US3484240A

US3484240A - Method of manufacturing screens for cathode-ray tubes

Info

Publication number: US3484240A
Application number: US535725A
Authority: US
Inventors: Johannes Josephus Anto Jonkers
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1965-04-01
Filing date: 1966-03-21
Publication date: 1969-12-16
Anticipated expiration: 1986-12-16
Also published as: ES324900A1; GB1089506A; CH448163A; DE1462819A1; AT264610B; BE678728A; DK118900B; NL6504104A

Description

'United States Patent M 4 Int. Cl. C09k 1/00; G03c 5/00; B44d 1/02 U.S. Cl. 96-361 6 Claims ABSTRACT OF THE DISCLOSURE A method of depositing indexing strips for a color television display tube in which a metal backing layer supported by an organic film over a phosphor screen is wetter with an interrupted liquid layer before a hardenable photosensitive binder layer is applied which is exposed to harden portions thereof supporting the indexing strips.

The invention relates to a method of manufacturing screens for cathode-ray tubes for reproducing color images comprising a luminescent layer containing at least two substances provided in discrete surfaces which luminesce in different colors upon excitation by electrons. More particularly the invention relates to a method of wetting and coating such a luminescent layer with a solution of an organic substance which forms a film after drying. Thereafter, a metal layer pervious to electrons is applied to this film. A substance which provides an index signal upon electron excitation then is applied to given areas with the aid of a photosensitive binder.

In such a cathode-ray tube, the luminescent layer generally contains three substances luminescing in different colors, green, red and blue. These substances are provided in form of strips between which are interposed strips consisting of a non-luminescent substance which is impervious to light. The substance providing an index signal upon electron excitation is furnished in the form of strips which occupy a given position with respect to the strips of the luminescent layer.

The index signal may be obtained in different ways. Thus, if the substance consists of secondary-emission material, electron excitation results in an electron current which then is collected on a collector electrode. In another case, the substance has the property that upon electron excitation it emits radiation, generally ultraviolet radiation, which is collected in a photocell. The signals obtained in this manner are used for the co ordination of the instantaneous modulation of the electron beam, and the spot on the screen struck by the electron beam.

It has been customary to apply to the metal layer an organic film in order to protect that layer because of its extreme thinness. For this purpose, a solution of an organic substance which forms a film after drying is applied to the layer. If this solution is applied while the organic film is still present below the metal layer, difficulties may arise, since the thin metal layer always contains small pores through which the solution of the organic substance may penetrate and may thus attack the subjacent organic film, resulting in damage to the metal layer.

If the solution is applied while the organic film is no longer present below the metal layer, this implies that the screen is first baked out after the application of the metal layer. This involves an additional process, since after the application of the organic film and the sub- 3,484,240 Patented Dec. 16, 1969 stance supplying an index signal upon electron excitation the baking-out process must be repeated.

It has been found that especially in case of rectangular windows, the expansion and contraction of the window involved in baking out are generally not entirely reversible. The correlation between the pattern used in applying the discrete surfaces then no longer exists. The substance supplying an index signal upon electron excitation must accurately occupy a given position with re spect to the discrete surfaces of the differently luminescing substances, which can no longer be exactly attained in this case.

It is a principal object of the invention to provide a method of manufacturing a luminescent screen comprising at least two phosphors which luminesce in different colors in response to electron excitation, and which is provided with a thin metal layer and indexing strips in which damage to the layer is avoided and repeated bakeout steps are unnecessary.

This and further objects of the invention will appear as this specification progresses.

According to the invention, the electron pervious metal layer below which the organic film is provided is wetted without the formation of an uninterrupted liquid layer and a solution of the photosensitive binder is spread thereon. The solution then is dried and exposed at the given areas to the influence of hardening radiation to harden the binder. After removal of the non-exposed binder the screen is baked out.

In this method, the substance supplying an index signal upon electron excitation may be applied in various ways. The solution of the photosensitive binder may contain this substance in the form of a suspension, This substance is then already present at the given areas after the exposure to the hardening radiation and at the other areas the substance is removed together with the non-exposed binder.

According to another method, the substance is not suspended in the solution of the photosensitive binder. Consequently, in this case only the layer of binder is exposed to the influence of hardening; radiation. At the irradiated areas, the binder becomes insoluble, but if at least the irradiation is not continued for an excessively long time, it remains slightly sticky. The substance may subsequently be applied in the form of a suspension, during which process it adheres to the slightly sticky annealed parts so that it is not washed away during the subsequent removal of the non-exposed binder; or, the substance may be applied in the form of a suspension after the non-exposed binder has been removed. During the final baking-out of the screen, the binder 'of the luminescent layer, the organic film and the binder of the substance supplying an index signal upon electron excitation are removed.

In this method, during the application of the photo sensitive hinder the organic film is still present below the electron pervious metal layer which always contains small pores. When this layer is wetted, the liquid penetrates through the po es into the organic film and, also, through this film into the luminescent layer. Gas bubbles then ascend which due to the fact that the metal layer is not covered with a noninterrupted liquid layer can escape through the pores in the metal layer so that they do not damage the metal layer. The organic film provides a sufficient strength for the metal layer so that the solution of the photosensitive binder does not adversely affect the metal layer during the applica ion and the following processes. For wetting a liquid is used which does not attack the organic film, preferably a liquid which can readily be mixed with the solvent of the photosensitive binder. It is advantageous to carry out the wetting process by means of spraying or atomization, during which processes fine drops are formed.

For the photosensitive binder, an aqueous solution of polyvinylalcohol in which a bichromate, for example, ammonium bichromate, serving as a sensitizer may be used. For wetting, water or a mixture of water and alcohol may be used, for example. A dried layer of the solution can be hardened by exposing it to a radiation having a wave length lying between 3600 A. and 5000 A., whereupon the binder is no longer soluble in water and alcohol.

In one embodiment the luminescent layer, which is composed of differently luminescing strips with the interposition of non-luminescent strips, is wetted with water. On this layer, an organic film is formed using a solution of one or more methacrylates in toluene. An aluminum layer is deposited by evaporation thereon in vacuo. By means of an atomizer, the aluminum layer is wetted with water. After the water has been allowed to penetrate through the pores of the aluminum layer, an aqueous solution is applied which consists of polyvinyl alcohol containing as a sensitizer, ammonium bichromate, and in the form of a suspension, a cerium-activated calcium-aluminum silicate. After drying, given areas are exposed to radiation having a wave-length lying between 3600 A. and 5000 A.

in a manner such that these exposed parts occupy a given position with respect to the strips of the luminescent layer. The non-exposed parts are then rinsed away with water, whereupon the screen is baked out, during which process the binder of the luminescent layer, the organic film and the polyvinyl alcohol are burned out. Thus, strips of cerium-activated calcium-aluminum silicate are present on the aluminum layer which supply long wave-length ultraviolet radiation upon excitation by electrons.

While the invention has been described in connection with specific embodiments and applications thereof, other modifications will be apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. In the method of manufacturing a luminescent screen for a cathode-ray tube for reproducing color images comprising the steps of applying to given areas of a transparent substrate a luminescent layer consisting of at least two substances luminescing in different colors upon excitation by electrons, wetting and coating said luminescent .4 layer with a solution of an organic substance, drying said organic substance, applying a metal layer pervious to electrons to said film, and forming over a portion at said metal layer a strip of a substance supplying an indexing signal upon excitation by electrons the steps of wetting the metal layer with an interrupted liquid layer so as to penetrate said metal layer and first organic film, applying a solution of photosensitive binder on said liquid layer, drying the solution and exposing the same at areas corresponding to the location of the indexing strip to the influence of hardening radiation, removing the unexposed binder, and baking out the screen.

2. A method as claimed in claim 1, in which the solution of the photosensitive binder contains in the form of a suspension the substance supplying an index signal upon excitation by electrons.

3. A method as claimed in claim 1, in which the substance supplying an index signal upon excitation by electrons is applied in the form of a suspension after the dried solution of the photosensitive binder has been exposed at the said given areas to hardening radiation before removing the unexposed binder and baking out the screen.

4. A method as claimed in claim 1, in which the substance supplying an index signal upon excitation by electrons is applied in the form of a suspension after the nonexposed binder has been removed and before baking out the screen.

5. A method as claimed in claim 1, in which the photosensitive binder is an aqueous solution of polyvinylalcohol containing ammonium bichromate.

6. A method as claimed in claim 2, in which the suspension is cerium-activated calcium-aluminum silicate.

References Cited UNITED STATES PATENTS 7/1956 Barnett 9636.1 X 7/1961 Kaplan et al ll7-33.5 X

U.S. C1.X.R. ll733.5