AU2017101420A4 - Functional straps for voiding items of value - Google Patents

Abstract

The present invention relates to deterring the theft of valuable items by causing damage or an indelible alteration to the items if stolen. Accordingly, a first aspect of the present invention provides a system for voiding items of value to deter theft, the system comprising: a strap for retaining a number of the items together, the strap having a destructive section for damaging the items in response to an input triggered by an event predetermined as indicative of theft. Fr /4,0 ,o Figure 1

Description

Functional Straps for Voiding Items of Value Field of the Invention [0001] The present invention relates to deterring the theft of valuable items by causing damage or an indelible alteration to the items if stolen.

Background of the Invention [0002] Valuable items are naturally prone to theft and often kept locked in secure locations. Resourceful thieves may circumvent locks and other security measures to successfully steal the goods, but damaging or marking the goods as stolen provides a significant deterrent. The value of the stolen items is voided or at least greatly reduced, and may also mark and incriminate the thieves. For example, clothing retailers often attach a security tag to items which stain the fabric with a dye in the event they are removed from store prior to purchase.

[0003] Dye packs are also used to mark banknotes that have been stolen. SecurityPac TM (https://www.3sisecurity.com/products/securitypac) made by ICI Security Systems is a dye pack inserted somewhere in the middle of a stack of banknotes. Initially, these devices were constructed of rigid plastic and readily detected by skilled thieves. More recently, the dye is housed in a thin flexible package so that the stacked bundle of banknotes is nearly indistinguishable from a ‘normal’ bundle of banknotes.

[0004] Bank tellers will have a number of these dye packs near their work stations at all times. These packs are maintained in a ‘safe’ mode by attachment to a specialised magnetic plate. In the event of a robbery, the teller will attempt to surreptitiously slip one of the dye packs into the money bag without the thief noticing. The dye pack remains dormant while the moneybag is still within the bank, however a small radio receiver activates upon removal from magnetic plate. A hidden radio transmitter at each entrance to the bank signals the radio receiver in the dye pack as the money bags are removed from the premises. The dye pack usually counts down a timer to ensure that the thief is a good distance from the bank before the dye pack explodes.

[0005] When the dye pack explodes, it releases an aerosol of red smoke, red dye (1-methylamino-anthraquinone) and, in some cases tear gas. The dye pack also ignites and burns at a temperature of about 200°C to frustrate efforts to remove it from the money bag. The tell-tale red smoke, red dye and tear gas may compel the thief to discard the bag allowing the authorities to retrieve the money. The red dye is formulated to stain and mark the banknotes as stolen and also indelibly stain the thief’s clothes or any exposed skin to indicate their involvement in the robbery.

[0006] Some organisations equip the money storage bags with dye packs as well as GPS trackers. The dye boxes used by Brinks (http://www.brinks.ca/solutions/dye-box.php-1) are an example of these devices. These are not bags, but rather rigid containers with a hard, lockable exterior shell containing the banknotes (or other valuables), a GPS tracking device and non-toxic dye pack. Any tampering or damage to the box such as exposure to extreme heat or cold, triggers the dye pack to permanently mark the banknotes and stain the thief. This type of secure container is very difficult to open without activating the dye packs. Only authorised staff at an authorised location can successfully remove the banknotes without activating the dye pack.

[0007] Unfortunately, the dye packs are not a strong theft deterrent to some criminals, as banknotes stained with dye can often be used in general circulation. The pattern and area covered by dye on a banknote can vary widely (from more than 90% to less than 1%) in large splotches right through to narrow bands or lines along the edges. To add to the difficulty of detecting dyed areas, criminals have been known to bleach dyed banknotes in order to reduce the intensity of the dyed areas. To better highlight the dye stains some organisations, such as Sweden’s RiksBank, use a number of different dye colours to better signify that the banknote is stolen (see http://www.riksbank.se/en/Notes-coins/Banknotes/Security-ink-dyed- banknotes/). However, due to the amount of handling most banknotes receive, they can often be soiled or stained by other coloured contaminants through regular use. For example, some food stuffs or spilled liquids can dye or change the colour of a banknote in some areas. This is more of an issue for porous paper banknotes than polymer banknotes, although both types of banknotes now have similar over-coating layers.

[0008] Banknotes that have been a little stained at corners or edges can still be used if these areas are carefully removed. Generally the public will simply view this as a slightly torn or damaged banknote.

[0009] The variability of dye coverage across the banknote is due to the fact that the dye packs are placed in the middle of the bundle of banknotes and the liquid dye flows largely under the action of gravity once it is release. This coupled with the improvement in modern over-coating layers (discussed above) reduces the ability of the dye to stain the banknotes.

[0010] An added inconvenience associated with dye packs relates to the need for cleaning up residual dye after a robbery attempt. For example, the dye packs within cash containers in ATMs will usually release their dye during a robbery tampering attempt and leak from the container to the floor and surrounding areas. Cleaning away the residual dye is difficult and time consuming for staff.

[0011] Any reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

Summary of Invention [0012] Accordingly, a first aspect of the present invention provides a system for voiding items of value to deter theft, the system comprising: a strap for retaining a number of the items together, the strap having a destructive section for damaging the items in response to an input triggered by an event predetermined as indicative of theft.

[0013] In a second aspect, the present invention provides a method of damaging items of value to deter theft, the method comprising the steps of: retaining a number of the items together with a strap having a destructive section for damaging the items in response to an input; and triggering the input in response to an event predetermined as indicative of theft.

[0014] In a third aspect, the present invention provides a strap for holding items of value together in a bundle, the strap comprising: a destructive section for damaging the items in response to an input, the input being generated in response to an event that is predetermined to be indicative of theft of the items.

[0015] Using a strap to void or damage items is unexpected and therefore far less likely to be circumvented by thieves. In the context of banknotes, the straps around bundles of notes have traditionally had no other purpose apart from holding the bundled notes. Thieves would be unsuspecting of the straps and instead focus on locating more traditional deterrents like the dye packs discussed above. This element of surprise greatly improves the chances the notes will be damaged in the intended way. As for the user (i.e. banks), use of a strap is part of normal process and does introduce additional steps to banknote handling.

[0016] Preferably the items are documents of value and the strap is configured to hold a plurality of the documents stacked into a bundle, the destructive section having a blade edge to initiate a cut into an edge section of the documents and shrink material that is sensitive to an input for reducing the strap length in response to said input, the system further comprising a trigger configured to apply the input to the shrink material in response to an event predetermined as indicating theft of the documents.

[0017] Optionally, the input is heat.

[0018] Preferably the strap further comprises conductive material configured for connection to electrical power source such that the input heat is generated by resistive heating of the conductive material.

[0019] A preferred form of the system further comprises a container for holding the bundle of documents held by the strap wherein the input heat is provided by a steam generator configured to release steam in response to unauthorised attempts to open the container.

[0020] Optionally, the input is electromagnetic radiation of a specified wavelength such as UV.

[0021] In a preferred form, the system further comprises a container for holding the bundle of documents held by the strap wherein, the container has an emitter to irradiate the shrinkable material with the radiation of specified wavelength upon unauthorised attempts to open the container.

[0022] Optionally, the input is a specified gas such as oxygen, exceeding a threshold concentration level such as atmospheric 02 levels.

[0023] A preferred form of this system further comprises a container for holding the bundle of the documents, wherein the container has a source of the gas configured to release the gas upon unauthorised attempts to open the container.

[0024] Optionally, the input is cold or a reduction in heat from a heat sink.

[0025] A preferred form of this system further comprises a container to hold the bundle of documents held together by the strap, wherein the container has a store of refrigerant configured for release upon unauthorised attempts to open the container.

[0026] Preferably the strap is configured to contact the items of value during transport or storage, and the destructive section has conductive material for connection to an electrical power source to provide a current path to resistively heat the strap to a temperature that causes irreversible damage to the items of value.

[0027] In a further preferred form, the items of value incorporate a polymer and the conductive material which heats the strap to a temperature above the melting temperature of the polymer. In this form of the system, the destructive section also has heat sensitive shrinkage material to increase contact pressure between the strap and the items of value in response to resistive heating by the conductive material.

[0028] Preferably, the strap has a piercing element to pierce at least some of the items in response to the resistive heating of the conductive material. Preferably, the piercing element is a blade. In this form, the blade may cut a portion of at least one item in response to the increased contact pressure.

[0029] Optionally or additionally, the blade cuts a portion of at least one item by drawing across the at least one item in response to the heat sensitive shrinkage material reducing the strap length or change in shape.

[0030] Preferably, the blade forms part of the current path.

[0031] In some embodiments, the strap further comprises a flexible printed battery to provide the electrical power source.

[0032] Preferably, the strap further comprises a trigger mechanism to initiate the resistive heating in response to an event predetermined to indicate an attempted theft of the items of value.

[0033] In some embodiments, the strap further comprises a clasp with a locking mechanism for authorised removal of the strap from the items.

[0034] The events may be one or more of: unauthorised opening of a container holding the items contacting the strap; unauthorised removal of the items bound by the strap from a building; unauthorised attempts to unlock the clasp; an input signal transmitted by an authorised party; and an input signal transmitted by a weight sensitive surface supporting the items bound by the strap.

[0035] Preferably, the strap has flammable material adjacent to the conductive material, the flammable material having an ignition temperature lower than a maximum temperature of the conductive material during resistive heating.

[0036] Preferably, the strap has a substrate of flexible material to support the conductive material, wherein the flammable material is a coating on the substrate adjacent the conductive material. The flammable coating composition may be selected from one or more of perchlorates, alkali metals, magnesium and encapsulated forms of these.

[0037] Preferably the items are security documents with a polymer substrate stacked into a bundle and held together by the strap such that the conductive path contacts an edge section of each of the documents. In a further preferred form, the security documents are polymer banknotes with a biaxially orientated polypropylene (BOPP) substrate. In this form, the conductive material is preferably configured to heat to a temperature of at least 130^. Furthermore, it is preferable if the conductive material resistively heats to 130^ in less than 5 seconds from activation of the trigger mechanism.

[0038] In some embodiments, the shrink material is a shape memory polymer. Optionally, the shape memory polymers are sensitive to UV light (photomobile polymer).

[0039] In other embodiments, the shrink material is a shape memory alloy. Optionally, the shape memory alloy is nitinol.

[0040] Preferably, the shape memory alloy is the conductive material.

[0041] Throughout the description and claims of the specification, the word “comprise” and variations of the word, such as “comprising” and “comprises”, is not intended to exclude other additives, components, integers or steps.

Brief Description of Drawings [0042] The invention will be described by way of example only with reference to the preferred embodiments shown in the accompanying drawings, in which:

Figure 1 is a schematic representation of a banknote bundle held together by a strap according to the present invention;

Figure 2 is a schematic representation of the straps shown in Figure 1 unclasped and laid flat;

Figure 3 is a schematic representation of a banknote bundle held together by a strap according to another form of the invention;

Figure 4 is a schematic representation of a strap according to another form of the invention, unclasped and laid flat;

Figure 5 is a schematic cross-section through the destructive section of a strap according to the present invention;

Figure 6 is a schematic representation of a cross-section through the destructive section of another embodiment of the strap according to the present invention;

Figure 7 is a schematic cross-section through yet another embodiment of the destructive section of a strap according to the invention; and

Figure 8 is a schematic representation of a rigid cash container with internal electrical terminals for direct contact with banknotes in the container.

Detailed Description of Preferred Embodiment [0043] Referring to Figure 1, a system 2 for voiding a bundle of banknotes 4 is provided by the strap 6 used to retain the banknotes. The strap has a destructive section in the form of conductive material 8 that can resistively heat to a temperature that damages banknotes 16 in the bundle 4. The conductive material 8 electrically connects to a power supply 14 that initiates the current flow for resistive heating in response to an input triggered by an event indicating the banknotes have been stolen.

[0044] In the case of polymer banknotes 16, the conductive material resistively heats until the polymer melts, thereby damaging an edge portion of each banknote in the bundle 4. To enhance this damage and resist removal the strap 6, sections of heat shrink material 10 and 12 are incorporated on the top and bottom of the bundle 4. As the conductive material 8 resistively heats the heat shrink material 10 and 12, reduces the length of the strap to tighten it around the bundle 4. The additional tension in the strap 6 increases contact pressure between the conductive material 8 and the banknotes 16 for a greater degree of melting. The tightened straps 6 are also more difficult to remove should the thief seek to extract the banknotes before they are damaged.

[0045] The increased contact pressure between the strap and the banknotes 16 reduces the temperature of the conductive material 8 at which melting damage initiates. This in turn reduces the time period in which the strap causes damage, which restricts the thieves opportunity to circumvent or otherwise remove the strap 6 prior to damage. Suitable heat shrink polymers include the polymers used to produce heat shrink tubing and heat shrink sleeves such as those marketed under the name Raychem ATUM by TE Connectivity Corporation (see www.te.com/global-en/products/heat-shrink-tubing.html). This type of polyolefin material is often used to environmentally seal and protect electrical conductors with shrink ratios typically around 3:1 to 4:1. Typically, the polymer will shrink at temperatures between 80°C and 100°C, which is similar to the melting temperature of polypropylene (around 120°C and 140°C) which is the polymer substrate used in the majority of polymer banknotes.

[0046] The heat shrink sections 10 and 12 used in strap 6 have a minimum shrink temperature of 125°C and shrink ratios of 3:1 which ensures the banknotes 16 are melting while the strap continues to tighten around the bundle 4. This promotes further damage to the banknotes when the melted strap is removed because it has bonded with the polymer of the banknotes.

[0047] As shown in Figure 1, the heat shrink sections 10 and 12 are spaced from the parts of the conductive material 8 that contact the edge of the banknotes 16. As the heat shrink material 10 and 12 reduces the length of the strap, the conductive material 8 extending along the sections may bend and buckle outwards and away from the top and bottom banknotes of the bundle 4. However, the conductive material 8 remains tightly pressed against the edges of the banknotes 16.

[0048] In other forms of the strap 6, the shrink material sections 10 and 12 may be a shape memory polymer or a shape memory alloy, such as nitinol. Similarly, the trigger need not be heating of the conductive material 8 but rather a chemical heating mechanism actuated by water or other chemical released in response to the event indicating theft.

[0049] The power supply 14 is incorporated into the strap 6 as a printed battery, such as those produced by Fraunhofer Institute for Electronic Nanosystems (see www.enas.fraunhofer.de) and Xymox Technologies Inc. (see www.xymox.com/printed-battery).

[0050] The trigger used to close the circuit to initiate current flow may be an RFID tag or similar device which is responsive to a transmission generated when the theft occurs. In other forms, the trigger can be sensitive to externally applied heat or cold, contact with water or another liquid, or gas (e.g. oxygen at atmospheric concentration levels), or light sensitive/UV sensitive triggers. These later triggers are best suited to straps holding bundles of cash within closed cash containers such that exposure to light at a particular wavelength (not present during the authorised removal of cash from the container) damages or destroys the banknotes once the thieves have successfully broken into the cash container.

[0051] Referring to Figure 2, the strap 6 is shown laid out flat in an open configuration. The clasp 18 is lockable to the other end of the strap 6 such that the conductive material 8 provides a continuous current path between the terminals of the battery 14, and through the sections of heat shrink material 10 and 12 designed to contract longitudinally as indicated by the large arrows. Furthermore, attempts to force open the clasp 18 or otherwise unlock it in an unauthorised way will trigger the power supply 14. As discussed below, the printed batteries in the power supply 14 can adopt a number of different configurations and may conveniently extend outwards from one or both sides of the strap to achieve the required milliamp hour capacity.

[0052] Figure 3 shows an alternative in which the bundle of banknotes 4 is held by a strap supporting the power supply 14 against a stable non-shrinking substrate polymer 20. This effectively allows the power supply battery 14 to occupy a longer section of the strap 6 while reducing the amount of conductive material 8 required.

[0053] Figure 4 shows a version of the strap 6 in which the heat shrink polymer 10 provides the substrate support for the majority of the strap. In this way, the whole strap compresses inwards on to the banknote bundle 4 (see Figure 3) and the conductive material 8 may be a simple metallic wire or serrated wire to melt and/or cut the banknotes. In this form of the strap, the conductive wire or serrated wire 8 is attached to the supporting substrate of shrink polymer by providing a shallow groove extending longitudinally along the strap’s interior surface. The groove is dimensioned such that the wire 8 remains partially exposed. As the shrink material 10 reduces in length, the embedded wire 8 becomes more exposed in the slot and more effectively melts the polymer banknotes.

[0054] In some embodiments of the strap, the heat shrink polymer substrate 10 shrinks in the longitudinal direction more than the transverse direction (see for example, Propafilm™ RXE biaxially orientated polypropylene film with polyvinylidene chloride (PVDC) copolymer coating marketed by Innovia Films Ltd of Wigton, Cumbria, United Kingdom). This allows the strap to shrink predominantly lengthwise rather than in the transverse direction which may wrinkle or buckle and lift the conductive wire 8 away from the banknotes.

[0055] The destructive section of the strap 6 may also damage the notes by forming a small cut or nick along the edge sections. In these forms of the strap 6, a ratcheted one-way cable tightening mechanism is most effective, whilst the use of a shape memory polymer with relatively low transition temperature can induce a spiral shape to cause the wire to form the necessary cuts and tears. However, cutting and tearing the banknotes can be less effective than melting as cuts repaired with clear adhesive tape will usually be accepted in normal circulation.

[0056] As discussed above, the system requires a mechanism for triggering the destructive section of the strap. This triggering mechanism will require appropriate failsafe measures to guard against an accidental voiding of the banknotes. Broadly speaking, suitable failsafe measures may include multi-step additional verification systems, such as a physical key (or keyhole made accessible) after the lock has been deactivated or electronically interfaced with an electronic (e.g. RFID-based) dongle. Other measures may include demagnetisation of elements in a combination lock.

[0057] Heat may be used as the input that triggers the destructor section of the strap. For example, heat generated by equipment used to break open a rigid container holding the cash bundles may shrink part of the strap which in turn closes the circuit between the power supply 14 and the conductor from material 8. Similarly, the locked rigid cash containers holding bundles of banknotes with straps according to the invention may be fitted with a heater or steam generator in response to unauthorised attempts to open the lid. This has the advantage of disbursing the heat throughout the container such that the input heat reaches each of the banknote bundles. To further facilitate this, the trigger material may have a lower shrinking temperature than the other shrink material in the strap. For example, the heat shrinkable polymers marketed by Tyco Electronics in the “Versafit E4 range can trigger at lower temperatures (approximately 70Ό to ΙΟΟΌ). While this is suitable use as a trigger to close the circuit, the heat shrink material in the remainder of the strap 6 should activate (and shrink) at higher temperatures to allow time for the resistive heating of the conductor material 8 and subsequent melting at the banknote edges. If the activation temperature was as low as that of the trigger material, the conductor material 8 can buckle outwards away from the banknote edges so that the resistive heating fails to cause sufficient melting.

[0058] Referring to Figure 8, a hard-walled cash container 28 is shown as part of the overall system 2. Bundles of banknotes are stored or transported in the locked cash container 28 and in the event of theft, the container will need to be unlocked or pried open to retrieve the cash. Within the container 28 are one or more pairs of conductive terminals 32 which are in contact with the straps on the cash bundles or directly in contact with the cash itself. A battery or other power supply 30 is incorporated into the container 28 with a trigger that is sensitive to unauthorised attempts to open the container. Triggering allows the internal conductors 32 to become live thereby melting the banknotes or powering the straps around the bundles of banknotes to resistively heat the conductive material 8 which in turn melts and/or the banknotes. Each pair of internal conductors 32 will require further conductors 34 to complete the circuit. The electrical resistance of the conductors 34 can be relatively high such that the current flow is preferably via the straps on the bundles of cash. The advantage of this system is the ability to use a large capacity battery at a relatively high voltage (9 bolts or higher) to simultaneously damage a large number of banknotes (either directly or via the destructive sections of the banknote bundle straps).

[0059] As discussed above, some forms of the system damage the banknotes by nicking or cutting the notes bundled by the straps. The destructive section of the strap can incorporate a piercing element such as a blade. The blade may be in the form of a serrated edge similar to that of a hacksaw but thinner and more flexible. Heating (or cooling) activates the shrink materials to draw the blade from a sheath incorporated into the strap. The blade is drawn across the banknotes as the shrink material continues to increase the contact and pressure between the strap and the banknotes. The destructive section of the strap may also use a shape memory polymer or shape memory alloy to drive the cutting action of the blade. In these forms of the strap, the shape memory alloy can be used to form the blade itself. Shape memory alloys such as Nitinol have a transition temperature that can be reached via resistive heating.

[0060] Some forms of the invention incorporate a flammable chemical coating into the destructive section of the strap. In these versions of the strap, parts of the shrink material 10 may not be directly or uniformly heated by the resistive heating provided by the conductor material 8. A chemical heating mechanism can be used to better control the heating profile of the shrink material such that the strap contracts in a controlled manner. The chemical heating can be triggered by the resistive heating or conversely the chemical coating can be added to trigger material that shrinks to close the circuit with the power supply to initiate resistive heating. In these cases, the chemical coating may be activated by water or another substance such as oxygen at a necessary concentration. In this form, the hard-walled cash container may be purged of oxygen by flushing the interior with nitrogen. Opening the container 28 (see Figure 8) exposes the straps to air with oxygen at normal atmospheric concentrations. This provides an unexpected trigger that is difficult to circumvent for the thief.

[0061] In a similar way, the destructive sections of the straps may be triggered heat, or a solar/UV sensitive switch. This also provides an unexpected trigger mechanism to catch the thief off-guard.

Conductive Material 8 [0062] The conductive material 8 will have numerous characteristics similar to fuse elements or metallic solder. However, while fuse elements and solder metal have generally low melting and vaporisation temperatures, the conductive material 8 of the present invention should have a relatively high melting temperature such that resistive heating does not melt or weaken the conductive material 8 as it is drawn into tension by the shrink material. However, apart from this difference, the conductive material should have low specific heat, low latent heat and high thermal conductivity so that it heats to a high temperature quickly across its entirety.

[0063] By way of example, the system requirements for straps holding banknotes are derived using the techniques set out below.

[0064] Banknotes are processed and banded into 500 pieces per bundle after note-printing.

[0065] At thickness of 100 microns each, 500 banknotes corresponds to a 5cm high bundle. While this invention can be used for any size bundle which can be secured properly, without the bands slipping. Calculations here are based on 5cm bundle height.

[0066] A selection of typical dimensions of widely used high denomination banknotes are shown below:

[0067] Calculations are based on the greatest height because this represents a scenario where a longer piece of wire forming the current path will need higher current to bring it to a sufficiently high temperature.

[0068] Using:

Maximum width (GBP50)= 85 mm

Height of bundle= 5 cm [0069] And assuming the wire goes all the way around the bundle, this would be the worst case of power source needed to heat/near melt the wire.

Total circumference for wholly strapped bundle (of 5cm height) = 180 mm [0070] Calculate the amount of current that can be generated from this piece of wire (conductive material) using the maximum available voltage, e.g. 1.5V that can be generated from printable batteries available using existing technology. Constructing a device using a lower voltage is obviously better for cost and safety reasons.

[0071] Calculate the current flowing through this piece of wire. The example below is for Aluminium - which can be metallized onto BOPP.

[0072] Calculations done for 180mm and 10mm piece.

Calculating resistance

To calculate the resistance R of a wire, we need to know three things: • its length t - the longer the wire, the greater its resistance • its cross-sectional area A - the greater the area, the less its resistance • the resistivity of the material p - the greater the resistivity, the greater its resistance. resistance = resistivity x length / area

This equation defines resistivity. We can rearrange it to get a formula for resistivity: resistivity = resistance * area / length

Metal type = Aluminium, 99.99%

Resistivity = 2.66E-08 ohm.m

[0073] Using the Onderdonk equation (see extract below taken from http://pcdandf.eom/pcdesign/index/.php/magazine/10179-pcp-design), enter the amount of current, work out how long (fusing time) it would take before a wire of this dimension melts, when this amount of current is passed through it. Areas must be converted to square mm.

Melting temp (Tm) = 660

Ambient temp (Ta)= 25

Other units. If we rearrange the terms of Eq. 15 and recognize the melting temperature of copper is 1083'C, we can obtain (in circular mils):

[Eq 16]

If we further let the ambient temperature equal 20"C, we can obtain: t = c * (A/l)2 [Eq 17] where c = 0.0213 in circular mils.

[0074] These calculations determine what voltage of battery to use and the dimension of wire, required when aiming for a fusing time of 2 to 5 seconds. Ideally, these conditions should not cause the wire to melt or vaporise. The metal needs to get to as high a temperature as possible and above 130°C in the shortest amount of time. Increasing the mass in the wire (i.e. larger dimensions) will prevent melting and vaporisation. So long as the wire does not vaporise but melts, the banknotes will still be damaged in the intended way.

Heating through Chemical Reaction [0075] In some forms of the invention, the destructive section uses an exothermic chemical reaction to generate damaging heat. In the case of polymer banknotes with a polypropylene substrate, relatively safe and stable chemicals can be used for the exothermic reaction (e.g

[0076] Hand warming heat packs such as those made from iron powder, salt, water and an absorbent material (e.g. Fe2C>3 forms from the reaction of atmospheric oxygen with the iron powder to release heat). Unfortunately, these mechanisms do not reach the required temperature in a short period of time, but can still provide a back-up heat input if the printed battery or other heat input mechanism is disabled. In particular, the temperature reached can be used to activate the shrinking material attached to the strap containing a blade.

[0077] Faster reaction times require more explosive or flammable chemical reactions. However, this necessitates secure and reliable encapsulation methods and activation mechanisms. Typically, each component is stored separately and when the individual compartments are ruptured, mixing occurs to initiate the reaction. Rupturing may be provided by a physical input or a more controlled trigger mechanism involving a resistively heated wire or similar.

[0078] For safety reasons, it will be appreciated that particular chemical reactions should be avoided in light of toxicity to the general public and unpleasant odours:

Acids with cyanide salt or cyanide solution will generate highly toxic hydrogen cyanide gas

Acids with sulphide salts or sulphide solutions will generate highly toxic hydrogen sulphite gas.

Acids with bleach generate highly toxic chlorine gas such as mixing bleach with vinegar;

Ammonia with bleach will release toxic chloramine vapours.

Phosphides such as sodium phosphide mixed with water may form highly toxic phosphine gas.

Profiled Conductive Material [0079] Figures 5 to 7 show cross sections of the strap 6 through the conductive material 8. The supporting substrate for the strap 6 may be the heat shrink polymer 10 or another suitable backing material. As shown in Figure 5, the conductive material can be laid down in a longitudinal trace along the strap with a pointed tip or ridge facing inwardly to the banknote. Using a sharp pointed tip will hasten and/or deepen the melting of the banknote substrate material.

[0080] As shown in Figure 6, the conductive material 8is formed with a uniquely shaped inner surface. The uniquely shaped surface will leave a tell-tale impression on the banknote when melting or cutting the substrate. This allows the voided and stolen banknotes to be differentiated from any banknotes that may be accidentally melted or cut in the course of normal use. When forming the unique shape 24, the sharp outer ends must not be too close to one another, nor should they be too delicate or fine as they simply fuse from melting the polypropylene and lose their characteristically unique shape.

[0081] This problem is effectively addressed by the arrangement shown in Figure 7. Providing parallel conductive traces 26 will generate discreet melt points on the edge of the banknote at a specific placing.

[0082] Using a system according to the present invention will void the items of value in a unique or characteristic manner that is easily distinguished from accidental damage through routine wear and tear. Location of the damage is controlled and reproducible by placing the straps onto the items of value in a consistent manner. The melted edge will have a distinct pattern or form that precisely compliments the shape of the conductive material used to melt the polymer substrate. In some forms, the banknotes are printed with thermochromic or reactive ink at the site of the damage to enhance the pattern created by the destructive section of the strap. Furthermore, polymer banknotes with melted edges are difficult to use in vending machines and tend to jam the feed path due to the sudden change in note thickness.

[0083] By initiating a small cut or nick in the banknote, it is prone to tear completely through due to the nature of polypropylene and other polymers in general. Furthermore, the banknote will be nicked in a location that is close to its middle and hence most probably tear roughly into halves. In most cases, substantially more than 50% of the banknote must be intact before the bearer can exchange it for a new banknote at the bank.

[0084] The present invention has been described herein by way of example only. Many variations and modifications will be readily apparent to the ordinary worker, which do not depart from the spirit and scope of the broad inventive concept.

Claims (5)

1. The claims defining the invention are as follows

   1. A system for voiding items of value to deter theft, the system comprising: a strap for retaining a number of the items together, the strap having a destructive section for damaging the items in response to an input triggered by an event predetermined as indicative of theft.
2. 2. A system according to claim 1, wherein the items are documents of value and the strap is configured to hold a plurality of the documents stacked into a bundle, the destructive section having a blade edge to initiate a cut into an edge section of the documents and shrink material that is sensitive to an input for reducing the strap length in response to said input, the system further comprising a trigger configured to apply the input to the shrink material in response to an event predetermined as indicating theft of the documents.
3. 3. A system according to claim 1 or claim 2, wherein the input is heat.
4. 4. A method of damaging items of value to deter theft, the method comprising the steps of: retaining a number of the items together with a strap having a destructive section for damaging the items in response to an input; and triggering the input in response to an event predetermined as indicative of theft.
5. 5. A strap for holding items of value together in a bundle, the strap comprising: a destructive section for damaging the items in response to an input, the input being generated in response to an event that is predetermined to be indicative of theft of the items.