US3814629A

US3814629A - Method of manufacturing a luminescent screen of a color television display tube

Info

Publication number: US3814629A
Application number: US00182492A
Authority: US
Inventors: N Hansen; W Littmann
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1970-09-25
Filing date: 1971-09-21
Publication date: 1974-06-04
Anticipated expiration: 1991-06-04
Also published as: FR2108548A5; GB1337779A; JPS5332677B1; BE773009A; NL7112928A; DE2047262A1; CA933576A; DE2047262B2; HK60276A

Abstract

A METHOD OF MANUFACTURING A LUMINESCENT SCREEN OF A CATHODE-RAY TUBE FOR DISPLAYING COLORED PICTURES. THE LUMINESCENT AREAS OF THE SCREEN ARE SEPARATED BY LIGHT ABSORBING AREAS. THE LUMINESCENT AREAS ARE APPLIED BY MEANS OF ANY METHOD PREVIOUS TO THE APPLICATION OF THE LIGHT ABSORBING AREAS WHICH ARE APPLIED BY MENS OF ELECTROSTATIC DEPOSITION. FOR THE ELECTROSTATIC DEPOSITION OF THE LIGHT ABSORBING AREAS A CONDUCTIVE LAYER AND A DIELECTRIC LAYER ARE FORMED IN THE INTERMEDIATE SPACES BETWEEN THE LUMINESCENT AREAS. THE LAYERS ARE FORMED BY MEANS OF RINSING WITH DILUTE, I.E., LOW VISCOSITY, SOLUTIONS BY WHICH THE FORMATION OF THE LAYERS ON THE LUMINESCENT AREAS IS IMPEDED.

Description

June 1974 N. E. F. HANSEN ETAL METHOD OF MANUFACTURING A LUMINESCENT SCREEN OF A COLQR TELEVISION DISPLAY TUBE Filed Sept. 21, 1971 INVENTORS NORBERT E. F. HANSEN WALTER F. K. LITT MANN United States Patent US. Cl. 117-211 9 Claims ABSTRACT OF THE DISCLOSURE A method of manufacturing a luminescent screen of a cathode-ray tube for displaying colored pictures. The luminescent areas of the screen are separated by light absorbing areas. The luminescent areas are applied by means of any method previous to the application of the light absorbing areas which are applied by means of electrostatic deposition. For the electrostatic deposition of the light absorbing areas a conductive layer and a dielectric layer are formed in the intermediate spaces between the luminescent areas. The layers are formed by means of rinsing with dilute, i.e., low viscosity, solutions by which the formation of the layers on the luminescent areas is impeded.

The invention relates to a method of manufacturing a luminescent screen of a cathode-ray tube for displaying colored pictures comprising discrete areas of materials which upon excitation by electrons luminesce in different colors, the luminescent areas being separated by lightabsorbing material. The luminescent materials are first provided on the window of the tube by means of a photosensitive binder and the light-absorbing material is provided afterwards.

A screen constructed in this manner provides the advantage that with the same contrast the tinting of the Window glass may be omitted or be at least smaller. As a result of this the observed brightness of the picture is greater.

US. Pat. No. 3,365,292 describes a method of manufacturing such a screen. After the various luminescent materials have been provided on the window by means of a photosensitive binder, they are provided with a filter layer. The window, which is provided with the surface regions of the various luminescent materials, is then covered with a photosensitive binder. The photosensitive binder is soluble in a solvent but after exposure to a certain radiation which is not passed by the filter layer, the binder becomes insoluble in the relevant solvent. The layer of binder comprises a material which does not or only slightly absorbs the relevant radiation and which can be converted into a dark light-absorbing material. After drying the layer of binder it is exposed to the relevant radiation through the window. Since the filter layer is present on the surface elements which are covered with surface regions of the various luminescent materials, the

binder layer is prevented from adhering in these places.'

The binder is hardened in all the free surface regions of the window. -After dissolving the non-hardened binder the material present in the hardened layer of binder is converted into a dark light-absorbing material by heating.

The difiiculty of this method is that a large number of operations are necessary.

US. Pat. No. 3,475,169 discloses a method of manufacturing a luminescent screen of a cathode-ray tube for displaying colored pictures which comprises in discrete surfaces substances which upon excitation by electrons "ice luminesce in different colors, said surfaces being separated by surfaces of a light-absorbing material. In this method the surfaces of the various luminescent materials and of the light-absorbing material are provided electrophotographically, in which for the formation of the charge image for the light-absorbing material a radiation is necessary. Also described in this patent specification is a method in which the surfaces of the various luminescent materials are provided electrophotographically but in which a binder is added to the luminescent materials which is modified in a further manufacturing step so that in the subsequent charging for the light-absorbing material it will not absorb any charge. In all these methods the window is entirely provided with a conductive layer and a photoconductive layer.

According to the invention, a conductive layer is provided, by rinsing with a low viscosity solution, i.e., one having a maximum concentration of about 10%, on the window which comprises the discrete surfaces of the various luminescent materials, the conductive layer being formed only in the intermediate spaces located between the luminescent areas, a dielectric layer being then provided on the conductive layer by means of rinsing with a maximum 10% solution, the dielectric layer then being dried and charged by means of a corona discharge, and the light-absorbing material being provided on the charged dielectric layer by means of electrostatic deposition from a suspension in an apolar solvent. In this method the light-absorbing material is provided on parts of the window which are still uncovered after providing the luminescent materials. Because of the low viscosity of the solution having a maximum concentration of 10% the porous structure of the luminescent dots prevents the formation of a coherent conductive layer in the region of the luminescent dots so that the conductive layer is actually formed only in the intermediate spaces between the luminescent dots. The formation of a coherent dielectric layer on the luminescent dots is strongly impeded by the structure of the luminescent dots so that the di electric layer is present only on the conductive layer. The dielectric layer after drying should preferably have a thickness of less than 10 ,um., in particular from l5 m.

During charging, the dielectric layer is charged to a high charge density as a result of its large capacity. Owing to the absence of a capacitive layer structure there is no charge on the luminescent dots. The formed charge image in the intermediate spaces is pigmented by means of an electrostatic deposition from a suspension of the black pigmentation agent in an apolar solvent. An apolar solvent must be used in order that the charge image be not discharged in contact with the solvent. According to this method in which only three treatments with a liquid are effected without irradiation a readily covering black pigmentation of the intermediate spaces between luminescent dots of any size is obtained without a disturbing deposition of the black pigmentation agent on the luminescent dots occurring.

The invention furthermore relates to a cathode-ray tube comprising a luminescent screen manufactured by this method.

In order that the invention may readily be carried into effect, it will now be described in greater detail, by way of example, with reference to the accompanying drawing, the sole figure of which shows a part of a window of a tube during the manufacture. The inside of the window of a shadowmask tube is provided with green, blue and red luminescent phosphor dots. In every case the inside of the window and the possibly already provided luminescent dots for producting a certain color are covered with a suspension of a relevant luminescent material (for producing another color) in a polyvinyl alcohol solution to which ammoniumdichromate has been added. After drying the layer, during an exposure to ultraviolet radiathe photo-hardening, the swelling powder of the layer in the exposed places is reduced and the excessive material is then washed away. A conductive layer is first provided on the window comprising the luminescent dots which layer is formed only in the intermediate spaces between the luminescent dots. This is achieved by rinsing with dilute solutions of ionogenic materials in polar and nonpolar solvents, possibly with the addition of wetting agents. The conductive layer which in a subsequent manufacturing step serves as an opposite electrode should have only a minimum conductivity because only very small currents must flow through the conductive layer. For example, 0.5 to 3% solutions of potassium silicate in Water or a mixture of polyvinylalcohol and glycerine in water are successfully used. Other substances for manufacturing said conductive layer may be used by those skilled in the art. On said conductive layer a dielectric layer of approximately 1-5 am. thickness is provided. For that purpose the inside of the window is treated, for example, with a 15% solution of polyvinyl-carbazol in parts of chlorobenzene and 1 part of dichloromethane. Instead of the polyvinylcarbazol may be used a variety of organic film-forming polymers having good dielectric properties. In the places of the luminescent dots the formation of a coherent layer is again strongly impeded. The layer is then dried. The figure shows the resulting structure. Luminescent dots 2 are present on a window 1. The intermediate spaces of the window 1 are provided with a conductive layer 3 on which a dielectric layer 4 is present. The picture screen is now exposed to a positive or negative corona discharge. One or several needleshaped tips or thin wires are connected to a high-voltage source of 6-30 kv. direct voltage and guided over the grounded layer 3 at a distance of a few centimeters therefrom. The dielectric layer 4 is charged to a high charge density in the intermediate spaces as a result of its large capacity and the counter charges are present in the conductive layer 3. No charge occurs on the luminescent dots owing to the lacking capacity. This charge image in the intermediate spaces is now pigmented by means of an electrostatic deposition from a suspension of a black pigmentation agent and an apolar solvent. Any black, finely divided dye may be used as a black pigmentation agent. A suitable prescription for a positively charged pigmentation agent for the black matrix is as follows:

Black pigmentation agent Bayer 7454 Ca 30 Polymetacrylate SV 46 .Rohm und Haas 5 Ca-diisopropylsalicylate 0.01 Ca-dodecylsulfosuccinate 0.01

Other black pigmentation agents, for example, soot may be used in a similar manner. By using other ionogenic materials, negative charges of the pigmentation agents can also easily be reached for the case in which a positive charge of the dielectric layer is to be used.

What is claimed is: 1. A method of manufacturing a luminescent screen for a color display cathode ray tube, said screen comprising a transparent substrate and discrete areas of electronexcitable color luminescent materials disposed thereon and separated by a light absorbing material, said method comprising the steps of:

(a) providing a structure comprising said substrate and said discrete luminescent areas located directly on a first face thereof;

(b) forming at only exposed regions of said first face a conductive layer such that said discrete luminescent areas are substantially completely surrounded there- (c) forming at only said conductive layer a layer of dielectric material;

(d) charging said dielectric layer by corona discharge;

and

(e) electrostatically depositing said light-absorbing material on said charged dielectric layer.

2. A method of manufacturing a luminescent screen for a color display cathode ray tube, said screen comprising a transparent substrate and discrete areas of electronexcitable color luminescent materials disposed thereon and separated by a light absorbing material, said method comprising the steps of:

(a) providing a structure comprising said substrate and said discrete luminescent areas located directly on a first face of said substrate;

(b) rinsing exposed regions of said first face with a low viscosity solution of an ionogenic material carried in a medium of at least one of a polar and an apolar solvent, thereby forming a conductive layer at only said exposed regions surrounding said discrete luminescent areas;

(0) rinsing said conductive layer with a low viscosity solution of a dielectric material, thereby forming a layer of dielectric material at only said conductive layer, said conductive and dielectric layers substantially completely surrounding said discrete luminescent areas and being only laterally disposed with respect to said discrete areas;

((1) charging said dielectric layer by corona discharge;

and

3. A method as recited in claim 2, wherein the thickness of said dielectric layer is less than about 10 microns.

4. A method as recited in claim 2, wherein each one of said first and second solutions has a concentration of said ionogenic material and said dielectric material, respectively, not exceeding 10%.

5. A method as recited in claim 2, wherein said first solution further comprises a wetting agent.

6. A method as recited in claim 2, wherein said first solution is an aqueous solution of potassium silicate.

7. A method as recited in claim 2, wherein said first solution is an aqueous solution of polyvinyl alcohol and glycerine.

8. A method as recited in claim 2, wherein said second solution consists essentially of polyvinyl carbazol, chlorobenzene, and dichloromethane.

9. A method as recited in claim 2, wherein said second solution consists essentially of dielectric film forming polymer, chlorobenzene, and dichloromethane.

References Cited UNITED STATES PATENTS 3,113,037 12/1963 Watanabe 1l793.4 R 3,206,323 9/1965 Miller et al. 117- 93.4 R 3,108,893 10/1963 Oliphant 11793.4 R. 3,251,551 5/1966 Walberg 117-93.4 R 3,365,292 l/l968 Fiore et al. 96-32.6 3,475,169 10/1969 Lange 117335 CM 2,682,478 6/ 1954 Howse 11733.5 CM 2,787,556 4/1957 Haas l1733.5 CM 3,593,678 7/1971 Miller 11733.5 CM

WILLIAM D. MARTIN, Primary Examiner W. R. TRENOR, Assistant Examiner US. Cl. X.R.

96l, 1.2, 2.5, 36.2; 11717.5, 33.5 C, CM, 37, 93.4 A, 212, 215, 218, 219; 33-92 P0405) UNITED STATES PATENT OFFICE I CERTIFICATE OF CORRECTION Patent No. 3,814,629 Dated J uge 4, 1974 In nt r(s) NORBERT E. F. HANSEN ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 49, after "30" insert --g--;

line 50, after "5" insert --g-- line 51, after "0.01" insert --g-;

line 52;, after "0.01" insert -g--.

Signed and sealed this 8th day of October 1974.

(SEAL) Attest:

' MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents