US2792315A

US2792315A - Method of metallizing the screen of a cathode ray tube

Info

Publication number: US2792315A
Application number: US397695A
Authority: US
Inventors: Levy Sidney
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1953-12-11
Filing date: 1953-12-11
Publication date: 1957-05-14
Anticipated expiration: 1974-05-14

Description

May 14, 1957 s. LEVY 2,792,315

METHOD OF METALLIZING THE SCREEN OF A CATHODE RAY TUBE! Filed Dec. 11, 1955 'INVENTOR SIDNEY LEVY METHOD F METALLIZING THE SCREEN OF A CATHODE RAY TUBE Sidney Levy, Garden City, N. Y., assignor to Sylvania Electric Products Inc, a corporation of Massachusetts Application December 11, 1953, Serial No. 397,695

11 Claims. (Cl. 117-335) This invention relates to a luminescent phosphor screen. More particularly it relates to an improved method of metallizing the screen of a cathode ray tube.

The light output and resolution of a cathode ray tube is materially increased when an electron pervious light reflecting metallic film is applied to the beam side of its luminescent screen. This fact has been known for some time and consequently those cathode ray tubes which have been used for projection television have been pro vided with such a metallized screen. In order that the screen can give optimum results it has been said that the metallized film should be thin enough to cause negligible absorption of the electron beam, should be opaque, should be relatively smooth and highly light reflecting and should also have suificient conductivity to conduct the full beam current. Furthermore, it should be strong enough to withstand the stresses due to the effect of the focused beam, should be durable enough to withstand the processing of the cathode ray tube and finally should not react chemically with the luminescent materials forming the screen.

in order that the metallized screen could be made opaque, relatively smooth, and highly reflecting, it has been found necessary to cover the luminescent phosphor with a thin film of organic material which presumably is stretched over the depressions in the phosphor deposit so as to present a surface which is more nearly plane. This organic film is then covered with a film of metal, usually aluminum which is deposited thereon by a vaporization technique. Although the presence of the organic film prior to the metallizing step might seem to be highly questionable it has been found that Without this organic film the metal film does not possess the necessary light reflecting property and that the brightness is reduced to as low as /3 of the value obtained when an organic film is present.

In accordance with the established methods of the prior art a lacquer film is usually applied by spreading a collodion solution on a water surface overlaying the phos phor deposit allowing the lacquer to spread outwardly over the entire surface until the solvent evaporates leaving a thin film of collodion (nitrate of cellulose) behind; thereupon the water beneath the lacquer film is decanted and the lacquer film is allowed to drop down into intimate contact with the phosphorescent screen below. The depth of the water level varies somewhat dependent upon the curvature of the face-plate of the picture tube. However, it is usually at least a half inch at the shallowest point. After the water has been allowed to flow out from underneath the film and the film has been allowed to adhere to the powder deposit, the tube is dried in a current of warm air and the film stretches over the microscopic depressions and gaps in the luminescent powder deposit.

This method of applying a lacquer film gives rise to a considerable proportion of rejects in production inasmuch as the film is mechanically weak; further subject to tearing and the spreading and adherence of the film are affected by the conditions of the interior surface of a cathode ray tube and the surface of the phosphor.

It isan object of this invention to provide a method of coating the phosphor screen with an organic film which is not dependent upon a relatively deep cushioning lacquer.

It is a further object of this invention to provide a method of applying an organic film over the phosphor screen in such manner that any desired thickness and hence mechanical strength of the film may be attained.

It is a still further object of this invention to provide a method which will insure complete coverage of the phosphor screen by the applied organic film.

It is a still further objectof this invention to provide a method which will increase the uniformity of the film over its entire surface area.

These objects and other advantages incidental thereto can be obtained in accordance with this invention by spray ing a film forming material, such as collodion, in a suitable solvent either directly onto a luminescent screen or else spraying this film forming material onto a phosphor screen which is still wet but not necessarily covered to any substantial degree with a water layer.

These and other objects, features and advantages of this invention will become apparent when considered in view of the following description and the accompanying drawings wherein:

Figure 1 illustrates a particular step in the practice of this invention, and

Figures 2 and 3 are enlarged fragmentary sectional views showing a fluorescent cathode ray tube screen in successive stages of treatment.

Referring particularly to Figure 2 there is shown an enlarged bulbous portion of the envelope 1d of a television picture tube with the bottom or face portion of the envelope 10 covered with a screen or layer of phosphor material 12. This layer in the illustrated case shown in the drawing is at the stage obtained after decantation and drying of the phosphor screen material. As shown in the drawings the spray nozzle 20 projects downwardly through the neck portion of the enevlope and is positioned a sufiicient distance from the face of the envelope to permit the emulsion to be sprayed in such manner as to cover the entire face plate of the envelope as shown a at 22 in the drawing.

The emulsion which is to be used for this purpose can be any of the well known organic heat decomposible film forming materials now used in the prior art for this purpose, such as, for example, nitro-cellulose lacquer, flexible collodion, or parlodion. The material is emulsified in water, the amounts and the proportions of the ingredients kept Within the limit which will cause a thin water film to be produced and cover the phosphor layer when the emulsion is sprayed thereon and leave a film of lacquer over this water layer. In order to pro mote or improve the wetting characteristics of the phosphor it has been found desirable in some instances to incorporate a small amount of potassium silicate in the water phase of the emulsion.

When an emulsion of the type hereinabove described is used as the spray lacquer to cover the dry phosphor complete coverage is assured which is not the case when the water spreading technique of the prior art is used for when the water spreading technique is used in a large tube the solvent often evaporates and the lacquer or film sets before the solution had a chance to spread to the wall of the tube. This is occasioned by the fact that as the solvent evaporates the viscosity increases rapidly and at the edges of the spreading film there may be sufficient evaporation to form a rigid film which will resist fupther spreading. Furthermore, in the case of the water spreading technique unless the film stretches during the decantation the latter stages of the decantation of the film will not cover the entire phosphor surface.

When the film is. to be formed in accordance with this invention the phosphor layer can, of course, be formed on the face of the tube in accordance with the 'usual practice such as, for example, by the settling process from a liquid suspensiom After the phosphor has been settled onto the face of the tube and the supernatant liquid has beendecanted the phosphor screen is dried. An emulsion is formed by diluting one volume of a nitrocellulose solution which has been formulated, for example, by mixing the following ingredients in the proportions given: 7.5% cellulose nitrate, 1.5% glycol sebacate, 26.2% ethyl acetate, 19.6% butyl acetate, 7.8% butyl alcohol and 36.4% aromatic petroleum naphtha with four volumes of amyl acetate. One milliliter of dioctyl phthallate is added per liter of solution. One volume of this solution is then emulsified with nine volumes of water in a blender. The Water contains one half percent by weight of potassium silicate. This emul sion is then sprayed onto the face of the dried phosphor screen. As the emulsion hits the dried phosphor it breaks up and the water tends to wet the phosphor particles leaving the organic film forming material to float on top of the very thin layer of water. As the solvent evaporates the film hardens whereupon the sprayed tube is sent through an oven and the water beneath the film is evaporated leaving the phosphor covered with a thin uniform coating of organic film which presents a smooth plane surface ready for further processing to form a metallized film by a vaporization technique for example. It is, of course, understood that the nitrocellulose solution described above is merely illustrative and is not to be considered as critical.

The spraying of the emulsion may be used on a dried phosphor screen Without previously wetting the screen or providing a water cushion as would be required previous to spraying lacquer solution. Certain screening processes produce phosphor screens which must be dried in order to achieve adherence of the phosphor to the glass. It would be an advantage therefore to be able to spray emulsion directly onto such screens without intermediary steps.

Control of the thickness and uniformity of the lacquer film is more convenient with the emulsion than with the solution because of the greater volume which must be sprayed for the same organic film thickness. Also, the size of the droplets of lacquer is determined by the emulsification conditions and not by the spraying conditions, and is, therefore, uniform throughout the spray.

While the above description and drawings submitted herewith disclose a preferred and practical embodiment of the luminescent screen of this invention it will be understood that the specific details of construction and arrangement of parts as shown and described are by way of illustration and are not to be construed as limiting the scope of the invention.

What is claimed is:

1. In the method of metallizing the screen of a cathode ray tube including the steps of settling a phosphor screen from a settling solution onto the screen-forming surface of the cathode ray tube, vaporizing a metallic coating onto said phosphor screen, and baking the tube, the -improvement in preparing said phosphor screen for the application of said metallic coating which comprises spraying an emulsion of an organic heat decomposable film forming material onto said phosphor screen to form a coating, and drying the coating so formed to present a surface over said phosphor screen which is to receive said metallic coating.

2. In the method of metallizing the screen of a cathode ray tube including the steps of settling a phosphor screen from a settling solution onto the screen forming surface of the cathode ray tube, vaporizing a metallic coating 4 onto said phosphor screen and baking the tube, the improvement in preparing said phosphor screen for the ap"- plication of said metallic coating which comprises spraying an emulsion of an organic heat decomposable film forming material having a nitrocellulose base onto said phosphor screen to form a coating, and drying the coating so formed to present a surface over said phosphor screen which is to receive said metallic coating.

3. In the method of aluminizing the screen of a cathode ray tube including the steps of settling a phosphor screen from a settling solution onto the screen forming surface of the cathode ray tube, vaporizing an aluminum coating onto said phosphor screen, and baking the tube, the

improvement in preparing said phosphor screen for the application of said aluminum coating which comprises spraying an emulsion of an organic heat decomposable film forming material onto said phosphor screen to form a coating, and drying the coating so formed to present a surface over said phosphor screen which is to receive said aluminum coating.

4. In the application of a reflective metallic coating to a fluorescent screen of a cathode ray tube, the improvement comprising the preparation of said fluorescent screen to receive said reflective metallic coating which includes the steps of spraying an emulsion of an organic heat decomposable film forming material and water onto said fluorescent screen, the spraying being effective to cause the emulsion to produce a water film covering said fluorescent screen and an organic heat decomposable film over the water film, and drying said organic film to form a smooth organic coating over said fluorescent screen which is to receive said reflective metallic coating.

5. In the application of a reflective metallic coating to afluorescent screen of a cathode ray tube, the improvement comprising the preparation of said fluorescent screen to receive said reflective metallic coating which includes the steps of spraying an emulsion of an organic heat decomposable film forming material and water onto said fluorescent screen, the spraying being effective to cause the emulsion to produce a water film covering said fluorescent screen and an organic heat decomposable film over the water film, drying said organic film to form a smooth organic coating over said fluorescent screen which is to receive said reflective metallic coating, and after applying said reflective metallic coating, baking said tube to drive otf residual film forming material.

6. In the application of a reflective metallic coating to a fluorescent screen of a cathode ray tube, the improvement comprising the preparation of said fluorescent screen to receive said reflective metallic coating which includes the steps of spraying an emulsion of an organic heat decomposable film forming material and water onto said fluorescent screen, the emulsion having potassium silicate in the water phase and the spraying being effective to cause the emulsion to produce a water film covering said fluorescent screen and an organic heat decomposable film over the water film, and drying said organic film to form a smooth organic coating over said fluorescent screen which is to receive said reflective metallic coating.

7. In the application of a reflective metallic coating to a fluorescent screen of a cathode ray tube, the improvement comprising the preparation of said fluorescent screen to receive said reflective metallic coating which includes the steps of spraying an emulsion of an organic heat decomposable film forming material having a nitrocellulose base and water onto said fluorescent screen, the spraying being effective to cause the emulsion to produce a water film covering said fluorescent screen and an organic heat decomposable film over the water film, and drying said organic film to form a smooth organic coating over said fluorescent screen which is to receive said reflective metallic coating.

8. In the manufacture of a cathode ray tube including the steps of settling a phosphor screen from a settling solution onto the screen forming surface of the cathode ray tube, decanting the settling solution, and applying a reflective metallic coating over said phosphor screen, the improvement in preparing said phosphor screen for the application of said reflective metallic coating which comprises preparing an emulsion of water and an organic heat decomposable film forming material, spraying said emulsion onto said phosphor screen such that said emulsion breaks up whereby the water tends to wet said phosphor screen and said organic film forming material floats as a film on top of the water in said emulsion, and hardening said film to present a smooth planar surface over said phosphor screen which planar surface is to receive said reflective metallic coating.

9. In the manufacture of a cathode ray tube including the steps of settling a phosphor screen from a settling solution onto the screen forming surface of the cathode ray tube, decanting the settling solution, and applying a reflective metallic coating over said phosphor screen, the improvement in preparing said phosphor screen for the application of said reflective metallic coating which comprises preparing an emulsion of water and an organic heat decomposable film forming material with the water phase of said emulsion containing potassium silicate, spraying said emulsion onto said phosphor screen such that said emulsion breaks up whereby the water tends to wet said phosphor screen and said organic film forming material floats as a film on top of the water in said emulsion, and hardening said film to present a smooth planar surface over said phosphor screen which planar surface is to receive said reflective metallic coating.

10. In the manufacture of a cathode ray tube including the steps of settling a phosphor screen from a settling solution onto the screen forming surface of the cathode ray tube, decanting the settling solution, applying a reflective metallic coating over said phosphor screen, the improvement in conditioning said phosphor screen for the application of said reflective metallic coating which comprises preparing an emulsion of water, a solvent and an organic heat decomposable film forming material, spraying said emulsion onto said phosphor screen such that said emulsion breaks up whereby the water tends to wet said phosphor screen and said organic film forming material floats as a film on top of the water in said emulsion, and hardening said film to present a smooth planar surface over said phosphor screen which planar surface is to receive said reflective metallic coating.

11. In the manufacture of a cathode ray tube including the steps of settling a phosphor screen from a settling solution onto the screen forming surface of the cathode ray tube, decanting the settling solution, applying a re- Elective metallic coating over said phosphor screen, the improvement in preparing said phosphor screen for the application of said reflective metallic coating which comprises preparing an emulsion of water and an organic heat decomposable film forming material having a nitrocellulose base, spraying said emulsion onto said phosphor screen such that said emulsion breaks up whereby the water tends to wet said phosphor screen and said organic film forming material floats as a film on top of the water in said emulsion, hardening said film to present a smooth planar surface over said phosphor screen which planar surface is to receive said reflective metallic coating, and after applying said reflective metallic coating, baking said tube to drive off residual film forming material.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. IN THE METHOD OF METALLIZING THE SCREEN OF A CATHODE RAY TUBE INCLUDING THE STEPS OF SETTLING A PHOSPHOR SCREEN FROM A SETTLING SOLUTION ONTO THE SCREEN-FORMING SURFACE OF THE CATHODE RAY TUBE, VAPORIZING A METALLIC COATING ONTO SAID PHOSPHOR SCREEN, AND BAKING THE TUBE, THE IMPROVEMENT IN PREPARING SAID PHOSPHOR SCREEN FOR THE APPLICATION OF SAID METALLIC COATING WHICH COMPRISES SPRAYING AN EMULSION OF AN ORGANIC HEAT DECOMPOSABLE FILM FORMING MATERIAL ONTO SAID PHOSPHOR SCREEN TO FORM A COATING, AND DRYING THE COATING SO FORMED TO PRESENT A SURFACE OVER SAID PHOSPHOR SCREEN WHICH IS TO RECEIVE SAID METALLIC COATING.