GB2448836A - Optically variable magnetic stripe assembly - Google Patents

Abstract

An optically variable magnetic stripe assembly includes a magnetic layer (5), an optically variable effect generating layer (1,2) over the magnetic layer (5), and an electrically non-conductive reflective layer (12) between the magnetic layer (5) and the optically variable effect generating layer (1).

Description

OPTICALLY VARIABLE MAGNETIC STRIPE ASSEMBLY

The current invention is concerned with magnetic data stripes, and in particular optically variable magnetic stripe assemblies, such as those found on financial transaction cards.

It has been conventional practice now for many years, to provide a magnetic stripe on payment and identity documents such as credit cards, debit cards, cheque cards, transport tickets, savings books and other forms of security documents. The presence of the magnetic stripe allows such documents to become carriers of non-visual machine readable data.

In many instances such documents have also been provided with a vtsual security or authentication device in the form of an embossed hologram or diffractive image.

However the presence of both such devices on such documents significantly reduces the remaining surface area of document available to carry other information, security features and design elements.

There has therefore been a drive to combine the two devices in one integrated structure, which we refer to henceforth as an optically variable-magnetic (OVM) stripe The resultant device may be regarded as either a visually secured magnetic data carrier or alternatively a "hologram" which can be personalised with machine readable data (and read in an open architecture environment).

Prior art constructions for OVM stripes have been detailed US-A-4684795, US-A- 4631222, US-A-5383687 and EP-A-0998396. In principle the OVM stripe can substitute for all applications where currently high and low coercivity tape is currently applied, the most significant application by value is that in which the OVM stripe is applied to plastic financial transaction cards.

Figure 1 is a cross-sectional schematic of a conventional prior art OVM stripe applied to a financial card as described in the prior art cited above.

Essentially it comprises 2 functional sub-structures 1. A transparent lacquer layer 1 embossed with an holographic or diffractive surface relief structure 2 and coated with a continuous reflection-enhancing layer of metal 3, typically aluminium, bonded by an adhesion promoting primer layer 4 to 2. A magnetic layer 5 that is coated on the primer layer 4. The magnetic layer 5 is further coated with a heat activated adhesive layer 6 to bond the structure to the card substrate 7 The plastic transaction card 7 is typically a tn-laminate structure (not shown) comprising an opaque central polymeric core layer printed with information on either side, laminated between 2 transparent polymeric overlay sheets.

The OVM stripe is first applied to that transparent overlay sheet pertaining to the rear of the card, by a heat activated continuous roll-on transfer process. Subsequent to this the three laminate layers are then fuse bonded together in a laminating press. In order to apply the magnetic tape to the transparent overlay sheet, through in essence a hot-stamping process, it is first necessary to provide the OVM stripe structure onto a release coated carrier or backing layer.

However a structural drawback of the prior art OVM stripe has been identified.

Unlike conventional non-holographic magnetic stripes the pnor art OVM stripes are provided with a continuous metallic reflection enhancing layer 3. This metallic reflection enhancing layer is conductive and this has led to problems with static discharges in automatic teller machines.

It is well known that under conditions of low environmental humidity, substantial electrostatic surface charges can build up on articles or bodies which are poor conductors or conversely good insulators. For example a person walking around in a carpeted room wearing shoes with insulating (e.g. rubber) soles, can acquire a very significant amount of electrostatic surface charge this will become evident when that person touches a good conductor such a metal door handle, thus effecting rapid discharge of this electrostatic charge and experienced as a minor electric shock.

In particular as the air humidity drops below 25% the conductivity of the air becomes low enough to prevent any leakage of electrostatic charge into the atmosphere in such circumstances electrostatic potentials in excess of several kilovolts can build up on the human body Consider next a plastic, typically PVC, transaction card containing a conventional magnetic stripe.

PVC when compared to the human body is a very good insulator, hence we should expect, in absence of a conductive element within the card making contact with a second conductor external to the card, that there will be a distribution of electrostatic charge on the surface of the card.

Now the magnetic oxide layer within the known non-holographic magnetic stripe is currently exposed at either edge of the card and hence there exists the potential that when the card is inserted into an automated transaction machine (ATM) or magnetic card reader the exposed edge may contact a conductive component within the reader and rapidly discharge the electrostatic build-up on the surface of the card into the electrical circuitry of the ATM or reader. The associated voltage spike may be sufficiently large to damage or de-activate the machine. However tests conducted by the inventors have confirmed that the conductivity of the magnetic oxide layer is poor resulting at worst in a very slow transfer or discharge of the electrostatic potential built up on the card However moving our consideration of this electrostatic discharge problem on from the scenario of using a card containing a standard magnetic stripe to that where the card contains an OVM stripe, we now have the opportunity for conduction and thus electrostatic discharge through the reflective metal layer 3 applied to the surface relief 2 present on the holographic diffractive layer. Tests conducted by the inventors, wherein the exposed edge of the OVM stripe (present on a PVC transaction card) is brought into contact with a metal sphere connected to a device capable of measuring the transit dynamic changes in the charge or voltage transferred to the metal sphere confirm that the reflective metal layer very rapidly and efficiently discharges the electrostatic charge that had resided on the exterior of the card onto the metal sphere.

Furthermore such tests also confirm that if an individual holds the card in such a way that one finger contacts the near edge of the OVM stripe, whilst the other end of the OVM stripe is allowed to touch the conducting sphere then whatever electrostatic charge and potential is present on the individual will also be rapidly discharged onto the conducting sphere.

Clearly since the electrostatic build up on an individual under the right environmental conditions can be very considerable, there is therefore a significant risk that when a transaction card is located into an ATM or reader in the manner described (causing discharge of the electrostatic present on card and card holder into the circuitry of the machine) the machine may be damaged or its operation disrupted.

In accordance with the present invention, an optically variable magnetic stripe assembly includes a magnetic layer, an optically variable effect generating layer over the magnetic layer, and an electrically non-conductive reflective layer between the magnetic layer and the optically variable effect generating layer.

The inventors recognised that a modified OVM stripe structure was required in order to eliminate risk in the field that cards containing an OVM stripe may cause operational problems associated with electrostatic discharge through the metal layer and in particular end to end discharge electrically linking the body of the card holder to conductive elements in the transaction device or reader.

In the invention, we replace the metal reflecting layer of the prior art with an electrically non-conductive reflective layer. This then reduces or avoids the problem of electrical discharge when the edge of a security document provided with the magnetic stripe assembly is touched.

The non-conductive reflective layer can be fabricated in a number of ways by, for example. using a non-metallic material such as a high refractive index material The magnetic stripe assembly can be used with a variety of security articles including security documents as will be readily apparent to a person of ordinary skill in the art An example of an optically variable magnetic stripe assembly according to the invention will now be described and contrasted with a comparative example with reference to the accompany drawings, in which -Figure 1 is a schematic cross-section (not to scale) through a conventional assembly adhered to a card substrate; Figure 2 is a view similar to Figure 1 but of an example of the invention, and, Figure 3 illustrates in cross-section (not to scale) the assembly of Figure 2 supported on a carrier layer and prior to mounting to the card substrate In the following description, those layers which are substantially the same as layers described earlier will be given the same reference numerals Figures 2 and 3 show a cross sectional illustration of the example Figure 2 shows the construction after application to a card substrate 7 Figure 3 shows the construction prior to application to a card substrate Figure 3 shows the presence of a supporting polymeric carrier layer 10 and a release layer 11 Typically the carrier layer 10 is a 19-23 micron PET layer and the release layer his typically a wax or silicone layer between 0 01 and 0 1 microns in thickness. Here the highly conductive metal reflection-enhancing layer 3 of the prior art has been replaced with a non-conducting reflection enhancing layer A first example of a suitable alternate reflection-enhancing layer is a coating 12 of a material which has an optical index of refraction of at least 2 0 and in electrical terms is such a poor conductor that it may be classified as an insulator (in electromagnetic theory known as a dielectric) An index of refraction of 2 0 or more is usually necessary to ensure that there is a minimum refractive index change of 0 5 or more between the embossed lacquer layer 1 which typically has a index of refraction of around 1 4 and the dielectric reflection coating 12 The skilled practitioner will know both from experience and the application of Fresnel equation for reflection efficiency that this refractive index step will provide a holographic or diffractive image of acceptable visual brightness under most ambient lighting conditions.

Suitable dielectric materials with a refractive index = 2 0, with good optical transparency and amenable to coating by the processes of vacuum deposition are Ti02, ZnS & Zr02 -though there a number of other suitable metal oxide materials Such materials are known within the optical coatings industry as high refractive index (HRI) materials.

These materials are deposited to create the layer 12 with a thickness range between 0 07 micrometers and 0.15 micrometers, depending on the particular dielectric chosen and the optical effect required.

Note that because these HRI coatings are transparent the holographic image will be viewed against the reflective hue provided by the underlying coatings Surprisingly, the inventors found that this was not necessarily a disadvantage despite the fact that a fully obscuring metal layer had been used in the past.

In fact, it can be advantageous. For example, coloured magnetic materials exist for which it is a benefit to be able to view through the high refractive index layer. It makes the assembly much more difficult to copy because colours or indicia can be provided on the magnetic layer.

The use of a high refractive index layer also avoids problems associated with metallic layers such as corrosion.

For the case in which adhesion promoting layer or primer 4 has no colorants present and has reasonable optical transparency then the background hue will be provided by the black (Hi-Co) or brown (Lo-Co) magnetic oxide layers. These dark colours will naturally have the desirable effect of increasing the perceived brightness and contrast of the holographic image. Should it be desirable that the underlying coatings not be visible through the HRI layer 12 for aesthetic reasons a further optical obscuring layer such as a coloured or metallic ink coated layer (not shown) can be provided between the HRI and magnetic layers. Metallic ink may be used so long as it is non-conducting Indeed the majority of metallic inks are non-conducting as a non-conducting resin binder wholly surrounds the metal pigment particles. As a further enhancement this additional coated layer may be provided in the form of a single or multicolour design defining visibly readable information.

Rather than providing an additional layer similar effects could also be achieved by adding colorants to the primer 4 and/or adhesive layers 6.

The primer layer 4 may be a purely organic layer (possibly cross-linked) with a thickness of about 0.7 microns. Inorganic materials are also suitable. One particular example is described in US-A-5383687 in which the layer is a layer of at least one organic polymer to which at least inorganic pigment is added. The polymers used may be for example high-molecular acrylic resins, polyvinylidene chloride PVC, PVC-copolymers, chlorinated rubber, polyester, and silicone-modified binder. The inorganic pigments used may be for example silicates and/or titanium dioxide.

It should be recognised that although we have shown the adhesion promoting primer layer 4 as single layer or coating we anticipate that this layer system may in effect be comprised of sub-layers or coatings, each with a separate and distinct formulation optimised for adherence to the reflection layer and magnetic layer respectively.

In such cases it may be preferable to provide the colorant (which may take the form of an organic dye or inorganic pigment) in only one of these sub-layers The inventors also recognised that in addition or as an alternative to modifying the hue or colour of the OVM stripe it may be also be advantageous to provide a luminescent material. Such materials are widely used within security printing to add additional security and can be verified using non-visible light sources.

As a further alternate to using a HRI layer 12 other non-conducting reflection-enhancing layers may be used. For example acceptable effects can be achieved using a non-conductive metallic ink instead of the HRI. This differs from the example above where a metallic ink is used in combination with a HRI layer.

Claims (13)

1. An optically variable magnetic stripe assembly including a magnetic layer, an optically variable effect generating layer over the magnetic layer, and an electrically non-conductive reflective layer between the magnetic layer and the optically variable effect generating layer.

2. An assembly according to claim 1, wherein the reflective layer has an optical index of refraction of at least 2.0.

3 An assembly according to claim 1 or claim 2, wherein there is a refractive index change of at least 0 5 between the optically variable effect generating layer and the reflective layer.

4 An assembly according to any of the preceding claims, wherein the reflective layer is a high refractive index material such as Ti02, ZnS or Zr02

5. An assembly according to any of the preceding claims, wherein the reflective layer has a thickness in the range 0.07-0.15 microns.

6 An assembly according to any of claims 1 to 3, wherein the reflective layer comprises a non-conductive metallic ink.

7 An assembly according to any of the preceding claims, further comprising an adhesion promoting layer between the magnetic layer and the reflective layer.

8 An assembly according to claim 7, wherein the adhesive promoting layer includes an optically obscuring material.

9. An assembly according to any of claims 1 to 7, further comprising an optically obscuring layer between the reflective layer and the magnetic layer.

An assembly according to claim 9, wherein the optically obscuring layer is a non-conducting metallic ink.

11 An assembly according to claim 9 or claim 10, wherein the optically obscuring layer is provided in a single or multicoloured design defining visibly readable information.

12 An assembly according to any of claims 7 to 11, wherein the adhesion promoting layer is formed by a plurality of sub-layers each with a formulation optimized for adherence to the associated layers.

13. An assembly according to any of the preceding claims, wherein the magnetic layer is a magnetic oxide layer.

14 An assembly according to any of the preceding claims, wherein the optically variable effect generating layer comprises a lacquer provided with a surface relief 15. A security document provided with an optically variable magnetic stripe assembly according to any of the preceding claims.

16 A security document according to claim 15, the security document comprising a payment or identity document such as a credit card, debit card, cheque card, ticket, savings book, banknote and the like.