Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2002-03-15
2004-11-30
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S159000, C349S062000, C349S061000, C362S035000, C362S035000
Reexamination Certificate
active
06825895
ABSTRACT:
The present application is based on Japanese Patent Applications No. 2001-076396 and 2001-109555, which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid-crystal display apparatus having substrates which are little bent and hardly broken by pressure so that a display image is little disordered.
2. Description of the Related Art
A liquid-crystal display apparatus (hereinafter also abbreviated to “LCD”) is used in a desktop electronic calculator, an electronic clock, a personal computer, or a word processor. The demand for the liquid-crystal display apparatus has increased rapidly in recent years. The application of the LCD has been widened. Reduction in thickness and weight of a liquid-crystal display panel has been required with the popularization of portable information apparatuses such as a cellular phone and a PAD in recent years. Accordingly, the LCD as a whole needs to be as thin in thickness as possible and as light in weight as possible. Further, it is preferable that the LCD is hard to break because, in most cases, the LCD has been used for portable purposes in recent years.
In the liquid-crystal display apparatus, upper and lower transparent substrates as constituent members of the apparatus were equal in thickness to each other. If reduction in thickness and weight was attended to be attained, the upper and lower transparent substrates were too thin to obtain sufficient stiffness against external force. For this reason, there was a problem that the cell gap varied to cause disorder of a display image when pressure was applied on the upper transparent substrate.
In order to make the strength against external force sufficient, the upper and lower transparent substrates needed to be made thick. This attempt was, however, contrary to the purpose of reduction in thickness and weight of the LCD. On the other hand, when the transparent substrates were made thin and impact was applied on the LCD, there was another problem that the LCD was easy to break.
On the other hand, as a reflection type LCD (liquid-crystal display) apparatus which can used both in an external light mode and in an illumination mode, there is heretofore known an apparatus using a front light system in which a side light pipe is disposed on a visual side surface of a liquid-crystal display panel so that display light can be viewed through the light pipe (Japanese Patent Laid-Open No. 147499/2000). The side light pipe, however, needs a plate thickness of about 2 mm or greater because of necessity in light transmission. Hence, there was a problem that increase in thickness and weight of the liquid-crystal display apparatus could not be avoided. Therefore, reduction in thickness and weight is an important issue particularly in a reflection type liquid-crystal display apparatus used in a portable system such as a portable personal computer or a cellular phone. In a thickness and weight reducing system in which cell substrates in a liquid-crystal display panel are made thin, there arises a disadvantage in that the panel is easy to break because of deterioration of mechanical strength.
SUMMARY OF THE INVENTION
An object of the invention is to provide a liquid-crystal display apparatus which is thin in thickness, light in weight, hard to break and easy to view.
The invention is devised on the basis of the knowledge that the stiffness of a liquid-crystal portion is determined by the stiffness of upper and lower transparent substrates of an LCD because each of the transparent substrates is bonded only around its circumference, and that the lower transparent substrate may be thinner than the upper transparent substrate because a large part of pressure is applied on the LCD particularly against the front surface thereof, that is, because pressure is little applied on the lower transparent substrate.
That is, in accordance with the invention, there is provided a liquid-crystal display apparatus having a liquid-crystal cell, the liquid-crystal cell including a lower transparent substrate having a transparent electrode on at least one of its opposite surfaces, an upper transparent substrate having a transparent electrode opposite to the transparent electrode of the lower substrate, and liquid crystal held between the lower substrate and the upper substrate, wherein the upper substrate is thicker than the lower substrate.
In order to achieve reduction in thickness and weight of the liquid-crystal display apparatus according to the invention more effectively, it is preferable that the thickness of the lower substrate is not larger than ⅔ as large as the thickness of the upper substrate.
In order to make the liquid-crystal display apparatus according to the invention harder to break, it is preferable that the lower substrate is constituted by a member having flexibility.
Assume two cases in the liquid-crystal display apparatus as follows. One is the case where the thicknesses of the upper and lower transparent substrates are equal to each other and, for example, each of the thicknesses is 0.6 mm. The other is the case where the total thickness of the upper and lower transparent substrates is equal to that in the former case and, for example, the thickness of the upper transparent substrate is 1.0 mm and the thickness of the lower transparent substrate is 0.2 mm. In the case where the thicknesses of the upper and lower transparent substrates are equal to each other, the strengths of the two substrates are also equal to each other. In the case where the thicknesses of the upper and lower transparent substrates are-different from each other in the same manner as in the invention, the strengths of the two substrates are also different from each other. When the same material is used to form the upper and lower substrates, the thicker substrate has stronger stiffness so that strain of display can be reduced.
As described above, the LCD is, however, often used in the environment that pressure is mainly applied on the upper transparent substrate. Accordingly, stiffness in the case where the upper transparent substrate is made as thick as 1.0 mm is stronger than that in the case where the thicknesses of the upper and lower transparent substrates are equal to each other. Hence, strain in the former case is smaller than that in the later case. When the same material is used, the thinner substrate is more advantageous in flexibility. Hence, the lower transparent substrate has larger flexibility as its thickness is thinner, so that the lower transparent substrate can follow bending of the upper transparent substrate, and, accordingly, can act in the direction of further reducing the influence of the bending on the whole display.
From the description, in the case where the thicknesses of the upper and lower transparent substrates in the liquid-crystal display apparatus are equal to each other, each of the thicknesses needs to be 1.0 mm and the total thickness needs to be 2.0 mm in order to obtain the same strength as that in the case where the upper transparent substrate is 1.0 mm. However, when the upper transparent substrate is made thicker than the lower transparent substrate, sufficient strength can be obtained even in the case where the total thickness is kept constant. Accordingly, when the upper transparent substrate is made as thick as possible and the lower transparent substrate is made as thin as possible relative to the total thickness of the liquid-crystal display apparatus, strain and disorder of a display image can be reduced.
According to the invention, there is also provided a reflection type liquid-crystal display apparatus having: a reflection type liquid-crystal display panel; at least one illuminator; and an optical path control layer, the liquid-crystal display panel including a liquid-crystal cell and a reflection layer, the liquid-crystal cell having a back side cell substrate, a visual side cell substrate, and a layer of liquid crystal, the back side cell substrate being made of a support substrate at least having an elec
Abe Hideo
Ariyoshi Toshihiko
Kinoshita Ryoji
Nakano Yuuki
Umemoto Seiji
Kim Richard H
Nitto Denko Corporation
Sughrue & Mion, PLLC
Ton Toan
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