US3302579A - Electrostatic printing with oscillating screen frame and dual printing at a single station - Google Patents

Description

Feb. 7 1967 J. W. EDWARDS ET AL ELECTROSTATIC PRINTING WITH OSCILLATING SCREEN FRAME AND DUAL PRINTING AT A SINGLE STATION Filed Aug. 25, 1965 l0 Sheets-Sheet 1 INVENTORS JAMES W. EDWARDS SHELLY W MAYS RODNEY W. STOUT ATTORNEY 1.0 Sheets-Sheet 2 J. W. EDWARDS ETAL SINGLE STATION FRAME AND DUAL PRINTING AT A ELECTROSTATIC PRINTING WITH OSCILLATING SCREEN Feb. 7, 1967 Filed Aug. 25, 1965 INVENTORS JAMES W. EDWARDS SHELLY W. MAYS ATTORNEY RODNEY w. STOUT BY MW% Mg Feb. 7, 1967 J. w. EDWARDS ET AL 3,302,579 ELECTROSTATIC PRINTING WITH OSCILLATING SCRE Filed Aug. 25, 1965 EN FRAME AND DUAL PRINTING AT A SINGLE STATION FIG. 4

l0 Sheets-Sheet 5 INVENTORS JAMES w. EDWARDS SHELLY w. MAYS RODNEY w. STOUI BYW% W ATTORNEY 7, 1967 J w. EDWARDS mm 3,3,57

ELECTROSTATIC PRINTING WITH OSCILLATING SCREEN FRAME AND DUAL PRINTING AT A SINGLE STATIOH Filed Aug. 25, 1965 1.0 Sheets-Sheet 4,

INVENTORS JAMES W. EDWARDS SHELLY W. MAYS RODNEY W. STOUT AT TOR NEY Feb. 7, 1967 J. w. EDWARDS ET AL 3,3925? ELECTROSTATIC PRINTING WITH OSCILLATING SCREEN FRAME AND DUAL PRINTING AT A SINGLE STATION Filed Aug. 25, 1965 10 Sheets-Sheet 5 FIG. i0

INVENTORS 74 JAMES w. EDWARDS SHELLY w MAYS RODNEY w STOUT ATTORNEY Feb. 7, 1967 J. w. EDWARDS ETAL 3,392,579

ELECTROSTATIC PRINTING WITH OSCILLATING SCREEN FRAME AND DUAL PRINTING AT A SINGLE STATION Filed Aug. 25, 1965 l0 Sheets-Sheet 6 FIG. Ii

INVENTORS JAMES W EDWARDS SHELLY W. MAYS RODNEY W. STOUT WAM ATTOR N EY 1967 J. w. EDWARDS ETAL 3,392,579

ELECTROSTATIC PRINTING WITH OSCILLATING SCREEN FRAME AND DUAL PRINTING AT A SINGLE STATION Filed Aug. 25, 1965 1.0 Sheets-$heet 7 as Q INVENTORS JAMES W EDWARDS SHELLY W. MAYS RODNEY W. STOUT ATTORNEY Feb. 7, 1967 J. w. EDWARDS ETAL 3,302,579

ELECTROSTATIC PRINTING WITH OSCILLATING SCREEN FRAME AND DUAL PRINTING AT A SINGLE STATION Filed Aug. 25, 1965 1,0 Sheets-Sheet a INVENTORS JAMES W. EDWARDS SHELLY W. MAYS RODNEY W. STOUT ATTORNEY Feb. 7, 1967 J. w. EDWARDS ET AL 3,302,57

ELECTROSTATIC PRINTING WITH OSCILLATING SCREEN FRAME AND DUAL PRINTING AT A SINGLE STATION Filed Aug. 25, 1965 10 Sheets-Sheet 9 & WP, 208 Iq 9 N0 234 V r Y 24o Fama I 240 233 MA INVENTORS JAMES W. EDWARDS SHELLY W. MAYS RODNEY W. STOUT ATTORNEY Feb. 7, 1967 J w, EDWARDS ET AL 3,302,579

ELECTROSTATIC PRINTING WITH OSCILLATING SCREEN FRAME AND DUAL PRINTING AT A SINGLE STATION Filed Aug. 25, 1965 10 Sheets-Sheet 1O n :nll

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FIG. l9

INVENTORS JAMES w. EDWARDS SHELLY w. MAYS RODNEY W. STOUT ATTORNEY United States Patent ELECTROSTATIC PRINTING WITH OSCILLATING SCREEN FRAME AND DUAL PRINTING AT A SINGLE STATION James W. Edwards, Creve Coeur, Shelly W. Mays, St.

I .0uis, and Rodney W. Stout, Webster Groves, Mo., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware Filed Aug. 25, 1965, Ser. No. 482,447 20 Claims. (Cl. 10139) containers in addition to the long-used conventional nestable paperboard containers. It is generally necessary, in this type of industry, to imprint the contents of the container, the name of the manufacturer, and/or distributor, and any other advertising and identification material on the sidewall of the container. The conventional printing methods employing offset printing techniques were not generally acceptable, because they were not adapted to mass-production operation and did not produce a desired quality of print. Because of the low profit margin on disposable containers, profits in this type of field are generally made on a volume sale basis. Accordingly, it is necessary to print containers of this type in an economically feasible manner and the containers must be printed automatically by suitable apparatus.

In an effort to find a suitable method of imprinting con tainers having frustro-conical shapes, there have been certain investigations in the field of electrostatic printing. However, the art of electrostatic printing is relatively new and this particular type of printing was only available for printing on flat or relatively fiat items. static printing techniques have not been adaptable for use in printing relative large areas on non-planar surfaces.

The presently known techniques in electrostatic printing are described in United States Letters Patent No. 3,081,- 698 which relates to a method of electrostatic printing by elimination of pressure or contact between the printing element and the subject material being printed. This technique involves the transfer of a liquid based ink or a resinous based ink through an electrostatic field to an image-receiving object. The ink or pigments are usually in the form of a fine powder having a particle size which is small enough to pass through the interstices of the open areas of a stencil or so-called screen. A roller or similar mechanical device normally carries the ink particles to a point in close proximity to the stencil and where the ink is carried through the stencil by the electrostatic field to the image-receiving object. During this transfer, the ink particles are triboelectrically charged and are thus attracted toward the image-receiving object by a dielectric potential applied to the object or to a backing electrode. The charge of the particles is, of course, opposite to the backing plate and they are, therefore, accelerated through the openings or interstices in the open areas of the screen. Moreover, they are propelled toward the image-receiving object. The image-receiving object normally consists of a mandrel which is capable of retaining the article to be printed. Thereafter, the pigment will collide with and adhere to the article which is to be printed and the image is subsequently fixed by heat or solvent or a vapor or by other suitable means which are known in the prior art.

To date, electro- 3,302,579 Patented Feb. 7, 1967 Since the initial development of the theory of electrostatic printing, there have been many attempts to produce devices which are capable of automatic printing. Moreover, there have been attempts to print non-linearly shaped articles by electrostatic methods. However, all of the attempts to produce these automatic and semi-automatic devices for electrostatic printing have been rather unsuccessful and commercially unfeasible for a number of reasons. All of the electrostatic printing devices thus far employed have involved the transfer of ink across a definite and appreciable space and the particles of ink had to be physically transported across this space. However, surface tension effects on the delivery roller often prevented an even and uniform distribution of ink flow. Accordingly, the devices of the prior art had to be constructed in such manner that the field across which the particles moved had an extremely large potential difference. Moreover, the various electrodes had to be specially designed in order to prevent uneven distribution and flow of ink particles.

Moreover, the devices of the prior art were not designed with a wide range of utility, and accordingly, were not capable of printing with a wide variety of types, colors and ink particle sizes. Relatively heavy electron space currents were used to assist in the movement of ink in order to attain even distribution with various sized particles of ink. However, the relatively high ionization level at the air gap for printing, often causes arcing which interferes with and materially reduces the overall efiiciency of the electrostatic printing device. Furthermore, with the devices of the prior art, it was difiicult to achieve a carefully controlled quantity of electricity for effecting optimum results of the transfer of ink to the article being printed. As a result thereof, the devices of the prior art were not suitably designed for mass-production printing operations.

The substitution of a plate electrode for flat items was not an expensive or time consuming procedure when printing on relatively flat surfaces. However, there was no available technique or device which was capable of accepting a large number of mandrels or article supporting spindles. It is not a particularly difficult function to change a mandrel, but the devices presently available are not designed to accommodate mandrels of a different size or shape. Inasmuch as electrostatic screen process printing involves accurate positioning of the electrodes within a very close tolerance limit, the conventional printing apparatus of the prior art are not adaptable to electrostatic printing techniques.

It is, therefore, the primary object of the present invention to provide an electrostatic printing apparatus which is capable of electrostatically printing a large variety of articles having sizes and shapes.

It is another object of the present invention to provide an electrostatic printing apparatus and method of the type stated which is capable of achieving a high degree of printing precision on a mass-production basis.

It is a further object of the present invention to provide an electrostatic printing apparatus and method of the type stated which is characterized by simplicity, dependability, ruggedness and low cost.

It is also an object of the present invention to provide an electrostatic printing apparatus of the type stated which is capable of being altered for employment in a multi-color printing system.

It is an additional object of the present invention to provide an electrostatic printing apparatus of the type stated which is particularly adaptable to partial or complete circumferential printing on articles having curvilinear shapes.

It is another salient object of the present invention to provide an electrostatic printing apparatus and method 3 of the type stated where tangential approach and tangential departure is maintained between an article being printed and the screen for printing to occur along an elemental line of closest approach, for each succeding article on a mass-production basis.

With the above and other objects in view, our invention resides in the novel features of form, construction, arrangement and combination of parts presently described and pointed out.

In the accompanying drawings (10 sheets):

FIGURE 1 is a front elevational view, partially broken away, of an electrostatic printing apparatus constructed in accordance with and embodying the present invention;

FIGURE 2 is a top plan view of the electrostatic printing apparatus of FIGURE 1;

FIGURE 3 is a vertical sectional view taken along line 33 of FIGURE 2;

FIGURE 4 is a fragmentary vertical sectional view taken along line 4-4 of FIGURE 3 and showing the details of the Geneva type drive mechanism of the present invention;

FIGURE 5 is a fragmentary vertical sectional view taken along line 55 of FIGURE 3 and showing the details of construction of the pneumatic control system forming part of the present invention;

FIGURE 6 is a fragmentary vertical sectional view taken along line 66 of FIGURE 3 and showing the pneumatic duct work in the turret forming part of the present invention;

FIGURE 7 is a fragmentary vertical sectional view taken along line 77 of FIGURE 3 and showing the details of construction of the mechanism for driving the mandrel shafts forming part of the present invention;

FIGURES 8, 9 and are fragmentary sectional views taken along lines 8-8, 9-9, 1010, respectively, of FIGURE 4 showing the details of construction of the Geneva type drive mechanism forming part of the present invention;

FIGURE 11 is a fragmentary sectional view taken along line 11-11 of FIGURE 1 and showing the details of construction of one of the mandrels forming part of the present invention;

FIGURE 12 is a fragmentary sectional view taken along line 1212 of FIGURE 1 and showing the mechanism for mounting the electrostatic printing screens forming part of the present invention;

FIGURE 13 is a fragmentary vertical sectional view taken along line 1313 of FIGURE 1 and showing the details of construction of a motion arresting apparatus forming part of the present invention;

FIGURE 14 is a top plan view of a modified form of electrostatic printing apparatus constructed in accordance with and embodying the present invention;

FIGURE 15 is a vertical sectional view of the electrostatic printing apparatus of FIGURE 14;

FIGURE 16 is a vertical fragmentary sectional view taken along line 16-16 of FIGURE 14 and showing the screen drive cam forming part of the present invention;

FIGURE 17 is a fragmentary sectional view taken along line 17-17 of FIGURE 16;

FIGURE 18 is a horizontal fragmentary sectional view showing the relationship between the mandrel and the dual cooperating ink feeding mechanism forming part of the electrostatic printing apparatus of FIGURE 14; and

FIGURE 19 is a fragmentary top plan view of another modified form of electrostatic printing apparatus constructed in accordance with and embodying the present invention.

The art of electrostatic printing is still a recent technological innovation, and the terminology peculiar to this technology has not yet achieved a commonly acceptable and understood usage and definition. Accordingly, the term printing as used herein, is employed to describe the operation of a delivery of ink from the to the electric motor.

inking member to the element being printed, although it is to be understood that the word printing as used herein does not connote any mechanical pressure. The word printing is used in its much broader sense of the word merely to mean transfer of a design from one element to another in analogous form to the use of the term printing in photography where mechanical pressure is not the cause of transference of the design. In interpretation of the specification and the following claims, all terminology borrowed from the conventional printing art must therefore be given a broad meaning appropriate to this specialized field of electrostatic printing.

General description Generally speaking, the present invention relates to an apparatus which is automatic in its operation and method for electrostatic printing of conically shaped articles. The apparatus is designed to imprint desired information on the side walls of generally frustro-conically shaped containers of the nestable disposable type. However, the apparatus of the present invention is, of course, adaptable to electrostatic printing of many types and sizes of articles capable of receiving electroscopic ink. The apparatus generally comprises a base with a supporting frame constructed of standard roll-shaped channels.

Operatively mounted on the supporting frame is an electric motor for operating a screen support frame which oscillates between upper and lower positions. The screen support frame is provided with a single electrostatic printing screen and a complete upper and lower movement constitutes one printing cycle. The screen support frame is driven by a round friction gear having a fiat urface or so-called fiat. The screen support frame is mounted on a drive shaft, which is, in turn, operatively connected The friction gear meshes with a flange on the screen support frame and while the peripheral margin of the friction gear is in contact with the flange, the screen support frame will pivot upwardly. However, when the flat becomes aligned with the flange on the screen support frame, the frame will drop to its lower position. A pivotally mounted pneumatic cylinder is operatively connected to the screen support frame and drives the screen support frame downwardly to its lower position. The pneumatic cylinder also serves to dampen the downward movement of the screen support frame as it reaches its lower position.

The electric motor also operates a main drive shaft which, in turn, drives a primary Geneva shaft through a pair of meshing pinion gears. A primary Geneva mechanism is rigidly mounted on the primary Geneva shaft and comprises a pin-wheel with a radially extending lobe and an axially extending actuating pin. The primary Geneva mechanism is adapted to actuate a secondary Geneva mechanism which is, in turn, mounted on a secondary Geneva shaft, the latter being, in turn, operatively mounted on the supporting frame.

The secondary Geneva mechanism generally comprises a slot-wheel which is provided with four radially paced elongated slots. Each of the slots is engageable by the actuating pin on the pin-wheel forming part of the primary Geneva mechanism. In its operation, the pin-wheel of the, primary Geneva mechanism rotates approximately 270 during which time the secondary Geneva mechanism is not moved. During the last rotation of the pin wheel, which will constitute one complete revolution thereof, the actuating pin of the pin-wheel will engage a slot in the slot-wheel and rotate the slot-wheel through a 90 turn. It can be seen that the secondary Geneva shaft is, in effect, an idler shaft and is only rotatable through the actuation of the secondary Geneva mechanism by the primary Geneva mechanism.

While the drive mechanism described herein is referred to as 21 Geneva mechanism, including primary and secondary Geneva mechanisms, it is to be understood that the components described herein do not comprise a true Geneva mechanism. The components described herein have been uniquely designed for purposes of this electrostatic printing apparatus. However, the terminology of the conventional Geneva mechanism has been employed as the unique drive means disclosed herein and operates on a principle similar to the operation of the conventional Geneva mechanism. Moreover, the drive means disclosed herein is adaptable for use in driving a turret having more than four positions, while the conventional fourposition Geneva mechanism employed herein is a device which is capable of attaining only four positions in a 360 rotation.

A pneumatic control system is Operatively mounted on the main drive shaft and is operable by the secondary Geneva mechanism. The pneumatic control system comprises a valve drum which has a pulley or sprocket affixed to one end thereof. The pulley or sprocket is operatively connected to a matching pulley or sprocket on the secondary Geneva mechanism and is operable by means of a belt or chain trained around each of the matching sprockets. The sprocket on the valve drum, however, is twice the size of the sprocket on the secondary Geneva mechanism so that rotation of the sprocket on the secondary Geneva mechanism will only rotate the sprocket on the valve drum one-half the angle of the rotation of the Geneva mechanism. The valve drum is rotatably mounted on the drive shaft and in effect, thereby forms a quill on the drive shaft. The valve drum is concentrically disposed within and in fluid communication with a valve manifold, the latter being rigidly secured to the supporting frame. The valve manifold is provided with a primary air passage or so-called vacuum passage which extends approximately through a 270 arc. The primary air passage is designed to maintain a vacuum on the valve drum in a manner hereinafter described. A secondary air passage formed by an aperture in the valve manifold is equidistantly disposed between the opposite ends of the 270 vacuum or primary air passage. The valve drum is provided with eight sets of radial and communicating axial ducts, each of which, in turn, communicates with container supporting mandrels, to be hereinafter described.

A turret is operatively mounted on one end of the valve drum and is rotatable therewith. Operatively mounted on the turret are eight sets. of pillow blocks for supporting mandrel shafts and mounted on the outer end of the mandrel shafts are the container supporting mandrels. The mandrel shafts and the turret are provided with pneumaticduct work for communication with the axial ducts in the valve drum. Thus when one of the radial ducts in the valve drum is in communication with the secondary air passage, air will be supplied to the mandrel causing the container disposed on the mandrel to be ejected therefrom. When the radial duct associated with the mandrel is in communication with the primary air or vacuum passage, a vacuum is maintained on the mandrel thereby holding the container onto the mandrel.

Each of the mandrel shafts is provided at its lower end with bevel gears which match with a bevel drive gear rigidly mounted on the main drive shaft. Therefore, it can be seen that as the main drive shaft rotates, the main bevel drive gear will rotate and rotate each of the mandrel shafts and the mandrels mounted on the outer ends there- Moreover, the turret which holds the mandrel shafts will rotate in response to the rotation of the slot-wheel forming part of the secondary Geneva mechanism.

A suitable cup dispensing mechanism is disposed in proximate relationship to the uppermost mandrel for selectively dispensing a single container or cup and depositing the same on the mandrel as the mandrel passes the container dispensing mechanism. The placing of a container on the mandrel constitutes a first work station or so-called loading station. Thereafter, the turret is rotated through successive 45 movements where the man- 6 drel is shifted to a second work station or printing station which is located approximately with respect to the loading station. In the printing station, the mandrel is positioned in relationship to the printing screen where electrostatic printing on the container will take place. The screen is oscillated through a complete cycle including the upper and lower movement in the manner previously described, while the mandrel with container supported thereon is rotated in timed relation to the oscillation of the screen. The container is rotated at approximately the same rate of speed or at the same peripheral speed as the movement of the screen so that a continuing line of tangency or tangential approach and departure occurs between the surface of the container supported on the mandrel and the surface of the screen. Actual tangential contact may not occur, however, the axis of rotation of the container may be axially translated slightly to prevent any tangential contact but still maintain tangential approach and departure. An ink dispensing mechanism is disposed in close relationship to the screen on the opposite side thereof with respect to the mandrel and is designed to supply-electroscopic ink to the screen at this continuing line of tangency or tangential approach. The electroscopic ink passes through the open mesh portions of the screen onto the container and thereby forms the image on the container. A unique feature of the apparatus of the present invention is that the solid space generated by the article moving around the turret intersects or approaches the printing screen in only one position, namely at the printing station so that axial translation of neither the turret nor screen is required.

After deposition of the ink image on the article, the turret is then moved through .two successive 45 movements to a third work station or fixing station, permitting the image formed on the container to harden. The mandrel is thereafter rotated through two additional 45 movements to a fourth work station or discharge station Where the container is aligned with a discharge tube maintained under a vacuum. The printed container is thereafter ejected from the mandrel and carried into the discharge tube for further dispatchto a conveyor or other processing station. When the mandrel then reaches the loading station again, a complete printing cycle has been performed.

The present invention also provides a modified form of electrostatic printing apparatus which employs two electrostatic printing screens. Each of these screens is mounted on opposite sides of the container supporting mandrel and is designed to shift in opposite directions. Thus when one screen shifts upwardly, the opposite screen shifts downwardly. Each of the screens .is operated by a heart-shaped cam which is designedto perm-it. this type of screen trajectory. The screens are so positioned so that the images produced thereby are marginally registered. Moreover, different colored inks can be employed with each of the electrostatic printing screens, and accordingly, multicolor printing can be employed on'the second embodiment of the electrostatic printing apparatus. The modified form of electrostatic printing apparatus also provides an alternate form of driving the mandrels. The mandrels are free wheeling on the mandrel shafts and are provided with friction rollers which bear against a friction wheel, the latter being mounted on the screen drive shaft. 1 I

The present invention also provides another modified form of electrostatic printing apparatus which similarly employs two electrostatic printing screens mounted on opposite sides of the container supporting mandrel. Moreover, each of these screens is designed to shift in opposite directions where one screen will shift upwardly While the other screen shifts downwardly. The heartshaped cam drive mechanism used to operate each of these screens is similar to the heart-shaped cam mechanism for driving the screens in the previously described embodiment of the invention. However, in the previously described embodiment of the invention, the axis of rotation or oscillation of the electrostatic printing screen was perpendicular to the axis of rotation of the container supporting mandrel. In the present modification, the axis of oscillation or movement of the electrostatic printing screens is perpendicular to the side wall of the mandrel.

Detailed description of apparatus A Referring now in more detail and by reference characters to the drawings which illustrate practical embodiments of the present invention, A designates an electrostatic printing apparatus generally comprising a supporting frame 1, which includes 'a pair of spaced longitudinally extending base channels 2, 3 provided at their corners with uprights 4. The uprights 4 are connected by a pair of upper longitudinally extending support channels 5 and the upper channels 5 and the base channels 2 are connected by transverse channels 6. Extending between each of the transverse channels 6 and being spaced between the longitudinally extending support channels 5 are a pair of transversely spaced, longitudinally extending intermediate support channels 7, 8, which are connected centrally thereof by a cross-bar 9. The channels 2, 3, 5, 6, 7 and 8, the uprights 4 and the cross-bar 9 may be formed of any suitable standard roll shape of channel, such as an I-beam shape, an H-beam shape, a standard U-beam shape or an L-beam shape as illustrated, and which is preferably formed of a relatively hard steel.

Bolted or otherwise rigidly secured to the upper surface of the longitudinally extending support channels 5 and the intermediate support channels 7, 8 are four transversely aligned pillow blocks 10, 11, 12, 13 and journaled therein is a transversely extending drive shaft 14, substantially as shown in FIGURE 2. The drive shaft 14 is held in transverse alignment Within the respective pillow blocks by means of conventional washers and lock rings 15 mounted on each side of each of the respective pillow blocks. Also welded or otherwise rigidly secured to the forwardly presented support channel 5 is a mounting plate 16 for supporting a conventional variable speed electric motor 17, which is preferably of the explosion-proof type. A suitable speed reducing mechanism 18, which is conventional in its construction is connected to the main drive of the motor 17 and operatively connected to the speed reducing mechanism 18 is a V-belt pulley 19, which matches and is in longitudinal alignment with a V-belt pulley 19', the latter being keyed or otherwise secured to the main drive shaft 14. A V-belt 20 is trained around each of the pulleys 19, 19' for driving the main drive shaft 14.

Extending transversely across the intermediate support channel 7, 8 is a rotatable screen drive shaft 21 which is journaled in transversely aligned pillow blocks 22 and which are, in turn, bolted to the upper surfaces of the intermediate support channels 7, 8, in the manner as shown in FIGURE 2. The screen drive shaft 21 is suitably retained in alignment within the pillow blocks 22 by means of washers and lock rings 23 mounted on each side of each of the pillow blocks 22. Rigidly mounted on a forwardly projecting end of the screen drive shaft 21 is a sprocket 24, which is located in longitudinal alignment with a sprocket 25 mounted on the main drive shaft 14 and trained around the sprockets 24, 25 is a roller chain 26. Thus, as the electric motor 17 is energized, it will drive the main drive shaft 14 through the pulleys 19, 19' and the screen drive shaft 21 through the sprockets 24, 25.

Bolted or otherwise rigidly secured to the right transverse channel 6, reference being made to FIGURE 2, are

a pair of upstanding brackets 27, which form a vertical support plate 28 and bolted thereto are a pair of transversely aligned pillow blocks 29. Extending between the pillow blocks 29 and being journaled therein is a screen support shaft 30. The shaft 30 is pivotal within the pillow block 29 and is retained by means of conventional washers and locking nuts 31. Mounted on the shaft 30 is an oscillating screen support frame 32 having an enlarged hub 33, which is concentrically disposed about the shaft 30 and keyed thereto. The screen support frame 32 is shiftable between upper and lower limits, and a shifting movement from the lower position to an upper position, and back to a lower position constitutes one printing cycle.

The screen support frame 32 is driven by means of a friction gear or so-called friction wheel 34, which is mounted on the rearward end of the screen drive shaft 21 and is provided with an annular peripheral gear surface 35, which bears against and is in frictional contact with a flange 36, extending forwardly of the screen support frame 32, all as can best be seen in FIGURES 12 and 13. The friction wheel 34 is also provided with a flat surface or so-called fiat 37 which permits downward shifting movement of the screen support frame 32, when the flat 37 becomes aligned with the flange 36. The wheel 34 is provided with an internal metal hub 38, which is, in turn, keyed to a reduced end of the shaft 21. Moreover, the friction wheel 34 is retained in position on the shaft 21 by means of a thrust washer and locking rirfg 39. Thus, it can be seen that as the screen drive shaft 21 rotates, the friction wheel 34 will rotate in a clockwise direction, reference being made to FIGURES 1 and 2, causing the gear surface 35 to bear against the flange 36. Clockwise rotation of the friction wheel 34 will create an upwardly directed force on the flange 36, causing the screen support frame 32 to ride and pivot about the screen support shaft 30. As the screen support frame 32 reaches its upper limit of movement, the gear surface 35 will move out of contact with the flange 36, and the flat 37 will become aligned with the flange 36. Removing the upwardly directed force on the screen support frame 32 will permit the support frame 32 to fall to its lower position.

The lowermost position of the screen support frame 32 is regulated by means of an adjustable stop 40, substantially as shown in FIGURE 13. The adjustable stop 40 generally comprises an adjustable bolt 41, which is secured to a flange 42 extending rearwardly and horizontally of the screen support frame 32. The relative position of the adjustable bolt 41 within the'flange 42 can be regulated through a pair of locking nuts 43 disposed upon opposite sides of the bolt 41 with respect to the flange 42. As the screen support frame 32 shifts downwardly, the lower end of the bolt 41 will strike a bumper pad 44, which is fairly resilient and adapted to provide a cushion for the movement of the screen support frame 32. By reference to FIGURE 13, it can be seen that the bumper pad 44 is mounted on an inwardly extending bracket 45, the latter in turn being secured to the rearward support channel 5.

A pneumatic drive mechanism 46 is provided for moving the screen support frame 32 to its initial or lowermost position. The pneumatic drive mechanism is of the single acting type and generally comprises a cylinder 47 which is pivotally secured to an upright 48, the latter forming part of the supporting frame 1. The pneumatic drive mechanism 46 also includes a piston 49 which is pivotally secured to the screen support frame 32 by means of a hub 50, substantially as shown in FIGURE 13. The cylinder 47 is, of course, provided with the necessary air duct work as illustrated and which is connected through a suitable source of air pressure (not shown). Moreover, the pneumatic drive mechanism 46 is electrically connected to a conventional control mechanism (not shown) for moving the screen support frame 32 downwardly in timed relation to the other operations in the electrostatic printing apparatus A. By reference to FIG- URE 1, it can be seen that the hub 50 can be secured to any of a plurality of selected apertures 51 formed in the screen support frame 32 by means of a pivot pin 52.

Thus if it is desired to increase or decrease the downward action of the drive mechanism 46, the pin 52 can be removed for shifting the hub 50 to any of the selected apertures 51.

It should be recognized that as an alternate method of driving the screen support frame, the friction wheel 34 could be eliminated and the screen support frame 32 could be driven by means of a double acting pneumatic cylinder. In this manner, the pneumatic cylinder would drive the screen support frame both upwardly and downwardly and could be controlled in timed relation to the other operations in the electrostatic printing apparatus A. The pneumatic drive mechanism 46 is generally provided inasmuch as a free fall movement of the screen support frame 32 during shifting to its lowermost position, would not be sufliciently fast for the desired speed of operation of the electrostatic printing apparatus A. However, if printing on fairly large objects were performed, the speed of operation would be substantially reduced and the screen support frame 32 could be permitted to shift to its lowermost position in a free fall. For this type of operation, the pneumatic drive mechanism 46 would be replaced by a pneumatic damper. The pneumatic damper would be similar to the conventional shock absorber and would be designed to reduce the downward movement of the screen support frame 32. Again the pneumatic damper similarly could be constructed in the same manner as the pneumatic drive mechanism and damping action could be increased or decreased by selectively positioning the hub 59 at any one of the apertures 51 by means of the pin 52. Naturally, if one of the apertures 51 near the screen support shaft 30 was selected, dampening action would be reduced. It is also possible to use a combination of roller drive and pneumatic drive mechanism for shifting the screen to upper and lower positions. During the action of shifting the screen to its uppermost position, the pneumatic cylinder would assist the wheel 34. Problems of timing would not be critical inasmuch as the roller would tend to act as a brake mechanism if the upward force created by the pneumatic drive mechanism was too great for the desired speed of operation.

The screen support frame 32 is provided with a recess 53 at its outer end for accommodating a screen retaining frame 54, the latter being secured to the screen support frame 32 by means of bolts 55. The screen retaining frame 54 is designed to retain an electrostatic printing screen 56 and is so designed so that electrostatic printing screens 56 may be easily removed and inserted therein when it is desired to changed the printing design. Furthermore, by reference to FIGURE 1, it can be seen that the screen retaining frame 54 is arcuately shaped and has an arcuate distance of approximately 45 with respect to the screen support shaft 3t Furthermore, the screen 56 is arcuately shaped or curvilinear about an axis which is perpendicular to the first axis of rotation forming the arcuate shape, for reasons which Will presently more fully appear.

The electrostatic printing screen 56 is generally formed of a fine mesh conductive material or a material which is rendered conductive and wherein the non printing areas are suitably masked. The non-masked portion or printing areas of the screen 56 is designed to permit pigments in the form of ink powders to pass through the interstices of the open areas. The screen 56 may be constructed by any of the presently known methods of making electrostatic printing screens. One particularly effective screen is provided where the mesh material is stainless steel with 250 wires to the inch. This screen element is then provided with a photosensitive coating so that it spans all of the interstices of the screen. The sensitized screen is then exposed to an are which is preferably rich in ultraviolet light, through an interposed positive image of the desired copy. Exposure to the light is maintained for a time which is suflicient to harden the areas where the interposed image transmits light. The coated screen is then developed to dissolve the areas of the coating which were protected from the light by the opaque areas of the film image, thereby leaving a solid mask in the areas atfectecl by the light.

Various methods of preparing the screen can be used. It is only necessary that the non-printing area be effectively masked to prevent the movement of pigment thereth-rough in subsequent electrostatic printing operation. This is accomplished very well by various known methods as well as the use of photosensitive coatings on the open mesh. Techniques familiar in the screen-silk process printing may also be employed in the production of stencils or screens for electrostatic printing operation. It is not necessary to have the regularity of openings of a fine mesh screen or sensitized net. The regular openings in fibrous materials and the like can be satisfactory as long as the openings in the particle size of the pigment are compatible for movement therethrough.

In many electrostatic printing operations which can be performed with the apparatus of the present invention, it has been found to be desirable to use a curved elect-rostatic printing screen. The screen 56 may also be manufactured or :produced in the manner as described in my copending application Serial No. 463,251, filed June 11, 1965, and which relates to the method of producing curved electrostatic screens. In this method, a photosensitive emulsion is applied to a wire mesh support and held in a screen chase. The screen is then exposed to light through a photographic negative of the required print or design to be ultimately imprinted upon a substrate. A washout of the exposed emulsion leaves a positive image on the screen which can be subsequently converted to a negative image required for printing by means of electroplating. The plating adheres preferentially to the open mesh portions of the screen. Subsequent treatment with an emulsion remover such as hydrogen peroxide and various acid etches will clear the print areas leaving a negative screen in which the non-print areas have interstices filled with metal. The plating metal is chosen to give a final screen which is rigid but formable by various forming methods such as rolling and drawing. The final screen thereafter can be shaped into a desired surface which will parallel complex surfaces to be printed.

Extending between the intermediate support channels 7, 8 is an ink feeding mechanism support frame 57 for retaining a suitable air operated ink feeding mechanism 58 of the type described in copending application Serial No. 461,044, filed June 3, 1965. It has been found in connection with the present invention that an air operated ink feeding mechanism provides substantially superior results with certain electroscopic inks of low thermal softening point due to the fact that the electroscopic ink particles in these inks are relatively small and extremely light in weight. Moreover, they are readily compressible and very difficult to control. Particles of this type have a tendency to cling together in agglomerates and due to the resinous nature thereof tend to become permanently bonded when subjected to even moderate compression. Many mechanical systems for delivering electroscopic ink create undesirable situations in that heat and friction have been generated at the place of contact between the me chanical mechanism, such as the rotating brush and the image screen or other transfer media. Furthermore, the inks which are used in this type of system are thermoplastic in nature and, therefore, are sensitive to both heat and pressure with regard to softening and fusing. Consequently, it has been found that the air operated ink feeding mechanism of the type described substantially eliminates the various problems in ink delivery which have been present in the devices of the prior art.

The air operated ink feeding mechanism 58 is prefer-ably provided with a suitable positioning mechanism for accurately positioning the ink feeding mechanism 58 with regard to the electrostatic printing screen 56. The air operated ink feeding mechanism 58 also includes a hopper 59 which deposits ink in an ink delivery tube 60. The ink delivery tube is provided with a discharge nozzle 61 which terminates in close proximity to the electrostatic printing screen 56, substantially as shown in FIGURES 2 and 11. By further reference to FIGURE 11, it can be seen that the discharge nozzle 61 has a relatively small height and a relatively wide width. In fact, it can be seen that the Width of the discharge nozzle 61 is approximately equal to the width of the electrostatic printing screen 56. Furthermore, the air gap between the terminal end of the discharge nozzle 61 and the surface of the electrostatic printing screen 56 is only about 0.005" to 0.12". For the purposes of the present invention, it has been found that when the discharge nozzle 61 is produced with a height relative to the direction in which the screen moves within the range of to A", optimum results have been obtained.

The ink feeding mechanism 58 is also provided for an air removal system (not shown) for removing the fluid which carries the ink particles to the electrostatic printing screen 56. If the air was forced through the openings of the screen or designed to carry the ink particles through the open portions of the screen, the final print would become blurred. The air removal system is designed to reduce the air velocity to substantially zero at the discharge nozzle 61 so the ink particles, which are triboelectrically charged, will be carried by an electrostatic field. The ink feeding mechanism herein described also includes a triboelectric charging chamber where the ink particles are bombarded against a metal wall and become triboelectrically charged. The ink feeding mechanism 58 is, however, more fully described in said copending application Serial No. 461,044, filed June 3, 1965 and is, therefore, not described in detail herein.

It is possible to use a belt-feed type of ink delivery system of the type described in copending application Serial No. 453,706, filed May 6, 1965, which is also efliciently employed in electrostatic printing operations of the type performed by the apparatus A. This type of electrostatic printing apparatus includes a hopper for containing the desired electroscopic ink and rotatably mounted in the hopper is a continuously moving agitator for keeping the ink particles in a suspended or levitated state. A distributor roller is disposed beneath the hopper and communicates internally therewith to receive a charge of ink and deposit the same on a continuously rotating belt. The distributor roller in combination with the agitator of the hopper also functions as a metering roller for metering a preselected charge of the ink. Provided for operative communication 'with the surface of the belt is a charging roller with a surface speed different from the surface speed of the belt. The charging roller also aids in providing an even distribution of ink particles transversely across the belt and for creating a triboelectric charge on the ink particles contained on the surface of the belt. The belt is driven by a pair of rollers, one of which is charged and serves as the discharge electrode in the electrostatic printing system. This type of feeding mechanism is also provided with a series of suitable adjustments in order to vary dimensions and distance between the moving parts, which are essential for providing a wide degree of utility so that the feeding mechanism and hence the electrostatic printing apparatus A is capable of handling a wide variety of types and sizes of electroscopic inks.

Any of a variety of electroscopic inks can be employed in the present invention. Generally, the electroscopic inks comprise a finely dispersed powder which is capable of being triboelectrically charged. The powder generally carries a desired pigment. A number of satisfactory powders can be employed in the present invention and each must be in a finely divided state. Suitable powders are dyed thermoadhesive resins such as rosin, gum copal, gum sandarac, ethyl cellulose, Egyptian asphalt and the like. A very satisfactory thermoadhesive powder can be produced by dissolving equal parts of ethyl cellulose and Vinsol resin in acetone together with a small amount of spirit soluble aniline dye such as Nigrosine or aniline blue and spray drying the solution to produce an extremely fine powder having substantially spherical particles. Dyed Lycopodium powder is suitable where theremoadhesive properties are not required of the powder, as is also starch, cellulose flour, powdered metal and copper powder.

Whether fusible, thermoadhesive or non-fusible powders or others are used, the particle size is preferably near the limit of definition of the eye under ordinary reading conditions. Excessive powder size contributes to graininess in appearance of the image. On the other hand, extremely fine powder may be undesirable in many instances due to its tendency to ball up or cling together in clusters. It is, therefore, desirable to use a powder in which substantially all the particles are within the size range from 2 to 20 microns. If spherical powders are used, this refers to their diameters, otherwise to the largest dimension. For most purposes, it is preferred to use an equidimensional powder particle, the sphere being the preferred form.

Bolted or otherwise rigidly secured to the undersurface of each of the intermediate support channels 7, 8 directly beneath the pillow blocks 11, 12 are a pair of transversely aligned pillow blocks 62 for journaling a primary Geneva shaft 63. The primary Geneva shaft 63 is retained in transversely aligned position by means of washers and lock rings 64 mounted on each side of each of the pillow blocks 62. Keyed or otherwise rigidly secured to the primary Geneva shaft 63 is a pinion gear 65, which meshes with a driving pinion gear 66 mounted on the main drive shaft 14. Thus as the main drive shaft 14 is rotated, the primary Geneva shaft 63 will be continuously rotated through the action of the meshing pinion gears 65, 66. The pinion gears 65, 66 are conventionally provide with hubs '67 for mounting on their respective shafts 63, 14 and the hubs 67 may be provided with keys or set screws (not shown) for securing the pinion gears 65,66 to their respective shafts.

Mounted on the rearward end of the primary Geneva shaft 63 is a primary Geneva mechanism 68 which generally comprises a pin-wheel or so-called pin-gear 69. The pin-wheel 69 is generally circular in cross section and is provided with an outwardly extending lobe 70 and mounted on the lobe 70 is an axially extending actuator pin 71. By reference to FIGURES 8 and 9, it can be seen that the lobe 70 is somewhat triangularly shaped and extends beyond the line which would form the peripheral margin of a truly circular wheel. The pinwheel 69 is also provided in the area of the lobe 70 with a quarter-round or arcuate recess 72 having an arcuate guide wall 73.

Similarly journaled in a pair of transversely aligned pillow blocks 74 which are bolted to the upper surfaces of the intermediate support channels 7, 8 is a transversely extending secondary Geneva shaft 75. The shaft 75 is spaced to the left of and extends in parallel relation to the primary Geneva shaft 63 and the main drive shaft 14. Furthermore by reference to FIGURES 1 and 3, it can be seen that the secondary Geneva shaft 75 is disposed within approximately the same horizontal plane as the main drive shaft 14. However, it is to be noted that the primary Geneva shaft 63 is disposed beneath the main drive shaft 14 and the secondary Geneva shaft 75, as illustrated in FIGURE 3. Rigidly mounted on the secondary Geneva shaft 75 and being rotatable therewith is a secondary Geneva mechanism 76 which generally comprises a slot-wheel or so-called star-wheel 77. The slot-wheel is provided with four outwardly extending radially spaced crowns 78, which are connected by arcuately shaped webs 79. Thus by reference to FIGURE 4, it can be seen that each of the crowns 78 is spaced at intervals and are connected by the arcuately shaped webs 79. The radius of curvature of the arcuately shaped webs 79 is substantially equal to the radius of the pinwheel 69 for reasons which will presently more fully appear. Each of the crowns 78 is provided with relatively deep pin-engaging slots 80 and which are sized to accommodate the actuator pin 71. By reference to FIG- URE 4, it can be seen that the webs 79 are provided with arcuately shaped concave guide surfaces 81. By further reference to FIGURES 4 and 10, it-can be seen that the slots 89 are sufliciently deep so that the actuator pin 71 is extended therein to the full length of the guide slot 80 when the crown 78 of the slot-wheel 77 are engaged with the guide wall 73 of the pin-wheel 69. Thus by further reference to FIGURES 4, 9 and 10, it can be seen that the concave guide surfaces 81 are formed with the same radius of curvature as the outer peripheral wall of the pin-wheel 69.

The electrostatic printing apparatus A also includes a pneumatic control system 82, which comprises a valve drum 83 concentrically disposed about the main drive shaft 14 in a free wheeling relationship with respect thereto. The valve drum 83 is also concentrically disposed within a valve manifold 84, the latter being rigidly secured to a pair of L-shaped brackets 85 which are in turn, secured to the upper surface of the intermediate support channel 8. Secured to the forward end of the valve drum 83 by means of bolts 86 is a sprocket 87, which is longitudinally aligned with a sprocket 88, the latter being secured to the rearward face of the slotwheel 77 by means of bolts 89, and trained around the sprockets 87, 88 is a drive chain 90. Thus when the secondary Geneva mechanism 76 is rotated through the action of the primary Geneva mechanism 68, the valve drum 83 will be rotated therewith. Also secured to the forward face of the sprocket 87 through the bolts 86 is a roller bearing 91. Rigidly secured to or integrally formed with the rearward face of the valve drum 83 is a turret plate or so-called turret 92. Also secured to the turret plate 92 by means of bolts 93 is a roller bearing 94. In this manner, it can be seen that the valve drum 83 and the turret 92 carried therewith is rotatable on a free wheeling relationship with respect to the main drive .shaft 14. Furthermore, the valve drum 83 and the turret 92 are rotatable with the slot-wheel 77 for reasons which will presently more fully appear.

It should be recognized that the component 68 is termed a primary Geneva mechanism, and the component 76 is termed a secondary Geneva mechanism, whereas in fact, these two components do not form a true Geneva mechanism. However, the terminology of the conventional Geneva mechanism has been employed as the unique drive disclosed herein operates on a rinciple similar to the operation of the conventional Geneva mechanism. Nevertheless, it is pointed out that the drive mechanism provided herein is not the conventional well known Geneva mechanism.

The rotation of the transversely extending drive shaft 14 will rotate the pinion gear 66 which will, in turn, rotate the pinion gear 65 and the primary Geneva shaft v63. Thus, it can be seen that as the main drive shaft 14 is continually rotated, the primary Geneva shaft 63 will be continually rotated. Rotation of the primary Geneva shaft 63 will cause the pin-wheel 69 to rotate in a counterclockwise direction, reference being made to FIGURE 4. As this occurs, the annular side wall of the pin-wheel 69 will be slightly spaced from the concave guide surfaces 81 in one quadrant. Inasmuch as the guide surface 81 has the'same radius of curvature as the annular surface of the pin-wheel 69, the secondary Geneva mechanism 76 and the slot-wheel 77 will not rotate on the secondary Geneva shaft 75. Continued rotation of the pin-wheel 69 in the counterclockwise direction will cause the outwardly extending actuating pin 71 to engage a slot 80 in the next adjacent crown 78. Engagement of a pin 71 in this slot 80 is more fully shown in FIGURE 4 as the pin 71 begins to enter the slot 80. Continued rotation of the pin-wheel 69 will cause the slot-wheel 77 to rotate in a clockwise direction, reference being made to FIGURE 4 until the pin 71 reaches a position where it sits immediately beneath the lowermost slot 80 in the slot-wheel 77. It can be seen that the pin-wheel 69 rotates for approximately 270 during the time that the slotwheel 77 remains in a stationary position. The additional rotation of the pin-wheel 69 through a 90 angle will cause the pin 71 to move inwardly in one of the slots 80 and cause the slot-wheel 77 to rotate in a clockwise direction through a 90 angle until the pin 71 moves downwardly in the slot 80.

As the slot-wheel 77 on the secondary Geneva shaft 75 is rotated through a 90 arc, the gear drive chain 90 trained around the sprockets 87, 38 will cause the valve drum 83 and the turret 92 to rotate. However since the sprocket S7 is twice the diametral size of the sprocket 88, the valve drum 83 and the turret 92 will only rotate one half the angle of the 90' are or 45. Hence, for every 90 rotation of the secondary Geneva mechanism 76, the turret will rotate 45 Accordingly, the turret is an eight position turret which is actuated by a four position Geneva mechanism.

The modified Geneva mechanism can be adapted to other values of multiplicity for the number of stops per revolution of the turret 92. The following general relationship governs the adaptation of multiplicity to the modified Geneva mechanism. In the following relationship n represents the number of stations on the turret 92, n represents the number of slots on the slot-wheel 77 of the secondary Geneva mechanism, N represents the number of teeth on the sprocket 88 attached to the secondary Geneva mechanism; and N, represents the number of teeth on the sprocket 87 directly attached to the turret 92. The relationship governing this adaptation of multiplicity is therefore:

Thus for a given n a wide range of multipilicity is possible by varying N, and N; or corresponding diameters of pulleys or gears.

Bolted to the rearward face of the turret 92 are eight pairs of radially aligned bearing blocks 95, 96 for rotatably supporting mandrel shafts 97. Each of the mandrel shafts 97 is provided at its lower end with bevel gears 98, which mesh with an enlarged bevel gear or spiral gear 99, the latter being mounted on the rearward end of the main drive shaft 14, substantially as shown in FIGURES 2 and 7. As the enlarged bevel gear or spiral gear continuously rotates with the main drive shaft 14, each of the mandrel shafts 97 will be continuously rotated as the bevel gears 98 are in continuous meshing engagement with the spiral gear 99.

Welded to the outer end of each of the mandrel shafts 97 is a mounting plate 100 and bolted to each of the mounting plates 100 are conically shaped container supporting mandrels 101 which are more fully illustrated in FIGURE 11. The container supporting mandrel 101 is generally formed of a frustro-conical shape and has an annular tapering side wall 102, and a hollow interior forming an axial chamber 103. The mandrel 101 is also provided with a relatively flat centrally apertured end wall 104 and which abuts against the mounting plate 100 in the manner as shown in FIGURE 11. It can be be seen that the mandrel 101 is secured to the mounting plate 100 by means of screws 105. By this construction, it is possible to easily remove the screws 105 for changing of any of the mandrels 101. The mandrel 101 is also provided with a concave end wall 106, which is centrally apertured and in communication with the axial chamber 103. Moreover, by further reference to FIGURE 11, it can be seen that the axial chamber 103 communicates with a fluid duct 107 in the hollow mandrel shafts 97.

The end wall 106 is integrally formed with a plurality of radially spaced axially extending container engaging fingers 108 for engaging the bottom wall of a container C, which may be disposed thereon. The container engaging fingers 108 are designed to engage the bottom wall of the container C in order to prevent collasping thereof When a vacuum is applied to the mandrel shaft 97 and to the mandrel 101.

The container supporting mandrel 101 is designed to accommodate disposal, nestable, thin-Walled plastic cups of the type which are commercially available and usually found in vending machines. However, it should be understood that the mandrel 101 can be readily removed and replaced with a similar mandrel accommodating cups or containers of a different size or shape by merely removing the screws 105. In this connection, it should be obvious that it is possible to provide mandrels to accommodate such containers as ice cream containers, cheese container, or any similar open-ended container of this type. Moreover, it should be understood that the present invention is not limited to printing of plastic containers but can be employed to suitably imprint containers formed of paper, paperboard, etc.

The apparatus of the present invention is capable of exhibiting a wide degree of utility through its versatility of operation. When printing various size containers, the mandrels 101 can be replaced. Moreover, the screen support frame 32 can be axially translated to oscillate in a different plane for accommodating larger or smaller sized mandrels. Similarly, the ink feeding mechanism 58 can be axially translated for accurate positioning with respect to the screen support frame 32. Details of providing axial translation of the above components are contentional and are, therefore, not described in further detail herein.

By reference to FIGURES and 11, it can be seen that each of the mandrels 101 become aligned with the electrostatic printing screen 56. Thus, it can be seen that the annular side Wall 102 parallels the surface of the electrostatic printing screen 56. Through this positioning, it is possible to employ the principles of electrostatic printing on curved surfaces in the manner described in copending application Serial No. 472,829 filed July 19, 1965. In the printing of curvilinear shaped surfaces such as on conically shaped containers, the container is positioned in an axis of rotation so that the exterior wall thereof tangentially approaches and departs from the screen. Thus, printing will occur along an elemental line of closest approach between the container and the electrostatic printing screen. Moreover, the mandrel 101 with the container C supported thereon is rotated at approximately the same rate of speed or at the same peripheral speed as the oscillating movement of the screen 56 so that a continuing line of tangency occurs between the surface of the container C supported on the mandrel 101 and the surface of the electrostatic printing screen 56.

By reference to FIGURE 2, it can be seen that the screen retaining frame 54 and hence the electrostatic printing screen 56 is not perpendicular to the axis of rotation of said frame. Accordingly while the screen 56 is arcuately shaped in one plane, that is a plane parallel to the side wall of the mandrel 101, is it also arcuately shaped about an axis which is axially translated from and parallel to the side wall of the mandrel 101. This screen is often referred to as a conically shaped screen and is oscillated or rotated in timed relation to the rotation of the mandrel 101 so that each of the two elements tangentially approaches and tangentailly departs along a continuing line of closest approach. However, is should be understood that a relatively fiat screen, that is a screen which lies in a relatively fiat plane parallel to the side wall of the mandrel 101, could be employed if the axis of rotation or oscillation of said screen was directly perpendicular to the side wall of the mandrel 101. However, by reference to FIGURE 2, it can be seen that the axis 16 of oscillation or movement of the screen 56 is directly perpendicular to the axial centerline of the mandrel 101 and accordingly, the curved screen must be employed.

Simultaneously with the rotation of the container C supported on the mandrel 101 and the oscillation of the screen support frame 32 electroscopic ink will be passed through the screen 56 to the container C in a manner hereinafter described in more detail. The ink particles will pass through the screen 56 along this line or band of tangency. In this manner, it is possible to provide electrostatatically printed images on the surface of a curvilinearly shaped article, such as conically shaped container.

By the process of the present invention, and by using the techniques employed in said copending application Serial No. 472,829 filed July 19, 1965, it is also possible to use contact electrostatic printing between the substrate and the electrostatic printing screen. In this process, the fiat surface or the container C is retained in very light tangential contact with the surface of the electrostatic printing screen. Both the screen and the container are moved so that a line of continuing light tangential contact is maintained therebetween and electroscopic ink is applied through the screen to the container at this line of tangential contact. Thus, it should be understood that each of the bevel gears 98 is sized so that the speed of rotation of the mandrel 101 is such that it has the same peripheral speed as the movement of the oscillating screen support frame 32 and the electrostatic printing screen 56.

It is possible to synchronize the rotation of the mandrels 101 with the screen support frame 32 by means of the mechanism described in our copending application Serial No. 482,475, filed Aug. 25, 1965, wherein a friction driven free-wheeling mandrel is employed. In this mechanism, the bevel gears 98 on each of the mandrel support shafts 97 could be eliminated. Furthermore, the outer ends of each of the mandrel support shafts would be provided with bearings for rotatably mounting the mandrels. Each of the mandrels will be provided with a friction wheel for meshing engagement with a drive wheel operatively mounted on the screen drive shaft 21. Moreover, a variable speed transmission in the form of a variable belt drive trained around the sprockets 24, 25 could be employed. However, the gear drive mechanism of the present invention is the preferred embodiment inasmuch as the possibility of slippage is substantially reduced.

The pneumatic control system 82 is more fully illustratedin FIGURES 5, 6 and 8, and as previously indicated, includes the rotatable valve drum 83 and the valve manifold 84. The valve manifold 84 is cylindrical and is sized to snugly and yet rotata-bly accommodate the valve drum 83. By reference to FIGURE 8, it can be seen that a pair of washers and lock rings 109 are disposed on opposite sides of the valve manifold 84 and which bear against the annular side walls of the manifold 84 for holding the latter in axial alignment with the valve drum 83. Furthermore, it can be seen that the valve drum 83 is annularly grooved in the provision of a pair of annular slots to accommodate sealing rings 110. The sealing rings 110 may be formed of any suitable material normally employed in the manufacture of sealing rings, such as neoprene rubber.

The valve manifold 84 is provided on its interior surface with a primary air passage or recess 111. The primary air passage 111 is generally maintained under conditions of reduced air pressure and for the purposes of the present invention is often referred to as a vacuum passage. A suitable source of air under reduced pressure (not shown) may be supplied to the primary air passage 111 through a tube 112 connected to a fitting 113, which is in turn connected to the valve manifold 84. The fitting 113 and tube 112 communicate with the primary air passage 111 in the manner as shown in FIG- URE 5. By further reference to FIGURE 5, it can be seen that the primary air passage 111 extends for approximately 270". A secondary air tube 114 is connected to a fitting 115 which in turn communicates with the valve drum 83 in a manner to be hereinafter described in detail. The secondary air tube or air line 114 is connected to a suitable source of air pressure (not shown) for providing positive fluid pressure to the valve drum 83 in a manner also hereinafter to be described in more detail.

The valve manifold 83 and the turret 92 are so positioned with respect to the secondary Geneva mechanism 76 so that the primary air passage 111 remains in contact with seven of eight radially spaced, radially ex tending fluid ducts 116. By reference to FIGURES and 8, it can be seen that the eight radially extending fluid ducts 116 each communicates with the surface of the valve drum 83. Moreover, the first and seventh radial fluids ducts 116 communicate with the ends of the primary air passage 111. The eighth radial fluid duct 116 thereby remains in communication with the secondary air tube or air line 114. By reference to FIG- URES 8, 9 and 10 which show the operative connection between the pneumatic control system 32, the primary Geneva mechanism 68, and the secondary Geneva mechanism 76, it can be seen that the valve drum 83 is located so that it stops in a position where one radial fluid duct 116 is always located in communication with the secondary air line 114 as the secondary Geneva mechanism 76 rotates through a complete revolution. The eight radially spaced fluid ducts 116 in the valve drum 83 in turn, communicate with eight axially extending fluid ducts 117, also formed in the valve drum 83.

integrally formed with the rearward end of the valve drum 83 is a diametrally enlarged circular plate 118 which is held in fluid-tight communication with the forwardly presented surface of the turret 92 by means of an annular sealing ring 119. The circular plate 118 is provided with radially extending fluid ducts 120, which in turn communicate with a hollow fluid channel 121 formed in the bearing block 95. By reference to FIG- URES 7 and 8, it can be seen that the bearing blocks 96 are not the same as the bearing block 95. The bearing block is a conventional thrust hearing which includes an annular type bushing for retaining the mandrel shaft 97. The bearing block 96, however, includes a bushing 122, which is cut away in the provision of an annular fluid duct 123, and which, in turn, is maintained in continual communication with the hollow fluid channel 121. The fluid duct 123 in turn communicates with the fluid duct 107 formed in the mandrel shafts 97 through a pair of connecting fluid ducts 124.

By means of the above outlined construction, the mandrel 101 is maintained in fluid communication with the primary air passage 111 in the valve manifold 84 and the secondary air line 114. Thus, when the valve drum 83 is located in the position as shown in FIGURE 5, seven of the radial ducts 116 in the valve drum will be in communication with the primary air passage 114, causing a reduced air pressure through the radial fluid ducts 116, and the axial ducts 117. Inasmuch as the axial fluid ducts 117 communicate with the radially extending fluid ducts 120, the hollow fluid channels 121 and the fluid channels in the bearing blocks 96 and the fluid ducts 107 in the mandrel shaft, fluid communication is maintained between the valve manifold 84 and the mandrel 101. Accordingly, a container C disposed upon the mandrel 101 will be retained thereon by means of a vacuum on the mandrel 101. Similarly, air pressure may be supplied to the mandrel 101, which is in communication with the secondary air line 114, where a container C on the mandrel 101 will be ejected therefrom.

By further reference to FIGURE 1, it can be seen that the mandrel 101, which is located in communication with the secondary air tube 114 is positioned in alignment with a discharge tube 125. The discharge tube 125 is maintained under a vacuum by a suitable vacuum source (not shown) in order to carry the containers disposed in the discharge tube to a suitable collection area (also not shown). Thus, when the mandrel 101 is maintained under a positive pressure, the container C disposed thereon is eject-ed and deposited into the discharge tube 125. Inasmuch as the discharge tube 125 is maintained under vacuum conditions, the container C is thereupon carried to a suitable collection area.

The electrostatic printing apparatus A also includes a container dispensing mechanism 126 for intermittently dispensing or depositing containers C on each of the mandrels 161 as they pass the dispensing mechanism 126. The container dispensing mechanism 126 is vertlcally positioned and is disposed above the mandrel 101 as it reaches its upper most position, reference being made to FIGURE 1. The container dispensing mechanism is similar to the mechanism described in our copending application Serial No. 482,475, filed Aug. 25, 1965, and is designed to dispense a single container pursuant to a control signal. A simple control circuit (not shown) may be provided for actuating a solenoid on the container dispensing mechanism 126 pursuant to a positioning of a mandrel 101 in alignment with the dispensing mechanism 126. Furthermore, by reference to FIG- URES 1 and 5, it can be seen that the mandrel 191, which is positioned beneath the container dispensing mechanism 126 is maintained in fluid communication with the primary air passage 111, thereby creating a condition of reduced pressure or a vacuum on the mandrel 101. Thus as the container C is dispensed from the mechanism 126, it will be deposited on the manirel and retained thereon due to the vacuum maintained across the mandrel 101.

An ink fixing tank 127 is also mounted on the frame 1 and is disposed between two lower longltudinal base channels 2, 3 in the manner as shown in FIGURES 1 and 3. The method of fixing the electrostatic printing image is not critical to the present invention and various well known methods in the prior art can be employed, such as the fixing by means of heat or selectively filtered radiation. However, it has been found that solvent vapor fixing of electrostatic printing images has proved to be one of the most effective methods of permanently fixing electroscopic ink on a substrate. In solvent vapor fixing, it is often desirable to construct the solvent tank with cooling coils in order to prevent any of the vapor from escaping into the atmosphere. The cooling coils surrounding the tank, generally along the upper margin, will cause any escaping vapors to condense and drain back into the liquid bath and then become vaporized. The choice of the solvent depends upon the composition of the powder images to be fixed. With powders formed of pigmented rosin, copal, asphalt and other natural resins as well as several synthetic resins and plastics, such as cellulose, a desirable solvent is trichlorethylene. Amylacetate or butylacetate can likewise be used with many resins. Also butyl alcohol and perchloroethylene are particularly useful as they are somewhat less volatile.

It is generally desirable to maintain the solvent in the form of a saturated vapor, where the solvent is held at its boiling point. Fusion of the powder image much more readily takes place provided that the powder is soluble in a solvent. In the fixing chamber, the solvent from the vapor phase condenses on the printed article and is absorbed in the ink powder, causing it to soften and conlesce to a continuous film and adhere to the article. It is necessary to adjust the degree of saturation of the solvent vapor and exposure time in order to obtain coalescence and adhesion without absorbing enough solvent to cause excessive liqueflcation and running of the images. The fusing time in solvent vapor fixing is not usually critical, whereas it may be with heat fusing of thermoplastic based ink on plastic articles. When the 19 substrate is then removed from the vapor chamber, the solvent evaporates from the image and the image solidifies and becomes permanently bonded or fixed onto the substrate in a matter of a few seconds.

By reference to FIGURE 1, it can be seen that the mandrel 101 is moved to its lowermost position when it is introduced into the ink fixing tank 127. Continued rotation of the turret 92 in a clockwise direction, reference being made to FIGURE 1 removes the mandrel 101 from the ink fixing tank permitting the container disposed thereon to air dry. Generally, the tme required for the movement of the mandrel through three successive 45 movements to the discharge position where it is in alignment with the discharge tube 125 provides sufiicient time for evaporation of the solvent, so that the image on the container C is permanently hardened.

By reference to FIGURE 1, it can be seen that the electrostatic printing apparatus A is so constituted and arranged that there are, in effect, five work stations which are located in a 360 circle, namely the arcuate movement of at least one mandrel 101 in a full cycle. It can be seen that each of the mandrels 101 rotates in a clockwise direction, reference being made to FIGURE 1, and that each printing cycle actually starts at the point where the mandrel 101 is in horizontal alignment with the container dispensing mechanism 126. Thus, the dispensing of a container C on a mandrel 100, which is located at the container dispensing mechanism 126 constitutes a first work station or so-called loading station S As the mandrel 101 with the container C supported thereon moves in a clockwise direction to the screen support frame 32, it is moved into a printing position for receiving a desired printed image. The printing of the container C at the screen support frame 32 constitutes a second work station or so-called printing station 8;. It can be seen that the printing station S is located at two successive 45 positions in a clockwise direction from the loading station S After the container C has re ceived the electrostatic printing image from the work station S it is transferred to a fixing station S which constitutes a third work station. After the container is introduced into the solvent vapor at the fixing station S the mandrel is again rotated through three successive 45 movements until it becomes aligned with the discharge tube 125. During the time that it passes through two successive 45 movements after introduction into the fix ing tank 127, it is positioned in a so-called drying station or fourth work station, 8,. Sufficient timeis provided for release of the solvent contained in the ink on the image by air drying during the time that the container C is positioned at the drying station S of the mandrel 101 at the discharge tube 125 constitutes a fifth work station or so-called discharge station S where the container is ejected from the mandrel 101.

It should be recognized that an electrostatic field is maintained between the electrostatic printing screen 56 and each of the mandrels 101. The apparatus A may be conventionally provided with the necessary insulating sleeves and washers and electrical circuit necessary to provide the electrostatic field. This type of construction is conventional and is, therefore, neither illustrated nor described in detail herein. However, it should be pointed out that while current requirements for electro static printing of the type herein employed are not heavy in the ordinary sense, a very definite electron current or space current flows across the printing space during the printing operation. It is desirable to have a space current of at least 1 to 2 milliamperes per square inch of printing area. Moreover, the high potential source should be capable of maintaining a desired voltage under current drains in the range of approximately 100 milliamperes or slightly more.

The ink feeding mechanism 58 may also be electrically charged to serve as one of the elements forming the electrostatic field. In actuality, the feeding tube 60 of the ink feeding mechanism 58 would be the element to The positioning be established as an electrode. However, any metallic electrode in close proximity to the discharge end or nozzle 61 of the ink feeding tube 60 could serve as an electrode. In the event that the ink feeding mechanism 58 is employed as one of the poles or electrodes forming the electrostatic field, the ink hopper 59 would be insulated from the remainder of the ink feeding mechanism. The mandrel 101, screen 56 and ink delivery tube 60 are charged in such manner so that an electric field existing therebetween is in the form of a potential gradient. The direction of the potential gradient depends on the charge of the ink particle. If the ink particles are charged positively, the electric field Will create a negative charge or less positive charge on the mandrel 1G1. Generally, an ideal situation exists where the mandrel can be charged in one polarity, the ink delivery tube charged at the opposite polarity and the screen maintained at ground polarity. Thus, if the ink particles were positively charged, the mandrel 101 would be negatively charged and similarly, if the ink particles were negatively charged, the mandrel 101 would be positively charged. It is not necessary to have a positive-negative type potential gradient existing between the three aforementioned components. The potential gradient which exists may be either wholly positive or negative. Thus if the ink particles were positively charged, the ink delivery tube 60, the screen 56 and the mandrel 101 could have successively less positive charges so that a potential gradient still exists and where this current is capable of moving the triboelectrically charged ink particles from the delivery tube 60 through the screen 56 and to the mandrel 101.

The electrical circuitry may include a high voltage re versing switch (not shown) which is designed to reverse the potential gradient existing between the delivery tube 60, the screen 56 and the mandrel 101. For example, if the mandrel 101 were positive and the delivery tube 60 were negative, position reversal of the switch would cause the mandrel 101 to be charged negatively and the delivery tube 60 to be charged positivelv. If on the other hand, the potential gradient which existed was all of one charge, position reversal of the switch would reverse the direction of the potential gradient. In this manner, the direction of the lines of force of the electrostatic field which exists between these various components may be reversed. This type of reversal would occur after each printing cycle so that any excess ink which is gathered on the screen would be automatically removed therefrom prior to the start of the next printing cycle with the last named screen.

Operation of Apparatus A In use, the ink hopper 59 is filled with a desired electroscopic ink. The electroscopic ink has been previously fluidized as indicated above by passing low pressure air through a porous membrane in which the particles are maintained in combination with a vibratory action. A suitable electrostatic printing screen 56 is mounted Within the screen retaining frame 54 and the screen retaining frame 54 is then secured to the screen support frame 32 by means of the bolts 55. The mandrels 101 mounted on each of the mandrel shafts 97 are sized to accommodate containers C which are then loaded into a suitable delivery mechanism for delivery to the container dispensing mechanism 126.

Upon energization of the electric motor 17, the drive belt trained around the pulleys 19, 20 will drive the main drive shaft 14 which will, in turn, through the roller chain 26 drive the screen drive shaft 21. Rotation of the drive shaft 21 will cause the friction wheel 34 to rotate. At the start of a printing cycle, the screen support frame 32 is located in its lowermost position, that is the position as shown in FIGURE 1 where a mandrel 101 is positioned in horizontal alignment with the upper margin of the electrostatic printing screen 56.

Claims (1)

1. AN ELECTROSTATIC PRINTING APPARATUS COMPRISING: (A) BASE MEANS, (B) A FIRST CONTINUOUSLY ROTATABLE SHAFT OPERATIVELY MOUNTED ON SAID BASE MEANS, (C) AN ACTUATING WHEEL OPERATRIVELY MOUNTED ON SAID SHAFT AND ROTATING THROUGH CONTINUOUS 360* REVOLUTIONS, (D) A SECOND SHAFT OPERATIVELY DISPOSED IN SPACED RELATION TO SAID FIRST SHAFT, (E) A SLOT-WHEEL HAVING A PLURALITY OF ENGAGEABLE SLOTS OPERATIVELY MOUNTED ON SAID SECOND SHAFT AND BEING INTERMITTENTLY ROTATABLE, (F) AN EXTENDED PIN ON SAID ACTUATING WHEEL FOR ENGAGING ANY OF SAID SLOTS ON SAID SLOT-WHEEL AND ROTATING THE SLOT-WHEEL THROUGH 90* ARCS DURING 90* ARCUATE ROTATIONAL MOVEMENTS OF SAID ACTUATING WHEEL, (G) A TURRET OPERATIVELY CONNECTED TO SAID SLOT-WHEEL AND BEING ROTATABLE THEREWITH SO THAT SAID TURRET IS MOVED TO SUCCESSIVE POSITIONS WHICH ARE SPACED 45* APART, (H) A PLURALITY OF ARTICLE RETAINING MEANS MOUNTED ON SAID TURRET AND BEING SIZED TO RETAIN DESIRED ARTICLES FOR PRINTING, (I) AN OSCILLATING SCREEN FRAME OPERATIVELY MOUNTED ON SAID BASE MEANS AND BEING SHIFTABLE BETWEEN UPPER AND LOWER POSITIONS DURING A PRINTING CYCLE, (J) AN ELECTROSTATIC PRINTING SCREEN OPERATIVELY ASSOCIATED WITH SAID SCREEN FRAME AND BEING MOVABLE THEREWITH, (K) MEANS FOR FEEDING A SUPPLY OF ELECTROSCOPIC INK TO SAID SCREEN WHEN SAID ARTICLE RETAINING MEANS ARE ALIGNED WITH SAID SCREEN, (L) MEANS FOR MOVING SAID MOVABLE SCREEN FRAME IN PRETIMED RELATIONSHIP TO SAID TURRET SO THAT EACH ONE OF SAID ARTICLE RETAINING MEANS BECOMES ALIGNED WITH SAID SCREEN, (M) AND MEANS FOR CREATING AN ELECTROSTATIC FIELD BETWEEN SAID SCREEN AND ARTICLE RETAINING MEANS SO THAT INK WILL PASS THROUGH THE OPEN PORTIONS OF THE SCREEN TO THE ARTICLE RETAINING MEANS.

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