Illumination – Revolving
Reexamination Certificate
2001-12-28
2003-03-11
O'Shea, Sandra (Department: 2875)
Illumination
Revolving
C362S339000, C362S019000, C349S065000
Reexamination Certificate
active
06530671
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display using a component for liquid crystal displays, such as rear illumination equipment.
In recent years, the implementation of personal computers, inclusive of so-called word processors, in a small size has been promoted, and portable type personal computers, known as lap-top type or notebook type computers, are now widely used. In such a portable type personal computer, a liquid crystal device is commonly used as a display unit. In this regard, there is an increasing tendency for adopting a color display in portable type personal computers. In line with such a trend, a backlighting type display device is coming into wide use, in which a light source is disposed at a rear side of a liquid crystal display screen for lighting the whole display screen from the rear or back side. Needless to say, the backlighting light source for the color liquid crystal display device is required to emit light with high luminance. Besides, it is necessary to illuminate the display screen with uniform luminance over the whole planar surface thereof. Luminance of the backlighting can easily be increased by increasing the luminance of the light source. However, taking into consideration the fact that a portable-type personal computer or word processor or the like is usually operated br using a battery or storage cell, a limitation concerning the voltage supply is necessarily imposed on any attempt to increase the luminance of the light source. Stated in another way, no other effective method or measures for increasing the luminance of the liquid crystal display screen have been proposed to date.
For having better understanding of the present invention, a description will first be made in some detail of conventional liquid crystal display devices, such as disclosed, for example, in JP-A-4-162002 and JP-A-6-67004.
FIG. 2
shows a lateral source type backlighting device employed conventionally in a liquid crystal display device known heretofore. Referring to
FIG. 2
, a lamp, such as a cold-cathode discharge tube or a hot-cathode discharge tube, is employed as a light source
1
which is disposed at and along one lateral side of a light guide plate (also known as optical waveguide plate)
2
which is made of a light-transmissive material. Here, an optical scattering layer
3
from which light is scattered and reflection sheet
4
that causes light to reflect are provided on the underneath side of said light guide plate
2
. And, a diffusion sheet
5
, that consists of synthetic resins of milk-white color that have an optical scattering effect, is provided in the area over the surface of said light guide plate
2
to pass and to illuminate the whole face with a uniform brightness. In addition, a first condensation sheet
6
to converge diffused light to some extent on the face and to improve the brightness of the front face of the display and a second condensation sheet
7
are arranged above the diffusion sheet
5
. As to the optical scattering layer
3
, which is shown in more detail in
FIG. 3
, it consists of a plurality of ink dots
8
, formed of optical scattering materials, such as oxide titanium, arranged on the surface of light guide plate
2
. As the distance increases from the light source
1
, the optical intensity from light source
1
is reduced. Therefore, as the distance increases from the light source
1
, as shown in
FIG. 3
, the area of the ink dots
8
is increased.
As described above, there is a problem of the brightness declining due to the loss of optical scattering in conventional illumination equipment. The reason is because light is emitted from light source
1
, conducted to light guide plate
2
, scattered by optical scattering material
8
that is contained in the optical scattering layer, passes through a diffusion board later, and then irradiates a liquid crystal element.
There is a light guide plate not using ink dots, to solve this problem, as described in JP-A-9-269489. This light guide plate has a small convex or a small concave area formed on the surface thereof. These small convex or small concave areas reflect light, and a liquid crystal element is illuminated thereby. But the shape and distribution of these areas were not optimized, and so there was still room for a further improvement in brightness.
In addition, as one of the narrow advances that led to an improvement in the brightness of a liquid crystal display, it has been proposed that the permeative rate of a polarization filter should be raised. The polarization filter is an element that is arranged between a liquid crystal cell and the back light and which has the function of passing only a specified polarization light into a liquid cell. The polarization filter can be manufactured by adsorbing a dichroic material in the micell pipe of a macromolecule film that generally arranges a micell in a constant direction. As a macromolecule film, polyvinyl alcohol is used. Between rollers on which this polyvinyl alcohol spins at a different speed, it is drawn about 3-5 times in the constant direction. The micell of a drawn PVA (polyvinyl alcohol) is arranged in the drawing direction, and the arranged film has a strong double refraction. There are halogen materials, such as a iodine and a dyestuff, as a material to give dichroism. By adsorbing the above material in the film being drawn, polarization characteristics are expressed. As for the above polarization filter, a polarization separation function is gained easily. But the permeative rate is small, being 50% or less. Because a dichroic material is used theoretically, polarization light that is orthogonal with the polarization light that is transmitted is absorbed. Therefore, it is a present condition that 50% or more of the optical energy is lost by a polarization filter, and the brightness of a liquid crystal display element using such a filter is remarkably reduced as a result.
It has been proposed to adopt a method of using a polarizability film of a reflection type as a means of obtaining improved brightness. A polarizability film of a reflection type is a film that has a property such that all polarization components other than a polarization component of a specific kind are reflected and only the specific polarization component is passed, like a cholesteric liquid crystal film, etc. That is, the polarizing natural light that comes out through a light guide plate is applied to a polarizability film of a reflection type, whereby only a specific polarization component is transmitted, and all other polarization components are reflected. A reflected polarization component is reflected again by a reflection board later, the polarization state is changed, it is applied to the polarizability film of a reflection type again, and only the specific polarization component is allowed to pass through. By repeated reflections, all components of light can be used.
A method of using a cholesteric liquid crystal film representing a polarizability film of a reflection type has been proposed in JP-A-3-45906 and the JP-A-6-281814. The cholesteric liquid crystal film consists of optical active layers of a polymer material that has cholesteric regularity. The cholesteric liquid crystal film transmits only a circular polarization component of the same direction as the spiral direction of a cholesteric layer in the polarizing natural light that comes out through a light guide plate from the light source, and the circular polarization component of a reverse direction is reflected. Therefore, when has the structure shown in
FIG. 16
, a reflected circular polarization component is reflected again with a reflection sheet, it is returned, it returns it to a state that is close to natural light, and the cholesteric liquid crystal film is entered again. By a repeat of this cycle, all components of light can be used. When a ¼ phase sheet is formed on the surface at which light appears on this cholesteric liquid crystal film, a circular polarization component is converted into a straight line polari
Hira Yasuo
Hirayama Hisao
Miyawaki Toshitsugu
Mori Yuji
Taniguchi Hitoshi
Alavi Ali
Hitachi Electronic Devices Co. Ltd.
O'Shea Sandra
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