MXPA98001463A - Catodic cooling ray tube panel - Google Patents

Abstract

The present invention relates to a color cathode ray tube panel having a glass surface portion that includes a substantially flat external surface facing an observer and an internal surface on which a phosphor screen is coated; the inner surface is curved in concave shape with a radius of curvature Rx in a direction of a horizontal axis H of the cathode ray tube, and the following conditions are met: (See Formula) where Wh denotes a horizontal width of an effective area of image in the portion of surface, L denotes an optimum observation distance, n1 denotes a refractive index of the surface portion and t denotes a thickness of the surface portion in its cent

Description

COLOR CATHODE RAYS TUBE PANEL.

BACKGROUND OF THE INVENTION The present invention relates to a panel surface of a color cathode ray tube. Figure 8 shows cross sections of a conventional color cathode ray tube (CRT). An upper half of the Figure is the cross section in one direction of a vertical axis V (designated as a vertical cross section), and a lower half of the Figure is the cross section in a direction of the horizontal ejet H (designated as a section horizontal cross section). As shown in Figure 8, the conventional color CRT has a panel surface 1 (designated as a panel 1), and a funnel 2 that forms a cover of the CRT together with the panel 1. The color CRT also has a phosphor screen 3 comprising red, green and blue phosphorous points disposed in an orderly fashion and formed on an internal surface 10a of a portion 10 of the panel surface 1, an electron gun 4 for emitting an electron beam 5, a reflection stock to electromagnetically deflect the electron beam 5, and a tense shadow mask 7 which functions as a color selection electrode. A perspective view of the tensioned shadow mask 7 is shown schematically in Figure 9. In addition, Figure 10A shows cross sections of another conventional color CRT. An upper half of the Figure is the vertical cross section, and a lower half of the Figure is the horizontal cross section. Figure 10B shows a perspective view of the color CRT of Figure 10A. The color CRT shown in Figures 10A and 10B uses a pressed shadow mask 77 having a curved surface in the directions of vertical, horizontal and diagonal axes V, H and D. A perspective view of the pressed shadow mask 77 is shown schematically in Figure 11. A high vacuum is maintained within the color CRTs of Figure 8 and Figure 10A by the coverage comprising panel 1 and funnel 2 When the electron beam 5 is emitted from the electron gun 4 it strikes the phosphor screen 3 formed on the inner surface 10A of the surface portion 10 of the panel 1, to which high voltage is applied, the screen 3 of phosphorus emits light. At the same time, the electron beam 5 is deflected vertically and horizontally by the deflecting magnetic field generated by the reflection head 6, and forms on the phosphor screen 3 an area showing images designated as a screen. When the red, green and blue light from the area showing the image of the phosphor screen 3, whose intensity depends on the intensity of the electron beam 5 striking the phosphor screen 3, is observed from the outside of the panel 1, an image is recognized. The shadow mask 7 (77) has a very large number of holes arranged in an orderly manner. The electron beam 5 passes through the hole in such a manner as to strike geometrically on the red, green or blue phosphor point on the phosphor screen 3 at a predetermined location to effect the precise color selection. Because the color selection in the color CRT of the shadow mask type is performed geometrically, as described above, a predetermined positional relationship between panel 1, electron gun 4 must be accurately maintained. and the shadow mask 7 (77).

In the conventional color CRTs of "Figure 8 and Figure 10A formed as described above, the outer and inner surfaces 10b and 10a of the surface portion 10 of the panel 1 on which the area showing the images are curves such that they are convex to the outside (i.e., the outer surface 10b is convex and the inner surface 10a is concave) in order to withstand atmospheric pressure from the outside and maintain a high vacuum within the CRT of color, however, has caused various problems including the following: the image shown is convexly perceived, the image is distorted when viewed obliquely, and portions of the image that are near the edges are hidden. In order to solve these problems, a color CRT was developed in which the area showing the images of the surface portion of the panel is flat on its internal and external surfaces. This CRT color, however, requires a flat shadow mask in order to accurately maintain a predetermined positional relationship between the panel and the shadow mask for color selection, and such a shadow mask is very difficult to to form. Due to the difference between the refractive index of the atmosphere and that of the glass material of the panel, an image that is floating on the edges of the screen is perceived, that is, a deployed image is perceived in a concave shape.

BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to provide a color CRT panel that can display an image that is perceived in a flat, uniform brightness, that is, little difference between the brightness of the image in the center and that in the images. edges, and have little deterioration in contrast. A color CRT panel according to one aspect of the present invention comprises a glass surface portion that includes a substantially flat external surface facing an observer and an internal surface on which a phosphor screen is coated. The inner surface is concavely curved with a radius of curvature Rx in a direction of a horizontal axis of the cathode ray tube, the following conditions are satisfied: c or s 2 T? t t * 1 - 2 h n. - * se n 2? n 2 h where Wh denotes a horizontal width of an effective image area in the surface portion, L denotes an optimum observation distance, or denote a refractive index of the surface portion, and t denotes a thickness of the surface portion in a center of it. In this panel, a cross section of the inner surface in a direction of a vertical axis perpendicular to the horizontal axis is straight. In addition, a color CRT panel according to another aspect of the present invention comprises a portion of glass surface that includes a substantially planar external surface facing an observer an internal surface on which a phosphorus p n-t is coated. 2 +? t 2 *? t c or s T? t t * 1 - 2 h n * s e n 2 T n 2 h ? 2h ta \ 2 * The inner surface is concavely curved with a radius of curvature Rx in a direction of a horizontal axis of the cathode ray tube, and the following conditions are satisfied: wherein h denotes a horizontal width of an effective image area in the portion of surface, L denotes an optimum observation distance, neither denotes a refractive index of surface, and t denotes a thickness of surface portion at a center thereof; the inner surface is concavely curved with a radius of curvature Ry in a direction of a vertical axis perpendicular to the horizontal axis and the following conditions are satisfied: - s or s 2 T? t t * 1 - n, -. Sen 2? n where Wv denotes a vertical width of the effective area of the image; and the inner surface is concavely curved with a radius of curvature Rd in a direction of a diagonal axis of the cathode ray tube, and the following conditions are satisfied: ?, ta V 2 * L J where Wd denotes a diagonal width of the effective area of the image. In addition, the surface portion may include compression stress layers each forming the outer and inner surface. Furthermore, it is desirable that a condition 1000 (psi) = sc = 2000 (psi) can be satisfied, where sc denotes a stress value generated in the compression stress layers. In addition, a transmittance of the glass material of the surface portion varies as follows: where R denotes a reflectance of the glass material, k denotes a coefficient of absorption of the glass material, to denote a thickness of the surface portion at a center thereof, and ti denotes a thickness of the surface portion in the edges of it. In addition, the color CRT panel may additionally comprise a surface treatment film having a transmittance ranging from 50% to 90% on the surface portion using such glass material offering a transmittance of 60% or more, of such that a global transmittance of the surface portion and the surface treatment film varies from 30% to 60%.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood more fully from the following detailed description given below and the accompanying drawings which are given by way of illustration only and in which: Figure 1A and Figure IB show cross sections and a perspective view of a color CRT using a panel of a color CRT according to a first embodiment of the present invention. Figure 2 shows transverse sections of a color CRT with flat internal and external surfaces to explain a floating distance (buoyancy deformation) of an image; Figure 3 is a diagram for explaining the float distance? t of the image on the panel of the color CRT shown in Figure 2; Figure 4 is a cross section of the color CRT panel taken along the direction of the horizontal axis according to a second embodiment of the present invention; Figure 5 shows the characteristic transmittance of the glass materials of a color CRT panel according to a third embodiment of the present invention; Figure 6 shows cross sections of a color CRT using a panel of a color CRT according to a fourth embodiment of the present invention, Figure 7A and Figure 7B show cross sections and a perspective view of a CRT of color using a panel of a color CRT according to a fifth embodiment of the present invention, Figure 8 shows cross sections of a conventional color CRT, Figure 9 shows a perspective view of a taut shadow mask of the Figure 8, Figure 10A and Figure 10B show cross sections and a perspective view of other color CRTs using a conventional color CRT panel, and Figure 11 shows a perspective view of a pressed shadow mask of the Figure 10A.

DETAILED DESCRIPTION OF THE INVENTION The additional scope of applicability of the present invention will be apparent from the following detailed description. However, it should be understood that the detailed description and specific examples, while - indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications will be apparent to those skilled in the art from the description Detailed First Modality Figure IA shows cross sections of a color CRT using a panel according to a first embodiment of the present invention and Figure IB is a perspective view of the color CRT of Figure IA. A top half of Figure IA is the cross section in one direction of the vertical axis V (designated as a vertical cross section), and a lower half of Figure 1A is the cross section in a direction of a horizontal H axis (designated as a horizontal cross section) perpendicular to the vertical axis V. As shown in Figure 1A, the panel 11 of the color CRT according to the first embodiment has a glass surface portion 12 including a substantially planar external surface 12b facing an observer and an internal surface 12a on which it is placed. It has a phosphor screen 3. A cross section of the inner surface 12a taken along the direction of the vertical axis V is straight, and a cross section of the inner surface 12a taken along the direction of the horizontal axis H is concavely curved with a radius predetermined curvature Rx. The panel 11 constitutes a wrapper of the color CRT together with a funnel 2. The color CRT is provided with the phosphor screen 3 on the inner surface 12a of the surface portion 12 of the panel 11. The phosphor screen 3 includes dots of phosphorus of red, green and blue arranged in an orderly manner.

The CRT is also provided with an electron gun 4 in the funnel 2 to emit the electron beam 5 and a reflection head 6 around a neck portion of the funnel 2 to electromagnetically deflect the beam 5 of ect ectons. The color CRT is further provided with a tense shadow mask 17 which faces the inner surface 12a of the panel 11 in the envelope and functions as a color selection electrode. Next, the operation of the color CRT will be described. High vacuum is maintained in the color CRT by the envelope comprising the panel 11 and the funnel 2. When the electron beam 5 emitted from the electron gun 4 strikes the phosphor screen 3 formed on the inner surface 12a of the portion 12 of panel surface 11, to which high voltage is applied, the phosphor screen 3 emits light. In addition, the electron beam 5 is deflected vertically and horizontally by a reflective magnetic field generated by the reflection head 6 and forms an area showing images designated as a screen on the phosphor screen 3. When from the outside of panel 1 red, green and blue light is observed from the area showing images from the phosphor screen 3, whose intensity depends on the intensity of the electron beam 5 striking the phosphor screen, it is observed from On the outside of panel 1, an image is recognized. The tense shadow mask 17 has a very large number of holes arranged in an orderly manner. The electron beam 5 passes through the hole in such a manner as to geometrically strike the red, green or blue phosphor point of the phosphor screen 3 at a location, predetermined to effect the precise color selection. Because the color selection in the color CRT of the shadow mask type is performed geometrically, as described above, it must maintain a predetermined positional relationship between the panel 11, the electron gun 4 and the mask 7. of Shadows . The function of the panel 11 having the surface portion 12 comprising the flat external surface 12b and the internal surface 12a concavely curved with the predetermined radius of curvature Rx will be described below. The light moves straight in a homogeneous medium. However, when light encounters a boundary between two different media, part of the light is reflected by the boundary, and the remaining part of the light is refracted and passes through the different medium. The same phenomenon occurs when an image displayed on the color CRT is observed. Due to the difference between the refractive index of the atmosphere and that of the glass, the image shown is generally perceived as floating near the edges of the screen. With reference to Figure 2 and Figure 3, a phenomenon that occurs in a currently used CRT, which comprises a panel 31 having the flat inner and outer surfaces 31 a and 31 b of the surface portion, will be described. and a flat shadow mask 37. As illustrated in Figure 2 and Figure 3, the emitted light, from an image produced on the phosphor screen 3, progresses straight through the panel glass 31 (a refractive index ni) until it meets the limit (for example the outer surface 31b) between the panel 31 and the atmosphere (a refractive index n2). The light is refracted at the limit and continues straight into the atmosphere towards an eye 32 of an observer, and then the image is recognized. The incident angle ®? The light of the image at the boundary between the atmosphere and the glass of the panel 11 depends on a position of the eye 32 of the observer and a position on the display surface of the color CRT (especially a distance between the center and the edge) . Consequently, an angle ®? Refraction varies according to the positions, making the displayed image perceive itself as floating near the edges of the screen. In Figure 3, ni denotes the refractive index of the panel glass 31, n2 denotes the refractive index of. the atmosphere, ®? denotes an incident angle of the light advancing from the phosphor screen 3 through panel 31 to the atmosphere at a point above the limit, and ®2 (in the first mode, "2 is expressed as" 21. and in the fifth modality described below?. is expressed as? 2h_ "2v or? 2d) denotes a refraction angle.In addition, t denotes a panel thickness 31,? t (in the first modality,? t is expressed as? th, and in the fifth modality described below? t is expressed as? th, tv or? 'td) denotes a float distance (or buoyancy deformation) at the edges of the screen, and d denotes a depth in the image perceived by the observer --.-- ^ - «^ 18 With reference to Figure 2 and Figure 3, the following relationship is obtained. d * tar_02 ** xx On the other hand, neither sen? - n2 sen? ri2 = 1 According to, Therefore, the following relationship is obtained Using this relationship, the float distance? Th is calculated at each location on the screen (for example, at each location on the horizontal axis) of panel 11 of the color CRT of Figure IA. The inner surface 12a of the surface portion 12 is formed in order to have the horizontal radius of curvature Rx calculated by the float distance tt at each location on the screen. In other words, the horizontal radius of curvature Rx of the inner surface 12a of the surface portion 12 is determined in accordance with the float distance? Th at each location on the screen. The inner surface 12a of the surface portion 12 is formed to be concave in the horizontal h-axis direction (such that the distance between the inner surface 12a and the outer surface 12b of the panel 11 increases as it approaches the edge. ) in such a way that the image produced is not perceived as concave, but as visually flat. Because the human eye is aligned horizontally, a depth is perceived when mainly processing horizontal information and it is difficult to obtain the depth information from the vertical information. Thus, the float distance in a vertical direction produces little effect on the perceived plane of the image. Accordingly, with the color CRT having the shade mask 17 stretched in the horizontal direction, it is difficult to perceive the buoyancy caused by the vertical flatness of the inner surface 12a of the surface portion 12 of the panel 11. Due to the above-mentioned function, by forming the internal surface 12a to have the curvature only in the horizontal direction, as shown in Figure 1, the image shown is visually perceived in planar form. When a color CRT whose effective image area has a horizontal width Wh is observed at a distance L in its current state of use, as shown in Figure 2, the float distance Ath at the edges of the screen of a CRT color is expressed as indicated below: c or s 20? t t * 1 - 2 h O * sin 20 n 2 h Accordingly, when the float distance? Th in the first embodiment is compensated by setting the radius of curvature of the surface Rx of the inner surface 12a of the panel 11 in the direction of the horizontal axis H shown in the Figure I as indicated below (such that the distance between the inner surface 12a of the panel II and the outer surface 12b of the panel 11 increases as it approaches the edges), the image is not perceived to be concave even if the surface portion 12 of the panel 11 has the flat outer surface 12b. As a result, the produced image is visually perceived as flat. The horizontal radius of curvature Rx of the inner surface 12a of the surface portion 12 is expressed as the following approximation such that the produced image is perceived in planar form: However, because the image surface of the conventional CRT is convexly curved, the convexly curved image can often be preferred. Accordingly, it is desirable that the following conditions are met: c or s 20? t t * 1 - 2 h n, - * s e n 20 n 2 h where t denotes the thickness of the glass in the center of the screen. • The normal optimum observation distance L used for color CRTs is generally up to approximately 500 [mm] even when used as display monitors. The radius of curvature Rx of the inner surface 12a of the surface portion 12 of the panel 11 in the H direction of the horizontal axis must be set as follows: eo s 2 T? t t * .2 h n, - * sin? n 2 h The optimum observation distance L for color CRTs used in television sets in general is approximately 5 * h, where h is the height of the screen (vertical width of the effective image area). As a result, the image can be perceived as flat when setting Rx approximately as indicated below: With the panel 11 having a surface 12b c or s 2 T? t t * 1 - n * s e n? n 2 h e, - ta 2 * 5 * h and geometrically planar external of the surface portion 12 and a surface 12a of the curved surface portion 12 with such calculated radius to produce a flat perceived image, allowing the difference between the index of refraction of the atmosphere and that of the panel glass, an image that is perceived to be really flat can be exhibited.

Second Mode A color CRT panel according to a second embodiment of the present invention is the same as that according to the first embodiment except that the compressive stress layers are formed under the outer and inner surface 12b and 12a of the portion 12 of panel surface 11. Figure 4 shows a horizontal cross-section showing panel 11 of the second embodiment. As shown in Figure 4 by the dotted lines, the compression stress layers 20 and 21 are formed respectively under the external and internal surfaces 12b and 12a of the surface portion 12 of the panel 11. The thickness of the layers 20 and 21 of compressive stress is not less than tc / 10, where it denotes a thickness of the surface portion 12 of the panel 11 in the center. The compression stress layers 20 and 21 are formed by pressing the panel 11 from molten glass and cooling them slowly in an annealing furnace such that they are physically reinforced. The magnitude of the stress generated by this process depends on a time required to gradually decrease a temperature of the surfaces of the panel 11 from the annealing temperature to the point of deformation. As the cooling range increases, a difference between the shrinkage of the surface and the central shrinkage increases, increasing the compressive stress on the surfaces after the cooling process. The compressive stress layers 20 and 21 improve the mechanical strength of the panel surfaces 11. Real implosion resistance tests and the like have proven that if an effort value sc is below 1000 (psi), the compressive stress layers 20 and 21 do not contribute to physical reinforcement, if the stress value sc exceeds 2000 (psi), the glass surface of the panel 11 flakes off when it receives a mechanical impact. Therefore, a desired range of sc is: [70.3 kg / cm2 manomét rico] (1000 psi) = sc = [140.6 kg / cm2 gauge] (2000 psi). In general, a glass bulb for a CRT is used as a vacuum vessel. The atmospheric pressure applied to the external surface of the bulb therefore generates effort. The glass bulb is not spherical, but has an asymmetric structure that results in comparatively high areas of compression stress and tensile stress. It is well known that a local rupture or failure made by mechanical impact is instantaneously extended to release the stored deformation energy, resulting in implosion. The panel 11 whose surface portion has the flat outer surface 12b has low resistance to mechanical impact. The panel 11 whose surface portion has the flat outer surface 12b, however, can maintain predetermined mechanical strength when the compression reinforcement layers 20 and 21 for physical reinforcement are provided as in the second embodiment.

Next, Table 1 is shown indicating an effect of compression stress layers 20 and 21. Table 1 Table 1 indicates data of the rejection range in the implosion resistance test with respect to the samples without physical effort (Sample 1 and Sample 2) and samples with physical reinforcement (Sample 3 and Sample 4). As defined in the UL safety standards in the United States, the glass panels of the CRTs were struck with a steel ball on the surface portion with an energy of 7 (J), and the quantity and size of the glass chips and the like to determine if the glass panels present sufficient security.

Sample 1 is a glass bulb for a 41 cm color CRT using a panel in which the compression stress layers 20 and 21 are not formed. The surface portion of the panel has a flat external surface and a cylindrical internal surface whose radius of curvature Rx at 'the direction of the horizontal axis is 2300 [mm]. Sample 2 is a glass bulb for a 50cm color CRT that uses a panel in which layers 20 and 21 of compression stress are not formed. The surface portion of the panel has an approximately flat outer surface (R = 50000 [mm]) and a cylindrical internal surface whose radius of curvature Rx in the direction of the horizontal axis is 2500 [mm]. Sample 3 is a glass bulb for a 41 cm color CRT using a panel in which compression stress layers 20 and 21 are formed. The surface portion of the panel has a flat outer surface and a cylindrical internal surface whose radius of curvature Rx in the direction of the horizontal axis is 2300 [mm]. The stress value of layers 20 and 21 of compression stress is 77.33 kg / cm gauge (1100 [psi]) and is almost uniform throughout the effective area of the image. The compression stress layers 20 and 21 are of a thickness of approximately 2 [mm], which is 1/10 or more of the thickness of the panel at the center. Implosion resistance tests have proven that sample 3 has a superior resistance to impact, due to the presence of layers 20 and 21 of compression stress, and a lower rejection range, compared to sample 1 which is the panel in the same way. Sample 4 is a glass bulb for a 50 cm color CRT using a panel in which compression layers 20 and 21 are formed. The surface portion of the panel has an approximately flat outer surface (R = 50000 [mm]) and a cylindrical internal surface whose radius of curvature Rx in the direction of the horizontal radius is 2500 [mm]. The stress value of layers 20 and 21 of compression stress is 87,875 kg / cm gauge (1250 [psi]) and is almost uniform throughout the effective area of the image. The compression stress layers 20 and 21 are approximately 2.5 [mm] thick, which is 1/10 or more of the panel thickness in the center. Implosion resistance tests have proven that sample 4 has a superior resistance to impact, due to the presence of layers 20 and 21 of compression stress, and a lower rejection range, compared to sample 2 which is the panel in the same way.

Third Modality In panel 11 whose surface portion 12 has flat outer surface 12b and curved inner surface 12a, as described in the first and second embodiments, the thickness of panel 11 at the center of surface portion 12 differs greatly of that at the edges of the surface portion 12, resulting in a difference in light transmission. Consequently, in the image shown on the phosphor image, the transmittance of light in the center differs from that at the edges, resulting in variety in the brightness along the screen. Especially, a difference between the brightness in the center to that at the edges, resulting in a variety of brilliance along the screen. Especially, a difference between the brightness in the center and that in the edges significantly affects a perceived depth of the image, which affects the perceived flatness of the image. Glass materials currently used for color CRT panels include A, B, C, D, E and F shown in Figure 5. A glass plate E, which is used for most panels, shows a transmittance of approximately 52% when the thickness is 12 [mm]. If the inner surface of the panel made from this material is curved to increase its thickness by 4 [mm] at the edges, for example, the transmittance at the edges is about 43%. The ratio of transmission in the center to that at the edges is therefore approximately 100: 82. As a result, the uniformity of brightness throughout the entire screen deteriorates. The deterioration of uniformity in terms of brightness, or the difference between the brightness in the center and that in the edges, due to the difference between the thickness of the glass plate in the center and that in the edges can be reduced by increasing the transmittance of the glass. glass material used for the panel. In commercially available glass panels, a uniformity ratio at the edges with respect to that in the center of the screen is usually 85% or higher. A glass material having such persistence that it bears the ratio of the deviation of the edges to that in the center of the screen to 85% or more should be used for the glass plate in which the thickness at the edges is greater than that in the middle. Generally, the glass transmittance T [%] is defined as follows: T = (1-R) 2 * e t * 100 where R denotes a reflectance of the glass, k denotes an absorption coefficient and t is the thickness of the glass. Therefore, a glass material that satisfies the following condition should be used: _2? (l - R) * ek l * 100 = 0.85 (l - R) * ekt ° * 100 where to denotes a thickness of the surface portion 12 in the center of the screen, and ti denotes a thickness 12 of surface at the edges of the screen. If a glass material characterized by R = 0.045 and k = 0.00578 is used for example, a glass plate that is 12 [mm] thick at the center and 16 [mm] at the edges can satisfy the condition indicated above.

As described in the foregoing, the panel whose surface portion has the flat outer surface and the curved inner surface has the difference between the transmittance at the center and that at the edges, which is caused by the variation in the thicknesses of the glass. By forming the panel from the glass material with a high transmittance that satisfies the aforementioned condition, the effect of the variation in the thickness can be reduced and the difference in the transmittance is almost eliminated along the entire length of the screen. Except for the above points, the color CRT panel according to the third embodiment is equal to that according to the first or second modality.

Fourth Mode The use of a glass material with a high transmittance in the panel increases the reflection of external light on the phosphor screen, thereby degrading the contrast, which is an important feature of color CRTs used for exhibitions. . The color CRT formed as described in the third mode can maintain the difference between the brightness in the center and that in the edges within a permissible range if the panel has a transmittance of 60% or more. This color CRT, however, has low contrast. Generally, the color CRT panel formed as described in the first embodiment must have a transmittance of 60% or above, when the size of the screen and the observation distance are taken into consideration. On the other hand, sufficient contrast can be maintained when the transmittance of the panel varies from 30% to 60%. Therefore, a global transmittance within the range of 30% to 60% can be maintained and sufficient contrast can be maintained by using a glass material with a transmittance of 60% or more and by providing the surface of the panel 11 with a film 8 of surface treatment having a transmittance of about 50% to 90%, as shown in Figure 6. The surface treatment film 8 on the panel 11 can be made on the following methods: a film adhesion method in the which a base film provided with a light absorbing layer, a layer. antistatic, an antireflection layer and the like is disposed on the surface of panel 11 of the color CRT; a wet coating method in which a light absorbing layer and the like are formed by coating the surface of the CRT panel 11 with a liquid mixture of an organic or inorganic based coating and an organic or inorganic dye or pigment, by spraying or spin coating; and a dry coating method in which a light absorbing layer and the like are deposited on the surface of panel 11 of the CRT by coating it by vacuum evaporation and the like. As described above, if the material with high transmittance is used for the panel, the contrast could be degraded, but the contrast is improved by optimizing the overall transmittance through the surface film 8. As a result, the color CRT that reproduces a high quality image that is perceived in a flat way with no difference in brightness can be provided. In addition, the film 8 of the surface treatment can also be provided on the color CRT panel according to the first, second or third embodiment.

Fifth Mode The first _ mode described above belongs to the color CRT with the taut shadow mask formed to be almost flat in the direction of the vertical axis of the screen and curved in the direction of the horizontal axis. The color CRT (Fig. 10A) which uses the pressed mask formed to be curved in the directions of the vertical and horizontal axes of the screen as shown in Fig. 11 can produce the similar effect. That is to say, as shown in Figure 7A and Figure 7B, the color CRT may have the panel 71 that is formed to have a substantially planar external surface 72b and a concave shaped curved inner surface 72a with predetermined radius of curvature in the direction of the vertical axis V as in the direction of the horizontal axis H in a manner similar to that of the first embodiment, a predetermined radius of curvature in the direction of the vertical axis V and a predetermined radius of curvature in the direction of the diagonal axis D. The distance The float is calculated and the inner surface 72a is formed to compensate for the float distance, i.e., a radius of curvature Rx of the inner surface 72a of the panel 71 in the horizontal H-axis direction, is expressed substantially as: wherein Wh denotes a horizontal width of an effective area of image in the surface portion, L denotes an optimum observation distance, or denotes a refractive index of the portion of surface 72, and t denotes a thickness of the surface portion 72 at a center of the surface portion 72. c or s 20? t t * 1 - 2 v »I". Sin 20 n 2 v In addition, the inner surface is concavely curved with a radius of curvature Ry in a direction of a vertical axis of the cathode ray tube and the following conditions are satisfied: wherein Wv denotes a vertical width of the effective image area. In addition, the inner surface is concavely curved with a radius of curvature Rd of a diagonal axis of the cathode ray tube and the following conditions (V.) 'are satisfied. * ... 2 * ? t eos? t - t * • * sin 2 T where Wd denotes a diagonal width of the effective area of the image. As described in the first modality, due to the characteristics of the human eye, the depth in the horizontal direction is difficult to perceive. Thus, if the radius of curvature in the direction of the vertical axis is determined in the consideration of formability of the pressed shadow mask, the effect of the present invention is not eliminated. As described in the foregoing, the color CRT according to the present invention uses the panel which is flat on its outer surface and curved on its inner surface with such a curvature that produces the perceptible plane. The image shown can be visually perceived in a flat way. In addition, in the CRT that uses the pressed shadow mask, without using a special shadow mask, the image that is displayed can be visually perceived as flat. In addition, the color CRT panel according to the fifth embodiment may also be provided with the compression stress layers in the second embodiment and / or the surface treatment film in the fourth embodiment. In addition, the color CRT panel according to the fifth embodiment can also be satisfied with the condition with respect to the transmittance in the third embodiment.

Claims (7)

1. A color cathode ray tube panel (11, 71) comprising: a portion of glass surface (12, 72) that includes a substantially planar external surface (12b, 72b) facing an observer and an internal surface ( 12a, 72a) on which a phosphor screen is coated; wherein the inner surface (12a, 72a) is curved in concave shape with a -radio of curvature Rx in a direction of a horizontal axis H of the cathode ray tube and the following conditions are satisfied: s or s T? t t * 1 - 2 h n, - * se n 2? n 2 ß ', 2"h = ta 2 * h) wherein Wh denotes a horizontal width of an effective image area on such surface portion (12, 72), L denotes an optimum observation distance, or denote a refractive index of such a surface portion (12, 72) and t denotes a thickness of such surface portion (12, 72) in a center of the same.

2. A color cathode ray tube panel (11) according to claim 1, wherein a cross section of the inner surface (12a) in a direction of a vertical axis (V) perpendicular to the horizontal axis (H) is straight .

3. A color cathode ray tube panel (71) according to claim 1, wherein the inner surface is concavely curved with a radius of curvature Ry in a direction of a vertical axis (V) perpendicular to the horizontal axis ( H) and the following conditions are met: ? 2v ta \ 2 * h} where Wv denotes a vertical width of the effective image area; and the inner surface (72a) is concavely curved with a radius of curvature Rd in a direction of a diagonal axis (D) of the cathode ray tube,. and the following conditions are met: 2 * ? t c or s 20? t __ t * 1 - 2 d n, - * sin 0 n 2 d where Wd denotes a diagonal width of the effective area of the image.

4. The color cathode ray tube panel (11, 71) according to any of claims 1 to 3, wherein the surface portion (12, 72) includes the compression stress layers (20, 21) each formed under the external surface (12b, 72b) the inner surface (12a, 72a).

5. The color cathode ray tube panel (11, 71) according to claim 4 wherein a condition of 70.3 kg / cm2 gauge (1000 psi) = sc = 140.6 kg / cm2 gauge (2000 psi) is satisfied, where sc denotes a stress value generated in the compression stress layers (20, 21).

6. The color cathode ray tube (11, 71) according to any one of claims 1 to 5, wherein a transmittance of a glass material of said surface portion (12, 72) varies as indicated then: where R denotes a reflectivity of the glass material, k denotes a coefficient of absorption of the glass material, to denote a thickness of such a portion of surface (12, 72) at a center thereof, and ti denotes a thickness of the portion of surface (12, 72) on one edge thereof.

7. The color cathode ray tube panel (11, 71) according to claim 6 ,. wherein a surface treatment film (8) having a transmittance ranging from 50% to 90% using such a surface portion (12, 72) using such glass material offering a transmittance of 60% or more, of so that a global transmittance of such surface portion (12, 72) and such surface film (8) varies from 30% to 60%.