Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-03-02
2001-07-24
Malinowski, Walter J. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06266111
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a diffuse reflection plate to be used in a reflection-type display device and a manufacturing method thereof as well as to a reflection-type display device using a diffuse reflection plate.
2. Description of the Related Art
Having a flat panel shape, display devices using a liquid crystal or the like as an electro-optical layer have features that they are light, thin, and of low power consumption. For this reason, such display devices are being developed enthusiastically as displays of portable equipment, for example. Electro-optical materials such as a liquid crystal are not of a spontaneous light emission type and produce an image by selectively transmitting and interrupting external light. Passive display devices of this type are classified into the transmission type and the reflection type by the illumination method.
In a transmission-type display device, a panel in which an electro-optical layer such as a liquid crystal layer is held between two transparent substrates is manufactured and a light source (backlight) for illumination is disposed on the back side of the panel. An image is observed from the front side of the panel. In the case of the transmission type, the backlight is indispensable and a cold-cathode tube or the like is used as a light source. Since the backlight consumes most of the energy that is consumed by the entire display, transmission-type devices are not suitable for a display of portable equipment. On the other hand, in the case of the reflection type, a reflection plate is disposed on the back side of a panel and external light such as natural light is input from the front side. An image is observed from the front side as in the case of the transmission type by utilizing reflection light of the input external light. Not using a light source for back illumination unlike transmission-type devices, reflection-type devices are of relatively low power consumption and hence suitable for a display of portable equipment.
In reflection-type display devices, because display is performed by utilizing incident light coming from the environment, it is necessary to increase the luminance by effectively utilizing the incident light. Further, to realize white display (what is called paper white), basically it is necessary to diffuse-reflect incident light within the panel. To this end, conventional reflection-type display devices incorporate a diffuse reflection layer within the panel. It is intended that the diffuse reflection layer have a characteristic that is close to perfect diffusion and assume an appearance that as close to paper white as possible.
However, display devices have a mode in which an image is produced by utilizing a linearly polarized component of incident light. In this mode, there may occur a case that when a diffuse reflection plate having a perfect diffusion characteristic is used, sufficiently high contrast cannot be obtained because the polarization state of incident light is disordered.
Where a reflection-type display device is illuminated in a room by using an auxiliary light source such as a desk lamp, causing incident light from the light source to be reflected efficiently toward a viewer is effective for increase in luminance. However, conventional diffuse reflection layers having perfect diffusion do not have what is called directivity and hence cannot make effective use of incident light when combined with an auxiliary light source or the like.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-described problems in the art, and an object of the invention is therefore to increase the luminance of a reflection-type display device.
A more specific object of the invention is to provide a manufacturing method of a diffuse reflection plate having high diffusion efficiency and desired directivity.
To attain the above objects, according to the invention, a diffuse reflection plate is manufactured by the following process. First, a photosensitive resin film is formed on a substrate. Then, the resin film is patterned by photolithography into a collection of quadrilateral prisms that are arranged discretely. Then, the individual quadrilateral prisms are deformed so as to be undulated gently by performing a heat treatment. Finally, a metal film is formed on the collection of gently undulated quadrilateral prisms. Preferably, a resin film is applied to the collection of gently undulated quadrilateral prisms, whereby flat gap portions between the discrete quadrilateral prisms are filled in and curved surfaces are formed there. A diffuse reflection plate manufactured in the above manner is configured in such a manner that a resin film formed with asperities and a metal film are formed on a substrate.
A diffuse reflection plate manufactured by the above method and having the above structure can be incorporated in a reflection-type display device. In this case, the reflection-type display device comprises, as a basic configuration, a transparent first substrate disposed on the incidence side; a second substrate disposed on the reflection side and bonded to the first substrate via a predetermined gap; an electro-optical layer disposed in the gap on the side of the first substrate; a diffuse reflection layer disposed in the gap on the side of the second substrate; and an electrode formed on at least one of the first and second substrates, for applying a voltage to the electro-optical layer. The diffuse reflection film is composed of a resin film formed with asperities and a metal film formed on the surface of the resin film. An important feature is that the asperities have been gently undulated by patterning a resin film into discrete quadrilateral prisms so as to leave gaps in between and then causing the quadrilateral prisms to reflow. Preferably, the asperities have been gently undulated by filling in gaps remaining after reflow of the quadrilateral prisms with another resin film. Preferably, the asperities have an inclination angle of about 10° to about 20°. Also preferably, the individual quadrilateral prisms have been patterned so that their edges are arranged in a fixed direction.
According to a preferred embodiment of the invention, a polarizing plate is disposed on the side of the first substrate, and the electro-optical layer is a liquid crystal layer that functions as a quarter-wave plate depending on a voltage application state. In this case, a quarter-wave plate is disposed between the polarizing plate and the liquid crystal layer, and the liquid crystal layer is a nematic liquid crystal having positive dielectric anisotropy and aligned in a twisted manner, and functions as a quarter-wave plate when supplied with a voltage and loses the function of a quarter-wave plate when not supplied with a voltage.
In the manufacturing method of a diffuse reflection plate according to the invention, asperities having a diffusive property are formed by causing discrete quadrilateral prisms made of a resin to reflow. It is conceivable to use cylindrical patterns instead of the quadrilateral prisms. However, a diffuse reflection plate manufactured according to the invention is superior in light diffusing power because quadrilateral prisms can be patterned at a higher density than cylinders. Since the gaps between the individual discrete quadrilateral prisms have a smaller area than the gaps between the individual discrete cylinders, the asperities having diffusing power can be arranged at a higher density accordingly. When the quadrilateral prisms made of a resin are caused to reflow by a heat treatment, the edge portions of each quadrilateral prism are deformed so as to be curved gently, to thereby provide desired light diffusing power. By arranging edges of the individual quadrilateral prisms in a fixed direction, desired directivity can be given to the diffuse reflection plate. This effect is made more remarkable by an additional measure of making the cross-section of each quadrilateral prism rectangular. In contrast, where cylinders
Fujioka Takayuki
Kataoka Hideo
Urabe Tetsuo
Kananen Ronald P.
Malinowski Walter J.
Rader Fishman & Grauer
Sony Corporation
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