Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
1999-09-16
2001-11-06
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C313S112000
Reexamination Certificate
active
06313577
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to glass articles coated with an antireflection film combining electrical conductivity and light absorbing properties. More particularly, this invention relates to face panels made of glass for cathode-ray tubes or to glass plates to be bonded to such face panels.
BACKGROUND OF THE INVENTION
In displays employing a cathode-ray tube, such as television receivers, measures are being taken to diminish the reflection of external light from the display surface to improve display quality. Since a high voltage is used in these displays employing a cathode-ray tube because of the use of an electron gun therein, the display surface is electrostatically charged and thus attracts dust particles floating in the air. Measures are hence being taken to impart electrical conductivity to the surface of a cathode-ray tube in order to prevent the electrostatic charging of the display surface. Furthermore, electron rays accelerated by a high voltage generate electromagnetic wave and this electromagnetic wave may exert an adverse influence on the human body. Displays are hence being produced in which the front side of the display area is coated with a conductive film for electromagnetic wave shielding. Specifically, such displays are produced by a technique in which a glass plate coated with a conductive antireflection film is bonded with a resin to the outer surface of the face panel of a cathode-ray tube, or by a technique in which the outer surface of a face panel itself is directly coated with a conductive antireflection film.
Examples of such glass articles used for the purpose of improving the display quality of cathode-ray tubes include the multilayer structure represented by glass plate/ITO/praseodymium titanate/magnesium fluoride/praseodymium titanate/magnesium fluoride as disclosed in JP-A-6-263483. (The term “JP-A” as used herein means an “unexamined published Japanese patent application”.)
Examples of conductive antireflection films comprising superposed layers of a. metal and a transparent oxide include the multilayer structure represented by glass plate/metal/titanium oxide/silicon oxide as disclosed in JP-A-64-70701, the multilayer structure represented by glass plate/magnesium fluoride/metal/titanium oxide/magnesium fluoride as disclosed in JP-A-1-180333, and the multilayer structure represented by glass/praseodymium titanate/metal/praseodymium titanate/magnesium fluoride as disclosed in Japanese Patent 2,565,538. The metal layers disclosed in these references are constituted of stainless steel, titanium, chromium, zirconium, molybdenum, nickel, chromium alloys, etc.
JP-A-1-200952 discloses multilayer structures having four layers including two metal layers, such as that represented by glass plate/stainless steel/praseodymium titanate/stainless steel/magnesium fluoride.
Furthermore, a conductive antireflection film formed by superposing a nonmetallic light-absorbing film and transparent dielectric films is disclosed in JP-A-9-156964. This multilayer structure is represented by glass plate/titanium nitride/silicon nitride/silicon dioxide.
The above-described antireflection films composed of superposed layers comprising one or more light-absorbing films made of a metal or metal nitride and transparent dielectric films are known to be effective in reducing transmittance and enhancing display contrast when directly or indirectly disposed on the front surface of a cathode-ray tube.
However, the antireflection film disclosed in JP-A-6-263483 does not absorb light because all the layers are constituted of a transparent oxide. Consequently, when this antireflection film is disposed on the front side of a cathode-ray tube, it does not function to enhance display contrast to make the display easy to view, although it has electrical conductivity and a high transmittance.
On the other hand, in the prior art conductive antireflection films comprising superposed layers of a metal and a transparent oxide, transmittance can be controlled by regulating the thickness of the metal layer. In this manner, the transmittance thereof can be regulated to a value in the range of from 30 to 50%, which range is advantageous for enhancing display contrast. However, these antireflection films have found to have a problem that when the thicknesses of the constituent films are regulated so as to reduce the reflectance of external light on the outer surface of the antireflection film, the reflectance at the interface between the transparent substrate and the antireflection film is increased.
A high reflectance at the interface between the glass and the antireflection film in a cathode-ray tube poses a problem that the cathode-ray tube display exhibits double images in each of the case where the cathode-ray tube employs a glass panel directly coated with the antireflection film and the case where the cathode-ray tube employs a face panel to which a glass substrate coated with the antireflection film has been bonded. This problem of image doubling is severe especially in cathode-ray tubes in which the face panel itself has a high internal transmittance. The prior art antireflection film disclosed in JP-A-9-156964, composed of superposed layers comprising a metal nitride film and transparent dielectric films, also has the above problem.
The face panels of cathode-ray tubes tend to become flatter and larger. Accordingly, the glass articles for use as such face panels are designed so that the peripheral parts thereof have a far larger thickness than the central part thereof in order to maintain strength. Although the above-described problem of image doubling may be eliminated by employing a glass having a reduced internal transmittance, this means has a drawback that the peripheral parts of the cathode-ray tube exhibit darker images than the central part thereof. In order for a face panel glass to have a larger thickness in its peripheral parts, which is necessary for securing mechanical strength, and to cause no difference in image brightness between the peripheral parts and the central part thereof, the glass itself should have a heightened internal transmittance. When such a face panel having a high internal transmittance is coated on the outer side with the prior art antireflection film containing a light-absorbing metal or metal nitride film, the coated panel has a high reflectance at the interface between the glass and the antireflection film to thereby pose the problem of image doubling.
SUMMARY OF THE INVENTION
One object of the present invention is to eliminate the problem of image doubling which arises, for example, when an antireflection film containing a light-absorbing film is formed on the outer surface of the face panel of a cathode-ray tube, or when a glass plate coated with an antireflection film containing a light-absorbing film is bonded to the face panel of a cathode-ray tube.
Another object of the present invention is to prevent the reflection of external light on a display surface to obtain high display contrast.
The present invention provides an optical article having antireflection coating which comprises a light-transmitting substrate having a refractive index of 1.4 to 1.7 and an antireflection film composed of superposed layers comprising, formed on the light-transmitting substrate in this order, a light-absorbing film as a first layer, a transparent dielectric film having a refractive index of 1.6 to 2.4 as a second layer, a light-absorbing film as a third layer, a transparent dielectric film having a refractive index of 1.6 to 2.4 as a fourth layer, and a transparent dielectric film having a refractive index of 1.35 to 1.5 as a fifth layer.
The values of refractive index herein mean those measured at a wavelength of 550 nm. Examples of the materials constituting the light-absorbing films include metals, alloys, and metal nitrides. The embodiment that each of two light-absorbing films is laminated by sandwiching the same between transparent dielectric films having a refractive index of 1.6 to 2.4 is important in enabling the light which h
Kunisada Terufusa
Nakanishi Koji
Ogino Etsuo
Sakai Chihiro
Taninaka Yasunori
Nippon Sheet Glass Co. Ltd.
Patel Vip
Sughrue Mion Zinn Macpeak & Seas, PLLC
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