US3508491A - Printing apparatus for filled containers - Google Patents

Description

April 28, 1970 D. T. N. WILLIAMSON ETAL 3,503,491

PRINTING APPARATUS FOR FILLED CONTAINERS Original Filed May 31, 1967 2 Sheets-Sheet 1 9 f J y 2- I April 28, 1970 D. T. N. WILLIAMSON ETAL 3,503,491

PRINTING APPARATUS FOR FILLED CONTAINERS Original Filed May 31, 1967 2 Sheets-Sheet 2 United States Patent M 3,508,491 PRINTlNG APPARATUS FOR FlLLED CONTAINERS David T. N. Williamson and Michael Aren Pym, London, England, assignors to The Molins Organisation Limited, London, England, a corporation of Great Britain Continuation of application Ser. No. 642,406, May 31, 1967. This application Feb. 7, 1969, Ser. No. 800,817 Claims priority, application Great Britain, June 6, 1966, 25,120/ 66 Int. Cl. B41m 1/10 US. Cl. 101-150 7 Claims ABSTRACT OF THE DISCLOSURE Apparatus for printing on containers which, although themselves electrically non-conductive, contain an inner wrapper of conductive foil, uses the foil as an electrode of an electrostatic printer. Ink is supplied between another electrode and the container, and different potentials applied to the foil and the other electrode to produce an electric field propelling the ink onto the container. Various methods of forming the ink into desired images are mentioned.

This application is a continuation of application Ser. No. 642,406, filed May 31, 1967.

This invention relates to electrostatic printing apparatus for use in printing on containers of electrically non-conductive material (cg. packets, boxes or the like of card or of plastic material) in which goods wrapped in electrically-conductive foil are packed.

By electrostatic printing is meant any process in which a marking medium (hereinafter termed ink) is placed upon a surface to be marked by applying an electric field in such manner as to propel the ink towards the surface. To apply such a field requires the establishment of a potential difference between a pair of electrodes, one behind and the other confronting the surface to be marked. The electrode behind said surface is desirably as close to said surface as is practicable, as the greater the separation between the electrodes the greater the potential difference required. Electrostatic printing on webs of paper or like material can readily be effected with a metal plate or drum in contact with the rear surface of the web serving as the electrode behind the surface. Where however printing is to be effected on one wall of a container such as a packet, box or the like, it will be apparent that an electrode behind the packet, box or the like will be spaced from the print-receiving surface by at least the thickness of the packet, box or the like, hence the potential difference needed to establish a desired field intensity will be substantially higher than if the electrode were close behind the printing surface. When printing on empty packets, boxes or the like this disadvantage may be avoided by inserting the electrode into the packet, box or the like at the appropriate time but when printing on filled packets, boxes or the like this expedient is seldom practicable.

It has been discovered that where, as for example is common with cigarettes and chocolate, a metallic or other electrically-conductive foil is wrapped around the goods in the packet, box or the like, that foil may advantageously be employed as the electrode behind the printing surface.

According to the invention, is provided apparatus for printing on a container of electrically non-conductive material containing an electrically-conductive foil as an inner wrapper for goods packed in said container, said apparatus comprising a first electrode arranged to confront a surface of the container to be printed, means for 3,508,491 Patented Apr. 28, 1970 supplying ink between said first electrode and said surface, a second electrode for applying electric potentials to said foil, and means for creating an electric potential difference between said first and second electrodes so that an electric field is established between said first electrode and said foil to propel said ink on to said surface.

The second electrode may be in the form of a probe arranged to make contact with the foil; such a probe may be a fixed member against which the container may be placed, or alternatively may be movable towards and away from the container; the latter alternative is preferable when as is common, it is required to print containers in rapid succession, possibly even while the containers are in motion. For example, a conveyor belt may be arranged to carry containers in succession past a printing station at which the electrodes and ink supply means are located and the probe may be arranged to engage the foil of each container as it comes to the printing station and to disengage from said foil as the container leaves the printing station; in place of the probe, there may be a contact roller engageable by the foil of each container While passing the printing station.

Alternatively, the second electrode may be in the form of a plate so placed as to apply a suitable potential to the foil by electrostatic induction. A convenient position for such a plate is parallel to the first electrode at such a distance as to permit the container to be placed therebetween.

The ink supply means may take various forms, depending in part upon the manner in which desired printed images are to be formed. Thus where a stencil-like screen is arranged to lie between the ink supply means and the container surface to be printed, the ink supply means and first electrode may in effect be combined by providing an ink reservoir with electrically-conductive walls. If however the ink supply means is adapted to form a desired ink image on a temporary support, said image being then transferred by the electric field to the container surface to be printed, the first electrode may serve as the temporary support; said first electrode may then be an intaglio or gravure plate, inked in any convenient manner, or it may be an offset roller. If it is desired to form the ink image electrically, then said first electrode may be a plate of photo-conductive or P.I.P. material. (By P.I.P. material is meant material having the property known as persistent internal polarisation, i.e. acquiring what appears to be an electrostatic charge trapped under its surface as a consequence of subjecting the material to an electric field either simultaneously with or shortly after exposure to light.)

The ink employed is preferably a dry particulate ink; when the first electrode is in the form of an intaglio or gravure plate, a particle size of 2-10 microns is suitable. When the first electrode is a plate of P.I.P. material, a dry particulate ink of high resistance material (i.e. having a resistivity greater than 10 ohm cm.) is used, and prior to its application to the plate, the ink may be charge triboelectrically (e.g. by shaking with glass beads).

It will be appreciated that when a container is being printed by apparatus embodying the invention, if the second electrode is a probe required to make contact with the foil the container cannot be fully closed; if the container has a separate lid, such lid must be applied after printing has been effected while if the container has an integral hinged lid or closure flap, such lid or fiap must be at least partly open during the printing operation.

In order that the invention may be fully understood, a preferred embodiment thereof will now be described in more detail, referring to the accompanying drawing in which:

FIGURE 1 shows, in section, a cigarette packet together with a diagrammatic representation of apparatus embodying the invention, and

FIGURE 2 illustrates an apparatus similar to that of FIGURE 1 but adapted for continuous operation.

In FIGURE 1, a cigarette packet 1 of the hinged-lid or flip-top type is shown in a partly-packed condition, namely after a bundle of cigarettes 2 wrapped in metal foil 3 has been inserted into the packet but before its lid has been closed. In this condition the packet is ready to be printed upon by apparatus embodying the invention and comprising an electrode 4 confronting and parallel to the outer surface of a front wall 5 of the packet 1, with a small gap (not exceeding 0.050") between said electrode and said surface. At the open end of the packet 1, a probe 6 is held in contact with the foil 3 and a DC. source 7, represented as a battery, with a control switch 8 is connected between the electrode 4 and probe 6.

The electrode 4 is in the form of an intaglio printing plate, the surface of said electrode facing the packet 1 being formed with raised portions 9 and recessed portions 10, the portions 10 defining the image to be printed on the packet 1. Before each printing operation, i.e. before the packet 1 and electrode 4 are in the relative positions shown, the electrode 4 must be inked. This involves depositing a dry particule ink (such as the toner employed in xerographic machines) in the recessed portions 10, while keeping the raised portions 9 clean. Then the deposited ink must be electrostatically charged-the manner in which this is done depends upon the conductivity of the ink. If the ink is a conductive ink which in this context may be taken as meaning that it has a resistivity less than 10 ohm cm.) then the charge may be applied by contact, i.e. by connecting a voltage source (which may be the source 7) to electrode 4, so that with this type of ink a separate charging operation is not needed. If however the ink is resistive (i.e. has a resistivity exceeding 10 ohm cm.) then it may be subjected to a corona discharge.

With the electrode 4 thus prepared, and the packet I placed as shown relative to the electrode 4 and probe 6, switch 8 is closed; the connection of source 7 between probe 6 and electrode 4 creates a potential dicerence between these parts and hence (as the probe 6 is touching foil 3 and the latter is electrically conductive) between the electrode 4 and foil 3. An electric field is accordingly established between the electrode 4 and the portion of the foil 3 lying immediately behind the front wall 5; the presence of the cigarettes within the foil 3 maintains the latter in contact with the inner surfaces of the walls of the packet 1. Said electric field causes the ink in the recesses 10 of electrode 4 to be transferred to the outer surface of the wall 5 and, as is known, the ink transfer will be along paths normal to the facing surfaces of electrode 4 and wall 5 so that the ink on its arrival on the outer surface of wall 5 forms the desired image thereon. It will be understood that the polarity of source 7 must be correct relative to the charge on the ink, i.e. the positive terminal of source 7 is connected to the electrode 4 if the ink is positively charged.

As with any form of electrostatic printing, the packet 1 should be free of stray electrostatic charges when a printing operation is to be performed and any convenient expedient may be adapted to this end, e.g. as the packet is being brought into the printing position it may be subjected to an AC. corona discharge.

It will be appreciated that printing with apparatus embodying the invention does not require that pressure be exerted on the surface to be printed, and this of course is of great advantage when printing upon a container packed with crushable articles such as cigarettes. Moreover, it will be observed that the front wall 5 of packet 1 is shown as having upstanding ribs 11, which ribs could well be damaged by mechanical pressure in a conventional printing operation. This difiiculty does not arise when using apparatus embodying the invention, nor does the presence of ribs 11 affect the uniformity of printing. It will be noted that the presence of ribs 11 will not affect the uniformity of the electric field, as the foil 3 does not follow the contour of said ribs and hence the spacing of foil 3 from electrode 4 is uniform over the area to be printed.

The gap between the electrode 4 and the packet is kept as small as possible, as it is found that the larger this gap is, the worse the resolution of the image obtained, due to repulsion between adjacent ink particles crossing the gap. With single colour printing, the electrode 4 may touch the packet; with multi-colour printing, involving the use of a difference electrode 4 for each colour, and the execution of a printing operation with each such electrode in turn, a gap is however necessary to avoid disturbance of ink already applied to the packet while performing the second and subsequent printing operations, and in these circumstances a gap of the order of .005" is appropriate.

The voltage provided by source 7 should be as high as can be tolerated without breakdown between the electrode 4 and foil 3, hence a small gap confers the additional benefit of reducing the voltage required.

If preferred, the probe 6 in contact with the foil may be omitted and, instead, a plate 6A provided; the plate 6A is so positioned as to lie parallel to the electrode 4 but on the other side of the packet, i.e. confronting the rear wall of the latter. Plate 6A is connected to source 7 and serves to induce a suitable potential in the foil.

Turning now to FIGURE 2, here in outline is illustrated a form of apparatus which is in principle similar to that of FIGURE 1 but is adapted for continuous operation. In this form of apparatus, the packet 1 is carried by a conveyor belt 20 which is continuously driven, travelling at right angles to the plane of the drawing. Said packet 1 (which is of course but one of a succession of similar packets carried by belt 20) lies on the conveyor belt 20 with its open lid overhanging the edge of said belt. An electrode 21, corresponding to electrode 4 of FIGURE 1, takes the form of an intaglio printing roller carried by a shaft 22 above the path of the packets 1 and in operation of the apparatus the electrode 21 is rotated in synchronism with the movement of belt 20, i.e. so that the peripheral speed of the electrode is equal to the linear speed of the belt. In place of the probe 6 is provided a contact roller 23, rotatably carried by a forked arm 24 pivoted at 25 to a portion 26 of a frame (not shown) for the apparatus. The arm 24 is so disposed as to be inclined in a trailing direction, considered in relation to the movement of belt 20, and lightly sprung by means not shown so when no packet is in engagement with the roller 23' the latter obtrudes slightly into the path of the packets; when however a packet engages the roller 23 the latter is moved out of the way, arm 24 yielding by movement on its pivot 25, until the position shown is reached, whereupon the arm 24 ceases to move and the roller 23 is lightly pressed against foil 3 as the packet 1 passes through the position shown.

The electrode 21 bears images 31 of Whatever letterpress, trademarks, or other matter it is required to print on the packet 1 and above said electrode is an inking device 27. Against one end portion of shaft 22 a carbon brush 28 is held by a spring 29, said brush 28 providing for connection to one terminal of DC. source 7. The other terminal of said source is connected through switch 8 to the pivot 25 of arm 24.

A stationary masking plate 30 is provided immediately below the electrode 21, said plate having a narrow slot extending the whole length of the electrode adjacent its lowest part, so that transfer of ink from the electrode 21 to the packet 1 may only occur over the width of said slot, to avoid distortion of the image during transfer due to the curvature of the electrode 21. Plate 30 is connected to brush 28, so that plate 30 is at the same potential as electrodes 21 to prevent transfer of ink to the plate 30. The DC. source 7 may be arranged to provide a succession of electric pulses, rather than a steady D.C. output, at intervals corresponding to the time taken for a print on packet 1 to move past the slot in masking plate 30; when this is done, it will be apparent that the operation of source 7 must be synchronised with the movement of belt and electrode 21.

Apart from the differences in structure shown in FIG- URE 2 as described above, the apparatus of FIGURE 2 functions exactly as the apparatus of FIGURE 1, except that in the apparatus of FIGURE 2 the transfer of the image proceeds either progressively (if source 7 provides a steady output) or strip by strip (if source 7 provides pulses). Inking is accomplished progressively, as the periphery of the electrode 21 moves past inking device 27.

In the apparatus of FIGURE 2, the roller 23 and associated parts may be omited and in their place is provided a plate 6A connected to source 7 and serving (as does plate 6A in FIGURE 1) to apply a suitable potential to the foil by induction.

Various changes and modifications in details of the apparatus described may be made Without departure from the scope of the invention. Thus for example when dealing with packets similar to the packet 1, but with separate lids, the packets may be arranged to be carried on belt 20 with their open ends to the rear, and projecting pushers attached to said belt may serve to make the necessary contact with foil 3. When using apparatus embodying the invention, it will be appreciated that some means for fixing the printed image to the container will be required. Such fixing may for example be accomplished by the application of heat or of a solvent vapour, depending upon the composition of the ink. Fixing need not be effected immediately after ink transfer to the container, as it is found the electrostatic attraction serves to secure the ink to the container for some time after transfer, therefore the fixing means may be spaced from the transfer position.

What we claim as our invention and desire to secure by Letters Patent is:

1. Apparatus for printing on the surface of a succession of sealed containers of electrically non-conductive material, said containers being packed with goods wrapped in electrically conductive foil, said apparatus comprising conveyor means for carrying a succession of said packed containers past a printing station, said printing station including a first electrode positioned to confront a surface of each of said containers and to temporarily retain a desired ink image thereon, means for supplying ink to said first electrode, a second electrode positioned to confront a further surface of each of said containers, both said first and second electrodes being positioned such as to be spaced from the respective surfaces of said containers as said containers pass through said printing station, and electric source means connected to said first and second electrodes for applying a potential through said second electrode to said foil within said packed containers by electrostatic induction whereby said foil is electrically charged to establish an electric field between said first electrode and said foil to propel said ink onto said container surface.

2. Apparatus as claimed in claim 1 wherein said first electrode comprises an intaglio printing roller mounted for rotation in synchronism with the movement of said packed containers past said printing station.

3. Apparatus as claimed in claim 2 further comprising a perforated stationary masking plate positioned between said roller and each of said packed containers at said printing station to prevent transfer of ink from said roller to said packed container except through said perforations whereby distortion of the image during transfer is avoided.

4. Apparatus as claimed in claim 1 in which said second electrode is parallel to the first electrode and spaced therefrom at such a distance as to permit the containers to pass therebetween.

5. A method for printing on a succession of containers of electrically non-conductive material, comprising the steps of inserting goods wrapped in electrically conductive foil in said containers, feeding a succession of said packed containers past an electrode positioned to confront a surface of each of said containers, placing an ink image on said electrode, creating an electrical circuit be tween said foil and said electrode, and applying an electrical potential between said electrode and said foil to generate an electrostatic field therebetween to propel said ink from said electrode onto the surface of said container.

6. A method for printing on a succession of containers of electrically non-conductive material as claimed in claim 5 wherein said step of creating an electrical circuit between said foil and said electrode comprises feeding said succession of packed containers past both said electrode and a further electrode positioned to confront a further surface of each of said containers and said step of applying an electrical potential between said electrode and said foil comprises applying a potential through said further electrode to the foil by electrostatic induction.

7. A method for printing on a succession of containers of electrically non-conductive material as claimed in claim 5 wherein said step of creating an electrical circuit between said foil and said electrode comprises feeding a succession of said packed containers past said electrode and a contact element, said contact element contacting said foil, and said step of applying an electrical potential between said electrode and said foil comprises the appli cation of electrical potential through said contact element to said foil.

References Cited UNITED STATES PATENTS 2,787,556 4/ 1957 Haas. 3,218,967 11/1965 Childress. 3,228,326 1/1966 Childress 101-114 3,245,341 4/1966 Childress et al. 3,276,358 10/1966 Lusher. 3,285,168 11/ 1966 Childress. 3,296,963 1/1967 Rarey et al. 3,296,965 1/1967 Reif et al. 3,302,561 2/1967 Edwards.

EDGAR S. BURR, Primary Examiner US. Cl. X.R. l0-1-17O

Images