EP1774558A1

EP1774558A1 - Cathode ray tube having an enhanced internal neutral density filter

Info

Publication number: EP1774558A1
Application number: EP04757423A
Authority: EP
Inventors: Farzad Parsapour; Bhanumurthy Venkatrama Subrahmanya Gunturi; Steven Anthony Colbert; Brian Thomas Collins
Original assignee: Thomson Licensing SAS
Current assignee: Thomson Licensing SAS
Priority date: 2004-08-05
Filing date: 2004-08-05
Publication date: 2007-04-18
Also published as: WO2006022692A1; EP1774558A4; CN101040363A

Abstract

A composition and method of forming an enhanced internal neutral density filter on a luminescent screen assembly of a cathode ray tube (CRT) is disclosed. The luminescent screen assembly is formed on an interior surface of a glass faceplate panel of the CRT tube. The luminescent screen assembly includes a patterned light-absorbing matrix that defines three sets of fields corresponding to one of a blue region, a green region and a red region. An enhanced internal neutral density filter is formed on the light-absorbing matrix. An array of blue, green and red color phosphors is formed on the internal neutral density filter corresponding to one of the blue region, the green region and the red region defined in the light-absorbing matrix. The enhanced internal neutral density filter has a composition including a red pigment, a blue pigment, one or more surface active agents and at least one non-pigmented oxide particle. The enhanced internal neutral density filter preferably has the surface active agent in the amount of about 0.7 to 1.2 weight % based upon the total mass in the filter.

Description

CATHODE RAY TUBE HAVING AN ENHANCED INTERNAL NEUTRAL DENSITY FILTER

Related Application

This application is a continuation-in-part of U. S. Patent application Serial No. 10/375,416 (Atty Docket PUO3OO55), filed on February 27, 2003, the entirety of which is incorporated herein by reference.

Field of the Invention

[0001] This invention relates to a color cathode ray tube (CRT) and, more particularly to a luminescent screen assembly including an enhanced internal neutral density filter.

Background of the Invention [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 have 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] The faceplate of the CRT tube typically comprises a glass panel having a low transmission coefficient. However, the use of a glass panel with a low transmission coefficient may cause the CRT tube to exhibit a "Halo" effect, particularly tubes with a flat face and formed aperture mask. As a result, the perimeter of the faceplate of the CRT undesirably appears darker than the center, when the tube is off. The "Halo" effect can be reduced by lowering the transmission of the panel glass further; however, insufficient tube brightness in the on-state would result. [0005] Thus, a need exists for a luminescent screen that overcomes the above drawbacks.

Summary of the Invention

[0006] The present invention relates to a composition and method of forming an internal neutral density filter on a luminescent screen assembly of a cathode ray tube (CRT). The luminescent screen assembly is formed on an interior surface of a glass faceplate panel of the CRT tube. The luminescent screen assembly includes a patterned light-absorbing matrix that defines three sets of fields corresponding to one of a blue region, a green region and a red region. An enhanced internal neutral density filter is formed on the light-absorbing matrix. An array of blue, green and red color phosphors are then formed on the enhanced internal neutral density filter corresponding to one of the blue region, the green region and the red region defined in the light-absorbing matrix.

[0007] The enhanced internal neutral density filter has a composition including a red pigment, a blue pigment, one or more surface active agents and at least one non-pigmented oxide particle. The enhanced internal neutral density filter described herein provides for improved phosphor adherence. In view of the improved adherence, it is possible to reduce phosphor exposure time as compared to exposures of other internal neutral density filters. In addition, the enhanced internal neutral density filter functions to minimize the "Halo" effect of the CRT tube as well as to maintain the brightness contrast performance of the CRT tube.

Brief Description of the Drawings [0008] The invention will now be described in greater detail, with relation to the accompanying drawings, in which:

[0009] FIG. 1 is a side view, partly in axial section, of a color cathode ray tube (CRT) made according to embodiments of the present invention; [0010] FIG. 2 is a section of the faceplate panel of the CRT of FIG. 1 , showing a luminescent screen assembly including an internal neutral density filter; [0011] FIG. 3 is a block diagram comprising a flow chart of the manufacturing process for the screen assembly of FIG. 2;

[0012] FIGS. 4A-4C depict views of the interior surface of the faceplate panel luminescent screen assembly during internal neutral density filter formation.

Detailed Description of the Invention

[0013] 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.

[0014] 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 and B phosphor stripes extend in a direction that is generally normal to the plane in which the electron beams are generated. The R, G and B phosphor stripes are formed on an internal neutral density filter 40. The enhanced internal neutral density filter 40 - A - comprises a blend of red pigment, blue pigment, one or more surface active agents and at least one non-pigmented oxide particle.

[0015] A light-absorbing matrix 23, formed beneath the enhanced internal neutral density filter 40, separates each of the phosphor lines. A thin conductive layer 24 (shown in FIG. 1), 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. [0016] 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.

[0017] 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.

[0018] The CRT of FIG. 1, is designed to be used with an external magnetic deflection yoke, such as 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. [0019] 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 preferably 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. The faceplate panel 12 is preferably formed of a glass having a nominal glass transmission of about 57% (for a reference thickness of 10.16 mm) at wavelengths of 450 nm to 650 nm. The combination of the glass with the internal neutral density filter provides the desired transmission and brightness contrast performance while avoiding the "Halo" effect. [0020] The interior surface of the faceplate panel 12 is then provided with a 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 January 26, 1971 to

Mayaud, 6,013,400, issued January 11, 2000 to LaPeruta et al., or 6,037,086 issued March 14, 2000 to Gorog et al.

[0021] 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) and a flat face, the openings 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 red field, R, a green field, G, and a blue field, B. [0022] Referring to reference numeral 304 in FIG. 3 as well as FIG. 4B, an enhanced internal neutral density filter 40 is applied over the light-absorbing matrix 23 on the interior surface of the faceplate panel 12. The enhanced internal neutral density filter 40 may be applied from an aqueous suspension that may comprise blue pigment, red pigment, one or more surface active agents and at least one non-pigmented oxide particle. [0023] The enhanced internal neutral density filter functions to improve the brightness- contrast performance of the screen as well as to minimize the "Halo" effect of the CRT tube. The particles comprising the enhanced internal neutral density filter should have an average particle size in the range of about 30 to about 140 nm (nanometers) in order to reduce excess scattering of phosphor emission from the CRT screen. The particle size also contributes to the formation of uniform filter layers without discontinuities that may result in a decrease in CRT performance.

[0024] The enhanced internal neutral density filter should include a total pigment weight % of the blue pigment and the red pigment within a range of about 4 weight % to about 12 weight %. The total pigment weight % should include blue pigment within a range of about 3.6 weight % to about 11.6 weight % and red pigment within a range of about 0.12 weight % to about 1.2 weight %. The above-mentioned range for the total pigment content reduces the reflection of ambient light by the faceplate panel when combined with glass of appropriate transmission to a desired level. Varying the ratio of the blue pigment to the red pigment provides the desired optical response of the filter. An effective ratio range of the blue pigment to red pigment has been found to be about 9: 1 to about 32: 1. Most preferably, the effective ratio of blue pigment to red pigment is about 95:5. The thickness for the internal neutral density filter should be within a range of about 1-2 micrometers. [0025] The blue pigment, for example, may be cobalt aluminate pigment such as CoOAl₂O₃ daipyroxide blue pigment TM-3490E, commercially available from Daicolor-

Pope, Inc. of Patterson, NJ. Another suitable blue pigment may include for example, EX1041 blue pigment, commercially available from Shepherd Color Co. of Cincinnati, Ohio, among other pigments. [0026] The blue pigment 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 blue pigment may be ball milled using for example, 1/16 inch ZrO₂ balls for at least about 19 hours up to about 72 hours. Alternatively, 1/32 inch ZrO₂ balls can be used in the process. Preferably, the blue pigment may be ball milled for about 62 hours. The average particle size for the blue pigment was about 135 nm (nanometers) after ball milling for about 62 hours. [0027] The red pigment, for example, may be an iron oxide pigment such as Fe₂O₃ daipyroxide red pigment TM-3875, commercially available from Daicolor-Pope, Inc. of Patterson, NJ. Another suitable red pigment may include, for example, R2899 red pigment, commercially available from Elementis Pigments Co. of Fairview Heights, Illinois, among other red pigments.

[0028] The red pigment 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 pigment may be ball milled using for example, 1/16 inch ZrO₂ balls for at least about 15 hours up to about 90 hours. Alternatively, 1/32 inch ZrO₂ balls can be used in the process. Preferably, the red pigment may be ball milled for about 48 hours. The average particle size for the red pigment was about 90 nm after ball milling for about 48 hours.

[0029] The at least one non-pigmented oxide particle may comprise a material, such as, for example, silica, alumina, or combinations thereof. The at least one non-pigmented oxide particle should have a size comparable to the size of the pigment. Preferably the average size of the at least one non-pigmented oxide particles should be less than about 30 nm. Most preferably, the non-pigmented oxide should have an average particle size in the range of about 8 nanometers. The at least one non-pigmented oxide particle is believed to enhance the adhesion of the filter layer to the faceplate panel as well as enhance the wetting of the glass substrate. 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 total pigment mass. Most preferably, the non-pigmented oxide particle may be present in a concentration of about 7% by weight with respect to the total pigment mass.

[0030] The internal neutral density filter may also include one or more surface-active agents such as, 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, stabilization of nanoparticles, improved wetting of the faceplate panel, as well as the reduction of phosphor exposure time, 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, North Carolina) as well as block copolymer surface active agents such as Pluronic Series (ethoxypropoxy co-polymers) L-62, commercially available from Hampshire Chemical Company of Nashua, New Hampshire, and carboxymethyl cellulose (CMC) commercially available from Yixing Tongda Chemical Co. of China. The surface active agent can be added to each of the pigments by themselves or to a mixture of the two pigments in the suspension. Preferably, the surface active agent is used in the amount of about 0.7 to about 1.2 weight % based upon the total mass. [0031] The aqueous suspension used to form the enhanced internal neutral density filter may be applied to the faceplate panel by, for example, spin coating in order to form the internal neutral density filter 40 over the light-absorbing matrix 23 on the interior surface of the faceplate panel 12. The spin-coated internal neutral density filter 40 may be heated to a temperature within a range from about 40 ⁰C to about 55 ⁰C to provide increased adhesion of the internal neutral density filter 40 to the faceplate panel 12. [0032] Referring to reference numeral 306 in FIG. 3 as well as FIG. 4C, the faceplate panel 12 is then screened with green phosphors 42 with exposure for about 23 seconds, blue phosphors 44 for about 20 seconds, and red phosphors 46 for about 23 seconds, preferably using a screening process in a manner known in the art. The screening process is for example described in U. S. Patent Nos. 3,313,643 and 3,406,068, the contents of which are hereby incorporated into this specification. The panels were developed with de-ionized water at 30 psi for 30 seconds.

[0033] With the use of the enhanced internal neutral density filter described herein, phosphor line adherence was increased at constant exposure energy as compared to other internal neutral density filters. As a result, the phosphor exposure time was reduced significantly as compared to exposure times used for other internal neutral density filters. In one instance, the exposure times were reduced by as much as 49%.

[0034] Phosphor adherence to the internal neutral density filter may be further improved by modifying the process parameters and/or changing the development parameters. For example, an internal neutral density filter coated faceplate panel may use a higher slurry drying temperature, a lower developer pressure and/or a shorter development time than a standard uncoated faceplate panel when the phosphors are applied thereto.

[0035] If desired, a pre-coat layer may be applied over the internal neutral density filter prior to screening the phosphors. The pre-coat layer should form an interface on the internal neutral density filter to which the phosphor layer can further adhere. The pre-coat layer may include for example, polyvinyl alcohol (PVA) as well as functionalized silanes, silanols and siloxanes.

[0036] By way of example, two aqueous pigment blends to be used for the internal neutral density filter were prepared. The aqueous pigment blends comprised a blue pigment suspension, a red pigment suspension, surface active agents, and a silica suspension. The first aqueous pigment blend prepared is described in further detail in U. S. Patent Application

Serial No. 10/354,308 (Attorney Docket PU030046), filed January 30, 2003, and used herein for comparative purposes.

[0037] The blue pigment suspension for the first aqueous pigment blend was prepared by placing 190 grams of water, 8 grams of a polymeric dispersant DISPEX N-40 (commercially available from Ciba Specialty Chemicals of High Point, North Carolina) and 50 grams of TM- 3480 Daipyroxide blue pigment (commercially available from Daicolor-Pope, Inc. of Patterson, New Jersey) in a ball mill. The blue pigment suspension was ball milled using 1/16-inch zirconium oxide balls for 66 hours to form a blue pigment concentrate. The average particle size of the blue pigment in the suspension was 120 nm after ball milling. The recovered blue pigment suspension had a solid content of about 20 weight % which was diluted to about 14 weight % with de-ionized water.

[0038] The red pigment suspension for the first aqueous blend was prepared by placing 190 grams of water, 8 grams of a polymeric dispersant DISPEX A-40 (commercially available from Ciba Specialty Chemicals of High Point, North Carolina) and 50 grams of TM-3875

Daipyroxide red pigment (commercially available from Daicolor-Pope, Inc. of Patterson, New Jersey) in a ball mill. The red pigment suspension was ball milled using 1/16-inch zirconium oxide balls for 19 hours to form a red pigment concentrate. The average particle size of the red pigment in the suspension was 85 nm after ball milling. The recovered red pigment suspension had a solid content of about 20 weight % which was diluted to about 10 weight % with de-ionized water.

[0039] The silica suspension utilized in the first aqueous blend was SNOWTEX S (commercially available from Nissan Chemical Industries of Tokyo, Japan). The silica suspension had a solid content of about 30 weight % and an average particle size of 7-9 nm. [0040] A 1000 gram first aqueous pigment blend containing 611 grams of the blue pigment suspension at 14 weight %, 45 grams of the red pigment suspension at 10 weight %, and 20.6 grams of the silica suspension, with the remaining mass added as de-ionized water was prepared. [0041] In accordance with the teachings of this application, a second aqueous pigment blend was prepared. The blue pigment suspension for the second aqueous pigment blend was prepared by placing 190 grams of water, 5 grams of a polymeric dispersant DISPEX N-40 (commercially available from Ciba Specialty Chemicals of High Point, North Carolina) and 50 grams of TM-3490E Daipyroxide blue pigment (commercially available from Daicolor- Pope, Inc. of Patterson, New Jersey) in a ball mill. The blue pigment suspension was ball milled using 1/16-inch zirconium oxide balls for 62 hours to form a second blue pigment concentrate. The average particle size of the blue pigment in the suspension was about 135 nm after ball milling for 62 hours. The recovered blue pigment suspension had a solid content of about 20 weight % which was diluted to about 14 weight % with de-ionized water. [0042] The red pigment suspension for the second aqueous blend was prepared by placing 190 grams of water, 5 grams of a polymeric dispersant DISPEX A-40 (commercially available from Ciba Specialty Chemicals of High Point, North Carolina) and 50 grams of TM-3875 Daipyroxide red pigment (commercially available from Daicolor-Pope, Inc. of Patterson, New Jersey) in a ball mill. The red pigment suspension was ball milled using 1/16-inch zirconium oxide balls for 48 hours to form a red pigment concentrate. The average particle size of the red pigment in the suspension was 90 nm after ball milling. The recovered red pigment suspension had a solid content of about 20 weight % which was diluted to about 10 weight % with de-ionized water.

[0043] The silica suspension utilized in the second aqueous blend was SNOWTEX S (commercially available from Nissan Chemical Industries of Tokyo, Japan). The silica suspension had a solid content of about 30 weight % and an average particle size of 7-9 nm. [0044] A 1000 gram second aqueous pigment blend containing 271.4 grams of the blue pigment suspension at 14 weight %, 20.0 grams of the red pigment suspension at 10 weight % and 9.3 grams of the silica suspension, with the remaining mass added as de-ionized water was prepared. [0045] Each of the first and second aqueous pigment blends was mixed for about 10 minutes and thereafter applied to a glass panel having a nominal glass transmission of about 57% (for a reference thickness of 10.16 mm) at wavelengths of 450 nm to 650 nm, such as the faceplate panel 12, described above with reference to FIG. 4B. The panel had a light- absorbing matrix layer, similar to the light-absorbing matrix 23, described above with respect to FIG. 4A. Each aqueous pigment blend was applied to the faceplate panel at a temperature of about 30 ⁰C and then the coated panel was spun at a speed of about 80 rpm at an angle of 95° for about 20 seconds. Each of the faceplate panel was then heated to 65 ⁰C and cooled to 34 ⁰C.

[0046] The second aqueous pigment blend had enhanced particle -particle interaction and adherence with lower levels of surface active agents being used. In these examples, there was about a 25 to about 50% reduction in the amount of the surface active agent used in the second aqueous pigment blend as compared to the first aqueous pigment blend. Even with this reduction in the surface active agent, enhanced particle-particle interaction was obtained. In addition, the reduction in surface active agent resulted in significantly higher phosphor to internal density filter layer adherence at constant exposure energy. Consequently, it is possible to reduce the phosphor exposure times with the use of the enhanced internal neutral density filter. In these examples, there was a 49% reduction in exposure times. [0047] Results for the two aqueous pigment blends are summarized below in Table 1.

[0048] Alternatively, the aqueous pigment blends may be applied by adjusting the application parameters, such as for example, the speed of rotation and the tilt angle of the faceplate panel during rotation.

[0049] The foregoing illustrates some of the possibilities for practicing the invention. Many other embodiments are possible within the scope and spirit of the invention. It is, therefore, intended that the foregoing description be regarded as illustrative rather than limiting, and that the scope of the invention is given by the appended claims together with their full range of equivalents.

Claims

What is Claimed is:

1. An aqueous suspension for use as an enhanced internal neutral density filter on a luminescent screen assembly of a cathode-ray tube, comprising: at least two pigments, wherein the at least two pigments are present in a concentration within a range of about 4 weight % to about 12 weight %; one or more surface agents, and at least one non-pigmented oxide particle.

2. The aqueous suspension of claim 1 wherein the at least two pigments include a blue pigment and a red pigment.

3. The aqueous suspension of claim 2 wherein the ratio of the blue pigment to red pigment is within a range of about 9: 1 to about 32: 1.

4. The aqueous suspension of claim 2 wherein the blue pigment comprises cobalt aluminate.

5. The aqueous suspension of claim 2 wherein the red pigment comprises iron oxide.

6. The aqueous suspension of claim 1 wherein the at least two pigments have an average particle size in the range of about 30 of about 100 nanometers.

7. The aqueous suspension of claim 1 wherein the surface active agent is present in the amount of about 0.70 to about 1.2 weight % based upon total mass.

8. A method of manufacturing a cathode-ray tube having a luminescent screen assembly, comprising: providing a faceplate panel having a patterned light-absorbing matrix thereon; and applying an aqueous suspension for use as an enhanced internal neutral density filter on the faceplate panel, wherein the aqueous suspension comprises at least two pigments, one or more surface active agents and at least one non-pigmented oxide particle, and wherein the at least two pigments are present in a concentration within a range of about 4 weight % to about 12 weight % of the entire liquid suspension.

9. The method of claim 8 wherein the at least two pigments include a blue pigment and a red pigment.

10. The method of claim 9 wherein the ratio of the blue pigment to red pigment is within a range of about 9: 1 to about 32: 1.

11. The method of claim 9 wherein the blue pigment comprises cobalt aluminate.

12. The method of claim 9 wherein the red pigment comprises iron oxide.

13. The method of claim 8 wherein the at least two pigments have an average particle size of about 100 nanometers.

14. The method of claim 8 wherein a pre-coat layer is formed on the enhanced internal neutral density filter.

15. The method of claim 14 wherein the pre-coat layer comprises a material selected from the group consisting of polyvinyl alcohol, functionalized silanes, silanol and siloxane.

16. A cathode-ray tube having a luminescent screen assembly, comprising: a faceplate panel having a patterned light-absorbing matrix thereon; and an enhanced internal neutral density filter, wherein the enhanced internal neutral density filter comprises at least two pigments, one or more surface active agents and at least one non-pigmented oxide particle, and wherein the at least two pigments are present in a concentration within a range of about 4 weight % to about 12 weight %.

17. The cathode-ray tube of claim 16 wherein the at least two pigments include a blue pigment and a red pigment.

18. The cathode-ray tube of claim 17 wherein the ratio of the blue pigment to red pigment is within a range of about 9: 1 to about 32: 1.

19. The cathode-ray tube of claim 17 wherein the blue pigment comprises cobalt aluminate.

20. The cathode-ray tube of claim 17 wherein the red pigment comprises iron oxide.

21. The cathode-ray tube of claim 16 wherein the at least two pigments have an average particle size in the range of about 30 to about 140 nanometers.

22. The cathode-ray tube of claim 16 further comprising a pre-coat layer is formed on the enhanced internal neutral density filter.

23. The cathode-ray tube of claim 22 wherein the pre-coat layer comprises a material selected from the group consisting of polyvinyl alcohol, functionalized silanes, silanol and siloxane.