US2809128A - Electrostatic method and apparatus for atomizing and for coating - Google Patents

Description

Oct. 8, 1957 M. R. MILLER ELECTROSTATIC METHOD AND APPARATUS FOR ATOMIZING AND FOR COATING 2 Sheets-Sheet 1 Filed July 14, 1953 INVENTORT M r0/ v HI MIL LEI? ATTORNEY Oct. 8, 1957 M. R. MILLER ELECTROSTATIC METHOD AND APPARATUS FOR ATOMIZING AND FOR COATING 2 Sheets-Sheet 2 Filed July 14, 1955 JNVENTOR.

ME/PTO/V R. M/LLER BY A A7- 5 A zro R/VE) United States Patent ELECTROSTATIC METHOD AND APPARATUS FOR ATOMIZING AND FOR COATING Merton R. Miller, Whittier, Calif., assignor to Ransburg Electra-Coating Corp., Indianapolis, Ind., a corporation of Indiana Application July 14, 1953, Serial No. 367,880

19 Claims. (Cl. 11793) This invention relates generally to improvements in methods and apparatus for atomizing liquids and especially to methods and apparatus in which the liquid atomized is a coating material and in which the atomized material is electrostatically deposited on articles to be coated.

One object of the present invention is to provide a method and apparatus for atomizing liquids in which novel control is achieved over liquid supplied to a site of atomization.

Another object of the present invention is to provide a method and apparatus for atomizing liquids in which the direction of the spray is controllable and adjustable.

Still another object of the present invention is to provide novel apparatus for atomizing liquids which may be operated intermittently and, if desired, in co-ordination with the movement past it of articles to be coated with the atomized liquid.

A further object of the present invention is to make possible the electrostatic atomization of a liquid fed to a site of atomization as a film on the surface of a roller of such large diameter that without a discharge member it is impracticable to maintain at the surface of the roller an electrostatic field of suflicient strength to produce atomization.

In practicing the invention, the liquid material to be atomized is moved to a site of atomization in the form of a film, preferably on the surface of a rotating member between which and the article or articles to be coated an electrostatic field is maintained. To concentrate the field, or increase its potential gradient, where necessary or desired at the site of atomization a discharge member may be placed in the path of the moving film to deform it and increase its curvature. An electrostatic field is created between the site of atomization and an article or articles 7 to be coated, and the atomized particles proceed under the influence of such field as a divergent spray for electrostatic deposition on such article or articles. If it is desired to produce a confining effect on the atomizing spray, a feed member having a materally larger surface area than the surface area of the discharge member should be used. It it is desired to make the direction of the atomized spray adjustable, the discharge member is mounted for movement concentrically relative to the feed member so it may assume different relative positions with respect to the film-supporting surface of the feed member. Means may be provided for stopping atomization which moves the discharge member out of the path of movement of the liquid film supported on the feed member; and if desired, such discharge-member movement may be automatically coordinated with movement of the articles being coated.

The rotating feed member on whose surface the film is carried to the site of atomization may be provided with a shield or shroud which partially surrounds the feed member, such shield being interrupted to provide an opening for emergence of the spray. Such a shroud retards evaporation of the liquid in the film and aids in the appended claims.

2,809,128 Patented Oct. 8, i957 ice collection for reuse of any liquid which leaves the rotating member otherwise than in the spray projected toward the article.

For a better understanding of the invention, together with other and further objects, reference ishad to the following description taken in connection with the following drawings, and its scope will be pointed out in the In the accompanying drawings:

Fig. 1 is an isometric view illustrating the invention as embodied in apparatus for electrostatically atomizing a liquid coating material and electrostatically depositing the atomized particles on a moving sheet;

Fig. 2 is a partial isometric view of modified electrostatic atomizing apparatus;

Fig. 3 is a diagrammatic elevational view of another modification of electrostatic atomizing apparatus utilized for coating sheet material;

Fig. 4 is an end view partially in section of still another modified electrostatic atomizing apparatus for coating articles; and

Fig. 5 is a section through Fig. 4 along the line 55 looking in the direction of the arrows.

Referring to the drawings and more particularly to Fig. 1, a sheet 10 is moved in the direction of the arrow 12 by suitable means (not shown) past and in spaced relation to an atomizing device 14. As the sheet 16 moves past the atomizer 14 a spray of electrostatically atomized liquid from the atomizer 14 is deposited on the sheet.

The electrostatic atomization and deposition of the liquid coating material is effected by an electrostatic field of appropriate characteristics which is established between the atomizer 14 and the sheet 10. For this purpose the sheet 10 may be grounded in any suitable manner and the atomizer 14 insulated from ground and connected by means of conductor 16 to the ungrounded terminal of a high-voltage source 18, the other terminal of which is grounded.

The atomizer 14 comprises a supporting structure which includes vertical posts 20, 21, 22 and 23 of electrical insulating material and horizontal frame 24. A dip tank 26 is suitably mounted on the frame 24. A roller 28, provided with liquid supporting surface 29 and shaft 30, is

rotatably mounted on bearings 32, which are suitably afiixed to the frame 24. The roller 28 is mounted relative to the tank 26 to dip into liquid in the tank as it is rotated about its axis so that a thin film of liquid is applied from the tank onto the surface 29. It is desirable that this film be thin enough so that negligible running and sagging occur on the roller 28. Factors which govern the thickness of the film that is produced are the rate of rotation of the roller 28 and the density, viscosity and surface tension of the liquid. As an aid to obtaining the desired thickness of liquid film on the surface 29, a doctor blade 34 may be provided. In Fig. 1 this blade is shown as mounted on the tank 26 for ad justment relative to the surface 29 by means of screws 36 and 38.

The roller 28 may be provided with a cover 40 mounted on bracket 42 made of insulating material which is supported on the vertical posts 22 and 23 for reducing to a minimum evaporation from the liquid film distributed over the surface 29.

The motive power for rotating the roller 28 is provided by motor 44 through variable speed transmissions 46 and 48, gears 50 and 52, shaft 54 and belt 56 made of insulating material.

The liquid coating material in the tank 26 which is applied to the roller 28 is supplied from container 58 through pipes 60 and 62 of insulating material by means of pump 64, which may be of any suitable type available commercially. The pump 64 is driven by motor 44 through variable transmissions 46 and 66 and gears 68 and 70. The tank 26 is provided with an overflow pipe 72 made of insulating material which leads to the container 58 and serves to maintain a constant level of liquid in the tank 26 by returning to container 58 liquid in tank 26 which reaches a predetermined level.

A discharge member 74, which is shown in Fig. l as a wire, is supported in spaced relation to the sheet and adjacent the peripheral surface 29 of the roller 28 by means of support members 76 and 78 of insulating material which are movable to carry the discharge member into and out of contact with the liquid film on the roller. Conveniently, the members 76 and 78 are slidahly associated respectively with solenoids 80 and 82. are biased by appropriate yielding means (not shown) to move the discharge member 74 out of contact with the liquid film on the surface 29, and are movable upon energization of the solenoids 80 and 82 to carry the discharge member in the opposite direction into engagement with the liquid film on the roller. The discharge member 74 is connected to the ungrounded terminal of the high-voltage source 18 by conductor 16 for establishing a hi h gradient electrostatic field adjacent thereto. When the discharge member is in contact with the liquid film on the rotating roller 28 such film is deformed by the discharge member and transferred thereto. The electrostatic field adiacent the discharge member 74 shapes the deformed liouid into a series of cusps 75 from the tips of which the liquid is electrostatically atomized and electrostatically deposited on sheet 10. Positioning the roller or feed member immediately adiacent the discharge member results in shielding a portion of the surface of the discharge member and limits atomization to only the unshielded surface of the discharge member. Thus, it has a confining effect on the spray produced. This shielding effect may be varied by changing the size of the feed member, the discharge member or both.

Electrostatic atomization by the device just described may be interrupted or stopped by dc-energizing the highvoltage source 18 or by moving the discharge member 74 out of contact with the liquid film. The latter operation may be accomplished by de-energizing the solenoid devices 80 and 82.

As shown the solenoids 80 and 82 are connected in parallel by conductors 84 and 86 and are connected to a suitable source of current by conductors 87, 88 and 89. A switch 90 is connected between conductors 88 and 89. This switch is provided with a. spring biased lever 91 which is located in the path of movement of the sheet 10 and which normally maintains the switch 90 open and the solenoids 80 and 82 de-energized. Under this condition the discharge member 74 is held out of contact with the liquid film on the surface 29. However,

when the lever 91 is moved by the sheet 10 the switch 90 is closed and the solenoids 80 and 82 are energized to move the discharge member 74 into contact with the liquid film on the surface 29.

The variable speed transmissions 46, 48 and 66 are arranged and constructed so that the ratio of fluid delivery of the pump 64 to the rate of rotation of the roller 28 may be established by the proper adjustment of knobs 92 and 94 of variable speed transmissions 48 and 66 respectively. For normal operation the speed of the pump and the rate of rotation of the roller are adjusted by the knobs 92 and 94 so that the liquid delivery of the pump to the tank 26 is slightly in excess of the volume of liquid delivered by the rotating roller from the tank 26 to the discharge member. After the knobs 92 and 94 are set to conform to the constants of the system, the rate of atomization of the liquid from the discharge member 74 may be controlled by the adjustment of the knob 96 of the common variable speed transmission 46 to increase the speed of the roller 28 for higher rates r 56 shown in Fig. 1.

of atomization and to decrease roller speed when lower rates of atomization are desired.

In considering the operation of the apparatus described, the atomizer is set into operation by energizing the motor 44, adjusting the knobs 92, 94 and 96 of the variable speed transmissions 46, 48 and 94 respectively, and energizing the high-voltage source 18 to establish a field of high gradient adjacent to the discharge member 74.

Under these conditions liquid is continually applied to the surface 29 in the form of a film the thickness of which is determined either by the rate of rotation of the roller 28 and the density, viscosity and surface tension of the liquid used or by the adjustment of the doctor blade 34 when present. However, electrostatic atomization does not take place from this liquid film so long as the discharge member 74 is held out of contact with the liquid on the surface 29. During periods of non-atomization the liquid on the surface 29 moves past the discharge member and will adhere to the surface due to surface tension until it is returned to the tank 26. This non-atomizing position of the discharge member 74 is maintained while switch 90 is open and solenoids and 82 are de-energized. When the sheet 10 engages the lever 91, the switch is closed, the solenoids 80 and 82 are energized and the discharge member 74 is moved into the path of the liquid on the surface 29 which causes the liquid, when it comes in contact with the discharge member, to be deformed and transferred to the surface of the discharge member. The electrostatic field adjacent the deformed liquid forms it into cusps from the tips of which liquid is electrostatically atomized into a spray of dispersed particles which are urged toward and deposited on the sheet 10. The position of lever 91 of the switch 90 relative to the path of article movement may be arranged so that the discharge member 74 is brought into atomizing position with the liquid on the surface 29 in suflicient time to apply a coating to the entire exposed surface of the sheet 10 being moved past the discharge member 74.

Because of the shielding effect of the roller, the initial direction of the atomized spray will be substantially radial of the roller and this characteristic may be utilized to control the direction of the spray in space. For example, when the discharge member 74 and roller 28 are positioned as shown in Fig. l the atomized spray moves from the discharge member 74 generally in a horizontal direction. If the position of the discharge member 74 is moved concentrically in a clockwise or a counterclockwise direction relative to the roller 28 from the position shown in Fig. l, the direction of the spray of atomized material is changed correspondingly in an upward or downward direction.

Fig. 2 shows an atomizing device modified from that shown in Fig. 1 to permit adjustment of the direction of the spray of atomized material. The device is similar to that shown in Fig. 1 except for the mounting of the discharge member. As illustrated in Fig. 2, this device includes roller 228, provided with film-supporting surface 229 and shaft 230, which is rotatably mounted on the bearings 232. The roller 228 may be rotated by suitable driving mechanism connected to a belt 256, for example mechanism such as that associated with the belt Liquid may be applied to the roller 228 by apparatus shown in Fig. l or any other suitable apparatus. A doctor blade 234 is provided for controlling the thickness of the liquid film on the surface 229. Discharge member 274 is supported on the adjustable brackets 233 by means of supports 278. The brackets 233 are adjustably mounted on the bearing structures 232. The position of the adjustable brackets may be changed by rotating them relative to the bearing structures and they may be fixed in any desired position by tightening the adjusting screws 235.

In operation this apparatus is similar to the apparatus shown in Fig. 1. However, as mentioned in the description, it has the additional feature of permitting adjustment for changing the direction of the spray of atomized material issuing from the discharge member 274. This adjustment may be carried out by properly orienting the discharge member 274 relative to the roller 223 and then fixing this adjustment by tightening screw 235.

Fig. 3 shows a further modification of the apparatus shown in Fig. 1. In this figure there is shown a sheet Ilitl which is moved in the direction of the arrow 312 by a suitable belt-conveyor 313 past and in spaced relation to an atomizing apparatus 314. The atomizer comprises a tank 325, auxiliary roller 327, feed roller 328, discharge member 374 and a high-voltage source 318. In this modification the discharge member 374% is shown as a thin strip and is mounted adjacent to the roller 32' by means not shown. The discharge member is connected to the high-voltage source 318 by means of conductor The tank 326, the rollers 327 and 328 and. the discharge member 37 2- are arranged so that liquid from the tank 326 is applied to the auxiliary roller 32.? in the form of a thin film as it moves therethrough and upon moving past the feed roller 32% transfers this film to it. As the roller moves past the discharge member 374 the liquid film on the roller 32% is transferred to the discharge member and fio'ws by gravity to the edge 373 remote from the roller 328. The electrostatic field adiacent the edge 373 forms the liquid film into a series of cusps 3'75 from the tips of which liquid is atomized in the form of a spray and urged downwardly and deposited on the article 35.0. Where it is desired, the rollers 327 and 328 may be covered by housing as shown to reduce to a minimum evaporation of the liquid material as it is being transferred to the discharge member. While a doctor blade is not sh wn in this embodiment of atomizing apparatus for controlling the thickness of the liquid film prior to its presentation to an atomizing field it is understood that one could be used in association with the roller 328.

The operation of the apparatus just described is similar to that of the apparatus shown in Fig. 1, the only difference being that the liquid is transferred from the dip tank to the discharge member by passing it over an auxiliary roller in addition to the feed roller.

The apparatus shown in Figs. 4 and 5 permits directing a spray of atomized material in a vertical plane. In this a paratus a series of articles 410 mounted on supports 411 are moved by suitable conveying means indicated by line past and in spaced relation to an atomizer 414. As the articles move past the atomizer 41 a spray of electrostatically atomized liquid from the atomizer 414 is deposited on the articles.

'lo effect electrostatic atomization and electrostatic deposition on the articles 41b, an appropriate potential difference is maintained between the articles 41% and the atomizer This is accomplished by means of highvoltage source which may have its ungrounded terminal connected to the atomizer 414 insulated from ground and its other terminal connected to the article through ground.

The atomizer 4114 includes an insulating supporting structure ll. on which roller 428 is rotatably mounted. The roller 42 3, which is shown as electrically insulating material, is adapted to be rotated about its axis by a belt of insulating material which may be connected to any suitable driving means (not shown). Liquid coating material is applied to the peripheral surface 429 or" the roller 42% by means of pipe s25 made of insulating material whose feed orifice 427 is located adjacent the upper edge portion of the surface 429.

The liquid may be forced through the pipe '425 by a pressurized fluid system similar to the motor, variable speed transmission and pump combination shown in Fig.

l or any other suitable system. The liquid flows downwardly along a cavity 433 formed along the surface 429 between seal 439 and doctor blade 434 both of which are mounted on bracket 435 which in turn is mounted on the supporting structure H9. The material which does not adhere to the surface 429 as it passes through the cavity 433 is deposited in receptacle 431 which is formed as a part of the supporting structure 419. The excess liquid may be returned through pipe 437 provided at the bottom of the receptacle 431 to the fluid system including the pipe 425 for further use. Preferably, the supporting structure 419 includes, in addition to the receptacle 431, a shroud-forming portion which extends upwardly and partially surrounds the roller 4-28. Such shroud serves, like the shield 40 and housing 34%, to retard evaporation from the exposed liquid film and also to collect and direct into the receptacle 431 any of the liquid which might be thrown from the surface of the roller. As in the apparatus previously described the doctor blade 434 serves to determine the thickness of the liquid film that is presented for atomization.

A discharge member 474 is supported adjacent the roller 428 and in opposed spaced relation to the articles 416. One end of the discharge member 474 is supported by fastening means 481 provided at the upper portion of the support structure 415 and its other end is connected to the tensioning spring 4 51 aflixed to the pipe 437. Intermediate its end the discharge member 474 passes through guide 477 and over pulley 47?.

Considering the operation of the apparatus just described the articles llil to be coated are moved past the atomizer 41 by the conveyor 413 and liquid material is applied to the rotating roller at a rate consistent with its speed of rotation and with the conveyor speed. Under the force of gravity the liquid spreads over the full longitudinal extent of the peripheral surface of the roller dZ and with the aid of the doctor blade 434 the liquid film is maintained at a desirable thickness for presentation to the discharge member 47%. Upon reaching the discharge member 4'74 the liquid film is deformed and transferred thereto and the field of high potential gra dient adjacent the discharge member forms the deformed liquid into a series of cusps 475 from the tips of which the liquid is atomized into a spray, urged toward the articles 4110 and deposited thereon.

While the apparatus for applying liquid to the feed member is shown as a dip tank or a stationary nozzle in the drawings, it is understood that my invention is not limited to such showings and may take the form of any other suitable applicator such as a reciprocating nozzle, etc.

By using a feed roller to present liquid to a site of atomization asillustrated in the various embodiments shown in the drawings, greater uniformity in the distribution' of the liquid is obtained which is advantageous in obtaining a more uniform spray pattern. However, the roller required for presenting a uniform, thin film at a site of atomization necessarily must be of such large diameter that the field adjacent the liquid film on its surface is not sufficiently intense without deforming the film to electrostatically atomize any liquid from the film. By placing a discharge member adjacent the roller so that it will contact the liquid film on its surface and deform it and also act as a concentrating terminating electrode for lines of force of the field, I am able to electrostatically atomize liquid in a spray of improved uniformity from the surface of such roller.

As shown in Fig. 1, the liquid is deformed by a discharge member which is in the form of a wire. As shown in Fig. 3 the liquid is deformed by a thin strip. However, it is understood that my invention is not limited to these types of discharge members, as other types of discharge members will also operate satisfactorily.

While in each embodiment of my invention illustrated in the drawings the discharge member is shown in contact with the feed roller, it is understood that my invention is not limited to this relationship. The atomizer will operate satisfactorily with the discharge member spaced from the roller so long as it is in contact with the liquid film on its surface. Of course, it is evident that less liquid is transferred to the discharge member as the discharge member is moved farther from the surface of the feed roller and as a result the rate of atomization per unit length of the discharge member is reduced.

Where the liquid has good insulating properties, the discharge member should be of conducting material. However, most liquids and especially most coating materials are sufiiciently conductive that if the discharge member is made of insulating material the potential can be applied to the liquid through the film itself.

The feed roller may be either of electrically insulating or conducting material. However, fields of greater intensity adiacent the discharge member are obtained if the feed roller is of insulating material.

To avoid any sparking between the discharge member and the feed member where the discharge member is mounted so that it may be moved radially of the feed member into and out of engagement with it, as illustrated in Fig. 1, both the feed member and the discharge member should be connected to the ungrounded terminal of the voltage source. If only the discharge member is connected to the ungrounded terminal of the voltage source, then it is desirable that a suitable switch be provided in the circuit including the high-voltage source which is adapted to be controlled by the switch fit) in such amanner that the voltage is applied to the discharge member only when the discharge member is in contact with the feed member.

The degree of conductivity of the liquid material likewise determines how great the electrical losses will be along the liquid supply line. If the liquid material has high conducting properties the entire liquid supply system must be insulated. If, however, liquid material has good insulating properties, it may only be necessary to insulate the atomizer itself.

While the present invention is, of course, not restricted to any particular design, satisfactory results may be obtained by using substantially the same apparatus described hereinabove and illustrated in Fig. 1, constructed in accordance with the following conditions:

Discharge member 74 Steel wire .01 in diameter. Potential of discharge member 100,000 volts (negative).

Spacing between discharge member 74 and sheet 10 8 Feed roller 28 Balrelite material 6" in diameter and 18 long.

Liquid coating material Synthetic enamel, modified urea formaldehyde 20 secs. vis cosity on Zahn #2 Cup,

75 F. Article being coated Sheet steel 18" wide.

The invention can be practiced without regard to the polarity maintained on the discharge member and the article being coated. In coating, either the discharge member or the article can be grounded or both may be maintained at a potential different from ground; but, in most instances, it will be more convenient to ground the article. However, any arrangement which results in maintaining a potential diiference between the article and the coating material and which attracts the coating material to the article will be satisfactory.

Articles of an insulating character as well as a conducting character can be coated with my atomizer. In many instances articles of insulating character can be coated without the necessity for a backing electrode so long as the surfaces are maintained at a different potential from the atomized material.

This application is a continuation-in-part of my prior application S. N. 163,203, filed May 20, 1950, and which is now abandoned.

What I claim is:

1. The method of electrostatically atomizing liquid,

comprising the steps of forming liquid material into a thin, uniform film, moving said film into an atomizing zone remote from the site of film formation, establishing an electrostatic field over said film in the atomizing zone, and mechanically obstructing movement of said film in the atomizing Zone along a line transverse to the direction of film movement to deform said film locally and thereby increase the gradient of the field at the site of deformation for forming the deformed liquid into a series of cusps and electrostatically atomizing liquid from the tips of such cusps.

2. The method of electrostatically coating articles, comprising moving articles over a predetermined path through a coating zone, forming liquid coating material into a thin, uniform film, moving said film from the site of film formation to the coating zone in spaced relation to the articles passing over said predetermined path, establishing an electrostatic field in the coating zone between said film and the articles moving over said predetermined path, and mechanically obstructing movement of said film in the coating zone to deform said film and thereby increase the gradient of the field locally at the site of deformation for forming the deformed liquid into a series of cusps, electrostatically atomizing liquid from the tips of such cusps, and electrostatically depositing the atomized particles on the articles.

3. In electrostatic coating apparatus, a support for an article to be coated, an elongated stationary discharge member having a discharge surface presented toward and in spaced relation to the supported article, a movable feed member having a liquid film-supporting surface adjacent the discharge member remote from the discharge surface, means for applying liquid to said liquid film-supporting surface to form a free-surface film thereon, means for driving said feed member for moving the liquid film thereon into contact with said discharge member and means for creating between the supported article and said discharge member a potential difference sufficiently great to atomize coating material from said discharge surface and deposit it on the supported article.

4. In electrostatic coating apparatus, means for moving an article over a predetermined path, a discharge member presented in spaced relation to the article path, a liquid supply means including a feed member for transferring liquid to said discharge member, means supporting said two members for relative movement into and out of liquid-transferring relationship, means operating in coordination with article movement for bringing said feed member and said discharge member into liquid-transferring relationship, and means including a high-voltage source for establishing an electrostatic field between said article and the coating material on said discharge member for electrostatically atomizing and depositing the coating material on the article.

5. Apparatus for applying a liquid coating to an article, a support for the article, a movable film-supporting member spaced from the supported article, means for applying liquid in the form of a film on said film-supporting member, a film-deforming member located in a predetermined position adjacent said movable member on the side nearest the supported article and close enough to the movable member to engage and deform the liquid film thereon, and means for maintaining a sufficient potential difference between a supported article and the deformed liquid film to electrostatically atomize liquid from said film and electrostatically deposit the atomized material on the supported article.

6. In an electrostatic atomizer, a feed member having an extended surface for supporting liquid in the form of a film, an extended discharge member positioned to engage such film at a transfer zone, means for supplying liquid to the feed member, means for moving one of said members relative to the other in a direction normal to the extent of the discharge member to cause said discharge member to pass through the film to create a localized deformation of said film, and means for creating at the site of such deformation an electrostatic field capable of atomizing fine particles ofliquid from the deformed film.

7. In an electrostatic atomizer, a rotatable feed member having a cylindrical liquid-supporting surface, a finewire discharge member extending parallel and close to said surface to engage liquid thereon, means for applying liquid on the cylindrical surface of the feed member, means for rotating said feed member to cause transference of the liquid thereon to the discharge member, and means for establishing adjacent the liquid on the discharge member an electrostatic field for electrostatically atomizing the liquid transferred to the discharge member.

8. In an electrostatic atomizer, a movable feed member having a liquid-supporting exterior surface, means for supplying liquid to the liquid-supporting surface of the feed member, a stationary discharge member positioned to engage liquid on said surface, means for driving said feed member for moving its liquid-supporting surface past said discharge member to transfer liquid thereto, and means for establishing adjacent the liquid on the discharge member an electrostatic field for electrostatically atomizing the liquid transferred to the discharge member.

9. The invention set forth in claim 3 with the addition that each of said members possesses a surface presented toward an article on said support, the surface of the feed member having many times the area of the surface of the discharge member.

10. in a method of creating a spray of finely divided electrically charged liquid particles, the steps of distributing liquid over an extended surface, moving the distributed liquid longitudinally of one dimension of said extended surface to an atomizing zone, and at said zone transferring said liquid from said extended surface onto a discharge member positioned at the atomizing zone said transfer being along a line generally transverse of the direction of liquid movement for atomization from said atomizing zone, and maintaining at such atomizing zone a particle-charging, atomization-affecting electrostatic field.

11. In a method of creating a spray of finely divided electrically charged liquid particles, the steps of distributing liquid over an extended surface, moving the distributed liquid longitudinally of one dimension of said extended surface to an atomizing zone extending transverse to the direction of liquid movement, maintaining at such atomizing zone over the liquid thereat, a particle-charging, atomization-aifecting electrostatic field, and obstructing the movement of the liquid in the atomizing zone along its extent to deform the liquid locally and thereby increase the gradient of the field at the site of deformation.

12. In an electrostatic atomizer, an extended discharge member having a curved discharge side and a liquid receiving side, a feed member having a curved liquid-supporting surface, said discharge member being disposed to engage liquid on the surface of the feed member, means for applying liquid to the surface of the feed member, means for producing at the point of closest approach of said members relative movement between them in a direction normal to the extent of the discharge member to cause liquid to be scraped from the feed member onto the discharge member, and means for establishing adjacent the discharge side of the discharge member an electrostatic field for electrostatically atomizing liquid, the radius of curvature of said discharge member at its discharge side being substantially less than that of the liquidsupporting surface of the feed member.

13. Means for electrostatically coating articles with a spray of atomized coating-material particles, a feed member having an extended exterior surface for supporting a film liquid thereon, means for distributing liquid as a film over said extended surface, a discharge member positioned in a transfer zone adjacent said feed member for engaging the liquid thereon, means for causing relative movement between said members at the point where said discharge member engages the liquid for causing liquid on said feed member to engage said discharge member and by said engagement to transfer said liquid onto said discharge member for atomization therefrom in the form of a spray, means for conveying articles in spaced relation and over a predetermined path through said spray, and means for maintaining an electrostatic field between said discharge member and articles so moved through such field, the distance between the articles moving over said predetermined path and the discharge member being great enough to permit the atomized particles of the spray to be dispersed over a substantial area.

14. Means for electrostatically coating articles, comprising a feed member having an extended surface for supporting liquid in the form of a film, a discharge member positioned to engage such film at a transfer zone, means for supplying liquid to the feed member, means for moving one of said members relative to the other at the transfer zone to cause engagement of the discharge member with the liquid film on the feed member and by said engagement to transfer liquid to said discharge member, means for conveying articles over a predetermined path in opposed spaced relation to such zone, and means for creating between the discharge member and articles moving past the transfer zone an electrostatic field capable of atomizing liquid at the transfer zone into finely divided particles and electrostatically depositing such particles on the articles.

15. The invention set forth in claim 6 with the addition that said feed member is a rotatable roller having a cylindrical film-supporting surface, means for rotating said roller, and a shroud surrounding said roller, said shroud being interrupted adjacent said discharge member to permit projection of the atomized particles as a spray.

16. In electrostatic coating apparatus having a support for an article to be coated and an atomizer for creating a spray of coating-material particles to be deposited on the article by an electrostatic field, said atomizer including a rotating member adapted to support a film of liquid coating material, means for rotating said member to move the film carried thereby to an atomizing zone, a mechanical support for the film at said atomizing zone, said support providing an edge of small radius to cause. the film to present an edge of small radius toward an article from which film edge atomization is to take place, means for creating an electrostatic charge differential between the atomized coating material particles and an article, means for supporting an article to be coated in spaced relation to said rotating member, a shroud enclosing said rotating member, said shroud being interrupted opposite said supporting means to permit the passage of atomized coating material for electrostatic deposition on the article by said field, a fluid supply system for supplying liquid coating material to said rotating member, and means for returning to said supply system any liquid coating material deposited on the inner surface of said shroud.

17. Apparatus for electrostatically coating articles, comprising a conveyor for moving the articles in succession over a predetermined path, an atomizer disposed at one side of said path in spaced relation thereto, said atomizer including a rotatable member adapted to support a film of liquid coating material, means for rotating said member to move the film carried thereby to an atomizing zone, mechanical means at said atomizing zone to form in the film an extended edge portion of small radius, a coating-material supply system for supplying liquid coating material to said member for formation into a film thereon, means for creating an electrostatic field between said edge portion and said articles capable of electrostatically atomizing coating material at said edge portion into a spray of finely divided particles, and means including a shroud partially surrounding said rotating member for collecting and returning to said supply system liquid coating material leaving said rotatable member otherwise than in said spray.

18. In a method of producing a spray of electrically charged liquid particles, the steps of forming a liquid body into an extended free-surfaced film, moving said film along a predetermined path to, through, and beyond an elongated atomizing zone extending transversely of the direction of film movement, maintaining an electrostatic field over the surface of said film at the atomizing zone, and mechanically contacting the film to increase the curvature of the free surface of the film at said atomizing zone to concentrate said field at the area of increased curvature.

19. In an apparatus for applying material to the surface of an article, a support for the article to be coated, an extended discharge member positioned in spaced relation to the article on said support, means for supplying liquid coating material to that portion of said discharge member which faces the article, said means including a surface shielding member adjacent and extending along said discharge member on that side thereof which is remote from the article, means for creating relative movement between said shielding member and said discharge member in a direction transverse to that in which said discharge member extends, and high-voltage means to establish adjacent the material on said discharge member a potential gradient to transfer said material from said discharge member to said article surface, said motion producing means being power driven and operative during the material transfer operation.

7 References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. THE METHOD OF ELECTROSTATICALLY ATOMIZING LIQUID, COMPRISING THE STEPS OF FORMING LIQUID MATERIAL INTO A THIN, UNIFORM FIL, MOVING SAID FILM INTO AN ATOMIZING ZONE REMOTE FROM THE SITE OF FILM FORMATION, ESTABLISHING AN ELECTROSTATIC FIELD OVER SAID FILM IN THE ATOMIZING ZONE, AND MECHANICALLY OBSTRUCTING MOVEMENT OF SAID FILM IN THE ATOMIZING ZONE ALONG A LINE TRANSVERSE TO THE DIRECTION OF FILM MOVEMENT TO DEFORM SAID FILM LOCALLY AND THEREBY INCREASE THE GRADIENT OF THE FIELD AT THE SITE OF DEFORMATION FOR FORMING THE DEFORMED LIQUID INTO A SERIES OF CUSPS AND ELECTROSTATICALLY ATOMIZING LIQUID FROM THE TIPS OF SUCH CUSPS.

Images