BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflection liquid crystal display and, more particularly, to a reflection liquid crystal 10 display capable of displaying pictures having improved color purity.
2. Description of the Related Art
There is a known color liquid crystal display of an electric field-controlled birefringence system (hereinafter referred to 15 as "ECB system").
In an STN liquid crystal display, a liquid crystal layer has a birefringent effect to split a light beam. Therefore, when white light linearly polarized by a back polarizing plate travels through the liquid crystal layer, there occurs wave- 20 length dispersion causing the combination of elliptically polarized light beams having major axes of different directions depending on wavelength. Therefore, different transmittance curves for light beams of different wavelengths, such as red, green and blue light beams, are obtained when 25 voltage applied across the liquid crystal layer is varied gradually to change And which is a product of An and d (An is the index anisotropy of the liquid crystal layer and d is the thickness of the liquid crystal layer).
When the product And in a state where any voltage is not applied across the liquid crystal layer is not greater than a predetermined value and a birefringent layer having And substantially equal to that of the liquid crystal layer is interposed between a liquid crystal cell and a front polariz- 3J ing plate, the birefringent effect of the liquid crystal layer in a state where any voltage is not applied across the liquid crystal layer can substantially completely be cancelled out and light of characteristics nearly equal to those of the incident white light can be emitted. Therefore, pictures can 4Q be displayed in different colors, such as red, green and blue, by continuously varying the And of the liquid crystal layer by controlling the voltage applied across the liquid crystal layer. Thus, color change can be achieved by voltage control.
The ECB system does not employ any color filter having disadvantages, such as high manufacturing cost and low transmittance. Therefore, the liquid crystal display of the ECB system displays pictures on a bright screen, does not consume much power and can be manufactured at a low 50 manufacturing cost. The ECB system can be applied to both transmission liquid crystal displays and reflection liquid crystal displays.
Referring to FIG. 3, a reflection liquid crystal display 51 of the ECB system has a liquid crystal layer 52, an upper 55 glass substrate 53 and a lower glass substrate 54. An upper transparent electrode layer 55 and an upper alignment layer 56 are formed in that order on the inner surface of the upper glass substrate 53. A lower transparent electrode layer 57 and a lower alignment layer 58 are formed in that order on go the inner surface of the lower glass substrate 54.
The liquid crystal layer 52 is sandwiched between the upper alignment layer 56 and the lower alignment layer 58. A phase plate 59 capable of functioning as a birefringent layer, and an upper polarizing plate 60 are placed in that 65 order on the outer surface of the upper glass substrate 53. A lower polarizing plate 61 and a reflecting plate 62 are placed
in that order on the outer surface of the lower glass substrate 54. The reflecting plate 62 is formed by coating an irregular surface of a polyester film 65 with a metal reflecting film 63 of aluminum or silver by evaporation or the like. The metal reflecting film 63 has an irregular surface 64. The reflecting plate 62 is placed on the lower polarizing plate 61 with the irregular surface 64 of the metal reflecting film 63 in contact with the lower polarizing plate 61.
The reflection liquid crystal display displays pictures by using only sunlight or illuminating light and does not use any backlight. Although the reflection liquid crystal display has the advantage of operating at low power consumption, the lightness of pictures displayed by the reflection liquid crystal display is somewhat lower than that of pictures displayed by the transmission liquid crystal display provided with a backlight.
The liquid crystal display of the ECB system displays colors only by controlling the voltage applied across the liquid crystal layer without using any color filters. However, the liquid crystal display of the ECB system has difficulty in clearly displaying red and green in a satisfactory color purity.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a reflection liquid crystal display of the ECB system capable of displaying pictures in improved lightness and of displaying particularly red and green in improved color purity.
According to one aspect of the present invention, a reflection liquid crystal display comprises a first transparent substrate, a second transparent substrate disposed opposite to the first transparent substrate, and a liquid crystal layer sandwiched between the first and the second transparent substrate; wherein a transparent electrode layer and an alignment layer are formed in that order on the inner surface of the first transparent substrate, a reflecting polarizing film formed by laminating a transparent scattering layer and a light absorbing layer is placed on the outer surface of the first transparent substrate, a transparent electrode layer and an alignment layer are formed in that order on the inner surface of the second transparent substrate, and a phase plate and a polarizing plate are placed in that order on the outer surface of the second transparent substrate.
The reflection liquid crystal display in accordance with the present invention is provided with the reflection polarizing film instead of the polarizing plate and the reflecting plate to improve the color purity of red and green.
Preferably, the liquid crystal layer of the reflection liquid crystal display has a helical structure twisted through an angle in the range of 240° to 260°, a value An^ which is a product of Ant and d1; where Ant is the index anisotropy of the phase plate and d1 is the thickness of the phase plate, is in the range of 1000 to 2000 nm, a value And which is a product of An and d, where An is the index anisotropy of the liquid crystal and d is the thickness of the liquid crystal layer, is in the range of 800 to 1800 nm, the absorption axis of the polarizing plate is inclined to the delay axis of the phase plate at an angle in the range of -40° to -60° in a counterclockwise direction as viewed from the side of incident light, the delay axis of the phase plate is inclined to the alignment direction of the second alignment layer on the second transparent substrate at an angle in the range of -65° to -85° in a counterclockwise direction as viewed from the side of incident light, the absorption axis of the reflecting polarizing film is inclined to the alignment direction of the
