Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-10-28
2003-06-17
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S117000
Reexamination Certificate
active
06580484
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a laminated phase plate for use in direct-viewing-type liquid crystal display devices used for office machinery including word processors and notebook-sized personal computers, various types of visual equipment and game equipment, a projection-type liquid crystal display device which displays an enlarged image by projecting an image of a reflective liquid crystal display illuminated by light source, and liquid crystal display devices such as a head-mount display which is fixed at the head of a viewer, and also relates to liquid crystal display devices incorporating the laminated phase plate.
BACKGROUND OF THE INVENTION
Conventionally, an optical phase difference compensation plate composed of an oriented polymer film has been used for various applications. Examples of the optical phase difference compensation plates includes a ¼ waveplate for giving a phase difference of {fraction (&pgr;/2)} between two linearly polarized lights having vibration planes perpendicular to each other, and a ½ waveplate for giving a phase difference of &pgr; between them. Since the phase differences of these optical phase difference compensation plates originated from their retardation vary according to the wavelength of light, it was difficult to provide a uniform polarization state, which is obtained as a result of a phase difference, for lights of different wavelengths by a structure including only a single optical phase difference compensation plate.
In order to solve such a drawback, Japanese laid-open patent publication No. (Tokukaihei) 5-100114 discloses a ½ waveplate produced by a combination of a polarizer and a plurality of ½ waveplates, and a circular polarizer obtained by further adding a ¼ waveplate to the combination.
In the former structure of these structures, by combining ½ waveplates, a condition for giving a phase difference of &pgr; to light whose linearly polarized component has been selectively transmitted by the polarizer is ensured within a wide wavelength range. On the other hand, in the latter structure, a condition for giving a phase difference of {fraction (&pgr;/2)} is ensured within a wide wavelength range by adding a ¼ waveplate to the above-mentioned structure. As a result, light having a wavelength within a range satisfying the ½ wavelength condition for giving a phase difference of &pgr; becomes linearly polarized light oriented in a different direction from linearly polarized light prepared by a polarizer. With this structure, it is possible to produce linearly polarized light having a uniform vibration plane for wavelengths satisfying the ½ wavelength condition.
Moreover, as a color display, a liquid crystal display device having thin and light weight characteristics has been put to practical use. At present, a transmissive type liquid crystal display device using a light source as an illumination from behind has been most widely used as a color display device, and the application thereof has increased to various fields because of the above-mentioned characteristics.
A reflective type liquid crystal display device does not require a backlight for display, and therefore it can lower the power consumption by cutting the power for the light source and reduce the space and weight by the space and weight of the backlight as compared with the transmissive type liquid crystal display device. In other words, the reflective type liquid crystal display device can achieve a reduction in the power consumption, and is suitable for use in apparatuses aiming at reductions in their thickness and weights.
Furthermore, regarding the contrast characteristic of the display screen, in a light emitting type display devices as CRTs, a substantial degradation in the contrast ratio, i.e., a so-called washout, occurs outdoors in daylight. Besides, in this aspect, even in a transmissive type liquid crystal display device to which a low reflection treatment was applied, a lowering of visibility is unavoidable in an environment in which ambient light such as direct sunlight is extremely strong compared with display light.
On the other hand, in the reflective type liquid crystal device, since display light proportional to the amount of ambient light is obtained, the reflective type liquid crystal device is particularly suitable for use as a display section of apparatuses used in outdoor, such as personal digital tools, digital still cameras, and portable comcorders.
However, although the reflective type liquid crystal display device has such very advantageous application fields, it does not have a sufficient contrast ratio and reflectivity, and performances for achieving multicolor display, high definition display, moving image display, etc. Therefore, a reflective type color liquid crystal display device having sufficient practical characteristics has not been realized so far.
The following description will explain a reflective type liquid crystal display device in detail.
Since a conventional twisted nematic (TN) liquid crystal element is constructed with the use of two polarizers, the contrast ratio and the viewing angle characteristic are improved. However, since a liquid crystal modulation layer and a light reflecting layer is separated from each other by a distance equal to the thickness of a substrate, etc., parallax occurs due to the difference between a light path along which illumination light is incident and a light path along which the light is outgoing. Thus, in particular, a structure in which the twisted nematic liquid crystal element is used for a normal conventional transmissive type liquid crystal display using a combination of a single liquid crystal modulation layer and color filters which apply a plurality of color elements to different pixels is not suitable for a high resolution, high definition color display device. The reason for this is that, when the traveling direction of light passing through a color element during the incidence of light and that of light passing through a color element after the light is reflected tilt with respect to each other, the light path varies according to the tilt direction and tilt angle. For such a reason, a color display of a reflective type liquid crystal display device using this display mode has not been put to practical use.
Meanwhile, a guest-host (GH) type liquid crystal display element in which no polarizer or one polarizer is used and dye is added to a liquid crystal has been developed. However, the guest-host type liquid crystal element suffers from problems that the reliability is not sufficient due to the addition of dye and a high contrast ratio is not obtained because the dichroism ratio of the dye is low. In particular, in a color display using color filters, since the reflected light of the pixel in the dark state is observed together with the reflected light of the pixel in the bright state, the color purity is substantially lowered by such an insufficient contrast. In order to prevent the degradation of color purity, it is necessary to apply color filters of high color purity. However, when color filters of high color purity are used, the brightness is lowered. Thus, there is a conflict between the lowering of brightness and an advantages of the GH technique of achieving a high brightness without using a polarizer because this advantage is spoilt.
In view of the above-mentioned circumstances, liquid crystal display devices employing a structure in which one polarizer which is expected to achieve a high resolution, high contrast display (hereinafter referred to as the single polarizer structure) have been developed. As one example, a reflective (450 twisted type) TN type liquid crystal display device using one polarizer and ¼ waveplates is disclosed in Japanese laid-open patent publication No. (Tokukaisho) 55-48733.
According to this prior art, a layer of liquid crystal twisted at 45° is used, and the vibration plane of incident linearly polarized light is switched between two states, i.e., a s
Hiraki Hajime
Minoura Kiyoshi
Mitsui Seiichi
Okamoto Masayuki
Ueki Shun
Birch & Stewart Kolasch & Birch, LLP
Kim Robert H.
Nguyen Dung
Sharp Kabushiki Kaisha
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