US2596617A

US2596617A - Increasing number of holes in apertured metal screens

Info

Publication number: US2596617A
Application number: US123875A
Authority: US
Inventors: Gordon K Teal
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1948-12-29
Filing date: 1949-10-27
Publication date: 1952-05-13
Anticipated expiration: 1969-05-13

Description

y 3, 952 G. K..TEAL 2,596,617

INCREASING NUMBER OF HOLES IN APERATURED METAL SCREENS Original Filed Dec. 29, 1948 5 Sheets-Sheet 1 FIG. 2

lNl/ENTOR G. K. TEAL ATTORNEY May 13, 1952 G. K. TEAL 7 7 INCREASING NUMBER OF HOLES IN APERATURED METAL SCREENS Original Filed Dec. 29, 1948 3 Sheets-Sheet 2 FIG. /3

FIG; l2

EVAPORATE lNl/ENTOR G. K, TEAL ATTORNEY May 13, 1952 G, K, TEAL 2,596,617

INCREASING NUMBER OF HOLES IN APERATURED METAL SCREENS Original Filed Dec. 29, 1948 3 Sheets-Sheet :5

/// ZZJ SOURCE S/l. VER ELECTRODE 0X YGE N A TMOSPHERE CURRENT DISCHARGE ALUMINUM ELECTRODE 'LGO INVENRDR G. K TEAL BY AZZZ ATTORNEY Patented May 13, 1952 INCREASING NUTMBER OF HOLES IN APERTURED METAL SCREENS Gordon K. Teal, Summit, N. J., assignor a Bell Telephone Laboratories, Incorporated, New York, N. Y., .a corporation of New York Original application December 29, 1948, Serial No.

Divided and this application October 27, 1949, Serial No. 123,875

4 Claims. (CI. 41-43) This invention relates to electro-optical devices and more specifically to methods of making target or screen structures for use in television transmitter tubes. This application isa division of application Serial No. 167,917 filed December 29, 1948.

It has long been recognized in the development of electron camera tubes for generating picture signals at a television transmitting station that there are many advantages in projecting an electron image of the object for transmission onto one side of the screen of the tube and scanning the opposite side of the screen with a cathode ray beam formed in the tube. An example of a camera tube employing such a two-sided target or screen is the so-called image orthicon" tube, described in an article entitled The Image rthicon-A Sensitive Television Pick-up Tube by Albert Rose, Paul K. Weimer and Harold B. Law, appearing in the July 1946 issue "of the Proceedings of the I. R. E., beginning on page 424. The two-sided target makes possible the separation of charging and discharging processes so that the sensitizing procedures and electric fields appropriate to each can be utilized in the tube without mutual interference. The target must conduct charges between its two sides or surfaces but not along either surface. Moreover, it should have a conducting element therein or nearby to act as the common capacitor plate for the separate picture elements. It has been found very difficult to construct satisfactorily commercial targets of this type.

It is an object of the present invention to provide novel and improved methods for making apertured metal screens which can .be used, for example, in the production of two-sided electron camera tube targets which have a large number of elemental discrete conducting elements .per square inch.

It is a further object of this invention to provide novel methods of preparing screens having an increased number of holes. I

In an exemplary method of making an apertured metal screen in accordance with the invention, which can be us'edin the production of a two-sided mosaic target for camera tubes and the like, a master apertured metallic screen is used to produce a final screen which has a much larger number of apertures than the master. A pattern of solid dots'is formedon apiece of pa-- per by evaporation through the holes of the master screen. The master screen is then shifted so that the holes fall in position between the dots already formed and. the evaporation process is repeated. A layer of silver or copper oxide is then producedupon the paper by vacuum filtering and the oxide is reduced to silver or copper. The solid dots are then etched out of the holes, giving a perforated metal screen having twice the number of holes possessed by the master screen. By using the final screen as a master in a repetition of the process, the number of holes in the resulting screen is even further increased.

The invention will be more readily understood by referring to the following description taken in connection with the accompanying drawings forming apart thereof, in which:

Figs. 1 to 6,, inclusive, illustrate various steps in a method of producing an apertured metallic screen which can be used in the process in accordance with the invention;

Figs. 7 to 11, inclusive, illustrate steps in the process of electrolytically polishing the screen shown in Fig. 6;

Figs. 12 to 16, inclusive, illustrate a method in accordance with the invention of increasing the number of holes in the screen shown in Fig. 11;

Figs. 17 to 20, inclusive, illustrate a method of filling the apertures in the screen shown in Fig. 16 with insulated plugs;

Fig. '21 is a top view of a schematic representation in greatly enlarged form of a portion of a target utilizing an apertured screen made in accordance with the invention;

Fig. 22 is a sectional side view of portions of such'a target; and

Fig. .23 shows apparatus used in making the target.

Referring more specifically to the drawings, Figs. 21 and 22 show, by way of example for purposes of illustrating one use of an apertured metal screen made in accordance with the invention portions of a two-sided mosaic target 30 suitable :for use in certain television transmitting tubes, such as, for example, the image orthicon type of tube briefly referred to above. It will be understood that Figs.2l and 22 are merely schematic "showings and the same applies to the other figures in the drawings. Target 30 comprises a thin metallic screen 53 of a suitable metallic material having a large number of holes to the linear inch, e. g., four hundred per inch or more. One surface, such as the top surface in Fig. '22, and theinteriors of all the aperture in a master in the process of Figs. 12 to 16, inclusive,

in accordance with the invention.

Fig. 1 shows a thin conducting layer 49 of platinum or other suitable material which is evaporated, sprayed, sputtered or otherwise deposited on a wax block 4|. Very small particlesv of uniform diameter are insuillated upon the surface of the film 40. These particles 42 may be any hard particle, such as diamond, sapphire, iron,-nickel or other solid. Fig. 2 shows these particleslon the conducting film 40.

As shown in Fig. 3, the particles 42 are pressed into the metal film 40 with a roller or a smooth fiat or curved plate. This breaks small areas of the metal 4|] away from the main part of the conducing film leaving thereby a perforated screen onthe surface of the wax. Small areas 43 of the screen are pressed into the wax block 4 l If the particles 42 are conductors such as iron or nickel, "they may be dissolved with nitric or hydrochloric acids. If the particles 42 are insulating particles this step can be omitted.

A thick a coat of nickel is applied to the platinurn screen 40 as is possible without closing up the holes 44. The coating 45 is shown in Fig. 5.

Let it be assumed that an enlarged side view of one of the apertures 44 and of its surrounding metal is shown inFig. '7, and a large cross-section of the aperture 44 is shown in Fig. 8. It is obvious that the actual aperture 44 is by no means as smooth .asis represented in Fig. 7. It has been shown in .this manner merely for convenience and simplicity in the drawings. It will be noted that the metal screen 46 shown in Fig. '7 has angular projections 41A around the hole and also small irregular projections 48A shown in Fig. 8. The screen 46 is then electrolytically polished 'by making it the anode in a solution of that the holes 44 fall in the positions indicated by the clear circles 49A in Fig. 14, and a solid is evaporated through the holes in the screen while .it is in this position to produce new thin solid dots 49 (shown in Fig. 16).

The metal screen 46 is then removed and the filter paper 41 upon which

aluminum dots

48 and 49 have been superimposed is placed upon a filter cylinder 50 ofsintered glass or glass containing a multiplicity of capillary holes and a layer of silver oxide or copper oxide 5| is deposited upon the paper while vacuum is applied to the underside of the cylinder. The entire assembly is then placed in a reducing atmosphere and the silver oxide or copper oxide reduced to silver or copper. The

aluminum dots

48 and 49 are now etched out of the holes with concentrated potassium hydroxide solution giving a perforated metal screen having twice the number of holes possessed by the original screen.

.The metal screen produced by the process illustrated by Figs. 12 to 15, inclusive, is now used in a repetition of this procedure to produce a metal screen having holes including those shown as 48 and 49 in Fig. 14 and also those shown in the positions of the dotted circles 52 in Figflfi. This produces a screen shown as 53 in Fig. 17 which contains four times the total number (if holes as the screen shown in Fig. 12 arid twice the numsulfuric acid and water (120 cc. H2SO4 to 80 cc.

H2O) at a high current density. This rounds off some of the projections and dissolves part of the nickel screen as indicated in Figs. 9 and 10 which otherwise correspond to Figs. 7 and .8, re-

spectively. A thin film of metal is then electro plated upon the screen 46 and the polishing process is repeated and re-repeated as often as necessary to give the smooth screen 46 shown in Fig. 11. It will'be noted that in Figs. 7 to 11, inclusive, no attempt has been made to show the various metal layers (such as, for example, layers 45 and 40) making up the screen, it being shown for simplicity merely as a solid metal screen 46.

Figs. 12 to 16, inclusive, illustrate a method in accordance with the invention of increasing the number of holes in the screen 46. As shown in Fig. 12, the metal screen 46 shown in Fig. 11 is placed upon and in intimate contact with a piece of thin filter material 41, such as paper, and a metal or other solid is evaporated through the holes 44 in the screen. This gives a pattern of thin solid dots 48 over the entire surface of the paper as indicated in Fig. 13. Obviously the dots are not perfect circles as shown in Fig. 13 but are shown thus for simplicity in the drawings.

The screen 46 is then shifted into position so ber of holes per linear inch as that shown in Fig. 12.

Figs. 1'7 to 20, inclusive, illustrate a method of filling the apertures in the screen 53 with insulated metallic plugs. Referring now' to Fig. 1'7, the metal screen 53 is coated with insulating layer 54. This is obtained by evaporating a suitable substance such as cryolite on the top of the screen orby insufiiatingglass on the screen and then fusing it to give the coating 54. A uniform coating of beeswax, asphaltum or other adhesive 55 is applied to a fairly thick stiff piece of metal or glass 56. The adhesive is flowed on the metal or glass 56 by melting or by use of a solution of the adhesive in a solvent such as carbon tetrachloride. Evenness of spreading can b'eassured by spinning in a horizontal plane. The coated metal screen 53 is pressed onto the wax'film 55 so that a small amount 55A of the wax is pushed into each hole'of thescreen as shown in 17. Silver oxide 51 is then applied to the surface of the unit of Fig. 17 by bombarding silver in oxygen 7 with high voltagev discharges.- This can be accomplished in the apparatus shown inFig. 23 wherein the unit 58 shown in Fig. 1'7 and represented schematically by a rectangle ,inFig. 23 is mounted in the path between a silver electrode 59 and an aluminum electrode 60 in an oxygen atmosphere, a source of high direct-current voltage 6| being connected between the two. electrodes. Because of the oxygen atmosphere, a multiplicity of silver oxide particles 51 is built up in the apertures of the unit 58.

The excess silver oxide isthen wiped off, leaving the silver oxide plugs 5'! in the holes of the screen 53 as shown in Fig. 19. The unit is then heated up and the screen is removed from its supports. l r j The screen of Fig. 19 is then heated in hydro-. gen to reduce the silver oxide '51 to silver buttons 51A. Alternatively, it can be treated'with a liquid reducing agent such as one of theon'es fre quently used in photography, for example. This produces a screen one elemental portion of which is shown in Fig. 20 and another larger portion thereof to a somewhat smaller scale is shown in Figs. 21 and 22.

Various alternative steps and procedures other than those mentioned above are of course possible without departing from the spirit of the invention, the scope of which is pointed out in the claims. The disclosed over-all process of making mosaic screens of the type shown in Figs. 21 and 22 is claimed in the parent application, Serial No. 67,917, filed December 29, 1948; the methods disclosed herein (Figs. 1 to 6, inclusive) of forming an apertured metal screen of the type shown in Fig. 6 are claimed in a copending application of the present inventor, Serial No. 123,873, filed October 27, 1949; the methods disclosed herein of electrolytically polishing apertured metal screens (Figs. 7 to 11, inclusive) are claimed in a copending application of the present inventor, Serial No. 123,874, filed October 27, 1949; and the sputtering method disclosed herein and the apparatus used therefor (Figs. 17 to 20, inclusive, and 23) are being claimed in still another copending application of the present inventor, Serial No.'123,876, filed October 27, 1949.

What is claimed is:

1. The method of producing a screen with an increased number of holes from a master screen having a smaller number of holes comprising the steps of placing said master screen upon a thin support member, depositing a solid material through the holes of the screen to produce a pattern of solid dots over the entire surface of the support member, shifting the master screen so that the holes fall in position between the dots on the support member, depositing a solid material through the holes in the screen while it is in this position, removing the master screen, depositing a layer of metallic oxide upon the support member, reducing the metallic oxide to metal, and then removing the solid dots.

2. The method of producing a screen with an increased number of holes from a master screen havin a smaller number of holes comprising the steps of placing said master screen upon a thin support member, evaporating a solid material through the holes of the screen to produce a pattern of solid dots over the entire surface of the support member, shifting the master screen so that the holes fall in position between the dots on the support member, evaporating a solid material through the holes in the screen while it is in this position, removing the master screen, depositing a layer of metallic oxide upon the support member, reducing the metallic oxide to metal, and then removing the solid dots.

3. The method of producing a screen with an increased number of holes from a master screen having a smaller number of holes comprising the steps of placing said master screen upon a thin support member, depositing a solid. material through the holes of the screen to produce a pattern of solid dots over the entire surface of the support member, shiftin the master screen so that the holes fall in position between the dots on the support member, depositing a solid material through the holes in the screen While it is in this position, removing the master screen, depositing a layer of metallic oxide upon the support member by vacuum filtering, reducing the metallic oxide to metal, and then removing the solid dots.

4. The method of producing a screen with an increased number of holes from a master screen having a smaller number of holes comprising the steps of placing said master screen upon a thin support member, depositing a solid material through the holes of the screen to produce a pattern of solid dots over the entire surface of the support member, shifting the master screen so that the holes fall in position between the dots on the support member, depositing a solid material through the holes in the screen while it is in this position, removin the master screen, depositing a layer of metallic oxide upon the support member, reducing the metallic oxide to metal, and then removing the solid dots by etchmg.

GORDON K. TEAL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,085,727 Dawson et a1. Feb. 3, 1914 2,116,901 Knoll May 10, 1938 2,118,186 Farnsworth May 24, 1938 2,120,916 Bitner June 14, 1938 2,447,836 Beeber et a1. Aug. 24, 1948 FOREIGN PATENTS Number Country Date 628,871 Great Britain Sept. 6, 1949 OTHER REFERENCES Wall: Three-Color Photography; published by American Photographic Publ. Co., Boston, 1925, pp. 490 and 491.