|Publication number||US2662833 A|
|Publication date||Dec 15, 1953|
|Filing date||Jun 16, 1948|
|Priority date||Jun 16, 1948|
|Publication number||US 2662833 A, US 2662833A, US-A-2662833, US2662833 A, US2662833A|
|Inventors||Helmuth Richard E|
|Original Assignee||Ransburg Electro Coating Corp|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (4), Referenced by (13), Classifications (10)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Dec. 15, 1953 R. E. HELMUTH ELECTROSTATIC COATING METHOD AND APPARATUS Filed June 16, 1948 Fig.l
RICHARD E. H ELMUTH HWXQMW v Patented Dec. 15, 1953 ELECTROSTATIC COATING METHOD AND APPARATUS Richard E. Helmuth, Carmel, Ind., assignor to Ransburg Electro-Coating Corp., Indianapolis, Ind., a corporation of Indiana Application June 16, 1948, Serial No. 33,371
6 Claims. (01. 117-93) 1 This invention relates to coating articles and. more particularly to improvements in an electrostatic method and apparatus for applying coatings to the exterior surfaces of hollow articles of dielectric or nonconductive material such as,
past an extended backing electrode has been provided for the interior of each article being coated. U. S. Patent No. 2,247,963, issued tol-I. P. Ransburg and H. J. Green on July 1, 1941, illustrates one form of such extended backing electrode.
It is apparent that the necessity for providing a backing electrode fitting the interior surface of the article surfaces of such article or for electrical conformation, requires the fabrication of especially shaped backing electrodes for each form of article which it is desired to coat. In cern tain instances, as where the opening leading into the interior surface of the article is restricted as, for example, the neck of a'bottle, such bottleneck renders the use of the process impracticable because of the difficulty of introducingthe backing electrode into the interior of the article.
In certain instances, even though the entrance opening of a particular article is of a size which would allow free and easy mounting or removal of the article 'over or from the backing electrode, such type of electrode frequently cannot be used because the highly irregular surface contour of the interior of the article renders it impracticable, if not impossible, to obtain the proper relationship between the article and the backing electrode.
An obg ect of the present invention is to provide a method and apparatus for electrostatically coating the exterior surfaces of hollow articles of dieletric material in such manner that the operations be simply and effectively carried out without necessitating the employment of 7 any backing electrodes, especially shaped with respect to the articles to be coated and irrespective of the widely varying sizes and shapes of the articles or their entrance openings or the degree of irregularity possessed by their interior surfaces.
For a better understanding of the invention, together with other and further objects thereof, reference is had to the following specification taken in connection with the accompanying drawing, and the scope of the invention will be pointed out in the appended claims.
In the drawing:
Fig. 1 is an end elevation of an electrostatic coating apparatus of the general character with which my invention may be employed, and illustrates a typical use of the invention in the coating of glass bottles.
Fig. 2 is a side elevation thereof,
Fig. 3 is a detailed sectional view illustrating the use of the invention in the application of coating to a glass tumbler or the like, and
' Fig. 4 is a detailed perspective view illustrating the use of the invention in conjunctionwith the coating of a plastic radio cabinet or the like.
The apparatus illustrated in Fig. 1 includes a conveyor 16 having spaced upstanding'spindles ll upon which articles are mounted. The'conveyor I0 is arranged to travel between oppositely disposed, spaced electrodes 12, which are suitably supported by insulators l3 suitably affixed to a conventional coating booth (not shown). Electrodes l2 generally comprise rectangular frames across which are strung in vertical spaced relation a series of fine ionizing or discharge wires l4. Conveyor ID and spindles H are connected through a conductor [5 to ground, whereas electrodes l2 and Wires M are connected through a conductor 16 to one terminal of a high voltage source ll, the opposite terminal of which is connected by a conductor l8 to ground. It will be understood,of course, that if desired, the oppo- .site terminal of the voltage source may be conll andthe grounded connection thereby dispensed with, although generally the ground type .of connection is preferred. Preferably, voltage nected directly. to the conveyor it and spindle source I! is adapted to supply direct current with a voltage of the order of 1G0,000 volts, and the electrodes are arranged so that the distance be conductive material are mounted upon and electrically connected to the spindles H, as such an article approaches the electrodes l2, an electrostatic field is created between the ionizing wires 14 and the surface of such article, the article becoming during its movement past the electrodes l2 a complementary or collecting electrode in the system.
One or more spray guns l9 are suitably supported beyond the electrodes (see Fig. 2) and are directed so as to introduce the coating material from a supply source (not shown) in a direction generally parallel to the path of travel of the articles into the space between the articles and the electrodes. In this manner, the finely divided particles issuing from the spray gun become charged by the wires l4, and are thus attracted to the surfaces of the oppositely charged article.
Heretofore, when hollow:- articlesof .noncon' ductive material such as,. for-example. ceramic ware, glass or plastic were to be coated, it has been the practice to back the interior. surface of the article with an extended metallic, form-fitting electrode supported upon and being electrically connected with the spindle ll. Such method and construction. is satisfactory in certain instances, as where the opening leading into the interior of the article to be coated is of. such size and shape with respect. to its inner surface as will permit the article to be placed upon and removed from the conforming electrode. However, even in such cases, it is noted that variations in size and shape of the interior surfaces of varying articles call for correspondingly varying conforming plate electrodes. This naturally requires the maintenance of a large inventory of such electrodes'in order to adapt the process and apparatus for use inconnection with articles of varying size and shape. Moreover, with certain types of articles, such as, for example, bottles and the like, which generally have a narrow neck opening leading into" their interior surfaces, the prior art type of backing electrode cannot be used because-the restricted opening prevents the mounting of such types of. articles thereover.
By my .inventionJ. have overcome such .diiiiculties and have provided. a method. and. apparatus for coating hollow articles which conveniently lends itself to applying. a uniformapplication of the coating material to such articles without requiring the use of especially shaped electrodes. I have discovered that if an. article with an opening which leads into its interior is placed at or adjacent an isolated, sharp ionizing point or points or a fine wire electrically connected with the spindle H, an ionizing zone or zone of corona discharge is created within the interior of the article. Such discharge, in effect, establishes an intimate electrical contact with the entire interior surface of the article by virtue of which positive charges" (assuming that the pointed electrode is charged positively) are distributed to every point on such surface. A possible explanation or theory of the operation in efiecting a uniform coating is that the nonconductive or dielectric character ofrthe article with ionizing zones or zones of corona discharge of opposite polarity located in spaced relation respectively, internally and exteriorly thereof,
causes a polarization or electrical stress to take place in the nonconductivematerial. sothatl'the negatively charged particles of coating material are evenly and thoroughly attracted to and. deposited upon the positively charged exterior surface of the article.
In explaining the theory of the operation of the apparatus and method, I do not wish to be confined to such theory in claiming my invention.
Referring again to Fig. 1 wherein is illustrated 4 the application of coating material to the exterior surface of a glass bottle 20, the spindle H is formed with an enlarged portion 2| which provides a shoulder 22 upon which the end of the inverted bottle 23 is seated. Extending upwardly and centrally of the enlarged portion 2! is a projection. 24" which terminates in a sharp ionizing. pointv 25. Projection 24 may be formed integrally with the spindle H or may constitute a fine ionizing wire suitably afiixed on the spindle. Preferably, the pointed end 25 of the projection 24 terminates slightly within the neck of the bottle. It has been found by experimentatinn, howeventhat if the point extends into bottle for a substantial portion beyond the bottle neck such as, for example, as indicated by dotted lines at 2B, the application of the coating material will be more heavily applied to the exterior surfaces of the bottle lying in a plane above the point.
Referring to Fig, 3, wherein is illustrated the application. of the improved process to the coating of a glass. tumbler. 2'! or. the like the spindle 3H is formed. witha flange or shoulder 3l'2 upon which rests a disk 3|3, preferably formed of insulatingv material. The upper end of the spindle projects centrally through an opening 3 provided in disk 31% and terminates in a sharpened point 3'15. The diameter of disk 3l3 is such that the edge of the inverted tumbler 21 .is supported thereby.
Referring. to Fig. 4 wherein is shown a modification for adapting the process and. apparatus to the use of applyingv coatings to radio cabinets or the lil e,.the spindle 4| I has affixed thereto adjacent its pointed end 4l2 a spider M3, preferably of insulating material, the outwardly projecting arms of which are of suflicient length to engage. and. support the edges of the radio cabi net 4 [4. Such radio cabinets are commonly made of electrically insulating or nonconducting ma- .fifilials.
In allof. the illustrations, it is noted that the terminal point 25, 315 0r 4 l 2 projects only slightly intov the interior of the hollow article. It has been found. in practice that the point may be so positioned that it is coplanar with or extends slightly below the plane of the edges defining the. opening in the article, and that satisfactory coating results may be achieved when the ionizing point is so positioned.
The point or wire may even be formed so as to come .in contact with the interior surface of the article when the article is mounted upon the spindle, the important requirement being that the point or wire be capable of creating an ionizingv zone or zone of corona discharge within the interior of the article. Preferably, in carrying out the operations, the spindles ll, 3 or 4H are arranged to. be. rotated so as to impart rotation to the articles during their traverse of the coating. zone. Such rotating mechanism may take the form of a. pulley such as 35 (Fig. l) aflixed to the spindles and arranged to be engaged by a continuously driven belt 3| mounted over driving pulleys such as 32.
While the invention is herein shown and described in connection with an upstanding spindle type of conveyor, it is to be understood, of course, that it is equally adaptable for use in conjunction with any type of article support.
It is noted that by using such a method and apparatus as herein described, articles of nonconductive material and of varying sizes and shapes. may be readily and easily accommodated without particular regard to the sizes of their entrance openings to their interior shape or to the degree of irregularity possessed by their interior surface formations.
The requirement for especially shaped, extended backing electrodes is completely eliminated. In practicing the invention, the coating material is issued from the spray guns such as 19, in exactly the same manner as described in the foregoing. The establishment of an ionizing or corona discharge zone within the interior of the nonconductive article, which zone is of opposite polarity to the ionizing zones created by wires is in spaced relation from the exterior surface of the article, is effective to establish an electrical field between the electrodes. The finely divided material issuing from the guns i9 is deposited upon the exterior surface of the article by the precipitating action of such field.
It has been found in practice that a coating of satisfactory thickness and having a very high degree of uniformity can be obtained simply and efiiciently by the use of this method and apparatus.
What I claim is:
1. Apparatus for electrostatically coating the exterior surface of a hollow article of non-conductive material having an opening leading into its interior, said apparatus comprising an ionizing discharge electrode, means for supporting the hollow article in spaced relation to said ionizing discharge electrode, said means being constructed and arranged relative to said ionizing discharge electrode whereby said ionizing discharge electrode is at the opening of the hollow article and within the lateral confines thereof, a second ionizing discharge electrode supported in spaced relation to the exterior surface of the article, means for establishing an electrostatic field between said electrodes of suflicient magnitude to create an ionizing zone about each, and means for introducing a spray of particled coating material into the field between the exterior surface of the article and said second discharge electrode for electrostatic deposition on the 1 article.
2. An apparatus according to claim 1 wherein said first mentioned ionizing discharge electrode and the support for said article are formed integrally.
3. A method of coating an exterior surface of a hollow article of non-conductive material which comprises the steps of creating in spaced relation from and substantially within the boundaries of the interior surface of said article a localized zone of corona discharge of predetermined polarity to establish internally of the article and substantially throughout its confines a cloud of charged atmospheric particles, simultaneously creating in spaced relation from the exterior surface of the article an ionizing zone of corona discharge of opposite polarity to that of the atmospheric particles within said article, introducing a gaseous dispersion of particled coating material into the ionizing zone exterior of said article to form a cloud of coating material particles charged oppositely to the internal atmospheric particles, and establishing across the nonconducting walls of the article an electric field whereby the internal atmospheric particles will be attracted to the internal surfaces of the Wall and the external coating material particles will be attracted to the external surfaces of the wall.
4. Apparatus for electrostatically coating the exterior surfaces of a series of hollow articles of nonconducting material, each of said articles having an opening leading into its interior, said apparatus, comprising a conveyor, a first discharge electrode spaced from said conveyor, a series of support members, each being carried by said conveyor and being adapted to support one of the hollow articles, a series of sharply pointed discharge electrodes, means for establishing an electrostatic field between said first discharge electrode and said pointed electrodes of suficient strength to create an ionizing zone in the vicinity of each electrode, each of said pointed electrodes being disposed at an articleopening and in such position that atmospheric particles charged by it and attracted by said first electrode will be intercepted by the interior surface of the associated hollow article, and means for spraying coating material into the field between said first electrode and the articles for electrostatic deposition on the exterior surfaces of the articles.
5. A method of coating the surface of a hollow article of nonconducting material which comprises establishing between an ionizing electrode within the article and an ionizing electrode outside the article an electrostatic field of sufficient strength to establish internally of the article and substantially throughout its confines a cloud of charged atmospheric particles and externally of the article a surrounding ionized atmosphere of a polarity opposite to that of the internal cloud, and introducing a gaseous dispersion of particled coating material into said surrounding ionized atmosphere and into the field exterior of the article for electrostatic deposition on the article under the action of said field.
6. Apparatus for electrostatically coating the exterior surface of a hollow article of non-conducting material having an opening leading into its interior, a first dischargeelectrode spaced from said support, a sharply pointed discharge electrode, means for establishing between said two electrodes an electrostatic field of sufiicient strength to create an ionizing zone in the vicinity of each electrode, said pointed electrode being disposed in alignment with the opening of an article on said support and sufficiently close to such article that atmospheric particles charged by it and attracted by said first electrode will impinge upon the interior surface of the article on the support to create a surface charge, and means for spraying coating material into the field between said first electrode and an article on the support for electrostatic deposition on the exterior surface of such article.
RICHARD E. HELMUTH.
References Cited in the file ofthis patent UNITED STATES PATENTS Number Name Date 2,152,077 Meston Mar. 28, 1939 2,224,391 Huebner Dec. 10, 1940 2,287,837 Smyser June 30, 1942 2,334,648 Ransburg Nov. 16, 1943
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|U.S. Classification||427/460, 118/318, 118/320, 118/635, 427/477, 427/472|
|Cooperative Classification||B05B5/08, B05B5/084|