Method of manufacturing a security item

A method of manufacturing a security item comprises extruding or casting a polymer plastics substrate and, during the forming process, introducing a security thread into the substrate. The security thread is embedded to different depths in the substrate so as to generate a windowed effect.

FIELD OF THE INVENTION

The invention relates to methods for manufacturing a security item which include forming a polymer plastics substrate.

DESCRIPTION OF THE PRIOR ART

Conventionally, security items having a polymer plastics substrate have been laminated structures secured against fraudulent reproduction and counterfeiting using suitable security print and the like. This is an expensive process. WO-A-99/46133 describes a coextrusion process and in one option a security thread is incorporated into the coextruded layers. However, this is not always satisfactory since the thread will be positioned on the surface of the substrate and can be removed or altered.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a method of manufacturing a security item comprises forming a polymer plastics substrate and, during the forming process, introducing a security thread into the substrate, and causing the security thread to be embedded to different depths in the substrate so as to generate a windowed effect.

We have found surprisingly that it is possible securely to embed a security thread in the substrate so as to generate a windowed effect without having to rely on conventional lamination. This is very difficult to counterfeit or fraudulently reproduce and until now has only been attempted with paper substrates.

There are a variety of ways in which the method can be implemented. In one approach, the forming process comprises extrusion through an extrusion die. In this case, the security thread may be introduced downstream of the extrusion die, while the substrate is still molten, the method further comprising selectively varying the depth of the thread in the substrate.

Conveniently, when the thread is pushed into the substrate, the security thread is preformed with an undulation generally corresponding with the pushing positions. This reduces the risk of breakage of the thread during the pushing process.

Alternatively, the thread may be fed through the extrusion die and oscillated in a direction with a component orthogonal to the substrate thickness. This will be more difficult to achieve than the process outlined above.

Further, in accordance with a second aspect of the present invention, we provide an elastomeric security thread.

In a second approach, the forming process comprises casting in which the plastics polymer is supplied onto a release substrate through a nozzle, a thread also being supplied, typically also, but not necessarily, through the nozzle.

In one example, the thread is oscillated in a direction with a component orthogonal to the substrate thickness.

By suitably controlling the manner in which the thread is embedded, the thread can be selectively exposed on only one side of the substrate or on both sides.

In other examples, the release substrate has recesses corresponding to the window effect, the security thread being guided over the recesses.

This is more straightforward than oscillating the thread and allows the windows to be more accurately defined.

In order to ensure that the thread is securely held on the release substrate, preferably the substrate is perforated, the method further comprising applying a vacuum to the perforations in the substrate to hold the thread on the substrate.

In some cases, the release substrate comprises an elongate web or even a plate but in preferred examples it comprises an endless belt.

The advantages of the invention are that there is no need to laminate plastics materials to achieve the embedded thread nor any need to use adhesives. In many cases, a constant thickness can be achieved across the resultant web enabling products to be produced in roll format. Furthermore, the resulting product is difficult to counterfeit and this reduces the need to provide substantial security printing on the substrate.

Although the invention has been described above in connection with the supply of a single thread, it will be readily apparent that more than one thread could be embedded, typically laterally spaced across the release substrate.

Following production of the security item, personalized indicia can be provided in a conventional manner, typically using a dye sublimation technique. This is described in more detail in WO-A-99/46133.

The invention is particularly suited for manufacturing items with thicknesses of 50-800 microns using the casting process and 30-200 μm using extrusion.

The invention is generally applicable to banknotes, cheques (whether bank or travellers), bonds, share certificates, licences, some types of identity cards, smart cards, passports, visas tickets, passbooks, vouchers, deeds, tamper revealing seals and labels, brand authenticity labels and the like. Indeed, any security item based on a plastics material could be implemented using this invention. Both flexible and rigid plastics substrates can be used, depending on the intended application.

DESCRIPTION OF THE EMBODIMENTS

In the process shown inFIG. 1, a plastics polymer3is extruded through an extrusion die1. A non-metallised, polyester security thread4is fed through the extrusion die1so that it is automatically embedded within the extruded material3. The extrusion is then fed to cooling rollers6and wound onto a take-up roll7.

In order to achieve a windowed effect, the thread4is oscillated in a vertical direction, i.e. orthogonal to the thickness of the substrate, as shown at8so that the thread will periodically be exposed above the surface of the polymer material and then embedded within it. In this way, the windowed effect can be achieved when viewed from above.

FIGS. 2A and 2Billustrate an alternative extrusion process. For simplicity, those elements ofFIG. 2Awhich correspond to similar elements inFIG. 1are given the same reference numerals and will not be further described. In this case, the thread4is supplied from a supply roll4′ to the extruded polymer3downstream of the extrusion die1. The polymer will still be molten at this point. To achieve the windowed effect, the thread is heated at2to bring it to a similar temperature to the film3and then supplied to the extruded plastics3at a point9at which it contacts rotating, rollers6A,6B. The lower roller6B is chilled and carries a relief pattern defined by projections11. As the rollers6A,6B rotate, projections on the rollers periodically contact the thread4and push it into the molten plastics3. In other regions, the thread4will lie on the surface of the molten plastics3. In this way, the windowed effect is achieved. By bringing the thread4into contact with the extruded film at9, the majority of the stretching is complete and so less stretchable threads can be used than in theFIG. 1example.

FIG. 3illustrates an alternative, casting process. In this process, plastics polymer is provided in a reservoir20defined between a back plate21and a knife plate22, the knife plate22defining with an opposed roller23a nozzle24(FIG. 4) through which polymer can exit, being carried on a release substrate10such as silizonized paper supplied from a roll12.

The cast material is then heated at50and cooled at6before being wound up on to take-up roll7.

As the thread4is fed through the nozzle24, it is oscillated in a vertical direction as shown at25,26.

The resultant product is shown schematically in cross-section inFIG. 3Awhere it will be seen that the thread4exhibits a vertically undulating path in the cured polymer27thus generating the desired windowed effect.

The oscillation of the thread is shown in more detail in FIG.4. When the thread is at its nominal central position30(FIG.4A), it will pass centrally through the nozzle24and be fully embedded in the plastics polymer27.

When the thread is oscillated to its lower position31(FIG.4B), it will contact the release substrate10and thus will be exposed on the bottom surface of the plastics polymer27.

When the thread is oscillated to its uppermost position32(FIG.4C), it will contact the underside of the knife plate22and be exposed on the upper surface of the plastics polymer27.

If therefore the thread is oscillated between positions i and iii inFIG. 4C, the windowed effect will be visible from both sides of the resultant substrate. Alternatively, the thread can he oscillated between positions i and ii or between ii and iii to achieve the windowed effect on just one side of the substrate.

Examples of suitable plastics polymer materials include thermoplastics and thermoset polymers such as polyvinylchloride (PVC), polyethylene terephthalate (PET), polypropylene terephthalate (PPT), polyurethane (PU), polybutylene terephthalate (PBT), polypropylene (PP) and polyethylene (PE).

In theFIG. 2example, the thread4is pushed into the polymer film9by the rollers6′. There is a risk that with certain threads, this could cause breakage of the thread. To overcome this, the system shown inFIGS. 5 and 6could be used. In this case, a security thread62is stored on a bobbin60and fed to a nip61between a support belt66and a pinch roller64. The support belt66is formed with a series of vacuum slots65substantially equally spaced apart and having perforations as shown in FIG.6. The support belt66is slidably mounted about the casting roll63and is drivingly entrained about a drive roller67.

As in theFIG. 2example, polymer70is extruded through a nozzle71onto the support belt66.

The stationary casting roll63has a cut-away portion72which communicates with a vacuum source (not shown).

In use, the support belt66is rotated about the casting roll63in a clockwise direction while the pinch roller64is rotated in an anti-clockwise direction at a faster peripheral rate so as to draw the security thread62off the bobbin60. This enables the security thread to be preformed into the corrugated or undulating form shown in FIG.6. The principle behind this is illustrated inFIGS. 7A-7C. Initially, a leading end of the thread is fixed to the support belt66as shown at75(FIG. 7A) and this fixing is achieved by virtue of the vacuum applied through an adjacent recess65. With the leading end of the thread fixed, a relatively fast rotation of the pinch roller64pushes a length of the thread62forward so as to form a loop76(FIG. 7B) and, due to movement of the support belt66, the next recess65is exposed to the vacuum thus fixing the thread62at a position77.

With the thread62preformed into a corrugated profile, it passes beneath the nozzle71so that a layer of molten polymer78is extruded onto the support belt66. Cooling is provided from above the thread62(not shown).

The extruded polymer78with the embedded thread62is then conveyed towards the drive roller67from where it is separated in a conventional manner from the support belt66for subsequent downstream processing.

FIG. 8Aillustrates an alternative casting process similar to the examples ofFIGS. 2 and 3. Those components which are the same as inFIG. 3have been given the same reference numbers and will not be described further. In this case, in contrast toFIG. 3, the release substrate now constitutes an endless belt80entrained about rollers23,81, one of which is driven by a motor (not shown).

The endless belt80has a number of projections11defining a windowed profile, an example of which is shown in FIG.8B. This is similar to FIG.2and avoids the need to oscillate the thread as shown inFIGS. 3 and 4. The thread4is supplied from a bobbin85.

The belt80is typically made of stainless steel or a plastics material such as Kevlar and is treated so as to have release properties. For example, it may be siliconised or provided with a PTFE coating.

In use, the thread4is fed to the nozzle24defined by the knife plate22and roller23in alignment with the projections11. Polymer is supplied to the belt through the nozzle24.

After heating50and cooling6, the finished cast product is separated from the belt80and wound onto the take-up roll7.