GB2553391A

GB2553391A - Security document

Info

Publication number: GB2553391A
Application number: GB1704314.2A
Authority: GB
Inventors: Wallington Sarah; Hatton Jan
Original assignee: De la Rue International Ltd
Current assignee: De la Rue International Ltd
Priority date: 2016-03-23
Filing date: 2017-03-17
Publication date: 2018-03-07
Also published as: GB201604957D0; GB201704314D0; AU2017201936A1

Abstract

A security document comprises a polymer substrate 100 including at least one tear propagation barrier 102; 102a-c, the barrier comprising an array of apertures 104 in the polymer substrate which are arranged to distribute stress in order to resist the propagation of a tear through the document, a component of the length of the barrier is parallel to a first edge 100a-d of the document and extends at least half of the length of this edge. The apertures may extend fully through the thickness of the substrate. The document may comprise a multilayer polymer where the apertures extend partially through the thickness of the document.

Description

(54) Title of the Invention: Security document

Abstract Title: Security document with perforations that form a tear resisting barrier (57) A security document comprises a polymer substrate 100 including at least one tear propagation barrier 102; 102a-c, the barrier comprising an array of apertures 104 in the polymer substrate which are arranged to distribute stress in order to resist the propagation of a tear through the document, a component of the length of the barrier is parallel to a first edge 100a-d of the document and extends at least half of the length of this edge. The apertures may extend fully through the thickness of the substrate. The document may comprise a multilayer polymer where the apertures extend partially through the thickness of the document.

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At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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SECURITY DOCUMENT

The present invention relates to security documents. In particular, the invention relates to a security document comprising a polymer substrate including at least one tear propagation barrier for resisting the propagation of a tear through the document, and a method of making the polymer substrate.

Security documents, such as banknotes, identification cards, passports, cheques, visas, certificates, and the like, are in common usage around the world every day. These documents are repeatedly handled and are liable to become worn. Banknotes in particular are handled very frequently and so are highly susceptible to wear. As a result a note will tend to become cut or nicked at the edges and a tear may spread across the note possibly even causing it to be separated into two or more pieces. It often happens that banknotes are torn inadvertently, for example upon removal from a cash register or wallet. Banknotes that are damaged in this way may no longer constitute legal currency and must be taken out of circulation and replaced, thereby causing inconvenience and cost.

Security documents are vulnerable to this kind of damage because they have relatively low tear strength, i.e. they do not resist the growth of cuts and nicks when under tension or shear stress. Banknotes (and other security documents) which are constructed from plastics/polymer materials may be more robust and longer-lasting than those made from paper but even these may be quite easily torn. Indeed, it has been found that once a nick has been formed in the edge of a polymer security document, a tear will typically propagate through the substrate from the nick more readily than will be the case in a document with a fibrous substrate, e.g. paper.

The present invention aims to alleviate at least to some extent the problem of damage to security documents formed of polymer substrates.

The invention is set out in the accompanying claims.

According to an aspect of the invention, there is provided a security document comprising a polymer substrate including at least one tear propagation barrier, the barrier comprising an array of apertures in the polymer substrate which are arranged to distribute stress in order to resist the propagation of a tear through the document, a component of the length of the barrier parallel to a first edge of the document having a magnitude of at least 50% of the length of the first edge.

The tear propagation barrier beneficially serves to resist/arrest the progress of a tear, which may be initiated at a nick at an edge of the security document.

The component of the length of the barrier parallel to the first edge of the document may have a magnitude of at least 60%, preferably at least 70%, more preferably at least 80%, more preferably at least 90%, and more preferably at least 95%, of the length of the first edge.

The apertures may be arranged such that at least 20%, preferably at least 30%, more preferably at least 40%, more preferably at least 50%, more preferably at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90%, and more preferably at least 95%, of points on the first edge of the document have at least one aperture of the array located on an imaginary straight line emanating from the respective point orthogonal to the first edge.

Each aperture may be shaped such that a portion of its periphery, which lies furthest from the first edge of the document, is curved and has a radius of curvature not less than 0.1 mm.

The apertures may extend fully through the thickness of the polymer substrate.

The polymer substrate may be multi-layered and the apertures may extend partially through the thickness of the document. The apertures may extend through an external layer of the document. The apertures may extend through an internal layer of the document.

The apertures may be of similar size and/or shape to one another. Or, the apertures may be of dissimilar size and/or shape to one another.

The barrier may comprise the said apertures arranged in at least one line on a face of the document, the apertures being separated from one another by interval portions of the document, the proportion of aperture-to-interval preferably being less than 50%, more preferably less than 30%, along the or each line.

The at least one line of apertures may be substantially straight. Or, the at least one line of apertures may comprise a curve, for example a wave.

The length of an interval portion between the edges of two adjacent ones of the apertures may be between about 0.05 to 5 mm, preferably about 1 mm.

The apertures may be arranged in two or more lines which are spaced apart in parallel relationship with one another. The security document may comprise three lines of apertures which are spaced apart in parallel relationship with one another. The apertures and interval portions of a first line may be staggered with respect to the apertures and interval portions of a second, adjacent line. Adjacent ones of the two or more lines may be spaced from one another by between about 0.5 and 1.5 mm, preferably about 1.0 mm.

The security document may be substantially rectangular, having two parallel longer edges and two parallel shorter edges, the longer edges being orthogonal to the shorter edges, wherein the first edge is one of the longer edges or one of the shorter edges. The barrier may comprise at least one line of the said apertures which extends longitudinally along the face of the document so as to be in generally parallel relationship with the longer edges of the document.

The at least one line of apertures may extend at least about 50% of the distance between the first shorter edge and the second shorter edge of the document, preferably at least about 60%, more preferably at least about 70%, more preferably at least about 80%, more preferably at least about 90%, more preferably at least about 95%, preferably other than 100%.

The ends of the at least one line of apertures may be equidistant from the respective shorter edges of the document. The at least one line of apertures may be spaced from the first longer edge of the document by no more than about 25% of the distance between the first longer edge and the second longer edge of the document, preferably by no more than about 20%, more preferably by no more than about 15%, more preferably by no more than about 10%, more preferably by no more than about 5%.

The barrier may comprise at least one line of the said apertures which extends laterally along the face of the document so as to be in generally parallel relationship with the shorter edges of the document. The at least one line of apertures may extend at least about 50% of the distance between the first longer edge and the second longer edge of the document, preferably at least about 60%, more preferably at least about 70%, more preferably at least about 80%, more preferably at least about 90%, more preferably at least about 95%.

The ends of the one line of apertures may be equidistant from the respective longer edges of the document. The barrier may comprise at least one line of the said apertures spaced from the first shorter edge of the document by no more than about 25% of the distance between the first shorter edge and the second shorter edge of the document, preferably by no more than about 20%, more preferably by no more than about 15%, more preferably by no more than about 10%, more preferably by no more than about 5%.

The barrier may comprise at least one line of the said apertures extending along the face of the document so as to be non-parallel with the longer and shorter edges of the document.

The security document may comprise two or more of the said tear propagation barriers. The security document may comprise first and second tear propagation barriers which are spaced apart from one another in parallel relationship. The first tear propagation barrier may be located on one side of an imaginary centre line which is parallel with the longer edges of the document, and the second tear propagation barrier is located on the other side of the centre line. The first tear propagation barrier may be located on one side of an imaginary centre line which is parallel with the shorter edges of the document, and the second tear propagation barrier is located on the other side of the centre line.

The security document may comprise first and second tear propagation barriers which are spaced apart from one another in parallel relationship on respective sides of an imaginary centre line which is parallel with the longer edges of the document, and third and fourth tear propagation barriers which are spaced apart from one another in parallel relationship on respective sides of an imaginary centre line which is parallel with the shorter edges of the document. The first, second, third and fourth tear propagation barriers may intersect such as to comprise a continuous substantially rectangular border within the substantially rectangular document.

The security document may comprise first and second tear propagation barriers which are arranged in orthogonal relationship with one another. The first tear propagation barrier may be located on one side of an imaginary centre line which is parallel with the longer edges of the document, and the second tear propagation barrier may be located on one side of an imaginary centre line which is parallel with the shorter edges of the document, and preferably ends of the first and second tear propagation barriers intersect one another. The first and second tear propagation barriers may be arranged to extend at a non-zero angle with respect to any one of the edges of the document.

The security document may comprise a bank note, an identity card, or a portion of a passport.

The apertures may be laser-cut apertures in the polymer substrate.

The polymer substrate or at least one layer thereof may comprise biaxially oriented polypropylene (BOPP).

Each of the apertures may be located away from the edges of the document such that no aperture intersects a said edge.

Each aperture may be partially or substantially circular in shape. Each substantially circular aperture may have a diameter of between about 0.05 to 1 mm, preferably about 0.1 to 0.5 mm and more preferably about 0.1 to 0.3 mm. Or, each aperture may be elliptical in shape. Or, each aperture may be rectangular in shape, preferably square. Or, each aperture may be shaped an as alphanumeric character.

Each aperture may have a maximum width, or diameter, of about 0.05 to 1 mm, preferably about 0.1 to 0.5 mm and more preferably about 0.1 to 0.3 mm.

The thickness of the polymer substrate may be between about 30 to 200 microns, preferably about 50 to 100 microns.

According to another aspect of the invention, there is provided a method of making a tear propagation barrier in a polymer substrate for a security document, comprising the steps: providing a polymer substrate; and providing an array of apertures in the polymer substrate, the apertures being arranged to distribute stress in order to resist the propagation of a tear through the substrate, a component of the length of the barrier which is parallel to a first edge of the substrate having a magnitude of at least 50% of the length of the first edge.

The step of providing an array of apertures in the polymer substrate may comprise removing substrate material using a laser to thereby form the apertures.

The term “polymer” is used herein to denote non-fibrous polymeric materials, preferred examples of which include polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP) (preferably OPP or BOPP), polycarbonate (PC), polyvinyl chloride (PVC), nylon, acrylic, Cyclic Olefin Polymer (COP) or Cyclic Olefin Copolymer (COC), or any combination thereof. In preferred examples, the polymeric material(s) may be transparent (i.e. optically clear but optionally with a coloured tint) or at least translucent. One or more opacifying layers may be applied to one or both surfaces of the substrate to provide a surface suitable for carrying printed graphics. Typically the opacifying layers may comprise a coating carrying a dispersion of opacifying pigments, such as a white ink. The apertures may or may not extend through such opacifying layers.

Embodiments will now be described, by way of example, with reference to the accompanying figures in which:

Figure 1 shows a plan view of an exemplary polymer substrate for a security document, the substrate comprising a tear propagation barrier in accordance with a first embodiment of the invention;

Figures 2 to 5 show embodiments comprising differing arrangements of the tear propagation barrier;

Figure 6 illustrates a part of a polymer substrate comprising a tear propagation barrier of the type shown in Figures 1 to 5;

Figures 7a to 7d show exemplary arrangements of the propagation barriers on security documents which include the polymer substrate; and

Figure 8 shows data from a test conducted on a sample polymer substrate comprising a tear propagation barrier in accordance with an embodiment of the invention.

Referring to Figure 1, a rectangular polymer substrate 100 comprises first and second longer sides or edges 100a, 100b of length Lx and first and second shorter sides or edges 100c, 100d of length Ly, and is bisected along its length and across its width by respective longitudinal and transverse centrelines X-X’,

Y-Y’. In this exemplary embodiment the polymer substrate 100 is constructed from biaxially oriented polypropylene (BOPP) material and is intended to form all or part of a banknote, but could equally be incorporated into a cheque, visa, passport, identification card, certificate, or other security document.

The polymer substrate 100 includes a tear propagation barrier 102 comprising a plurality of perforations or apertures 104. In this embodiment, each of the apertures 104 is circular and has a diameter d1 of about 0.1 mm. It will be understood that in the Figures presented herein the size of the apertures 104, relative to the polymer substrate 100, has been exaggerated for the sake of clarity. Each of the apertures comprises an unoccupied, or vacant, space. That is, while the apertures may contain air, they are devoid and free of solid material. In other words, the apertures are empty cavities. Also in this embodiment, the apertures 104 extend all the way through the polymer substrate 100 such as to provide through-holes. In an alternative embodiment, the polymer substrate 100 is multi-layered, i.e. comprising a plurality of stacked polymeric layers, preferably laminated to one another, and the apertures 104 extend fully through only one or more layers of the stack. For example, the apertures may extend through only one or more inner layers of the stack such that the apertures 104 comprise closed voids, or pockets, within the polymer substrate 100.

The apertures 104 are evenly spaced apart from one another at intervals by land regions 106 such that the tear propagation barrier 102 forms a single straight line extending across a face of the polymer substrate 100 in the longitudinal direction, parallel to the first and second longer sides 100a, 100b. In this embodiment, the spacing d2 between the apertures 104 is 1 mm and so the proportion of aperture-to-interval along the tear propagation barrier 102 is 10%. The line of apertures 104 is offset from the longitudinal centreline X-X’ such that it is closer to the first longer side 100a than to the second longer side 100b of the polymer substrate 100. More particularly, the line of apertures 104 is located within about 10% of the distance from the first longer side 100a toward the longitudinal centreline X-X’. First and second ends of the line of apertures 104 are located about 10% of the distance from the respective shorter sides 100c, 100d toward the transverse centreline Y-Y’. The length Lb of the tear propagation barrier 102 is defined as the distance between the outer edges of the outermost apertures 104 with respect to the transverse centreline Y-Y’. Accordingly, in this embodiment the length Lb of the tear propagation barrier 102 (which is parallel to the first longer side 100a of the polymer substrate) has a magnitude which is 80% of the length Lx of the first longer side 100a.

It will of course be understood that, while in Figure 1 the tear propagation barrier 102 is shown to be closer to the first longer side 100a than the second longer side 100b of the polymer substrate 100, this could be reversed such that the barrier 102 is closer to the second longer side 100b than the first longer side 100a.

Referring to Figure 2, in another embodiment the polymer substrate 100 is generally as described herein above, but in this case the tear propagation barrier 102 forms a single straight line extending across a face of the polymer substrate 100 in the transverse direction, parallel to the first and second shorter sides 100c, 100d of the polymer substrate 100. The line of apertures 104 is offset from the transverse centreline Y-Y’ such that it is closer to the second shorter side 100d than the first shorter side 100c of the polymer substrate 100. More particularly, the line of apertures 104 is located within about 10% of the distance from the second shorter side 100d toward the transverse centreline Y-Y’. First and second ends of the line of apertures 104 are located about 10% of the distance from the respective longer sides 100a, 100b toward the longitudinal centreline X-X’. The length Lb of the tear propagation barrier 102 is defined as the distance between the outer edges of the outermost apertures 104 with respect to the longitudinal centreline X-X’. Accordingly, in this embodiment the length Lb of the tear propagation barrier 102 (which is parallel to the second shorter side 100d of the polymer substrate) has a magnitude which is 80% of the length Ly of the second shorter side 100d.

It will of course be understood that, while in Figure 2 the tear propagation barrier 102 is shown to be closer to the second shorter side 100d than the first shorter side 100c of the polymer substrate 100, this could be reversed such that the barrier 102 is closer to the first shorter side 100c than the second shorter side 100d.

Turning now to Figure 3, in another embodiment the line of apertures 104 ofthe tear propagation barrier 102 is arranged to be non-parallel with the sides 100a-d of the polymer substrate 100. More particularly, a first end of the line of apertures 104 (left-most in the sense of Figure 3) is located about 10% of the distance from the first longer edge 100a toward the longitudinal centreline X-X’, while a second end ofthe line of apertures 104 (right-most in the sense of Figure 3) is located about 40% of the distance from the first longer edge 100a toward the longitudinal centreline X-X’. Thus, in this embodiment the tear propagation barrier 102 comprises both a longitudinal component along the length of the polymer substrate 100 and a transverse component across the width of the polymer substrate 100. As can be seen from Figure 3, the longitudinal component is greater than the transverse component and so the tear propagation barrier 102 may be said to extend across the face of the polymer substrate 100 predominantly in the longitudinal direction.

Accordingly, the tear propagation barrier 102 has a length Lb which is greater than that of the embodiment of Figure 1. Nevertheless, in this embodiment the longitudinal or lengthwise component Lbx ofthe tear propagation barrier 102 has a magnitude which is 80% of the length Lx of the first longer side 100a. In other words, the tear propagation barrier 102 is inclined with respect to the first longer side 100a and projects or presents an “effective length” which is 80% of the length Lx of the first longer side 100a (as is the case in the embodiment of Figure 1).

It will of course be understood that, while in Figure 3 the tear propagation barrier 102 is shown to be closer to the first longer side 100a than the second longer side 100b of the polymer substrate 100, this could be reversed such that the barrier 102 is located closer to the second longer side 100b than the first longer side 100a. Furthermore, the tear propagation barrier 102 may be arranged with a transverse component which is greater than the longitudinal component such that the barrier 102 extends across the face of the polymer substrate 100 predominantly in the transverse direction. Of course, the barrier 102 could be located closer to one of the shorter sides 100c, 100d than the other of the shorter sides 100c, 100d.

Referring to Figure 4, in another embodiment each one of first and second tear propagation barriers 102a, 102b is arranged generally as described herein above with respect to Figures 1 and 2, respectively. Ends of the first and second tear propagation barriers 102a, 102b intersect such that together the barriers form a continuous line of apertures 104 which extends generally along the first longer side 100a and the second shorter side 100d of the polymer substrate.

Referring now to Figure 5, another embodiment comprises first and second tear propagation barriers 102a, 102b as described herein above with respect to Figure 4, and further includes third and fourth tear propagation barriers 102c, 102d which extend respectively along the second longer side 100b and the first shorter side 100c of the polymer substrate 100. In this embodiment, ends of the four tear propagation barriers 102a-102d intersect such that together the barriers form a continuous line of apertures 104 which extends generally along all four sides 100a-d of the rectangular polymer substrate 100.

The function of the tear propagation barrier will now be described with particular reference to Figure 6, which illustrates part of a polymer substrate 100 of a banknote comprising a tear propagation barrier 102 of the type described herein above with respect to Figures 1 to 5. However, in this embodiment the tear propagation barrier 102 comprises two parallel lines 102a, 102b of apertures 104 as described further below. A nick or notch N in the first longer side 100a of the polymer substrate 100 is caused, for example, by repeated folding of the banknote in use. The notch N creates a stress concentration, which enables the initiation of a crack or tear T through the polymer substrate 100 under an applied force, for example as the banknote is handed from one person to another. Once initiated the tear T progresses though the material of the polymer substrate 100 and across the face thereof. The phenomenon of tear or crack propagation through a material is well understood and will not be discussed here, except to say that the tear T will become unstable and continue to propagate only if an increment in crack growth results in more stored energy being released than can be absorbed by the creation of a new crack surface. Each of the apertures 104 of the tear propagation barrier 102 serves to provide such a new surface. Thus, when the tear T encounters an aperture 104 its energy is dissipated with the effect that the progress of the tear T is arrested or at least resisted. According to established principles of fracture mechanics a curved surface will better resist crack propagation and for this reason at least the innermost portion of the aperture 104 (i.e. in this example that portion which is located furthest from the first longer side 100a of the polymer substrate 100) is curved in shape. More preferably the aperture 104 is circular, as shown in Figure 6.

It may be that the said encounter with an aperture 104 is insufficient to dissipate completely the energy of the tear T and in that case the tear T may continue to propagate through the polymer substrate 100. If the energy is high enough then the tear T could damage significantly the polymer substrate 100, perhaps even spreading as far as its opposite edge (i.e. in this example the second longer side 100b) and causing the polymer substrate 100 to be torn into two. To mitigate this risk, the tear propagation barrier 102 preferably further comprises at least one further line 102b of apertures. In the exemplary embodiment the second line 102b extends parallel with the first line 102a, and the apertures 104 of the two lines 102a, 102b are offset or staggered with respect to one another (in the longitudinal direction), in order to increase the likelihood that the tear will encounter an aperture 104 of the second line 102 rather than pass between two of the apertures 104. When the tear T reaches an aperture 104 of the second line 102b that aperture will serve to arrest or at least resist the progress of the tear T by the same mechanism described herein above.

It will be understood that one or more additional lines of apertures may be included to increase further the tear resistance of the tear propagation barrier

102. Moreover, any number of the propagation barriers (each including one or more lines of apertures) may be arranged on the polymer substrate in an almost infinite variety of positions, shapes and patterns, in order to provide increased tear resistance. Nevertheless, in order to have practical effect it is believed that the length of a said propagation barrier (or a component thereof) parallel to a side of the polymer substrate should have a magnitude of at least 50% of the length of that side. If the said magnitude is less than this the coverage provided by the propagation barrier is likely to be insufficient to prevent the polymer substrate from being torn.

Preferably, in any one tear propagation barrier 102 the apertures are arranged such that at least around 20% of points along the side of the polymer substrate have at least one aperture located on an imaginary straight line emanating from the respective point orthogonal to the first side. Thus a tear, which may spread from one of the possible initiation points along the side of the polymer substrate, and run in a direction which is substantially normal to the side, will encounter at least one aperture which will resist its further propagation.

Referring again to Figure 6 to provide an example, assuming the diameter of each aperture to be 0.2 mm and the spacing parallel to edge 100a between any two adjacent apertures in one of the lines to be 1 mm, if only one line 102a of apertures were provided, the relevant proportion of “protected” points on edge 100a from which a tear would intersect an aperture would be about 17% (0.2 mm I 1.2 mm). By adding second line of apertures 102b, staggered so that its apertures are equidistant between those of the first line 102a (as shown), the proportion of “protected” points on edge 100a is increased to approximately 33% (0.4 mm I 1.2 mm). An optional third such line of apertures (shown in dashed lines at 102c) would increase this still further to approximately 50% (0.6 mm /1.2 mm). The proportion of protected edge points can be further increased by increasing the sizes of the apertures relative to the intervals between them and/or increasing the number of staggered lines. It is preferred to provide the desired level of protection by increasing the number of lines whilst maintaining a reasonably low aperture-to-interval ratio in order to prevent the or each line of apertures from acting as a perforation line which might otherwise promote tearing of the document along that line. The aperture-to-interval ratio in any one line is preferably less than 50%, more preferably less than 30%.

The apertures of one tear propagation barrier may all be of similar size or different size to one another. Also the apertures may be of similar shape or different shape to one another. Furthermore the size and/or shape of the apertures of one tear propagation barrier may be the same as, or different from, another tear propagation barrier. For effective stress distribution, it is generally preferable that the apertures are evenly, or regularly, spaced from one another.

While in the above-described embodiments the apertures of the tear propagation barriers are arranged to form straight lines, it will be understood that in other embodiments they may form a variety of other shapes or patterns, for instance curves, waves, geometrical shapes, alphanumerical characters or other textual information, and the like. Examples of tear propagation barriers 102 comprising textual information (“100”) and waves are shown at Figures 7a and 7b respectively. The exemplary specimen banknotes depicted in Figures 7a and 7b additionally show a transparent window feature 110. It will be appreciated that this is not an aperture and does not form part of the tear propagation barrier 102. Rather, the windows 110 are formed by the absence of an opacifying layer on the otherwise transparent polymer substrate from which notes are formed. Figures 7c and 7d illustrate exemplary patterns, formed by tear propagation barriers 102 on security documents, for example banknotes.

Furthermore, while as described herein above the tear propagation barriers may be located about 10% of the distance from a side toward a centreline of the polymer substrate, it will be understood that the barriers may be located anywhere on the polymer substrate which enables the barriers to arrest or at least resist a tear and thereby usefully prevent or minimise damage to the polymer substrate.

A tear test was carried out by the inventors on a sample polymer substrate comprising tear propagation barriers as described herein above. The sample comprised three barriers arranged in parallel rows. The apertures of each of the barriers comprised circular holes extending fully through the polymer substrate. The holes were formed using a laser. Each hole had a diameter of 0.1 mm and was spaced from the next hole of the barrier by 0.5 mm. The rows of the barriers were spaced 0.5 mm apart. A small incision or notch was made at an edge of the polymer substrate and a tensile force was exerted on the polymer substrate by a machine in order to initiate a tear from the notch. As can be seen from the plot shown at Figure 8, the machine extension increased while the tear progressed toward the tear propagation barrier with little resistance and the applied load then rose abruptly as the tear encountered a hole of the first barrier. The material at the surface of the hole dissipated the tear energy and halted the progress of the tear through the polymer substrate. A substantially higher load of over 4 N was then required in order for the tear to progress any further.

It will be understood that the invention has been described in relation to its preferred embodiments and may be modified in many different ways without departing from the scope of the invention as defined by the accompanying claims.

Claims

1. A security document comprising a polymer substrate including at least one tear propagation barrier, the barrier comprising an array of apertures in the polymer substrate which are arranged to distribute stress in order to resist the propagation of a tear through the document, a component of the length of the barrier parallel to a first edge of the document having a magnitude of at least 50% of the length of the first edge.

2. A security document according to claim 1, wherein the component of the length of the barrier parallel to the first edge of the document has a magnitude of at least 60%, preferably at least 70%, more preferably at least 80%, more preferably at least 90%, and more preferably at least 95%, of the length of the first edge.

3. A security document according to claim 1 or 2, wherein the apertures are arranged such that at least 20%, preferably at least 30%, more preferably at least 40%, more preferably at least 50%, more preferably at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90%, and more preferably at least 95%, of points on the first edge of the document have at least one aperture of the array located on an imaginary straight line emanating from the respective point orthogonal to the first edge.

4. A security document according to any preceding claim, wherein each aperture is shaped such that a portion of its periphery, which lies furthest from the first edge of the document, is curved and has a radius of curvature not less than 0.1 mm.

5. A security document according to any preceding claim, wherein the apertures extend fully through the thickness of the polymer substrate.

6. A security document according to any one of claims 1 to 4, wherein the polymer substrate is multi-layered and the apertures extend partially through the thickness of the document.

7. A security document according to claim 6, wherein the apertures extend through an external layer of the document.

8. A security document according to claim 6, wherein the apertures extend through an internal layer of the document.

9. A security document according to any preceding claim, wherein the apertures are of similar size and/or shape to one another.

10. A security document according to any one of claims 1 to 8, wherein the apertures are of dissimilar size and/or shape to one another.

11. A security document according to any preceding claim, wherein the barrier comprises said apertures arranged in at least one line on a face of the document, the apertures being separated from one another by interval portions of the document, the proportion of aperture-to-interval preferably being less than 50%, more preferably less than 30%, along the or each line.

12. A security document according to claim 11, wherein the at least one line of apertures is substantially straight.

13. A security document according to claim 11, wherein the at least one line of apertures comprises a curve, for example a wave.

14. A security document according to any preceding claim, wherein the length of an interval portion between the edges of two adjacent ones of the apertures is between about 0.05 to 5 mm, preferably about 1 mm.

15. A security document according to any one of claims 11 to 14, wherein the apertures are arranged in two or more lines which are spaced apart in parallel relationship with one another.

16. A security document according to claim 15, comprising three lines of apertures which are spaced apart in parallel relationship with one another.

17. A security document according to claim 15 or 16, wherein the apertures and interval portions of a first line are staggered with respect to the apertures and interval portions of a second, adjacent line.

18. A security document according to any one of claims 15 to 17, wherein adjacent ones of the two or more lines are spaced from one another by between about 0.5 and 1.5 mm, preferably about 1.0 mm.

19. A security document according to any preceding claim, wherein the document is substantially rectangular, having two parallel longer edges and two parallel shorter edges, the longer edges being orthogonal to the shorter edges, wherein the first edge is one of the longer edges or one of the shorter edges.

20. A security document according to claim 19, wherein the barrier comprises at least one line of the said apertures which extends longitudinally along the face of the document so as to be in generally parallel relationship with the longer edges of the document.

21. A security document according to claim 20, wherein the at least one line of apertures extends at least about 50% of the distance between the first shorter edge and the second shorter edge of the document, preferably at least about 60%, more preferably at least about 70%, more preferably at least about 80%, more preferably at least about 90%, more preferably at least about 95%, preferably other than 100%.

22. A security document according to claim 21, wherein the ends of the at least one line of apertures are equidistant from the respective shorter edges of the document.

23. A security document according to any one of claims 19 to 22, wherein the at least one line of apertures is spaced from the first longer edge of the document by no more than about 25% of the distance between the first longer edge and the second longer edge of the document, preferably by no more than about 20%, more preferably by no more than about 15%, more preferably by no more than about 10%, more preferably by no more than about 5%.

24. A security document according to claim 19, wherein the barrier comprises at least one line of said apertures which extends laterally along the face of the document so as to be in generally parallel relationship with the shorter edges of the document.

25. A security document according to claim 24, wherein the at least one line of apertures extends at least about 50% of the distance between the first longer edge and the second longer edge of the document, preferably at least about 60%, more preferably at least about 70%, more preferably at least about 80%, more preferably at least about 90%, more preferably at least about 95%.

26. A security document according to claim 25, wherein the ends of the one line of apertures are equidistant from the respective longer edges of the document.

27. A security document according to any one of claims 24 to 26, wherein the barrier comprises at least one line of the said apertures spaced from the first shorter edge of the document by no more than about 25% of the distance between the first shorter edge and the second shorter edge of the document, preferably by no more than about 20%, more preferably by no more than about 15%, more preferably by no more than about 10%, more preferably by no more than about 5%.

28. A security document according to claim 19, wherein the barrier comprises at least one line of the said apertures extending along the face of the document so as to be non-parallel with the longer and shorter edges of the document.

29. A security document according to any one of claims 19 to 28, comprising two or more of the said tear propagation barriers.

30. A security document according to claim 29, comprising first and second tear propagation barriers which are spaced apart from one another in parallel relationship.

31. A security document according to claim 30, wherein the first tear propagation barrier is located on one side of an imaginary centre line which is parallel with the longer edges of the document, and the second tear propagation barrier is located on the other side of the centre line.

32. A security document according to claim 30, wherein the first tear propagation barrier is located on one side of an imaginary centre line which is parallel with the shorter edges of the document, and the second tear propagation barrier is located on the other side of the centre line.

33. A security document according to claim 29, comprising first and second tear propagation barriers which are spaced apart from one another in parallel relationship on respective sides of an imaginary centre line which is parallel with the longer edges of the document, and third and fourth tear propagation barriers which are spaced apart from one another in parallel relationship on respective sides of an imaginary centre line which is parallel with the shorter edges of the document.

34. A security document according to claim 33, wherein the first, second, third and fourth tear propagation barriers intersect such as to comprise a continuous substantially rectangular border within the substantially rectangular document.

35. A security document according to claim 29, comprising first and second tear propagation barriers which are arranged in orthogonal relationship with one another.

36. A security document according to claim 35, wherein the first tear propagation barrier is located on one side of an imaginary centre line which is parallel with the longer edges of the document, and the second tear propagation barrier is located on one side of an imaginary centre line which is parallel with the shorter edges of the document, preferably wherein ends of the first and second tear propagation barriers intersect one another.

37. A security document according to claim 29, comprising first and second tear propagation barriers which are arranged to extend at a non-zero angle with respect to any one of the edges of the document.

38. A security document according to any preceding claim, wherein the document comprises a bank note, an identity card, or a portion of a passport.

39. A security document according to any preceding claim, wherein the apertures are laser-cut apertures in the polymer substrate.

40. A security document according to any preceding claim, wherein the polymer substrate or at least one layer thereof comprises biaxially oriented polypropylene (BOPP).

41. A security document according to any preceding claim, wherein each of the apertures is located away from the edges of the document such that no aperture intersects a said edge.

42. A security document according to any preceding claim, wherein each aperture is partially or substantially circular in shape.

43. A security document according to claim 42, wherein each aperture is substantially circular and has a diameter of between about 0.05 to 1 mm, preferably about 0.1 to 0.5 mm and more preferably about 0.1 to 0.3 mm.

44. A security document according to any one of claims 1 to 41, wherein each aperture is elliptical in shape.

45. A security document according to any one of claims 1 to 41, wherein each aperture is rectangular in shape, preferably square.

46. A security document according to any one of claims 1 to 41, wherein each aperture is shaped an as alphanumeric character.

47. A security document according to any preceding claim, wherein each aperture has a maximum width, or diameter, of about 0.05 to 1 mm, preferably about 0.1 to 0.5 mm and more preferably about 0.1 to 0.3 mm.

48. A security document according to any preceding claim, wherein the thickness of the polymer substrate is between about 30 to 200 microns, preferably about 50 to 100 microns.

49. A method of making a tear propagation barrier in a polymer substrate for a security document, comprising the steps:

providing a polymer substrate; and providing an array of apertures in the polymer substrate, the apertures being arranged to distribute stress in order to resist the propagation of a tear through the substrate, a component of the length of the barrier which is parallel to a first edge of the substrate having a magnitude of at least 50% of the length of the first edge.

50. A method according to claim 49, wherein the apertures extend fully through the thickness of the polymer substrate.

51. A method according to claim 49, wherein the polymer substrate is multi5 layered and the apertures extend partially through the thickness of the polymer substrate.

52. A method according to any one of claims 49 to 51, wherein the step of providing an array of apertures in the polymer substrate comprises removing

10 substrate material using a laser to thereby form the apertures.

Intellectual

Property

Office

Mr Christopher Saul

3 August 2017