Patent Publication Number: US-2003232129-A1

Title: Method of manufacturing a color filter cathode ray tube (CRT)

Description:
BACKGROUND OF THE INVENTION  
       [0001] The invention relates to a color cathode ray tube (CRT) and, more particularly to the manufacturing of a luminescent screen assembly having at least one color filter.  
       DESCRIPTION OF THE BACKGROUND ART  
       [0002] A color cathode ray tube (CRT) typically includes an electron gun an aperture mask, and a screen. The aperture mask is interposed between the electron gun and the screen. The screen is located on an inner surface of a faceplate of the CRT tube. The aperture mask functions to direct electron beams generated in the electron gun toward appropriate color-emitting phosphors on the screen of the CRT tube.  
       [0003] The screen may be a luminescent screen. Luminescent screens typically comprise an array of three different color-emitting phosphors (e.g., green, blue and red) formed thereon. Each of the color emitting phosphors is separated from another by a matrix line. The matrix lines are typically formed of a light absorbing black, inert material.  
       [0004] In order to enhance the color contrast of the luminescent screen, a pigment layer, or color filter, may be formed between the faceplate panel and the color-emitting phosphor. The color filter typically has a color that corresponds to the color of the color-emitting phosphor formed thereon (e.g., a red-emitting phosphor is formed on a red pigmented filter). The color filter transmits light that is within the emission spectral region of the phosphor formed thereon and absorbs ambient light in other spectral regions, providing a gain in color contrast.  
       [0005] The color filters are typically formed using a subtractive process in which the color filter layer is deposited on the luminescent screen, and, in a subsequent development process, select portions of the filter layer are removed, such that a color filter is formed only on select portions of the faceplate panel. Unfortunately, color filters formed using such a process may adhere to the faceplate panel with sufficient tenacity on portions not intended to be covered therewith causing the faceplate panel to become contaminated. Color filter contamination reduces the contrast of the luminescent screen.  
       [0006] Thus, a need exists for a method of forming a color filter cathode ray tube (CRT) that overcomes the above drawbacks.  
       SUMMARY OF THE INVENTION  
       [0007] The present invention relates to a method of manufacturing a color filter luminescent screen assembly for a cathode ray tube (CRT). The luminescent screen assembly is formed on an interior surface of a faceplate panel of the CRT tube. The luminescent screen assembly includes a patterned light-absorbing matrix that defines a first set of fields, a second set of fields, and a third set of fields corresponding to one of a blue region, a green region and a red region.  
       [0008] A blocking layer is applied over the second set of fields and the third set of fields. The blocking layer may comprise a photosensitive material and optionally one or more filler materials. The one or more filler materials may function to increase the porosity of the blocking layer. A pigment layer is then applied to the first set of fields to form a color filter. The pigment layer may be, for example, either a red pigment layer or a blue pigment layer. After the color filter is formed, the blocking layer is removed from the second set of fields and the third set of fields. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009] The invention will now be described in greater detail, with relation to the accompanying drawings, in which:  
     [0010]FIG. 1 is a plan view, partly in axial section, of a color cathode ray tube (CRT) made according to embodiments of the present invention;  
     [0011]FIG. 2 is a section of the faceplate panel of the CRT of FIG. 1, showing a luminescent screen assembly;  
     [0012]FIG. 3 is a block diagram comprising a flow chart of the manufacturing process of the screen assembly of FIG. 2;  
     [0013]FIG. 4 depicts views of the interior surface of the faceplate panel of a luminescent screen assembly during formation of one color filter;  
     [0014]FIG. 5 depicts views of the interior surface of the faceplate panel of a luminescent screen assembly during formation of a second color filter. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0015]FIG. 1 shows a conventional color cathode ray tube (CRT)  10  having a glass envelope  11  comprising a faceplate panel  12  and a tubular neck  14  connected by a funnel  15 . The funnel  15  has an internal conductive coating (not shown) that is in contact with, and extends from, an anode button  16  to the neck  14 .  
     [0016] The faceplate panel  12  comprises a viewing surface  18  and a peripheral flange or sidewall  20  that is sealed to the funnel  15  by a glass frit  21 . A three-color luminescent phosphor screen  22  is carried on the inner surface of the faceplate panel  12 . The screen  22 , shown in cross-section in FIG. 2, is a line screen which includes a multiplicity of screen elements comprised of red-emitting, green-emitting, and blue-emitting phosphor stripes R, G, and B, respectively, arranged in triads, each triad including a phosphor line of each of the three colors. The R, G, B, phosphor stripes extend in a direction that is generally normal to the plane in which the electron beams are generated. At least one of the R and B phosphor stripes are formed on color filters  43 . The color filters  43  each comprise a pigment that corresponds to the color of the phosphor stripe formed thereon.  
     [0017] A light-absorbing matrix  23 , shown in FIG. 2, separates each of the phosphor lines. A thin conductive layer  24 , preferably of aluminum, overlies the screen  22  and provides means for applying a uniform first anode potential to the screen  22 , as well as for reflecting light, emitted from the phosphor elements, through the viewing surface  18 . The screen  22  and the overlying aluminum layer  24  comprise a screen assembly.  
     [0018] A multi-aperture color selection electrode, or shadow mask  25  (shown in FIG. 1) is removably mounted, by conventional means, within the faceplate panel  12 , in a predetermined spaced relation to the screen  22 .  
     [0019] An electron gun  26 , shown schematically by the dashed lines in FIG. 1, is centrally mounted within the neck  14 , to generate three inline electron beams  28 , a center and two side or outer beams, along convergent paths through the shadow mask  25  to the screen  22 . The inline direction of the beams  28  is approximately normal to the plane of the paper.  
     [0020] The CRT of FIG. 1 is designed to be used with an external magnetic deflection yoke, such as a yoke  30 , shown in the neighborhood of the funnel-to-neck junction. When activated, the yoke  30  subjects the three beams  28  to magnetic fields that cause the beams to scan a horizontal and vertical rectangular raster across the screen  22 .  
     [0021] The screen  22  is manufactured according to the process steps represented schematically in FIG. 3. Initially, the faceplate panel  12  is cleaned, as indicated by reference numeral  300 , by washing it with a caustic solution, rinsing it in water, etching it with buffered hydrofluoric acid and rinsing it again with water, as is known in the art.  
     [0022] The interior surface of the faceplate panel  12  is then provided with the light-absorbing matrix  23 , as indicated by reference numeral  302 , preferably using a wet matrix process in a manner described in U.S. Pat. Nos. 3,558,310, issued Jan. 26, 1971 to Mayaud, 6,013,400 issued Jan. 11, 2000 to LaPeruta et al., or 6,037,086 issued Mar. 14, 2000 to Gorog et al.  
     [0023] The light-absorbing matrix  23  is uniformly provided over the interior viewing surface of faceplate panel  12 . For a faceplate panel  12  having a diagonal dimension of about 68 cm (27 inches), the openings  21  formed in the layer of light absorbing matrix  23  can have a width in a range of about 0.075 mm to about 0.25 mm, and the opaque matrix lines can have a width in a range of about 0.075 mm to about 0.30 mm. Referring to FIG. 4A, the light-absorbing matrix  23  defines three sets of fields; a first set of fields  40 , a second set of fields  43 , and a third set of fields  44 .  
     [0024] As indicated by reference numeral  304  in FIG. 3, as well as FIG. 4B, a blocking layer  46  is deposited on the interior surface of the faceplate panel  12 . The blocking layer  46  may include a photosensitive material. The photosensitive material may comprise, for example, an aqueous solution of sodium dichromate and a polymer such as polyvinyl alcohol. The blocking layer  46  may be formed on the faceplate panel  12  by spin coating the aqueous solution of the polymer and dichromate thereon.  
     [0025] In addition to the photosensitive material, the blocking layer  46  may also comprise a filler material that may function to increase the porosity thereof. The filler material may comprise for example, a powder having a particle size less than about 10 microns and preferably within a range of about 7 microns to about 8 microns. Suitable filler material may include, for example, alumina or zinc sulfide.  
     [0026] Addition of the filler material to the blocking layer allows the subsequent development of the blocking layer  46  to be performed using milder conditions. The use of milder development conditions may reduce the risk for damaging portions of the light-absorbing matrix  23 .  
     [0027] Referring to reference numeral  306  in FIG. 3, the blocking layer  46  is irradiated using, for example, ultraviolet radiation, through the shadow mask  25  to cross-link the photosensitive material in the second set of fields  42  and the third set of fields  44 . Cross-linking the blocking layer  46  in the second set of fields  42  and the third set of fields  44  hardens the photosensitive material in such fields.  
     [0028] The irradiated blocking layer  46  is then developed, as indicated by reference numeral  308  in FIG. 3, as well as FIG. 4C. The blocking layer  46  may be developed using, for example, deionized water. After development, the blocking layer  46  is removed over the first set of fields  40 , while remaining on the faceplate panel  12  over the second set of fields  42  and the third set of fields  44 .  
     [0029] Referring to reference numeral  310  in FIG. 3 as well as FIG. 4D, a first pigment is applied to the first set of fields  40 . The first pigment may be applied from a first aqueous pigment suspension that may comprise, for example, the first pigment and one or more surface-active agents.  
     [0030] The first pigment suspension may further comprise at least one non-pigmented oxide particles. The at least one non-pigmented oxide particles may comprise a material, such as, for example, silica, alumina, or combinations thereof. The at least one non-pigmented oxide particles should have a size less than that of the pigment. Preferably, the average size of the at least one non-pigmented oxide particles should be less than about 50 nanometers. The at least one non-pigmented oxide particle is believed to enhance the adhesion of the pigment to the faceplate panel. The at least one non-pigmented oxide particle may be present in a concentration of about 5% to about 10% by weight with respect to the concentration the first pigment.  
     [0031] The first pigment may be, for example, a red pigment. Suitable red pigments may include, for example, a daipyroxide red pigment TM-3875, commercially available from Daicolor-Pope, Inc. of Paterson, N.J. Another suitable red pigment may include, for example, R2899 red pigment, commercially available from Elementis Pigments Co. of Fairview Heights, Ill., among other red pigments. Alternatively, the first pigment may be a blue pigment, such as a daipyroxide blue pigment TM-3490E, commercially available from Daicolor-Pope, Inc. of Paterson, N.J. Another suitable blue pigment may include, for example, EX 1041 blue pigment, commercially available from Shepherd Color Co. of Cincinnati, Ohio, among other blue pigments.  
     [0032] The pigments may be milled using a ball milling process in which the pigment is dispersed along with one or more surfactants in an aqueous suspension. The red pigments may be ball milled using for example, {fraction (1/16)}″ zirconium oxide (ZrO 2 ) balls for at least about 18 hours to about 92 hours. The blue pigments may be ball milled using for example, {fraction (1/16)}″ zirconium oxide (ZrO 2 ) balls for at least about 61 hours to about 90 hours.  
     [0033] The one or more surface-active agents may include, for example organic and polymeric compounds that may optionally adopt an electric charge in aqueous solution. The surface-active agent may comprise, anionic, non-ionic, cationic, and/or amphoteric materials. The surface-active agent may be used for various functions such as improving the homogeneity of the pigment in the aqueous pigment suspension, improved colloidal stability and improved wetting of the faceplate panel, among other functions. Examples of suitable surface-active agents include, various polymeric dispersants such as, for example, DISPEX N-40V and A-40 polymeric dispersants (commercially available from Ciba Specialty Chemicals of High Point, N.C.) as well as block copolymer surface active agents such as Pluronic Series (ethoxypropoxy co-polymers) L-62, commercially available from BASF Corp. of Germany, DAXAD 15 or 19, commercially available from Hampshire Chemical Company of Nashua, N.H., and carboxymethyl cellulose (CMC), commercially available from Yixing Tongda Chemical Co. Of China.  
     [0034] The first aqueous pigment suspension may be applied to the faceplate panel by, for example, spin coating in order to form a first color filter layer  60  in the first set of fields  40  of the faceplate panel  12 . After spin coating, the first color filter layer  60  may be heated to a temperature in a range from about 55° C. to about 90° C. to provide increased adhesion of the first color filter  60  to the first set of fields  40  of the faceplate panel  12 .  
     [0035] Referring to reference numeral  312  as well as FIG. 4E, the first color filter layer  60  is developed by applying an oxidizer to the first blocking layer  46 . Suitable oxidizers may include, for example, periodic acid and hydrogen peroxide, among others. Water may than be applied to the faceplate panel  12  in order to remove the blocking layer  46  as well as the first color filter layer  60  over the second set of fields  42  and the third set of fields  44 , leaving the first color filter  60  remaining in the first set of fields  40 .  
     [0036] In one embodiment, either of a red filter or a blue filter is formed using the process described above with reference numerals  302  through  312  in FIG. 3. Thereafter, referring to FIG. 4F, the faceplate panel  12  may be screened with pigmented green phosphors  72 , non-pigmented blue phosphors  74  and non-pigmented red phosphors  76 , preferably, using a screening process in a manner described in U.S. Pat. Nos. 5,370,952, issued Dec. 6, 1994 to Datta et al., 5,554,468, issued Sep. 10, 1996 to Datta et al., 5,807,435 issued Sep. 15, 1998 to Poliniak et al., or 5,474,866 issued Dec. 12, 1995 to Ritt et al.  
     [0037] Alternatively, after the first color filter  60  is formed in the first set of fields  40 , a second color filter may be formed in the second set of fields  42 . For example, after a red color filter is formed, a blue color filter may be formed on the faceplate panel  12 . For such an embodiment, the second color filter (blue color filter) may be formed on the faceplate panel by repeating the process steps described above with respect to reference numerals  302  through  312  in FIG. 3.  
     [0038] Referring to FIG. 5A, a second color filter, for example, a blue color filter may be formed by applying a second aqueous pigment suspension to the faceplate panel. The second aqueous pigment suspension may be applied to the faceplate panel by, for example, spin coating in order to form a second color filter layer  62  on the faceplate panel  12 . The spin coated color filter layer may be heated to a temperature within a range of about 50° C. to about 65° C.  
     [0039] After the second color filter layer  62  is applied to the faceplate panel  12 , a phosphor layer  82  may be formed thereon by, for example, spin coating. The spin coated phosphor layer  82  may be heated to a temperature within a range of about 50° C. to about 55° C.  
     [0040] The phosphor layer  82  is irradiated using, for example, ultraviolet radiation, through the shadow mask  25  to cross-link the phosphor layer  82  formed over the second color filter layer  62  in the second set of fields  42 . Cross-linking the phosphor layer  82  over the second color filter layer  62  in the second set of fields  42  hardens the phosphor material in such regions.  
     [0041] The irradiated phosphor layer  82  is then developed as shown in FIG. 5B. The phosphor layer  82  may be developed using, for example, deionized water. After development, the phosphor layer  82  and the second color filter layer  62  are both removed in the first set of fields  40  over the first color filter  60  and in the third set of fields  44 , while remaining on the faceplate panel  12  in the second set of fields  42 .  
     [0042] Referring to FIG. 5C, the faceplate panel  12  may be screened with pigmented green phosphors  84  and non-pigmented red phosphors  86 , preferably, using a screening process in a manner described in U.S. Pat. Nos. 5,370,952, issued Dec. 6, 1994 to Datta et al., 5,554,468, issued Sep. 10, 1996 to Datta et al., 5,807,435 issued Sep. 15, 1998 to Poliniak et al., or 5,474,866 issued Dec. 12, 1995 to Ritt et al.  
     [0043] In an exemplary luminescent screen assembly fabrication process, 20 inch faceplate panels having matrix lines formed thereon were soaked in warm water for 30 minutes, sprayed with water at 30 psi for 10 seconds and dried. The faceplate panels were then cooled to 27° C. A solution of 275 grams of water, 160 grams of 10% polyvinyl alcohol, and 21 grams of 10% sodium dichromate was prepared, and 120 milliliters of this solution was applied to the faceplate panels. The faceplate panels were spun at 190 rpm for 50 seconds, heated to 53° C. and cooled to 34° C. to form a photosensitive layer on each of the panels.  
     [0044] Each of the faceplate panels was irradiated using an ultraviolet source (0.4 milliwatts per square centimeter) for 40 seconds through a corresponding shadow mask, to cross-link the photosensitive material in the red fields and the green fields. The irradiated faceplate panels were developed using 43° C. water at 20 psi for 20 seconds and then dried. This resulted in the formation of a blocking layer in the red fields and the green fields, and the removal of the blocking layer in the blue fields.  
     [0045] A blue pigment concentrate was prepared by placing 190 grams of water, 7.5 grams of a polymeric dispersant, DISPEX N-40V (commercially available from Ciba Specialty Chemicals of High Point, N.C.) and 50 grams of TM-3480E Daipyroxide blue pigment (commercially available from Daicolor-Pope, Inc. of Paterson, N.J.) in a ball mill and milling the mixture using {fraction (1/16)}″ zirconium oxide balls for 62 hours. The average particle size of the pigment in the milled concentrate was 112 nanometers (nm) and the concentration of the red pigment in the milled concentrate was about 20 wt %.  
     [0046] Four batches of a blue pigment suspension, each having a different concentration of the blue pigment were prepared. Varying amounts of the pigment concentrate were mixed with 3.85-7.12 grams of a collodial silica, SNOWTEX XS (20% active silica, available from Nissan Chemical Industries of Tokyo, Japan), 2.5 grams of a 5% Pluronic Series (ethoxypropoxy co-polymer) L-62 solution (commercially available from BASF Corp. of Germany), and varying amounts of deionized water were mixed for 15 minutes to form the four blue pigment suspensions. The amount of deionized water added to each batch was sufficient to form individual blue pigment suspensions having concentrations of 10.0 weight % pigment, 12.5 weight % pigment, 14.0 weight % pigment and 18.7 weight % pigment.  
     [0047] Each blue pigment suspension was applied to one of the faceplate panels. The blue pigment suspension was applied to each faceplate panel at 28° C. and thereafter the panel was spun at 100 rpm for 20 seconds, heated to 65° C. and cooled to 34° C. to form a blue color filter layer on each faceplate panel.  
     [0048] Each of the blue color filter layers was developed by reheating the faceplate to 55° C. and applying 450 ml of 0.03-0.05% periodic acid solution to the faceplate. The periodic acid solution was swirled around the panel surface for 90 seconds. Thereafter, each faceplate panel was sprayed with 43° C. water at 40 psi for 15 seconds. This development step removed the blocking layer with the blue color filter layer thereon from both the red fields and the green fields, leaving a blue color filter in the blue fields.  
     [0049] Each of the faceplate panels with a blue color filter thereon was screened with standard green phosphors, non-pigmented blue phosphors and non-pigmented red phosphors.  
     [0050] Brightness contrast performance was measured for each of the four panels prepared above and compared to a luminescent screen assembly formed using a conventional slurry screening process, containing conventional pigmented red and blue phosphors but without the color filter layers. The brightness contrast performance for the screen assemblies prepared above exhibited enhancements of +8% to +11% compared to conventional tubes of the same type without color filter layers. The Contrast Ratio (CR) gain for the screen assemblies prepared above varied from +10% to +15% compared to conventional tubes of the same type without color filter layers. The tube face reflectance for the screen assemblies prepared above decreased between 15% to 22% compared to conventional tubes of the same type without color filter layers.