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Publication numberUS3811910 A
Publication typeGrant
Publication dateMay 21, 1974
Filing dateMay 17, 1972
Priority dateMay 17, 1972
Also published asDE2325129A1
Publication numberUS 3811910 A, US 3811910A, US-A-3811910, US3811910 A, US3811910A
InventorsChang Y, Golovoy A, Labana S
Original AssigneeFord Motor Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Two-step method of making a color picture tube
US 3811910 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

Unite States Patent 1191 Labana et a1.

[ May 21, 1974 1 1 TWO-STEP METHOD OF MAKING A COLOR PICTURE TUBE [73] Assignee: Ford Motor Company, Dearborn,

Mich.

22 Filed: May 17, 1972 21 Appl. No.: 254,231

[52] US. Cl 117/17, 96/36.1, 117/1.7.5, 117/21, 117/29, 117/33.5 CM, 117/99,

313/85 R, 313/85 S, 313/92 B [51] Int. Cl. H0lj 9/20, B44d 1/094 [58] Field of Search 117/17, 17.5, 21, 33.5 CM, 117/29, 99; 313/85 R, 85 S, 92 B; 96/361 [56] References Cited UNITED STATES PATENTS 3,070,441 12/1962 Schwartz ..96/36.1 3,653,901 4/1972 Etter 117/33.5 CM

Lerner 96/361 Lange 117/33.5 CM

Primary E.raminer'Michae1 Sofocleous Attorney, Agent, or FirmWilliam E. Johnson; Keith L. Zerschling [5 7 ABSTRACT In manufacturing a color picture tube, a plurality of color phosphor dots are placed on a face plate of the tube. A shadow mask used with the tube is made with a plurality of apertures arranged in a predetermined pattern. Each of these apertures have a predetermined size. The predetermined size of each aperture is reduced to a smaller size when the mask is used in placing the phosphor dots on the face plate. The size of each of the apertures is returned to its original, predetermined size when the mask is used for operating the color tube. This disclosure teaches an improvement in the method of reducing and, thereafter, returning the size of the apertures to the predetermined size. The improvement includes a two-step application of powder coating compositions to the shadow mask to reduce the size of the apertures. The first step in the method partially reduces the apertures and the second step in the method reduces the apertures to a final size needed for laying down the phosphor dot pattern on the face plate. Since a powder coating composition is used, the materials may be easily removed from the mask by utilization of a solvent for the composition.

10 Claims, No Drawings TWO-STEP METHOD OF MAKING A COLOR PICTURE TUBE BACKGROUND OF THE INVENTION Color television tubes are prepared by depositing a plurality of groups of color phosphor dots on a glass face plate of the tube. The size and location of the phosphor dots on the face plate are controlled by interposing a steel shadow mask having a plurality of apertures therein between a light source used in laying down the dots and the face plate.

The same shadow mask is also used to direct electron beams to illuminate the dots during operation of the tube.

The best colors and brightest shades are obtained from a tube when different phosphordots are separated from each other by dark areas. A shadow mask with aperturesof9 to 10 mils diameter is needed for depositing such well separated dots. During operation of the tube, however, the size of the shadow masks apertures must have a diameter in the range of 14 to 16 mils for transmission of a larger fraction of electron beam energy to illuminate fully the phosphor dots. The shadow masks apertures, therefore, are smaller in'size during deposition of the phosphor dots than for operation of the tube. The prior art has solved this problem in many ways which are disclosed in such U.S. patents as U.S. Pat. Nos.: 3,231,280 to Law, 3,574,013 to Frantzen, 3,604,081 to Moegenbier, and 3,616,732 to Rucinski.

The invention disclosed herein is an improvement in the method of reducing from a predetermined size the size of apertures of a shadow mask for deposition of color dots and for enlarging such apertures to the predetermined size for transmission of electron beams for illuminating the dots. The improved method employs a dual application of powder coating compositions to reduce the size of the shadow mask apertures in two steps. Since powder coating compositions are employed, they may be removed easily by solvents for the compositions after the mask has been used to deposit the color dot pattern on the face plate of the tube.

SUMMARY OF THE INVENTION This invention relates to a method of manufacturing a color picture tube and, more particularly, to an improvement in the method of manufacturing a color picture tube wherein powder coating compositions are employed in reducing the size of a shadow masks apertures so that the mask can be used in placing the color dots on the tube.

In the art of manufacturing a color picture tube having a plurality of groups of phosphor color clots placed on a face plate thereof, a metallic shadow mask is made with a plurality of apertures arranged in a predetermined pattern. Each of the apertures of the shadow mask has a predetermined size larger than the size of each of the dots to be laid down on the face plate of the tube. The predetermined size of these apertures is reduced to a smaller size and the phosphor color dots are placed on the face plate with the aid of the shadow mask having the smaller apertures therein. The size of the apertures of the shadow mask are returned to the predetermined size so that the same shadow mask can be used in operating the tube.

The method of this invention sets forth an improvement in reducing the size of the apertures and, thereafter, returning the size of the apertures to the predetermined size. The improvement includes the following steps. A first powder coating composition is applied to the shadow mask having apertures of the predetermined size in order to reduce partially the size of the apertures. The first powder coating composition has a molecular weight (M in the range of 10,000 to 100,000 and an average particle size below 30 microns.

Once the first powder coating composition is applied to the shadow mask, the mask is heated with the composition thereon to a temperature and for a time sufficient to sinter the composition together but insufficient to induce any substantial flow thereof. A second powder coating composition is applied to the first composition on the shadow mask. The second composition has a molecular weight (M,,) in the range of 1,800 to 6,000. The second composition also has an average particle size below 30 microns. After the second composition is applied to the first composition on the mask, the mask is heated to a temperature and for a time sufficient to sinter the second composition together and to smooth the edges of the apertures but insufficient to induce any substantial flow of the first composition. The application of the two compositions is effective to reduce the size of the apertures to that required for lying down the color dot pattern. After the color dot pattern is' laid down, the two compositions are removed from the mask and the mask is used in the tubes final construction for directing the electron beams against the dot pattern. The powder coating compositions can be applied to the mask by any known techniques used to coat metal by powder coatings. These techniques include electrostatic spray, fluidized bed, electrostaticfluidized bed, etc.

ln greater detail, thermoplastic and thermosetting polymeric materials which may be employed as either the first or the second powder coating composition include, but are not limited to, polystyrene, polymethylmethacrylate, epoxy resins, cellulose acetate butyrate and copolymers of glycidyl acrylate or glycidyl methacrylate. To these polymeric materials may be added such materials as carbon black which serves as an antistatic agent and also to absorb stray light during dot placement on the face plate, antistatic agents which aid in the deposition of the powder on the shadow mask and thixotropic agents if desired.

Since the powder coating compositions applied to the shadow mask are heated to a temperature and for a time sufficient only to sinter the particles of the compositions together, the compositions may be easily removed from the mask by common solvents. Thus, the predetermined size of the apertures may be reobtained with little diff culty after the color dot pattern has been placed on the face plate of the tube. More particularly, since the powder compositions do not substantially crosslink because of the limited heating, the compositions remain soluble in most common solvents.

DESCRIPTION OF THE PREFERRED EMBODIMENT This invention relates to a method of reducing the size of apertures of a shadow mask which is employed 1 in forming a color television tube. As is already well 16 mils. As is also well known in the art, the diameter of these apertures is reduced to 9 to 10 mils so that the shadow mask may be used in the deposition of color phosphor dots on a face plate of the tube. As is also known, each shadow mask is unique for a color tube in that it is utilized with the small apertures for laying down the color dot pattern on the face plate and with the larger apertures for use in directing electron beams toward dots on the face plate.

The improved method of this invention will be illus trated by a plurality of examples.

EXAMPLE 1 One hundred parts by weight of polymethylmethacrylate (M,,) 45,000) and three parts carbon black are mixed together in a twin shell tumbling mixer for 10 minutes. The mixture is extruded through a compounding extruder at a temperature of 180C. The extrudate is pulverized in a fluid energy mill so that is passes through a 270 mesh screen. The powder coating composition so produced has an average particle size of 15 microns and constitutes a first powder coating composition.

The first composition is sprayed onto a shadow mask, which'mask has a plurality of apertures aligned in a predetermined pattern. The diameter of these apertures is in the range of 14 to 16 mils. The first composition is applied by an electrostatic spray gun operating at 60 KV. The coated shadow mask is baked at 180C for 3 minutes. The size of the masks apertures is reduced to the range of 10 to l 1 mils without any of the apertures being plugged and with the apertures having a slight irregular shape and some rough edges.

A second powder coating composition is prepared by mixing 100 parts byweight epoxy resin, in this case,

, Epon l004, a trademark of the Shel l Chemical Company lnc., whose chemical formula is wherein n and havinga molecular weight of 1,800 with three parts carbon black. The mixture is extruded through a compounding extruder at a temperature of 130C. The extrudate is pulverized in a fluid energy mill so that it passes through a 270 mesh screen. The powder coating composition so produced has an average particle size of microns and constitutes a second powder coating composition.

The second composition is sprayed onto the first composition already on the mask by an electrostatic spray gun operating at 60 KV. The coated mask is baked at 90C for 3 minutes. The size of the masks apertures is reduced to the range of 9 to 10 mils without any of the apertures being plugged and with the apertures having uniform, circular and smooth edges.

The shadow mask prepared by using powder compositions in the two-step method is utilized to lay down the groups of three different color dot phosphors on a face plate of a TV tube in a normal manner. After the color dot pattern is laid down, the two powder compositions are removed from the shadow mask by washing 1 the mask in toluene. The cleaned shadow mask is assembled with the tube by a plurality of manufacturing steps known in the art. The color tube is operated by receiving a color signal and the signal so derived is employed to excite the phosphor color dot pattern on the face plate. A color picture of acceptable quality is received on the color tube.

EXAMPLE 2 A mixture containing parts by weight of polymethylmethacrylate (Kl, 30,000), two parts carbon black and one part of an antistatic agent, in this case, stearamidopropyl-dimethyl-beta-hydroxyethylammonium nitrate are mixed by shaking in a plastic jar. The materials are mill rolled at 180C for 20 minutes. The mixture is cooled and pulverized to pass through a 270 mesh screen. The mixture which passes through the mesh screen has an average particle size of about 10 microns and constitutes a first powder coating composition.

The first composition is sprayed onto a shadow mask by an electrostatic powder spray gun as described in Example 1 at an operating voltage of 40 KV. The.coated mask is baked at C for 3 minutes to sinter the first composition together. This baking is insufficient to induce any substantial flow in the composition. The size of the apertures in the shadow mask are reduced to a range of 10 to l 1 mils with slightly irregular shape and rough edges but with no plugging thereof.

A second powder coating composition is formulated by mixing 100 parts by weight of epoxy resin, in this case Epon 1007 which has a molecular weight of 4,500

and a structural formula identical to Epon 1004, with the exception that n is 14, with three parts carbon black. The materials are mixed by shaking in a plastic jar. The materials are mill rolled at 140C for 20 minutes. The mixture is cooled and pulverized to pass through a 270 mesh screen. This mixture which passes through the screen has an average particle size of about 10 microns and constitutes the second powder coating composition.

The second composition is sprayed onto the mask having the first composition thereon by means of an electrostatic powder spray gun as described in Example 1 at an operating voltage of 40 KV. The coated mask is baked at 120C for 3 minutes to sinter the second composition together. The size of the apertures in the EXAMPLE 3 A mixture containing 100 parts by weight of polymethylmethacrylate (R1,, 45,000) and three parts carbon black is prepared by the same precedure as desri ad Exama ar t .p sv ati of the first powder coating composition. The composition so produced has an average particle size of about 25 microns and is applied to a shadow mask as described in Example 1. The coated mask is baked at a temperature of C for 3 minutes and the size of the apertures are reduced to 10 to 11 mils without any apertures being plugged.

A second powder coating composition is prepared by mixing 100 parts of a glycidyl methacrylate copolymer ner as described in Example 1. The mask is baked at a temperature of l 10C for 3 minutes and produces apertures having a diameter range of 9 to l mils.

A TV tube is constructed and operated in a television set as described in Example 1. The tube produces a color picture of acceptable quality.

EXAMPLE 4 A first powder coating composition is obtained by mixing together 100 parts by weight of polystyrene (M,. 40,000) with two parts carbon black and one part of the antistatic agent of Example 2. The mixture is processed in the manner described for the first composition in Example 1. The average particle size produced is 20 microns.

The first composition is sprayed on a mask as described in Example 1. The mask is baked at a temperature of 160C for 3 minutes and the apertures size is reduced to 10 to 11 mils diameter.

A second powder coating composition is prepared by mixing together 100 parts by weight of an acrylic copolymer (methylmethacrykite 60 percent and butyl methacrylate 40 percent) M, 5,000, with three parts carbon black as described for the second composition in Example 1. The second composition is applied to the mask having the first composition thereon as described in Example 1 and the mask is baked at a temperature of l 10C for 3 minutes. This action reduces the size of the apertures to 9 to 10 mils diameter with no plugging of the apertures noted.

A color picture tube is manufactured and operated as described in Example 1. An acceptable quality picture is received on the tube. Prior to forming the complete tube, the compositions are removed from the mask by the use of acetone.

- EXAMPLE A first powder coating composition is formed by mixing 100 parts by weight of polystyrene (M,, 70,000) and two parts carbon black. These two ingredients are mixed together in a twin shell tumbling mixer for minutes and extruded through a compounding extruder at a temperature of 200C. The Extrudate is pulverized in a fluid energy mill to pass through a 270 mesh screen and the resulting powder has an average particle size of microns and constitutes the first powder coating composition.

The first composition is applied to a shadow mask in the same manner as described in Example 1 and is baked at a temperature of 180C for 5 minutes. The size of the apertures in the mask is reduced to the range of 10 to 11 mils.

A second powder coating composition is formed by a mixture of 100 parts by weight of an epoxy resin (Epon 1004) having a molecular weight of 1,800 and four parts carbon black. The ingredients are mixed together in a twin shell tumbling mixer for 10 minutes and extruded through a compounding extruder at a temperature of 130C. The extrudate is pulverized in a fluid energy mill to'pass through a 270 mesh screen and the resulting powder has an average particle size of 15 microns and is the second powder coating composition.

The second composition is applied to the already coated mask in the same manner described in Example 1. The coated mask is baked at a temperature of C for 3 minutes and the size of the apertures is reduced to 9 to 10 mils.

A color TV tube is constructed and operated as described in Example 1. An acceptable quality picture is received on the tube. Prior to forming the complete color tube, the compositions which have been sintered together in the heating steps are removed from the mask by the use of acetone.

EXAMPLE 6 A first powder coating composition is prepared by mixing parts by weight of a copolymer formed with 80 percent methyl methacrylate and 20 percent styrene (M,, 40,000) with two parts carbon black in the manner described for the first powder coating composition in Example 1. The material is applied to a shadow mask as described in Example 1 and baked at a temperature of C for 3 minutes to produce a final aperture size in the range of 10 to 11 mils.

A second powder coating composition is prepared by mixing 100 parts by weight of a copolymer containing 5 percent glycidyl methacrylate, 75 percent methyl methacrylate, 20 percent ethyl acrylate (IT/l, 5,000) and two parts carbon black. These materials are blended as described for the second composition in Example and applied to the already coated mask as described in Example 1. The mask'is baked at 100C for 5 m nu es, d th aperwa i is d s tqth an of 9 to 10 mils with no plugging of the apertures observed. A color TV tube is constructed and operated as described in Example 1. A good picture is received thereon.

EXAMPLE 7 A first powder coating composition is prepared by mixing 100 parts by weight of an epoxy resin, in this case, Epon 1010 similar to the epoxy resin previously described but with an n equal to 64 and a M 10,000, with four parts carbon black. The materials are mixed together in a twin shell tumbling mixer for 10 minutes and extruded througha compounding extruder at a temperature of C. The extrudate is pulverized in a fluid energy mill to pass through a 270 mesh screen. The powder so produced has an average particle size of 20 microns and is the first powder coating composition.

The first composition is applied to a shadow mask by an electrostatic spray gun operating at 60 KV and the coated mask is baked at 155C for 3 minutes to produce final apertures having a size in the range of 10 to 11 mils.

A second powder coating composition is formulated by mixing 100 parts by weight of an epoxy resin, in this case, Epon 1004 having a molecular weight of 1,800, and four parts carbon black. The materials are mixed together in a twin shell tumbling mixer for 10 minutes and extruded through a compounding extruder at a temperature of 130C. The extrudate is pulverized in a fluid energy mill to pass through a 270 mesh screen. The powder so produced'is the second powder coating composition and it has an average particle size of 20 microns.

The second powder coating composition is applied to the coating mask by an electrostatic spray gun operating at 60 KV and the so coated mask is baked at a temperature of 90C for 3 minutes. The baking sinters the compositions together and the final size of the apertures is in the range of 9 to 10 mils.

A color picture tube is manufactured as described in Example 1. The tube is operated and the quality of the picture is acceptable. The compositions are removed from the mask by a dichloromethane solvent in order to utilize the mask in the TV tube.

EXAMPLE 8 A first powder coating composition is prepared by mixing 100 parts by weight of an epoxy resin, in this case, Epon ll0, M 10,000, with two parts carbon black. The epoxy resin and carbon black are mixed together, mill rolled and pulverized to pass through a 270 mesh screen. After this mixing, five-tenths parts of fumed silica, in this case, Cab-O-Sil M-5, is dry blended with the materials by shaking. This produces a first powder coating composition.

The powder is applied to a shadow mask by an electrostatic spray gun operating at 60 KV and the coated mask is baked at 160C for 3 minutes to produce aperture sizes in the range of l0 to l l mils.

A second powder coating composition is formulated by mixing 100 parts by weight of a copolymer formed of 65 percent methyl methacrylate and 35 percent ethyl acrylate, (M, 5,000) with three parts carbon black. The second powder coating composition is applied to the previously coated mask as described in Example and baked at a temperature of 100C for 3 minutes to produce apertures in the size range of 9 to mils.

A color TV tube is constructed in the manner described in Example I. The tube is operated and. the quality of the picture is acceptable. The materials are removed from the mask prior to its assembly into the tube by utilization of acetone.

EXAMPLE 9 A first powder coating composition is prepared by mixing 100 parts by weight of cellulose acetate butyrate, in this case, EAB38l-2 of Eastman Chemical Company and two parts carbon black. The materials are processed as described in Example 1 to produce a first powder coating composition having average particle size of microns.

The first composition is applied to a shadow mask as described in Example 1 and baked at a temperature of 170C for 3 minutes to produce aperture sizes of 10 to ll mils.

A second powder coating composition is prepared exactly the same manner as described for the second composition of Example 8 and is applied in the exact manner as described in Example 8 to produce a coated mask having apertures with sizes in the range of9 to 10 mils. The shadow mask is used to construct a TV tube as described in Example 8 and a color tube of acceptable quality is produced.

EXAMPLE 10 A first powder coating composition is prepared by mixing 100 partsby weight of cellulose acetate buty;

rate, in this case, Eastman Chemical Company half sec ond butyrate, with three parts carbon black. These materials are processed as described in Example 9 to produce a first powder coating composition having an average particle size of 20 microns.

The first composition is applied to a shadow mask as described in Example 9 and baked at a temperature of 155C for 3 minutes. Such action produces aperture sizes of 10 to 11 mils in diameter.

A second powder coating composition is prepared in the exact same manner as described for the preparation of the second powder composition of Example 8. The second powder composition is applied and baked on the already coated mask as described in Example 8.

The so produced shadow mask is used to construct a TV tube as described in Example 8. A color television tube of acceptable quality is produced.

EXAMPLE l l A first powder coating composition is prepared by mixing 100 parts by weight of a copolymer containing 70 percent methyl methacrylate, 20 percent butyl methacrylate and 10 percent styrene, (M, 15,000) and three parts carbon black. The materials are processed as described in Example 1 to produce a first powder coating composition having a particle size of 30 microns.

The first composition is applied to a shadow mask as described in Example 1 and baked at a temperature of 150C for 3 minutes. This action produces aperture sizes of 10 to 11 mils.

A second powder coating composition is prepared and applied to the coated shadow mask in exactly the same manner as described for the second powder coating composition in Example 7. The coated mask is employed in preparing a color TV tube and the color TV tube is operated as described in Example 1 with an acceptable color picture being generated thereon.

EXAMPLE l2 A first powder coating composition is prepared in the same manner as described for the preparation of the second powder coating composition described in Example 2. The first powder coating composition is applied to a shadow mask and baked at a temperature of C for 3 minutes. i

A second powder coating composition is prepared and applied to the coated mask as described for the second powder coating composition of Example 3. The second composition is baked at a temperature of l 10C for 3 minutes.

Because the melt viscosity of these first and secondpowder coating compositions are too close together, not enough size reduction can be obtained in the shadow mask apertures and the final size thereof in a two-step coating process is only 13 to 14 mils. The shadow mask, therefore, is unacceptable for making a color TV tube.

We claim:

1. In the method of making a metallic shadow mask foruse in the manufacture of a color picture tube having a plurality of phosphor color dots placed on the face plate comprising the steps of making said metallic shadow mask with a plurality of apertures therein arranged in a predetermined manner, each of said apertures having a predetermined size larger than the size of each of said phosphor color dots, reducing the predetermined size of each of said apertures to a smaller size by applying a coating, and removing the applied coating from the coated shadow mask after said plurality of color dots have been placed on said face plate of said color picture tube to return the size of said apertures to said predetermined size prior to coating, wherein the improvement comprises: electrostatically spraying said coating upon said shadow mask, said coating being a first powder coating composition having an average particle size below 30 microns and comprising a synthetic polymeric material having a molecular weight M1, in the range of 10,000 to 100,000, heating said coated shadow mask to a temperature and for a time sufficient to sinter said coated powder coating composition together but insufficient to induce any substantial flow of said coated powder composition, electrostatically spraying a second coating upon said shadow mask, said coating being a second powder coating composition having an average particle size below 30 microns and comprising a synthetic polymeric material having a molecular weight (M,, ir1 the range of 1800 to ,000 and 7 heating said coated shadow mask, coated with said first and second coating composition, to a temperature and for a time sufficient to sinter said second coated polymeric material together but insufficient to induce any substantial flow of either of said second or said first coating composition. 2. The method as defined in claim 1 wherein: said first and said second powder coating compositions contain a small weight percentage of an antistatic agent.

3. The method as defined in claim 1 wherein: said step of removing comprises dissolving said first and second coating compositions in a suitable solvent therefor.

4. The method as defined in claim I wherein: said first powder coating composition is principally formed from polymethyl-methacrylate.

5. The method as defined in claim 1 wherein: said first powder coating composition is principally formed from polystyrene.

6. The method as defined in claim 1 wherein: said first powder coating composition is formed principally from glycidyl methacrylate copolymer.

7. The method as defined in claim 1 wherein: said first powder coating composition is principally formed from epoxy resin.

8. The method as defined in claim 1 wherein: said first powder coating composition is principally formed from cellulose acetate butyrate.

9. The method as defined in claim 1 wherein: said second powder coating composition is principally

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3922394 *Nov 9, 1973Nov 25, 1975Rca CorpMethod for coating ferrous-metal mask for cathode-ray tube
US3922395 *Nov 9, 1973Nov 25, 1975Rca CorpMethod for applying organic polymeric coating composition to ferrous-metal surfaces
US5474866 *Aug 30, 1994Dec 12, 1995Thomson Consumer Electronics, Inc.Fixing step utilizes an electrostatic spray to uniformly contact phosphors and underlying organic photoconductive layer with fixative without moving phosphors
US5629051 *Sep 18, 1995May 13, 1997Thomson Multimedia, S. A.Method and apparatus for forming an insulator on a uniaxial tension focus mask of a color selection electrode
US5834067 *Jan 28, 1997Nov 10, 1998Maytag CorporationPowder paint stenciling on a powder paint substrate
Classifications
U.S. Classification430/5, 427/282, 428/138, 430/23, 427/68, 427/468, 428/327
International ClassificationH01J9/14, H01J9/227
Cooperative ClassificationH01J9/2271
European ClassificationH01J9/227B