Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2000-02-09
2003-01-28
O'Shea, Sandra (Department: 2875)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S408000
Reexamination Certificate
active
06512326
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode-ray tube. More to particularly, this invention relates to structure of a shadow mask electrode and a shadow mask electrode supporting body which influence picture quality of the color cathode-ray tube.
DESCRIPTION OF THE PRIOR ART
In the color cathode-ray tube, the greater parts of electron beam meet a shadow mask electrode. Accordingly, temperature of the shadow mask electrode rises. Temperature rise deforms shadow mask electrode caused by thermal expansion. Picture quality deterioration occurs according to this deformation. It is necessary to prevent picture quality deterioration caused by the deformation. In order to prevent the picture quality deterioration, formerly, fixed tension is applied to the shadow mask electrode. The shadow mask electrode is fastened to a frame while applying fixed tension thereto.
In recent years, requirement with respect to picture quality becomes increasingly severe. For that reason, metal whose coefficient of thermal expansion is low such as Invar is used so that it is capable of reducing thermal expansion of the shadow mask electrode itself to the utmost.
Above-mentioned conventional techniques are combined with each other. Namely, the shadow mask electrode is made of metal such as Invar whose coefficient of thermal expansion is low. Tension is applied to the shadow mask electrode made of Invar in order to fasten it flatly to a supporting body. A frame body is made of the same metal as that of the shadow mask electrode. The shadow mask electrode is fastened to the frame body while applying fixed tension thereto. The thermal expansion rate of shadow mask electrode agrees with the thermal expansion rate of the frame body. It is capable of obtaining a color cathode-ray tube with very excellent picture quality.
However, the metal whose thermal expansion rate is low is very expensive. It is very expensive when the frame body is made of the metal with low thermal expansion rate. It is not practical. Consequently, as a practical method, the shadow mask electrode is made of metal whose thermal expansion rate is low such as Invar and so forth but expensive. The frame body is made of metal whose thermal expansion rate is high such as steel and so forth but cheap. Thus it can be considered that the shadow mask electrode made of metal with low rate of thermal expansion is combined with the frame body made of metal with high rate of thermal expansion.
However, such combination brings picture quality deterioration. The combination between the shadow mask electrode and the frame body with difference of thermal expansion rate described above brings difference of expansion and contraction between the shadow mask electrode and the frame body. Such combination brings shears, wrinkles, slackening and so forth from design dimension of the shadow mask electrode. Such wrong condition occurs either in temperature (about 400 to 500° C.) during manufacturing of color cathode ray tube, and in temperature (about 50 to 100° C.) in use of the color cathode ray tube.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention, in order to overcome the above-mentioned problems to provide a color cathode-ray tube which provides constitution both of a shadow mask electrode and a frame body in which difference of expansion and contraction between the shadow mask electrode and the frame body does not produce picture quality deterioration with practical cost.
In accordance with a first aspect of the present invention, in order to achieve the above mentioned object, there is provided a color cathode-ray tube which comprises a shadow mask electrode made of metal whose thermal expansion rate is low and to which tension is applied to be flatly supported, a color electrode supporting body made of metal whose thermal expansion rate is approximately the same as that of the shadow mask electrode, for supporting shadow mask electrode, and a frame body made of metal whose thermal expansion rate is different from that of the shadow mask electrode, for supporting the shadow mask electrode supporting body.
According to the first aspect, the shadow mask electrode and the shadow mask electrode supporting body are made of approximately the same metal whose thermal expansion rate is low. Relative difference of dimension between the shadow mask electrode and the shadow mask electrode supporting body is small in relation to temperature change. It is capable of preventing picture quality deterioration caused by shear, wrinkle, or slackening from design dimension of the shadow mask electrode in use or during manufacturing of the color cathode-ray tube. Further, the frame body is made of metal whose price is low, thus it is capable of constituting the color cathode ray tube in low cost.
In accordance with a second aspect of the present invention, in the first aspect, there is provided a color cathode-ray tube wherein tension in one-way direction is applied to the shadow mask electrode to be flatly supported.
As described-above according to the second aspect, since the tension in one-way direction is applied to the color section electrode, it is capable of being prevented the picture quality deterioration caused by shear, wrinkle, or slackening of the shadow mask electrode due to stress-strain convergence at the corner part of the shadow mask electrode.
In accordance with a third aspect of the present invention, in the second aspect, there is provided a color cathode-ray tube, wherein tension in one-way direction is applied to the shadow mask electrode to be flatly supported, and there is provided the shadow mask electrode supporting body for only two sides which stand opposite each other for applying tension to said shadow mask electrode.
As described above, according to the third aspect, since there is provided a color cathode-ray tube, wherein tension in one-way direction is applied to the shadow mask electrode to be flatly supported, and there is provided the shadow mask electrode supporting body for only two sides which stand opposite each other for applying tension to said shadow mask electrode. Thus, it is capable of prevented the picture quality deterioration caused by shear, wrinkle, or slackening of the shadow mask electrode due to stress-strain convergence at the corner part of the shadow mask electrode.
In accordance with a fourth aspect of the present invention, a color cathode-ray tube which comprises a shadow mask electrode made of metal whose thermal expansion rate is low and to which tension in one-way direction is applied to be flatly supported, color electrode supporting bodies consisting of different kind of metals, one metal whose thermal expansion rate is approximately the same as that of the shadow mask electrode for supporting shadow mask electrode in one-way direction, and the other metal whose thermal expansion rate is different from that of the shadow mask electrode does not support the shadow mask electrode, and a frame body made of metal whose thermal expansion rate is different from that of the shadow mask electrode, for supporting the shadow mask electrode supporting body.
As described-above according to the fourth aspect, since the shadow mask electrode supporting body which does not apply tension to the shadow mask electrode is made of metal whose thermal expansion rate is different from that of the shadow mask electrode, the shadow mask electrode is made of metal whose price is low resulting in cost down.
In accordance with a fifth aspect of the present invention, there is provided a color cathode-ray tube which comprises a shadow mask electrode made of metal whose thermal expansion rate is low and to which tension in one-way direction is applied to be flatly supported, color electrode supporting bodies made of metal whose thermal expansion rate is approximately the same as that of the shadow mask electrode for supporting shadow mask electrode in one-way direction, and a frame body made of metal whose thermal expansion rate is different from that of the shadow
Arai Shinji
Hasegawa Hiroshi
Alavi Ali
NEC Corporation
O'Shea Sandra
Sughrue & Mion, PLLC
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