US3016876A

US3016876A - Apparatus for electrostatically spray coating articles

Info

Publication number: US3016876A
Application number: US769633A
Authority: US
Inventors: Jr John Sedlacsik
Original assignee: Interplanetary Res and Dev Corp
Current assignee: Interplanetary Res and Dev Corp
Priority date: 1958-10-27
Filing date: 1958-10-27
Publication date: 1962-01-16
Anticipated expiration: 1979-01-16

Description

Jan. 16, 1962 J. sEDLAcslK, JR 3,016,876 APPARATUS PoR ELECTROSTATICALLY SPRAY coATING ARTICLES Filed Oct. 27, 1958 3,616,876 AEIARATUS FOR ELECTRSTATECALLY SPRAY CATNG ARTICLES lohn Sedlacsiir, ir., Garfield, NJ., assigner to Interpianetary Research e Development Corp., Garfield, NJ., a corporation of New Jersey Fiied Get. 27, 1958, Ser. No. 769,633 3 Claims. (Cl. lit-631) This application is a continuation-in-part of the copending application Serial Number 588,807, for Method and Apparatus for Coating Articles, liiled June 1, i956, and now abandoned.

The present invention relates to new and useful improvements in an apparatus and a method of operating the same for coating articles on a conveyor, such as paper sheeting, plastic webbing, leather hides, fabrics, metals, or the like, with a viscous material by the liquid spray mechanical process, and wherein an electrostatic eld established in an area beyond the mechanical spray as well as within the mechanical spray area, provides ancillary means for increasing the eiciency of the apparatus by electrostatically directing and depositing' rebound and otherwise waste vapors of coating material onto the articles.

An object of the present invention is to provide a coating apparatus and method of producing same whereby -a smooth continuous coating, particularly of electrical conducting material, may be applied with a minimum expenditure of labor and time, and by means of which the application of the desired coating may be'readily controlled and efficiency of the system increased.

In such apparatus, the discharge electrode or electrodes is/are connected to a suitable source of high voltage and is/are mounted in spaced relation to the article to be coated. The article is disposed within an area in which are disposed a plurality of other electrodes, which are connected to the said source through ground so that they function as collecting electrodes.

In this manner, an electrostatic iield is established therebetween as the article to be coated is carried by a conveyor means into through and away from the coating position.

It is another object of the present invention to obtain more efcient use of coating material.

it is still another object of the present invention to obtain more uniform coating.

lt is a still further object of the present invention to obtain better control over atomized coating material.

A further object or advantage of the invention is to provide means for spraying articles to be coated by using mechanical force and to provide an ancillary means utilizing electrostatic techniques for charging particles of spray deected from the article back onto the article.

A further object of the invention is to provide means for mechanically atomizing and depositing spray particles onto an article to be coated, and employing ancillary electrostatic means for charging the particles which are not deposited mechanically, whereby said particles will be deposited electrostatically.

A furthe object is to provide a spray coating apparatus wherein the spraying of the article by the coating material is substantially by air pressure or by centrifugal means, either directly or in conjunction with air pressure, and wherein electrostatic techniques are utilized to increase the eiiiciency of the apparatus by charging stray or deflected particles or vapors of coating material so that theyY will be attracted to the articles to be coated by electrostatic force.

A further object is to provide mechanical spraying of an article by placing the atomizer as close to the article as desired without creating any electrical arc between the States Patent atomizer and the article, and utilizing simultaneously A ice electrostatic means to increase the efficiency of the spraying.

A further advantage of the invention `is to provide an ancillary means for increasing the eiiiciency of mechanical spraying apparatus by utilizing electrostatic means disposed rearwardly of the mechanical spraying apparatus to electrostatically charge, direct and deposit suspended particles of coating material not otherwise deposited on the articles.

In accordance with the present invention, a new method and apparatus are provided for atomizing liquid material to form a spray which is utilized for coating surfaces in sheet like form such as a web of paper, a hide of leather, or the like.

Normally, in prior art methods of electrostatic deposition, the article is mounted on a grounded conveyor so as to make `the article itself (if it is of conducting material) or an electrode adjacent the same, an electrode at ground potential. Another electrode at high electrical potential is provided, same normally being the spraying device.

This invention relates to improvements in ancillary apparatus for applying a liquid coating to an article by electrostatically charging and depositing comminuted coating material upon the article within an electrostatic field created rearwardly or above the issuing source of the coating material. The coating material is issued from a spray gun or similar suitable atomizing device preferably utilizing air under pressure as a vehicle to convey the iinely divided or atomized particles onto the surface of the article to be coated and in a direction away from the source of the electrostatic eld. The spraying is substantially by air pressure or other mechanical means and utilizes electrostatic techniques to restrict the loss of rebound, misdirected or stray particles of coating beyond control of the mechanical spraying means.

It is directed particularly to providing means whereby arcing at the spray gun is obviated, direct contact between the high electrical potential and the gun being eliminated, the gun being grounded.

The invention involves the suspension of a fine liquid or powder coating material in air so that it can be charged by means of a unipolar corona discharge for uniform deposition on webs or sheets moving at relatively high rates of speed. Following such deposition, the coating particles are retained by the paper, plastic, leather or like surface being coated in such a manner that they can readily be fused with heat.

A superior degree of adhesion can be attained because the applied coatings are actually fused into the surfaces of a product, the same as in flame finishing, and a variety of materials (other than those employed by ame nishers) can be employed because the coatings do not have to be fused at temperatures that would cause most organic materials to oxidize.

Various pigments and fillers may be incorporated in the materials, prior to the application thereof, so that many unusual finish elects can be attained with unprecedented efficiency. This is primarily attributable to the fact that there is no specific limit to the thickness of the film that may be applied and fused herewith.

Typical organic thermoplasts that can be used as dry coating materials include waxes, polyvinyl alcohol, polyvinyl chloride, cellulose resins, acrylics, nylon, and certain synthetic elastomers.

Thinners, plasticizers, cxtenders, and drying agents of the types normally used in fluid coating dispersione are also generally adaptable for the practice of this invention.

Pigments and llersthat have been satisfactorilyused in dry coating mixtures include metallic powders, cotton flock, mica, cork, carbon black, and the like.

The output of the guus is controlled in accordance with the desired coating rate and the thickness of a specitied iinish. The electrical force, which is established by the electrostatic eld between the discharge electrode and the collecting electrode, combines with the mechanical action of the spray gun in a manner so that the resultant force is substantially uniform over lthe surface to be coated whereby the liquid coating material is uniformly and smoothly applied;

ln actual practice, the spray nozzle or spray gun is not connected to an electrostatic charge, but on the contrary is at the same ground potential as the conveyor. In other words, the conveyor and the spray devices or guns are connected to electrical ground. By this arrangement, the spray guns or nozzles may be placed as closely to the work as necessary so that the actual spraying of the articles carried by the conveyor is provided by the spray guns, yet there cannot be arcing from the nozzle to the articles or conveyor. With this arrangement, the major portion of the liquid material which forms the spray will actually directly engage the articles to be coated either by the force of the air pressure or any other suitable mechanical means. The spray apparatus or atomizing device is shown as a nozzle but may be a suitable disc or cone for directing the spray onto the article. The centrifugal force of the cone or disc, either with or without air, is` suiiicient to provide the basic spraying function of the article carried by the conveyor.

The discharge ring which is shown having needles, but which may be used without needles, is connected to a high voltage source, with the opposite terminal of the high voltage source connected to ground. Consequentl there will be an electrostatic pressure created in the space between the discharge ring, which may or may not carry the metallic needles, and the conveyor which carries the articles to be coated. -In any condition, the articles -to be coated may either be at ground potential, if they should possess adequate electrical conducting characteristics, since the articles will be carried by the conducting conveyor, or the articles, if substantially non-conducting, will be carried by the conveyor which is at ground potential. The articles to be coated are moved along a plane between the discharge ring and the conveyor carrying the articles. With this arrangement, while the spraying is done substantially by air pressure, centrifugal force, or a combination of mechanical forces, the rebound spray particles, vapors or mist regardless of how it is actually derivedwill be within the space, area or zone substantially between the discharge ring Aand the grounded conveyor. The particles of coating material which are not thrown mechanically directly onto the article to be coated, but rather rebound or otherwise become suspended in the air, will be in the electrostatic field between the discharge ring and lthe. grounded conveyor. These particles vwhich are not mechanically urged toward the article to be coated, will beV chargcdby the electrostatic field created by the high voltage charge of the ring, which is of one polarity, and attracted toward the conveyor, which is at 'the ground potential, and is of the opposite polarity.

Vaporized particles of coating material not deposited on the articles to be coated by mechanical means, will be charged by the electrostatic held and attracted to the yarticle carried on the conveyor. Consequently, particles which rebound from the article surface and which would beY otherwise lost or wasted, are charged electrostatically and directed toward the conveyor and the articles carried thereby.

The discharge electrode of this invention comprises a multiplicity of thin metallic rods having outer free needle like termini which are highly desirable in providing an electrostaitc eld of high potential.

The rods of 'this invention are vertically disposed with their lower free needle like termini depending downwardly so as to provide repulsion in a direction substantially perpendicular to their axes.

In this invention, a source of electrostatic high potential, having one terminal grounded and its opposite terminal connected Ato the discharge electrode surrounding the atomizing means, creates an electrostatic field extending between the discharge electrode and a collecting electrode on which the article to be coated is mounted, the article constituting the grounded collecting electrode when sprayed by an electrically conductive material from the gun. The force of this field transforms the atomizcd coating material into a spray of charged particles and creates an attraction which pulls the spray toward the grounded articles or the collecting `electrode upon which the articles to be coated are disposed.

A potential difference of suihcient magnitude is maintained so as to create an electrostatic field with a corona discharge in the region adjacent the discharge end of the discharge electrode.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings wherein:

FlG. l is a top plan view of the apparatus of the invention with certain parts shown in section;

FG. 2 is a side elevational view of the apparatus shown in FIG. l with certain parts shown in section; and

FIG. 3 is an enlarged sectional view of the swivel connection for the control of the coating material employed in spray form with the apparatus of the invention.

Before explaining the present invention in detail, it is to be understood that same is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments. The phraseology or terminology employed herein is for the purpose of description only and not of limitation.

It is further to be understood that forms of spraying devices other than the particular atomizing device shown may be utilized. Other apparatus may be employed for accomplishing the purposes and practicing the methods of the invention without departing from the contemplated scope thereof.

In the practice of this invention, there is provided a discharge member or spray head, a source of liquid or powder supply, and distributing means for transferring the liquid/ powder from the source of supply to the discharge member for dispersion therefrom.

For purposes of simplification, all of these members are not shown, they being more or less conventionalin spraying apparatus and not forming a part of this specific invention.

Referring to the drawing more in detail, and more particularly to the preferred' form or" my invention selected for illustrative purposes, l have shown an arrangement cf apparatus which is suitable for coating articles which are preferably moved along a path of article movement into, through, and out of a coating zone into which the device of the invention, normally fixed in location, is projected.

A travelling belt lit may be of the continuous type and may be movable around spaced rollers 12 and l2 supported on the usual stands il and one of which is driven by a motor 14 connected therewith by a belt 16 and pulley i8 in the usual manner. The belt travels in the direction shown by the arrows a.

Articlesrto be coated such as leather hides L as sho-wn in FIG. l` may be placed on the upper surface of the uppermost run of the belt l@ and are carried therealong through the areas or compartments now to be described.

A booth or enclosure generally designated by 29 comprises four connected together vertically disposed side walls 22; joined at their uppermost edges by a roof or cover member 24..

Opposite side walls 22 are slotted so as to permit the passage of the'travelingbelt l@ therethrough.

sordera Adjacent the enclosure 2i) and spaced therefrom is a second enclosure generally indicated by the numeral 3i) and comprising the usual vertically extending side walls 32, a top or cover wall 34 and a lower or bottom wall 36.

Certain of the walls 32 of the enclosure are slotted as shown to permit the passage of the travelling belt 1l) therethrough.

Enclosure 2d functions as the coating booth and the enclosure 30 functions as the heating or fusing chamber.

A Vspray apparatus comprises a vertically extending conduit 40 and a plurality of horizontally extending conduits or arms 42 connected thereto and extending therefrom at the lowermost portion thereof.

The upper extremity of the conduit #iti engages a swivel connection 46 which is iixed to a downwardly depend ing bracket 48 iixed to the wall member 24.

` The upper extremity of the conduit all is revolvably associated with the swivel connection 46.

The conduit il is rotatable and is driven by a motor 5i) and a belt 52 connected therewith in the usual manner as shown.

A pipe connection 54 has one end connected with a source of supply of coating material (not shown) and has its other end connected by means of a fitting 56 to the swivel connection 416. l

The coating material is yled from the source of supply through the connection 54 through the fitting 56 to an annular lchannel 53 interiorly of the swivel connection and through openings dii through the wall of the member 40 thence downwardly therethrough to each one of the horizontal arms 42 and thence outwardly through downwardly disposed discharge nozzles or outlets 62.

A metallic grid discharge ring 79 is horizontally disposed -within the enclosure 20 and is movably supported relative thereto by means of a supporting member 72 which is connected by a conductor or the like 73 to a high potential source S as diagrammatically shown in FIG. 1.

Depending downwardly from the grid ring 'iti at spaced intervals a plurality of vertically disposed needle like points 74 are provided, but a ring, or other conductor withoutneedles may be used as the charging electrode *for the `ancillary electrostatic apparatus to assist in depositing stray particles of spray onto articles to be coated.

The electrical charge is directed outwardly through the sharpened free ends of the needles.

The grid `discharge ring 70 is more or less curved so as to define a locus which is outside of and more or less surrounds the outer free ends of the horizontal anns 42 of the spraying apparatus as same rotate.

Said ring 70 is disposed above the discharge outlets 6'2 and further away from the belt l0.

It is conceivable that the ring 70 may be vertically adjustable so as to be moved towards :and away from the discharge outlets or nozzles of the gun mechanism in order to preclude arcing relative to the spray apparatus 0r nozzles.

The discharge electrode 70 is initially set far enough above the arms of the spray apparatus that the chances of arcing over to the arms is prevented. The ring is positioned to embrace the nozzle spray area and beyond said area.

'Ihe higher the voltage employed, the further `above the spray apparatus the grid discharge is disposed, it being appreciated that the voltage may conceivably reach as high as 250,000 volts. p

In operation, the liquid or powder material issues from the orices in the atomizing head in the form of high velocity streams which are directed downwardly with high turbulance in the form of a finely divided stream and onto the article to be coated. The employment of electrically conductive coating material, when sprayed onto the articles, insures the electrical conductivity of the articles whereby they constitute collecting electrodes.

As the stream is directed downwardly away from the 6 nozzles, it is subject to the ionizing effect of the discharge grid, heretofore described, which is disposed above the gun mechanism. By such means, the finely divided particles comprising the spray are each imparted electrical charges of polarity and of substantially equal potential with respect to the electrode.

The positively charged particles are attracted to the articles or the surrounding grounded belt carrying the articles to be coated. The particles are attracted to and precipitate in a layer upon the surface of each `article along with spray particles projected on the articles by mechanical means. The nozzle is not charged and therefore does not emit charged particles. The charging of the particles, if any, takes place after the material is sprayed toward the article, and usually, after rebound from the surface of the article.

In addition to the ionization function of the discharge electrode, it establishes the electrostatic field which precipitates the charged particles onto the article. The degree of intensity of this eld detines the area to be coated by the precipitated particles.

rlfhe nely divided particles of coating material after being sprayed may be ionized and thereafter movein an electrostatic held more or less along the lines of force created by the downwardly depending needle like electrodes as shown.

The distribution of such lines of force may be altered by altering the nature of the discharge electrode, or by. changing its position with respect to the article, that is by moving it toward or away from the spray apparatus to control the effectiveness of the electrostatic deposition to increase the overall efficiency of the system by depositing particles on the articles to avoid the otherwise loss of the particles.

While several embodiments of the invention have been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes may also be made in the design and arrangement ofthe parts without departing from the spirit and scope of the invention as the same will now be under stood by those skilled in the art.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. Apparatus for applying coating material to an article comprising a conveyor for carrying said article, applicator means adapted for deposition of :said coating material and having a spray discharge means positioned for spraying said coating material substantially by air pressure directly onto said article as it is carried by said conveyor, electrostatic means ancillary to said applicator means to facilitate deposition of said coating material including discharge electrode means positioned substantially rearwardly of said spray dischargeV means and collector electrode means positioned on the opposite side of said spraydischarge means, said article being disposed between said spray discharge means and said electrode whereby, when charged, said electrostatic means electrostatically repels particles of spray deected from the surface of the article and urges said particles back onto the surface of the article to be coated and in a direction away from the discharge electrode.

2. 'Apparatus for applying coating material to an article comprising a conveyor for carrying said article, applicator means adapted for deposition of said coating material and having a spray discharge means positioned for directly spraying said coating material onto said article as it is carried by said conveyor, electrostatic means ancillary to said applicator means to facilitate deposition of said coating material including discharge electrode means and collector electrode means positioned respectively, substantially on opposite sides of said spray discharge means and charged to electrostatically repel particles of spray deflected from the surface of the article and urge said particles back onto the surface of the article to be coated in a direction away from the discharge electrode, said spray discharge means spiegare being rotatable in a plane to provide the direction of spray therefrom substantially normal to the path of the conveyor.

3. Apparatus for applying coating material to an article comprising a conveyor for carrying said article, applicator means adapted for deposition of said coating material and having a spray discharge means positioned for spraying said coating material toward said article as it is carried by said conveyor, electrostatic means ancillary to said applicator means to facilitate deposition of said coating material including discharge electrode means and collector electrode means positioned respectively, substantially on opposite sides of said spray discharge means and charged to electrostatically repel particles of spray deilected from the surface of the article and urge said particles back onto the surface of the article to be coated and in a direction away from the discharge electrode, said spray dis charge means being free from direct electrical contact with either of said electrodes to permit said discharge means to be positioned relative to said article within a distance less than the arc-over distance of the electrostatic means.

4. Apparatus for applying coating material to an article comprising a conveyor for carrying said article, applicator means adapted for deposition of said coating material and having a spray discharge means positioned for directly spraying saidcoating material onto said article as it is carried by said conveyor, electrostatic means ancillary to said applicator means to facilitate deposition of said coating material including discharge electrode means and collector electrode means positioned respectively, substantially onopposite sides of said spray discharge means and charged to electrostatically repel particles of spray deiiected from the surface of the article and urge said particles back onto the surface of the article to be coated and in a direction away from the discharge electrode, said spray discharge means being rotatable in a plane to provide the direction of spray therefrom substantially normal to the path of the conveyor, said discharge electrode means including a plurality of conducting elements having their respective discharge ends formed in an arcuate rconiguration generally similar to the arcuate path of the rotatable spray discharge means.

5. Apparatus for applying coating material to an article comprising a conveyor for conveying the article over a predetermined path, applicator means including spray discharge means and motive means for projecting particles of coating material from said spray discharge means onto said article, discharge electrode means positioned later- -ally of said applicator means, and direct current supply means having one terminal connected to said discharge electrode means and the other electrode electrically coupled with said article for establishing an electrostatic iield between said. discharge electrode means and said article to facilitate deposition of coating material particles beyond influence of said motive means, said spray discharge meansbeing electrically insulated from said discharged electrode means and said other electrode.

6. Apparatus for applying coating material to an article comprising a conveyor forV conveying the article over a predetermined path, applicator means including spray discharge means and' motive means for protecting particles from said spray discharge means onto said article, discharge electrode means positioned laterally of said applicator means, and direct current supply means having one terminal connected tosaid discharge electrode means and the other electrode connected with said conveyor for establishing an electrostatic iield' between said discharge electrodeV meansv and said article to facilitate deposition of coating material particles beyond inuence of said motive'Y means, said spray discharge means being electrically insulated from said discharge electrode means and said other electrodel to permit said spray discharge means to be positioned relative to said article a distance less than the arc-over distance between the discharge electrode means and the conveyor.

7. Apparatus for electrostatically spray coating leather workpieces having a relatively large and relatively flat surface area to be coated, said apparatus comprising a spray chamber, an electrically grounded conveyor having its upper run extending through said chamber in a horizontal plane to support said leather workpieces in said spray chamber and movable to advance the workpieces therethrough, nozzle means for spray coating material on said workpieces carried on said upper conveyor run, said nozzle means being directed towards said conveyor and spaced thereabove and movable thereacross and positioned for spraying said coating material substantially by air pressure directly onto said workpieces, electrostatic discharge grids `ancillary to said nozzle means spaced apart in the direction of the conveyor movement with said spray chamber, means to establish an electrostatic held between said grids and said conveyor, said grids including means positioned rearwardly of said nozzle means and comprising elongated bars disposed above and parallel to said upper conveyor run-and extending generally transversely of the direction of conveyor movement, said grids further comprising depending needle-like electrodes spaced apart along the lengths of each bar and directed normal to the said upper conveyor run.

8. Apparatus for electrostatically spray coating lea-ther workpieces having a relatively large and relatively at surface area to be coated, said apparatus comprising a spray chamber, an electrically grounded conveyor having its upper run extending through said chamber in a horizontal plane to support said leather workpieces in said spray chamber and movable to advance the workpieces therethrough, nozzle means for spray coating material on said workpieces carried on said upper conveyor run, said nozzle means being directed towards said conveyor and spaced thereabove, said nozzle means being rotatable in a plane to provide the direction of spray therefrom substantially normal to the path of the conveyor and movable thereacross and positioned for spraying said coating material substantially by air pressure directly onto said workpieces, electrostatic discharge grids ancillary to said nozzle means spaced apart in the direction of the conveyor movement with said spray chamber, means to establish an electrostatic field between said grids and said conveyor, said grids including means positioned rearwardly of said nozzle means and comprising elongated bars disposed above and parallel to said upper conveyor run and extending generally trans versely of the direction of conveyor movement, said grids further comprising depending needle-like electrodes spaced apart along the lengths of each bar and directed normal to the said upper conveyor run, said grid means including a plurality of conducting elements having their respective discharge ends formed in an arcuate configuration generally similar to the arcuate path of the rotatable nozzle.

References Cited in the le of this patent UNITED STATES PATENTS 2,049,940 Barthel Aug. 4, 1.936 2,221,338 Wintermute Nov. l2, 1.940 2,397,482 Grifiin Apr. 2, 1946 2,462,487 Griith et al. Feb. 22, 1949 2,658,009 Ransburg Nov. 3, 1953 2,686,141 Sawyer Aug; l0, 1954 FOREIGN PATENTS 496,838 Canada Oct.- 13', 1953 679,751 Great Britain Sept. 24, 1952

Claims

1. APPARATUS FOR APPLYING COATING MATERIAL TO AN ARTICLE COMPRISING A CONVEYOR FOR CARRYING SAID ARTICLE, APPLICATOR MEANS ADAPTED FOR DEPOSITION OF SAID COATING MATERIAL AND HAVING A SPRAY DISCHARGE MEANS POSITIONED FOR SPRAYING SAID COATING MATERIAL SUBSTANTIALY BY AIR PRESSURE DIRECTLY ONTO SAID ARTICLE AS IT IS CARRIED BY SAID CONVEYOR, ELECTROSTATIC MEANS ANCILLARY TO SAID APPLICATOR MEANS TO FACILITATE DEPOSITION OF SAID COATING MATERIAL INCLUDING DISCHARGE ELECTRODE MEANS POSITIONED SUBSTANTIALLY REARWARDLY OF SAID SPRAY DISCHARGE MEANS AND COLLECTOR ELECTRODE MEANS POSITIONED ON THE OPPOSITE SIDE OF SAID SPRAY DISCHARGE MEANS, SAID ARTICLE BEING DISPOSED BETWEEN SAID SPRAY DISCHARGE MEANS AND SAID ELECTRODE WHEREBY, WHEN CHARGED, SAID ELECTROSTATIC MEANS ELECTROSTATICALLY REPELS PARTICLES OF SPRAY DEFLECTED FROM THE SURFACE OF THE ARTICLE AND URGES SAID PARTICLES BACK ONTO THE SURFACE OF THE ARTICLE TO BE COATED AND IN A DIRECTION AWAY FROM THE DISCHARGE ELECTRODE.