Patent Grant
7061172
1. Field of the Invention
The present invention generally relates to a flat color cathode ray tube, and in particular, to a flat color cathode ray tube with excellent doming quality by improving the structure of a flat panel and by using a shadow mask made of AK (aluminum-killed) material.
2. Description of the Related Art
Referring to
A fluorescent screen 13 is formed on the inner side of the panel 1, and an electron gun 8 is mounted in a neck portion of the funnel 2 that opposes the fluorescent screen 13.
A shadow mask 3 for dividing three color electron beams emitted from the electron gun 8, spaced at a given distance away from the fluorescent screen 13. The shadow mask 3 is combined with a mask frame 4, and is elastically supported by a spring 5, and further by the panel 1 with a stud pin 5.
The mask frame 4 is jointed with an inner shield 7 that is made of a magnetic material to reduce any movement of electron beam 11 due to an external magnetic field, particularly from the rear side of the cathode ray tube (or Braun tube).
On the other hand, a convergence purity magnet (CPM) 10 for adjusting R, G, and B electron beams to converge on a point, and a deflection yoke 9 for deflecting the electron beam 11 are mounted on a neck portion of the funnel 2.
Also, a reinforcing band 12 is included to reinforce the front surface glass in order to offset the influence of a vacuum state of the tube.
To explain the operation of a thusly constructed color cathode ray tube, the electron beams 11 emitted from the electron gun 8 are deflected vertically and horizontally by the deflection yoke 9, and the deflected electron beams 11 pass through beam pass holes in the shadow mask 3, and strike the fluorescent screen 13 on the front, consequently displaying designated color images.
Here, the convergence purity magnet 10 compensates the convergence and purity of R, G, and B electron beams 11, and the inner shield 7 blocks the influence of the magnetic field from the rear side of the cathode ray tube.
As depicted in the drawings,
It has been believed that the panel 1 of the cathode ray tube, on which images are displayed, should be curved both inside and outside in order to withstand the high vacuum state of the inside of the cathode ray tube, and to make the electron beams land easily.
However, external light is severely reflected on the peripheral side rather than at the center of the panel 1 in terms of the incidence angle of the external light, and this consequently makes users see very distorted images on the peripheral side. For such reason, the flat type panel 1 has drawn a lot of interests and in fact, most of panels 1 currently being used tend to be flat as shown in
Korean Patent Laid-Open No. 0282536 discloses a panel in which the outer surface is flat and the inner surface is curved.
As illustrated in
Keeping abreast of such trend, the curvature of the shadow mask in the panel 1 is also becoming flat similar to that of the panel's inner surface. The panel's inner surface is curved in connection with the dichroic function for images, while the shadow mask is curved for more convenient landing that determines convergence for converging R, G, and B electron beams to one point by deflection and color purity of images.
However, as the inner surface of the shadow mask became flatter, doming, which is thermal deformation of the shadow mask due to the electron beam, became a problem. To solve the problem, a shadow mask made of invar material having a relatively low coefficient of thermal expansion was introduced.
Unfortunately though, a shadow mask made of invar is too expensive, thus increasing the overall production cost.
It is, therefore, an object of the present invention to provide a flat color cathode ray tube which can address the effect doming on quality by improving the structure of a flat panel and by using a shadow mask made of AK (aluminum-killed) material.
Another object of the present invention is to provide a cathode ray tube whose transmittance ratio of the peripheral side to the central part is 0.4 to 0.6; thereby increasing the contrast and consequently picture quality, and whose curvature radius of the panel inner surface is changed to 1.29R to 4.35R, thereby reinforcing the doming characteristics and decreasing the curvature radius of the mask, and whose material of manufacture is AK, which has a relatively greater thermal expansivity than the thermal expansivity that of the conventional Invar mask and has a cost as low as half the price of the conventional cathode ray tube despite its poor doming characteristics.
Still another object of the present invention is to secure price competitiveness and to improve productivity by using a shadow mask made of lower priced AK material.
To achieve the above objects, there is provided a cathode ray tube, wherein an outer surface of a panel is substantially flat and an inner surface of the panel has a curvature, and the transmittance of the effective surface's ending portion in contraction with the central portion of the panel is in the range of 0.4 to 0.6, and the radius of diagonal curvature (Rd) of the panel's inner surface is in the range of 1.29R to 4.35R (R=1.767×diagonal length of the effective surface), and a shadow mask is made of AK material.
The cathode ray tube embodying the principles of the present invention is made of AK material, has a flat outer surface, which can minimize distortion of the screen and reproduces idealistic images, and has 5 an inner surface with a curvature, which can prevent deterioration of the picture quality due to the doming phenomenon of a shadow mask.
In addition, the cathode ray tube of the present invention has a price as low as half the price of the conventional panel, and uses the shadow mask made of AK material yet manifesting equivalent doming quality to that of the shadow mask made of Invar material.
Therefore, the cathode ray tube according to the present invention is advantageous in terms of price competitiveness and productivity because it uses a shadow mask made of low-price AK material.
The above objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:
A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in Unnecessary detail.
Normally, AK material indicates a material having Fe as a main component and a small amount of other components as shown in Table 1. The coefficient of thermal expansion of the AK material is in the range of 8 to 20×10−6, that is, its deformation due to heat is 5.3 to 13.3 times the deformation due to heat of Invar material.
The comparison result of Invar material and AK material is provided in Table 1 below.
As shown in Table 1, the shadow mask made of AK material, compared to the shadow mask made of Invar material has relatively good price, etchability, and plasticity, but it is weak at the doming phenomenon compared to the shadow mask made of Invar material because of its large coefficient of thermal expansion. As an attempt to solve the problem, some researchers tried to reduce the radius of curvature of the shadow mask made of AK material.
Unfortunately however, the curvature of the shadow mask is very closely related to the curvature of the panel's inner surface, so the radius of curvature of the shadow mask cannot be reduced indefinitely.
More specifically, if the radius of curvature of the shadow mask is reduced, the radius of curvature of the panel's inner surface should be reduced as well because when the peripheral portion is thicker than the central portion of the panel more than a fixed limit, the transmittance of the panel's peripheral portion gets decreased, which consequently lowers the brightness of the panel's peripheral portion.
Table 2 explains ratio of the transmittance at the corner to the transmittance at the center, radius of diagonal curvature, Td/Tc, Rd/(USD/2), according to the size of the panel.
With reference to Table 2, and
Also, Rd is radius of diagonal curvature of the panel's inner surface, and USD is diagonal length of the panel.
Referring to Table 2, as for the flat Braun tube having a flat outer surface and a curved inner surface, and using the shadow mask made of AK material, if the corner/center transmittance is below 0.4, the brightness at the peripheral portion gets so low that proper images cannot be reproduced. The panel's peripheral portion is very thick, and heavier thereby lowering productivity and increasing costs.
On the other hand, if the corner/center transmittance is higher than 0.6, the curvature is such that it cannot deal with the doming phenomenon by using the shadow mask made of AK material, and at the same time, the shadow mask becomes very weak, causing a problem such as a howling phenomenon or dropping the quality overall.
Further, if the radius of diagonal curvature is greater than 4.35R, a sufficient curvature for use of the shadow mask made of AK material cannot be formed, which consequently deteriorates the picture quality due to the doming phenomenon, and the thickened central portion of the panel for strengthening against the effect of high vacuum, instead lowers the brightness.
In the meantime, if the radius of diagonal curvature is lower than 1.29R, it makes the panel's corner too thick, and as a result, productivity is lowered and price is increased and an internal path is very easily damaged during the manufacturing process.
Therefore, it is preferable to have the corner/center transmittance between 0.4 and 0.6, and the radius of diagonal curvature between 1.29R and 4.35R.
Next, in case that Td/Tc is below 2.04, a sufficient curvature for use of the shadow mask made of AK material cannot be formed, which consequently deteriorates the picture quality due to the doming phenomenon, and lowers the landing and color purity overall because of too big of a gap between the panel and the shadow mask.
Meanwhile, if Td/Tc is greater than 2.50, images on the flat Braun tube become severely distorted, and the peripheral portion gets dark because the diagonal ending portions of the panel are too thick.
Although such problems may be overcome by using a clear panel whose transmittance at the center portion is higher than 80%, but the panel's outer surface must be coated to effect better brightness of images, thus incurring additional cost.
Accordingly, it is preferable to have Td/Tc in the range of 2.04 to 2.50.
Moreover, if Rd/(USD/2) is below 4.55, although the picture quality is not deteriorated due to the doming phenomenon, the diagonal ending portions of the panel become too thick, which consequently lowers the panel's plasticity, and increases image distortion. Further, the increased weight lowers productivity and increases manufacturing cost as well.
On the other hand, if Rd/(USD/2) is higher than 10.68, the central portion of the panel must be increased in order to secure the strength due to high vacuum, but it lowers the brightness instead.
Therefore, it is preferable to have Rd/(USD/2) in the range of 4.55 to 10.68.
Lastly, suppose that the transmittance at the central portion of the panel is 40–75%. If the radius of diagonal curvature in this case is greater than 4.35R, the resultant curvature is not sufficient for using the shadow mask made of AK material, eventually lowering picture quality due to the doming phenomenon. The thickened central portion of the panel to obtain strength due to high vacuum lowers brightness.
However, if the radius of diagonal curvature is below 1.29R (again, the transmittance at the central portion of the panel is 40–75%), it makes the panel's corner too thick. As the result thereof productivity is lowered and price is increased and an internal path is very easily damaged during the manufacturing process.
In short, if the transmittance at the central portion of the panel is 40–75%, it is preferable to have the radius of diagonal curvature in the range of 1.29R to 4.35R.
Table 3 below explains an embodiment to which 21-inch Braun tube is applied.
As manifested in Table 3, by using the shadow mask made of AK material and having the radius of diagonal curvature of the panel changed from 3.4R to 1.5R, the local doming, doming, and drop characteristics (breakage under force of a drop test) were greatly improved.
Table 4 shows the ratio of thickness toward every direction.
To explain with reference to Table 4, and
In the meantime, if Tv/Td is greater than 1.13, Th/Td 1.13, Th/Tc 2.21, and Tv/Tc 2.21, the scanning distortion problem becomes more serious, especially when the electron beam is deflected. Moreover, the thickened panel lowers productivity and eventually results in an increase in costs.
For such reasons, it is preferable to have 0.47<Tv/Td≦1.13, 0.47≦Th/Td≦1.13, 1.40≦Th/Tc≦2.21, and 1.40≦Tv/Tc≦2.21.
Suppose that the distance from the panel center to the actual skirt edge portion is OAH. Then, as shown in Table 4, by shortening the distance from the panel's central thickness (CFT) and the panel center to the actual skirt edge portion (OAH), it is now possible to decrease weight of the panel in the conventional flat color cathode ray tube.
Accordingly, the panel price can be reduced due to the improved productivity in panel industries, and the light weight of the glass. Also, the total length of the cathode ray tube is relatively shorter than the length of the conventional flat Braun tube.
Further, the shortened skirt portion makes it possible to cut down band and frame, and thermal damages on the internal path can be greatly reduced.
However, if OAH/(USD/2) is below 0.18, problems such as increase in power consumption and deteriorated picture quality occur due to optic angle deflection. Also, if OAH/(USD/2) is greater than 0.29, there are few advantages over the conventional flat Braun tube.
Thus, it is preferable to have 0.18≦OAH(USD/2)≦0.29.
In conclusion, the cathode ray tube of the present invention is very advantageous in that the flat outer surface of the panel minimizes the distortion of images, and reproduces idealistic images, and the curved inner surface of the panel can prevent any deterioration of picture quality due to the doming phenomenon of the shadow mask made of AK material.
Moreover, the cost of the cathode ray tube of the present invention is as low as half the price of the conventional art, yet its panel is useful for the shadow mask made of AK material and has quality equivalent to the shadow mask made of Invar material.
Lastly, the cathode ray tube of the present invention results price competitiveness and improved productivity by utilizing the shadow mask made of low-price AK material.
While the invention has been described in conjunction with various embodiments, they are illustrative only. Accordingly, many alternative, modifications and variations will be apparent to persons skilled in the art in light of the foregoing detailed description. The foregoing description is intended to embrace all such alternatives and variations falling with the spirit and broad scope of the appended claims.
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