Patent Grant
7265484
1. Field of the Invention
The present invention relates to a color picture tube. In particular, the present invention relates to a color picture tube in which a radius of curvature of a panel outer surface is 10,000 mm or more.
2. Description of Related Art
In general, as shown in
In such a color picture tube, in order to display an image without color displacement on the phosphor screen 3, it is necessary that the three electron beams 6B, 6G, and 6R having passed through the electron beam passage apertures formed in the shadow mask 4 should land correctly on the three-color phosphor layers. For this purpose, the relationship of the shadow mask 4 with respect to the panel 1 is important. Above all, it is necessary that an interval (q value) between the inner surface of the useful portion 1a of the panel 1 and a region (perforated region) of the shadow mask 4 in which the electron beam passage apertures are formed is within a predetermined allowable range.
Of all the electron beams emitted from the electron gun 7, only a part thereof reaches the phosphor screen 3. The remaining electron beams strike the shadow mask 4. At this time, the kinetic energy of the electron beams changes to thermal energy to heat the shadow mask 4. Therefore, the shadow mask expands thermally in accordance with the coefficient of thermal expansion of the material thereof, and its shape changes. Consequently, the positions of the electron beam passage apertures with respect to phosphors change, and when the change amount of these positions exceeds an allowable value, the electron beams cannot strike desired phosphors so that so-called mislanding occurs, which degrades the color purity of a display image.
In the thermal expansion of the shadow mask 4 caused by the irradiation with electron beams, in the case where only a part of the perforated region is irradiated with a large amount of electron beams, the change amount of the positions of the electron beam passage apertures with respect to the phosphors becomes particularly large, and the color purity is degraded significantly due to the mislanding of the electron beams. For example, as shown in
Recently, in order to enhance the visibility of a color picture tube, there is a demand that the radius of curvature of the outer surface of the useful portion 1a of the panel 1 is increased so as to bring the outer surface close to a flat surface. In this case, in terms of the strength of the vacuum envelope 9 with respect to the atmospheric pressure and visibility, it is necessary to increase the radius of curvature of the inner surface of the useful portion 1a. In order to obtain appropriate electron beam landing in accordance with the increase in the radius of curvature of the inner surface of the useful portion 1a, it is necessary to increase the radius of curvature of the perforated region of the shadow mask 4. However, when the radius of curvature of the perforated region of the shadow mask 4 is increased, the change amount of the positions of the electron beam passage apertures with respect to the phosphors due to doming increases, and the mislanding amount of the electron beams increases, so that the color purity is degraded significantly.
Therefore, in a color picture tube having the panel 1 with a substantially flat outer surface, in order to suppress doming, in most cases, an alloy mainly containing iron and nickel, having a low coefficient of thermal expansion, is used as a material for the shadow mask 4. For example, a 36 Ni Invar alloy or the like is used frequently. In this case, the iron-nickel alloy entails high cost, while providing a coefficient of thermal expansion of 1 to 2×10−6 at 0° C. to 100° C., which is effective for suppressing doming. Furthermore, the iron-nickel alloy has large elasticity after annealing, so that it is difficult to form a curved surface from such an alloy by press forming and to obtain a desired curved surface. Even if the iron-nickel alloy is annealed, for example, at a high temperature of 900° C., the yield point strength is about 28×107 N/m2. Thus, it is necessary to treat the alloy at a considerably high temperature in order to set the yield point strength to be 20×107 N/m2 or less at which press forming generally is considered to be easy. Particularly, in a color picture tube with a flat panel outer surface, the radius of curvature of the perforated region of the shadow mask is large, so that press forming is further difficult.
In the case where press forming is insufficient, and undesired stress remains in the shadow mask 4 after press forming, the residual stress changes the shape of the shadow mask 4 in the course of production of the color picture tube, which leads to the mislanding of the electron beams, resulting in significant degradation in the color purity.
On the other hand, with aluminum killed steel mainly containing high-purity iron, the yield point strength can be set to be 20×107 N/m2 or less by annealing at about 800° C., so that press forming is very easy. Thus, regarding the aluminum killed steel, it is not necessary to keep the press die temperature to be high in the course of press forming, which is required in an Invar alloy, and the productivity also is satisfactory.
However, the coefficient of thermal expansion of the aluminum killed steel is high (i.e., about 12×10−6 at 0° C. to 100° C.), which is disadvantageous for doming. Particularly, in the case of applying the aluminum killed steel to a color picture tube in which the outer surface of the useful portion 1a of the panel 1 is substantially flat, there arises a serious problem such as the significant degradation in color purity.
JP 10(1998)-199436 A discloses a shadow mask in the shape of a substantially cylindrical surface, in which the radius of curvature in a major axis direction is almost infinite, and the radius of curvature in a minor axis direction is almost constant irrespective of the position in the major axis direction. Even such a shadow mask has an effect of suppressing doming to some degree. However, in the case of using an inexpensive iron material, a sufficient effect cannot be obtained. Furthermore, there is a problem that the weight of a panel increases.
As described above, in the color picture tube, when the radius of curvature of the outer surface of the useful portion of the panel is increased so as to enhance visibility, and the radius of curvature of the perforated region of the shadow mask is increased in accordance with the increase in the radius of curvature of the outer surface of the useful portion, the mislanding amount of the electron beams increases due to the thermal expansion of the shadow mask, and consequently, the color purity is degraded significantly.
Furthermore, in the case of using an iron material that is inexpensive and has satisfactory formability as a material for the shadow mask, the mislanding amount of the electron beams caused by the thermal expansion of the shadow mask further increases due to its large coefficient of thermal expansion, and consequently, the color purity is degraded significantly.
The present invention has been achieved in view of the above-mentioned problems, and its object is to provide a color picture tube that has satisfactory visibility, and less degradation in color purity caused by doming while having a shadow mask with excellent formability and strength.
A color picture tube of the present invention includes a panel in which a phosphor screen is formed on an inner surface of a substantially rectangular useful portion, and a shadow mask.
The shadow mask includes a perforated region opposed to the phosphor screen and made of a substantially rectangular curved surface in which a number of electron beam passage apertures are formed, a non-perforated region placed on a periphery of the perforated region so as to surround the perforated region, and a skirt portion connected to the non-perforated region and bent with respect to the non-perforated region,
A radius of curvature of an outer surface of the useful portion of the panel is 10,000 mm or more.
It is assumed that a tube axis direction axis is a Z-axis, an axis orthogonal to the Z-axis and parallel to a long side (long edge) direction of the perforated region is an X-axis, an axis orthogonal to the Z-axis and parallel to a short side (short edge) direction of the perforated region is a Y-axis, a size of the perforated region on the X-axis is 2L, and s is a variable satisfying 0<s<1. It is assumed that sagging amounts in a Z-axis direction of a surface of the perforated region with respect to a mask center at respective points of X=0, sL, L on the X-axis are Z00, Z01(s), Z02, and sagging amounts in the Z-axis direction of the surface of the perforated region with respect to the mask center at respective points of X=0, sL, L on the long side of the perforated region are Z10, Z11(s), Z12.
When, using a sagging amount difference ΔZ01(s) at the point of X=sL with respect to the point of X=0 on the X-axis, defined by ΔZ01(s)=Z01(s)−Z00,
a sagging amount difference ΔZ02(s) at the point of X=L with respect to the point of X=sL on the X-axis, defined by ΔZ02(s)=Z02−Z01(s)
a sagging amount difference ΔZ11(s) at the point of X=sL with respect to the point of X=0 on the long side, defined by ΔZ11(s)=Z11(s)−Z10, and
a sagging amount difference ΔZ12(s) at the point of X=L with respect to the point of X=sL on the long side, defined by ΔZ12(s)=Z12−Z11(s),
α(s) represented by α(s)=(ΔZ01(s)/ΔZ11(s))/(ΔZ02(s)/ΔZ12(s)) is defined,
dα(s)/ds≧0.4 is satisfied in at least a part in a range of 0.2≦s≦0.8.
According to the present invention, a color picture tube can be provided, which has satisfactory visibility, and less degradation in color purity caused by doming while having a shadow mask with excellent formability and strength.
Hereinafter, the color picture tube of the present invention will be described with reference to the drawings.
The schematic configuration of the color picture tube according to the present invention is the same as that of the conventional color picture tube shown in
The outer surface of the useful portion 1a of the panel 1 forming the color picture tube of the present invention is a substantially flat surface with a radius of curvature of 10,000 mm or more so as to enhance visibility. Thus, in terms of the strength of the envelope 9 with respect to the atmospheric pressure and visibility, it is necessary to increase the radius of curvature of the inner surface of the useful portion 1a. In order to obtain appropriate electron beam landing in accordance with the increase in the radius of curvature of the inner surface of the useful portion 1a, it is necessary to increase the radius of curvature of the perforated region 41 of the shadow mask 4. In general, when the radius of curvature of the perforated region 41 of the shadow mask 4 is increased, it becomes difficult to press-form the perforated region 41 to a curved surface. According to the present invention, it is preferable to use a material containing 95% or more of iron as a material for the shadow mask 4. This can remarkably improve the formability of a curved surface at low cost.
However, such a material has a high coefficient of thermal expansion. Therefore, when an image pattern with locally high brightness is displayed as shown in
The present invention solves the above-mentioned problems. One example thereof will be described below by exemplifying a color picture tube with a diagonal size of 51 cm, an aspect ratio of 4:3, and a radius of curvature of the outer surface of the useful portion 1a of the panel 1 of 20,000 mm (hereinafter, referred to as “Example 1”).
The outer surface of the panel 1 of the color picture tube of Example 1 is flattened sufficiently as described above, and the shadow mask 4 is made of aluminum killed steel shown in Table 1 made of high-purity iron with a coefficient of thermal expansion of 12×10−6 at 0° C. to 100° C. Therefore, the sufficient formability is ensured while providing low cost.
As shown in
It is assumed that s is a variable satisfying 0<s<1, and as shown in the figure, sagging amounts in the Z-axis direction of the surface of the perforated region 41 with respect to the mask center at respective points (X=0, sL, L) on the X-axis are Z00, Z01(s), and Z02. Furthermore, it is assumed that sagging amounts in the Z-axis direction of the surface of the perforated region 41 with respect to the mask center at respective points (X=0, sL, L) on the long side 41a of the perforated region 41 are Z10, Z11(s), and Z12.
Furthermore, a sagging amount difference that is the difference in sagging amounts among these respective points is defined as shown in
α(s)=(ΔZ01(s)/ΔZ11(s))/(ΔZ02(s)/ΔZ12(s))
is defined.
The sagging amount at each point is determined by a position x (i.e., s) in the X-axis direction.
In the shadow mask in Example 1, the sagging amount Z12 at the diagonal axis end is the same as that of Comparative Example 1. Therefore, when the shadow mask in Example 1 is applied to a panel having a flat outer surface, a color picture tube having excellent visibility can be realized. Furthermore, the shadow mask is made of a material containing 95% or more of iron, so that the formability of the shadow mask is satisfactory and the cost thereof is low. Furthermore, since the sagging amount difference in a range of X=0.5 L to X=L is large, on the periphery of a point of X=0.5 L at which local doming as described with reference to
Table 2 shows the movement amount of electron beams due to doming at an intermediate position (intermediate position on the major axis) between the screen center and the X-axis end of the screen, when the display as shown in
As is understood from Table 2, the movement amount of electron beams is 400 μm or more in the single curved surface 1 and Comparative Example 1, while the movement amount of electron beams is less than 300 μm in Example 1. Thus, in Example 1, the movement amount of electron beams is reduced to 58% of that of the single curved surface 1.
An example of applying the present invention to another size will be described. As a second application example, a color picture tube with a diagonal size of 36 cm, and an aspect ratio of 4:3 will be described.
The sagging amounts along the X-axis and the long side 41a of the perforated region 41 can be approximated by a sixth degree polynomial of an X-coordinate value x, and coefficients of respective terms are as shown in bottom columns in
In Example 2 according to the present invention, dα(s)/ds≧0.4 is satisfied in a range of 0.22≦s≦0.72. More specifically, in a portion of 83% (=[(0.72−0.22)/(0.8−0.2)]×100) in the range of 0.2≦s≦0.8, the change curve of dα(s)/ds passes through the region 30. Furthermore, a maximum value of dα(s)/ds is present in the range of 0.2≦s≦0.8. In contrast, in Comparative Example 2, |dα(s)/ds|≦0.2 is satisfied in the range of 0.2≦s≦0.8, and in the single curved surface 2, dα(s)/ds=0 is satisfied over the entire surface of the perforated region 41 irrespective of the value of s. Thus, the change curve of dα(s)/ds does not pass through the region 30 in Comparative Example 2 and the single curved surface 2.
In the shadow mask in Example 2, the sagging amount Z12 at the diagonal axis end is the same as that of Comparative Example 2. Therefore, when the shadow mask in Example 2 is applied to a panel having a flat outer surface, a color picture tube having excellent visibility can be realized. Furthermore, the shadow mask is made of a material containing 95% or more of iron, so that the formability of the shadow mask is satisfactory and the cost thereof is low.
Table 2 shows the movement amount of electron beams due to doming at an intermediate position (intermediate position on the major axis) between the screen center and the X-axis end of the screen, when the display as shown in
As is understood from Table 2, the movement amount of electron beams is 300 μm or more in the single curved surface 2 and Comparative Example 2, while the movement amount of electron beams is 243 μm in Example 2. Thus, in Example 2, the movement amount of electron beams is reduced to 78% of that of the single curved surface 2. If at least a part of the change curve of dα(s)/ds passes through the region 30, the mislanding amount of electron beams due to doming can be reduced. Furthermore, as in Example 2, if the change curve of dα(s)/ds passes through the region 30 in a portion of 50% or more in the range of 0.2≦s≦0.8, the mislanding amount of electron beams due to doming can be reduced further.
An example of applying the present invention to still another size will be described. As a third application example, a color picture tube with a diagonal size of 60 cm, and an aspect ratio of 4:3 will be described.
When the shadow mask in Example 3 is applied to a panel having a flat outer surface, a color picture tube having excellent visibility can be realized. Furthermore, the shadow mask is made of a material containing 95% or more of iron, so that the formability thereof is satisfactory and the cost thereof is low.
Table 2 shows the movement amount of electron beams due to doming at an intermediate position (intermediate position on the major axis) between the screen center and the X-axis end of the screen, when the display as shown in
According to the present invention, the sagging amount Z12 at the diagonal axis end of the shadow mask also can be reduced while the mislanding of electron beams due to doming of the shadow mask is suppressed.
Even when the shadow mask in Example 4 is applied to a panel having a flat outer surface, a color picture tube having excellent visibility can be realized. Furthermore, the shadow mask is made of a material containing 95% or more of iron, so that the formability thereof is satisfactory and the cost thereof is low.
Table 2 shows the movement amount of electron beams due to doming at an intermediate position (intermediate position on the major axis) between the screen center and the X-axis end of the screen, when the display as shown in
As is understood from Table 2, in Example 4, the movement amount of electron beams is reduced to 88% of that of the single curved surface 3. As in Example 4, the radius of curvature of the inner surface of the useful portion of the panel can be increased by decreasing the sagging amount Z12 at the diagonal axis end, so that the thickness of the panel decreases, which makes it possible to reduce the weight of the panel. Thus, according to Example 4, the reduction in a panel weight, the enhancement of visibility, and the reduction in a mislanding amount of electron beams due to doming can be realized simultaneously.
In the present invention, it is preferable that the maximum value of dα(s)/ds is present in the range of 0.2≦s≦0.8 because it is advantageous for the reduction in the movement amount of electron beams due to doming.
Furthermore, in the present invention, the shadow mask may be coated with bismuth oxide for the purpose of suppressing doming. This can further reduce the mislanding amount of electron beams due to doming.
The color picture tube according to the present invention has excellent visibility owing to a substantially flat panel outer surface, and can reduce color displacement caused by doming even when a shadow mask made of an iron material is used for the purpose of reducing cost. Therefore, the color picture tube according to the present invention can be used widely as one capable of performing a satisfactory color display.
The embodiments as described above are all intended to clarify the technical contents of the present invention. The present invention can be modified variously in the scope of the spirit of the present invention and claims without being limited to only such specific examples, and should be interpreted widely.
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