GB2255317A - Foil blocking dies - Google Patents

Abstract

A foil blocking assembly comprises a die (24) mounted on a substrate (26), adapted to be secured round the circumference of a cylinder (12). <IMAGE>

Description

Foil Blocking Dies This invention relates to the process of foil blocking, and -in particular to dies for use in a foil blocking process.

In foil blocking, a thin coating of a decorative foil is transferred by heat and pressure from a carrier film onto a surface to be decorated by pressing a heated metal die against the surface, with the foil interposed between the die and the surface. The foil is supplied in the form of a laminate, with heat and pressure sensitive adhesive on one side of a decorative layer, a carrier layer on the opposite side of the decorative layer, and a release agent between the carrier layer and the decorative layer so that the two can be separated once the decorative layer has been adhered to the surface.

Foil blocking is conventionally carried out as a flat-bed process, with the die being mounted on a flat bed and the surface to which the decorative layer is to be applied (hereinafter referred to as print material) being mounted on the surface of an impression cylinder. The flat bed with the die moves backwards and forwards relative to the impression cylinder, along a path which is tangential relative to the cylinder. A band of foil is supported above the die. As the die approaches the cylinder surface, the foil is pressed by the die (which has been heated to a suitable temperature) against the print material on the cylinder, and the decorative layer is transferred to the print material. The print material is usually paper or card, but may be of plastics or other materials.When the die moves away from the cylinder, the release agent allows the carrier layer to be released from the decorative layer.

In order to avoid the inherent slowness of a flat-bed process, it has been proposed to carry out foil blocking by a rotary process. Hitherto, this has required the construction of cylinders on which the foil blocking dies are engraved. The construction of such cylinders is very expensive, and because the die surface is integral with the body of the cylinder, there are often problems in ensuring correct registration of the die surface with the print material.

According to the present invention, there is provided a foil blocking die mounted on a substrate, which substrate is adapted to be secured around the circumference of a cylinder.

The use of a die which can be mounted on a cylinder surface for operation, but can be dismounted from the cylinder surface has the particular advantage that the higher operating speeds possible with rotary equipment, as compared to reciprocating equipment, can be obtained.

Furthermore the cost of preparing each die is substantially less than when the die is a permanent part of the cylinder, and the die position can easily be adjusted on the cylinder to ensure correct registration.

The die may occupy any proportion of the cylinder circumference, and in appropriate cases there may be more than one die mounted around the cylinder circumference, and there may be several dies mounted along the length of the cylinder. The die or dies may be mounted on a flexible belt which can be pulled tight around the cylinder. It is in the nature of foil blocking dies that they have a relief surface and as a result that they have a significant thickness. The die itself may however be sufficiently flexible to follow the contour of the cylinder.

Alternatively, if the die is rigid, then it may be formed with an arcuate surface matching the curvature of the surface.

The die can conveniently be manufactured from copper or aluminium, possibly by a photographic technique using a suitable resist.

According to a second aspect of the invention, there is provided a foil blocking die having means by which the die can be secured around the surface of a cylinder in such a way that the operative surfaces of the die are all at substantially at the same distance from the cylinder axis.

This feature allows the foil blocking process to be carried out with the die rotating, rather than reciprocating as has been the case in the prior art.

It is a requirement of the foil blocking process that the die be maintained at an elevated temperature in order to activate the adhesive which fixes the foil to the print material. In a reciprocating process, the heated die remains at all times close to the foil, and therefore there is a tendency for the foil to degrade before the die approaches and closes with the impression cylinder.

However in a rotary process the heated die rotates around a circle, and for much of the time is some distance away from the foil. The foil is therefore only heated at the time when it is in contact with the die. If necessary, a heat shield can be provided to protect the foil on the feed side from radiant heat emitted by the rotating die cylinder.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a foil blocking process using a foil blocking die in accordance with the invention; and Figure 2 is a section through the apparatus of Figure 1, on the lines I-I.

Figure 1 shows two counter rotating cylinders 10 and 12 which are mounted parallel to one another and define a nip 14 between them. The cylinder 12 will be referred to as the die cylinder and the cylinder 10 as the impression cylinder.

The apparatus is set up to provide foil blocking on sheet fed print material which is picked up from a feed stack 16, secured around the surface of the impression cylinder 10, fed through the nip 14 and deposited on a delivery stack 18. The transport of these sheets is carried out using conventional handling machinery which forms no part of this invention.

A foil band 20 passes through the nip 14 in the direction indicated by an arrow 22. A foil blocking die 24 is mounted on a belt 26, the belt being secured around the circumference of the die cylinder 12. The die 24 may be formed integrally as part of the material of the belt 26, or may be formed separately and then be permanently secured to the belt. The belt will be held tightly around the circumference of the cylinder, with the two free ends of the belt being clamped by a tensioning arrangement 28 which is mounted on the circumference of the cylinder.

The print material feeding mechanism will be set up in conjunction with the cylinder rotation so that a sheet of print material passes through the nip 14 at the same time as the die 24 passes through the nip. As a result the die will press a section of the foil band 20 against the sheet of print material to leave a layer of foil on the print material in accordance with the pattern on the die 24. As can be seen on the left hand side in Figure 1, the print material in the stack 18 carries a pattern on its upper surface which matches that of the die 24, and as the foil band 20 leaves the nip 14, a section of the foil corresponding to the pattern of the die 24 will be missing as indicated in dotted lines at 30.

As previously mentioned the foil band itself is a laminate including a carrier layer and a metal or pigment layer. It is only the pigment layer (together with underlying adhesive) which will be transferred to the print material; on the left hand side of the nip 14 there will still be a continuous band present but the metal or pigment part of the foil laminate will have been removed as indicated at 30.

Figure 2 shows the situation as a sheet 32 of print material is having foil applied to it. The die 24 is passing through the nip 14, and the effective diameter of the surface of the die 24 is such that pressure will be applied to the foil and to the print material to apply the foil to the print material.

The die 24 is heated, possibly by high frequency induction heating. The thermal buffer formed by the mass of the cylinder 12 will help to ensure that a constant temperature is maintained at the surface of the die 24, in accordance with the desired process conditions. It is desirable if the heating effect is however concentrated at the surface of the die, rather than being constant around the surface of the cylinder. If this is achieved, there will be very little heating effect on the foil band 20 during the time when the die is absent from the nip 14. A heat shield 29 can be positioned as shown to protect the fresh foil from being heated before it enters the nip.

Although the die 24 is shown as extending over only a small arc of the cylinder circumference, it can in fact extend over a very much greater part of the cylinder circumference or alternatively two or more separate dies may be arranged at correctly located positions around the cylinder circumference.

In prior art flat-bed foil blocking processes, the flat-bed which carries the die has to be reciprocated between a position beneath the impression cylinder and a position away from the cylinder. This reciprocating motion requires considerable energy input and gives rise to considerable noise. Furthermore, the time spent by the bed in its return cycle is wasted time. These disadvantages are avoided by the use of a rotary apparatus because there is no reciprocating motion and because the only wasted time occurs when a non-impression area of the die cylinder is passing through the nip.

The invention thus provides an effective way of speeding up the foil blocking process.

Claims (15)

Claims

1. A foil blocking die assembly in which a foil blocking die is mounted on a substrate, which substrate is adapted to be secured around the circumference of a cylinder.

2. An assembly as claimed in Claim 1, wherein the substrate carries a plurality of dies.

3. An assembly as claimed in Claim 1 or Claim 2, wherein the die or dies extends around the whole circumference of the cylinder.

4. An assembly as claimed in Claim 1 or Claim 2, wherein the die or dies extends around part only of the circumference of the cylinder.

5. An assembly as claimed in any one of Claims 2,3 or 4, wherein the dies are axially spaced along the length of the cylinder.

6. An assembly as claimed in any one of Claims 2,3 or 4, wherein the dies are circumferentially spaced around the circumference of the cylinder.

7. An assembly as claimed in any preceding claim, wherein the die or dies are' mounted on a flexible belt which can be pulled tight around the cylinder.

8. An assembly as claimed in any preceding claim, wherein the die or dies are sufficiently flexible to follow the contour of the cylinder.

9. An assembly as claimed in any one of Claims 1 to 8, wherein the die is rigid and is formed with an arcuate surface matching the curvature of the cylinder.

10. An assembly as claimed in any preceding claim, wherein the die or dies are manufactured from copper or aluminium by a photographic technique using a suitable resist.

11. A foil blocking die having means by which the die can be secured around the surface of a cylinder in such a way that the operative surfaces of the die are all at substantially at the same distance from the cylinder axis.

12. A foil blocking machine having a foil blocking die assembly as claimed in any one of Claims 1 to 10 or a foil blocking die as claimed in Claim 11, wherein a heat shield is provided to protect the foil on the feed side of the machine from radiant heat emitted by the rotating die cylinder.

13. A foil blocking die assembly substantially as herein described with reference to the accompanying drawings.

14. A foil blocking die substantially as herein described with reference to the accompanying drawings.

15. A foil blocking machine substantially as herein described with reference to the accompanying drawings.