US3144350A

US3144350A - Electrostatic coating method and apparatus

Info

Publication number: US3144350A
Application number: US70740A
Authority: US
Inventors: Osame Gohei
Original assignee: NAKAKO ODA; SHIZUE OSAME; TAIJI OSAME
Current assignee: NAKAKO ODA; SHIZUE OSAME; TAIJI OSAME
Priority date: 1957-05-06
Filing date: 1958-01-03
Publication date: 1964-08-11
Anticipated expiration: 1981-08-11

Description

Aug. 11, 1964 GOHEI OSAME 3,144,350

ELECTROSTATIC COATING METHOD AND APPARATUS Filed Jan. 3, 1958 3 Sheets-Sheet 1 GOHEI 05mm:

IN VEN TOR.

811W, MVPM ATTORNEYS 1964 GOHEI OSAME I 3,144,350

ELECTROSTATIC COATING METHOD AND APPARATUS Filed Jan. 3, 1958 3 Sheets-Sheet 2 Fig. 5,

IO N z: J 4 i? E 6 7 60/151 OsAME IN V EN TOR.

BY h/MM in HPMJ Arrom/Ers Aug. 11, 1964 GOHEI OSAME 3,144,350

ELECTROSTATIC comma METHOD AND APPARATUS Filed Jan. 3, 1958 5 Sheets-Sheet 3 GOHEI OSAME INVENTOR.

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ATTOR/VE rs United States Patent M 3,144,350 ELECTRUSTATIC COATING METHGD AND APPARATUS Gohei Osame, Unagidani, Minarni-ku, Osaka, Japan, assignor, by inheritance andassignment, of eleven twentysevenths to Shizue Osame, eight twenty-seventies to Nalrako Gala, and eight twenty-sevenths to Taiji ()sazne Filed Jan. 3, 1958, Ser. No. 707,040 Claims priority, application Japan May 6, 1957 Claims. (Cl. 117-?3A) The present invention relates to improvements in the electrostatic coating method and apparatus, and the objects of the improvement are to make practicable the employment of coating materials irrespective of their properties and to simplify the electrostatic coating system itself.

According to the electrostatic coating system most extensively practiced, the atomizing and ionizing operation is usually performed either by projecting by means of a spray gun the material to be employed into the electrostatic coating field established between the grid electrode charged with high potential and the surface of the grounded article being coated, or by supplying the material upon a rotating ionizing means charged with high potential, either disc-like or cup-shaped. When a spray gun is employed, however, the coating material particles are not further atomized even when projected into the electrostatic coating field and not so fine and even enough in size so as to yield a uniform coating, and considerable loss of solvent is inevitable, as the forward movement of the particles is so fast that the particles are not so fully charged as required. And in case an ionizing member is employed as an atomizing means, a complicated device is required for rotating the member and a number of coating materials remain out of the application thereof, although the atomized particles are of fairly minute size.

The present invention, on the contrary, is characterized by atomizing with the aid of high pressure the coating material to be employed before the particles are brought into the electrostatic coating field. The particles thus obtained are considerably minute and uniform in size and no solvent is wasted during the operation, whereby the shortcomings inherent in the employment of a spray gun are eliminated, and there remains no need of rotating the ionizing means and almost all sorts of coating materials are made employable irrespective of their properties, contrary to the system where the ionizing member is used as an atomizing means.

The atomizing device of the present invention consists of a nozzle with a small opening and a deflecting member confronting therewith at a predetermined distance. The coating material to be employed is discharged in the form of a jet stream with the aid of high pressure through the opening of the nozzle, and the flow scatters in minute atomized particles around the deflecting member as a result of its impacting contact with the top surface of the deflecting member, with which member is associated an ionizing member at right angles to the direction of the discharged flow. The entire system is so designed as the electrostatic coating field be established exclusively between the fringe of the ionizing member and the surface of the grounded article which is spaced at a predetermined distance from said ionizing fringe, and the atomized particles scatter in directions substantially at right angles to the direction of the impacting flow to reach slightly beyond the ionizing fringe and to remain there in a state of suspension losing their movement, whereby the particles be deposited onto the surface of the grounded article by their interaction with the electrostatic coating field, when the ionizing member is charged with high potential.

Thus the coating material discharging pressure, the size of the opening of the nozzle and the distance between the 3,144,350 Patented Aug. 11, 1964 opening and the-top surface of the deflecting member wherewith the discharged coating material flow is brought into impacting contact-are determining factors in the present invention together with the property of the coating material to be employed, and the most desirable atomizing condition is obtained with'the opening 0.3 millimeter in diameter and the distance 30 to 70 millimeters under the pressure-of 20 kg./1'-cm. In practice, at least pounds per square inch is to be employed, and-the'stop surface of the deflecting member wherewith the coating material flow is brought into impacting contact is to be made as smooth and slippery as possible. The atomizing device is made of either conductive or nonconductive material.

. In order that the present invention be readily and clearly understood, preferred embodiments thereof are illustrated in the accompanying drawings, in which:

FIGURE 1 is a vertical section showing an atomizing device having a spherical top "surface for deflecting the coating material flow;

FIGURE 2 is also a vertical section showing an atomizing device having a flat top surface for deflecting the coating material flow;

FIGURE 3 is a perspective view diagrammatically showing an embodiment of the present-invention in an electrostatic coating system;

FIGURE 4 is a plan viewdiagrammatically illustrating the system shown in FIGURE 3;

FIGURE 5 is a vertical section of the manner in which I an atomizing device of the present invention is connected with an ionizing member, together with members for dividingthe scattering atomized coating material particles into desired segments;

FIGURE 6 is a plan view diagrammatically illustrating the manner in which the device shown in FIGURE 5 is utilized in an electrostatic coating system;

FIGURE 7 is a partial vertical section showing still another embodiment of the present invention for coating elongated articles in an electrostatic coating system; and

FIGURE 8 is a sectional-view of FIGURE 7'along the line 'AA.

The atomizing device of the present invention consists of, as shown in FIGURES 1 and 2, a nozzle 1 with an opening 2 and a member 3 confronting therewith at-a predetermined distance by means of a rod 4 which is provided with a conduit 5 connected with the opening 2. The coating material to be employed is conveyed toward the opening 2 through the conduit 5, and discharged therefrom upon the top surface of the member 3, the transmission of the coating material being conducted by means of either air or liquid pressure. The flowing stream of the coating material thus discharged then scatters around the member 3, forming quite minute particles, as a result of its impacting contact with said member. The distance between the opening 2 and the top surface of the member 3, wherewith the coating materialflow discharged from the opening 2 is brought into impacting contact, is

so arranged by means of a screwing device 6 connecting said member 3 with the rod 4 so that "the particles leaving the topsurface of the member 3, scatter at substantially right angles to the direction of the discharged coating material flow, in association with a given pressure and the property of a given coating material. The top surface of the member 3 wherewith the coating material flow is brought into impacting contact may be either halfsphericalor'flat-shaped. In FIGURE 1 is illustrated the member having a hemispherical surface, and the member having a flat surface is shown in FIGURE 2. In the case of the member having a hemispherical surface, the nozzle is to be so positioned as the flow of the coating material discharged from the opening thereof be in impacting contact with the top surface along the axial line a running through the nozzle and the member having said top surface to obtain the most effective atomizing condition and to keep as small as possible the loss of the coating material being employed caused by imperfect atomization. And in the event of the member having a flat surface, the nozzle is so positioned as the opening thereof is confronted with the central portion of said surface. In this case, however, the coating material to be employed may be discharged upon any part of the surface, and the direction of the forward movement of the scattering particles departing the deflecting member is freely modifiable by tilting the member to a desired angle.

An embodiment of the atomizing device of the present invention is illustrated in FIGURES 3 to 5, wherein the atomizing device including the coating material discharging nozzle 1 and the coating material flow deflecting member 3 is so connected with an ionizing member 7 that the discharged flow is deflected in the form of atomized particles in directions substantially at right angles to the direction of the flow by means of the impacting contact of the flow with the deflecting member 3, and the atomized particles in scattering movement reach slightly beyond the outer fringe of the member 7 and remain there in a state of suspension. The grounded article being coated is hung from a rotating device, described hereinafter, and moves around the ionizing member 7 at a predetermined distance therefrom. The entire system is so arranged as an electrostatic coating field is exclu sively formed between the fringe of the ionizing member 7 and the surface of the grounded article being coated 8 when the ionizing member 7 is charged negative with high potential. In other words, the atomized coating material particles reaching slightly beyond the ionizing fringe and remaining there in a state of suspension are charged negative and deposited onto the surface of the article being coated 8 by means of the established electrostatic coating field. The ionizing member may be either saucer-like or cup-shaped, and the entire system including the atomizing device and the ionizing member is contrived movable at a desired speed, if necessary, along the direction of the coating material flow so that the atomized particles are evenly deposited on the surface of the grounded article. But the ionizing member, as well as the deflecting member, is rotated in no way, contrary to the system where the ionizing member is employed as an atomizing means. Thus almost all sorts of coating materials are employed as electrostatic coating material irrespective of their properties. The coating material, furthermore, once atomized and reached slightly beyond the ionizing fringe, do not fiy back toward any part of the atomizing device, and the portion of the material which remain unatomized or shielded by means of the members for dividing the atomized scattering particles into segments which are to be explained later in connection with FIGURES and 6 is recollected and recovered by means of a tubing 9 attached to the bottom of the ionizing member 7.

In the rotating device, as shown in FIGS. 3 and 4, each of the articles 8 being coated is suspended from a roller 18 by means of a hook 19. The roller 18 travels along a circular rail 20 to carry the article 8 being coated around and at a predetermined distance from the peripheral edge of the ionizing member 7. This revolving movement, at the same time, causes a rotator 21, which is secured to the hook 19, to contact the outer surface 22 of the rail 20 so as to rotate the article 8 being coated. The rail 20 is connected to ground means of a line 23, the article 8 being coated thus being grounded. Said members 19 to 23 are all made of conductive material.

In FIGURE 3, the numeral 25 is a high voltage source with one terminal grounded by means of a line 26 and the other terminal 27 connected to the saucer-shaped member 7 by means of a line 28.

Throughout FIGURES 3 and 4, the saucer-shaped member 7 is made of conductive material as is conven- 4 tional in the art, because the member 7 is employed as an ionizing member.

In FIGURES 1 to 4, supporting rod 4 is made of either nonconducting or conducting material. When made of conducting material, said member is to be insulated, as is apparent in the art, from the ionizing saucer-shaped member 7 by covering each of the contact areas or sections 29 with a suitable insulating member. Otherwise, it is impossible to establish an electrostatic coating field exclusively between the peripheral edge 7a of the ionizing saucer-shaped member 7 and the surface of the grounded article 8 being coated. When this member is made of non-conducting material, it is apparent that the electrostatic coating field is exclusively established between said peripheral edge 70 and the surface of the grounded article 8.

A further point to be noticed in the present invention is that the atomizing action does not take place when the coating material discharging pressure is relatively low, even if the member wherewith the coating material flow is brought into an impacting contact is charged with the same potential as that of the ionizing member. This finding testifies to the fact that the electrostatic coating field is not set up between the nozzle and the deflecting member on the one hand and the article being coated on the other hand, but exclusively between the ionizing fringe and the grounded article, and that the atomization of the coating material simply takes place by the action of impacting contact.

Another embodiment of the atomizing device of the present invention in an electrostatic coating system is shown in FIGURES 5 and 6, wherein

members

10, 11 and 12, together with the rod 4, are employed for dividing the scattering atomized coating material particles into desired segments. Said

members

10, 11 and 12 are all so positioned upon the ionizing means 7 as segments 10a, 11a and 12a are formed corresponding to the segment 4a which is formed by lines 4b and 4c, both starting from the central point of the coating material flow deflecting member 3 and respectively passing by the rod 4, and said segments 4a 10a and 11a and 12a are all evenly distributed upon the ionizing member 7. The movement of the square article being coated 13 is so regulated as to have each of its angular portions brought into confronting relationship with each of the rod 4 and

members

16, 11 and 12 by causing it to rotate on its own axis once in the entire course of its moving around the ionizing member at a predetermined distance therefrom. The number of the segmenting members is dependent upon the shape of the article to be painted and the cycle of the rotating movement and the revolving movement thereof around the ionizing member, and said segmenting members are at least to be slightly higher than the coating material flow deflecting member. The portion ofthe coating material being employed which remains unatomized 'or shielded by the existence of the rod 4 and dividing

members

10, 11 and 12 is recollected and recovered by means of a tubing 9 attached to the bottom of the ionizing member 7.

In this embodiment, the saucer-shaped member 7 is of a conducting material, as in the embodiment of FIGS. 1-4, and is charged by means of a connection 28 to a high voltage source (not shown), and the article 13 is grounded as at 23.

The supporting rod 4 and segmenting

members

10, 11 and 12 are all made of either nonconducting or conducting material. If they are of conducting material, they are insulated from the saucer-shaped member 7 by covering each of the contact areas of the sections 29 with a suitable insulating member. Otherwise, it will be impossible to establish an electrostatic field exclusively between the peripheral edge 7a of the saucer-shaped member 7 and the surface of the grounded article 8. When these members are of nonconducting material, it is apparent that no insulating members are needed, the electrostatic coating field automatically being exclusively between the peripheral edge 7a and the surface of the grounded article 8,

A further embodiment of the atomizing device of the present invention in an electrostatic coating system is shown in FIGURES 7 and 8. The system illustrated therein is employed for the purpose of coating elongated articles such as wirings, tubings and the like, and consists of a tire-shaped housing 14 securing to each of the opposing sides of the interior surface thereof an atomizing device 150 and 15b parallel to the predetermined path for the article 16 passing through the central portion of the opening of the housing 14 at right angles to the plane of the housing 14, so that the atomized coating material particles are conveyed slightly beyond the ionizing fringe 14a of the housing 14 by means of the impacting contact of the coating material flow with the deflecting member 3, and an electrostatic coating field is exclusively established between the ionizing fringes 14a and the surface of the grounded article being coated 16 when the housing 14 is charged with high potential, whereby the atomized coating material particles lying in suspension slightly beyond the ionizing fringes 14a are deposited onto the surface of said article 16 from both sides but from different directions. The portion of the atomized coating material particles which is not deposited onto the surface of the article being coated and the portion of the coating material being employed which remains unatomized into fine particles are all shielded by means of the housing 14 and recollected .and recovered with the aid of a tubing 17 connected to the bottom of the housing 14.

In this embodiment, the housing 14 is of conducting material, as is the ionizing member 7 in the other embodiments, and is charged by means of a connection 28 to a high voltage source (not shown), and the article 16 is grounded as at 24.

The supporting rods 15a may be of either conducting or nonconducting material. When they are of conducting material, they are insulated from the housing 14 by means of insulating members (not shown). When they are of nonconducting material, no insulating members are needed.

It is thought that the present invention and its advantages will be understood from the foregoing disclosure, and it is apparent that various modifications may be made in the actual appliance of the present invention without departing from the spirit and scope of the invention or sacrificing its advantages, the embodiments thereof hereinbefore disclosed and illustrated being merely preferred embodiments of the invention.

I claim:

1. An electrostatic coating apparatus comprising a nozzle for discharging a coating material under high pressure in the form of a jet stream, a deflecting member spaced from the discharging nozzle in the direction of the discharged stream of coating material for deflecting the stream to scatter the coating material as fine atomized particles in directions substantially at right angles to the direction of the stream by the impact of the stream on the top surface of the deflecting member, a substantially saucer-shaped member behind the deflecting member from said nozzle and electrically insulated therefrom and curving toward said deflecting member with the peripheral edge of said saucer-shaped member near the level of said deflecting member and at a distance therefrom in the direction of movement of the deflecting coating material less than the distance the coating material particles are deflected, and means connected to said saucer-shaped member for applying a negative charge thereto, whereby when a grounded article to be coated is suspended at a point spaced from the peripheral edge of said saucer-shaped member an electrostatic coating field is established exclusively between the peripheral edge of the saucer-shaped member and the surface of the grounded article and the atomized particles floating in a state of suspension around the peripheral edge are electrostatically deposited on the surface of the grounded article.

2. An electrostatic coating apparatus as claimed in claim 1 in which the top surface of said deflecting member is substantially hemispherical.

3. An electrostatic coating apparatus as claimed in claim 1 in which the top surface of the deflecting member is substantially flat.

4. An electrostatic coating apparatus comprising a nozzle for discharging a coating material under high pressure in the form of a jet stream, a deflecting member spaced from the discharging nozzle in the direction of the discharged stream of coating material for deflecting the stream to scatter the coating material as fine atomized particles in directions substantially at right angles to the direction of the stream by the impact of the stream on the top surface of the deflecting member, a substantially saucer-shaped member behind the deflecting member from said nozzle and electrically insulated therefrom and curving toward said deflecting member with the edge of said saucer-shaped member near the level of said deflecting member and at a distance therefrom in the direction of movement of the deflecting coating material less than the distance the coating material particles are deflected, a plurality of segmenting members on said saucer-shaped member and extending in a direction parallel to the direction of the discharged stream and substantially above the level of said deflecting member for dividing the stream scattering atomized particles into segments, grounded means for rotating the article to be coated about its own axis and around said saucer-shaped member at a predetermined distance from the peripheral edge thereof so that each of the portions of the surface of the grounded article successively faces at least one of said segmenting members during the course of the rotating and revolving movements of the article, and means connected to said saucer-shaped member for applying a negative charge thereto, whereby when said saucer-shaped member is charged and the article to be coated is suspended from the means for rotating it at a point spaced from the peripheral edge of said saucer-shaped member, an electrostatic coating field is established exclusively between the edge of the saucer-shaped member and the surface of the article and the atomized particles floating in a state of suspension in the space slightly beyond the peripheral edge of the saucer-shaped member are electrostatically deposited on the desired portions of the surface of the article.

5. An electrostatic coating apparatus comprising an annular housing having a U-shaped cross-section with the U opening inwardly of the annulus, at least a pair of discharging and deflecting members mounted on diametrically opposite portions of the interior surface of said housing and insulated from said housing with each of said discharging and deflecting member having a nozzle for discharging a coating material under high pressure in the form of a jet stream and a deflecting member spaced from the discharging nozzle in the direction of the discharged stream for deflecting the stream to scatter the coating material as fine atomized particles in directions substantially at right angles to the direction of the stream by the impact of the stream on the surface of the deflecting member to a point beyond the inner edges of said housing, the nozzles of said deflecting members being parallel to each other and having discharge openings opening in opposite directions, means for passing a grounded elongated article through the central opening formed by said housing at right angles to the plane of the housing and parallel to the direction of each of the discharged streams, and means connected to said hous ing for applying a negative charge thereto, whereby when said housing is charged an electrostatic coating field is established exclusively between the edges of the housing and the surface of the grounded article, and the atomized particles floating in a state of suspension in the space slightly outside of the inner edges of said housing are electrostatically deposited on the surface of the grounded article from both sides.

6. An electrostatic coating apparatus comprising at least one discharging and deflecting member comprising a nozzle for discharging a coating material under high pressure in the form of a jet stream, and a deflecting member spaced from the discharging noule in the direction of the discharged stream of coating material for deflecting the stream to scatter the coating material as fine atomized particles in directions substantially at right angles to the direction of the stream by means of the impact of the stream on the top surface of the deflecting member, and a charging member behind the deflecting member of said discharging and deflecting member from said nozzle and insulated from said discharging and deflecting member and extending from said deflecting member a distance in the direction of movement of the deflected coating material less than the distance the coating material particles are deflected, and means connected to said charging member for applying a negative charge thereto, whereby when said charging member is charged and a grounded article to be coated is suspended at a point spaced from the edge of said charging member an electrostatic coating field is established exclusive between the edge of the charging member and the surface of the article and the atomized particles floating in a state of suspension around the edge are electrostatically deposited on the surface of the grounded article.

7. An electrostatic coating method comprising discharging a coating material under high pressure in the form of a jet stream, breaking up the discharged stream into fine atomized particles and deflecting said particles through space and in directions substantially at right angles to the direction of the stream, placing an article to be coated in the path of the deflected atomized particles and at a distance from the point of deflection greater than the deflected particles will travel under their own momentum, and establishing an electrostatic field beginning at a point of the point between deflection of said discharge stream and the point at which said particles lose the momentum imparted to them by the discharge and deflecting steps and extending to the article, whereby the atomized particles floating in a state of suspension are electrostatically deposited on the surface of the article.

8. An electrostatic coating method comprising discharging a coating material under high pressure in the form of a jet stream, breaking up the discharged stream into fine atomized particles and deflecting said particles through space and in directions substantially at right angles to the direction of the stream dividing the deflected stream of atomized particles into segments, placing an article to be coated in the path of the deflected atomized particles and at a distance from the point of deflection greater than the deflected particles will travel under their own momentum, rotating the article about its own axis and moving said article around the point of deflection so that each of the portions of the surface of the article successively faces each of the segments of the deflected stream, and establishing an electrostatic field beginning at a point between the point of deflection of said discharge stream and the point to which the particles will travel under their own momentum and extending to the article, whereby the atomized particles floating in a state of suspension are electrostatically deposited on the surface of the article.

9. An electrostatic coating method comprising discharging a coating material under high pressure in the form of a plurality of jet streams, breaking up the discharged streams into fine atomized particles and deflecting them through space and in directions substantially at right angles to the direction of the streams and toward a common point, placing an article to be coated at said common point, said deflecting points being spaced from said common point a distance greater than the deflected particles will travel under their own momentum, and establishing an electrostatic coating field beginning at points between the points of deflection of said discharged streams and the point to which the particles will travel toward each other under their own momentum and extending to the article, whereby the atomized particles floating in a state of suspension are electrostatically deposited on the surface of the article.

10. The method of electrostatically painting articles which comprises projecting a thin stream of paint substantially free of admixture with air or other gas and at a high pressure through a nozzle and against a strikeplate disposed in the path of the stream but at an angle to said path, whereby the paint, after striking the plate is deflected at the point of impingement in a direction angular to the direction of said stream, and is broken up into particles forming a fog-like vapor, and causing said vapor to pass through an electrostatic zone between said strike plate and said articles, to coat said articles.

References Cited in the file of this patent UNITED STATES PATENTS 2,546,701 Ransburg et a1 Mar. 27, 1951 2,698,814 Ransburg Jan. 4, 1955 2,766,064 Schweitzer Oct. 9, 1956 2,780,565 Juvinall Feb. 5, 1957 2,781,280 Miller Feb. 12, 1957 2,785,088 Ransburg Mar. 12, 1957 2,858,798 Sedlacsik Nov. 4, 1958 2,933,414 Beck Apr. 19, 1960

Claims

10. THE METHOD OF ELECTROSTATICALLY PAINTING ARTICLES WHICH COMPRISES PROJECTING A THIN STREAM OF PAINT SUBSTANTIALLY FREE OF ADMIXTURE WITH AIR OR OTHER GAS AND AT A HIGH PRESSURE THROUGH A NOZZLE AND AGAINST A STRIKEPLATE DISPOSED IN THE PATH OF THE STREAM BUT AT AN ANGLE TO SAID PATH, WHEREBY THE PAINT, AFTER STRIKING THE PLATE IS DEFLECTED AT THE POINT OF IMPINGMENT IN A DIRECTION ANGULAR TO THE DIRECTION OF SAID STREAM, AND IS BROKEN UP INTO PARTICLES FORMING A FOG-LIKE VAPOR, AND CAUSING SAID VAPOR TO PASS THROUGH AN ELECTROSTATIC ZONE BETWEEN SAID STRIKE PLATE AND SAIR ARTICLES, TO COAT SAID ARTICLES.