Improved counter-pressure ring and counter-pressure unit for sheet-fed stamping press having a foil laminating unit

Abstract

A counter-pressure ring for use with a counter-pressure unit of a foil laminating unit of a sheet-fed stamping press, the counter-pressure unit being rotatable around a drive shaft central axis, wherein the ring comprises a flange and is attachable by means of fasteners to a collar, and wherein the attachment between the ring and the collar allows for slight movement of the ring in a direction perpendicular to the central axis of the drive shaft.

Description

[0001] Improved Counter-Pressure Ring and Counter-Pressure Unit for Sheet-Fed Stamping Press Having a Foil Laminating Unit

[0002] Field

[0003] The present invention relates to the field of sheet-fed foil stamping units having a counter-pressure apparatus.

[0004] Background

[0005] Banknotes and other security documents may include security features comprising foil which is applied onto the surface of the document. Means for applying the foil to the document are therefore required. In some applications, sheetfed hot foil stamping presses may be used for this purpose.

[0006] Sheet-fed stamping presses comprise a foil laminating unit designed to allow for lamination of foil material onto document sheets. The foil laminating unit includes an upper cylinder or stamping cylinder and one or more lower cylinders, counterpressure units or rollers.

[0007] Each of the one or more counter-pressure units is cylindrical and is rotatable about a central axis. Counter pressure is applied on a sheet or substrate which is compressed between the upper, larger diameter cylinder and the lower, smaller diameter cylinder. The gap between the two cylinders is set to a distance that is less than the combined thickness of the substrate, foil, and foil carrier. There may be multiple rollers on a common driving shaft.

[0008] The design of counter-pressure units known in the prior art is flawed. The current design of the counterpressure mechanism used with, for example, the Koenig & Bauer OptiNota H™, requires an adhesive to secure an outer plastic ring to an inner steel ring. Applying the adhesive is unreliable. Inconsistent and insufficient volume of adhesive may be applied. This means that the outer ring often comes loose from the core and either spins around the inner steel ring or even migrates out of position. There is no method to test the effectiveness of the bonding once the adhesive has been applied, which means faults are only detected in a production setting after the rings have been mounted onto the press during production. In some designs there may be a chamfer at each end of the outer ring to hold a bead of adhesive, but this is not strong enough to bond the parts to withstand operational requirements.

[0009] Further, when the outer ring must be replaced due to damage or routine wear and tear, the adhesive may be difficult to remove. Removal of the adhesive may damage the inner metal ring.

[0010] Moreover, a pressing ring as described in, for example, EP 3 165 365 may be manufactured from a proprietary material such as Gesadur®. However, Gesadur®, when machined, produces a toxic dust.

[0011] Accordingly, there is a need for an improved counter-pressure ring and unit wherein the outer pressing ring is reliably and releasably secured to the inner portions, while maintaining the desired functionality of applying pressure to the substrate or documents and withstanding the temperatures and pressures observed during manufacturing.

[0012] There is also a need for an improved counter-pressure ring that can be easily and cost-effectively manufactured from safe materials, minimizing environmental impact. Summary

[0013] Provided herein is a counter-pressure ring apparatus which is fabricated without the need for adhesives. The apparatus comprises materials that are simple to acquire and to machine, and the apparatus is simple to install.

[0014] Disclosed herein is a counter-pressure ring and counter-pressure ring apparatus for use with a sheet-fed stamping press with a foil laminating unit. During operation of the foil laminating unit, the substrate, namely security document sheets and foil, is pressed between the foil laminating unit cylinder (stamping cylinder or upper cylinder) and one or more counter-pressure units.

[0015] In an embodiment, each counter-pressure unit or apparatus comprises a counter-pressure ring and a collar. The counter-pressure ring comprises a ring, the outer circumferential surface of which is adapted to contact the security document sheets. The collar is sized to fit within the ring, and the inner circumferential surface thereof is adapted to clamp onto a drive shaft. The collar may include a rubber or elastomer bumper in order to provide cushioning between the ring and the collar. The bumper may constitute an outer layer of the collar, may be sandwiched between inner layers of the collar, or may be sandwiched between the collar and the drive shaft.

[0016] In some embodiments, a flange or lip extends around the interior circumference of the counter-pressure ring, thereby providing a surface through which fasteners may be inserted in order to attach the counter-pressure ring to the collar. Small holes are pre-formed in the flange, in order to accommodate the fasteners. Corresponding holes are also pre-formed in the collar, such that when the collar and ring are assembled together, the fasteners will pass through the flange and into the collar, thereby reliably and releasably securing the ring and collar to each other.

[0017] In some embodiments, the pre-formed holes in the flange are slightly larger than the fasteners, allowing for slight movement of the counter-pressure ring relative to the drive shaft and collar. When the ring comes in contact with a substrate, it begins to rotate relative to the collar until the fasteners come into contact with solid material, such as the bumper. At such point, no additional rotation is possible.

[0018] In some embodiments, the size and shape of the fastener heads limits the flange from translating in the axial direction along the drive shaft. The head of the fastener may provide a slip fit against the flange surface, and prevent the flange from translating in the axial direction of the drive shaft.

[0019] Provided herein is a counter-pressure unit for use with a foil laminating unit of a sheet-fed stamping press, the counter-pressure unit being clamped to a drive shaft and rotatable around a drive shaft central axis, and the counter-pressure unit comprising a flanged ring and a collar, wherein the flanged ring is adapted to apply pressure to sheets during foil lamination, and wherein the flanged ring is fastened to the collar by means of fasteners inserted through the flange of the ring.

[0020] The flange may comprise a plurality of holes sized slightly larger than the diameter of the fasteners. The collar comprises cushioning on an outer surface thereof.

[0021] Also provided herein is a counter-pressure ring for use with a counterpressure unit of a foil laminating unit of a sheet-fed stamping press, the counterpressure unit being rotatable around a drive shaft central axis, wherein the ring comprises a flange and is attachable by means of fasteners to a collar, and wherein the attachment between the ring and the collar allows for slight movement of the ring in a direction perpendicular to the central axis of the drive shaft.

[0022] Additionally provided herein is a method for making a counter-pressure ring as described herein, the method comprising the steps of selecting a plastic material; casting, molding, 3-D printing or machining the plastic material; and machining an outer surface of the counter-pressure ring.

[0023] Brief Description of the Drawings

[0024] Fig. 1 illustrates an embodiment of the counter-pressure unit in both disassembled and assembled forms.

[0025] Fig. 2 is an enlarged fragmentary view of a shoulder screw and surrounding area in an embodiment of the counter-pressure unit.

[0026] Fig. 3 is a cross-sectional view of an embodiment of the counter-pressure unit, along line A-A.

[0027] Fig. 4 is a cross-sectional view of a counter-pressure unit according to an embodiment, shown when the counter-pressure unit is not under pressure or not in use.

[0028] Fig. 5 is a cross-sectional view of a counter-pressure unit according to an embodiment, shown when the counter-pressure unit is under pressure or in use.

[0029] Fig. 6 illustrates an embodiment of the counter-pressure unit in both disassembled and assembled forms.

[0030] Fig. 7 illustrates an embodiment of the counter-pressure unit in both disassembled and assembled forms.

[0031] Fig. 8 illustrates an embodiment of the counter-pressure unit in both disassembled and assembled forms. Fig. 9 is an end view of an embodiment of the counter-pressure unit.

[0032] Detailed Description

[0033] By the term “about” as used herein, it is meant that a figure or range of figures can vary plus or minus up to 10%. So in this embodiment if a figure of “about 1” is provided, then the amount can be up to 1 .1 or from 0.9.

[0034] By the term “unit” as used herein, it is meant to refer to a piece, portion or part of an apparatus that serves to perform one particular function. An apparatus may include multiple units, and may include units serving different respective functions.

[0035] The improved counter-pressure ring and unit described herein may be used with any suitable press with a foil laminating unit that includes a stamping cylinder and one or more rotating counter-pressure units. Non-limiting examples include Koenig & Bauer OptiNota H, Bobst MasterFoil, Gietz Foil Commander, and Steuer Foil-Jet.

[0036] In use, one or more than one counter-pressure unit may be present on one common drive shaft of the foil laminating unit. Additionally, one or more drive shafts may be present.

[0037] Provided herein is an improved counter-pressure unit 2 comprising at least a ring 4 and a collar 12. The collar 12 fits within the ring 4 (see Fig. 1), abutting with an inner surface 8 thereof. The collar 12 is clamped onto the drive shaft (not shown). Rotation of the drive shaft results in rotation of the counter-pressure unit 2 during operation of the foil application unit. The counter-pressure unit, or more specifically the outer surface 6 of the ring 4, contacts the substrate, thereby applying pressure thereto to assist in the foil application process. A flange or lip 10 extends around the interior circumference of the counterpressure ring, thereby providing a surface through which fasteners 18 may be inserted in order to attach the counter-pressure ring 4 to the collar 12. Small holes 14 are formed around the circumference of the flange, in order to accommodate the fasteners.

[0038] The flange 10 provides a means for attaching the ring 4 to the collar 12 by means of fasteners 18. The fasteners may be screws, bolts, pins, or other suitable means for attachment known in the art. The ring 4 is fastened to the collar 12 by fasteners 18 that are inserted through holes 14 in the ring flange 10 (see Figs. 2 and 3). In the illustrated embodiment, an elastomeric bumper 20 is also present.

[0039] In some embodiments (see. Fig. 2), the fastener 18 may be threaded only on the lower portion thereof.

[0040] As illustrated in Fig. 2, the flange 10 abuts against the collar 12 along a flange-collar slippage surface 26. Additionally, the head portion of the fastener 18 abuts against the flange along a fastener head-flange slippage surface 28. Thus, slight movement of the ring 4 relative to the collar 12 and relative to the fastener 18 is possible. The extent of the movement is determined by the size of the fastener-to- hole clearance 30.

[0041] During machine operation, as the outer surface 6 of the ring 4 comes in contact with the substrate (not shown), the ring begins to rotate relative to the collar until the fasteners 18 come into contact with solid material, and then no additional rotation is permitted.

[0042] As the driving shaft rotates, the ring 4 moves radially from the substrate contact point in a direction toward the shaft centre. There is relative motion between the mounting flange 10 and the collar 12 and the heads of the fasteners 18. Motion is permitted because the fasteners 18 are fastened with a slip fit to the mounting flange

[0043] 10.

[0044] As illustrated in Figures 4-5, in some embodiments the holes 14 have a greater diameter than that of the fasteners. This permits the ring 4 to move as the bumper 20 is deformed when pressure is applied to the drive shaft. As shown in Fig. 4, when no pressure is applied to the counter-pressure ring, the holes 14 are centered on the fastener 18. As illustrated in Fig. 5, when the counter-pressure ring is under pressure, the fastener 18 is offset in the hole 14.

[0045] In an exemplary embodiment, the hole 14 has an outer diameter of about 4.5mm, while the fastener 18 has an outer diameter of about 4mm. This allows for lateral movement of the fastener of about 0.5mm / 2 (0.25mm) in any direction. The over-travel of the ring against the stamping cylinder or upper die is about 150 microns or 0.15mm, which is within the designed clearance of 0.25mm. It is also possible for the ring 4 to be larger or smaller, as desired for the particular machine with which it is to be used. In this case, the hole size and fastener size may be increased or decreased proportionately. In an embodiment, the fastener diameter may be about 86%, 87%, 88%, about 89%, or about 90% of the diameter of the hole. In an embodiment, the fastener diameter may be about 80% to about 90% of the hole diameter, or about 85% to about 95%, or about 75% to about 95%.

[0046] In some embodiments (see e.g. Fig. 1), the collar includes an outer portion, a bumper 20, and an inner clamping portion which clamps the counter-pressure unit onto the drive shaft. The clamping portion may be of any known design in the art, for example a split-ring shaft collar (see clamping collar 24 in Figs. 6 and 8) or the inner clamping portion may be directly bolted onto the drive shaft (details not shown, but the collar is generally illustrated in Figs. 1 , 7). In an embodiment, an existing collar may be used by adding threaded holes to the collar side to allow for fastening of the ring.

[0047] In some embodiments, the fasteners 18 can alternately be extended through a bored hole 32 in the elastomer member 20. In this case, the ring 4 moves with movement in the compressed rubber. (See Fig. 7)

[0048] In some embodiments, the collar may include an elastomeric member 20 in the form of an O-ring, O-ring cord, or other forms known in the art. (see Fig. 6)

[0049] In some embodiments, spring plungers 22 are used instead of a bumper, (see Fig. 8). The spring plungers provide the desired cushioning to allow for movement of the ring 4 relative to the collar 12 and shaft. Other similar elements known in the art, such as leaf springs, may also be used.

[0050] In some embodiments, more than one counter-pressure unit may be present on a common drive shaft. The bumper or cushioning of each separate counterpressure unit compresses to allow multiple rollers or counter-pressure units, which may have different outer diameters, to simultaneously be in contact with the upper die cylinder.

[0051] In some embodiments, the total combined thickness of the substrate, foil and foil carrier may be different from one counter-pressure unit to the next. Thus, where multiple counter-pressure units are present, the bumper or cushioning allows all units to contact the respective substrates.

[0052] The fasteners may have a head that limits the flange from translating in the axial direction of the common drive shaft. Accordingly, by fastening the ring 4 with fasteners 18 on the flange 10, it is securely and releasably mounted onto the collar (save for the desired movement as described above) in two directions. As illustrated in an exemplary embodiment (Fig. 9), 6 holes 14 and 6 fasteners 18 may be present, spaced evenly around the ring 4, about 60° apart. However, fewer or more holes and fasteners may be possible in other embodiments.

[0053] A screw thread locking adhesive may be applied to prevent vibration from loosening the fasteners. If a shoulder screw is torqued correctly, no thread locker is required. However, a thread locker may be called for in accordance with safety protocols to avoid fasteners from becoming loose under vibration and falling into the machine, potentially causing damage.

[0054] Suitable materials for the ring 4 are homogenous plastic materials. Metals, thermosetting materials and hybrid materials are generally not suitable. Preferably, the material should have a slippery texture, be wear resistant, have low water absorption, and have low thermal expansion. In some embodiments, the impact strength may be poor while in others it may be good or excellent.

[0055] Suitable materials for making the ring 4 are those which can be fabricated with a precision outer diameter size and surface finish. Non-limiting examples include ABS, PEEK, ULTEM, Delrin, PVC, Polypropylene, Nylon and Polycarbonate.

[0056] The ring described herein does not need to be made from a specialized material such as Gesedur® (see EP3165365). In such case, manufacture is relatively inexpensive and relatively quick. Assembly of the ring with the collar does not require adhesive or cooling / heating steps. The ring and collar can be easily disassembled without damage to the ring.

[0057] In some embodiments, the ring may be molded, which becomes economical when producing larger quantities of, for example, at least 150 units.

[0058] In some embodiments, the ring should be able to resist deformation when exposed to temperatures as high as 105 degrees Celsius, while in other embodiments the ring needs only to resist deformation when exposed to temperatures of about 30 °C.

[0059] In some embodiments, the ring should be able to resist deformation when subject to pressure resulting from an over-travel of the counter-pressure ring against the die plate or stamping cylinder of 160 microns.

[0060] It is desirable that the ring is flexible and not brittle to allow the ring to become out-of-round under pressure, and to return to its round shape under minimal pressure. An out-of-round condition is possible since the ring is slim, and the presence of the bumper allows for slight deformation of the ring 4.

[0061] The ring may be manufactured by any suitable methods that would allow achievement of the desired ring shape. Such methods can include machining, molding, 3D printing, casting or any other methods known in the art. After manufacture, the outer surface of the ring may be machined to provide a smooth, slightly slippery surface. For example, a ring made from rubber was found not to be effective - the rubber material was not sufficiently slippery.

[0062] The critical shape is at the contact line of the roller (counter-pressure unit or ring) onto the substrate. The contact is a line of equal pressure over the width of the roller or counter-pressure unit. This means that the contact point is at the same radius to the centre of the drive shaft along this line. If the line of contact is not parallel to the drive shaft axis, there would be uneven pressure on the foil, and the transfer would not be consistent.

[0063] In accordance with machine maintenance and care, solvents such as CNBN (2-chloro-6-nitrobenzonitrile) may be used on the press. For example, the counterpressure unit (roller) may accumulate a deposit of a material that is on the bottom of the substrate, which must be periodically cleaned off. The ring material should be able to withstand exposure to such solvents.

[0064] The contact surface of the roller can have small inclusions, for example of not greater than about 0.25mm. The substrate lies between the roller (counter-pressure unit), the foil, and the upper die roller (stamping cylinder), so that these inclusions will not impact the foil transfer quality.

[0065] In an exemplary embodiment, a cast polymer ring was used that contained small voids less than about 0.25mm diameter, due to bubbles, and the foil transfer was acceptable. In a further exemplary embodiment, an extruded polymer ring was used to avoid the presence of bubbles on the ring outer surface.

[0066] The ring material should not offset any foreign material onto the substrate that will leave a mark or color.

[0067] In an exemplary embodiment, the outer diameter of the counter-pressure unit could be about 224mm which is the same as some existing counter-pressure units used in the art, so that the presently described counter-pressure unit could replace an existing counter-pressure unit in an existing sheet-fed stamping press, or so that the presently described ring could replace an existing ring in an existing counterpressure unit.

[0068] In an exemplary embodiment, the inner diameter of the ring is about 215mm. This gives a slim cross-sectional thickness of only (224-215) / 2 = about 4.5mm. The dimensions of this counter-pressure roller could be altered to result in the increase of the cross-sectional area (and increased mechanical properties), as needed.

[0069] In an exemplary embodiment, the ring has a width of about 49.62mm. This would allow the ring to be cut from a 2-inch-thick piece of plastic, which is a readily available material thickness. The plastic could then be machined and polished to achieve a finished surface.

[0070] In another embodiment, the ring may be wider, depending on the sheet-fed stamping press being used. The ring width must be shorter than the distance between two respective sheet stops or there will be interference.

[0071] In an exemplary embodiment, the flange is 6mm wide. So that foil transfer is not performed within this mounting flange area, the usable foil transfer region becomes 49.62mm minus 6mm, or 43.62mm. This will permit a foil width of about 43.62mm.

[0072] Embodiments

[0073] Embodiment 1 : A counter-pressure unit for use with a foil laminating unit of a sheetfed stamping press, the counter-pressure unit being clamped to a drive shaft and rotatable around a drive shaft central axis, and the counter-pressure unit comprising a flanged ring and a collar, wherein the flanged ring is adapted to apply pressure to sheets during foil lamination, and wherein the flanged ring is fastened to the collar by means of fasteners inserted through the flange of the ring.

[0074] Embodiment 2: The counter-pressure unit of embodiment 1 , wherein the flange comprises a plurality of holes sized slightly larger than the diameter of the fasteners, thereby permitting movement of the counter-pressure ring relative to the drive shaft and the collar. Embodiment 3: The counter-pressure unit of embodiment 1 or 2, wherein the collar comprises cushioning on an outer surface thereof.

[0075] Embodiment 4: A counter-pressure ring for use with a counter-pressure unit of a foil laminating unit of a sheet-fed stamping press, the counter-pressure unit being rotatable around a drive shaft central axis, wherein the ring comprises a flange and is attachable by means of fasteners to a collar, and wherein the attachment between the ring and the collar allows for slight movement of the ring in a direction perpendicular to the central axis of the drive shaft.

[0076] Embodiment 5: The counter-pressure ring of embodiment 4, wherein the flange comprises a plurality of holes sized slightly larger than the diameter of the fasteners.

[0077] Embodiment 6: The counter-pressure unit of any one of embodiments 1 to 3, or the counter-pressure ring of any one of embodiments 4 to 5, further comprising a bumper.

[0078] Embodiment 7: The counter-pressure unit or counter-pressure ring of embodiment 6, wherein the bumper constitutes an outer layer of the collar.

[0079] Embodiment 8: The counter-pressure unit or counter-pressure ring of embodiment 6, wherein the bumper is sandwiched between inner layers of the collar.

[0080] Embodiment 9: The counter-pressure unit or counter-pressure of embodiment 6, wherein the bumper is sandwiched between the collar and the drive shaft. Embodiment 10: The counter-pressure unit of any one of embodiments 1 to 3, or the counter-pressure ring of any one of embodiments 4 to 5, further comprising spring plungers adapted to provide cushioning to allow for movement of the ring relative to the collar and the drive shaft.

[0081] Embodiment 11 : A method for making a counter-pressure ring as defined in claim 4, comprising the steps of: a) selecting a plastic material; b) casting, molding, 3-D printing or machining the plastic material; and c) machining an outer surface of the counter-pressure ring.

[0082] The embodiments of the invention disclosed herein are exemplary only, and various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.

Claims

We claim:

1. A counter-pressure unit for use with a foil laminating unit of a sheet-fed stamping press, the counter-pressure unit being clamped to a drive shaft and rotatable around a drive shaft central axis, and the counter-pressure unit comprising a flanged ring and a collar, wherein the flanged ring is adapted to apply pressure to sheets during foil lamination, and wherein the flanged ring is fastened to the collar by means of fasteners inserted through the flange of the ring.

2. The counter-pressure unit of claim 1 , wherein the flange comprises a plurality of holes sized slightly larger than the diameter of the fasteners.

3. The counter-pressure unit of claim 1 , wherein the collar comprises cushioning on an outer surface thereof.

4. A counter-pressure ring for use with a counter-pressure unit of a foil laminating unit of a sheet-fed stamping press, the counter-pressure unit being rotatable around a drive shaft central axis, wherein the ring comprises a flange and is attachable by means of fasteners to a collar, and wherein the attachment between the ring and the collar allows for slight movement of the ring in a direction perpendicular to the central axis of the drive shaft.

5. The counter-pressure ring of claim 4, wherein the flange comprises a plurality of holes sized slightly larger than the diameter of the fasteners.

6. A method for making a counter-pressure ring as defined in claim 4, comprising the steps of: a) selecting a plastic material; b) casting, molding, 3-D printing or machining the plastic material; and c) machining an outer surface of the counter-pressure ring.

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