Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2000-04-26
2003-04-29
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S062000, C349S064000, C362S035000, C362S331000, C362S339000
Reexamination Certificate
active
06556259
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid-crystal display device which is so excellent in light utilizing efficiency that the device provides a bright display easy to see.
The present application is based on Japanese Patent Application No. Hei. 11-118142, which is incorporated herein by reference.
2. Description of the Related Art
There is investigation of a liquid-crystal display device which is used both in a reflection and a transmission mode so that the device can be visually recognized in use of the transmission type liquid-crystal display device in a dark place, or the like, by addition of an illuminator while the merit of a reflection type liquid-crystal display device of small power consumption is used widely. For example, there has been proposed a liquid-crystal display device using a semi-transmission type reflection plate, a liquid-crystal display device in which a back light used in the transmission type liquid-crystal display device is provided as a front light on the visual recognition side of liquid-crystal cells, and so on.
The system utilizing such a semi-transmission type reflection plate, however, had a disadvantage that the system in either mode was inferior in brightness to the reflection or transmission type device for exclusive use because light was separated into reflected and transmitted light by a half-mirror effect. There was a proposal to make an improvement by use of a reflection polarizer for reflecting polarized light selectively so that the sum of reflectivity and transmissivity was able to exceed 100%. However, there were problems in that the light utilizing efficiency in a transmission mode was reduced to be not higher than 50% because of absorption by a light absorber disposed for preventing both display inversion between reflection and transmission and emphasis of a black display, and display was hard to see in the evening twilight in either mode.
On the other hand, there was a problem in that the front light system was apt to make a display darker in a transmission mode than the general transmission type liquid-crystal display device because light went to light-crystal cells, or the like, and came back. Accordingly, an injury of a light pipe or a contaminant thereon became conspicuous as a bright spot, and display contrast was lowered by leakage of light from an upper surface of the light pipe.
SUMMARY OF THE INVENTION
An object of the present invention is to develop a liquid-crystal display device of good visual recognition which is excellent in brightness both in reflection and transmission modes, and in which both display inversion and lowering of contrast due to leakage of light do not occur.
According to the present invention, there is provided a liquid-crystal display device comprising: a light pipe including light output means formed on an upper surface of the light pipe; a light source disposed near to an incident side surface of the light pipe so that incident light from the light source is output from a lower surface of the light pipe through the light output means in the condition that a peak of intensity of the output light in a plane perpendicular to a reference plane of the incident side surface is at an angle within 30 degrees with respect to a normal direction of a reference plane of the lower surface; a reflection layer disposed on the lower surface of the light pipe so that reflected light of the output light is transmitted through the upper surface of the light pipe; and a liquid-crystal shutter disposed above the upper surface of the light pipe, the liquid-crystal shutter including liquid-crystal cells, and at least one polarizing plate.
According to the present invention, brightness approximately equal to that of the background-art reflection type liquid-crystal display device can be achieved in a reflection mode by a structure in which the light pipe is disposed between the liquid-crystal cells and the reflection layer because lowering of light utilizing efficiency caused by absorption loss, reflection loss, etc. due to the light pipe in the reflection mode is slight. Moreover, brilliance equal to that of the background-art transmission type liquid-crystal display device can be achieved in a transmission mode. Moreover, display inversion does not occur between reflection and transmission, so that lowering of contrast is prevented from being caused by leakage light out of the light pipe. Hence, a liquid-crystal display device of good visual recognition can be obtained.
Moreover, a light path in the light pipe in the transmission mode can be elongated by provision of the light output means on the upper surface of the light pipe. Hence, the spread of light is widened, so that the intensity of a bright line can be relaxed. This effectively acts on both prevention of occurrence of moire and enhancement of uniformity of brightness advantageously, so that the reflection layer can be disposed on the lower surface of the light pipe so as to be brought into contact with and integrated with the light pipe through a tacky layer, or the like, easily. If such light output means is provided on the lower surface of the light pipe, it is necessary to provide an independent reflection plate separately in terms of the maintenance of the function of the light output means. As a result, the structure of the device is complicated because of increase in the number of parts and arrangement and fixation of the reflection plate. As a result, there is a disadvantage that the weight of the device becomes heavy because a thick support is required for preventing disorder of display from being caused by generation of wrinkles.
Moreover, light reflected through the reflection layer is output efficiently in a direction advantageous to visual recognition in a transmission mode on the basis of the aforementioned output light characteristic of the light pipe, so that a bright display can be obtained. Contrariwise in the case of a light pipe provided with scatter type light output means such as dots, embossed irregularities, or the like, output light is emitted at a large angle of about 60 degrees, so that display in a transmission mode is dark and hard to see in a frontal (vertical) direction. If a prism sheet is disposed for the purpose of controlling the light path, light is scattered in a reflection mode, so that a display is made very dark because a large part of light does not contribute to visual recognition. If a diffusion layer of strong diffusing property is disposed in order to prevent dots, or the like, from being visible too clearly, a dark display is obtained in a reflection mode because both incident and reflected light thereof from the reflection layer are also scattered in the reflection mode.
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Chung David
Nitto Denko Corporation
Parker Kenneth
LandOfFree
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