SECURITY DEVICES

Abstract: A security tag film comprising: a carrier sheet; a layer of a pressure and/or heat sensitive adhesive; and a security structure located between the carrier sheet and the layer of adhesive, the security structure comprising: an active layer of a soft magnetic material; and a patterned deactivation layer of a hard or semi-hard magnetic material located in proximity to the active layer so that magnetisation of the deactivation layer may disrupt the uniformity of magnetisation of the active layer.

Description: SECURITY DEVICES This invention relates to security devices such as anti-theft devices. Anti-theft or anti-pilferage devices are used to reduce stock loss (shrinkage) from retail shops and similar outlets due to shoplifting or similar theft. The majority of anti-pilferage devices currently on sale take the form of a label or other tag that must be specifically applied to the packaging of goods. The tag interacts with a security system in the shop, which detects unauthorised movement of the goods or an unauthorised attempt to remove the goods from the shop. One form of security tag comprises a soft magnetic structure (e.g. a film) for use as an active element of the tag, which allows the tag to be detected by the security system, and a deactivation element, usually in the form of a layer of a hard or semi-hard magnetic material. If the active element is not deactivated at the point of sale, the active element will trigger an alarm signal in an alternating magnetic field, at a detection gate installed at the exit of a shop. After deactivation of the tag, usually at the point and moment of sale, the soft magnetic material is magnetised so as to hold parts of the active element, i.e. the soft magnetic film, in saturation so that it no longer causes a response at the detection gate. The general principles behind this method of detection are well known, and are described in US 4,960,651 , the contents of which are incorporated herein by reference. Conventionally the security tag is supplied to shops etc. in the form of a label or other tag that can be stuck on or otherwise attached to goods in the shop. The tags are often applied by hand to the goods, either by means of a self-adhesive area on the tag (for instance in the case of a self-adhesive label) or by pinning to the goods using a secure fixing. Attaching the tags one-by-one in this way is time consuming and therefore costly, and it is easy for the person applying the tags to omit to fit one to an article (in which case the security system will not detect theft of that article) or to fit the tag insecurely (in which case a thief may easily remove the tag). A number of additional problems arise from the difficulties of attaching the tags to the goods. First, many such tags are relatively bulky and/or unattractive, and spoil the appearance of packaged products in the shop. Second, the tags can often be stuck to the packaging in a way that obscures information on the packaging that a customer may want to read. And third, small or irregularly shaped packaging may provide no suitable location on which to attach the tag. Holographic stamping foils are well known for the purpose of authenticating products. WO 99/45513, which was published after the priority date of the present application, describes a holographic stamping foil that includes a soft magnetic layer to make the foil more difficult to copy. There is therefore a need for an improved form of security tag. According to one aspect of the present invention there is provided a security tag film comprising: a carrier sheet; a layer of a pressure and/or heat sensitive adhesive; and a security structure located between the carrier sheet and the layer of adhesive, the security structure comprising: an active layer of a soft magnetic material; and a patterned deactivation layer of a hard or semi-hard magnetic material located in proximity to the active layer so that magnetisation of the deactivation layer may disrupt the uniformity of magnetisation of the active layer. According to a second aspect of the invention there is provided a method for forming a security tag film, comprising: depositing over a carrier sheet a security structure comprising an active layer of a soft magnetic material and a patterned deactivation layer of a hard magnetic material located in proximity to the active layer so that magnetisation of the deactivation layer may disrupt the uniformity of magnetisation of the active layer; and depositing a layer of a pressure and/or heat sensitive adhesive over the security structure. According to a third aspect of the present invention there is provided a method for applying a security tag, comprising: locating against a substrate the adhesive layer of a security tag film according to the first aspect of the present invention; pressing and/or heating a region of the film against a substrate to adhere the film to the substrate by means of the adhesive layer; and withdrawing the carrier sheet of the film from the substrate to leave the active layer and the deactivation layer in that region adhered to the substrate. According to a fourth aspect of the present invention there is provided a packaging enclosure for a product, the enclosure having: a printed exterior surface; and an interior surface bearing a security tag comprising: a security structure comprising an active layer of a soft magnetic material, and a patterned deactivation layer of a hard or semi-hard magnetic material located in proximity to the active layer so that magnetisation of the deactivation layer may disrupt the uniformity of magnetisation of the active layer, and a layer of pressure and/or heat sensitive adhesive by which the security tag is adhered to the interior surface. According to a fifth aspect of the present invention there is provided a security tag comprising: a layer of a pressure and/or heat sensitive adhesive; and a security structure located between the carrier sheet and the layer of adhesive, the security structure comprising: an active layer of a soft magnetic material; and a patterned deactivation layer of a hard or semi-hard magnetic material located in proximity to the active layer so that magnetisation of the deactivation layer may disrupt the uniformity of magnetisation of the active layer. Suitably the carrier sheet is a flexible sheet. The carrier sheet may be made of plastics material. There may be a release layer between the carrier sheet and the security structure, most preferably adjacent to the carrier sheet. The release layer preferably has a weaker adhesion for a layer adjacent to it (for example the carrier sheet or a layer of the security structure) than does the adhesive layer for a layer adjacent to it (for example a layer of the security structure). The adhesive layer is preferably capable of activation in response to pressure and/or heating of the film against a substrate to adhere the film to the substrate. Prior to such activation the adhesive is preferably substantially inactive and/or of a low tack. The active layer and the deactivation layer (and most preferably any additional layers between the release layer and the adhesive layer) are preferably frangible, whereby on adhesion of a region of the film to a substrate by the adhesive the carrier sheet may be released from the active layer and the deactivation layer in that region, leaving the active layer and the deactivation layer in that region adhered to the substrate. The carrier sheet preferably has the greatest tensile strength in the plane of the film of any of the layers of the film. The coated carrier sheet is preferably a stamping foil, most preferably a hot stamping foil. It may be suitable for application to a substrate using a transfer machine, e.g. a hot stamping press or through the techniques of hot or cold foil blocking, dieless foiling, thermal transfer printing or similar transfer or similar printing technology. The transfer process is preferably a mechanical process that is capable of continuous operation.. There may be one or more lacquer layers between the security structure and the carrier sheet, preferably adjacent to the adhesive layer. There may be one or more layers having a surface relief between the security structure and the carrier sheet. The layer(s) having a surface relief may be lacquer layer(s). The layer(s) having a relief may provide a holographic structure. There may be a reflective layer between the security structure and the carrier sheet. The reflective layer is preferably between the security structure and any lacquer layer(s). The deactivation layer is suitably patterned into a plurality of spaced apart zones. Those zones may take the form of spots or stripes. The spacing between such zones may suitably be in the range from 0.5 to 2mm, preferably around 1mm. The width of such zones may suitably be in the range from 0.5 to 2mm, preferably around 1mm. The deactivation layer suitably comprises a dispersion of particles of a hard magnetic material, which may suitably be deposited by silk-screen printing, gravure printing, flexography, slot coating or Meyer bar coating. The deactivation layer may be joined to the active layer by a foil transfer process such as stamping from another carrier sheet or printed directly on to the active layer. The film is suitably a stamping foil film. A security tag may be stamped from the film by the pressing and/or heating and/or stamping of the film against a substrate. The said substrate may be a packaging material, preferably a sheet packaging material. The security tag film, and especially the security structure is adhered to the interior surface of the packaging material. There may be printing on the opposite surface of the packaging material to that on which the active layer and the deactivation layer are adhered. The printing may include indicia indicating the location at which the active layer and the deactivation layer are adhered. Those indicia may be located opposite the location of the security structure. The said indicia may be a machine readable product identification marking. The indicia may be a bar code. The substrate may be bent (and even folded) across the location at which the active layer and the deactivation layer are adhered. The tag and especially the security structure are preferably flexible. The thickness of the tag is preferably less than 50 microns. The thickness of the security structure is preferably less than 20 or less than 30 microns. The active layer is preferably adjacent to the deactivation layer. The active layer is preferably continuous and/or un-patterned and/or has a uniform magnetic polarisation, particularly before deactivation. The adhesive layer may be applied during coating of the other layers of the film on to the carrier sheet, or shortly before application of the sheet to a substrate. The security structure may be applied in-line during manufacture and/or printing of packaging. In this way the tag may be applied to a wide variety of paper based and flexible packaging items (and other forms of packaging) at the point of manufacture of the packaging. The coercive force of the hard magnetic material is suitably greater than that of the soft magnetic material. The coercive force of the hard magnetic material is preferably greater than 1000, 10000, 20000 or 30000 A/m. The coercive force of the soft magnetic material is preferably less than 500, 200, 100 or 50 A/m. The present invention will now be described by way of example with reference to the accompanying drawings, in which: figure 1 shows a schematic cross-sectional structure of a heat transferable security tag structure mounted to a carrier sheet; figure 2 shows a schematic cross-sectional structure of a security tag structure comprising a holographic element mounted to a carrier sheet; figure 3 illustrates a method for applying security tags to a substrate; figures 4 and 5 show deactivation layer patterns; and figure 6 shows a method for bonding a deactivation layer to an active layer, including a cross-section of a deactivation layer sheet. Figure 1 shows one form of security tag structure. The tag structure is provided in the form of a sheet having a carrier sheet 1 coated with a number of coatings (suitably in the form of parallel full or partial layers). In use the uppermost adhesive layer 2 is located against a substrate on to which a tag is to be fixed. Pressure and/or heat is then applied locally in order to locally activate the adhesive and cause it to bond to the substrate. The carrier 1 is then withdrawn from the substrate and the bond between the carrier and the substrate breaks cleanly between at the release layer 3, leaving a localised region of the substrate bearing the remaining layers 2, 4 and 5 of the corresponding localised part of the sheet. Those remaining layers constitute a security tag that can be used to detect movement or unauthorised taking of an article which, for example, comprises or is packaged in the substrate. The release layer may remain with the layer 4 or may be stripped off with the carrier 1 depending on the relative strengths of its adhesion to those layers. The remaining layers comprise a layer 4 of a soft magnetic material and a layer 5 of a hard magnetic material, which together allow the tag to be detected and deactivated in the way described above. Figure 2 shows another form of security tag structure, in which like parts are numbered as for figure 1. The tag of figure 2 additionally comprises a protective lacquer layer 6, which forms the outer surface of the tag once it has been released from the carrier, and an embossed lacquer layer 7 and a vacuum deposited aluminium layer 8 which together provide a holographic security feature by virtue of the embossed profile of the layer 7. The tag of figure 2 can be used in the same way as that of figure 1 , with the layers 2, 5, 4, 8, 7 and 6 forming the tag that is adhered to a substrate. Figure 3 shows a method for depositing security tags 10 on to substrates 11 from a web of film 12. The web of film 12 carries layers that can be deposited on to the substrates to define security tags. Thus the film 12 could have either of the structures of figures 1 or 2 or variant structures as described below. An unused region 13 of the film is located between a hot pressure die 14 and the next substrate 11a. Then the die approaches the substrate and presses the film against the substrate to activate the adhesive layer of the film and cause it to bond to the substrate 11a. Next the die is withdrawn and the film 12 and the substrate 13 are separated. This leaves a tag on the substrate. The used area of film is then taken up on to the rewind reel 15, fresh film is dispensed from the reel 16 and the substrates are indexed until the next one lies correctly below the die. The process can then be repeated. A magnetic security tag can thus be formed as a multi-layer structure on a coated carrier sheet and deposited on a substrate by pressing on to that substrate and subsequent removal of the carrier. This can provide a small, flexible tag which has a significantly simpler construction than existing systems The substrates could be discrete or could be regions of a continuous sheet or film. The coated material could be applied continuously to the substrate by pressing the film 12 against the substrate by a hot roller as the substrate moves past. The shape of the tags as applied to the substrates is determined by the shape of the die. The shape of the die could be chosen to yield a desired shape or pattern of tag. If pressure sensitive adhesive rather than heat sensitive adhesive were used then the die or roller need not be heated. The substrate could be a packaging or wrapping material such as paper, card or plastics sheet, or could be an article that is itself to be sold. The tags could be applied during manufacture or printing of the substrate or at later stages of the supply chain such as during filling of packaging or in retail outlets. The tag is thus suitable for high volume production and mass application to cartons, labels and flexible packaging If the tags are to be applied in retail outlets then the reels 15 and 16, the die 14 and the associated winding, heating (if necessary) and driving mechanism could be integrated into a portable gun for applying the tags. It will be appreciated that the order of the layers may be varied. For example, the active layer and the deactivating layer may be reversed from the arrangement shown above. Additional layers may be added. One specific example of a variation on the structure of figure 2 is that the lacquer layers 6 and 7 may be replaced by one or more non-embossed coloured lacquer layers, to give a coloured metallic foil visual effect to the tag. The active element of the tag is formed of a soft magnetic material. The term soft magnetic is used herein to refer to materials with a low coercive force (He). Such soft magnetic materials will typically have a coercive force in the range from 3 to 100 A/m, although materials having a coercive force outside that range may also be suitable. Such a soft magnetic material may comprise a metal in amorphous (glass) or semi-crystalline state (e.g. with only a limited number of crystalline phases or structures), for example as is described in EP 0 295 028 A1 , the contents of which are incorporated herein by reference. A film of such a soft magnetic material can be made by means of chemical vapour deposition techniques such as sputtering processes or by other processes. The deactivation element of the tag is formed of a hard magnetic material. The term hard magnetic is used herein to refer to materials with a high coercive force (He), including semi-hard magnetic materials. Such hard magnetic materials will typically have a coercive force in the range from 1000 to 20000 A/m, although materials having a coercive force outside that range may also be suitable. The coatings herein described may be preferably transferred using a stamping or most preferably hot stamping technique. (See figure 3). Stamping foil technology is extremely versatile and finds wide applicability across a broad range of industries from graphics enhancement of cartons and labels to variable data overprinting applications. In essence, a preferred form of stamping foil technology is a dry printing process through which a coating is prepared on a polymeric carrier sheet and then subsequently removed from the carrier at point of application using a combination of pressure and/or heat. Changing the design of the hot stamping die controls the area and pattern of material transferred. Alternatively, the coatings may be transferred using a computer controlled thermal transfer print head or a dieless transfer technique. Preferred features of the layers of the sheet will now be described. Carrier sheet The carrier sheet is the vehicle for carrying the various coatings or layers after they have been deposited and for the transfer of the various coatings to the substrate (e.g. the packaging material). It should be mechanically strong, in order to permit fast processing during manufacture, where coating speeds of 200 metres per minute are not uncommon. Furthermore, the carrier must be thermally stable, since it may be exposed to a high temperature profile during coating and could experience high temperatures and pressure during the ultimate application of the tags. The carrier should be chemically resistant, since several of the coatings may be deposited from solvent borne media. Typically a 19 micron polyester film can be used as the carrier, such as Mylar from DuPont or Melinex from ICI. In some cases, particularly where accurate control of printing or embossing processes is necessary, thicker gauges such as 23 or 50 micron polyester may be used. These provide additional dimensional stability during the coating, drying and embossing processes, which help to ensure accurate control of registered images. Oriented polypropylene, polyimide, polyethylene napthenate or cellulose acetate may also be used. In other cases 12 micron films may be preferable for speed of application and lower cost. In the case of thermal transfer ribbons, a carrier of typically 6 micron will be used. In general, carrier sheets used for conventional stamping foil applications may be considered. Release layer The release layer is designed to allow the coatings to be removed from the carrier using the chosen application technique. Its composition will vary depending on whether the coatings are to be transferred using a heat activation or cold (e.g. pressure) transfer technique. The release layer is typically a blend of one or more waxes, polymers and surface active agents applied at a very low coat weight by gravure, flexography or a similar coating process. The release layer is typically coated to a weight of less than 0.01 grams per square metre (gsm). The composition of the release layer may be selected depending on a number of factors including: how much of the coating needs to be applied during the printing process, at what temperature the product will be used and on what type of equipment. A coating to be applied over large areas or at high speeds will need to transfer from the carrier relatively easily, while a product needed to produce smaller areas of coverage is designed with greater adhesion to the carrier. Furthermore, the tag may need to be over-printed after having been applied to a substrate, and the presence of excess residue surface waxes and surfactants from the release layer should then be avoided by suitable design of the release layer. In some operations low temperature and pressure are needed during application of the foil to prevent damage to the substrate. This is often the case when foils are applied to flexible or thermoplastic substrates such as many packaging films. In this case the release system should be designed so the foil can easily be removed from the carrier. In one embodiment of the invention, the release layer may be composed of a polymeric coating deposited to a density in the range from roughly 0.5 to 5gsm. The release layer generally transfers with the remaining coatings when the tag is applied to the target surface. This simple construction avoids the need for an intermediate lacquer layer and is also suitable for dieless transfer techniques as described below and for laminating operations. Suitable polymeric materials include cellulose acetate propionate, polyurethanes and polyvinyl alcohol. In general, release layer compositions and weights used for conventional stamping foil applications may be considered. Lacquer layer The lacquer(s) used for the lacquer layer are typically around 1 micron coatings comprising a blend of polymers selected to provide high gloss, physical durability and resistance to the heat and pressure experienced during heat transfer processes. The lacquer is conveniently prepared by dissolving polymeric components of a lacquer in an organic solvent, typically methyl ethyl ketone, industrial methylated spirits, toluene or similar solvents. In some cases the polymeric material will be dissolved or dispersed in aqueous media. These solutions may be coated onto the carrier using gravure, flexography or a similar coating process. The lacquer layer preferably comprises thermoset or thermoplastic material such as an acrylic, a vinyl polymer, a polystyrene, polyamide, nitrocellulose, styrene maleic anhydride or copolymers thereof. The lacquer may contain a colouring agent to provide a specific shade to the final product, for example gold, which can be produced by incorporation of a suitable yellow or orange dye. The lacquer layer may be designed so that it can be embossed to contain a holographic pattern. Alternatively a second thermoplastic layer may be incorporated using similar coating techniques described above. This may, for example, be used where the first layer is required to posses high durability and less thermoplastic resins or cross-linked systems are used. The thermoplastic lacquer layer is holographically embossed using heat and pressure in combination with nickel shims or the like that carry a holographic pattern or image. It may be preferable to improve the visible appearance of the embossed hologram through incorporation of a highly reflective metallic layer. (Layer 8 in figure 2). This may be deposited by vacuum deposition. Aluminium is the most commonly used metal for this purpose. However, the deposition of other metals can lead to other effects, such as increased durability or added conductivity. It should also be noted that the active magnetic layer and/or the deactivation layer may be reflective, in which case the layer 8 can be omitted and the tag still have a reflective appearance. In general, lacquer layer compositions and weights, reflective metallic layer compositions and weights and holographic techniques used for conventional stamping foil applications may be considered. Active magnetic layer The active magnetic layer is formed of a thin film of a soft magnetic material. The active layer suitably has high intrinsic magnetic permeability, low or zero magnetostriction and a low coercivity. The layer may be formed of an amorphous metal glass. The layer may be composed of an alloy of elements - generally of metal and metalloid elements. Such an alloy may contain Co, Fe, Si and/or B. Ni and Mo may also be present. A typical range of composition of the alloy is 35- 70% Co, 2-7% Fe, 10-35% Ni, 0-2% Mo, 12-20% Si and 6-12% B by atomic percent. Examples of such alloys are described in US 4,960,651 , the contents of which are incorporated herein by reference. One specific example of a suitable material is Atalante, available from Innovative Sputtering Technologies. The active magnetic layer is suitably 0.5 to 5 microns thick, preferably around 0.9 microns thick. The active magnetic layer may be deposited, for example, by planar magnetron sputtering, electron beam evaporation or electroless or electrolytic chemical deposition. Electrodeposited Nickel/Iron alloys may also be used, as described in US 5,582,924, the contents of which are incorporated herein by reference. The active magnetic layer is suitably 0.5 to 5 microns thick, preferably around 0.9 microns thick. Deactivation layer The deactivation layer is suitably of a hard or semi-hard magnetic material, e.g. with a coercivity in the range 1000 - 100000 A/m, preferably 3000 - 5000 A/m. It is suitably 5 to 14 microns thick, preferably around 10 microns thick. Typical materials for the deactivation layer include mild or stainless steel foils, particulate ferrites as described in US 4,960,651 , or more preferably one or more ferrous oxide powders or films, optionally including pigments. Coating a suspension of mixed iron oxide particles may produce a suitable deactivation layer. The powders or particles could be deposited from a mixture of the powders or particles with a resin, and together with a solvent that could then be evaporated off to leave the powders or particles bound in the resin to form the deactivation layer. One example of a suitable powder for the deactivation layer is carbonyl iron powder HQ, available from BASF. Where the deactivation layer is formed from powders or particles the particle size is suitably less than 2 microns. A further suitable form of the deactivation layer is a sputtered coating of a semi-hard magnetic alloy, including an alloy of Co, Ni and Ti. Nickel with a planar crystal grain structure may also be used for the deactivation layer, as described in US 5,582,924. This may be produced by electrodeposition, electroforming, electroless chemical deposition, vacuum deposition or by coating or printing of nickel particles. The deactivation layer should be patterned so as to allow it, when magnetised, to break up the magnetic uniformity of the active layer and thereby prevent the active layer from triggering an alarm when in proximity to the detection equipment. When the islands of the deactivation layer are magnetised sufficiently intensely they each locally apply a magnetic field to the active layer. This can divide the active layer into short regions which are saturated, but polarised in an opposite direction to the neighbouring material. This effectively subdivides the active layer. The detection machinery (e.g. in shops) for detecting the security foil is arranged so that it generates an alarm if an effectively entire piece of the active layer passes it, but not if an effectively subdivided piece of the active layer passes it. The patterning of the deactivation layer may take any suitable form that is capable of properly deactivating the active layer by sufficiently disrupting its magnetic properties. In general, this means that the patterning should be designed so as to be capable of reducing the maximum continuous length of active layer that does not cross the edge of a region of deactivation layer to a suitably short length (e.g. 1 or 2mm or less) in at least one direction in the plane of the active layer, and preferably in two orthogonal directions in that plane. Appropriate dimensions for the widths of the islands in the deactivation layer pattern and the spaces between them depend on the thicknesses and materials of the active layer and the deactivation layer, and the sensitivity of the detection equipment to be used, but are generally in the range from V?. to 2mm, and preferably around 1mm. Examples of suitable patterns are individual dots as shown in figure 4 or individual stripes as shown in figure 5. (In figures 4 and 5 like parts are numbered as for figures 1 and 2). In the dotted pattern of figure 4, the dots are preferably arranged in a hexagonal close packed pattern, with each dot spaced equidistantly from its six neighbours. The dots may be circular. The diameter of the dots may be around 1mm. The spacing between each dot and its neighbours may be around 1mm. Other patterns, such as a chequered pattern, could be used. In selecting the materials and thicknesses for the active layer and the deactivation layer it is preferred that the product of the retentivity and the thickness of the deactivation layer is greater than twice the product of the saturation magnetisation and the thickness of the active layer. Thus, materials with relatively high retentivities - for example greater than 200mT or 250mT - are preferred for the deactivation layer. A number of routes are available for depositing the deactivation layer in a patterned form. These include conventional printing techniques that are suitable for printing of relatively heavy coat weights, such as flexography, gravure and silk- screen printing. Alternatively, the deactivation layer could be formed separately and then adhered locally to the security foil structure. One way of doing this is illustrated in figure 6. Figure 6 shows schematically the localized adhesion of a deactivation layer to a partially formed security tag film generally of the type shown in figure 1. Like parts are numbered as for figure 1. The partially formed security tag film 30 consists of the carrier layer 1 , the release layer 3 and the active layer 4. The film 30 is fed in the direction indicated by arrows A. An adhesive layer 31 is applied on to the active layer 4 of the film 30. The deactivation layer 5 is borne by a separately formed deactivation layer film 32 which consists of a carrier layer 33, a release layer 34 and the deactivation layer 5. The deactivation layer 5 may be as described above, and the carrier layer 33 and release layer 34 may be generally as described above for the carrier layer 1 and release layer 3: for instance the carrier 33 may be a polyester film and the release layer 34 may be a wax system. The film 32 is fed in the direction indicated by arrows B. The deactivation layer film is brought together with the partially formed security tag film 30, with the adhesive layer 31 directly between the deactivation layer 5 and the active layer 4. At a pressing station the deactivation foil is pressed against the security film by a shaped die or roller 35, which may be heated if necessary, in order to cause the adhesive layer of the deactivation foil to adhere to the active layer of the security film in the locations where the two are pressed together. The release layer 34 is bonded only weakly to the deactivation layer, so the substrate 33 the release layer 34 and the unadhered parts of the deactivation layer 5 can be stripped off the security film and removed, leaving islands 36 of the deactivation layer adhered locally to the active layer on the security film. The adhesive layer 31 which is left between the deactivation layer and the active layer is thin and not magnetically susceptible, so it does not significantly hinder the operation of the security foil. Instead of being applied to the film 30 the adhesive 31 could be applied to the deactivation layer 5. Instead of the roller 35 being patterned, a smooth roller may be used and the adhesive layer 31 printed in a patterned form so that the layer 5 adheres to the sheet 30 only in the regions where the adhesive has been deposited. Tie coat A tie coat, for example of a plastics material, could optionally be deposited over the deactivation layer to smooth out any surface roughness due to the patterning of the active layer and increase interlayer adhesion. Adhesive The final component of the tag structure is a heat and/or pressure activated adhesive system. This will normally be designed from a blend of synthetic and natural polymers, the choice of which will be greatly influenced by the type of substrate to which the coating is to be transferred and the equipment that will be used to apply it. The polymer type selected must give good adhesion to the substrate and at the same time provide sufficient tack within the temperature and pressure profile provided by the application equipment to pull all the coatings from the carrier to the target surface. In some cases relatively low pressures are applied to prevent damage to sensitive surfaces, while in very fast running foil transfer presses, extremely high pressures are applied for very short periods of time. The adhesives are typically a blend of polymeric materials and particulate fillers applied by gravure, Meyer bar coating, flexography or a similar technique. The melt and softening points of the adhesive are selected to provide adequate tack under specific application conditions. The electronegativity and chemical affinity of the polymers of the adhesive are selected to provide maximum adhesion to a broad range of surfaces or to a specific surface. The polymeric materials used may include acrylics, polyolefins and chlorinated polyolefins, polyamides, cellulose derivatives, vinyl and vinyl copolymers, hydrocarbons, cyclised rubbers, polyurethanes or polyesters. The adhesive used can be selected for optimum performance with the substrate on to which the tag is to be deposited. This allows tags to be made for a wide range of surfaces. In general, adhesive layer compositions and weights used for conventional stamping foil applications may be considered. The adhesive layer may be omitted if the tag is intended for application to an adhesive substrate or if an adhesive is to be introduced at the time of applying the tag. Application As indicated above, the security tag structure is preferably formed as a multi-layer film on a flexible carrier. After the security tag film has been formed regions of it can be applied as tags to packaging or to products themselves in a suitable size and shape to allow the tags to be detected by detection equipment of the type described above. At the point of sale a tag's deactivation layer can be suitably magnetised so as to disrupt the magnetic structure of the active layer and allow the tag to pass the detection equipment without causing an alarm. The security tag film may be applied to packaging material by an in-line process during manufacture, printing, cutting or shaping of the packaging material. The ability to apply the tags on to the packaging at source or during manufacture or post-manufacture mechanised processing of the packaging avoids slow application by hand at a later stage. The film may be applied to the material in a similar way to a conventional hot or cold stamping foil: that is by pressing the adhesive layer of the film against the surface of the packaging material using a die or roller, which may be heated if necessary, so that the film bonds to the packaging material, and then stripping off the carrier sheet 1. The die or roller may be profiled so that it presses only selected regions of the firmly against the packaging material. Those regions then define individual security tags. Transfer of the coating to a target surface may also be achieved using dieless techniques such as those described in US 5,368,689, US 5,708,047, GB 2,299,035, EP 0 108 320 A1 , W092/17338 A1 , US 5,603,259 and our co-pending UK patent application number 9806121.8. In such techniques a patch of adhesive is applied to the target surface and the coated carrier is brought into contact with the adhesive. At the point of contact either pressure alone or both heat and pressure are applied. This causes the carrier to transfer to the substrate in the areas where adhesive has been applied to the target surface. This technique has a number of advantages including transfer of coatings in line with other printing operations, ease of variation of transfer patch dimensions and lower package design. When using a dieless transfer system, the final adhesive coat may be omitted or optionally replaced with a layer that is designed for improved adhesion with the adhesive applied to the target surface. The security tags on the packaging material may suitably be on the face of the packaging material that is to be its rear in use, so that it is unobtrusive and very difficult for a potential thief to remove. Thus, if the tags are applied during printing of the packaging material the packaging material may be printed on one side, and the tag(s) applied on the other. Alternatively the tag(s) may be applied to the face of the packaging material that is to be its front in use. In that case, to make it less obtrusive, the tag(s) may be overprinted or may be integrated with other markings on the front face: for example they could form part of a larger foiled area of graphics or lettering on the packaging. Thus the present tag can be applied to the back of the package at the point of manufacture, or can be integrated accurately with the design of the packaging. In contrast, hand-applied tags must for convenience must go on the outside of a package, spoiling product image. Whether the tag(s) are on the inside or the outside of the packaging there is preferably a marking on the outside of the packaging to indicate the location of the tag(s) so that they can be readily reactivated at the point of sale. The indicia could be a discreet marking which explicitly indicates the location of the foil, or could be a marking which implicitly indicates the location. In the latter case the indicia could be the barcode on the packaging, which could give an additional advantage in ease of deactivation of the foil. In many shops the barcode is swiped at the checkout when the product is sold. If the foil is located in a known relationship to the barcode, preferably on the opposite side of the packaging at the same place as the barcode, the unit in the shop that reads the barcode can be integrated with the unit that deactivates the foil. This makes it easier for checkout staff to read the barcode and deactivate the foil, because only one action is needed for both purposes, as a result of which it may be economical to apply magnetic security tags to lower cost goods. In addition, since it extremely likely that the barcode will be swiped at the checkout, it reduces the risk of the tag not being deactivated before the customer leaves the shop. The packaging material may be in a continuous web at the time of printing and/or application of the tag(s) or it may be in sheet form. If the packaging material is in the form of a web then individual tags may be formed at regular intervals along the web. By using one or more reels of tag film more than one tag may be formed across the width of the web. The tag(s) may be applied to the packaging material so that they bridge a part of the packaging material that is to be bent (either gently or folded) to form the eventual package, for example with the result that the tag is positioned across the corner of a carton, with portions of the tag on both sides of the corner. One of the problems of soft magnetic film tags is that they are active only along a so called "easy axis" which is a magnetically preferential orientation. The axis lies in the plane of the film and the existence of the easy axis causes there to be dead angles for the label under which the soft magnetic film does not trigger the alarm of the detector gate. A similar problem may arise with some designs of patterning of the deactivation layer. By ensuring the tag is wrapped around the corner of the carton this problem is avoided as at least some portion of the tag lies outside the easy axis. Each tag is suitably around 25mm x 16mm. Applying tags during manufacture of packaging material is faster than individual application of tags to packaging in-store. This allows tags to be applied to a greater number of products and at lower unit cost. If the security foil is applied after manufacture it may be applied using a gun as described above. The tag(s) may be defined by stamping from a continuous reel of multi-layer tag material, or such material may be pre-divided into individual labels which can then be stuck on to packages. Since the tag is applied to the target surface without the polymeric or paper carriers included in previous systems such as self adhesive labels, it is thinner and therefore more easily incorporated into packaging and easier to handle than prior tags. The tag may be applied to a substrate in two or more stages. For example, a tag of the type illustrated by the structure of figure 1 may be applied to a substrate by a first step in which a film comprising only the layers 1 , 3, 5 and 2 (i.e. without the active layer 4) is pressed on to a substrate to adhere the layers 2 and 5 to the substrate, the carrier 1 is removed, and the active layer 4 is then deposited over the deactivation layer already formed on the substrate. Again, the layers 4 and 5 could be substituted for each other. Analogous processes could be performed for the structure of figure 2 and other structures. The thin-film nature of the tags described above means that even if they are applied to the outside of packaging it is very difficult for a potential thief to pick them off the packaging surface. Thus tampering is less likely than with prior art tags. In addition the construction of the foil using highly durable lacquer and adhesive layers will impart high levels of chemical and physical durability. This makes the tags suitable for high security applications. The invention is not limited to the details of the foregoing examples. The present invention may include any feature or combination of features disclosed herein either implicitly or explicitly or any generalisation thereof irrespective of whether it relates to the presently claimed invention. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims: CLAIMS 1. A security tag film comprising: a carrier sheet; a layer of a pressure and/or heat sensitive adhesive; and a security structure located between the carrier sheet and the layer of adhesive, the security structure comprising: an active layer of a soft magnetic material; and a patterned deactivation layer of a hard or semi-hard magnetic material located in proximity to the active layer so that magnetisation of the deactivation layer may disrupt the uniformity of magnetisation of the active layer. 2. A security tag film as claimed in claim 1 , wherein the carrier sheet is a flexible plastics sheet. 3. A security tag film as claimed in claim 1 or 2, comprising a release layer between the carrier sheet and the security structure. 4. A security tag film as claimed in claim 3, wherein the release layer has a weaker adhesion for a layer adjacent to it than does the adhesive layer for a layer adjacent to it. 5 A security tag film as claimed in any preceding claim, wherein the adhesive layer is capable of activation in response to pressure and/or heating of the film against a substrate to adhere the film to the substrate. 6. A security tag film as claimed in claim 5 as dependant on claim 4, wherein the active layer and the deactivation layer are frangible, whereby on adhesion of a region of the film to a substrate by the adhesive the carrier sheet may be released from the active layer and the deactivation layer in that region, leaving the active layer and the deactivation layer in that region adhered to the substrate. 7. A security tag film as claimed in any preceding claim, comprising a lacquer layer between the security structure and the carrier sheet. 8. A security tag film as claimed in any preceding claim, comprising a layer having a surface relief between the security structure and the carrier sheet. 9. A security tag film as claimed in claim 8, wherein the layer having a relief provides a holographic structure. 10. A security tag film as claimed in any preceding claim, comprising a reflective layer between the security structure and the carrier sheet. 11. A security tag film as claimed in any preceding claim, wherein the deactivation layer is patterned into a plurality of spaced apart zones. 12. A security tag film as claimed in any preceding claim, wherein the deactivation layer comprises a dispersion of particles of a hard or semi-hard magnetic material. 13. A security tag film as claimed in any preceding claim, wherein the film is a stamping foil film. 14. A method for forming a security tag film, comprising: depositing over a carrier sheet a security structure comprising an active layer of a soft magnetic material and a patterned deactivation layer of a hard magnetic material located in proximity to the active layer so that magnetisation of the deactivation layer may disrupt the uniformity of magnetisation of the active layer; and depositing a layer of a pressure and/or heat sensitive adhesive over the security structure. 15. A method as claimed in claim 14, wherein the deactivation layer comprises a dispersion of particles of a hard or semi-hard magnetic material. 16. A method as claimed in claim 15, wherein the deactivation layer is deposited by silk-screen printing, gravure printing, flexography or Meyer bar coating. 17. A method as claimed in claim 14 or 15, wherein the carrier sheet is a flexible plastics sheet. 18. A method as claimed in any of claims 14 to 17, comprising the step of, prior to depositing the security structure, depositing a release layer over the carrier sheet. 19. A method as claimed in claim 18, wherein the release layer has a weaker adhesion for a layer adjacent to it than does the adhesive layer for a layer adjacent to it. 20. A method as claimed in any of claims 14 to 19, wherein the adhesive layer is capable of activation in response to pressure and/or heating of the film against a substrate to adhere the film to the substrate. 21. A method as claimed in claim 20 as dependant on claim 19, wherein the active layer and the deactivation layer are frangible, whereby on adhesion of a region of the film to a substrate by the adhesive the carrier sheet may be released from the active layer and the deactivation layer in that region, leaving the active layer and the deactivation layer in that region adhered to the substrate. 22. A method as claimed in any of claims 14 to 21 , comprising the step of, prior to depositing the security structure, depositing a lacquer layer over the carrier sheet. 23. A method as claimed in any of claims 14 to 22, comprising the step of, prior to depositing the security structure, depositing a layer having a surface relief between the security structure and the carrier sheet. 24. A method as claimed in claim 23, wherein the layer having a relief provides a holographic structure. 25. A method as claimed in any of claims 14 to 24, comprising the step of, prior to depositing the security structure, depositing a reflective layer between the security structure and the carrier sheet. 26. A method as claimed in any of claims 14 to 25, wherein the deactivation layer is patterned into a plurality of spaced apart zones. 27. A method as claimed in any of claims 14 to 26, wherein the film is a stamping foil film. 28. A method for applying a security tag, comprising: locating against a substrate the adhesive layer of a security tag film according to any of claims 1 to 13; pressing and/or heating a region of the film against a substrate to adhere the film to the substrate by means of the adhesive layer; and withdrawing the carrier sheet of the film from the substrate to leave the active layer and the deactivation layer in that region adhered to the substrate. 29. A method as claimed in claim 28, wherein the substrate is a packaging material. 30. A method as claimed in claim 29, wherein the security tag film is adhered to the interior surface of the packaging material. 31. A method as claimed in claim 29 or 30, comprising the step of printing on the opposite surface of the packaging material to that on which the active layer and the deactivation layer are adhered. 32. A method as claimed in claim 31 , comprising printing on the opposite surface of the packaging material to that on which the active layer and the deactivation layer are adhered indicia indicating the location at which the active layer and the deactivation layer are adhered. 33. A method as claimed in claim 32, wherein the said indicia is a machine readable product identification marking. 34. A method as claimed in claim 33, wherein the indicia is a bar code. 35. A method as claimed in claim 34, comprising bending the substrate across the location at which the active layer and the deactivation layer are adhered. 36. A packaging enclosure for a product, the enclosure having: a printed exterior surface; and an interior surface bearing a security tag comprising: a security structure comprising an active layer of a soft magnetic material, and a patterned deactivation layer of a hard or semi-hard magnetic material located in proximity to the active layer so that magnetisation of the deactivation layer may disrupt the uniformity of magnetisation of the active layer, and a layer of pressure and/or heat sensitive adhesive by which the security tag is adhered to the interior surface. 37. A packaging enclosure as claimed in claim 36, wherein the printed exterior surface bears printed indicia indicating the location at which the security tag is adhered. 38. A packaging enclosure as claimed in claim 37, wherein the said indicia is a machine readable product identification marking. 39. A packaging enclosure as claimed in claim 38, wherein the indicia is a bar code. 40. A security tag comprising: a layer of a pressure and/or heat sensitive adhesive; and a security structure located between the carrier sheet and the layer of adhesive, the security structure comprising: an active layer of a soft magnetic material; and a patterned deactivation layer of a hard or semi-hard magnetic material located in proximity to the active layer so that magnetisation of the deactivation layer may disrupt the uniformity of magnetisation of the active layer. 41. A method for applying a security tag as claimed in claim 40 to a substrate, wherein the adhesive layer and at least part of the security structure are applied to the substrate by pressing and/or heating against the substrate to adhere the adhesive layer and the said at least part of the security structure to the substrate.

Inventors: ASLET JONATHAN RICHARD, FERGUSSON LYNN SHONA HARDIE, GOODFELLOW ROBERT JOHN, MARSHALL ALLAN CRAIG, ASLET, JONATHAN, RICHARD, FERGUSSON, LYNN, SHONA, HARDIE, GOODFELLOW, ROBERT, JOHN, MARSHALL, ALLAN, CRAIG
Applicants: API FOILS LTD, ASLET JONATHAN RICHARD, FERGUSSON LYNN SHONA HARDIE, GOODFELLOW ROBERT JOHN, MARSHALL ALLAN CRAIG, API FOILS LIMITED, ASLET, JONATHAN, RICHARD, FERGUSSON, LYNN, SHONA, HARDIE, GOODFELLOW, ROBERT, JOHN, MARSHALL, ALLAN, CRAIG
Application year: 2000
Main classification: G08B13
IPC codes: G01V15, G08B13