Electric lamp and discharge devices – Cathode ray tube – Envelope
Patent
1997-11-04
2000-02-15
Patel, Vip
Electric lamp and discharge devices
Cathode ray tube
Envelope
313402, 313408, H01J 2986
Patent
active
060256761
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube having a substantially flat face panel and a method of manufacturing the same.
2. Description of the Related Art
Generally, a color cathode ray tube is provided with a vacuum envelope having a glass face panel and a glass funnel. A phosphor screen having three-color phosphor layers is formed on the inner surface of the effective area of the face panel, and an electron gun is arranged in the neck of the funnel. Three electron beams emitted from the electron gun are deflected by the magnetic field generated by a deflector mounted on the outside of the funnel, and scan horizontally and vertically on the phosphor screen through a shadow mask, thereby displaying a color image.
The face panel of a color cathode ray tube having this configuration generally includes a substantially rectangular effective area and a side wall erected along the peripheral portion of the effective area. The face panel is formed with inner and outer surfaces curved so differently that the central portion of the effective area is thinner than the peripheral portion thereof in order to secure a sufficient strength to resist the atmospheric load applied to the vacuum envelope.
Generally, the outer surface of the effective area is formed with such a curvature that the height with respect to the sealed surface between the face panel and the funnel is greatest at the central portion of the effective area and lower toward the peripheral portion. Specifically known face panels include the one with the outer surface of the effective area having a spherical curvature, the one having a cylindrical outer surface with a substantially infinitely large radius of curvature along the vertical axis and a curvature along the horizontal long axis, and the one having a curved outer surface expressed by a high-order polynomial.
With respect to the shape of the outer surface of the effective area of the face panel, the recent trend is toward the flattening in order to improve the visibility. Depending on the curved geometry of the outer surface of the effective area of the face panel, a generally known method of indicating the flatness of the effective area includes the index R. The index R is given as the ratio of the average radius of curvature of the corners determined by the difference (the fall of the corners) between the height of the central portion of the face panel and the height of the corners of the face panel to the diagonal length of the effective area multiplied by a factor of 1.7. In the case where the flatness expressed by this index R remains the same, the fall at the corners is the same for any shape of the curved outer surface of the effective area, and though somewhat depending on the geometry of the curved surface, the feeling of flatness of the effective area of the face panel is substantially equal.
With the increase of the flatness of the face panel, however, the atmospheric strength of the glass vacuum envelope decreases. The flatness of the outer surface of the effective area, therefore, is at most about 2.0R even for a large cathode ray tube.
On the other hand, various shapes are available for the inner surface of the effective area of the face panel. The inner surface of the effective area, however, is often formed in the same type of curvature as the outer surface of the effective area so that the effective area is thinnest at the central portion thereof and thicker toward the peripheral area in order to maintain the atmospheric strength required of the glass vacuum envelope.
In recent years, the atmospheric strength of the glass vacuum envelope has improved due to an improved design accuracy of the face panel and an improved performance of the reinforcing band to such an extent that a predetermined strength is secured even with a flattened face panel. In the case where the inner and outer surfaces of the face panel are configured of the same type of curvature as described above, however, a still higher strength of the vacuu
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Fukuda Kumio
Inoue Masatsugu
Nakagawa Shinichiro
Ohama Shinji
Shimizu Norio
Gerike Matthew J
Kabushiki Kaisha Toshiba
Patel Vip
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