US3321263A - Cathode ray tube manufacture - Google Patents

Description

May 23, 1967 R. G. O'FALLON CATHODE RAY TUBE MANUFACTURE Filed Dec. 4, 1964 w r L mA e F W i G D R A 2 w m I G L, F m 2 9 M I g E 0 d we do. mm AC A 3 r O U 10 8 m A de @M 5 88 9 09 0G /I h" m% .l C Wm M. mm @H AH F \7 ATTYS.

United States Patent F 3,321,263 CATHGDE RAY TUBE MANUFACTURE Richard G. OFalion, Westchester, 11]., assignor to Motorola, Inc, Franklin Park, 111., a corporation of Illinois Filed Dec. 4, 1964, Ser. No. 415,977 4 Claims. ((31. 316-48) This invention relates to the manufacture of cathode ray tubes of the type used in television receivers, and more particularly to a process for manufacturing such tubes which reduce the tendency for arcing among the electrodes thereof.

A cathode ray tube may operate with a potential dif- .ference of the order of 24,000 volts among its electrodes. In a tribeam color tube, the three electron gun structures are positioned in the neck of the tube in closely spaced relation and the beams from the guns are deflected by a common deflection field. Furthermore, in such tubes adapted for Wide angle beam deflection, for example, 90 or more, the electron guns are particularly closely spaced in order to deflect the beams by a deflection field of satisfactory uniformity through this relatively wide deflection angle. These considerations of close spacing and high voltages cause cathode ray tubes for producing color images to be particularly susceptible to arcing which can make noise that is disturbing to the user of the tube or can cause current flow in the tube and associated circuitry which damages the television receiver.

Such arcing has been found to be largely a function of foreign matter or contamination within the tube, and of mechanical imperfections in the construction of the electron guns of the tube. Some improvement in arcing characteristics can be achieved by careful cleaning of the gun parts before they are assembled. Additionally, it is helpful to employ a high voltage arc-out to melt metal projections of the guns or stray particles of foreign matter within the tube after the tube has been evacuated and sealed so that these no longer tend to promote arcing.

However, there still may exist particular contaminants on the gun structure which are especially apt to producing arcing. For example, the stainless steel gun parts may have trace quantities of silicon, or other metals, or oxides thereof, which become focal points for the formation of arcs. In fact, as an example, minute quantities of silicon may actually emit electrons, such silicon becoming what is known as a cold emitter, so that an arc occurs between the gun part carrying the silicon, which may be operated at or near a ground potential, and a further nearby gun part having a potential of the order of 20,000 or 25,000 volts.

An object of this invention is to overcome the tendency for arcing in cathode ray tubes, which arcing would otherwise be caused by the presence of contaminants or impurities Within the tube.

Still another object is to reduce the effect of foreign matter within a cathode ray tube.

A still further object is to treat a tri-gun, color cathode ray tube which improves the arcing characteristics of the tube without materially increasing the processing time or cost in manufacture of the tube.

In brief the process hereof contemplates a high voltage arc-out to melt foreign particles, and after getter flashing, there is a high voltage aging of the components of the tube in which all of the various electrodes except the final anode are established at or relatively near a ground potential and the final anode is subjected to the continuous application of a potential substantially in excess of 3,321,263 Patented May 23, 1967 its normal operating potential (for example, twice norrnal operating) for an extended period of time so that emissive contaminants on the tube parts are rendered ineffectual to cause or promote arcing during later use of the tube.

In a specific form of the invention a three gun color cathode ray tube is treated in a high voltage aging process. By methods known in the art a tube is processed to the point of flashing a getter in the evacuated and sealed tube to absorb most of the remaining gas within the tube, although leaving a small residual amount of gas therein. Stray metal particles within the tube are burned away electrically in a matter of seconds by applying a high voltage between the second or final anode structure of the tube and its control grid, screen grid and focus grid. The cathode of the tube is activated or formed by heating its associated filament beyond the normal temperature and drawing current from the cathode to the screen grid. To stabilize the operation of the tube, the cathode is then aged at a lower temperature thereof than used in activation, and a limited current is drawn from the cathode to the screen grid. Simultaneously with such cathode aging, the control grid is grounded through a low impedance bus bar, and the electron beam is cutoff by application of a negative voltage on the focus electrode so that beam sweeping is unnecessary. A voltage substantially in excess of the normal operating final anode potential is applied to the final anode. This combined cathode aging and high voltage aging may continue for a period of an hour. During such time, emissive contaminants on the control grid, the screen grid, or the focus electrode, tend to emit electrons through cold emission, or field emission, and these electrons ionize the residual gases within the tube. The ionized gas particles, during this time, bombard the contaminants and poison them so that there is a gradual reduction in the emissive capability of the contaminants.

While initially there may be a pronounced blue glow in the neck of the tube surrounding the guns due to the ionization of the gases, the blue glow gradually disappears thus indicating that the cold emission of the contaminants is reduced. When the tube is subsequently used in a circuit which applies the normal operating potentials to its electrodes, there is a reduced tendency for arcing because the are producing contaminants of the gun structure have been rendered ineffectual.

In the drawing:

FIG. 1 is an elevational view, partly in section, showing a tri-beam shadow mask cathode ray tube for producing images in color;

FIG. 2 is a flow chart of manufacturing steps helpful to illustrate the invention; and

FIG. 3 is a sectional view of part of the neck of the cathode ray tube of FIG. 1, with one electron gun in section, and illustrating the application of certain potentials to the structure of the electron guns.

In FIG. 1 the tri-beam color cathode ray tube 10 includes connection pins 12, a neck section 14 and a funnel portion 16. Within the neck section 14 there is an electron gun assembly 18 comprising three separate, identical electron gun structures (one being 42", 44', 46', 50 in FIG. 3, e.g.) for producing three eletcron beams. The inside of the funnel portion 16 is coated with an aquadag coating 20 which is electrically connected to a portion of the gun structure 18 by means of the contacts 22.

The forward or flared portion of the funnel 16 is joined to a faceplate panel 24 along a frit sealing line 26. Faceplate panel 24 includes a shadow mask structure 28 supported by means of spring clips 30 and mounting studs 32 which are melted into the side walls of the faceplate panel 24. The viewing screen 34 of the picture tube comprises phosphor coatings which emit colored light when impinged by electron beams from the gun structure 18. As will be understood by those familiar with the cathode ray tube art, the screen 34 is composed of three complete sets of phosphors, and one of the three electron beams passes through the apertures of the shadow mask structure 28 to strike only one set of the phosphor dots. The energization of the three different sets of phosphors in the screen 34 by the beams produces an image having a color depending upon the relative energization of the different phosphors which individually produce light of red, green and blue color.

The tube has a faceplate panel 24 which is preferably of rectangular configuration when viewed from the front, and the tube has a relatively wide deflection angle for the beams (for example, 90 or more) so that the overall length of the tube may be as short as possible and the receiver in which the tube is used may be compact. The deflection angle referred to, of course, concerns the angle through which the beams are swept across in traveling across the screen 34.

In a tube of practical construction the neck section 14 may be of the order of 1 /2 inches in diameter so that the electron guns are closely spaced. Typical potentials applied to the electrodes of the gun structure, by way of the base pins 12 and the final anode connector 36, may be best considered by viewing FIG. 3. During operation of the tube in a television receiver the cathode electrode 40 may be operated at a D.C. potential of 260 volts, the first or control grid 42 may be operated at a D.C. potential of 130 volts, the second or screen grid 44 may be operated at a potential of 750 volts and the third or focus grid 46 may be operated at a potential of 5,000 volts. The potential of the screen 34, the aquadag coating 20, the convergence electrode structure 48 and the final anode member 50 may all be established at a potential of the order of 24 kv. Accordingly, it may be seen that various electrodes within neck 14 are at widely different potenitals and in closely spaced relation which can result in the production of damaging arcs. For example, the focus electrode 46 can are over to the electrode 50. While in the region of electrodes 42, 44 and 46 the inside of the neck section 14 is not coated with a conductive aquadag, this portion of the neck of the tube may assume a potential anywhere between ground and kv. or more, and thus there can be are between the neck 14 and one or more of the electrodes 42, 44 or 46.

One treatment that has been found effective to reduce the tendency for arcing within a television picture tube as described above, is very thorough cleaning of the electron gun structure before it is sealed within the tube neck. Each of the three different guns including the grids 42, 44, 46 and 50 may be made of stainless steel which may include trace impurities on the surface or trace amounts of foreign matter introduced in handling and manufacture. Thus, chemical cleaning and even electrochemical cleaning of the gun structure prior to sealing within the tube can be very helpful in reducing the tendency for arcing. However, it should also be recognized that further particles of foreign matter may be introduced on the gun structure after it is assembled in the tube and that despite careful chemical cleaning there may still be an undesirable tendency for arcing in a completely assembled tube. Thus, further provision for reducing arcing has been found necessary, particularly in the case of very closely spaced electron guns operating at high voltage in a color picture tube.

As indicated in FIG. 2 and considering the process at a time after the guns have been chemically cleaned and the tube is assembled with the guns in a tube neck which has been acid rinsed, the evacuated and sealed tube undergoes a getter flashing step 60. This is a known process involving the activation of gas absorbing material within the bulb of the tube to reduce the residual quantities of gas remaining after vacuum pumping of the tube. In step 62 the parts of the electron gun are arced out for a brief period to burn or melt any sharp points or imperfections in the tri-gun assembly or any foreign particles which are capable of destruction in this manner. The arc-out 62 is carried out with the grid 42, grid 44, and focus electrode 46 all grounded. A high voltage of the order of 40 kv. D.C. is applied for about one minute to electrode 50 and convergence assembly 48. Short pulses of 20 kv. R.M.S. A.C. of about 5 seconds duration are applied in series with the 40 kv. D.C. to foster arcing which is sustained by the 40 kv. DC. The voltage is applied through a relatively high impedance source in order to limit arcing currents within the tube to a value which would not destroy the gun structure itself.

In step 64 the cathode electrode 40 is activated. Itmay take a time of about /2 hour to form the cathode. To do so the heater or filament 65 (FIG. 3) is connected through switch terminal 67 to a transformer 68 providing a filament current considerably in excess of the normal operating current for high heating of the cathode 40. One side of the filament 65 is connected to ground and the other side is connected to the switch tenninal 67. Cathode 40 is connected to ground. In step 64 the cathode, thus elevated in temperature, provides current to control grid 42 and screen grid 44 which are established respectively at 20 volts and 500 volts. Control grid 42 is connected through switch terminal 74 and resistor 75 to its source of voltage to limit the current drawn and screen grid 44 is connected through limit resistor 77 to its source of operating voltage.

After thus forming or activating the cathode at step 64, the cathode is aged in order to stabilize operation in the tube in step 80. In step 80 the temperature of the cathode 40 is reduced by connecting the filament 65 through switch terminal 81 to a reduced operating potential. Furthermore, the control grid 42 is connected by a very low RF impedance to ground. In FIG. 3 this is indicated as a connection through switch contact 83, although it should be recognized that in practice the bus bar grounding of control grid 42 would not be through a switch but rather by a direct connection from one of the connector pins 12 to a large, low RF impedance connector forming the ground connection for the entire system.

Also as shown in FIG. 3, the focus electrode 46 is connected through switch contact 85 to a negative 250 volt potential which is sufficient to cutoff the flow of electrons beyond this electrode, the normal beam path being path 86. This makes it unnecessary to sweep the electron beams during the cathode and high voltage aging step. The electrode 50, the convergence assembly 48, and the drift space of the tube defined by the aquadag coating 20 (FIG. 1) are established at a potential of 4050,000 volts by connection of these parts of the tube through contact 87 and current limiting resistor 88 to a high voltage source. Resistor 88 may have an impedance of the order of 50,000 ohms to limit the amount of current that may be drawn in arcs during this process.

It is understood that FIG. 3 is a representation of the connections that are made and that in actual practice the switches shown may not be used, it being recognized that FIG. 3 merely indicates the difference in applied potentials between steps 64 and 80. Furthermore, it should be recognized that the connections to all of the parts of each of the three separate electron guns in the tube would be made through the normal connectors 12 and 36 and that the same electrode in each gun would be hooked up the same. Accordingly, the drawing of FIG. 3 is merely representative to facilitate an understanding, and is not intended to show the actual constructional features of the circuits supplying the potentials to the electron guns.

Step 80 may be carried out for a period of one or two hours. During that time current is drawn from the cathode 40 to the screen grid 44 so that there is cathode aging. 'While the high voltage aging aspect of step 80 could be successfully carried out separately and for a lesser time, rather than simultaneously with aging of the cathode, it is expedient from the manufacturing standpoint to have these two steps combined to run concurrently.

It is seen that the potentials of the electrodes 42, 44 and 46 are all relatively low and near zero as compared with the potential of the final anode structure including electrodes 48, 50, coating 20 and screen 34. With the very high potential difference thus established any emissive contaminants on the surfaces of the electrodes 42, 44, 46 and their supporting structures will emit electrons as cold emitters, or due to electric field emission. As an example of a trace impurity or contaminant, consider silicon or an oxide of silicon on the surface of one of the electrodes which would emit electrons under the conditions shown in FIG. 3. This electron emission will cause ionization of any residual gases in the tube which have not been absorbed in the getter flashing step 60 and a blue glow may be noted in the region of the neck 14 of the tube. With the residual gases thus ionized, these ions tend to strike or bombard the emissive contaminants on the surfaces of the grid electrodes and to poison them, or render them less effective as emitters. Accordingly, thoughout the treatment period, the blue glow gradually diminishes since the cold emission is reduced and, therefore, the ionization of the residual gases is reduced. It is possible to increase the potential at the final anode structure, applied through resistor 88, as the poisoning of the contaminants proceeds and this may be done without causing undue arcing since the high voltage aging is effectively cleaning up the surfaces of the components of the guns to reduce tendency for arcing. However, it is unnecessary to increase the final anode potential if it has been set sufliciently high and above its normal operating potential in the first instance. It has been found that a treatment of about one hour is sufficient, although a lesser time may be suflicient to reduce arcing tendency of a given tube.

It is necessary that the final anode cleanup potential applied through resistor 88 be low enough to prevent an amount of arcing within the tube that would cause heating of an arcing element and thermionic emission of that element. If thermionic emission does take place, the arcing may likely continue and cause further heating and further thermionic emission to establish a current run away condition which would destroy the tube. Accordingly, the potential applied to the final anode structure should be low enough to avoid this back heating and therminonic emission. However, it is also necessary that the final anode potential be high enough above the normal operating potential of the tube that the emissive contaminants on the electrode structure emit more electrons than they usually would under normal operating conditions of the tube. This can take place, for example, when the potential applied to resistor 88 is 50% or more higher than the normal or rated operating potential of the final anode structure.

During the initial stages of the high voltage aging process of step 80 there may be some amount of arcing if the final anode voltage is relatively high and if there are sufiicient contaminants. However, if the arcing ceases before a runaway condition develops, it is unlikely that this arcing will damage the tube. It should also be noted that the control grid 42 is grounded through a low impedance source so that arcing currents would be arrested at this grid and would not be drawn from the cathode 40, thus avoiding damage thereof.

Referring again to FIG. 2 after the completion of step 80, certain further steps may be necessary in the production of a finished tube ready for use. Such steps would include the application of an outer acquadag coating to the tube at step 92. Subsequently the tube may be given a final test at 95 to insure that it meets with whatever specifications may be established by the manufacturer. It will be seen, however, that the high voltage aging process in step is carried out very near the end of the manufacturing operation so that it is unlikely that any further handling of the tube will cause introduction of foreign matter which might promote arcing.

The above described process has been f und to be particularly elfective with tri-beam cathode ray tubes of wide deflection angle. It is possible to improve arcing characteristics of the tube without increasing the processing time or substantially affecting the cost of the manufacture of the tube since the high voltage aging can take place simultaneously with the aging of the cathode. While the described high voltage aging process is very effective in itself, it may be found that it can be most successfully carried out only after thorough chemical cleaning of the electron gun structure prior to installing it in the tube, and after getter flashing and normal arc-out of the gun structure for destroying certain imperfections as has been done in tubes of prior art construction. However, a complete process as described above goes beyond what has been usually employed in the construction of television picture tubes and provides an. improvement in arcing characteristics which has heretofore been difii cut to achieve in manufacture of tubes in production quantities.

I claim:

1. A process for treating a cathode ray tube to reduce the tendency for arcing among the parts thereof, including the steps of, providing a cathode ray tube having an electron gun structure including a plurality of grids subject to contamination by trace impurities capable of undesired emission of electrons, and a final anode structure to be established at an operating potential of the order of 20,000 volts during operation of said tube, getter flashing said tube after evacuation thereof whereby traces of residual gas may remain therein, and applying a high voltage aging potential of the order of 50% greater than said operating potential between said final anode structure and said grids from a current limited power supply, said high voltage aging potential and the limited current therefrom having values to cause trace impurities on said grids to produce field emission of electrons and ionization thereby of said residual gas so that such ionized gas renders said trace impurities ineffectual to cause arcing within said tube during operation thereof with the operating potential applied to said final anode structure, and said high voltage aging potential and the limited current therefrom having values less than that which will cause thermionic emission by said grids.

2. A process for treating a cathode ray tube to reduce the tendency for arcing among the parts thereof, including the steps of; providing a cathode ray tube having an electron gun structure including a control grid, a screen grid and a focus grid subject to contamination by trace impurities capable of undesired emission of electrons, and a final anode structure to be established at a high voltage anode potential during operation of said tube, getter flashing said tube after evacuation thereof whereby traces of residual gas may remain therein, applying an are producing potential to said final anode structure with respect to at least one of said grids for causing destruction of foreign particles in said tube. and applying a high voltage aging potential substantially in excess of said high voltage anode potential between said final anode structure and at least one of said grids from a current limited power supply, said high voltage aging potential and the limited current therefrom having values to cause trace impurities on said grids to produce cold emission of electrons and ionization thereby of said residual gas so that said trace impurities are bombarded by such ionized gas to be rendered ineffectual to cause arcing within said tube during operation thereof with the high voltage anode potential applied to said final anode structure, and said high voltage aging potential and the limited current therefrom having values less than that which will cause thermionic emission by said grids.

3. The process according to claim 2 in which said high voltage aging potential is applied to said final anode structure for the order of 1 hour.

4. The process according to claim 2, after applying said are producing potential to said final anode structure, performing the steps of, activating said cathode by heating the same above a normal operating potential and drawing current therefrom to one of said grids, and aging said cathode for stabilizing operation of said tube by drawing current therefrom to said screen grid simultaneously with the application of said high voltage aging potential to said final anode structure.

3 References Cited by the Examiner UNITED STATES PATENTS 2,583,029 1/1952 Townsend 316-1 References Cited by the Applicant UNITED STATES PATENTS 1,297,309 3/1919 Arnold. 1,854,376 4/1932 Kra-hl. 1,964,978 7/ 1934 Edelman. 1,966,496 7/1934- Fruth. 2,109,225 2/1938 Ulrey. 12,141,644 12/1938 Eddison.

2,41 1,5 22 11/ 1946 Chevigny. 2,726,311 12/1955 Ropes. 3,004,133 10/ 1961 Berghaus et a1.

RICHARD H. EANES, JR., Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,321,263 May 23, 1967 Richard G. O'Fallon It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 63, for "aquadag" read Aquadag (A registered trademark of Acheson Industries, Inc. for their brand of colloidal graphite in water.) column 3, lines 38 and 48, column 4, line 57, and column 6, line 2, for "aquadag", each occurrence, read Aquadag Signed and sealed 5th day of November 1968.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

Claims (1)

1. A PROCESS FOR TREATING A CATHODE RAY TUBE TO REDUCE THE TENDENCY FOR ARCING AMONG THE PARTS THEREOF, INCLUDING THE STEPS, OF PROVIDING A CATHODE RAY TUBE HAVING AN ELECTRON GUN STRUCTURE INCLUDING A PLURALITY OF GRIDS SUBJECT TO CONTAMINATION BY TRACE IMPURITIES CAPABLE OF UNDESIRED EMISSION OF ELECTRONS, AND A FINAL ANODE STRUCTURE TO BE ESTABLISHED AT AN OPERATING POTENTIAL OF THE ORDER OF 20,000 VOLTS DURING OPERATION OF SAID TUBE, GETTER FLASHING SAID TUBE AFTER EVACUATION THEREOF WHEREBY TRACES OF RESIDUAL GAS MAY REMAIN THEREIN, AND APPLYING A HIGH VOLTAGE AGING POTENTIAL OF THE ORDER OF 50% GREATER THAN SAID OPERATING POTENTIAL BETWEEN SAID FINAL ANODE STRUCTURE AND SAID GRIDS FROM A CURRENT LIMITED POWER SUPPLY, SAID HIGH VOLTAGE AGING POTENTIAL AND THE LIMITED CURRENT THEREFROM HAVING VALUES TO CAUSE TRACE IMPURITIES ON SAID GRIDS TO PRODUCE FIELD EMISSION OF ELECTRONS AND IONIZA-

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