Cathode ray tube

Abstract: A cathode ray tube comprising a vacuum enclosure including a panel glass (1) whose inner face is coated with a phosphor film (4) to form a screen; a neck housing an electron gun; and a funnel connecting the panel glass and the neck. A multi-layered anti-reflection anti-electrostatic charge film formed on the outer face of the panel glass is constructed of a high refractive index film (21) having a refractive index of 1.6 to 2.2 and a low refractive index film (22) having a refractive index of 1.3 to 1.58. The high refractive index film is sandwiched between the outer face of the panel glass (1) and the low refractive index film, and an unevenness having an average diameter of 5 to 80 µm is provided at the interface between the high refractive index film and the low refractive index film. The interface has a height of 10 to 40 nm. The unevenness of the surface of the low refractive index film is made smaller than the average roughness Rz of the unevenness of the interface between the high refractive index film and the low refractive index film, or the surface of the low refractive index film is flat.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a cathode ray tube and, more particularly, to a cathode ray tube which prevents the reflection of external light to a panel glass to raise the contrast and to prevent electrostatic charge. Description of the Prior Art In a cathode ray tube to be used in a TV receiver or a personal computer monitor, a vacuum enclosure comprises a panel glass forming a screen or an image display screen, a neck housing electron guns, and a funnel connecting the panel glass and the neck, and a phosphor film formed on the inner face of the screen and excited with modulated electron beams emitted from the electron guns, to display a desired image. Fig. 11 is a schematic section for explaining the structure of a shadow mask color cathode ray tube as one example of the cathode ray tube of this kind. In Fig. 11: reference numeral 1 designates a panel glass portion; numeral 2 a neck portion; numeral 3 a funnel portion; numeral 4 a phosphor film; numeral 5 a shadow mask; numeral 6 a mask frame; numeral 7 mask support mechanism; numeral 8 support pins; numeral 9 an inner magnetic shield; numeral 10 anode button; numeral 11 an internal conductive coating; numeral 12 a deflector; numeral 13 electron guns; and numeral 14 electron beams (red, green and blue). In the cathode ray tube shown in Fig. 11, a vacuum enclosure is constructed of the panel glass portion 1 forming the screen, the neck portion 2 housing the electron guns, and the funnel portion 3 connecting the panel glass portion and the neck portion. The inner face of this vacuum enclosure is coated with the internal conductive coating 11 for supplying a high anode voltage applied to the anode button 10 to the screen and the electron guns. The shadow mask 5 is welded to the mask frame 6 and is suspended by the support mechanism 7 with the support pins 8 which are buried in the inner wall of the skirt portion of the panel glass portion 1, so that it is held at a predetermined small spacing from the phosphor film 4 formed on the inner face of the panel glass portion 1. The inner magnetic shield 9 is provided for shielding the image display of the external magnetic field from bad influence such as the earth magnetism upon the electron beams 14, and is welded to and held by the mask frame 6. On the neck portion side of the funnel portion 3, there is mounted the deflector 12 for establishing a horizontal magnetic field and a vertical magnetic field in the passage of the electron beams emitted from the electron guns, so that the three electron beams emitted from the electron guns 13 are deflected in the horizontal direction and in the vertical direction to scan the phosphor film two-dimensionally and thereby to display a desired image. Generally, this cathode ray tube is provided with an anti-reflection anti-electrostatic charge film for preventing the reflection of external light incident upon the panel glass portion or the image display screen from being reflected thereby to prevent the contrast deterioration of the image display or for preventing the panel glass portion from being charged with static electricity. Fig. 12 is a schematic section showing on an enlarged scale a portion A of Fig. 11 for explaining one example of an external light anti-reflection structure of the cathode ray tube. In Fig. 12: reference numeral 42 designates a black matrix; numeral 43 a phosphor screen; numeral 44 a metal back; numeral 51 an electron beam passing opening of the shadow mask; symbols R, G and B electron beam trajectories of individual colors; numeral 20 an anti-reflection anti-electrostatic charge film; numeral 23 light emitted from the phosphor film; numeral 24 external light; and numerals 25 and 26 reflected light of the external light. The same reference numerals as those of Fig. 11 designate the identical portions. In Fig. 12, the three electron beams (R, G and B) emitted from the electron guns are subjected to color selection for the individual phosphor screens 43 of the R, G and B by the electron beam passing opening 51 of the shadow mask 5 until they impinge upon the phosphor film 4. The phosphor screen 43 is excited by the impingement of the electron beams to emit light, which emanates through the panel glass portion 1. The anti-reflection anti-electrostatic charge film 20 is formed on the surface of the panel glass portion. The external light 25 having reached the anti-reflection anti-electrostatic charge film 20 of the panel glass portion 1 is suppressed in light energy through absorption or interference in the anti-reflection anti-electrostatic charge film 20 so that the normal reflection to the surface side is prevented together with the diffuse reflection 26 by the surface of the anti-reflection anti-electrostatic charge film 20. This anti-reflection anti-electrostatic charge film is formed by one of various methods but generally by the so-called "sol-gel-method." Specifically, (1) there is disclosed in Japanese Patent Laid-Open No. 334853/1992 a method of forming a two-layered anti-reflection anti-electrostatic charge film by forming a film of a mixed composition in which ultra fine particles (having a diameter no more than several tens nm) of a conductive oxide (e.g., A.T.O.: tin oxide containing antimony oxide, or I.T.O.: indium oxide containing tin oxide) for forming a high refractive index film are dispersed in an alcoholic solution, by the so-called "spin-coating" to form a flat lower film having a thickness of about 60 to 100 nm, and by spin- or spray-coating the underlying film with a hydrolysate solution of silicon alkoxide to form a flat upper film having a thickness of 80 to 130 nm. (2) There is also disclosed in Japanese Patent Laid-Open No. 343008/1993 (corresponding to EP-A-0 565 026) a method in which a film of organic or inorganic tin compound containing antimony is formed on the panel glass of a cathode ray tube by chemical vapor deposition (hereinafter abbreviated to CVD) to form an A.T.O. film having a high refractive index, the A.T.O. film is coated flatly with a hydrolysate solution of silicon alkoxide of a thickness of 80 to 100 nm to form a film having a low refractive index, the second-layer film is spray-coated with the hydrolysate solution of silicon alkoxide of a thickness of 10 to 50 nm to form a third-layer scattering film having a low refractive index so as to reduce the density of the reflected color exhibited by the second-layer anti-reflection anti-electrostatic charge film and the reflectance in the human visible region of 400 to 700 nm, and the third-layer film is made uneven. In the prior art described above, the structure, in which the high refractive index film and the low refractive index formed over the former are individually made flat, is made substantially identical to the theoretical one for the two-layered anti-reflection film (described on pp. 100 to 103, OPTICAL THIN FILM written by Kozo Ishiguro et al., 1986, KYORITSU SHUPPAN). As a result, the structure has a V-shaped reflection characteristics, a reflection spectrum such that the reflectances at the two wavelengths at the ends of the visible region of 400 to 700 nm are higher than that at the central wavelength. When the reflectance in the visible region is lowered, therefore, the reflectances at the two wavelengths at the ends are higher than that at the central wavelength. As a result, the color of the reflected light, i.e., the reflection color is intensified; and that the reflectance is raised when the reflection color is reduced. In order to diminish this defect, as the third-layer film, an uneven film having a small thickness and a low refractive index is formed. However, this effect is not sufficient when the height of unevenness is small and the formation density is high, namely, the number of projections and recesses per unit area is large. When the height of unevenness is large and the formation density is high, the intensity of scattering is increased to lower the resolution of the cathode ray tube. Since the high refractive index film is formed by spin-coating or CVD, there arises a problem that the process is complicated to raise the manufacture cost. SUMMARY OF THE INVENTION An object of the present invention is to solve the aforementioned several problems of the prior art. Another object is to provide a cathode ray tube having an anti-reflection anti-electrostatic charge film which prevents the reflection of external light to a panel glass portion to raise the contrast while preventing electrostatic charge. A cathode ray tube according to the present invention is defined in claim 1 and prefered embodiments are set out in the dependent claims. The unevenness of the surface of the low refractive index film is preferably smaller than the average roughness Rz of the unevenness of the interface between the high refractive index film and the low refractive index film, or the surface of the low refractive index film is flat. Moreover, the high refractive index film and the low refractive index film are preferably made of anti-reflection anti-electrostatic charge films which are formed by a spray-coating step, a spin-coating step or a spray-coating step, and a spray-coating step in this order. Moreover, the surface of the low refractive index film of the first aspect is preferably flattened (the average roughness Rz is no more than 10 nm). In this construction, the characteristic curve of reflection is flattened to lower the average reflectance of 400 to 700 nm and the dependence of the intensity of the reflected light on the wavelength is weakened to improve the image clarity of the cathode ray tube. The low refractive index film has preferably an average roughness Rz of more than 10 nm on its surface. Thanks to this construction, the image clarity of the cathode ray tube is improved better by the diffuse reflection of external light from the low refractive index film. Moreover, the average roughness Rz of the surface of the low refractive index film of the above construction is preferably smaller than the average roughness Rz of the unevenness of the interface between the high refractive index film and the low refractive index film. Thanks to this construction, the image clarity of the cathode ray tube is improved better by the diffuse reflection of external light from the low refractive index film. Here, the image clarity of the cathode ray tube is improved better if the average roughness Rz of the unevenness of the surface of the low refractive index film and the number of projections and recesses per unit area are smaller than those of the interface between the low refractive index film and the high refractive index film. Moreover, the material for forming the high refractive index film contains preferably particles of a conductive oxide or metal, and the material for forming the low refractive index film contains a silicon compound or a fluorine compound such as MgF 2 or CaF 2 . Thanks to this construction, the dependence of the intensity of the reflected light on the temperature is weakened to flatten the reflection characteristic curve and the density of the reflected color is lowered to improve the image clarity of the cathode ray tube. Here, the particles of the conductive oxide or metal contained may be so-called ultra fine particles having an average diameter less than 70 nm. By employing the so-called "sol-gel-method, the high refractive index film of the anti-reflection anti-electrostatic charge film having the two layers basically is given a structure in which the interface between the interface of the high refractive index film on the side opposed to the panel glass plate is made of an uneven film, so that the density of the reflected light, which is a defect of the two-layered anti-reflection anti-electrostatic charge film of the prior art, is lowered to flatten the reflection curve. As a result, it is possible to provide a display device such as a cathode ray tube which can have a lowered average reflectance of 400 to 700 nm and which can have a less light scattering, improving the contrast of the display screen and the image clarity. Moreover, the high refractive index film can be formed by spray-coating to reduce the consumed amount of expensive solution, the manufacture process is simplified and the maintenance cost of the manufacturing facility is lowered. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic section showing a portion for explaining the construction of a panel glass portion of a cathode ray tube of an embodiment of the present invention; Fig. 2 is an enlarged top plan view for explaining the surface state of a film of high refractive index layer constituting the anti-reflection anti-electrostatic charge film of Fig. 1; Fig. 3 is a schematic section showing a portion for explaining the construction of a panel glass portion of a cathode ray tube of another embodiment of the present invention; Fig. 4 is an explanatory view illustrating the characteristics of reflection of a two-layered anti-reflection anti-electrostatic charge film; Fig. 5 is an explanatory view illustrating the characteristics of reflection of an uneven portion; Fig. 6 is a schematic flowchart for explaining an example of a process for manufacturing the cathode ray tube of the present invention; Fig. 7 is a schematic flowchart for explaining another example of a process for manufacturing the cathode ray tube of the present invention; Fig. 8 is a schematic flowchart for explaining still another example of a process for manufacturing the cathode ray tube of the present invention; Fig. 9 is an explanatory view illustrating the relations between the average diameter of unevenness and the intensity of scattering of uneven fine particles of a film of high refractive index; Fig. 10 is an explanatory view illustrating the relations between the maximum height of unevenness and the bottom reflectance of the uneven fine particles of the film of high refractive index; Fig. 11 is a schematic section for explaining the structure of a shadow mask color cathode ray tube as one example of the cathode ray tube; and Fig. 12 is a schematic section showing on an enlarged scale a portion A of Fig. 11 for explaining one example of an external light anti-reflection structure of the cathode ray tube. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail in connection with its embodiments. Fig. 1 is a schematic section showing a portion for explaining the construction of a panel glass portion of a cathode ray tube of a first embodiment of the present invention. In Fig. 1: reference numeral 1 designates a panel glass; numeral 4 a phosphor film; numeral 20 an anti-reflection anti-electrostatic charge film; numeral 21 a film of high refractive index; numeral 21a a projection; numeral 21b a recess; and numeral 22 a film of low refractive index. In this embodiment, the surface of the high refractive index film 21 is uneven, and the overlying low refractive index film 22 is given a flat or generally flat surface. The high refractive index film 21 is formed by spray-coating the surface of the panel glass 1 with an alcohol suspension containing ultra fine particles of metal oxides. A desired unevenness is formed on the surface of the high refractive index film 21 by controlling the content of the material of the spray-coating and the coating conditions. Here, the ultra fine particles of metal oxides have an average diameter of unevenness of 70 nm. The low refractive index film 22 is formed by spin- or spray-coating with an alcoholic solution of silicon alkoxide. Fig. 2 is an enlarged top plan view for explaining the surface state of the high refractive index film constituting the anti-reflection anti-electrostatic charge film of Fig. 1. As shown in Fig. 2, the surface of the high refractive index film 21 is given unevenness in which the recesses 21b are enclosed by the projections 21a, and is coated with the low refractive index film 22. Thanks to this construction, the characteristic curve of reflection is flattened to lower the average reflectance of 400 to 700 nm, thereby reducing the density of the color of reflected light and improving the image clarity of the cathode ray tube. Fig. 3 is a schematic section showing a portion for explaining the construction of a panel glass portion of a cathode ray tube of a second embodiment of the present invention. The same reference numerals as those of Fig. 1 designate the same portions. In this embodiment, the surface of the low refractive index film 22 forming the upper layer of the anti-reflection anti-electrostatic charge film 20 has an unevenness corresponding to that of the underlying high refractive index film 21. Thanks to this construction, the reflection characteristic curve is flattened by the scattering function of incident light due to the unevenness formed on the surface of the low refractive index film 22, and the average reflectance of 400 to 700 nm is lowered, thereby reducing the density of the color of the reflected light and improving the image clarity of the cathode ray tube. Fig. 4 is an explanatory view illustrating the characteristics of reflection of a two-layered anti-reflection anti-electrostatic charge film. The abscissa of Fig. 4 marked with wavelength (nm), and the ordinate with reflectance (%). Here, the graph of Fig. 4 is obtained under measurement conditions of non-polarized light and an incident angle of 5 degrees by using a spectrophotometer U3400 of HITACHI, Ltd. The minimum reflectance indicated in Fig. 4 will be referred to as the bottom-reflectance Rb, and the corresponding wavelength will be referred to as the bottom-wavelength λ b. Generally, with reference to the thicknesses of the high refractive index film exhibiting the minimum reflectance Rb and the low refractive index film the bottom-reflectance Rb rises and the reflection curve becomes gentle, when the thickness of the high refractive index film deviates from the aforementioned reference. The low refractive index film 22 exerts little influence upon the bottom-reflectance Rb. When the low refractive index film 22 is thicker than the aforementioned reference, however, the bottom-wavelength λ b has a tendency to shift to the longer wavelength side than the bottom-wavelength λ b corresponding to the bottom-reflectance Rb of the layer having the reference thickness. If, therefore, the unevenness is within a small range such as a square having a side larger by about 10 to 100 times than the wavelength of the incident light or a circle having a diameter larger by about 10 to 100 times than the same, a variety of characteristic curves of reflection are achieved correspondingly to the shape of the unevenness. The unevenness height acts, if no more than 40 nm, as a two-layered reflection film. Here, if the aforementioned one side or diameter is as large as or larger by several times than the wavelength of the light, the scattering of the light is so intensified undesirably as to lower the interfering action of the light. Fig. 5 is an explanatory view illustrating the characteristics of reflection of the uneven portion. In Fig. 5, the dotted lines show reflection curves (the characteristics of reflection of arbitrary small area portions), and the solid line shows the reflection curve (the total characteristic of reflection) of the panel glass portion of the cathode ray tube of the present invention, obtained by combining the reflection characteristics of the small areas. Macroscopically, as illustrated in Fig. 5, the total characteristic of reflection shown by the solid curve is observed. In the characteristics, the bottom-reflectance Rb slightly rises, but the reflection curve is flat the reflection color is light, and the reflectance is as low as 400 to 700 nm. If this unevenness is made only on the surface of the low refractive index film, the refractive index is too low to allow the light interference to act. As a result, the height of the unevenness has to be increased to intensify the scattering of the reflection light, thereby degrading the display image of the cathode ray tube. As having been described in the individual embodiments of the present invention, therefore, a cathode ray tube of high quality, in which the reflection of external light is drastically reduced and the electrostatic charging is prevented, can be provided which has a two-layered structure, in which the low refractive index film is laid over the high refractive index film formed on the outer face of the panel glass, the small unevenness is formed at least in the interface between the high refractive index film and the low refractive index film, and a conductive substance is used as the material for the underlying high refractive index film. Here will be described a process for manufacturing the cathode ray tube of the present invention. Fig. 6 is a schematic flowchart for explaining a first example of a process for manufacturing the cathode ray tube of the present invention. First, the surface of the panel glass of a color display tube having a phosphor screen pitch of 0.26 mm and an effective diagonal length of 41 cm is polished to remove the contamination (at Step 1). Next, the surface temperature of the panel glass is heated up to 40°C (at Step 2), and the panel surface is spray-coated with a suspension of a high refractive index material having the under-specified composition (1) (at Step 3). This spray-coating step is performed all over the surface by sweeping the surface of the panel glass at a liquid flow rate of 2 liters/h, at an air flow rate of 2 liters/min and at a spray width of 70 mm. After spraying the whole surface, similar step is suitably repeated once, twice, or three times. The consumption of the suspension of the high refractive index material used at Step 3 is totally 20 milliliters. Composition (1): Suspension of High Refractive Index Material A.T.O.: Average Particle Diameter of 30 nm 2 wt. % Ethanol 16 wt. % Dispersion Agent (KAO Ltd., Trade Name: Demol N ) 0.05 wt. % Ethylene Glycol 0.1 wt. % Ion-Exchange Water the Balance After the spraying of the suspension of the high refractive index material, the surface temperature of the panel glass is adjusted to 35°C (at Step 4), and 50 milliliters of a solution of a low refractive index material having the under-specified composition (2) is fed and the coater is spun at 150 RPM for 70 secs. to remove the excess solution (at Step 5), followed by a heat treatment at 160°C for 30 mins. (at Step 6). Composition (2): Solution of Low Refractive Index Material Si(C 2 H 5 O) 4 : Average of Degree of Polymerization: 1000 1.1 wt. % Hydrochloric Acid (in terms of HCℓ) 0.005 wt. % Ethanol the Balance As a result, there is formed a two-layered anti-reflection anti-electrostatic charge film, as shown in Fig. 1, which is composed of the lower layer of a high refractive index film having an average diameter of unevenness of 25 µm, the maximum unevenness height of 40 nm, an average film thickness of 80 nm and a refractive index of 1.8, and the upper layer of a low refractive index having an average thickness of 110 nm and a refractive index of 1.46. Here, the average diameter of unevenness is determined by taking a photograph of a magnification of 400 times with an optical interference microscope of OLYMPUS Ltd., sampling ten to 20 particles at random in one field of view, measuring their diameters on the photograph and arithmetically averaging the measured values. Moreover, the maximum height of the unevenness is the maximum roughness Rmax which is calculated from the image in the field of observation of the scanning electron microscope S-2250N of HITACHI, Ltd. by using an image processor RD550. The average roughness of the unevenness is likewise determined by using the image processor of the scanning electron microscope. The refractive index is obtained by using the automatic ellipsometer (having a light source wavelength of 550nm) DVA-36VW of Mizojiri Kogaku Kogyo, Ltd. This anti-reflection anti-electrostatic charge film has a surface resistance of 8 × 10 6 Ω/□, a bottom refractive index of 0.8%, a bottom-wavelength of 570 nm, a refractive index of 3.2% for 400 nm and a refractive index of 2.1% for 700 nm. Here, the surface resistance is measured by using Roresta IP apparatus of DIA INSTRUMENT Ltd. in the atmosphere at a temperature of 25°C while applying the measurement probe directly to the surface of the formed film. The refractive index is measured under the conditions of non-polarized light and an incident angle of 5 degrees by using a spectrophotometer U3400 of HITACHI, Ltd. Fig. 7 is a schematic flowchart for explaining a second example of a process for manufacturing the cathode ray tube of the present invention. First, the surface of the panel glass of a color display tube having a phosphor screen pitch of 0.26 mm and an effective diagonal length of 41 cm is polished to remove the contamination (at Step 1). Next, the surface temperature of the panel glass is heated up to 40°C (at Step 2), and the panel surface is spray-coated with a suspension of a high refractive index material having the aforementioned composition (1) (at Step 3). This spray-coating step is performed all over the surface by sweeping the surface of the panel glass at a liquid flow rate of 2 liters/h, at an air flow rate of 2 liters/min and at a blow width of 70 mm, and similar step is suitably repeated once, twice or three times. The consumption of the suspension of the high refractive index material, as used, at Step 3 is totally 20 milliliters. After the spraying of the suspension of the high refractive index material, the surface temperature of the panel glass is adjusted to 50°C (at Step 4), 50 milliliters of a solution of a low refractive index material having the under-specified composition (3) is fed, and the coater is spun at 150 RPM for 70 secs. to remove the excess solution (at Step 5), followed by a heat treatment at 160°C for 30 min (at Step 6). Composition (3): Solution of Low Refractive Index Material Si(C 2 H 5 O) 4 : Average of Degree of Polymerization: 100 0.95 wt. % Hydrochloric Acid (in terms of HCℓ) 0.007 wt. % Ethanol the Balance As a result, there is formed a two-layered anti-reflection anti-electrostatic charge film, as shown in Fig. 2, which is composed of the lower layer of a high refractive index film having an average particle diameter of 25 µm, the maximum unevenness height of 40 nm, an average film thickness of 80 nm and a refractive index of 1.8, and the upper layer of a low refractive index having an average thickness of 95 nm and a refractive index of 1.46. This anti-reflection anti-electrostatic charge film has a surface resistance of 8 × 10 6 Ω/□, a bottom refractive index of 0.9%, a bottom-wavelength of 530 nm, a refractive index of 3.0% for 400 nm and a refractive index of 2.0% for 700 nm. Fig. 8 is a schematic flowchart for explaining a third example of a process for manufacturing the cathode ray tube of the present invention. First, the surface of the panel glass of a color display tube having a phosphor screen pitch of 0.26 mm and an effective diagonal length of 41 cm is polished to remove the contamination (at Step 1). The surface temperature of the panel glass is heated up to 40°C (at Step 2), and the panel surface is spray-coated with a suspension for a high refractive index material having the aforementioned composition (1) by using a two-fluid nozzle of SPRAYING SYSTEM Ltd. (at Step 3). This spray-coating step is performed all over the surface by sweeping the surface of the panel glass at a liquid flow rate of 2 liters/h, at an air flow rate of 2 liters/min and at a blow width of 70 mm, and similar step is suitably repeated once, twice, or three times. The consumption of the suspension of the high refractive index material used at Step 3 is totally 20 milliliters. After the spraying of the suspension of the high refractive index material, the surface temperature of the panel glass is adjusted to 25°C (at Step 4), and a solution of a low refractive index material having the aforementioned composition (3) is spray-coated under the same spray conditions as those of the high refractive index material by using an aforementioned two-fluid nozzle (at Step 5), followed by a heat treatment at 160°C for 30 min (at Step 6). As a result, there is obtained an anti-reflection anti-electrostatic charge film which has characteristics substantially similar to those of the aforementioned second example. Fig. 9 is an explanatory view illustrating the relations between the average diameter and the intensity of scattering of the unevenness at the interface of the high refractive index film and the low refractive index film. In Fig. 9, the abscissa is marked with the average diameter (µm), and the ordinate is marked with the intensity (in a relative value) of scattering of the high refractive index film. A lower intensity (in the relative value) of scattering of the film, shown on the ordinate of Fig. 9, is more desirable, and the allowable level of the image display screen of the cathode ray tube is no more than the intensity (in the relative value) of scattering of 3. In Fig. 9, the dotted curve shows the case that the maximum height of the unevenness is 10 nm, and the solid curve shows the case that the same is 40 nm. Fig. 10 is an explanatory view illustrating relations between the maximum height of the unevenness and the bottom-reflectance at the interface of the high refractive index film and the low refractive index film. In Fig. 10, the abscissa is marked with the maximum height of the unevenness (nm), and the ordinate is marked with the bottom-reflectance (%) of the high refractive index film. In Fig. 10, the dotted curve shows the case that the average diameter (the average diameter of the circumcircles of the photograph taken-by using a phase-contrast microscope) is 5 µm, and the solid curve plots the case that the same average diameter is 20 µm. In order to form an anti-reflection anti-electrostatic charge film having little scattering of light and a low bottom-reflectance, it is desirable that the average diameter be 5 to 80 µm and the maximum height of unevenness be no more than 40 nm. When the maximum height of unevenness is no more than 10 nm, the reflection curve takes a V-shape, so that the dependence of the reflectance on the wavelength is intensified the reflected light is colured in blue. Therefore the maximum height of unevenness of no more than 10nm is not practical. When the diameter is more than 100 µm, on the other hand, the roughness of the displayed image is undesirably increased, lowering the smoothness of the displayed image. In the foregoing embodiments described the A.T.O. is used as the conductive material of the high refractive index film, but similar reflection characteristics were obtained when I.T.O. was employed, and an anti-reflection anti-electrostatic charge film having a surface resistance of 3 to 8 × 10 4 Ω/□ was formed. By a similar process using ultra fine particles of various metals, moreover, there were formed anti-reflection anti-electrostatic charge films, which have surface resistances and bottom-reflectances, as listed in Table 1: Substance Bottom-Reflectances Surfaces Resistance Silver 0.08% 2-5 × 10 2 Ω/□ Platinum 0.1% 1-3 × 10 3 Ω/□ Gold 0.1% 1-5 × 10 3 Ω/□ Palladium 0.2% 3-5 × 10 3 Ω/□ Rhodium 0.2% 1-6 × 10 3 Ω/□ Iridium 0.2% 3-8 × 10 3 Ω/□ Incidentally, other anti-reflection anti-electrostatic charge films were formed on trial by a similar process using other materials including aluminum, nickel, copper cobalt, chromium, silver alloy, platinum alloy, gold alloy, palladium alloy, rhodium alloy and iridium alloy. Oxides, hydroxides or carbonates were produced depending upon the atmosphere except for the anti-reflection anti-electrostatic charge films made of precious metals, the bottom-reflectance or the surface resistance changed with time, and the characteristics were unstable. The foregoing embodiments have been described by way of an example in which the anti-reflection anti-electrostatic charge film is formed of the two layers. Despite of this description, however, the present invention should not be limited to the example, but can be modified into either a three-layered anti-reflection anti-electrostatic charge film in which a high refractive index film having the same uneven film as the low refractive index film and a high intensity of scattering is laid over the two-layered structure, or four- or more-layered film structure in which a high refractive index film and a low refractive index film, basically of the two-layered structure, are alternately formed and the interfaces of layers of different refractive indices are uneven. According to the individual embodiments thus far described, it is possible to provide a cathode ray tube having an anti-reflection anti-electrostatic charge film, which prevents the reflection of external light on a panel glass to have a high contrast and has little roughness of the panel surface so that it can display an image of high resolution while preventing the electrostatic charge.

Claims: A cathode ray tube comprising a vacuum enclosure including a panel glass (1) whose inner face is coated with a phosphor film (4) to form a screen; a neck (2) housing an electron gun (13); and a funnel (3) connecting said panel glass (1) and said neck (2), wherein a high refractive index film (21) of a refractive index of 1.6 to 2.2 and a low refractive index film (22) of a refractive index of 1.3 to 1.58 are formed on the outer face of said panel glass (1), said high refractive index film (21) is sandwiched between the outer face of said panel glass (1) and said low refractive index film (22), characterised in that an unevenness having an average diameter of 5 to 80 µ m and a height of 10 to 40 nm is provided at the interface between said high refractive index film (21) and said low refractive index film (22). A cathode ray tube according to claim 1, wherein said low refractive index film (22) has an average roughness Rz of no more than 10 nm on its surface. A cathode ray tube according to claim 1, wherein said low refractive index film (22) has an average roughness Rz of more than 10 nm on its surface. A cathode ray tube according to claim 3, wherein the average roughness Rz of the unevenness of the surface of said low refractive index film (22) is smaller than the average roughness Rz of the unevenness of the interface between said high refractive index film (21) and said low refractive index film (22). A cathode ray tube according to claim 1, wherein said high refractive index film (21) contains particles of a conductive oxide or metal, and said low refractive index film (22) contains a silicon compound or a flourine compound. A cathode ray tube according to claim 1, wherein said phosphor screen pitch (43) is less than 0.26 mm.

Inventors: NISHIZAWA MASAHIRO, TOJO TOSHIO, UCHIYAMA NORIKAZU, NISHIZAWA, MASAHIRO, TOJO, TOSHIO, UCHIYAMA, NORIKAZU
Applicants: HITACHI DEVICE ENG, HITACHI LTD, HITACHI DEVICE ENGINEERING CO., LTD., HITACHI, LTD.
Application year: 1997
Main classification: H01J29
IPC codes: C03C17, H01J31, H01J29, G02B1