Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-10-08
2004-11-23
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S095000, C349S005000
Reexamination Certificate
active
06822707
ABSTRACT:
The present application is based on Japanese Patent Application No. 2001-313983, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical sheet used as a transmission type screen member in a back projection type display device or as a viewing angle enlarging member in a liquid-crystal display device, and a display device using the optical sheet.
2. Description of the Related Art
Generally, a back projection type display device using a liquid-crystal display element or a dot matrix display element such as a digital mirror device has a projector for outputting image light formed through a display element, a reflecting mirror having a function of reflecting the image light outputted from the projector to change the direction of movement of the image light, and a transmission type screen for spreading the incident image light moderately to the observer side to display an image.
Generally, the transmission type screen includes a Fresnel lens sheet, and a lenticular lens sheet. The Fresnel lens sheet is an optical component having the same function as that of a convex lens. That is, the Fresnel lens sheet has a function of changing the direction of the image light outputted from the projector to the observer side to enlarge an optimal viewing range. On the other hand, the lenticular lens sheet has a function of distributing the limited image light outputted from the projector into an observer's observation range effectively.
The lenticular lens sheet includes a plurality of cylindrical lenses arrayed in one direction, and a light absorbing layer disposed in other regions than light-condensing regions through the lenses for absorbing light inputted from the environment surrounding the lenticular lens sheet (hereinafter, the light being referred to as “external light”). When focal points of the lenses are located on an observation surface of the screen, reflection of the external light is reduced without any loss of the image light ideally to thereby suppress lowering of contrast ratio under the bright environment.
Unexamined Japanese Patent Publication No. Hei. 10-260638 has disclosed a lenticular lens sheet having a transparent resin formed as lenses for achieving a wide viewing angle and a bright image, a light absorbing layer patterned, and a diffusing layer having a thickness of from 20 to 500 &mgr;m and laminated between the transparent resin and the light absorbing layer.
Incidentally, a direct-vision liquid-crystal display device using TN (Twisted Nematic) liquid crystal or the like generally has viewing angle dependence in which luminance or chromaticity varies in accordance with the direction of observation. On the other hand, Unexamined Japanese Patent Publication No. Hei. 10-39769 has described an optical member which can eliminate the view angle dependence and reduce reflection of external light to thereby suppress lowering of contrast ratio under the bright environment when the optical member is disposed in front of a liquid-crystal display device.
The optical member is provided as a micro lens array sheet having a transparent substrate, a plurality of micro lenses constituted by fine convex surfaces and arrayed planarly on one surface of the transparent substrate, and a light absorbing layer disposed on the other surface of the transparent substrate and having opening portions located in places corresponding to apices of convex portions of the micro lenses.
Examples of the method for producing lenses of an optical member such as a lenticular lens sheet or a micro lens array sheet applied to a display device include: a method using a mold such as a metal mold, a resin mold or a stamper for transferring the shape of the mold; and a method of forming patterns from a resist material at intervals of a required pitch by photolithography and hot-melting the patterns.
A method using a metal mold for transferring the shape of the mold is most preferred as the method for producing a large-area lens array inexpensively. In this case, a transparent resin such as an ultraviolet-setting resin, a thermosetting resin or a thermoplastic resin is used as the lens material. The refractive index of the practical lens material is in a range of from about 1.48 to about 1.66.
FIG. 21
is a graph showing the relation between luminance and viewing angle characteristic in accordance with the refractive index n of a lens.
FIG. 21
shows results of calculation in the case where rays of parallel light are incident on a hemispherical lens. In
FIG. 21
, the horizontal axis shows an emission angle (viewing angle), and the vertical axis shows a relative value of luminance.
As the refractive index n of a lens increases, the difference between luminance in a frontal direction (at an emission angle of 0 degrees) and luminance in an oblique direction decreases so that the viewing angle is widened.
If “At Panels session 1.5.2.B” in “TCO (The Swedish Confederation of professional Employees) 99 requirement” is now noticed as a standard for display devices, TCO 99 cannot be satisfied even in the case where the refractive index of a lens is 1.7, in accordance with the estimation. That is, an optical member capable of achieving a sufficient viewing angle cannot be obtained by use of only the refracting function of a lens using a practical lens material. It is therefore necessary to provide a diffusing layer for enlarging the viewing angle.
In the related art, there has been disclosed a lenticular lens sheet having a transparent substrate including lenses formed on one surface, a light absorbing layer, and a diffusing layer laminated between the transparent substrate and the light absorbing layer. In this case, the thickness of the diffusing layer is defined to be in a range of from 20 to 500 &mgr;m from the point of view of preventing generation of a hot band and suppressing lowering of light transmittance but there is no particular consideration for display of a high-precision image.
The resolution of an image displayed on a general optical sheet such as a lenticular lens sheet or a micro lens array sheet depends on the pitch of lenses arrayed. As the pitch of lenses decreases, a higher-precision image can be displayed. It is therefore necessary that the pitch of lenses constituting an optical member is selected to be not larger than tens of microns in order to meet higher resolution of an image advanced with the popularization of HDTV (High Definition Television) in the future.
In this case, the following problem may arise if the diffusing layer is not sufficiently thin.
FIG. 22
is a partly schematic sectional view of an optical sheet for explaining a problem in the case where the thickness d of the diffusing layer is not sufficiently small compared with the lens pitch.
Image light
2101
incident on an optical sheet is refracted by lenses
2000
so as to be condensed into a diffusing layer
2001
. If the diffusing layer is not sufficiently thin, a part
2100
of light scattered by the diffusing layer is absorbed to a light absorbing layer
2002
to thereby cause a problem that transmittance is reduced.
On the other hand, it may be conceived that opening portions
2003
of the light absorbing layer are widened in order to suppress the reduction of transmittance. In this case, however, there arises another problem that lowering of contrast ratio under the bright environment occurs because absorption of external light to the light absorbing layer is reduced. It may be also conceived that the diffusing characteristic of the diffusing layer is reduced in order to suppress the reduction of transmittance. In this case, however, there arises a problem that the viewing angle is narrowed.
When, for example, the thickness of the diffusing layer is selected to be not smaller than 20 &mgr;m in the condition that the pitch of lenses is selected to be 50 &mgr;m in order to satisfy high-precision image display, there arises a problem that transmittance is reduced or contrast ratio is lowered.
SUMMARY OF THE INVENTION
Under such circ
Adachi Masaya
Ariyoshi Toshihiko
Tsumura Makoto
Nitto Denko Corporation
Ton Toan
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