US2604870A - Electrostatic coating apparatus - Google Patents

Description

y 29, 1952 w. R. BLOOD ET AL ELECTROSTATIC COATING APPARATUS Filed Feb. 1 1950 I 1 I I "I Invewbovs:

e .,w mm m m m/% /IT R m. A a ks W 6 G In m T 'J b 6 H Patented July 29, 1952 ELECTROSTATIC COATING APPA ATUS" Q. 1

. iwwalter' Roy. Blood and James- Willi'a'in Moorer Rugby;'England, assignors to General Electric Company, acorporation of New York g Application February 1, 1950, Serial No. 141,705

In England February 1, 1949 This invention relates to the formation of the. luminescent screen or layer of a fluorescent-lamp by the electrostatic precipitation of powdered luminescent materialont'ozthe-surface which is to sustain thescreen;

In. the carrying. out ofsthis process; powder is introduced into the container which is toform the envelope of the fluorescent-lamp in the form of a smoke and the-powder particlesin the smoke are ionized by the-application of a high potentialbetween any electrode positionedwithin the containerand the container wall.

Iii-order thatauniiorm depositof the particles be obtained, it. is necessary that the part of the wall of the container which is being coated be maintained at a substantially uniform potential.

According to" the" invention, the substantially uniform potential is obtained by providing an electrode outside the wan of the container being coated with a plurality f point-like extensions toward said wall, the point-like extensions being uniformly distributed over the portion of the wall on which coating is being effected:

The uniform distribution .of'the point-likteextensions over the surfaceof a tubular container may be obtained by employing a conducting sleevesurrounding the container wall and uniformly distributing the point-likeextensionsifrom the 'innersuriace of the sleev;.' of by employing an electrode of limited extent axially and/or transversely of the container and rapidly moving the electrode axially of and/or rotating it around the container so as to cause the point-like extensions from it to be eiiectively distributed over the portion of the surface being coated. We preier to use an electrode in the form of a stirrup, the axes of which extend parallel to the axis of the container and are provided with the extensions, the stirrup being rotated rapidly around the container.

The point-like extensions may be constituted by pointed wires, e. g., phonograph needles, the tips of which are spaced a short distance from the wall.

It will be understood that in carrying out the electrostatic precipitation process smoke is introduced into the container so that it drifts along the container, which is assumed to be tubular, the production and application of the smoke being arranged to this end. An inner electrode is arranged within the container and is moved axially thereof in the path of the advancing body of smoke. A difference of potential is maintained between the inner electrode and the wall of the container by applying a high D, C. potential bewhich is earthed'. The outer'electrod'e i s moved with the inner electrode and 'the powder is uniiormly electrostatically precipitated from the.

smoke onto th'e'i nner surface 01 the container. The tube to be coated is preferably mounted with its longitudinal axis vertical' and is held in this position by meanso'f aclip-whi-ch is mounted on a" standard extending alongside the-tube,- and canbe' moved along the standard toenable the tube to be inserted in positionfor coating",- and removed. after coating. The outer electrodeis then rotatably mountedon a carriage movable along the standard.

For afurther understanding oi our invention ref erence may bet had to. the accom anying: drawing wherein Fig l." is a somewhatdiag'ramrnatic elevation of a form of apparatus com prising' our invention; Fig. 2 is a plan view 0t the-Fig; 1- device; Figs: 3 and 4 are views,-'cor'r es'p'ondii'1,,i to Figs; 1 and 2, of a modification and-Fig. 5 is a planview oi a' furthermodification- I 3 The device shown in 'Figsll and 21's generally similar to-that shown in Patent 2,44%),655 ofR; L. Keiiier andassigned' 'to the: same assignee as the present invention.v .The' glass: bulb or container I is supported vertically onthe upper end'iof a hollow head or holder 2 which may b'e-sup'por'ted bya bracket 3 from a standard 4; The bulb l is additionally supported at its upper end by a suitable clip 5 extending from the standard 4. An inner electrode in the form of a rod 6 having a pointed lower end is suitably mounted to extend axially within the bulb I and to be moved vertically therethrough. The movement may be effected by means of a flexible cord or cable I connected to the upper end of the rod 6 and extending over pulleys 8 to a suitable winding drum or spindle.

The outer electrode is shown in the form of a stirrup having axes or leg portions ill, ii] ex-- tending longitudinally along opposite sides of the bulb l and provided with a multiplicity of pointlike extensions H the tips of which are spaced 2. short distance from the wall of the bulb I. As here shown, the base portion of the stirrupshaped electrode 9 is provided with a pulley l2 for rotation by a belt l3 from a suitable drive, and is supported on a suitable bearing M attached to the holder 2.

In carrying out the coating process, a smoke or gaseous suspension of finely divided particles of the fluorescent coating material is formed in any suitable generator such, for example, as that shown in the aforesaid patent to Keifler. The

smoke is introduced into the lower end of the bulb I through the hollow head 2 so that it drifts upwardly along the bulb. The inner electrode 6 is moved axially of the bulb, from the bottom to the top thereof, in the path of the smoke. A difference of potential is maintained between the inner electrode 6 and the wall of the bulb I by applying ahigh D. C. potential (8,00012,000 volts, for example) between the inner electrode 6 and outer electrode 9, the outer electrode being grounded. During the movement of the inner electrode 6, the outer electrode 9 is rotated and the powder is uniformly electrostatically precipitated from the smoke onto the inner surface of the bulb I.

In the apparatus shown in Figs. 3 and 4, the

supporting structure for the bulb I and inner electrode 6 is like that shown in Figs. 1 and 2 and corresponding parts have been similarly numbered. However, in this case the outer electrode I5 is of relatively short axial length and is arranged tomove vertically along with the inner electrode 6. The electrode I5 is provided with a semi-cylindrical portion I6 having the point-like extensions I6 projectingrfrom its inner surface, and an upper annular portion I! to which is fixed a gear I8. The said gear. I8 meshes with a gear I9 which is driven by a motor 20. The assembly of electrode I5, gears I8 and I9 and motor 20 may besuitably supported on a bracket or carriage 2| which is slidably mounted on the standard 4, and which may be moved vertically by a cord or cable 22 attached to the cord 1 by a cross member 23.

v The inner electrode 6 may be guided by one or more brackets 24 mounted on and electrically insulated from the standard 4.. The same arrangement maybe employed in the apparatus shown in Figs. 1 and 2.

.It will be understood that upon the introduction of the smoke into the head 2 of the Fig. 3 device, both the inner electrode 6 and the outer electrode I5 are moved upward and the outer electrode is simultaneously rotated about the axis of the bulb I while maintaining a. difierence of potential between the electrodes to deposit the powder progressively along the inner wall of the bulb I.

If desired, the outer electrode in either of the 4 arrangements illustrated in Figs. 1 or 3 could be made cylindrical, as indicated at 25 in Fig. 5. Also, provision may be made for rotating the bulb 6 about its axis as in the apparatus shown in the aforesaid patent to Keifier. It will be understood by those skilled in the art that the construction and arrangement of parts may be widely modified within the spirit and scope of our invention as defined by the appended claim.

What we claim as new and desire to secure by Letters Patent of the United States is:

In apparatus for electrostatically coating tubular glass containers, the combination of support means including holder means for the container, an inner electrode mounted on said support means to extend axially of the container, means including an outer electrode mounted on said support means adjacent the outer wall of the container and arranged to effectively present a multiplicity of discrete sharply pointed extensions uniformly over and projecting toward the wall of the said container, said outer electrode extending a limited distance axially of the container and being located adjacent an end of the inner electrode, means for moving said inner and outer electrodes in cooperative relation longitudinally of the container and means for simultaneously rotating said outer electrode about the axis of the container, means for conducting a gaseous suspension of finely divided coating material into the container, and means for impressing upon said electrodes a potential of sufiiciently high potential to cause deposition of said coating material upon the inner wall of said envelope.

WALTER ROY BLOOD. JAMES WILLIAM MOORE.

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

UNITED STATES) PATENTS

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