US3376153A

US3376153A - Method of coating cathode-ray tubes

Info

Publication number: US3376153A
Application number: US405076A
Authority: US
Inventors: Joseph P Fiore
Original assignee: Rauland Borg Corp
Current assignee: Rauland Borg Corp
Priority date: 1964-10-20
Filing date: 1964-10-20
Publication date: 1968-04-02
Anticipated expiration: 1985-04-02
Also published as: GB1101565A

Description

April 2, 1968 J. P. FIORE METHOD OF COATING CATHODE*RAY TUBES 2 Sheets-Sheet 1 Filed 001;. 20, 1964 Aprifl 2, 1968 J. P. FIORE METHOD OF COATING CATHODE-RAY TUBES Sheet 2 M ENTOR 1/ 056793 231* LOTQ I BY 2 Sheets Tilt Angle Filed Oct.

Time

3,376,153 METHOD 6F ATING CATHGDE-RAY TUBES Joseph P. Flore, Wheeling, lll., assignor to The Rauiand Corporation, Chicago, 111., a corporation of Illinois Filed Oct. 20, 1964, Ser. No. 405,076 Claims. (Cl. 1l733.5)

ABSTRACT OF THE DISCLOSURE In the disclosed method of coating a cathode-ray tube, the cap section of the tube is supported in a horizontal plane with its flange extending upwardly and coating material is deposited on the central surface of the cap in an amount exceeding that required to coat the screen area. The cap is then tilted and concurrently rotated at speeds selected in relation to the charge and viscosity of the coating material to distribute the material uniformly over the screen as the cap is tilted to an angle of about degrees from the horizontal. Tilting is then interrupted and the excess coating material is removed while the rotation of the cap is continued. Thereafter, the tilting is resumed and the cap is quickly displaced to an angle of the order of 90 degrees relative to the horizontal and, while in that position, the coating is dried by rotating the cap at a higher speed in front of suitable heaters.

The present invention concerns a method of coating a cathode-ray tube and is useful in the fabrication of monochrome tubes but is even more applicable to the screen forming procedure of tri-color cathode-ray tubes. For convenience, it will be described in connection with the latter type of device.

The color cathode-ray tube currently in commercial use is of the so-called shadow-mask variety. It has a screen which bears a regular interlaced pattern of phosphors which, when energized by electrons, emit light of the primary colors. Usually all three primaries are employed and the screen has a repeating pattern of phosphor triads, that is, of clusters of three phosphor dots each of which is capable of emitting light of one of the three primary colors.

While such a tube may utilize a single electron gun, it is customary to employ a family of three guns disposed in a delta arrangement. Each gun develops an electron beam which is directed toward the screen and each beam is permitted to impact upon phosphor dots of a single assigned color. This color selection or assignment of a particular gun to a particular color phosphor is accomplished by means of a shadow-mask which is a mask having a pattern of apertures corresponding to the pattern of triads on the screen, usually with one aperture in the mask for each triad on the screen. The fabrication of such a device is a difficult process especially in the formation of the screen.

A variety of ways have been suggested for depositing phosphor dots on the internal surface of the tube faceplate which serves as the screen area. It is known, for example, to apply the phosphors through techniques of dusting, printing, electrostatic deposition and so forth. The present invention concerns what has become to be known as the slurry process of screen formation. It should be observed in passing that the method to be described is also of use in filming the mu1ti-color phosphor screen preparatory to aluminizing.

In the slurry process, a slurry mix is prepared of a photosensitive resist and the particular phosphor that is to be applied. A measured quantity of this slurry is deposited in the center of the screen portion of the cathode-ray tube which, at this juncture in the manufacturing process, is merely the faceplate of the tube bounded by a peripheral flange and is supported in plane canted to the vertical. The quantity of slurry deposited is much in excess of that re- 3,376,153 Patented Apr. 2, 1968 quired to form a uniform layer over the screen of the tube and a uniform distribution of the slurry is achieved by rotating the tilted screen or cap, as it is referred to, at a high speed. Much of the excess slurry accumulates at the meeting area of the screen and the flange due to the influence of centrifugal force and a probe may be inserted into that area as the cap rotates in order to draw off most of the excess slurry. After removing such excess, the slurry coating is dried and the tube cap is equipped with its mask and positioned on an exposure device where selected areas are exposed to a radiation, such as ultraviolet light, which causes the exposed areas of the coating to become insoluble in water. Exposure through the mask in this fashion subjects separated dots or small islands of the coating to the radiation so that development of the coating thereafter establishes a field or pattern of dots of the particular phosphor that has been contained in the slurry. Repeating this general process three times and with appropriate geometrical positioning of the exposure source permits the formation of the phosphor triads on the cap or screen of the tube.

The described process has proved satisfactory in the manufacture of round tubes but its application to tubes of other configuration, specifically to rectangular tubes, is obviously diflicult. For example, the slurry tends to develop swirls at the corners of the cap which may cause irregularities or non uniformity in the coating and, additionally, the use of a simple probe to remove excess slurry is no longer feasible because of the abrupt changes in contour of the flange surrounding the screen area.

Accordingly, it is a specific object of the invention to provide a novel method of coating the internal surface of the screen portion of a cathode-ray tube.

A further object of the invention is to provide an improved method for coating the screen area of a color cathode-ray tube by the use of a slurry.

A specific object of the invention is to provide a new and improved method of slurry coating a tri-color cathoderay tube that is useful irrespective of the specific configuration of the tube being manufactured.

Still another specific object of the invention is to improve the slurry coating method of screening a color cathode-ray tube to minimize the deposit of slurry on the flange that borders the periphery of the screen area.

The method of the invention for selectively coating the internal surface of the screen portion of a cathode-ray tube comprises supporting the cap in a horizontal plane with its peripheral flange extending upwardly and depositing upon its screen surface a quantity of viscid coating material in an amount substantialy exceeding that required to coat the screen. The cap is then rotated at a first speed and concurrently tilted to distribute the coating material over the screen. Thereafter the tilt rate is increased to quickly position the cap in a predetermined tilt plane, preferably about 100 degrees, and the cap is rotated in that plane at a speed which is higher than the first rotational speed to dry the coating on the screen.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is an elevational view, partially broken away, of a screening apparatus for practicing the coating method of the invention;

FIGURE 2 is a view taken along line 22 of FIG- URE 1;

FIGURE 3 is a side elevational view taken as indicated by line 33 of FIGURE 2;

FIGURES 4-6, inclusive, are functional views used in describing the method carried out by the apparatus of FIGURE 1; and

FIGURE 7 comprises curves used in explaining the coating method of the invention.

Before describing the apparatus represented in the drawings and the coating process that it performs, it is appropriate to consider the structure of the tube being processed, at least that part of the structure that is to be operated upon by the coating apparatus. Where a slurry coating technique is to be employed, especially if the tube is to have a tri-color phosphor screen, the envelope comes in two initially separate parts. One part is the cap which includes the faceplate of the tube bounded by a peripheral flange and the internal surface of the faceplate serves as the screen portion. Of course, the process to be described may also be employed in the fabrication of a screen pack wherein the screen structure is separate from the tube envelope but current practice is to have the internal surface of the cap constitute the image area. The other envelope portion is the conical section which terminates at its smallest diameter in the cylindrical neck which is to house the gun assembly. After the screen has been formed and after the aperture mask has been installed, if the tube is of the shadow-mask variety, the cap and funnel portions are united by a frit seal and the envelope is then ready to receive the gun assembly, the base and so forth. The cap may either be round or rectangular and, of course, the meeting surfaces of the cap and funnel sections have identical cross-sectional configurations and dimensions.

The apparatus of FIGURE 1 for coating the cap section of a cathode-ray tube has a frame structure 10 supporting a driving motor 11 which drives a link chain 12 through a variable speed reducing gear system 13. The driving speed of the chain is selectable by means of a speed selection lever 14 that may be displaced between either of two positions by means of a hydraulic cylinder 15 the piston of which mechanically couples to lever 14.

Link chain 12 extends the driving system to a shaft 16 which carries a gear 17 near one end for engaging link chain 12 and a bevel gear 18 at its opposite end. Shaft 16 is supported by means of a bearing block 19 and also by a housing 20 in which gear 18 is enclosed. Finally the mechanical drive is continued through another bevel gear 21 in engagement with gear 18 and affixed to a shaft 22 extending through housing 20 and carrying at its forward end a workholder 23 for removably supporting the cap 5 of a cathode-ray tube being processed. The workholder is a spider type of structure with three arms extending radially from a hub and having a lock 23a (FIG- URE 3) which may be closed to lock the tube cap within the holder. It is desirable to interpose resilient pads on the inner faces of the arms of workholder 23 to avoid damage to cap 5. The mechanism as thus far described permits cap 5 to be mounted in position within the coating apparatus and to be rotated at any one of two selected speeds.

In addition to being rotated, workholder 23 and the cap which it supports are subject to la tilting movement in order to control the angle of the cap with respect to a reference plane such as the horizontal bed or plane of the coating apparatus. For this purpose there is a second shaft 30 in coaxial alignment with shaft 16, supported by a bearing block 31 and also extending into housing 20. A flange coupling 32 secures housing 20 to shaft 30 so that they rotate together about the axis of

shafts

16, 30 although shaft 16 rotates independently of housing 20. The drive for shaft 30 comprises a second link chain 35 which threads over a gear 36 at one end of shaft 30 and an idler gear 37 rotatably supported on a shaft 38' at the base of frame 10. Displacement of chain 35 and rotation of gear 36 is under the control of another hydraulic cylinder 40 which has a piston rod mechanically coupled by means of a link 41 to chain 35. By virtue of this mechanical coupling, rectilinear motion of the piston of cylinder 40 occasions displacement of shaft 30 and tilting of workholder 23.

The coating process involves programmed changes in both the angle of tilt and the speed of rotation of the workholder. These parameters are controlled, in part, by a family of cams that are carried by a shaft 45 rotatably supported in bearing blocks 46. Shaft 45, is driven concurrently with tilt shaft 30 by means of another link chain 47 engaging a gear 48 carried by tilt shaft 30 and a gear 49 carried by cam shaft 45. The family ofcams on shaft 45 are two

limit cams

45a and 45d and two

other cams

45b and 45c which control programming of the tilting and rotating of workholder 23. Their control is exercised through a control system 50 of conventional design which includes timers as well as electrically actuated valves for admitting fluid under pressure to

cylinders

15 and 40 and to another cylinder 55 (FIGURE 1) which controls the position of a panel 56 slidably supported on the front portion of frame 10 of the coating apparatus. The coupling of panel 56 to the piston rod ofcylinder 55 is by means of a cable 57 passing over suitable rollers supported on the frame of the coating machine. Conduits 63 extend from the various hydraulic cylinders to control system 50 for conveying a fluid under pressure required to displace the piston of any of these cylinders in a particular direction determined by the admission of fluid into one end or the other of its associated cylinder in the usual way.

Panel 56 carries a housing 58 in which are mounted a series of infrared heaters 59. The housing of the heaters may be polished to be reflecting and the side thereof which faces workholder 23 is open in order that heat may be directed from housing 58 into the tube cap being processed.

Also secured to the frame of the machine is a large enclosure 60 having an aperture 61 to be closed by housing 58 when panel 56 is in its lower position. Enclosure 60 protects workholder 23 from the atmosphere during much of the coating process so that foreign particles are not admitted to the cap being coated. There is a further container or shield 62 secured to the mount of workholder 23 and enclosing the workholder except for its forward portion. This is to confine the coating material and protect against scattering.

The coating method of the invention may be carried out by the described apparatus and is best explained by considering an illustrative cycle of the machine. Initially or at the start of any cycle, the apparatus is conditioned as represented in FIGURE 1 with panel 56 in its extreme upper position to have workholder 23 available or accessible through opening 61 ofenclosure 60. The cap 5 of a cathode-ray tube which is to be processed is inserted into workholder 23 and locked in position. It will be apparent in FIGURES 1 and 3 that the cap is supported in a plane which is slightly in excess of the vertical,

approximately to degrees in relation to the bed operator which causes control system 50 to admit fluid under pressure to cylinder 55.and lower panel 56 to its lowermost position in which opening 61 of enclosure 60 is closed by the panel and heater housing 58.-Concurrently control system 50 actuates the hydraulic system to admit fluid under pressure to cylinder 40 at a reasonably fast rate to cause its piston to descendand rotate shaft 30 and along with it workholder .23 in a clockwise direction as viewed in FIGURE 3. At this time, control system 50 is unresponsive to the. series of cams on shaft 45 and remains so until limit cam 45a has operated its cam follower. This occurs when workholder 23 has positioned cap 5 in a horizontal plane as shown in FIGURE 4. The effect of limit cam 45a in displacing its cam follower is to terminate clockwise displacement of shaft 30 and workholder 23 by interrupting the fluid supply to cylinder 40 and to condition control system 50 to respond to the other cams on shaft 45.

With the cap in its horizontal position a second start button (not shown) is manually operated to actuate control system 50 and a measured quantity of viscid coating material 6 is deposited upon the internal surface of screen 5a. The quantity placed in the cap substantially exceeds the amount that is required for a uniform coating of screen 5a. While a variety of coating materials may be employed, for the illustrative case it is a photosensitive resist such as polyvinyl alcohol with a phosphor that emits light of red, green or blue color. An automated coating dispenser may be utilized but the simple coating apparatus represented in the drawing contemplates that the coating is to be deposited manually. In the laboratory, for example, a cup or other container of coating material is poured into the cap. The broken-line representation 5 in FIGURE 3 of the workholder assembly makes clear that the cap is accessible from the portion of the machine rearwardly of the back panel of enclosure 60. As the coating material is poured into the cap, the dispenser is preferably moved or oscillated so that the whole charge is not dumped into a particular spot at the center of the cap. Moving the pouring stream about, in the central area of the cap, lends to uniformity of the coating.

Control system 59 includes a first timer which is operated when the second start button is pressed. The first functions controlled by this timer are the energizing of motor 11 and the opening of the valve feeding fluid under pressure to cylinder 40 to rotate workholder'23 at a constant speed of about 5 r.p.m. and concurrently effect tilting or canting of the workholder in a counterclockwise direction, also at a constant rate. By properly adjusting the speed of rotation of workholder 23 and the rate of its tilt, selecting these parameters in relation to the viscosity and the amount of coating material poured into cap 5, the coating material may be distributed over screen 5a by the time the cap has attained the position of FIG- URE 5 at which it is approximately at an angle of 30 relative to the horizontal reference plane. As indicated in that figure, coating material 6 will now have been distributed over the whole screen 5a. For slurries of the type used in commercial production of cathode-ray tubes today, having a viscosity of the order of 25 to 100 centipoise, an acceptable tilt rate is one degree per second and the displacement time from the position of FIGURE 4 to that of FIGURE 5 is of the order of seconds.

The rate at which the workholder is tilted has a very pronounced effect on the coating pattern accomplished with the apparatus. It will be apparent that the deposit of slurry is heaviest and is subject to the greatest gravitational force at the very start of the coating cycle because as the workholder is rotated and tilted the pool of coating material tends to traverse a spiral path, continually losing some of its mass due to its viscid nature. As a consequence, the mass and gravitational effect decrease with coating time. Consequently, if the speed and rate of tilt are maintained uniform, as represented by curve A of FIGURE 7, the entirety of the screen area may be coated but the coating will not have a uniform thickness. There will tend to be a heavier coating in the central portion of the screen than at the edges. Ideally, assuming a constant rate of rotation, the rate of tilt should vary as indicated by curve B of FIGURE 7 in order to attain uniformity of the coating over the entire screen area. That is to say, the rate of tilt decreases throughout the coating interval. The phenomenon may, for convenience of explanation, be likened to settling in which a given time is required to settle a coating of a particular thickness from a settling solution of a certain height but a longer settling period is necessary to attain the same depth of coating with a settling solution of lesser height. An acceptable compromise is the condition of curve C, indicating a uniform tilting rate for a certain period of time plus further rotation of the workholder at a fixed tilt angle.

By way of example, the workholder may be tilted at the aforementioned rate of one degree per second until the spiraling pool of coating material just spans to the edge of the screen area. When this point is reached, the tilt angle is maintained fixed and continued rotation of the workholder permits the coating at the edge portion of the screen to achieve substantially the same thickness as that of the remainder or central part of the screen. It is this coating method that is easily accomplished with the described apparatus in which timer number 1 of control system 51 interrupts the fluid supply to cylinder 40 and counterclockwise rotation of workholder 23 when it has arrived at the 30 tilt angle of FIGURE 5. The timer maintains thi condition for a measured hold interval in which the Workholder continues to rotate but at a fixed angle of tilt.

With the workholder supporting cap 5 in this tilted plane excess coating material from screen 5a tends to drain downwardly in the direction of flange 5b and after a hold time of approximately 4 seconds, the excess coating material is removed. One convenient way of removing the excess coating is through the agency of a syringe 749 that may be immersed in the pool of coating material as indicated in FIGURE 5. The excess coating material is reclaimed, that is to say, when it is removed from the tube cap under process it is returned to the reservoir or supply from which the initial charge has been taken. This is obviously easily done by discharging the contents of syringe 70 into the reservoir.

The first timer of control system 5% affords a sufiicient interval for removal of the excess coating material and at the conclusion of that interval once again admits fluid under pressure to cylinder 40 to continue the tilting of workholder 23 and the drive of cam haft 45 at the original slow rate. At this juncture, the timer will have completed its program and shut oif. Immediately thereafter the rotation of shaft 45 causes cam 45b to displace its follower and cause control system 50 to admit fluid into cylinder 49 at a faster rate. As a consequence workholder 23 tilts at a much more rapid rate and in a very short interval cam 45c actuates its follower to cause control system 50 to admit fluid under pressure to cylinder 14, displacing speed control lever 14 to its alternate position 14b (FIG- URE 3). This position of the speed selector cause the workholder to be rotated at a speed which is high compared to its previous rotational speeds, an illustrative value is r.p.m.

In about 6 seconds workholder 23 returns to its initial position having a tilt angle of the order of degrees, between 90 and degrees as indicated in FIGURE 6, and at this time limit cam 45d actuates its follower to initiate a second timer included Within control system 50. The first function performed by this timer is interruption of the fluid supply to cylinder 4-0 and termination of the counterclockwise displacement of workholder 23. Concurrently the timer closes the energizing circuit for heaters 59, permitting cap 5 to be dried while it is rotated at its high speed. After a suitable interval determined by the second timer, about 4 minutes, heaters 59 are turned off, motor 11 is de-energized, and fluid is admitted to cylinder 55 only long enough to elevate panel 56 to its starting position. In short, the apparatus is restored to its initial condition and the cycle has been completed. The operator may now release the coated cap from workholder 23 and direct it for the further processing steps such as its lighthouse exposure and development none of which are of concern to the subject invention.

The speeds of the processing cycle are rather slow and the method may be easily practiced in a manually adjusted apparatus. That is to say, both control of the rotational speed of Workholder 23 and its degree of tilt may be performed manually by the operator with little difiiculty.

7 If desired, tilt cam 45b may be contoured to exercise control of a needle valve in the supply conduit to cylinder 40 to control the fluid admitted thereto and the tilting of workholder 23 in accordance with curve B of FIG- URE 7. However, the described process of a constant tilt rate followed by a hold period is acceptable in tube production.

It will also be appreciated that the starting quantity of coating material has a direct bearing on the time required to coat. Experience has proven that a 25 inch rectangular cap may be coated with 200 cc. of coating material in approximately one minute although this necessarily involves quite an excess of coating material Which may spread to flange 51), especially during the high-speed rotation, and require the usual trim operation. Generally 40 to 50 cc. of material is suflrcient to coat the screen. On the other hand, the starting amount of coating material may, if desired, be only 75 cc. which has the distinct advantage that very little spreads to the flange and the trim step may be drastically reduced if not entirely eliminated but at the cost of coating time because the cycle with this small amount of coating material increases to about four minutes.

Coating by means of the described process has distinct advantages in that the specific configuration of the cap under processing is of no particular consequence. The swirling or disturbances encountered at the corners of a rectangularly shaped cup with other coating processes are completely avoided. Further, it may be arranged that only a minor fractional portion of flange b becomes coated at all so that trimming is either obviated or greatly reduced with a commensurate reduction in the danger of screen spoilage because of errors committed during trimming.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim: 1. In the manufacture of a cathode-ray tube of the type having a cap section with a screen portion bounded by a peripheral flange, the method of selectively coating the internal surface of said screen portion which comprises:

supporting said cap in a horizontal plane with said flange extending upwardly and depositing upon the central internal surface of said screen portion a quantity of viscid coating material in an amount substantially exceeding that required to coat said screen portion; tilting said cap at a first rate and rotating said cap at a first speed both of which are chosen in relation to the quantity and viscosity of said coating material to distribute said coating material over said screen portion as said cap is positioned in a first tilt plane substantially less than 90 degrees relative to said horizontal plane; thereafter increasing said tilting rate to quickly position said cap in a second tilt plane of the order of 90 degrees relative to said horizontal plane;

interrupting the tilting of said cap and removing excess coating material therefrom while said cap is in one of said tilt planes;

and drying said coating while rotating said cap in said second tilt plane at a higher speed than said first speed.

2. In the manufacture of a cathode-ray tube of the type having a cap section with a screen portion bounded by a peripheral flange, the method of selectively coating the internal surface of said screen portion which comprises:

supporting said cap in a horizontal plane With said quantity of viscid coating material in an amount sub-.

stantially exceeding that required to coat said screen portion; tilting said cap at a first rate and rotating said cap at a first speed both of which are chosen in relation to the quantity and viscosity of said coating material to distribute said coating material over said screen portion as said cap is tilted to a plane of the order of 30 degrees relative to said horizontal plane;

interrupting the tilting of said cap While maintaining its rotation and removing excess coating material from said cap;

resuming the tilting of said cap at a rate exceeding said first rate to quickly position said cap in a predetermined tilt plane of the order of degrees relative to said horizontal plane;

and drying said coating While rotating said cap in said predetermined plane at a higher speed than said first speed.

3. In the manufacture of a cathode-ray tube of the type having a cap section with a screen portion bounded by a peripheral flange, the method of selectively coating the internal surface of said screen portion which comprises:

supporting said cap in a horizontal plane with said flange extending upwardly and depositing upon the central internal surface of said screen portion a quantity of viscid coating material in an amount substantially. exceeding that required to coat said screen portion;

tilting said cap at a in relation to the quantity and viscosity of said coating material until the charge of coating material extends to the edge of said screen portion;

interrupting the tilting of said cap for a predetermined hold interval;

removing excess coating material from said cap;

resuming the tilting of said cap at a rate exceeding.

said first rate to quickly position said cap in a predetermined tilt plane;

4. In the. manufacture of a cathode-ray tube of the type having a cap section with a screen portion bounded by a peripheral flange, the method of selectively coating the internal surface of said screen portion which comprises:

supporting said cap in a horizontal plane with said flange extending upwardly and depositing upon the surface of said screen portion a quantity of viscid coating material in an amount substantially exceeding that required to coat said screen portion;

tilting said cap at a first rate and rotating said cap at a first speed both of which are chosen in relation to the quantity and viscosity of said coating material to distribute said coating material over said screen portion as said cap is tilted to a plane at an angle of approximately 30 degrees relative to said horizontal plane;

interrupting the tilting of said cap at a tilt angle .of

approximately 30 degrees and removing and reclaimin excess coating material from said cap;

resuming the tilting of said cap at a rate exceeding said first rate to quickly position said cap at a tilt angle of the order of 90 degrees;

and rotating said cap While at said tilt angle of the order of 90 degrees at a higher speed than said first speed to dry said coating. 5. In the manufacture of a cathode-ray tube of the type having a cap section with a screen portion bounded by a peripheral flange, the method of selectively coating first constant rate and rotating said cap at a first speed both of which are chosen 9 the internal surface of said screen portion which comprises:

supporting said cap in a horizontal plane with said flange extending upwardly and depositing upon the central internal surface of said screen portion a quantity of viscid coating material at least in an amount required to coat said screen portion; tilting said cap at a first rate and rotating said cap at a first speed both of which are chosen in relation to the quantity and viscosity of said coating material to distribute said coating material over said screen portion without contacting any appreciable portion of said flange with said coating material as said cap is tilted from said horizontal plane by an angular amount substantially less than 90 degrees; removing any excess material from said cap;

thereafter increasing said tilting rate to quickly position said cap in a predetermined tilt plane of the order of 90 degrees relative to said horizontal plane;

and drying said coating while rotating said cap in 5 said predetermined plane at a higher speed than said first speed.

References Cited UNITED STATES PATENTS 10 2,821,160 1/1958 Atti 11856 X 2,902,973 9/1958 Weingarten et 'al. 118-56 3,143,435 8/1964 Martyny 11733.5

5 ALFRED L. LEAVITT, Primary Examiner.

H. COHEN, Assistant Examiner.