US 3876465 A
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United States Patent 1191 1111 3,876,465
Prazak, III Apr. 8, 1975  METHOD AND APPARATUS FOR COATING 3.364.055 1/1968 Nelson 118/324 SKIRTLESS CATHODE RAY TUBE PANELS 3365325 1/I968 .Fraenkel et al 117/1053 75 Inventor: Charles J. Prazak, 111, Elmhurst, 111. OTHER PUBLICATIONS  Assignee: Zenith Radio Corporation, Chicago, g322 fi gfiag gfg f y M322: 7 Reprinted from Hitchcocks Wood Working Dig.,  Filed: Mar. 12, 1973 Dec., 1959.
 Appl' 340634 Primary Examiner-William R. Trenor Attorney, Agent, or Firm-John H. Moore  US. Cl 1l7/33.5 C; 117/34; 117/1053;
118/324; ll8/D1G. 4  ABSTRACT  a 344d 1/02; 844d 1/09; 6036 1/74. This disclosure depicts method and apparatus for ap- Fleld of Search l 4, a ccating f p ph or other screen 1 17/335 104 34 terial to the concave inside surface of a curved skirtless cathode ray tube front panel. A panel is conveyed  References cued with its concave surface facing upwardly along a pre- UNITED STATES PATENTS determined path through a liquid curtain of the coat- 77l.443 10/1904 Perkiewicz 118/D1G. 4 ing material. The path along which the panel is con- 1.200 065 10/1916 Yingling veyed is caused to have a curvature through the cur- 2.745.4l9 5/195 slingerlflnd-w tain which is so related to the curvature of the panel gimdtke as to produce a high degree of uniformity in the coatrown 3.341.354 9/1967 Woods et al a. 117/1053 mg received by the panel 3.345.973 10/1967 Glaus 118/324 7 Claims, 12 Drawing Figures WALL-L4 1 Reservoir PATENTEDAPR ei'vs 3.876.465
sum 1 0F 4 Reservoir FIGJA FIG. 2
PATENTEDAPR 81975 COATING WEIGHT DJSTRIBUTION VsLFLAT AND CU RVED PANEL TRAJECTORIES 3 a v G G I T I s f F m 0 c m n .l ,1 U Q 8 6H G m .W n s G e D 4 ..2 mm .m d .2, Q m A R o '4 I .6 B 8 b .r m w w 9 8 Percentage of Center Coating 00 'Weight FIG. 7 FIG. 7A
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lllllll 'lllllllll NW METHOD AND APPARATUS FOR COATING SKIRTLESS CATHODE RAY TUBE PANELS BACKGROUND OF THE INVENTION The present invention pertains generally to the manufacture of cathode ray tubes. It is specifically directed toward improved apparatus and method for depositing phosphor or other material coatings onto the front panels of such tubes.
Picture tubes of the type with which this invention is concerned consist of two separate units, a front panel assembly and a funnel assembly, each manufactured and processed separately, which are ultimately united. In conventional color picture tubes, the front panel as sembly includes a glass front panel having a 2 to 3 inch glass skirt around its perimeter and an aperture mask assembly comprising an aperture (shadow) mask mounted on and supported by a steel frame which is in turn supported and positioned within the front panel by studs extending inwardly from the panel skirt. A glass funnel which comprises part of the funnel assembly mates with the front panel and is frit-sealed thereto.
One phase of the manufacture of cathode ray tubes. both black-and-white and color. involves depositing one or more phosphor coatings onto the front panels of such tubes. In the case of color tubes. successive coatings of green-emitting, blue-emitting and red-emitting phosphor materials are applied to each front panel. The most common way of applying such phosphor coatings on cathode ray tube (CRT) front panels has been to dispense a phosphor slurry into an inverted front panel. The panel is then tilted and spun in a manner well known in the art in order to provide a uniform slurry coating over the inner surface of the panel. The panel is then tilted further in order to dump any excess slurry.
This dispense and spin" method, although subject to certain disadvantages. has found considerable application in the commercial production of color CRTs. While this method is reasonably well suited for processing conventional skirted panels. it is not well suited for processing a new type of CRT front panel which has no skirt around its perimeter. A fuller discussion of such new panels and the reasons why the dispense and spin method of phosphor coating is unsuitable for them will be deferred until certain problems which are associated with the dispense and spin method have been exam ined. This will help to clarify the objectives of the pres ent invention and to illuminate the particular problems to which the invention is addressed.
One problem which contributes to the high cost of manufacturing CRT's is that the dispense and spin method. as practiced in the manner described above. is a relatively slow process. The total time required for the application of one coating is in the order of l or 2 minutes. In color tube screening. the process must be repeated for each of the three phosphor materials, re sulting in a total elapsed time for the application of the phosphor coatings, exclusive of the time required for exposure, developing and drying. of 5 minutes or more.
Another problem which exists in the above-described dispense and spin method of phosphor coating is that any contaminants which are found on the panel will be mixed in with the dispensed slurry and may find their way back into the phosphor source when the excess slurry is dumped and'reclaimed. Since this reclaimed slurry is. generally reused, those contaminants can be undesirably recycled back onto another panel where their presence may cause pock marks or other disturbances inthe coating. Such irregularities in phosphor coatings can cause a significant drop in the production yield factor. thus adding to the per unit cost of the finished product.
A third disadvantage which is inherent in the dispense and spin procedure is that the excess slurry which is dumped and reclaimed has a phosphor content which is less than that of an unused slurry. This is because the phosphor particles which are suspended within the slurry tend to settle onto the panel surface. A certain amount of phosphor material must be added, therefore, to the reclaimed slurry before it can be re used. The added step of restoring the reclaimed slurry to its former state further complicates an already complex process. In addition to complicating the entire process. this step is subject to errors which can adversely affect product uniformity and yield.
A fourth problem with this method of applying the phosphor coating is that during the coating of the panel, the larger phosphor particles tend to settle out first. When the excess slurry is dumped, it will contain fewer of the large phosphor particles than an unused slurry and, if mixed directly with that unused slurry, may cause subsequent panels to receive coatings which do not have the desired phosphor particle distribution. This problem, along with the one discussed immediately above, tend to cause long term process variations which result in nonuniform phosphor weight distribu tions in panel coatings. Such variations are particularly evident between panels processed soon after production start-up and those processed later.
This invention is directed toward apparatus and method well suited for the application of coatings of phosphor and other materials onto skirtless CRT panels while avoiding the above-described problems which are associated with the application of phosphor coatings onto conventional skirted CRT panels.
PRIOR ART The following patents are believed to disclose the most pertinent prior art:
PATENT NUMBER ISSLED TO 2.916.012 R. C. Hergenrother 3. 45.933 B. Glaus 3526.535 E. Plumat OBJECTS OF THE. INVENTION It is a general object of this invention to provide improved method and apparatus for applying one or more coatings of phosphor or other CRT screen material to the inside surface of a cathode ray tube front panel, particularly to the inside surface of a skirtless cathode ray tube panel.
It is another object of this invention to provide method and apparatus for applying such coatings in a way which is substantially faster than prior art methods.
It is another object of this invention to provide method and apparatus for applying such coatings in a way such that the excess coating material which does not adhere to the front panel surface remains substantially free from contaminants and retains the content uniformity of unused coating material, so that the excess material may be reclaimed and directly combined with unused coating material.
It is still another object of this invention to provide method and apparatus for applying a uniform liquid coating over the concave inside surfaces of skirtless. spherically or cylindrically curved cathode ray tube front panels.
It is yet another object of this invention to provide method and apparatus for applying phosphor coatings to skirtless cathode ray tube panels in a way which is relatively insensitive to variations in the viscosity of the coating material. but which is readily adjustable to compensate for variations in the phosphor content of the applied coating material.
BRIEF DESCRIPTION OF THE DRAWINGS The features of this invention which are believed to be new are set forth with particularity in the appended claims. The invention. together with further objects and advantages thereof. may be best understood by reference to the following description in conjunction with the accompanying drawings in which like numbers refer to like elements and in which:
FIGS. 1 and 1A illustrate sphericallyand cylindrically-shaped skirtless CRT panels, respectively;
FIG. 1B illustrates a cathode ray tube and the way in which the front panel mates with the glass funnel;
FIG. 1C illustrates a conventional skirted CRT front panel;
FIG. 2 depicts schematically a curtain coating apparatus in accordance with the principles of this invention for applying a highly uniform coating of phosphor or other material onto a skirtless CRT front panel;
FIG. 3 is a graph which indicates the uniformity of phosphor coatings received by panels coated by the FIG. 2 apparatus and by prior art curtain coating methods;
FIG. 4 gives a detailed perspective view, in schematic form. of the FIG. 2curtain generating apparatus;
FIG. 5 is a sectional view depicting schematically the construction of a panel support used with the FIG. 2 apparatus and certain features of the FIG. 4 apparatus;
FIG. 6 is a side view schematically depicting an alternate embodiment of this invention; and
FIGS. 7, 7A and 7B depict, in schematic form, yet another embodiment of this invention in various views.
DESCRIPTION OF THE PREFERRED EMBODIMENT As described above. a number of problems exist when applying a slurry coating to a cathode ray tube front panel using the dispense and spin method. It was noted that the use of this or a similar method for applying a slurry coating to the surface of a skirtless panel might introduce even more problems. The invention to be described below is specifically directed to the solution of these problems in connection with applying a coating of phosphor or other material onto the surface of a skirtless cathode ray tube front panel.
Before proceeding to a description of the present invention. a few remarks are in order regarding the cathode ray tube front panels which preferably are to be coated according to this invention. Typical examples of skirtless front panels are illustrated in FIGS. 1 and 1A. In FIG. 1, there is shown a spherically curved front panel 11 which is adapted to be bonded to the funnel of a cathode ray tube as shown in FIG. 1B. The panel ll mates flush with the funnel l2 and is preferably attached thereto by a glass frit sealing process. The skirtless panel shown in FIG. 1A is cylindrical in shape and is bonded to a mating funnel also by a frit sealing pro- CESS.
Panels of the type presently in commercial use resemble the FIG. 1C skirted panel. The skirt l3 wraps around and is an integral part of this type of panel.
In the discussion above. the dispense and spin phosphor coating method was described in connection with the processing of a skirted front panel. In practicing that method. the panel is supported in a generally horizontal plane with its skirt l3 directed upwardly. After the slurry has been dispensed onto the upwardly facing surface, the panel is tilted and rotated in order to insure that the entire panel surface receives a uniform phosphor coating. This method is reasonably well suited to processing of skirted panels, despite the aforementioned deficiencies of that method. because the skirt 13 provides a convenient boundary for containing the dispensed slurry. However. in the case of the skirtless panels as shown in FIG. 1 and IA. the lack ofa skirt to contain the slurry as the panel is tilted and spun precludes the use of this process. Keeping in mind this and the other above-described problems associated with the use of the dispense and spin phosphor coating method. the advantages of my invention will become apparent.
It is well known that certain objects, particularly flat objects. can be coated with a liquid material by means of a curtain coating process. In this process, a liquid curtain of the desired coating material is established in a generally vertical plane. The object to be coated is I passed through the liquid curtain of coating material in a generally horizontal plane, as on a belted conveyor. That portion of the curtain which comes in contact with the object to be coated adheres to it and thus forms a liquid coating on the surface of the object.
This invention is specifically aimed at providing improved curtain coating structures and methods for use in coating skirtless CRT front panels with one or more coatings of phosphor or other CRT screen materials.
In FIG. 2 there is illustrated a curtain coater representing a preferred structure for practicing this invention. A liquid curtain 14 of slurry, for example, is established having a width at least as wide as the object to be coated. A path through the curtain is established by means of a set of parallel tracks which describes a curved locus through the curtain along which panel 11 is conveyed. As shown, the tracks include an elevated,
inclined section 20 and a lower, curved section 22. A-
wheeled panel support 18 supports the panel 11 and conveys it by force of gravity through the liquid curtain 14 along the path defined by the tracks in the manner of a roller coaster.
When a panel is in the position indicated in FIG. 2, that is, with its leading edge contacting the curtain 14, there is defined an angle (1) between the panel edge 24 and the curtain 14. The curved section 22 of the tracks and panel support 18 are both designed to convey the panel in a way which causes the angle d) to be preferably not greater than With an angle d) of 90 or less, the leading edge 24 of the panel 11 is less apt to tear or otherwise disrupt the curtain as it passes through. The panel then continues through the curtain and is carried by its momentum up inclined section 26 of the tracks. Suitable means (not shown) may be provided for stopping the advance of panel support 18.
The curved section 22 of the tracks describes an are through the liquid curtain. which are preferably has a radius of curvature generally equal to the radius of curvature of the panel 11. By so conveying the panel along the described arcuate path. it is possible to obtain a coating on the panel which is substantially more uniform than could have been obtained by prior art curtain coating procedures which convey the objects to be coated along a linear path under the liquid curtain.
Although the path along which a panel is conveyed has been described in connection with the FIG. 2 apparatus as having a radius of curvature generally equal to the radius of curvature of the conveyed panel. no such limitation is intended. According to my invention. the curvature of the path through the curtain need only correspond or conform to the curvature of the panel to a degree which will produce a coating of the desired uniformity. For example, it may be desirable in some cases to decrease the radius of curvature of the arcuate path in order to provide a greater concentration of coating material near the center of the panel. The correspondence between the radius of curvature of the arcuate path and the radius of curvature of the panel need. therefore. not be limited to a substantial equality between the radius. The above-mentioned radii will. however. normally be of lengths which are of at least the same order of magnitude, that is, one radius will be no greater than ten times the other.
The efficacy of coating a spherically-shaped panel in accordance with the teachings of this invention is illustrated graphically in FIG. 3. The graph indicates that a substantial improvement in coating uniformity can be obtained by the use of the roller coaster-like apparatus of FIG. 2. rather than conveying a panel along a linear. horizontal path through the curtain. Curve A illustrates the case of a spherically-shaped panel which has been coated using the FIG. 2 apparatus. Note that the phos phor coating weight over a majority of the panel surface area is within 2% of the coating weight at the cen ter of the panel. Curve B illustrates the case of the same spherically-shaped panel which was coated by conveying it along a flat linear path through the curtain. While the coating weight at the leading edge of the panel is nearly 87: greater than the center coating weight (curve A), it is still a substantial improvement over the 18% deviation in coating weight which resulted from conveying the same panel along the linear horizontal path through the curtain (curve B).
In the case of panels which are cylindrical in shape and which exhibit an arcuate curvature in one set of parallel planes. it is possible to provide material coatings which exhibit even greater uniformity than that indicated by the FIG. 3 graph. This can be effected by choosing a radius of curvature for the curved track 22 which is generally equal to the radius of curvature of the panel and. by conveying the panels through the curtain such that their direction of motion vectors lie in one of the parallel planes. each elemental surface area of such panels will meet the curtain at an angle of approximately 90. By so maintaining each elemental surface area of the panel approximately normal to the curtain when passing thereunder, it is possible to obtain a high degree of coating uniformity.
Having discussed the operation of the FIG. 2 apparatus and the method it implements in general terms. various aspects thereof will now be discussed in more detail.
Referring again to FIG. 2, there is shown a static electricity neutralizer which consists of nozzles 28 for directing streams of de-ionized air onto the surface of panels as they are conveyed along the tracks. The blast of deionized air serves to assist in the removal of lint and other light. charged particles which cling to the panel surface.
The way in which the liquid curtain of coating material is formed is illustrated in FIGS. 2 and 4. A basin 30 is provided with a supply of coating material through a conduit 32. The coating material enters cylinder 33 and is discharged downwardly into basin 30 through a series of downwardly facing apertures 34. When the level of the coating material is raised to the point where it is free to spill over the lip 35 of the basin. the material flows downwardly along the path defined by guide 36 which is provided with a knife edge 38 to insure the generation of a smooth. uniform liquid curtain.
When using this invention to apply a phosphor coating to a skirtless panel. the ingredients which make up the liquid curtain preferably include a water soluble photosensitizer. a water soluble acrylic or cellulose thickener. a polyvinyl -alcohol binder and phosphor particles of one of the three primary colors. The viscosity of the slurry thus obtained is preferably 100-300 centipoise to insure a good flow rate and to suspend the heavier phosphor particles in the slurry to avoid forming a phorphor sediment. The slurry is preferably 3071-4071 phosphor by weight. although the usable range is much broader l07r-607r Maintaining the flow of slurry at 100-300 cubic centimeters per second will allow a curtain one meter wide (measured at the top of the curtain) to coat a 25 inch panel with a slurry coating sufficiently thick to provide the normal phosphor weight. This flow rate contemplates a panel movement through the curtain at a speed of 80-l20 meters per minute.
Coating material which does not come in contact with a panel surface is collected in a pan 40 which is returned to a reservoir 42 for recycling back to basin 30 by means of pump 44. This arrangement makes evident an advantage of coating a panel in this way; namely. that the coating material which is collected in pan 40 may be recycled without the need to make corrections or additions thereto before combining the recycled material directly with unused material. This is possible be cause whatever part of the curtain that comes into contact with a panel will adhere to the panel rather than running off with contaminants which may be picked up from the surface of the panel. That part of the curtain which does not contact a panel is not contaminated and may be recycled directly.
Referring now to FIG. 4. details of the curtain coater are shown which were either not visible or omitted for purposes of clarity in the FIG. 2 illustration. Pan 40 is shown as containing baffles 46 which prevent splashing ofthe coating material. Supported by angle irons 48 are two deflectors 50 which are positioned directly above that portion of curved track sections 22 which lie beneath the liquid. curtain. The purpose of the deflectors is to deflect the slurry coating around track sections 22 and to thereby prevent a slurry buildup on the tracks which could impair the movement of wheeled panel support 18 thereupon.
Details of the construction of panel support 18 are more evident in the FIG. 5 illustration. Each panel support 18 is provided with four suction cups 52 which are mounted on the panel support and adapted to hold a panel 11 throughout its conveyance along the track. The wheels 54 of panel support 18 are provided with V-shaped grooves which enable the panel support to follow the tracks and to ride above a small amount of coating material which may adhere to the upper surfaces of the tracks.
Having described the details of one of the contemplated embodiments of this invention. the important aspects thereof may be more succinctly stated as follows: the conveying of panels through a liquid curtain with their inside curved surfaces facing upwardly: the path along which the panels are conveyed is given a predetermined curvature through the curtain which corresponds generally to the curvature of the panels themselves in order to deposit a substantially uniform coating of slurry or other material on each panel.
In accordance with one aspect of this invention, each panel is conveyed along a path which has an effective curvature through the curtain such that the curtain contacts consecutive elemental surface areas of the panels at substantially the same angle during the time the panel is conveyed through the curtain. Where a panel is said to enter the curtain with its leading edge first and its trailing edge last, this angle is preferably about 90 as measured between the curtain and a point on the upwardly facing panel surface, which point lies on a line connecting the midpoint of the leading edge with the midpoint of the trailing edge of the panel.
Many variations are contemplated in the details of the curtain coater, in the panel support and in the means for conveying the panel through the curtain along the described predetermined curved path, all of which are within the scope of the invention; two such variations will be briefly described hereinafter.
Before proceeding to a discussion of certain variations in the above-described preferred embodiment of this invention, other advantages of this invention not described above should be noted. First since the slurry which is collected in pan 40 has not contacted a panel surface. its phosphor content is identical to that of any unused slurry remaining in reservoir 42. This makes it possible to recycle the used slurry directly back to the basin 30 and allows for a faster production start-up because no additions need be made to the recycled slurry.
Second, a rather obvious advantage which this invention provides is that a panel may be coated much faster than by prior coating methods. The coating process described above may be completed in a second or less, which compares very favorably with the l-2 minutes required by the dispense and spin coating method.
Third. the phosphor weight of the slurry coating which adheres to the panel surface is easily adjustable by varying either the speed of the panel as it passes through the curtain or by varying the rate offlow of the slurry itself. The rate of flow of the slurry is most easily adjusted by changing the speed of pump 44. In connection with this advantage, it should be noted that the resultant phosphor weight of the slurry which adheres to .the panel surface is substantially independent of certain viscosity of the slurry. Because the dispense and spin method coats the panel by creating a slurry puddle on the inverted panel surface and then spinning the panel to force the slurry to move over the panel surface in order to generate the preferred coating thickness. it is evident that the viscosity of the slurry is a parameter which must be closely controlled when using that process.
FIG. 6 illustrates, in a side view, an embodiment of this invention in which the panel movement is effected by a moving conveyor 56 rather than by gravity. In this embodiment, conveyor 56 follows a path 58 which defines an arc beneath curtain l4 and which has a radius of curvature generally equal to the radius of curvature of the panel 11. As in FIG. 2, this FIG. 6 embodiment also directs the leading edge 24 of panel 11 toward curtain 14 so that the angle defined by their intersection is 90 or less to prevent the leading edge of panel 11 from tearing the curtain as it passes thereunder.
The speed with which panel 11 passes through curtain 14 may be somewhat less than the speed with which panels proceed in the FIG. 2 embodiment. However, the rate of flow of slurry may be adjusted to compensate for this difference in speed and may thus be adapted to provide a slurry coating which is of a predetermined thickness, or as it is stated in the art, to provide a predetermined phosphor weight for panel 11.
FIGS. 7, 7A and 7B illustrate another embodiment of this invention in which the panel movement is provided by a conveyor 56. In this embodiment, however, the conveyor passes beneath curtain 14 in a straight line. Panel 11 is made to follow an arc whose radius of-curvature is generally equal to the radius of curvature of the panel by the interaction of rollers 60, spring 62, post 64 and rotatable shaft 66. As illustrated in FIG. 7, panel 11 is conveyed to curtain 14 with the leading edge of the panel meeting the curtain at an angle appropriate to avoid tearing as discussed above. Panel support 18 then engages rollers 60 as shown which, along with spring 62, exert a rotational force on panel support 30 which cause it and its associated panel to rotate around the axis of shaft 66 so that, in passing under curtain 12, the movement of panel 11 defines the described arc.
FIG. 7A illustrates the position of the panel as it leaves the curtain and how spring 62 compresses to allow the panel to rotate. FIG. 7B shows another view Even though the conveyor of FIG. 7 moves along a straight line through the curtain, the panel itself is so conveyed and supported that the panel follows a path having an effective curvature which corresponds generally to the curvature of the panel, thus causing a substantially uniform coating to be applied to the inner panel surface.
Other embodiments of this invention are contemplated, but not shown. For example, the panels to be coated may be supported and swung in a pendulum-like manner beneath a cantilevered curtain former to cause the panels to move through the liquid curtain along a path which defines an arc through the curtain. By choosing an arc with a curvature which corresponds generally to the curvature of the panel and by swinging the panel through the curtain with its concave surface facing upwardly in a way which causes the leading edge of the panel to meet the curtain at the proper angle to avoid tearing. the curtain will contact consecutive elemental surface areas of the panel at substantially the same angle. The theory behind the pendulum approach is basically the same as that of the embodiments described above except that the pendulum approach limits the path through the curtain to a path described by a true arc. in the other embodiments described above, the apparatus is designed to provide a path through the curtain which has a curvature related to the curvature of the panels so as to produce the high degree of uniformity in the coating received by the panel. but the path thereby formed is not limited to an arcuate path.
Although the discussion up to this point has been primarily directed toward an invention which deposits at phosphor coating onto the front panel of a cathode ray tube. no such limitation is intended. The invention is intended to be used for the application of any liquid coating to a skirtless front panel of a picture tube. For example. the use of this invention is contemplated in the coating of the black carbon-type material which surrounds each color dot in modern high-brightness color picture tubes, as disclosed in US. Pat. No. 3,l46.368. issued to .I. P. Fiore, et al. This invention is also adaptable for use in applying a phosphor coating to a skirtless front panel of a black-and-white picture tube.
While the invention has been described in conjunction with specific embodiments thereof. it is evident that many alterations. modifications and variations will be apparent to those skilled in the art in light of the above disclosure. Accordingly, it is intended to embrace such alterations. modifications and variations which fall within the spirit and scope of this invention as defined by the appended claims.
1. A method for applying a material coating to the concave inside surfaces of a curved skirtless cathode ray tube front panel, comprising:
establishing a liquid curtain of said coating material;
conveying said panel with its concave surface facing upwardly along a predetermined path through said curtain, said path being caused to have a curvature through said curtain which corresponds generally to the curvature of said panel such that each consecutive elemental surface area of said panel meets LII LII
the curtain at an angle of approximately 90. thereby producing a high degree of uniformity in the coating received by the panel.
2. The method as defined in claim 1 wherein said material to be applied to said panel surface consists of a slurry which includes phosphor particles and a photoresist material.
3. A method as set forth in claim 1 wherein said panel is conveyed in an attitude which is such that the angle formed between the curtain and the leading edge of each panel as it enters the curtain is not greater than 90, thus preventing the leading edge of a panel from tearing said curtain as it passes therethrough.
4. A method for depositing a slurry coating which includes phosphor particles and a photoresist material onto the concave inside surface of a curved. skirtless cathode ray tube front panel having a predetermined curvature in at least one plane, comprising:
establishing a liquid curtain of said slurry; and
conveying said panel through said curtain with its inside curved surface facing upwardly such that the direction of motion vector of said panel lies in said plane such that said curtain can contact consecutive elemental surface areas of said panel at substantially the same angle during the time the panel is conveyed through said curtain to deposit a substantially uniform coating of said slurry on said panel.
5. The method as defined in claim 4 wherein each of said panel possesses a curved surface defined by a radius of curvature and wherein said path is defined by an are through said curtain. said arch being defined by a radius generally equal to said radius of curvature of each of said panel.
6. A method as set forth in claim 4 wherein said panel is conveyed in an attitude which is such that the angle formed between the curtain and the leading edge of each panel as it enters the curtain is not greater than 90, thus preventing the leading edge of a panel from tearing said curtain as it passes therethrough.
7. A method as set forth in claim 4 wherein said angle is substantially 90 as measured between the curtain and a point on the upperly facing panel surface, which point lies on a line connecting the midpoint of the leading edge with the midpoint of the trailing edge of said