Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
2002-03-25
2003-01-21
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C313S47700R
Reexamination Certificate
active
06509684
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for producing a CRT panel glass or a CRT having improved contrast and uniformity in brightness.
BACKGROUND ART
A panel glass for CRT is required to present a uniform brightness of an image displayed in the picture plane.
As a method to display an image brightness uniformly, a method wherein the transmittance of the panel glass is made constant in the plane, or a method wherein, while a transmittance distribution is permitted to be present in the panel glass, it is corrected by an intensity distribution of an electron beam, and a distribution is imparted to the emission intensity of the phosphor, may be mentioned.
However, the latter method has a technical limit such that when a panel glass which necessarily has a thickness in glass thickness in production of television, has a large transmittance distribution, such as a transmittance distribution with a difference of at least 10% between the center portion and the peripheral portion of the panel glass, it cannot cope therewith.
On the other hand, as a conventional method wherein the transmittance of a panel glass is made constant, the glass base material is made to be transparent to eliminate the difference in the transmittance due to the thickness of the glass. However, this method cannot cope with flattening of recent panel glasses where the center portion and the peripheral portion are large, and it is difficult to make the transmittance of such panel glasses to be uniform. Further, it has been attempted to solve the above problems by increasing the transmittance of the glass base material as a panel glass provided with an antireflection film and by reducing the transmittance of the antireflection film, but there has been a problem that the internal reflection tends to be high, and a double image is likely to form. Consequently, in a case of a flattened panel glass, there have been problems such that the contrast is poor, and a double image forms, in addition to a problem that uniformity cannot be attained in the brightness of images.
Further, as another related technology, JP-A-61-185852 discloses a method wherein the total glass thickness within the display area is made constant by attaching a front panel made of glass and provided with a thickness variation on the front surface of the panel glass by a resin. However, this method has had a problem that the weight of CRT increases, or the cost increases due to the bonding of the front panel.
Further, JP-A-6-308614 discloses a projection type display wherein, in order to improve the contrast, the projection screen is made to be a colored screen having an outer light absorption characteristic on its surface, and the color density is continuously changed from the center towards the periphery, so that the brightness distribution of the screen will be uniform, as seen by an observer. This publication also discloses that a similar effect can be obtained also by providing a distribution to the thickness of the colored screen. These methods are considered to be effective as means to make the brightness over the entire surface of the display uniform by intentionally providing a transmittance distribution to the display. However, in a case where such methods are applied to a panel glass for CRT, it will be required to have a resin face or a whole area panel corresponding to the colored screen, thus leading to a problem of the weight increase or the increase of the costs, as in the case described above.
Further, JP-A-10-177850 discloses a method for making the transmittance of the center portion and the peripheral portion uniform by bonding a resin film on the front surface of a panel glass for CRT and by adopting any one of {circle around (1)} coloring the resin film, {circle around (2)} applying a colored coating on the resin film surface and {circle around (3)} coloring the adhesive used for bonding the resin film to the panel glass. However, this method also has had a problem of the weight increase or the increase of the costs.
On the other hand, along with flattening of an image display plane, a problem of reflection of an outer image has newly arisen. This is caused because a flat image display plane acts as a mirror surface, and an external image is faithfully reproduced, whereby the reflection of the image is more likely to be recognized. In order to suppress this reflection of the image, it is simple and effective to apply an antireflection treatment to the image display plane. In WO00/44029, low reflection is attempted by forming a low refractive index film further on a light-absorbing film.
However, according to makeup examinations and studies by the present inventors, it has been found to be difficult to suppress reflection of the image uniformly over the entire surface of the image display plane only by providing a low refractive index film. Particularly with respect to the CRT for which a high precision image is required such as a display for computers, the reflectance in the image display plane is considered to be preferably at most 1.5%, particularly preferably at most 1.0%, however, it is very difficult to attain such a low reflectance uniformly over the entire surface of the image display plane.
FIG. 12
is a graph illustrating simulation of the relation, with respect to a glass plate having a low-reflection film comprising a light-absorbing film (titanium nitride film) and a low refractive index film (silicon oxide) formed thereon, between the light transmittance of the low-reflection film alone and the reflectance of the low-reflection film against light from the low refractive index film side. From the results of this simulation, it is found that the reflectance tends to be high along with an attempt to increase the light transmittance of the low-reflection film alone, and if light transmittance collection is carried out to make the brightness uniform, if the light transmittance is set to exceed 80% for example, the above low reflectance can not be realized.
The object of the present invention is to provide a method for producing a CRT panel glass or a CRT whereby the uniform brightness image can be seen with a good contrast, even with a flattened panel glass whereby the difference in brightness between the center portion and the peripheral portion becomes distinct especially when a colored glass is employed.
The present invention further has an object to provide a panel glass which has uniform brightness and contrast particularly over the entire surface of the image display plane, with which reflection is low and reflection of the image can be suppressed.
The present invention further has an object to provide a method for producing a CRT panel glass or a CRT, whereby the above panel glass can be obtained in a simple method at a low cost.
The present invention further has an object to provide a method for producing a CRT panel glass or a CRT having also an electromagnetic wave shielding performance.
The present invention further has an object to provide a method for producing a CRT panel glass or a CRT having also a low reflection performance.
Further, the present invention has an object to provide a method for producing a CRT panel glass or a CRT having occurrence of a double image suppressed.
Further, the present invention has an object to provide a CRT panel glass or a CRT obtained by the above production methods.
DISCLOSURE OF THE INVENTION
In order to achieve the above objects, the present invention provides the following method for producing a CRT panel glass or a CRT, and a CRT panel glass or a CRT, and the above objects of the present invention have been achieved.
1) A method for producing a CRT panel glass or a CRT, which comprises disposing baffle plates between an outer surface of a CRT panel on which a film is formed and a sputter target, and forming a surface treating film on the outer surface of said panel by a sputtering method so that the value A defined by the following mathematical expression (1) is less than 1 within an effective picture plane on the outer surface of said panel:
A
Horie Noritoshi
Ikezawa Toshikazu
Mizukami Junnosuke
Oyama Takuji
Shidoji Eiji
Asahi Glass Company Limited
Patel Vip
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