention As described above, in the field effect type liquid crystal display of large torsion angle white mode where it is difficult to improve visibility by color contrast, light leakage between display dots can be effectively prevented, so that display contrast is increased. In particular, visibility is significantly improved in positive display.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a liquid crystal display according to an embodiment of the present invention, and FIG. 2 is a characteristic diagram of the liquid crystal display. (1) (2) ... substrate, (1
1) (11) ... (21) (21) ... striped electrode, (23)
... (light-shielding) film, (4) ... nematic liquid crystal,
(5) (5): Polarizer.

Claims (1)

(57) [Claims] Two substrates having striped electrodes for performing dot matrix display, and 200 to 2 substrates sandwiched between the substrates.
Helical molecular orientation with a torsion angle of 70 degrees and a · Δn value
A nematic liquid crystal of 0.40 to 0.70, and a polarizer sandwiching the nematic liquid crystal, wherein the upper and lower polarization axes are at 60 to 90 degrees to each other, and at least one of the polarization axes is approximately 45 degrees to the alignment processing direction of the adjacent nematic liquid crystal. A liquid crystal display, comprising: a grid-like light-shielding film provided on an effective display surface on one of the substrates. 2. 2. The liquid crystal display according to claim 1, wherein the light-shielding film is sufficiently thicker than the stripe-shaped electrode, and the thickness of the nematic liquid crystal is thinner at the position of the light-shielding film. .