Explosion-proof film and cathode-ray tube

Abstract: An explosion-proof film (6) being good in visibility, scratch-resistance, and workability, and a cathode-ray tube (1) using the film. The explosion-proof film (6) includes a transparent plastic film (3) as a base material; and a reflection-preventive film having two or more layers (4, 5), which is formed on one surface of the plastic film; wherein, of the two or more layers (4, 5) of the reflection-preventive film, at least one has a light-absorption function, and at least another has a conductive function. The explosion-proof film (6) is stuck on a surface of a panel glass (2) constituting a display screen of a cathode-ray tube, to thereby give an explosion-proof function to the cathode-ray tube (1), to achieve lightweightness of the cathode-ray tube, and to obtain the optimum visual contrast. The explosion-proof film (6) may be formed of three or more layers.

Description: BACKGROUND OF THE INVENTION The present invention relates to an explosion-proof film good in visibility, scratch-resistance, and workability, which is stuck on a display screen of a cathode-ray tube. To prevent scattering of glass due to implosion of a cathode-ray tube, there has been proposed a method of sticking an explosion-proof plastic film on a display screen of the cathode-ray tube. The sticking of such an explosion-proof film on the display screen of the cathode-ray tube is effective to reduce the thickness of the panel glass and hence to contribute to lightweightness of the cathode-ray tube, because the explosion-proof film shares a function of preventing scattering of glass which otherwise has been dependent on the panel glass or a tension band. With respect to a transparent material through which a substance is to be viewed, when light is intensively reflected from the surface of the transparent material or when an image is clearly formed on the surface thereof, it becomes very difficult to view the substance through such a transparent material. For example, in the case of spectacle lenses, a reflected image called "ghost" or "flare" formed thereon gives discomfort to eyes, and in the case of looking glass, reflected light on the glass surface obstructs clear viewing of a substance. Such a phenomenon also occurs for a panel glass of a cathode-ray tube, and to cope with such an inconvenience, various countermeasures have been proposed. As one example of the countermeasures, there has been known a method of preventing reflection of light from the surface of a base member by coating the surface of the base member with a material having a refractive index different from that of the base member by vacuum deposition or the like. In this method, to improve the reflection preventive effect, it is important to control the thickness of the coating material. In the case where a single layer film is used as the coating material, the minimum reflectance, that is, the maximum transmittance is obtained by forming the film using a material having a refractive index lower than that of the base member and selecting any optical film thickness of the material to be equal to a quarter-wavelength of light or the quarter-wavelength multiplied by an odd number. The optical film thickness is given by a product of the refractive index of the film-forming material and the thickness of the film. As the material for forming a reflection-preventive film, there is generally used a material exhibiting a low reflectance and a high transmittance of visible rays, which is represented by an inorganic oxide or an inorganic halide. Further, there are proposed several methods of forming a reflection-preventive film having a plurality of layers. In general, the transmittance of a display screen of a cathode-ray tube is adjusted by a panel glass; however, in the case of sticking an explosion-proof film on the panel glass for reducing the thickness of the panel glass and achieving lightweightness of the cathode-ray tube, the transmittance of the display screen is increased, resulting in reduced contrast. In particular, in the case of sticking a film with a reflection-preventive film made from an inorganic oxide on the panel glass, the reflection-preventive film exhibits little light absorption and the degree of reflection on the surface is reduced, so that the actual transmittance is further increased, thereby further reducing the contrast. European patent EP 0 626 717 (Matsushita Electronics Corporation) shows an explosion-proof film for a cathode ray tube comprising an organic polymer film being a multilayer resin film in which some layers have a reflection-preventative function. SUMMARY OF THE INVENTION An object of the present invention is to provide a cathode-ray tube in which an explosion-proof film is stuck on a panel glass in order to reduce the thickness of the panel glass for achieving lightweightness of the cathode ray tube, wherein visibility is enhanced by keeping at optimum values the light reflectance and transmittance of a display portion composed of the explosion-proof film and the panel glass. To achieve the above object, according to the present invention as disclosed in claim 1, there is provided an explosion-proof film for a cathode ray tube including: an organic polymer film as a base layer; and a reflection-preventive optical thin film having two or more layers, which is formed on one surface of said organic polymer film; wherein, of said two or more layers of said reflection-preventive film, at least one has a light-absorption function. The present invention also provides an explosion-proof film including: an organic polymer film; and a reflection-preventive film having two or more layers, which is formed on one surface of said organic polymer film; wherein, of said two or more layers of said reflection-preventive film, at least one has a light absorption function, and at least another has a conductive function. The present invention also provides an explosion-proof film including: an organic polymer film; and a reflection-preventive film having two or more layers, which is formed on one surface of said organic polymer film; wherein, of said two or more layers of said reflection-preventive film, at least one has a light-absorption function and a conductive function. The present invention also provides an explosion-proof film including: an organic polymer film; and a reflection-preventive film having three or more layers, which is formed on one surface of said organic polymer film; wherein, of said three or more layers of said reflection-preventive film layer, at least one has a light absorption function, at least another has a conductive function, and at least the third is a dielectric layer. The present invention also provides an explosion-proof film including: an organic polymer film; and a reflection-preventive film having two or more layers, which is formed on one surface of said organic polymer film; wherein, of said two or more layers of said reflection-preventive film, at least one has a light-absorption function and a conductive function, and at least another is a dielectric layer. According to the present invention as disclosed in claim 5, there is provided a cathode-ray tube including a panel glass on which the above explosion-proof film is stuck. In this cathode-ray tube, said panel glass may be made from a tinted material or a dark tinted material. The explosion-proof film of the present invention makes it possible to reduce the thickness of the panel glass and hence to reduce the weight of the cathode-ray tube; to give a good reflection-preventive function with a small number of layers; and to set the transmittance of light at the optimum state and hence to keep the contrast at a good state. Also, the explosion proof film having a conductive layer exhibits an antistatic effect and an electromagnetic shielding effect. Further, since the contrast can be adjusted at the optimum value by the explosion-proof film without changing the glass material, it is possible to form various panels using only one kind of the glass material, and hence to simplify the manufacturing process and reduce the cost. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view showing an explosion-proof film of the present invention; Fig. 2 is a graph showing light reflectance of an explosion-proof film according to a first embodiment of the present invention; Fig. 3 is a graph showing light transmittance of the explosion-proof film according to the first embodiment; Fig. 4 is a graph showing light reflectance of an explosion-proof film according to a second embodiment of the present invention; and Fig. 5 is a graph showing light transmittance of the explosion-proof film according to the second embodiment. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference the accompanying drawings. The present inventor has found that the above-described problem can be effectively solved by preparing an explosion-proof film in which two or more reflection-preventive films including at least one layer having a light-absorption function are formed on one surface (front surface) of a transparent plastic film as a base material, and sticking the back surface of the base material on a panel glass of a cathode-ray tube. Specifically, as shown in Fig. 1, an explosion-proof film 6 of the present invention is prepared by forming a first reflection-preventive film 4 and a second reflection-preventive film 5 in this order on a transparent plastic film 3 as a base material, and the explosion-proof film 6 thus obtained is stuck on a surface of a panel glass 2 constituting a display screen of a cathode-ray tube 1, to thereby give an explosion-proof function to the cathode-ray tube 1, to achieve lightweightness of the cathode-ray tube 1, and to obtain the optimum visual contrast. The explosion-proof film 6 may, of course, be formed of three or more layers. First, a thin film to which the present invention pertains will be described. In some types of heat-ray-blocking films which are filters making use of optical thin films, a light absorption material such as Au, Pt, Pd, Ni-Cr, Al, In 2 O 3 -SnO 2 , CuI, or CuS is contained in the film to adjusted the transmittance of light. The transmittance of visible rays of the heat-ray-blocking film containing the above light absorption material is generally in a range of 60% to 90%. As the reflection-preventive film, there has been used a light-absorption film called "dark mirror", "selective absorption mirror" or "enhanced absorption mirror". In particular, the dark mirror is known to be useable as the reflection-preventive film applied in a visible ray region. A two-layered dark mirror having a light-absorption metal film in combination with a dielectric film has been proposed in "Optical Thin Film User's Handbook" (published by Nikkan Kougyo Sinbunsha, page 160). Such a reflection-preventive film, in spite of a small number of layers, exhibits a high reflection-preventive function in a wide visible ray region. On the other hand, for a reflection-preventive film having only a transparent dielectric film, it needs to be of a multi-layered structure for exhibiting the same function, that is, it becomes complicated in film structure. Next, the explosion-proof film 6 of the present invention will be described. The plastic film as the base material of the explosion-proof film 6 can be made from any organic polymer. However, from the viewpoint of optical characteristics such as transparency, refractive index, and dispersibility, and further impact resistance, heat resistance, and durability, the plastic film is preferably made from one of the following organic polymers: polymethylmethacrylate and its copolymer; polycarbonate; diethylene glycol bisallylcarbonate (CR-39); polymer of diacrylate with bisphenol A or brominated bisphenol A, and its copolymer; polymer of dimethacrylate with bisphenol or brominated bisphenol A, and its copolymer; polymer of urethane modified monoacrylate with bisphenol A or brominated bisphenol A, and its copolymer; polymer of urethane modified monomethacrylate with bisphenol A or brominated bisphenol A, and its copolymer; polyester, particularly, polyethyleneterephthalate, polyethylene naphthalate, or unsaturated polyester; acrylonitrile-styrene copolymer; poly (vinyl chloride); polyurethane; and epoxy resin. In addition, the plastic film can be made from an aramid based resin. The plastic film is formed by drawing the above material typically to a thickness of about 25 µm to 500µm. As the base material of the explosion-proof film 6, on which the reflection-preventive film is to be formed, there is preferably used the above-described plastic film coated with a coating material such as a hard coat. In particular, the coating material provided under the reflection-preventive film of the present invention is allowed to improve various properties such as adhesive strength, hardness, chemical resistance, durability, and dye-affinity. For example, to improve the hardness of the plastic film as the base material, the plastic film may be coated with a material known to give a high hardness to the film surface. Further, to improve the hardness, the plastic film may be coated with a coating material composed of an acrylic crosslinking material obtained by acrylic acid or methacrylic acid, pentaerythritol and the like. As an adhesive for sticking the explosion-proof film 6 on the surface of a panel glass, there may be used one of the following adhesives: epoxy-based adhesive; rubber-based adhesive; acrylic-based adhesive; silicone-based adhesive; and the above adhesives added with a ultraviolet crosslinking agent. With respect to such an adhesive, not to degrade quality of characters and graphic patterns to be displayed on a display screen, the haze value is specified to be 20% or less, preferably, 5% or less, and the absorptance of light is specified to be 95% or less, preferably, in a range of 40% to 90%. The reflection-preventive film having a light-absorption function according to the present invention can be formed by a physical film formation process such as vacuum deposition, ion plating, or sputtering; or a chemical film formation method such as spraying, dipping, CVD, or coating. Specific examples of materials suitable for CVD include, in addition to SiO 2 , inorganic oxides such as Al 2 O 3 , ZrO 2 , TiO 2 , TaHf 2 , SiO, TiO, Ti 2 O 3 , Y 2 O 3 , YbO 3 , MgO, and CeO 2 . The present invention will be more clearly understood with reference to the following examples: Example 1 A transparent polyethyleneterephthalate (PET) film (thickness: 100 µm) was used as a base material for a reflection-preventive film. One surface of the PET film was subjected to hard-coating treatment for ensuring a specific surface hardness. The hard-coating treatment is generally performed by coating the surface of a member with a raw material of an acrylic crosslinking resin and crosslinking/hardening it by ultraviolet rays or electron rays; or coating the surface of the member with a raw material of a silicone-based resin, melamine-based resin or epoxy-based resin and thermally hardening it. A light-absorption layer as the reflection-preventive film was formed on the resultant PET film by sputtering metal chromium to a thickness of 1 nm and then sputtering SiO 2 to a thickness of 80 nm. The reflectance and transmittance of the reflection-preventive film thus obtained at the coat surface are shown in Figs. 2 and 3, respectively. As will be apparent from Fig. 3, the transmittance at a wavelength of 546 nm is 82.6%. The back surface of the PET film, opposite to the surface formed with the reflection-preventive film, was uniformly coated with an acrylic adhesive to a thickness of 50±2 µm. The adhesive was then dried at 60°C, to form an adhesive layer having a specific adhesive strength. The explosion-proof film thus formed was stuck on the surface of a panel glass by applying a pressure using a rubber roller. By sticking of the explosion-proof film on the panel glass, the thickness of the panel glass of a cathode-ray tube having a size of 82 cm (≅ 32 inch) (aspect ratio: 16:9) was able to be 3 mm reduced from a usual value, 16 mm to 13 mm with the same strength being kept. In addition, there was used the glass panel made from a glass material specified in H-4601 of the Standard EIAJ. For the panel glass having a thickness of 16 mm, the transmittance of light at the wavelength of 546 nm was 31.5%, while for the panel glass having a thickness of 13 mm, it was 38%. Accordingly, the transmittance of light (wavelength: 546 nm) of the panel glass having stuck thereon the explosion-proof film was calculated from the following equation: transmittance of panel glass (38%) × transmittance of explosion-proof film (82.6%) = 31.3% In addition, reflection at the boundary between the PET film and the adhesive and reflection at the boundary between the adhesive and the panel glass are very small in difference in refractive index, and therefore, is omitted. As described above, for the panel glass having stuck thereon the explosion-proof film having the specific reflectance and transmittance, the contrast was similar to that obtained in the related art one and the glass thickness was reduced from 16 mm to 13 mm. In other words, the panel glass in this embodiment was reduced in weight with the contrast being kept at a value comparable to the related art. While, in the above example, the explosion-proof film of the present invention was used for a cathode-ray tube of size 82 cm (≅ 32 inch) (aspect ratio: 16:9), the same effect can be of course obtained by applying the explosion-proof film to cathode-ray tubes having other sizes. Example 2 A transparent polyethyleneterephthalate (PET) film (thickness: 100 µm) was used as a base material for a reflection-preventive film. One surface of the PET film was subjected to hard-coating treatment in the same manner as described in Example 1 for ensuring a specific surface hardness. A light-absorption layer as the reflection-preventive film was formed on the resultant PET film by sputtering metal gold to a thickness of 8.5 nm and then pre-sputtering SiO 2 to a thickness of 63 nm. The reflectance and transmittance of the reflection-preventive film thus obtained at the coat surface are shown in Figs. 4 and 5, respectively. As will be apparent from Fig. 5, the transmittance at a wavelength of 546 nm is 91%. The back surface of the PET film, opposite to the surface formed with the reflection-preventive film, was uniformly coated with an acrylic adhesive to a thickness of 50±2 µm. The adhesive was then dried at 60°C, to form an adhesive layer having a specific adhesive strength. The explosion-proof film thus formed was stuck on the surface of a panel glass by applying a pressure using a rubber roller. By sticking of the explosion-proof film on the panel glass, the thickness of the panel glass of a cathode-ray tube having a size of 67 cm (≅ 28 inch) (aspect ratio: 16:9) was able to be 2 mm reduced from a usual value, 14.5 mm to 12.5 mm with the same strength being kept. In addition, there was used the glass panel made from a glass material specified in H-5702 of the Standard EIAJ. For the panel glass having a thickness of 14.5 mm, the transmittance of light at the wavelength of 546 nm was 46%, while for the panel glass having a thickness of 12.5 mm, it was 50.5%. Accordingly, the transmittance of light (wavelength: 546 nm) of the panel glass having stuck thereon the explosion-proof film was calculated from the following equation: transmittance of panel glass (50.5%) × transmittance of explosion-proof film (91%) = 46%. In addition, reflection at the boundary between the PET film and the adhesive and reflection at the boundary between the adhesive and the panel glass are very small in difference in refractive index, and therefore, is omitted. As described above, for the panel glass having stuck thereon the explosion-proof film having the specific reflectance and transmittance, the contrast was similar to that obtained in the related art and the glass thickness was reduced from 14.5 mm to 12.5 mm. In other words, the panel glass in this embodiment was reduced in weight with the contrast being kept at a value comparable to the related art. While, in this example, the explosion-proof film of the present invention was used for a cathode-ray tube of size 67 cm (≅ 28 inch) (aspect ratio: 16:9), the same effect can be of course obtained by applying the explosion-proof film to cathode-ray tubes having other sizes. While the preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the invention as defined in the following claims.

Claims: An explosion-proof film (6) for a cathode ray tube comprising: an organic polymer film (3) as a base material, and a reflection-preventive optical thin film having two or more layers (4, 5), which is formed on one surface of said organic polymer film; wherein, of said two or more layers of said reflection preventive film, at least one has a light absorption function. An explosion-proof film (6) according to claim 1, wherein: at least another of said two or more layers (4, 5) of said reflection-preventive film has a conductive function. An explosion-proof film (6) according to claim 1, wherein: of said two or more layers (4, 5) of said reflection-preventive film, at least one has a light-absorption function and a conductive function. An explosion-proof film (6) according to claim 3, wherein: at least another of said two or more layers (4, 5) of said reflection-preventive film is a dielectric layer. An explosion-proof film (6) according to claim 1, wherein: the reflection-preventive film has three or more layers; and of said three or more layers of said reflection-preventive film layer, at least one has a light-absorption function, at least another has a conductive function, and at least a third is a dielectric layer. A cathode-ray tube (1) comprising a panel glass (2) on which said explosion-proof film (6) described in any one of claims 1 to 5 is stuck. A cathode-ray tube according to claim 6, wherein said panel glass (2) is made from a tinted material. A cathode-ray tube according to claim 6, wherein said panel glass (2) is made from a material tinted in a dark colour.

Inventors: HANAOKA HIDEAKI, HANAOKA, HIDEAKI
Applicants: SONY CORP, SONY CORPORATION
Application year: 1997
Main classification: H01J29
IPC codes: C08J7, B32B7, H01J29