US2894691A - Electrostatic deposition - Google Patents

Description

July 14, 1959 J. SEDLACSIK ELECTROSTATIC DEPOSITION Filed Jan. 11. 1955 United States Patent ELECTROSTATIC DEPOSITION John Sedlacsik, Garfield, N .J.

Application January 11, 1955, Serial No. 481,162

2 Claims. (31. 239-15 This invention relates to an improved means for imparting an electrical charge to coating materials, which electrical charge is of such character that when the material is atomized, precipitated, and dispersed, the spraying charge is smoothly deposited upon the object toward which the atomized material is directed.

The invention relates to the formation of a paint spray or similar spray from a liquid material capable of relatively rapid atomization by expelling same from the device in which the material is held in the liquid form. This is preferably done through the use of air, in conjunction with an electrostatic attraction toward an adjacent article or target, as well as by the repulsion between the charged surface portions of the liquid and other adjacent parts of the mass. As is well known, small particles when electrified by charges of like sign repel one another, whereas particles or masses of opposite sign are attracted.

Broadly speaking, my invention relates to improvements in a method of an apparatus for applying a liquid coating to an article by electrostatically charging and depositing the comminuted coating material upon the article within an electrostatic field created between the article to be coated and the issuing source of the coating material.

The invention relates to an apparatus for coating surfaces by depositing the coating material thereon from a spray gun or other suitable atomizing device preferably utilizing air under pressure as a vehicle to convey the finely divided or atomized particles onto the surface to be coated.

In carrying out the present invention, any of the conventional coating materials commonly applied by spray methods may be used, such as paint, lacquer, plastic compositions and metals in the fused or molten state.

An important object of the invention is to control more efficiently the deposit of the sprayed material on the surface to be coated, thereby not only reducing and minimizing the waste of material due to loss by dispersion into the atmosphere, but also effecting substantial savings in labor and equipment while increasing the coverage of the coating material issuing from the spray device.

In prior art devices, it is known that, in spray coating surfaces utilizing air pressure to atomize the coating material, the spray mixture issuing from the spray nozzle spreads outwardly or expands uniformly taking the form of a generally conical mistlike stream. The sides of this stream travel outwardly in diverging paths toward the surface to be coated and upon impact therewith result in considerable of the coating material, entrained with the air, being deflected in a swirling action away from this surface and dispersed into the atmosphere. Thus, a great deal of the coating material discharged from the nozzle is lost and, therefore, more material than actually needed is usually used to produce the required coating.

In order to avoid some of this waste of material and also to eliminate fire hazard, where inflammable coating materials are used, it has been the practice in some industries to provide special spray booths or chambers in 2,894,691 Patented July 14, 1959 which to conduct the spray operations. These booths are often equipped with high powered suction or blower systems to remove the wasted material from the atmosphere and convey it away. In some cases, special equipment is installed for salvaging the material thus conveyed away as well as reclaiming wasted material deposited on the walls of the spray booths.

The present invention, therefore, has for its primary purpose the provision of an improved spray coating apparatus capable of reducing the loss and waste of coating materials as above mentioned, increasing the amount of effective coverage which may be obtained from a given quantity of coating material, reducing fire hazard in cases where inflammable materials are used, and improving the character of the coating produced by the spray device while enabling a more uniform coating to be applied.

A further object of the invention is to provide means for controlling the diverging column or stream of atomized coating material after issuance from the spray nozzle so that lateral deflection and dispersion of the mixture along the margin of impact of the stream with the coated surface will be greatly reduced and all of the material which would otherwise be dispersed into the atmosphere will be forced onto the surface.

A still further object of the invention is to provide an apparatus for inhibiting the loss of coating material by dispersion into the atmosphere, in which a curtain or wall of air under pressure is set up around or adjacent the margin of the column or stream of sprayed material thereby trapping it at the region of contact with the surface to be coated and restraining it against internal dispersion.

The principal object of this invention is directed to an apparatus and method for improving this dispersion and deposition of the atomized particles from a charged gun mechanism upon an oppositely charged article. Same is accomplished by a means which provides greater stability to the projected spray or jet and imparts a sharper edge definition to its issuing pattern.

This invention contemplates a paint spray gun mechanism wherein the forward atomizing and spray elements are isolated from the rearward support and control elements. The rear portion of the mechanism is at ground potential for the convenience and safety of the operator while, at the same time, the forward portion thereof is connected to the high electrical potential. The structure prevents the possibility of a transmittal of an electrical charge from the forward area of the mechanism rearwardly to the rearward area thereof.

By surrounding in close proximity the atomized coating material with envelopes of air, both of which air envelopes are substantially coextensive longitudinally with the coating spray, the projecting spray jet is stabilized, and is made more definite in its shape and more constant in its direction.

The objectionable scattered spreading effect upon the particles, particularly at the outer portions of the jet, is materially reduced. This results in a deposited pattern which is more uniformly dense throughout and which has a desired sharp edge definition.

Under the influence of the electrostatic expulsion, in combination with the air, sprays of extreme fineness can be attained. Further, the sprays may be directed forwardly in a straight manner toward the article to be coated or they may be made irregular so as to have a more or less conical contour by subjecting them, during their expulsion from the liquid mass and before their complete atomization, to an intermittent force acting in line with their direction of travel.

One of the objects of this invention is to provide a stabilizing area adjacent the electrostatic spray atomizing, projecting and depositing field, which area is effective to stabilize the jet produced by the latter, both in respect to direction and in respect to shape, and to give a resulting deposited pattern having relatively sharper edge definition throughout its entire periphery and/or over one or more portions thereof.

The atomizing element of my apparatus consists essentially of a small head or nozzle having a sharply defined distributing or atomizing point or tip from which the coating material is metered at a predetermined rate in the form of atomized particles.

The point at which the coating material escapes from the head or nozzle can be controlled and the efficiency of the apparatus increased by providing the device with an annular edge or lip so that, as material is supplied to it, said material tends to flow out over the lip.

A source of electrostatic high potential, having one terminal grounded and its opposite terminal connected to the atomizing head creates a strong electrostatic field be tween the head and the article to be coated, which article is also grounded. The force of this field transforms the coating material into a spray of fine, charged particles and created an attraction which pulls the spray to the grounded article, thus accounting for complete electrostatic deposition.

Herein, the coating material is normally supplied to the discharge edge or lip and its region of corona discharge at a rate at which it can be electrically atomized by the corona discharge most efficiently and effectively, after which the charged particles are projected in spray form toward and deposited upon the oppositely charged article.

A further object of this invention is to provide an improved spray gun or device having a nozzle through which a jet of spray mixture is discharged under pressure, said device being provided with means for directing a cuttain of moving air under pressure around or along the outside and/or the inside of the coating stream. This wall or curtain not only entraps the spray material but also entrains with it whatever material is deflected laterally by impact with the surface being coated and deposits this material onto the surface.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification, wherein like reference characters desig nate corresponding parts in the several views.

Fig. 1 is a sectional elevational view of the device of the invention;

Fig. 2 is an enlarged end elevational view of the head end of the device shown at the right side of the figure in Fig. 1; and

Fig. 3 is a sectional view on the line 33 of Fig. 1.

Before explaining in detail the present invention, it is to be understood that the invention 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 and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

In Figs. 1 to 3 inclusive, there is illustrated by way of example, a form of apparatus or device embodying certain features of the invention as applied to a manually operable spray gun especially adapted for depositing paint, varnish or the like upon a surface to be coated. It will, of course, be understood that the invention in accordance with its broader aspects may be embodied in other forms of apparatus in which the spraying operation is performed otherwise than by the device shown such as by apparatus which is mechanically operated and which may either be mounted in stationary manner with respect to moving articles or objects or supported for movement relatively to stationary objects to be coated. Furthermore, the spraying apparatus may comprise a succession or gangs of nozzles or spray devices for applying the coating.

Referring now to the drawing more in detail, and referring more particularly to the preferred form of my invention selected for illustrative purposes, 1 have shown an arrangement of apparatus which is suitable for coating articles (not shown) which are preferably moved along a path of article movement through a coating zone into which the device of the invention, normally fixed in location, is projected. It will be appreciated, however, if desired, that the apparatus of the invention could be reciprocated through the coating zone.

Disposed at one side of the path of article-movement is a horizontally positioned atomizing head generally designated by the numeral 10, by means of which head the liquid coating material is electrostatically atomized.

The liquid spray material is led from a source (not shown) through a conduit (also not shown) to the nozzle or head end of the structure which incorporates the features of this specific invention.

Likewise air is led from its source (not shown) through a different conduit (also not shown) to the nozzle or head end of the structure.

The elements of the spray gun as thus far described are of conventional design and therefore a detailed description thereof is not deemed necessary herein.

At the head or nozzle end of the structure, a nose piece is provided and the liquid and gas tubes may be connected thereto. Interior passageways within the nose piece (not shown) connect the respective tubes with appropriate means at the forward face of the nose piece whereby the liquid and air may pass therethrough to the forwardly disposed members, about to be described.

The spray gun contemplated for use in this invention consists of a conventional main body portion which is disposed rearwardly of the apparatus of this invention. Same does not form a part of this invention and accordingly is not shown. It also includes a spray head sim ilar to the type disclosed in U.S. Letters Patent #2070,- 696, dated February 16, 1937.

The nose piece is of such configuration as to be adapted to receive, in threaded engagement therewith, the spray head of the above patent or of any other of the well known commercial types of atomizing spray guns using air for the atomizing medium.

The spray head comprises an inner liquid or fluid nozzle 40 formed with a forwardly disposed tip 42 having a central orifice 44 therethrough through which the coating material is emitted into the spray head device of the invention.

The nozzle 40 abuts against the outer surface of a washer 46 and the tip 42 extends into, if not through, a centrally disposed opening 48 in the washer 46.

The inner fluid nozzle 40 is threadedly receivable in a sleeve 50 which is receivable in an appropriate opening in the forward face of the nose piece.

Forwardly of the member 40, an elongated connecting member 60 is provided having a central orifice 62 extending therethrough throughout the longitudinal length thereof. The orifice 62 communicates with the opening 44 in the tip 42 of the nozzle 40.

The member 60 has an outwardly extending annular skirt portion 64 which is adapted to be engaged along its outer peripheral edge by a union nut 66 so as to hold the member 60 in extended coaxial relation with member 40 with the tip 42 of the member 40 extending into the opening 62 and affording direct comunication therebetween as aforesaid.

An air opening 68 extends through the member 60 in a direction parallel to the plane of the central orifice 62, at a distance away therefrom, as shown.

The washer 46 is seated in an appropriate opening in the rearward end of the member 60, as shown.

A sleeve or barrel like outer shell member 7'3 may be provided with a central opening 72 extending therethrough.

The rearmost portion of the inside wall of the memher 70 is threadedly engaged with the member 60 at 74, as shown.

An insert member 80 having an annular sheath 82 therearound is insertable into the member 70 at the open forward end thereof.

A rearmost stem like portion 84 of the member 80 is threadedly engaged at 86 with the forward free end of the member 60 and a centrally-located longitudinallydisposed opening 88 is provided through the inlet member 80, which opening 88 is in communication with the opening 62 of the member 60.

A T-shaped annular plug member or cap 90 has a stem portion 92 which extends rearwardly into the outer end of the opening 80 so as to seal the same, the stern portion 92 being press-fitted into the opening.

An annular ring of openings 94 lead obliquely from the opening 88 to the outer wall of the member 80 and terminate at their outer ends along an annular shoulder 96 of the member 80.

An offset wall portion 98 of the member 80 extends outwardly away from the shoulder 96 whereby the coating material pasing through the opening 88 and the opening 94 passes outwardly between the wall portion 98 and the outer end portion of the annular sheath 82.

Air in the opening 72 within the barrel 70 moves for wardly through the forward portion of the head in one of two ways.

Firstly, a plurality of openings 100 extend from the area 72 into the member 80 and communicate with an annular slot 102 around the members 80 as shown. Another plurality of openings 104 are provided in the member 80 forwarly of the slot 102 and same communicate with the annular passageway 106 between the member 90 and the wall portion 98. By means of this circuitous route, air may be conducted forwardly from the chamber 72 to the head end of the device.

Secondly air may pass through the annular passageway 110 between the barrel 70 and the sheath 82.

In this manner, it will be appreciated that a ring like or sheath like envelope of air surrounds the outer side of the spray of coating material and a secondary ring like sheath surrounds it on the inner side of the spray of coating material.

By judicious experimentation, I have determined that by increasing or decreasing the amount of air forming the inside cone or sheath, the size of the formed cone of coating material may be varied.

That is, when there is more air in the inside than in the outside sheath, the size of the sheath of the coating material is increased. increased whereby a variation in the coating material pattern is obtainable.

Conversely, where there is more air in the outside sheath than in the inside sheath, the size of the sheath of coating material is decreased.

Such variance in control can be attained by closing off certain of the openings 100 leading through the member 80.

Further I have determined that by decreasing the amount of air pressure used in the device, the halo etiect is increased.

If desired, means may be provided whereby the air passing through the device may be pulsated so as to distinguish it from the normal situation where it passes through all openings evenly. By passing the air intermittently through the device the air issuing therefrom has a pulsating action causing the air to deflect the liquid material first in one direction and then in another. This resultant effect is known as a pulsating efiect.

Or if desired, the device may be operated without air at all, the coating material being drawn through away from the device by means of the electrical force itself.

The nose piece and the other elements at the forward end of the gun are preferably made from electrical conducting material, the nose piece being connected to the In other words, its diameter is ungrounded terminal of a high voltage source (not shown).

The coating material passes from the source thereof to the member 40 and out through the opening thereof into the opening 62 of the member 60 and thence into and through the opening 88 in the member 80.

The atomizing air is adapted to be supplied to the nose piece, then through an opening around the member 64, thence through openings 68 in member 60 and into and through the opening 72 in the barrel 70, and thence through the annular pasageway 110 or the openings and 104 in the member 80.

As the stream of liquid passes outwardly through the passageway 96 and as the streams of air pass outwardly on either side thereof, the same are subjected to the atomizing effect of the corona discharge from the electrode whereby the finely divided particles comprising the spray are each imparted electrical charges of like polarity. A halo efiect is attained thereby.

With voltage applied directly to the spray head structure, a corona discharge is formed in the region around the edges or lips adjacent the outermost peripheries which is of an intensity sufficient to atomize into particled form the coating material being discharged from the nozzle and to project the coating material in spray form toward the surface of the article being coated.

In actual operation, the electrical energy is maintained at the high potential nozzle or spray assembly. The material being atomized and the gas are delivered through the respective delivery tubes and connections to the head assembly. The material and gas are released in the form of high velocity streams where they meet and mix with each other under pressure, are atomized and electrically charged and pass outwardly with high turbulence.

Under certain conditions in prior art devices, the projected jet wavers erratically resulting in a scattered dispersion of the particles comprising the jet and causing the deposited pattern upon the article to have irregularly disposed lakes. In addition, the mutual electrical repulsion of the particles due to their being charged to the same sign causes them to spread and scatter laterally, particularly at the outer portions of the jet. This makes a less sharply defined edge at the boundary of the deposited pattern. To overcome these objectionable characteristics, I provide concentric gaseous fields in close proximity within and without the coating field.

In this manner, air shields are provided adjacent the peripheries of the lips whereby a gaseous medium of any desired intensity may be introduced around and within the coating stream being dispersed.

By the use of these gaseous envelopes the paint or other material being sprayed with the apparatus may be better concentrated or dispersed over a given area of an article being coated.

The liquid and gaseous materials are supplied through their respective conduits to the nozzle assembly as previously described. These materials issue from their respective orifices at the outermost free end of the nozzle in the form of streams where they mix with each other. The resulting mixture is directed outwardly with high turbulence in the form of a finely atomized stream.

In operation, an unidirectional electric potential is maintained at the high potential nozzle assembly and, as the formed stream is directed outwardly through and away from the nozzle, it is subjected to the ionizing elfcct of the corona discharge from the isolated nozzle whereby the finely divided particles of like polarity and of substantially equal potential with respect to the atomizing lips.

The positively charged particles tend to repel one another aud thus resist coalescence with the result that the electrified cloud of spray is attracted to surrounding grounded article desired to be sprayed and/or coated. The particles are attracted to and precipitate in a layer upon the nearest surface of the grounded article which is to be coated.

Coating material is urged forwardly to the discharge ips where it is electrostatically atomized and precipitated ipon the article passing the head by the action of the elecrostatic field which exists between the article and the lead. The particles are electrostatically dispersed as they ire formed or produced along the line of atomization and hey are electrostatically deposited while still in the liquid state upon the article surface so as to form a finished :oating.

As aforesaid, the spray head is connected to a source of high voltage (not shown) through one terminal thereof. The other terminal of the source is grounded and through ground is connected with the article to be coated and/ or the conveyor therefor all to the end that the space or field between the spray head and article is electrostatically charged.

The electrical force acts on the coating material causing same to be broken up into finely divided or minute particles of coating material, so as to be attracted to the grounded article for deposition thereon.

The grounded article is referred to as a collecting electrode of one potential with the applicator head serving as a discharge electrode of a different potential.

The electrostatic force set upon the field between the electrodes transmits the finely divided particles of the coating material from one electrode to the other.

The same action will take place when the spray head is grounded and the article is directly connected with the source of high voltage and is charged at a high potential.

With voltage applied directly to the spray head structure, a corona discharge is formed in the region there around and adjacent the outermost periphery thereof and is of an intensity sufficient to break up or to atomize into particled form the coating material and to project the coating material in a spray form toward the surface of the article being coated.

The foregoing reveals the gist of my invention whereby others can, by applying current knowledge, readily adapt it for various applications Without omitting features which, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

What it is desired to claim and secure by Letters Patent of the United States is:

1. In an aero-electrostatic atomizing device attachable to a spray device receiving and discharging a supply of a fluent material and a motive agent and being adapted to electrically charge particles of the fluent materials discharged therefrom toward an electro-conductive surface for deposition thereon comprising in combination, an outermost cylindrical shell-like member provided with a forward-most opening and having a rearmost extremity attachable to the spray device, an insert member having a plurality of motive agent passages extending longitudinally therethrough and terminating at their forward-most extremities in an innermost annular primary motive agent discharge mouth and having a fluent material passage extending longitudinally therethrough terminating at and communicating with a plurality of passages terminating at their forward-most extremities in an outer annular fluent material discharge mouth concentric with and exteriorly surrounding the innermost annular motive agent discharge month, said insert member being spaced relative to said shell-like member to provide an annular secondary motive agent passageway terminating in an outermost motive agent discharge mouth concentric with and exteriorly surrounding the annular fluent material discharge mouth.

2. In the structure of claim 1, with the forward planar edge of the outermost motive agent discharge mouth being spaced rearwardly from the forward planar edge of the fluent material discharge mouth.

References Cited in the file of this patent UNITED STATES PATENTS 1,813,083 Pyankow July 7, 1931 1,827,235 Jarvis Oct. 13, 1931 1,832,096 Chafiee Nov. 17, 1931 1,861,475 Hopkins June 7, 1932 2,070,696 Tracy Feb. 16, 1937 2,221,338 Wintermute Nov. 12, 1940 2,247,000 Popoh June 24, 1941 2,302,185 Campbell Nov. 17, 1942 2,302,289 Bronston-Cook Nov. 17, 1942 2,491,889 Bennett et a1 Dec. 20, 1949 2,658,009 Rausburg Nov. 3, 1953 2,685,536 Starkey et a1. Aug. 3, 1954 2,738,230 Pillard Mar. 13, 1956

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