Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
2002-06-17
2004-01-13
Vu, David (Department: 2821)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C313S479000, C359S609000, C445S024000
Reexamination Certificate
active
06677703
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cover plate for a display device using a liquid crystal display (LCD) or the like and intended for use as a display unit for various electronic devices, such as portable telephones, a method of making such a cover plate, a display device employing such a cover plate, and a low-reflection structure.
2. Description of the Related Art
Various current electronic devices are provided with a display unit including a liquid crystal display (LCD) as a display panel, and the display panel is not exposed to protect the same from water, dust, external forces and the like. A window paned with a cover plate, such as a transparent plastic plate, is disposed on the outer side of the display panel with a space between the cover plate and the display panel (JP-A No. 66859/1995). For example, a portable telephone has a case formed by molding a resin or the like and provided with a window corresponding to a display unit and paned with a transparent cover plate, and a liquid crystal display panel mounted on a base plate is disposed on the inner side of the window to protect the liquid crystal display panel.
The additional, protective cover plate lying between the display panel and the user reflects external light to make it difficult for the user to see an image displayed on the display panel, and reflects image light emitted by the display panel to reduce light utilization efficiency. Thus, while the cover plate achieves protective purposes, the same deteriorates visibility.
To solve such a problem, a method proposed in JP-A No. 127852/2001 forms a single-layer antireflection film or a multilayer antireflection film consisting of a layer having a high refractive index and a layer having a low refractive index by a vapor deposition process, a sputtering process or a coating process on a cover plate, and a method proposed in JP-A No. 325202/1995 applies an antireflection film to a cover plate. The antireflection films formed by a vapor deposition process, a sputtering process or such have problems in stability and the ratio of good antireflection films, and cannot be manufactured at a high productivity because thin films having a controlled refractive index must be formed by one or a plurality of cycles of a batch process. The antireflection films formed by a coating process must be formed individually on cover plates and hence cannot be formed at a high productivity.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a cover plate to be disposed in front of a display panel, capable of reducing reflection of light, of maintaining its function and of improving visibility, a method capable of stably making the cover plate at a high productivity at a low fraction defective, a display device provided with the cover plate, and a low-reflection structure.
According to the present invention, a cover plate for a display device provided with a display panel, disposed so as to cover the display panel has a transparent base having a surface facing the display panel and provided with reflection-reducing minute irregularities; wherein the reflection-reducing minute irregularities of the transparent base consist of numerous projections and numerous valleys lying between the projections, and meet a condition expressed by:
P
MAX
≦&lgr;
MIN
where P
MAX
is the maximum distance between the tips of the adjacent projections, and &lgr;
MIN
is the minimum wavelength in a visible region of visible light in a vacuum, and the sectional area ratio of the total area of sections of the projections of the transparent base in a plane parallel to the transparent base in the plane increases continuously and gradually in a direction from the tips of the projections toward the bottoms of the valleys.
In the cover plate according to the present invention, the transparent base meets a condition expressed by:
P
MAX
≦&lgr;
MIN
b
where n
b
is a refractive index of the transparent base.
In the cover plate according to the present invention, the minimum wavelength &lgr;
MIN
in the visible region in a vacuum is 380 nm and hence P
MAX
≦380
b
.
In the cover plate according to the present invention, the projections and the valleys of the reflection-reducing minute irregularities have substantially the same shapes, respectively.
In the cover plate according to the present invention, the projections and the valleys of the reflection-reducing minute irregularities are arranged at the same pitches.
In the cover plate according to the present invention, the projections of the reflection-reducing minute irregularities meet a condition expressed by:
H
MIN
≧0.2&lgr;
MAX
where H
MIN
is the minimum height of the projections.
In the cover plate according to the present invention, the projections of the reflection-reducing minute irregularities meet a condition expressed by:
H
MIN
≧0.4&lgr;
MAX
In the cover plate according to the present invention, the projections of the reflection-reducing minute irregularities meet a condition expressed by:
H
MIN
/P
MAX
=1/2 to 4/1
The refractive index between the back surface of the cover plate and air can be made to change continuously and gradually instead of discontinuously and sharply. Since the reflection of light at the interface between substances is caused by the sudden change in refractive index, the reflection of light by the back surface of the cover plate can be reduced by making the refractive index at the back surface of the cover plate change continuously and gradually. Consequently, light rays reflected by the back surface of the cover plate among light rays reflected toward the user by the front and the back surface of the cover plate among external light rays that affect the visibility of a displayed image, more strictly, visible light fallen on the cover plate, can be eliminated and hence the total amount of the light rays reflected by the cover plate can be reduced accordingly. Thus, the deterioration of visibility by the reflected external light can be reduced. Since the specific minute irregularities are formed only on the back surface of the cover plate and is not formed on the front surface of the same, the reduction of the reflection-reducing effect of the reflection-reducing minute irregularities due to the abrasion of the reflection-reducing minute irregularities and soiling of the reflection-reducing minute irregularities with oil, i.e., filling of the valleys with oil, does not occur.
In a display device provided with this cover plate, reflection of display light (image light) emitted by a display panel disposed behind the cover plate by the back surface of the cover plate can be reduced and the cover plate has a high transmittance, whereby the reduction of contrast in the displayed image and the resultant whitening due to multiple reflection of the display light between the front and the back surface of the cover plate can be prevented and the visibility of the displayed image can be improved. Since visibility is improved, the power demand of the back light or front light of the liquid crystal panel or the power demand of the display panel, such as an EL panel can be reduced, which contributes to the reduction of the power demand and power consumption of the related electronic devices.
The reflection-reducing effect of the specific minute irregularities can be enhanced by determining the relation between P
MAX
and &lgr;
MIN
by using the refractive index n
b
of the transparent base, taking into consideration the wavelength of light which becomes shorter when the light enters the transparent base from a vacuum.
According to the present invention, a cover plate making method of making a cover plate for a display device, having a transparent base having one surface provided with reflection-reducing minute irregularities includes the steps of: forming a resist film on a glass plate, forming a resist pattern by subjecting the resist film to exposure and developing processes for patterning; forming a mold provided with mold minute irregularities b
Ito Arimichi
Suzuki Toshiyuki
Dai Nippon Printing Co. Ltd.
Parkhurst & Wendel L.L.P.
Vu David
LandOfFree
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