Electric lamp and discharge devices – Cathode ray tube – Screen
Reissue Patent
2000-08-21
2002-06-18
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Screen
C313S474000, C313S478000
Reissue Patent
active
RE037750
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color picture tube, in particular, to a color picture tube for displaying data with high luminance and high contrast.
2. Description of the Related Art
A conventional color picture tube has a face plate that has light transmissivity and an effective display surface for displaying a picture. A fluorescent substance layer is deposited on the inner surface of the effective display surface of the face plate.
A funnel that is a hollow cone with a tube extending from the smaller rear end is disposed on the rear end of the face plate. The front end of the funnel is connected to the rear end of the face plate. Thus, a sealed vessel as a sheath of the color picture tube is formed.
An electron gun is disposed inside the rear end of the funnel. The electron gun scans and radiates an electron beam to the fluorescent substance layer corresponding to a display picture.
The path of the electron beam emitted from the electron gun is controlled by the magnetic field generated by a deflecting yoke that surrounds the electron gun so as to radiate the electron beam to a desired position of the fluorescent substance layer.
An importance factor of the characteristics of the picture display quality of the color picture tube is the brightness of the display picture. The brightness of the picture is evaluated with the luminance and the contrast ratio.
The brightness and contrast of a picture displayed on the screen and perceived by the viewer depends on not only the luminance of the picture, but the brightness of the front surface of the display screen. In other words, the brightness and contrast perceived by the viewer depends on the relation between the sum of the reflected light of the screen in non-picture display state and the perceived brightness of the fluorescent substance layer and the luminance of the display picture emitted on the fluorescent substance layer.
To improve the brightness and contrast of the display picture, the display quality can be improved.
However, with the conventional technologies, it is difficult to improve both the brightness and contrast.
In other words, when the light transmissivity of the material of the face plate is improved, since the light emitted at the fluorescent substance and transmitted to the front surface of the face plate can be effectively used, the picture is brightly perceived.
However, due to the lightness of the fluorescent substance layer in the non-emitting state, when a picture is not displayed, the brightness of the face plate composed of the material with high light transmissivity is high.
The contrast of a picture displayed by light emitted from the fluorescent substrate layer depends on the brightness of the screen in the non-picture display state. Thus, the brightness of the screen in the non-picture display state is reversely proportional to the contrast characteristics. Since the color of the fluorescent substance layer is normally a white type, the lightness thereof is very high.
Thus, in the conventional color picture tube, to improve the luminance, the drive voltage of the color picture tube is increased and thereby the energy of the electron beam is increased so as to improve the luminance of the light emitted by the fluorescent substance.
On the other hand, to improve the contrast characteristics, a colored glass is used as the material of the face plate so as to decrease the light transmissivity to 40% or more. Thus, the brightness of the screen in the non-picture display state is suppressed. Alternatively, a pigment is mixed with the material of the fluorescent substance layer so as to darken the color of the fluorescent substance layer.
However, when the energy of the electron beam is increased, the current consumption of the color picture tube increases. Thus, the power consumption of the color display apparatus increases. From this point of view, it is not preferable to increase the energy of the electron beam.
On the other hand, when the colored glass is used for the material of the face plate and thereby the light transmissivity is decreased to 40% or less, since the reflection of the external light decreased reversely proportional to the square of the light transmissivity, the contrast characteristics are improved. However, due to the low transmissivity of the face plate, the transmissivity of the light that is emitted from the fluorescent substance layer and imaged through the face plate is decreased to 40% or less. Thus, the luminance of the display picture remarkably decreases.
In the case of a flat type color picture tube of which the glass wall thickness of the face plate peripherally increases with a predetermined change ratio, since the light absorbing ratio at the peripheral portion with large all thickness is high, the luminance of the picture at the peripheral portion is remarkably different from that at the center portion.
Practically, it is very difficult to equalize the wall thickness of the entire face plate of the flat type color picture tube. This is because the shape of the inner shadow mask, the scanning method of the electron beam, and the fabrication method of the entire color picture tube should be changed.
When a pigment is mixed with the material of the fluorescent substance layer and thereby the color of the fluorescent substance layer is darkened, since the pigment is not a fluorescent substance, the ratio of the substance that does not contribute to the light emission increases in the fluorescent substance layer. Thus, the light emitting performance of the fluorescent substance layer decreases and thereby the luminance of the display picture decreases.
Alternatively, the voltage for emitting the electron beam from the electron gun is increased and thereby the energy of the electron beam is increased so as to increase the light emission of the fluorescent substance layer. However, in this case, the power consumption increases. In addition, the voltage for deflecting the electron beam with high energy increases. Thus, the total power consumption of the color picture tube remarkably increases.
A surface coat may be deposited on the outer surface of the face plate so as to prevent the external light from reflecting. However, with this method, a good result cannot be obtained.
To solve such a problem, a technology for disposing a color filter layer between the inner surface of the face plate and the fluorescent substance layer has been proposed and is becoming popular.
The color filter layer has many color cells corresponding to fluorescent substance dots or fluorescent substance stripes corresponding to pixels. The color cells transmit only emitted color light or respective pixels. The color filter layer transmits only emitted light corresponding to each pixel. In addition, the color filter layer prevents external light from reflecting at the interface between the fluorescent substance layer and the face plate. Thus, it is said that with such a color filter layer, the contrast characteristics can be effectively improved without a decrease of the chromaticity of bright points of each color of the screen (namely, the purity of the colors) and a decrease of the luminance.
However, since the color filter layer is disposed inner surface of the face plate, the color filter layer should be composed of an inorganic pigment whose material withstands the inner environment of the color picture tube and the heating process at a temperature of around 500° C. Nevertheless, the filter performance of the color filter layer composed of such an inorganic pigment is not satisfactory.
In other words, for pigments used for red cells and blue cells, with Fe
2
O
3
particles and Al
2
O
3
—CoO particles, desired characteristics can be obtained with conventional technologies.
However, a pigment for green cells that satisfies such characteristics is not known. In other words, with conventional pigments for green cells, satisfactory selective absorbing characteristics cannot be accomplished (namely, good coloring characteristics cannot be acco
Itou Takeo
Matsuda Hidemi
Nakazawa Tomoko
Oyaizu Tsuyoshi
Tanaka Hajime
Haynes Mack
Kabushiki Kaisha Toshiba
Pillsbury & Winthrop LLP
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