US3638275A

US3638275A - Methods and apparatus for the manufacture of color cathode-ray tube screens

Info

Publication number: US3638275A
Application number: US75170A
Authority: US
Inventors: John F Larson; Walter A Polashenski
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1970-09-24
Filing date: 1970-09-24
Publication date: 1972-02-01
Anticipated expiration: 1989-02-01

Abstract

Methods for drying the upstanding walls of a cathode-ray tube faceplate, particularly around the area of the mask supporting studs are disclosed. The methods utilize an accurately controlled and automatically positionable head for removing excess liquid from the walls and stud area after a processing step. The liquid may be that remaining from either a prerinse in which case either forced air or a vacuum system may be utilized for the liquid removal; or after a developing step in the actual screen formation when a vacuum principle along is utilized for drying the wall area. The described apparatus for carrying out the method comprises a free-floating, self-orienting head which is pivoted to provide arcuate movement in a given substantially vertical plane, and reciprocatable shaft means connected to the free-floating head for indexing the head in a substantially perpendicular direction. Cam means associated with the reciprocatable movement causes engagement and disengagement of the head with the faceplate in accordance with the direction of movement thereof. The cam means causes the head to pivot in a substantially horizontal plane to bring the head into engagement with the faceplate wall.

Description

Larson et a1.

[ 1 Feb. 1, 1972 METHODS AND APPARATUS FOR THE MANUFACTURE OF COLOR CATHODE-RAY TUBE SCREENS John F. Larson, Seneca Falls, N.Y.; Walter A. Polaslienski, Roanoke, Va.

Inventors:

Sylvania Electric Products Inc.

Sept. 24, 1970 Assignee:

Filed:

Appl. No.:

Related U.S. Application Data Division of Ser. No. 723,098, Apr. 22, 1968.

References Cited UNITED STATES PATENTS Primary ExaminerWalter A. Scheel Assistant Examiner-C. K. Moore Attorney-Norman .l. OMalley, Donald R. Castle and William H. McNeill [57] ABSTRACT Methods for drying the upstanding walls of a cathode-ray tube faceplate, particularly around the area of the mask supporting studs are disclosed. The methods utilize an accurately controlled and automatically positionable head for removing excess liquid from the walls and stud area after a processing step. The liquid may be that remaining from either a prerinse in which case either forced air or a vacuum system may be utilized for the liquid removal; or after a developing step in the actual screen formation when a vacuum principle along is utilized for drying the wall area. The described apparatus for carrying out the method comprises a free-floating, self-orienting head which is pivoted to provide arcuate movement in a given substantially vertical plane, and reciprocatable shaft means connected to the free-floating head for indexing the head in a substantially perpendicular direction. Cam means associated with the reciprocatable movement causes engagement and disengagement of the head with the faceplate in accordance with the direction of movement thereof. The cam means causes the head to pivot in a substantially horizontal plane to bring the head into engagement with the faceplate wall.

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ATTORNEY METHODS AND APPARATUS FOR THE MANUFACTURE OF COLOR CATHODE-RAY TUBE SCREENS CROSS-REFERENCE TO RELATED APPLICATION This application is a division of Ser. No. 723,098 filed Apr. 22, 1968 and assigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION This invention relates to apparatus utilized in the manufacture of color cathode-ray tube screens and more particularly to apparatus for removing excess liquid from the upstanding walls and studs of a cathode-ray tube face plate after either a prerinse or developing step.

In the currently used methods of forming color cathode-ray tube screens of the shadow mask variety, a photographic deposition technique is utilized. This type of color tube has a screen formed of a set pattern of triads of different color emissive phosphors. The colors generally emitted are red, green and blue. The patterns are generally formed by applying each color phosphor individually in the following steps: applying to the screen area of the face plate a photosensitized material such, for example, as polyvinyl alcohol (PVA) sensitized with ammonium dichromate. This photosensitized material may or may not have the phosphor particles dispersed therein. In either case, after the deposition of the photosensitized material, the shadow mask structure, which comprises a thin apertured metal plate portion having one aperture for each of the triads to be placed on the screen and which is usually mounted on a heavier frame structure, is releasably mounted within the face plate portion by means of apertured springs attached to the shadow mask frame and fixed studs which are positioned on the upstanding face plate wall and project inwardly thereof. After the mask is in position, the face plate-mask assembly is positioned on an exposure device and the coated screen area is exposed to a suitable source of radiation, usually actinic, from a point source of light which is positioned to substantially duplicate the position of the electron gun to be associated with that color in the finished tube. After exposure, which causes the exposed areas of the screens to become polymerized and thus insoluble in a given solvent, the mask is removed from the face plate and the screen area is developed by washing the screen with a solvent for the unexposed areas remaining which removes them from the screen. When a PVA solution is used, the solvent is water.

The above steps are repeated twice more to complete the screen each time using a different phosphor and, during the exposure step, with the source of exposure radiation in a different position corresponding to the gun position to be utilized in the finished tube. For a more detailed explanation of one particular method of screen deposition, reference may be made to U.S. Pat. No. 3,025,] 61. For a more detailed explanation of the operation of a shadow-mask type of color cathoderay tube, reference is made to U.S. Pat. No. 2,986,080.

Because of the sequence of coating, exposing and developing necessary to form the screen and because of the fact that the developing is done with water which is a solvent for the photosensitized PVA, it becomes necessary to insure that the upstanding walls on the face plate are dried between each of the screen-forming operations since any water remaining thereon would tend to cause dilution of the PVA being applied for the subsequent operation. Prior to applicants invention, this drying was usually accomplished either by an operator using a sponge or by a hand-held operator-controlled jet of high pressure air. Both of these prior methods had disadvantages which adversely affected the quality of the finished tube. Namely, hand-wiping with a sponge clearly lacks uniformity of control. It was also possible for the operator, through carelessness, to inadvertently wipe away part of the previously formed screen. Also, it was very difficult to dry the areas around the inwardly projecting studs, and water which often collected therearound sometimes caused sufl'lcient rust accumulation thereon to subsequently contaminate the screen. Further, the sponge material would often tear off when wiping the stud areas, and these particles remaining on or near the screen could also cause contamination thereof.

The operator-controlled, hand-held high pressure air method of removal also left much to be desired in that it too lacked uniformity of removal and, when being utilized on a partially patterned screen, it could cause damage to the pattern formed thereon.

OBJECTS AND SUMMARY OF THE INVENTION Therefore, it is an object of the invention to obviate the disadvantages of the prior art methods.

Yet another object of the invention is to provide apparatus ideally suited to carrying out the above cited objects.

Yet another object of the invention is to eliminate the inaccuracies and inconsistencies inherent in the prior art hand operated methods.

These objects are accomplished in one aspect of the invention by the provision of apparatus for removing the excess liquid from the interior upstanding walls of a cathode-ray tube face plate, the wall having a given thickness and having inwardly projecting studs thereon, by contacting the wall and the edge thereof formed by the thickness of the wall with an excess liquid removal system. The wall contacting portion of the system is formed to provide clearance over the inwardly projecting studs. While contact between the wall and the excess removal system is being maintained, relative movement is caused to occur between the system and the face plate whereby excess liquid is removed and the upstanding wall and stud areas sufficiently dried before the next operation in the screen process takes place.

It will be seen from the above that this method of excess liquid removal obviates the disadvantages of the prior art and has many advantages thereover. The excess removal system formed to contact the wall portion eliminates operator error and does not introduce possibly contaminating substances into the screen area. Further, it is more accurately controllable and thus precludes screen damage caused by operator carelessness.

Apparatus for carrying out the above methods comprises a face plate wall contacting head which is formed to contact the edge of the wall formed by the thickness thereof and project inwardly of the wall a distance at least sufficient to encompass the studs and being further formed to provide clearance over the studs. The head is mounted at one end of a free-floating counterbalanced arm which is pivoted for arcuate movement about a given axis at a point intermediate the head and the counterbalance. The arm is mounted on a reciprocatable shaft having means attached thereto for causing the desired reciprocation. Cam means are provided, operative with the reciprocatable shaft for causing the head to follow an arcuate path in a second direction to engage and disengage from the wall in accordance with the direction of movement of the shaft. An excess liquid removal force supply, which may be either vacuum or high pressure air, depending upon the condition of the face panel at a particular stage of screening, is connected to the head. Also provided are means for causing relative movement to occur between the head and the face plate at least during engagement of the head with the wall.

This apparatus has many advantages over the previous hand-operation methods and provides extremely accurate control over the excess liquid removal operation. The freefloating head arrangement is ideally suited to cooperate with the variable path traced by rotative movement of a rectangular face plate and it also permits immediate self-orientation with the wall of the face plate regardless of the angular orientation of the face plate when the excess removal system is energized. This feature makes this apparatus ideally suited to performing its functions as a single station on an automated or conveyorized screen application apparatus. However, it is to be noted that its use is not restricted thereto.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a typical color cathode-ray tube face plate;

FIG. 2 is a flow diagram of one embodiment of the invention;

FIG. 3 is a flow diagram of a second embodiment of the invention;

FIG. 4 is a diagrammatic representation of one means for causing rotation of the face plate;

FIG. 5 is an elevational view of one type of apparatus that may be utilized in carrying out the methods of the invention and is taken along the line 5-5 of FIG. 6;

FIG. 6 is a plan view of the apparatus and is taken along the line 6-6 ofFIG. 5;

FIG. 7 is a sectional view of the wall contact head in its operative position with the wall of the face plate and is taken along the line 7-7 of FIG. 6; and

FIG. 8 is a perspective view of the head in its entirety.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above described drawings.

Referring now to the drawings with greater particularity, there is shown in FIG. 1 a typical color cathode-ray tube face plate 10 having a concave interior surface 11 on which the screen will be formed and an upstanding wall portion 12. The external edge of wall 12 has an edge 13 formed by the thickness of the wall. The interior surface of wall 12 is provided with at least two inwardly projecting, mask supporting studs 14. It is the studs 14 which provide most of the difficulty in removing excess liquid from the face plate.

Referring now to the flow diagram of FIG. 2, there are shown the basic steps utilized in one embodiment of the invention. In this embodiment which might, for example, be a prerinse of the face plate prior to screen deposition, the face plate 10 would be wetted with the rinsing material and then positioned in a manner to facilitate drainage of the liquid. An exemplary position of the face plate could be with the plane of the face plate angled from the vertical at approximately This position is a compromise well suited to cooperate with automatic machinery; however, any orientation between 0 andl80 might also be appropriate depending upon circumstances. After a sufficient time to allow some natural drainage caused by the force of gravity, the wall of the face plate 10 and the edge 13 thereof formed by the thickness of the wall are contacted by an excess liquid removal system. The wall contacting portion of this system is formed to project inwardly of the wall and provide clearance over the studs 14 positioned therein. After contacting the wall 12 and edge 13 with the excess liquid removal system, an excess liquid removal force is supplied to the wall contacting portion thereof and relative movement is caused to occur between the face plate and the system. When this embodiment is utilized with a prerinse cycle; that is, prior to any screen deposition, the excess liquid removal force may be either a vacuum or a source of high pressure air.

The flow diagram of FIG. 3 illustrates an embodiment of a process wherein the invention is utilized during the actual screening formations. In this instance, the interior surface of the face plate 11 is coated with a pattern forming material such as PVA sensitized with ammonium dichromate, and is then mated with an exposure negative which is generally the shadow mask to be utilized in the finished tube. The mated face plate-negative assembly is then placed on an exposure device and exposed to a suitable source of point radiation as discussed above. After the exposure, the negative is removed from the face plate and the face plate is processed in the first developing sequence which comprises washing the interior of the face plate with a solvent for the unexposed portions of the PVA. When PVA is the material being utilized, the solvent is water. After developing, the face plate is again positioned in a manner to facilitate drainage and the wall 12 and edge 13 of the face plate 10 are dried in accordance with the last two steps of the embodiment described in FIG. 2. The only exception to this is that after a partially patterned screen appears on the face plate, such as is illustrated in FIG. 7, the excess liquid removal force supply is best restricted to a vacuum removal system, since the application of high pressure air at this point may tend to destroy the previously formed patterns. A suitable flow of air for a vacuum system would be one utilizing a velocity of between 5075 ft./sec.

One means for accomplishing relative movement between the face plate 10 and the excess liquid removal system is shown diagrammatically in FIG. 4, wherein there is shown a suitable face plate-holding device which may be a common vacuum chuck 30. This type of vacuum chuck is well understood by those skilled in the art and needs no further explanation. The chuck 30 is connected to a rotatable shaft 32 which is journaled in a bushing 34 fixed in a gear housing 36. The end of shaft 32 remote from chuck 30 is provided with a miter gear 38 which engages a mating miter gear 40 mounted on a second shaft 42. Shaft 42 is journaled by means of bushing 44 in a second wall of gear housing 36 at one end thereof, and at its other end is journaled by means of a bushing 46 mounted in a wall of a second gear housing 48. This end of shaft 42 is also provided with a miter gear 50 which mates with miter gear 52 which is fixedly mounted on a third shaft 54; shaft 54 being journaled by means of a bushing 56 in a second wall of housing 48. The end of shaft 54 remote from miter gear 52 is provided with a coupling portion 58 which is formed to provide selective engagement and disengagement with a source of rotative power. The source of rotative power 60 is shown in this instance as comprising a motor 62 having a shaft 64 projecting therefrom and having affixed thereto a pulley 66. Pulley 66 is connected by means of a belt 68 to a second pulley 70 mounted on the reciprocatable shaft 72 of a fluid motor 74. A key 76 is provided on shaft 72 to cooperate with a keyway formed in pulley 70 so that shaft 72 may be reciprocated therethrough while still maintaining its ability to cause rotation of shaft 72. Any suitable means may be provided for maintaining pulley 70 in its properly aligned position, such, for example, as a bifurcated U-shaped structure which engages the sides of pulley 70 and which is fastened to the supporting table. The external end of shaft 72 is provided with coupling means 78 formed to cooperate and engage and disengage from the coupling means 58 formed on shaft 54. Thus, to cause rotative movement of the panel, fluid motor 74 is energized causing shaft 72 to extend and complete the coupling between coupling means 78 and 58. Motor 62 is then energized which causes shaft 72 and coupled shaft 58 to rotate and, through the intermediary of miter gears 52 and 50, shaft 42, miter gears 40 and 38, and shaft 32 provides the desired rotative movement of the face plate. It will be obvious to those skilled in the art that this manner of obtaining rotation of the face plate is exemplary only and that certainly other apparatus may be utilized to achieve the same function. Further, it will also be obvious to those skilled in the art that it would be possible to maintain the face plate stationary and revolve the excess liquid removal system therearound.

The apparatus for accomplishing the desired excess liquid removal is shown in FIG. 5 wherein there is provided a face plate wall contacting head 80 to be more fully described hereinafter. Head 80 is mounted at one end of a free-floating counterbalanced arm 82 which is pivoted as at 84 for arcuate movement about a given axis at a point intermediate head 80 and the counterbalance weight 86. The arm 82 is supported by the pivot point, provided by bolt 87, and an arm-supporting beam 88 which is secured at its ends to a cylindrical sleeve 90 and at substantially the center thereof to the reciprocatable shaft 92 of a fluid motor 94. The securernent of the supporting beam to the reciprocatable shaft 92 may be by any conventional means such as by welding or by a bolt 96 as is shown in FIG. 7. Sleeve 90 is coaxial with and slidably fits over a second sleeve 98 which is coaxial with and surrounds shaft 92 to allow reciprocation of shaft 92 therein. Cam means 100 are provided for causing the head 80 to follow an arcuate path in a second direction to engage and disengage from the wall of the face plate in accordance with the direction of movement of the shaft and comprises a cam track 102 formed in sleeve 98 and a cam follower 104 affixed to shaft 92 for cooperation with the cam track. The view of the apparatus in FIG. 5 shows the head in its uppermost and disengaged position. This view corresponds to the phantomed position shown in FIG. 6 wherein the solid representation of the head and arm structure is shown in its engaged position.

In the particular embodiment shown, head 80 is disclosed as being fixedly attached to the upper portion of a rigid tube 106 which is attached to arm 82 by means of clamps 108. A downwardly projecting portion of the rigid tube 106, designated 110, is connected to the excess liquid removal force supply 112 by means of flexible tubing 114. The excess liquid removal force supply may either be a source of vacuum or a source of high pressure air, depending upon which of the methods of the invention described above are being utilized. A motor 116 is shown diagrammatically as being connected to force supply 112 to provide the necessary power therefor.

Fluid motor 94 may be conventionally controlled as by means of a timer-actuated solenoid 118 which is actuated by standard timing equipment, not shown.

In operation, when fluid motor 94 is energized, shaft 92 begins movement in a downward direction carrying with it arm 82 which is afiixed to the end thereof, and, of course, head 80 which is mounted on the end of arm 82. At the beginning of the downward cycle, the action of cam follower 104 in cam track 102 is such as to cause shaft 92 and the associated arm 82 to follow an arcuate path so that head 80 enters the interior of the face plate 10 at approximately the center thereof. As the shaft 92 continues its downward movement, the head 80 contacts the wall 12 of the face plate and, by virtue of the counterbalanced action of the arm, remains in contact with the wall 12 while shaft 92 moves downwardly to its farthest limits. At this time, the rotation of the face plate 10 is begun, as described by the apparatus shown in FIG. 3, and the rotation thereof is continued for a time sufficient to complete the liquid removal operation. It will be seen that, while the face plate is rotating about a fixed center, the rectangular nature of the panel is such that an imaginary line traced by the wall 12 thereof will be quite irregular. However, the nature of the free-floating counterbalanced arm 82 is such that head 80 remains in contact with the wall 12 regardless of its angular orientation. Likewise, it is this free-floating action of the counterbalanced arm 82 which allows head 80 to make contact with the wall 12 regardless of the angular orientation of the face plate at the beginning ofthe cycle.

It should be here noted that the drawings, for the sake of simplicity, have shown the apparatus and the face plate 10 in a substantially vertical position. As was pointed out above, this may or may not be the most suitable position for facilitating excess fluid drainage and therefore, should the face plate 10 be mounted at some angle other than zero from the vertical, the excess liquid removal system should be mounted at substantially the same angle so that the head 80 and the wall 12 and the edge of the wall of the face plate 10 are substantially parallel in their contacting position.

After a sufficient number of revolutions of the face plate 10 to insure adequate removal of any excess liquidthis, of course, to be determined by the airflow of the removal system and the speed and number of rotations of the panelthe panel rotation is stopped and solenoid 118 again actuated by the timing mechanism to start shaft 92 in its upward direction. This upward movement of shaft 92, of course, simply reverses the downward process in that arm 82 and head 80 continue to rise until head 80 disengages in the vertical direction from the wall 12 of the face plate 10 and is then horizontally removed from the interior of the face plate 10 as cam follower 104 reaches the upper contoured portion of cam track 102.

Referring now more particularly to head which is shown in greater detail in FIG. 7, the head comprises a body portion having a first stepped portion 122 formed thereon to remove excess liquid from the edge 13 of the face plate 10. A second stepped portion 124 is adjacent said first portion and is formed to project inwardly of the wall 12 to remove excess liquid from the interior surface of the wall over the distance from the edge of the wall to a point closely adjacent the stud 14. A third stepped portion 126 is adjacent said second stepped portion and is formed to provide clearance over the stud 14. Aperture means 128 are formed in body portion 120 and interconnect the stepped portions with the excess liquid removal force supply 112. A partically patterned screen comprised of phosphor dots 129 is shown as being formed on the interior surface 11 of face plate 10.

The external surfaces of body portion 120 which enclose and form the apertures 128 are formed to facilitate fluid flow therearound. This formation is shown more clearly in FIG. 8 wherein the facilitating means comprises angled walls 130 around stepped portion 126 and angled walls 132 formed about stepped portion 124. These inwardly formed angles allow the moisture remaining on the face plate wall portion to be drawn more easily into the aperture when vacuum is being applied since the surrounding air is more readily drawn therethrough and helps to carry the excess liquid away from the face plate.

Thus, it can be seen that there is herein provided methods and apparatus having great advantages over the prior art hand methods. The control of the excess liquid removal is easily maintained and is consistent throughout the entire operation, thus operator error is eliminated. Further, the invention is well suited to adaption as a stage in a conveyorized or automated processing setup.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

We claim:

1. An apparatus for removing excess liquid from the upstanding wall of the face plate of a cathode-ray tube, said wall having a given thickness and having at least two inwardly projecting studs thereon, said apparatus comprising: a face plate wall contacting head formed to contact the edge of said wall formed by said given thickness thereof and project inwardly of said wall a distance at least sufficient to encompass said studs and being further formed to provide clearance over said studs; a free-floating, counterbalanced arm mounting said head and being pivoted for arcuate movement about a given axis at a point intermediate said head and said counterbalance; a reciprocatable shaft mounting said arm; means for causing reciprocation of said shaft; cam means operative with said shaft for causing said head to follow a partially arcuate path to engage and disengage from said wall in accordance with the direction of movement of said shaft; an excess liquid removal means; means interconnecting said removal means and said head; and means for causing relative movement to occur between said head and said face plate at least during engagement of said head with said wall.

2. The apparatus of claim 1 wherein said means for causing reciprocation of said shaft is a fluid motor.

3. The apparatus of claim 1 wherein said cam means comprises asleeve coaxially aligned with and external of said shaft and having a cam track formed therein and a cam follower affixed to said shaft and formed to cooperate with said track.

4. The apparatus of claim 1 wherein said excess liquid removal means comprises a vacuum system.

5. The apparatus of claim 1 wherein said means for causing said relative movement between said head and said face plate comprises; means for mounting said face plate for rotation about a given axis; means for causing rotation of said face plate; means for intermittently engaging and disengaging said rotation causing means; and motor means for supplying rotative power to said rotation causing means.

Claims

3. The apparatus of claim 1 wherein said cam means comprises a sleeve coaxially aligned with and external of said shaft and having a cam track formed therein and a cam follower affixed to said shaft and formed to cooperate with said track.