Abstract:
An improved resin layer used in the manufacture of cathode ray tube assemblies incorporates inorganic particles in the resin. The resin layer with particles is coated on a CRT screen prior to coating with aluminum film. The resin layer is volatilizable, so that following applying the aluminum film, the screen is baked to drive off the resin. The inorganic particles in the resin layer create an uneven boundary with the screen, so that during baking, volatilized resin in the form of gases can escape from between the aluminum and screen without forming bubbles or causing swelling.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a solution for making a resin film, a method for manufacturing a screen of a CRT using the solution and a CRT manufactured by the method, and more particularly to a solution for making a resin film, by which an aluminum thin film having an improved effective plane of reflection can be formed. 
     DESCRIPTION OF THE PRIOR ART 
     A known CRT screen and method of making a CRT screen will now be described with reference to FIGS. 1-3E, which illustrate the prior art. 
     Referring to FIG. 1, a color CRT  10  generally comprises an evacuated glass envelope consisting of a panel  12 , a funnel  13  sealed to the panel  12  and a tubular neck  14  connected by the funnel  13 , an electron gun  11  centrally mounted within the neck  14 , and a shadow mask  16  removably mounted to an inner sidewall of the panel  12 . A three color phosphor screen is formed on the inner surface of a display window or faceplate  18  of the panel  12 . 
     The electron gun  11  generates three elect-on beams  19   a  or  19   b , said beams being directed along convergent paths through the shadow mask  16  to the screen  20  by means of several lenses of the gun and a high positive voltage applied through an anode button  15  and being deflected by a deflection yoke  17  so as to scan over the screen  20  through apertures or slits  16   a  formed in the shadow mask  16 . 
     In the color CRT  10 , the phosphor screen  20 , which is formed on the inner surface of the faceplate  18 , comprises an array of three phosphor elements R, G and B of three different emission colors arranged in a cyclic order of a predetermined structure of multiple-stripe or multiple-dot shape and a matrix of light-absorptive material  21  surrounding the phosphor elements R, G and B, as shown in FIG.  2 . 
     A thin film of aluminum  22  or electro-conductive layer, overlying the screen  20  in order to provide a means for applying the uniform potential applied through the anode button  15  to the screen  20 , increases the brightness of the phosphor screen, prevents ions from the phosphor screen and prevents the potential of the phosphor screen from decreasing. And also, a resin film  22 ′ such as lacquer is applied to the phosphor screen  20  before forming the aluminum thin film  22 , so as to enhance the flatness and reflectivity of the aluminum thin film  22 . The resin film  22 ′ must be burned to volatilize after the aluminum thin film  22  is formed, so as to improve the life of the tube. 
     In a photolithographic wet process, which is well known as a prior art process for forming the phosphor screen, a slurry of a photosensitive binder and phosphor particles is coated on the inner surface of the faceplate. It does not meet the higher resolution demands and requires a lot of complicated processing steps and a lot of manufacturing equipments with the use of a large quantity of clean water, thereby necessitating high cost in manufacturing the phosphor screen. In addition, it discharges a large quantity of effluent such as waste water, phosphor elements, 6th chrome sensitizer, etc. 
     To solve or alleviate the above problems, an improved process of electro-photographically manufacturing the screen utilizing dry-powdered phosphor particles is developed. 
     U.S. Pat. No. 4,921,767, issued to Datta at al. on May 1, 1990, discloses the improved method of electro-photographically manufacturing the phosphor screen assembly using dry-powdered phosphor particles through a series of steps represented in FIGS. 3A to  3 E, as is briefly explained in the following. 
     After the panel  12  is washed, an electro-conductive layer  32  is coated on the inner surface of the faceplate  18  of the panel  12  and the photo-conductive layer  34  is coated thereon, as shown in FIG.  3 A. Conventionally, the electro-conductive layer  32  is made from an inorganic conductive material such as tin oxide or indium oxide, or their mixture, and preferably, from a volatilizable organic conductive material such as a polyelectrolyte commercially known as polybrene (1,5-dimethyl-1,5-diaza-undecamethylene polymethobromide, hexadimethrine bromide), available from Aldrich Chemical Co. 
     The polybrene is applied to the inner surface of the faceplate  18  in an aqueous solution containing about 10 percent by weight of propanol and about 10 percent by weight of a water-soluble adhesion-promoting polymer (poly vinyl alcohol, polyacrylic acid, polyamide and the like), and the coated solution is dried to form the conductive layer  32  having a thickness from about 1 to 2 microns and a surface resistivity of less than about 10 8  Ω/□ (ohms per square unit). 
     The photo-conductive layer  34  is formed by coating the conductive layer  32  with a photo-conductive solution comprising a volatilizable organic polymeric material, a suitable photo-conductive dye and a solvent. The polymeric material is an organic polymer such as polyvinyl carbazole, or an organic monomer such as n-ethyl carbazole, n-vinyl carbazole or tetraphenylbutatriene dissolved in a polymeric binder such as polymethylmethacrylate or polypropylene carbonate. The photo-conductive composition contains from about 0.1 to 0.4 percent by weight such dyes as crystal violet, chloridine blue, rhodamine EG and the like, which are sensitive to the visible rays, preferably rays having wavelength of from about 400 to 700 nm. The solvent for the photo-conductive composition is an organic material such as chlorobenzene or cyclopentanone and the like which will produce as little contamination as possible on the conductive layer  32 . The photo-conductive layer  32  is formed to have a thickness from about 2 to 6 microns. 
     FIG. 3B schematically illustrates a charging step, wherein the photo-conductive layer  34  overlying the electro-conductive layer  32  is positively charged in a dark environment by a conventional positive corona discharger  36 . As shown, the charger or charging electrode of the discharger  36  is positively applied with direct current while the negative electrode of the discharger  36  is connected to the electro-conductive layer  32  and grounded. The charging electrode of the discharger  36  travels across the layer  34  and charges it with a positive voltage in the range from +200 to +700 volt. 
     FIG. 3C schematically shows an exposure step, wherein the charged photo-conductive layer  34  is exposed through a shadow mask  16  by a xenon flash lamp  35  having a lens system  35 ′ in the dark environment. In this step, the shadow mask  16  is installed on the panel  12  and the electro-conductive layer  32  is grounded. When the xenon flash lamp  35  is switched on to shed light on the charged photo-conductive layer  34  through the lens system  35 ′ and the shadow mask  16 , portions of the photo-conductive layer  34  corresponding to apertures or slits  16  a of the shadow mask  16  are exposed to the light. Then, the positive charges of the exposed areas are discharged through the grounded conductive layer  32  and the charges of the unexposed areas remain in the photo-conductive layer  34 , thus establishing a latent charge image in a predetermined array structure, as shown in FIG.  3 C. In order to exactly attach light-absorptive materials, it is preferred that the xenon flash lamp  35  travels along three positions while coinciding with three different incident angles of the three electron beams. 
     FIG. 3D schematically shows a developing step which utilizes a developing container  35 ″ containing dry-powdered light-absorptive or phosphor particles and carrier beads for producing static electricity by coming into contact with the dry-powdered particles. Preferably, the carrier beads are so mixed as to charge the light-absorptive particles with negative electric charges and the phosphor powders with positive electric charges when they come into contact with the dry-powdered particles. 
     In this step, the panel  12 , from which the shadow mask  16  is removed, is put on the developing container  35 ″ containing the dry-powdered particles, so that the photo-conductive layer  34  can come into contact with the dry-powdered particles. In this case, the negatively charged light-absorptive particles are attached to the positively charged unexposed areas of the photo-conductive layer  34  by electric attraction, while the positively charged phosphor particles are repulsed by the positively charged unexposed areas but attached by reversal developing to the exposed areas of the photo-conductive layer  34  from which the positive electric charges are discharged. 
     FIG. 3E schematically represents a fixing step by means of infrared radiation. In this step, the light-absorptive and phosphor particles attached in the above developing step are fixed together and onto the photo-conductive layer  34 . Therefore, the dry-powdered particles includes proper polymer components which may be melted by heat and have proper adhesion. 
     The steps of charging, exposing, developing and fixing are repeated for the three different phosphor particles. Moreover, the same process of the above steps can be repeated also for the black matrix particles before or after the three different phosphor particles are formed. 
     After the three different phosphor particles and the black matrix particles are formed through the above process, a lacquer film is formed through a lacquering step and an aluminum thin film is formed through an aluminizing step respectively by a conventional method. Thereafter, the faceplate panel  12  is baked in air at a temperature of 425° C., for about 30 minutes to drive off the volatilizable constituents such as the organic solvents from the conductive layer  32 , the photo-conductive layer  34 , the phosphor elements and the lacquer film, thereby forming a screen array  20  of light-absorptive material  21  and three phosphor elements R, G and B in FIG.  2 . 
     The conventional method of electro-photographically manufacturing the phosphor screen assembly using dry-powdered phosphor particles as described above has one problem that it requires dark environment during all the steps until the fixing step after the photo-conductive layer is formed, because the photo-conductive layer is sensitive to the visual light. Also, the fixing step of FIG. 3E is still necessary even after the developing step. 
     To overcome this problem, the applicant proposed a method of forming the photo-conductive layer using a photo-conductive solution responsive to the ultraviolet rays. The solution for the photo-conductive layer  34  responsive to the ultraviolet rays, for example, may contain: an electron donor material, such as about 0.01 to 1 percent by weight of bis-1,4-dimethyl phenyl (-1,4-diphenyl (butatriene)) or 2 to 5 percent by weight of tetraphenyl ethylene (TPE); an electron acceptor material, such as about 0.01 to 1 percent by weight of at least one of trinitro-fluorenone (TNF) and ethyl anthraquinone (EAQ); a polymeric binder, such as 1 to 30 percent by weight polystyrene; and a solvent such as the remaining percent by weight of toluene or xylene. 
     As the polymeric binder, poly(α-methylstyrene) (PαMS), polymethylmethacrylate (PMMA), and polystyrene-oxazoline copolymer (PS-OX) may be employed instead of the polystyrene. 
     However, in the fixing step of FIG. 3E for fixing the phosphor particles, the developed phosphor particles P come down into the photo-conductive layer  34  as shown in FIGS. 4A and 4B. After that, when the resin film  22 ′ has been formed, the surface of the resin film  22 ′ becomes smooth as the inner surface of the panel  12 . Then, gas generated from the conductive layer  32 , the photo-conductive layer  34  and the resin film  22 ′ during the burning step in a frit furnace for sealed-assembling the panel and the funnel or during the baking step applies an over-pressure to the aluminum thin film  22 , so that the aluminum thin film  22  becomes swollen and unfastened upward from the screen easily. In result, the plane reflectivity of the aluminum thin film  22  is deteriorated, and moreover the volatile resin remains therein to deteriorate the picture quality. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to overcome the above described problems, and therefore it is an object of the present invention to provide a solution for making a resin film, a method for manufacturing a screen of a CRT using the solution and a CRT manufactured by the method, in which a resin film in a wet slurry method, or a conductive layer, a photo-conductive layer and a resin film in the dry-electrophotographically manufacturing method can be completely volatilized without the upward swelling and unfastening of the aluminum thin film. 
     To achieve the above objects, the present invention provides a solution for making a resin film in a cathode ray tube, the cathode ray tube having a phosphor screen formed on an inner surface of a faceplate, the phosphor screen comprising: 
     an array of three phosphor elements R, G and B of three different emission colors arranged in a cyclic order of a predetermined structure of multiple-stripe or multiple-dot shape and a matrix of light-absorptive material surrounding the phosphor elements R, G and B; 
     a resin film such as a lacquer film formed on the light-absorptive material and the phosphor elements; and 
     an aluminum thin film formed on the resin film just after the resin film is formed, the resin film enhancing a flatness and a reflectivity of the aluminum thin film, the aluminum thin film functioning as a conductive film and a plane of reflection; 
     wherein the solution comprises inorganic particles. 
     The resin film, which is formed with the solution, comprises a harsh and rugged surface due to the inorganic particles. Therefore, the aluminum film can be strongly attach to the resin film, and the gas generated from the conductive layer, the photo-conductive layer and the resin film during the burning step in a frit furnace for sealed-assembling the panel and the funnel is dispersed and discharged through the harsh and rugged surface over the entire area of the resin film, to thereby apply a decreased pressure to the aluminum thin film. Accordingly, the conductive layer, the photo-conductive layer and the resin film can be completely volatilized without the upward swelling and unfastening of the aluminum thin film and the refletivity of the aluminum film can be improved. 
     The present invention further provides a cathode ray tube having a phosphor screen formed on an inner surface of a faceplate, the phosphor screen comprising: 
     an array of three phosphor elements R, G and B of three different emission colors arranged in a cyclic order of a predetermined structure of multiple-stripe or multiple-dot shape and a matrix of light-absorptive material surrounding the phosphor elements R, G and B; 
     a resin film such as a lacquer film formed on the light-absorptive material and the phosphor elements, the resin film being applied by a solution containing inorganic particles, said inorganic particles remaining after the resin film is volatilized by heat; and 
     an aluminum thin film formed on the resin film after the resin film is formed, the resin film enhancing a flatness and a reflectivity of the aluminum thin film. 
     In addition, the present invention provides a method for electro-photographically manufacturing a screen of a CRT utilizing dry-powdered phosphor particles, the method comprising the steps of: 
     forming a volatile conductive layer on an inner surface of a panel by utilizing at least one of the phosphor elements and the light-absorptive material; 
     forming a volatile photo-conductive layer on the volatile conductive layer, the volatile photo-conductive layer containing a material responsive to visible rays or ultraviolet rays; 
     charging the volatile photo-conductive layer with uniform electrostatic charges; 
     exposing the volatile photo-conductive layer through a shadow mask to a light source so as to selectively discharge the electrostatic charges from the volatile photo-conductive layer; 
     developing the photo-conductive layer by charging powdered particles to be attached on one of an exposed area and an unexposed area of the photo-conductive layer; 
     forming a resin film on the light-absorptive material and the phosphor elements with a resin solution such as lacquer containing inorganic substance; 
     forming an aluminum thin film on the resin film, the aluminum thin film functioning as a conductive film and a plane of reflection; and 
     driving off volatilizable constituents from the conductive layer, the photo-conductive layer, and the resin film by heat. 
     Preferably, the inorganic particles are 0.01 to 50% by weight of solid substance of the resin film, and the inorganic particles may be SiO 2 , which has no color or a white color, thereby exerting no bad effect on the quality of the screen even if the inorganic particles remain on the screen. And, it is preferred that the inorganic particles respectively have a diameter equal to or smaller than 0.5 μm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above object, and other features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings, in which: 
     FIG. 1 is a partial sectional plan view of illustrating the construction of a prior art color cathode ray tube; 
     FIG. 2 is an enlarged partial sectional plan view-of a screen assembly of the prior art tube of FIG. 1; 
     FIGS. 3A-3E are schematic sectional diagrams illustrating a prior art method of dry-electrophotographically manufacturing a screen assembly for the prior art tube of FIG. 1; 
     FIGS. 4A &amp; 4B are schematic diagrams illustrating the problems associated with the prior art method diagramed in FIGS. 3A-3E; and 
     FIG. 5 is a schematic diagram illustrating the process of the invention for forming a resin film during manufacture of a screen assembly for the cathode ray tube of FIG. 1 to overcome the problems of the prior art process. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. 
     When a screen of a color CRT is manufactured, a resin film  22 ′ such as lacquer is formed between an aluminum thin film  22  and a light-absorptive material  21  together with the phosphor particles R, G and B, so as to enhance the flatness and reflectivity of the aluminum thin film  22 , just before the aluminum thin film  22  is formed. The resin film  22 ′ is burned to volatilize in a frit furnace for sealed-assembling the panel and the funnel with each other, so as to eliminate the possibility of generation of gas after the aluminum thin film  22  is formed, to thereby improve the life of the CRT. 
     According to the present invention, the surface of the resin film  22 ′ is formed uneven as shown in FIG. 5 to enhance the adhesion of the aluminum thin film  22 . Also, the gas generated from the conductive layer  32 , the photo-conductive layer  34  and the resin film  22 ′ during the burning step in a frit furnace for sealed-assembling the panel and the funnel is dispersed and discharged along the gaps between the regional uneven portions over the entire area, to thereby apply a decreased pressure to the aluminum thin film  22 . Therefore, the conductive layer  32 , the photo-conductive layer  34 , and the resin film  22 ′ can be completely volatilized without the upward swelling and unfastening of the aluminum thin film  22 . 
     As an example, the solution for making a resin film of a CRT according to the present invention includes a lacquer solution containing silicon dioxide SiO 2  as inorganic particles of diameters equal to or smaller than 0.5 μm, the quantity of which is 0.01 to 50% by weight of the solid substance of the resin film  22 ′. 
     After forming a predetermined array of the light-absorptive material  21  and three phosphor elements R, G and B by the method of dry-electrophotographically manufacturing the phosphor screen assembly through a series of steps represented in FIGS. 3A to  3 E, the resin film  22 ′ is formed on the inner surface of the light-absorptive material  21  and the three phosphor elements R, G and B with lacquer containing inorganic particles utilizing the above solution for making a resin film of a CRT. Thereafter, an aluminum thin film  22  which functions as a conductive film and a plane of reflection is formed on the resin film  22 ′, and then subjected to a baking step in order to volatilize the volatile ingredient by heat from the conductive layer  32 , the photo-conductive layer  34 , and the resin film  22 ′. The resultants according to the changes of the remaining quantities of the inorganic particles are as follows. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 quantity of SiO 2  (wt %) 
                 number of swollen aluminum 
               
               
                   
                 among inorganic solid 
                 thin 
               
               
                   
                 material 
                 film 22 (number of swollen 
               
               
                   
                 of the resin film 22′ 
                 film/number of test piece) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0.00% 
                 7/10 
               
               
                   
                 0.01% 
                 2/10 
               
               
                   
                 1.00% 
                 0/10 
               
               
                   
                 10.00% 
                 0/10 
               
               
                   
                 50.00% 
                 0/10 
               
               
                   
                   
               
             
          
         
       
     
     As apparent from the above table, although 1 to 10% by weight based on the solid substance is most proper for the quantity of the SiO 2  to be used, only 0.01% by weight can have a good effect. 
     The above method for electro-photographically manufacturing a screen of a CRT utilizing dry-powdered phosphor particles, comprises the steps of: (1) forming a volatile conductive layer on an inner surface of a panel with a conventional organic conductive solution; (2) forming a volatile photo-conductive layer on the volatile conductive layer with the photo-conductive solution of the present invention; (3) charging the volatile photo-conductive layer with uniform electrostatic charges; (4) exposing the volatile photo-conductive layer through a shadow mask to a light source so as to selectively discharge the electrostatic charges from the volatile photo-conductive layer; and (5) developing the photo-conductive layer by charging powdered particles to be attached on one of an exposed area and an unexposed area of the photo-conductive layer. 
     In case of a color CRT, the above steps are repeated for the three different phosphor particles. Moreover, the same process of the above steps can be repeated also for the light-absorptive material or black matrix particles  21  before or after the three different phosphor particles are formed. In this case, the employed panel  12  may have an array of a predetermined pattern of the black matrix particles  21  by a conventional wet slurry method. 
     After the three different phosphor particles and the black matrix particles are formed through the above process, a lacquer film or resin film  22 ′ is formed by a resin-film-applying solution containing silicon dioxide SiO 2  particles as inorganic particles according to the present invention in a lacquering step. Then, an aluminum thin film is formed through an aluminizing step by a conventional method. Thereafter, the faceplate panel  12  is baked in air at a temperature of 425° C., for about 30 minutes to drive off the volatilizable constituents such as the organic solvents from the conductive layer  32 , the photo-conductive layer  34 , the phosphor elements and the lacquer film, thereby forming a screen array of light-absorptive material  21  and three phosphor elements R, G and B as shown in FIG.  2 . 
     In the meantime, though detailed description is omitted, the same effect as above is obtained by not only the above dry method for electro-photographically manufacturing a screen of a CRT but also another process in which the resin film  22 ′ containing the inorganic material according to the present invention is formed after the phosphor elements and the light-absorptive material are formed by the wet slurry method. However, the lacquer containing SiO 2  is more proper for the dry method of electro-photographically manufacturing a screen of a CRT as shown in FIGS. 4A and 4B because the flatness of the surface of the resin film is greater in case of the dry method of electro-photographically manufacturing a screen of a CRT than in case of the wet slurry method. 
     In the CRT manufactured through the above process, silicon dioxide (SiO 2 ) particles remain on the phosphor screen  20 . Further, the above effect is also achieved even when the resin film  22 ′ is formed to contain other inorganic material. However, the silicon dioxide (SiO 2 ) employed in the present invention is more preferable in that, because it has no or white color and thus is transparent, it cause no deterioration of brightness and has no effect on the picture quality even in case it remains. 
     Moreover, in the developing step, instead of being charged by such contact as shown in FIG. 3D, the powdered particles may be charged by a contact with a pipe in the course of being supplied, or charged by a corona discharge just before being sprayed by a spray coater. 
     The fixing step as shown in FIG. 3E may employ a vapor swelling method wherein the fixing is performed by a contact with a solvent vapor such as acetone and methyl isobutyl ketone, or a spraying method wherein an electrostatic solution spray gun sprays a mixture of more than two kinds among methyl isobutyl ketone, TCE, toluene, and xylene of the petroleum group on the developed powdered-particles of red, green, and blue. Otherwise, the fixing step may be omitted partly or totally. 
     As apparent from the above description, by the construction and the function of the solution for making a resin film, the method for manufacturing a screen of a CRT using the solution and the CRT manufactured by the method according to the present invention, the adhesion of the aluminum thin film  22  is greatly improved, and as well the conductive layer  32 , the photo-conductive layer  34 , and the resin film  22 ′ can be completely volatilized without the upward swelling and unfastening of the aluminum thin film  22  during the burning step in a frit furnace for sealed-assembling the panel and the funnel, so that the plane reflectivity of the aluminum thin film  22  is improved and thus the picture quality of the CRT is greatly improved. 
     While the present invention has been particularly shown and described with reference to the particular embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be effected therein without departing from the spirit and scope of the invention as defined by the appended claims.