Background of the invention Hot foil stamping is a process by which decorative foils are applied to a substrate such as a label, in place of, or in addition to ink. Platen presses may be used for relatively lower speed applications. However, for high speed applications where a high throughput of stamped product is required, such as in the manufacture of labels for packaged products, rotary foil stampers are used. Existing rotary foil stampers comprise a solid brass cylinders defining a cylindrical surface onto which with a pattern is cut using an NC machine or the like and that pattern determines the pattern of foil which is transferred to the substrate.

Being made of machined solid brass, rotary foil stampers are expensive and relatively time consuming to manufacture. Typically each cylinder costs in the order of $2,000 to $3,000, depending on the size of the cylinder and the complexity of the pattern. The cylinders are also heavy and are thus expensive to transport.

The existing cylinders are also wasteful since of materials, since each cylinder can only be used to foil stamp one pattern.

It is the aim of the present invention to address and alleviate some or all of the above mentioned problems of the prior art.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Summary of the invention In a first broad aspect the present invention provides a rotary stamping cylinder comprising a base cylinder and a copper plate engaged around the exterior of the

cylinder and clamped thereto by means of mechanical clamping means at each axial end of the cylinder.

More particularly, according to one aspect of the present invention there is provided a stamper for rotary hot foil stamping comprising: a base cylinder defining a longitudinally extending slot in an exterior cylindrical surface of the cylinder and further defining chamfered circumferential edge portions at each end of the cylinder; a metal plate wrapped around the cylinder, one end of the metal plate being inserted into the longitudinally extending slot; and clamp means clamped to each end of the cylinder the clamp rings defining a circumferential protrusion defining an interior edge portion configured to generally mate with the chamfered portion of the edge of the cylinder for clamping edge portions of the metal plate to the base cylinder and securing the plate to the base cylinder.

Typically the metal plate will be from O. 5mm to l. Omm in thickness most preferably about 0.8mm and will be formed from copper as copper has optimal heat transfer characteristics, although other metals could be used. The pattern for the foil stamping process may be etched on the copper using any known chemical etching process.

The present invention has a number of substantial advantages over the prior art discussed in the background of the invention. A copper plate can be manufactured and etched for a fraction of the price of the existing solid brass cylinders. The base cylinders may be re-used many times as it is only necessary to change the copper plate when the pattern is to be changed. It is only necessary to purchase the copper plates themselves or images and not the entire cylinders as in the prior art which results in substantial cost savings.

A further significant advantage is that the copper plates weigh considerably less than the solid brass cylinder typically around 500g compared with 20kg therefore the costs of freighting the copper plates from a manufacturer to a customer are much less than the costs for air freighting a solid brass cylinder.

The present invention also encompasses a metal plate for use with a base cylinder embodying the present invention to form a cylinder for rotary hot foil stamping as well as a base cylinder and clamp means for receiving such a metal plate.

Brief description of the drawings Specific examples of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows an assembled rotary foil stamper embodying the present invention; Figure 2A is a side view of a base cylinder which forms part of the rotary stamper shown in Figure 1; Figure 2B is an enlarged view of a chamfered edge portion of the base cylinder of Figure 2A.

Figure 2C is an end view of the base cylinder of Figure 2A; and Figure 2D is an enlarged view of a slit defined in the base cylinder shown in Figure 2C; Figure 3A is an end elevation of a clamp ring which forms part of the rotary foil stamper of Figure 1 ; Figure 3B is a cross-sectional view on lines 111-111 of Figure 3A; Figure 3C is an enlarged view of a protrusion defined by the clamp ring illustrated in figure 3B; Figure 4 is a plan view of a copper plate; and Figure 5 is a schematic side view of a copper plate pre-curved prior to application to the base cylinder of Figures 2A to 2D.

Detailed description and preferred embodiment Referring to the drawings Figure 1 shows an assembled rotary stamper 10 embodying the present invention.

The stamper comprises a base cylinder 12 typically made of brass, around which is wrapped a copper plate 14. Two end clamp means in the form of clamp rings 16 are

bolted or screwed to axial ends 18 of the base cylinder 12 to lock the copper plate 14 in place.

Figures 2A to 2D illustrate the base cylinder of the stamper 10 in more detail.

The base cylinder 12 includes a central cylindrical portion 20 having a length of about 300mm and a diameter of approximately 11 lmm. and defining a central axis or centre line 20A The central cylindrical portion defines a cylindrical outer surface 20. Clearly the particular dimensions of the cylinder 20 may be varied. A co-axial end cylindrical portion 22 of lesser diameter (typically about 50mm) protrudes from each axial end 18 of the base cylinder 17.

As is best seen in Figure 2B which is an enlarged view of the top right hand chamfered edge, as oriented in Figure 2A, the distal edges 24 of the central cylindrical portion adjoining the axial ends 18, are chamfered at an angle a of approximately 15° to the surface of the central cylindrical portion which is parallel to the centre line 20A of the cylinder. The chamfered edge 24 is about 5mm long.

Figure 2C illustrates a series of threaded holes defined in the axial ends 18 of the cylinder being four inner holes 26, and four outer holes 28 spaced at 90° apart, the outer holes 28 being used for mounting the clamp rings 16 to the base cylinder 12, as will be described hereinafter. Figure 2C also illustrates a central bore 29 by means of which the cylinder 10 may be mounted on a rotary stamping apparatus, and about which bore, the stamper 10 rotates, in use.

Also formed in the cylinder and best shown in Figure 2D is a longitudinally extending slit 20B which has a depth D of approximately 6mm and which extends along the full length of the cylindrical surface 20 parallel to the centre line 20A. As shown in Figure 2D, depth-wise the slit extends at an angle ß of 30° to the radius R of the cylinder, and at the surface 20 of the cylinder opens at an angle y of 60°.

Figures 3A to 3C illustrate the clamp rings 16 which are generally annular defining a central circular aperture 31 having a diameter which is slightly larger than the end cylindrical portions 22 and which define four holes 34 at the same radius and spacing as the four holes 28 defined in the axial ends 18 of the base cylinder for use in fixing the clamp rings 16 to the axial ends 18 of the base cylinder using bolts, screws or the like.

Figure 3C is an enlarged detail view which illustrates that one face of the clamp ring defines a circumferentially extending protrusion 30 which is generally triangular in cross section and defines an angled face 32 which is oriented at the same 15° angle a as the chamfered edge portion 24 of the cylinder.

Figures 4 and 5 show the copper plate 14 in more detail. The copper plate is most preferably about 0.8mm in thickness but may range from 0. 5mm to l. Omm in thickness so as to be"generally flexible"but not flimsy, in the sense that it can be wrapped around the base cylinder albeit with the use of some force. Although a copper plate is described and preferred since, copper has optimal heat transfer characteristics, other metals could be used. The pattern for the foil stamping process may be etched on the copper using any suitable known chemical etching process.

The plate 14 is dimensioned to fit over the base cylinder 17. It has a leading edge 34 and a trailing edge 36 and it carries an image 38. A number of folds 40,42, are formed in the plate 14. With reference to Figure 5 the copper plates is bent and curves slightly and the leading edge 34 is bent to define a"hook"which can engage in the slit 20B as the copper plate is wrapped around the base cylinder. The trailing end 36 is then wrapped around the base cylinder and, if necessary, cut so that the trailing end abuts against the leading edge of the plate but does not overlap the same. The clamp rings 16 are then used to secure the copper plate to the cylinder with the angled face 32 securing the longitudinal edges 44 of the copper plate between that angled face and the chamfered edge portion 24 of the cylinder.

In use the present invention has been found to be extremely reliable and retains the copper plate in position on the cylinder in a secure fashion with the copper plate held flat against the cylinder by the action of the clamp rings 16.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.