The present invention relates to security fibres for use in security papers with counterfeit protection. In particular, the invention relates to security fibres having a number of coloured fluorescent stripes or regions. The invention also relates to a method for producing such fibres, and paper products incorporating such fibres. It is well known to provide security paper products, such as bank notes, cheques, passports, identity papers and fiduciary papers, with some form of counterfeit protection. The counterfeit protection measures may include watermarks, holograms, the provision of one or more metallic strips though the paper, the use of fluorescent particles and the use of optically variable inks and coatings. Problems with known counterfeit protection measures include the expense of some measures and the ease with which some measures can be overcome, for example by utilising methods including digital and laser printing, scanning, photography and xerography. Another example of a security feature that is incorporated into a security paper is a security fibre.

Paper is made from paper pulp, which contains cellulose fibres, for example wood, hemp, straw and cotton linters (note that, whilst those cellulose fibres are used to make paper, they are not themselves made from paper) . A known security technique is to replace, with artificial fibres made from materials such as polyester, nylon and rayon, some of the cellulose fibres used to make a security paper. A relatively small number of the artificial fibres can be included in the paper pulp, along with a majority of

^■ cellulose fibres, which results in the security paper that is manufactured from the pulp having the artificial fibres embedded within it and randomly distributed. The artificial fibres can be dyed or coated, resulting in the paper including a random pattern of small coloured regions. The dye can be a dye that is responsive to ultraviolet (UV) light, so that the coloured random pattern is visible only under UV light. Such artificial fibres are generally fibrous in shape (i.e. predominantly one-dimensional, rather than two- dimensional or sheet-like) , like the cellulose fibres they replace. WO2004/025028A1 (D W Spinks (Embossing) Ltd) describes security features that are referred to as "fibres" because they substitute for and bond with the cellulose fibres used in the manufacture of security paper, and because, in the manufactured paper, they give a visual impression that suggests that they are similar to such fibres. In fact, however, the paper fibres described in that document are small strips of paper, and are not fibrous in shape.

Thus, security fibres in the form of small strips of paper, (for example approximately 4mm x 0.3mm) can be added to the paper pulp during manufacture and become embedded in the sheets of paper that are produced. The security fibres are often invisible in daylight and remain unseen by the naked eye. However, when irradiated by ultra-violet light they become fluorescent and visible in the sheet of paper.

Mono-colour fibres are relatively easy and inexpensive to produce. However, counterfeiters have been able to use highlighter-type fluorescent marker pens to simulate mono- colour fibres in a sheet of paper. Invisible fluorescent inks are becoming widely available, and the ease of the counterfeiting process, making a few pen strokes on a sheet of paper, are reducing the effectiveness of mono-colour fibres as a security device.

One solution is to make security fibres comprising different colour regions, which raises the difficulty and cost of producing counterfeit fibres. Such security fibres are described in detail in WO2004/025028 Al. The "fibres" are intended for incorporation into paper products as a form of counterfeit protection. Each fibre has a plurality of coloured regions visible on front and rear sides of said fibre, wherein the colours are visible only under UV light. The regions may be in the form of stripes, or may be arranged in a pseudo-random pattern. The regions may be differently- coloured. The security fibres become much more difficult to simulate if the different colour regions are printed with a particular colour sequence, for example, the colours of a national flag.

Such security fibres are very small, for example, approximately 4mm x 0.3mm, as it has been found larger fibres or other larger types of security element are difficult to incorporate into the paper and are easily removed. This may be a particular problem when printing bank notes, which undergo several print processes using high pressure and high tack inks. Larger security fibres may be accidentally removed during the printing process, causing the paper to be rejected.

Producing such a small fibre with different colour regions, in particular different colour regions with distinct colour combinations in register with and in the same pattern as all of the other small fibres produced, is a highly difficult process. In the existing process, the pattern is printed on a large surface area of material and then small fibres are cut from the large surface area; however it is difficult to cut the fibres in perfect registration. Existing methods of high-volume cutting of material do not provide a means of registering the print with the cutter and many fibres are produced that do not have colours in register with each other. Existing methods do not allow the cutting to be controlled consistently within a tolerance between 0.125mm and 0.25mm which is believed to be the maximum tolerance for the colours in those fibre to appear to be equal in size and position.

The present invention seeks to mitigate or overcome one or more of the above-identified disadvantages associated with the prior art.

The invention provides a security fibre for use in counterfeit protection, the security fibre being suitable for incorporation into a paper product, the security fibre comprising (i) a coloured region, wherein the coloured region is made up of a plurality of different colours, and (ii) a margin adjacent to the coloured region.

Preferably, the margin comprises an unprinted region of the security fibre i.e. a region free from print. The margin may provide a greater adhesion when embedded as a security fibre in a paper product than a security fibre without such a region. Preferably, margin is an unprinted region of the security fibre which provides greater adhesion when embedded as a security fibre in a paper product than a security fibre without an unprinted region. The coloured region of the security fibre may include a varnish to make the coloured region impervious to water, or hydrophobic. Advantageously, this prevents the coloured region being degraded when the security fibre is being mixed with paper pulp or in a later printing process. The varnish may increase the abrasion resistance of the coloured region of the security fibre. However, such a varnish may reduce the adhesion of the coloured region of the security fibre with the paper product in which it is to be embedded. Advantageously, the margin is unprinted, and/or porous, which increases the adhesion between the paper fibre and a paper product in which it is embedded.

The coloured region may be visible only under ultraviolet light. Preferably the coloured region fluoresces under ultra-violet light. Providing a coloured region that is visible only under ultra-violet light enables counterfeit protection which is not visible with the naked eye to be added to paper.

Preferably, the margin contains no markings visible under ultra-violet light. Preferably, the security fibre comprises a second margin adjacent to the coloured region, such that the coloured region is situated between the first and second margins.

Advantageously, the margin or margins adjacent to the coloured region act to provide a margin of error when producing the fibre. The security fibre may be cut from a substrate, for example a sheet of paper, such that the cutting takes place in the margin or margins. A certain level of inaccuracy during the cutting process can thus be tolerated, as it no longer affects the appearance of the coloured region, which will still appear to be in perfect register.

The coloured, region may be printed on both the front and the rear sides of the security fibre. The security fibre may be printed on both its front and its rear sides by printing on one of the front and rear sides and allowing the ink to soak or bleed through to the other side of the security fibre. Alternatively, the security fibre may be printed on both its front and its rear sides by printing on one side of the security fibre and then printing on the other side of the security fibre.

The margin or margins may be transparent. The security fibre may be printed on a paper, which may be a transparent paper. When using a transparent paper, it may be that the coloured region is printed onto one-side only of the paper, but is visible through the paper from the other side. The paper substrate may be made to be transparent by applying a varnish to it; thus, a varnish may be applied to the paper, and then the coloured region printed onto the varnish. Alternatively, the security fibre may be printed on a plastic or cellulose-based substrate. It may be that the material on which the security fibre is printed has no background fluorescence. The margin or margins may completely surround the first, coloured, region. The margin or margins may extend 0.5mm to 5mm from the edges of the coloured region to which they are adjacent.

The fibre may be a sheet of paper. The paper may have a basis weight of between 10 gsm and 75 gsm. Preferably, the paper has a basis weight of between 10 gsm and 35 gsm; according to American Paper Weights and Measures, tissue paper has a basis weight of between 10 gsm and 35 gsm, and thus the sheet may be a sheet of tissue paper. It may be that the paper has a wet tensile strength of at least 1 N/15mm, more preferably at least 3 N/15mm. It may be that the paper has a wet tensile strength of less than 15 N/15mm, preferably less than 7 N/15mm. (The wet tensile strength may be the wet tensile strength of the paper itself, or it may be the wet tensile strength of the paper including any print, varnishes, or other material which increases the wet tensile strength relative to that of the paper itself.) The paper may have a dry tensile strength of about 5 daN/30mm. The paper may have an opacity of up to 90% or more, or alternatively may be transparent. The paper may include a varnish. The coloured region may comprise a plurality of different coloured stripes. There may be two, three, four or more stripes in the first, coloured, region. The said striped regions may include for example, any or all of the colours red, green, yellow, and blue. The stripes may be placed at approximately lmm graduations. The stripes may appear in the same order, i.e. in a repeating pattern. Advantageously, the stripes appearing in the same order in a repeating pattern makes it more difficult to forge the paper fibre. The coloured region may be rectangular in shape. The coloured region may measure between 3mm and 5mm in length, and 0.2mm to lmm in width. The coloured region may comprise a more complex pattern than stripes. For example, the coloured region may be a two dimensional pattern. The coloured region may include an image of a flag, and/or a combination of numbers and/or letters or some other recognisable image.

The margin or margins may extend 0.5mm to 2mm from the edge of the coloured region to which they are adjacent. It may be that the security fibre is between 3.5mm and 9mm in length. It may be that the security fibre is between 0.2mm and 6mm in width. Preferably, the coloured region is located approximately at the centre of the paper fibre, with the first and second margins located at each end of the paper fibre.

Preferably, the security fibre is a 5mm, 6mm, or 7mm long security fibre with a first, coloured, region of 3mm, 4mm, or 5mm respectively. However, it is clear that the invention can be applied such that a longer or wider security fibre is produced, although excessively large fibres are undesirable, as they can "pick out" from the security paper. The dimensions of the .coloured region and the margin or margins may be increased correspondingly proportionally.

The invention also provides a method of manufacturing a security fibre for use in counterfeit protection, the security fibre being suitable for incorporation into a paper product, the method comprising the steps of printing a plurality of coloured regions onto a substrate, each of the plurality of coloured regions being printed adjacent to at least one margin, and cutting the substrate to create a security fibre including at least one of the coloured regions, wherein the substrate is cut in at least one margin.

Preferably, a margin is an unpfinted region of the substrate. Advantageously, the substrate onto which the coloured regions are printed has no background fluorescence under ultra-violet light.

Advantageously, the margins increase the margin of error permitted during the cutting process without the appearance of the coloured regions being affected.

Preferably, coloured regions are visible only under ultra-violet light.

Preferably, the method includes the step of cutting the substrate to create a plurality of security fibres. The plurality of coloured regions may be printed on the substrate in a series of rows. Each coloured region may comprise a plurality of colours printed side by side. The plurality of colours may be printed to form stripes. There may be two, three, or four stripes printed in each coloured region. The stripes may include any or all of the colours red, green, yellow, and blue. The plurality of colours may be printed to form a more complex pattern than stripes. The coloured region may comprise a more complex pattern than stripes. For example, the coloured region may be a two dimensional pattern. The coloured region may include an image of a flag, and/or a combination of numbers and/or letters or some other recognisable image. >

Each coloured region may be located between two margins that are unprinted areas of the substrate. The printing of the plurality of the coloured regions in this way may create a corrugated effect due to the raised level of the coloured regions once the ink has been printed on the substrate, such that when one piece of substrate printed in this way is stacked on top of another piece of substrate printed in this way, the sheets fall into a natural alignment. Preferably, several sheets of substrate are stacked on top of each other and are cut simultaneously. The stack of sheets of substrate to be cut may be between 10mm and 20mm high. The natural alignment of the sheets of substrate, together with the cutting taking place within the margins, allows the cutting process to deviate, for example, by up to lmm without any affect on the appearance of the coloured region of the paper fibre. The coloured region may for example be, and appear to be, 4mm long and in the correct red, green, blue, and yellow proportion, despite the variance in the cutting of the security fibre. The cutting process may also include the substrate being cut such that the coloured regions are cut perpendicular to the cuts made along the margins. As these cuts are across the coloured region, the colour seguence of any strips or patterns included in the coloured regions are not affected due to any cutting inaccuracy. The cuts may produce a paper fibre with for example a length between 3.5mm and 9mm, and a width between 0.1 and 0.5mm. The cuts may be made with a specially developed knife, the knife being arranged such that it can cut the substrate both in at least one margin and across a coloured region simultaneously. Preferably, the knife is arranged to be able to cut the substrate with a single cut in order to produce the security fibres. Preferably, the knife comprises a crenellated blade.

The method may include the step of the coloured regions being printed on both the front and the rear sides of the substrate. The step of printing the coloured regions on both the front and the rear sides of the substrate may include the substrate .being printed on one of its front or its rear sides and allowing the ink to soak through to the other side of the substrate. Alternatively, the step of the coloured regions being printed on both the front and the rear sides of the substrate may include printing on one side of the substrate and then printing on the other side of the substrate.

The substrate may comprise paper. Alternatively, the substrate may comprise a plastics or cellulose-based substrate . The present invention also provides a method of manufacturing a paper product, wherein the method comprises the steps of mixing a plurality of the security fibres as described above with slurry paper pulp such that the security fibres form a hydrogen bond with the cellulose fibre in the paper pulp and forming the paper pulp and security fibre mix into a continuous web of paper.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings of which:

Figure 1 is a schematic drawing of an example of a sheet of paper printed according to an embodiment of the invention;

Figures 2a and 2b is a schematic drawing of an example of the security fibres according to an embodiment of the invention;

Figure 3 is a schematic view of an example security paper according to a embodiment of the invention, illuminated by (a) visible light; and (b) UV light;

Figure 4 is a flowchart showing steps in the manufacture of the example security fibre of Fig. 2;

Figure 5 is a flowchart showing steps in the manufacture of the example security paper of Fig. 3; and

Figure 6 is a schematic drawing of an example of a knife blade used to cut the security fibres.

Figure 1 shows a piece of substrate 1, onto which a plurality of coloured regions 2 have been printed. The coloured regions 2 are visible only when viewed under ultraviolet light. The coloured regions are generally rectangular in shape and are made up of four different coloured stripes, 21, 22, 23, and 24, printed side by side. The four different colours 21, 22, 23, and 24, are fluorescent colours that are visible only under ultra violet light. The colours in this example are red, green, yellow, and blue. In one embodiment, the colours are visible when ultra-violet light having a wavelength of between 245nm and 365nm is shone at the fibre. In any particular embodiment and for any particular colour, the wavelengths at which the colours are visible are of course dependent on the pigments used to generate the prints.

In this embodiment of the invention, both sides of the substrate 1 are printed with the coloured regions 2. In this case, the substrate 1 is a thin and porous paper and printing on a single side of the substrate 1 with an appropriate amount of ink means that the ink soaks through the substrate 1 and so both sides of the substrate 1 have been printed on. In an alternative embodiment, each side of the substrate 1 is printed individually, such that the coloured regions 2 on each side of the paper line up in register with each other. Figure 1 shows three coloured regions 2 printed on the substrate 1. Adjacent to the coloured regions 2, and separating the coloured regions 2 from each other, there are a plurality of margins 3 that do not fluoresce under ultraviolet light. In this case, the margins 3 are areas of the substrate 1 that have not been printed. The printing of the coloured regions 2 and the margins 3 not being printed creates a minor corrugation effect due to the printed regions being slightly raised in comparison with the unprinted regions. The corrugation effect can advantageously be used when stacking several sheets of similarly printed substrate

1, as it brings the sheets substrate 1 into natural alignment with each other. The cutting of the substrate 1 can then advantageously be performed with several sheets of substrate on top of each other, thus saving time and effort. Figure 1 also shows, with dashed lines, the planned cut lines 4. In Figure 1, only the cut lines parallel to the margins are shown, in order to best demonstrate the advantages of the invention. Figure 6 shows the cutting outline of a knife which is designed to cut the substrate 1 in such a way that a single cutting step can produce rectangular security fibres. The knife comprises a blade with a crenellated cutting edge. The size of the • crenulations corresponds to the size of the security fibres. The knife is brought down onto the stack of the sheets of substrate, thus cutting out a plurality of rectangular security fibres. The sections of the knife blade that are designed to cut along the cut lines 4 shown as parts 41, and the sections of the knife blade that cut across the coloured regions 2 are marked 42. The knife or the sheets of substrate is then moved (in the direction parallel to the length of each stripe 21, 22, 23, 24 i.e. up or down the page in Fig.l) and a further cut made, thus creating more security fibres . Due to the margins 4 between the coloured regions 2, minor deviations of the cutting from the planned cut lines 4 can be tolerated without affecting the shape, size and appearance of the coloured regions 2.

The substrate 1 from which the security fibres are produced in the embodiment of the invention as described above is a tissue or thin paper without optical brighteners. The optimum paper is a high porosity, high wet strength tissue paper with a nominal basis weight of 25 grams per square metre. The substance of the paper is significant since the ability to print and cut a thin substrate provides a technical barrier to duplicating the fibres.

Fibres in accordance with the present invention have been manufactured using paper having the properties listed below. These properties have been developed with the intention of providing a fibre that works well, but are only one example. Other papers could be used.

In addition, the target Bensten porosity (defined by ISO standard 5636/3) is 1500ml/mm, the minimum Bensten values is 700 ml/mm. As described for the embodiment ^' of the invention as shown in Figure 1, four different colour stripes are printed in the coloured regions 2. Suitable products for the printing process have been developed from commercially available pigments. Each of the red, green, yellow, and blue prints has a Blue Wool lightfastness of 3, an excitation wavelength in the region of 365nm and good chemical resistance .

The coloured regions 2 may also be coated with a varnish. The varnish protects the coloured regions 2 against abrasion and also improves the affinity of the fibres in the finished paper. In one embodiment, the varnish is a 4% solution of Solvitose NX in acrylic water based binder.

Figure 2a shows a paper fibre 51 which has been cut out in accordance with the planned cut lines 4 (and also in the direction perpendicular to the cut lines 4 as described above, such that a thin, approximately rectangular security fibre has been produced) . The security fibre 51 is approximately 5mm x 0.3mm, the coloured region being approximately 3mm long. The coloured region 2 is approximately in the centre of the paper fibre 51, located between two equally sized margins 31 and 32. The margins 31 and 32 are approximately lmm long each. Figure 2b shows a security fibre 52, with approximately the same dimensions as the security fibre 51, which has been cut out with a deviation from the planned cut lines 4 due to the cutting machine tolerances. The coloured region 2 is located to the left hand side of the paper fibre 52 as seen on the figure. The coloured region 2 is located between two margins 33 and 34, although ^' the margin 33 is smaller than the margin 34.

However, despite the inaccuracy of the cutting process, when viewed under ultra-violet light, the coloured regions in security fibre 51 and security fibre 52 will appear to be identical . The fibres 51, 52 are incorporated into paper pulp used to manufacture a security paper, in this example a banknote 50 (Fig. 3) . Under visible light (Fig. 3 (a)), the fibres 51, 52 are unremarkable, blending in with other, cellulose, fibres that make up the paper of the banknote 50. However, under long-wavelength UV light) , the fibres 51, 52 fluoresce, forming a random pattern of multicolour markings in the banknote 50 (shown schematically for ease of illustration by the dotted pattern in Fig. 3 (b) ) . Thus a UV light is used for a check of the validity of the security paper, e.g. in a shop, or by a bank teller.

Fibres 51, 52 are manufactured by the process shown in Fig. 4. Paper is drawn from a roll in a paper store 60 and passed to a printing machine 70. Printing machine 70 includes ink reservoirs 80 (a) to (d) , which contain four inks containing pigments that fluorescent in different colours when illuminated with UV light. The printing machine prints regions 21, 22, 23, 24 onto to form multiple copies across the paper substrate 1. The printed paper substrates passes to cutting machine 90, where it is cut into fibres 51, 52. The cut fibres 51, 52 are deposited into a bin 100 for transport to a paper mill.

At the paper mill, the banknote of Fig. 3 is manufactured by the method shown in Fig 5. Security fibres 51, 52, produced by the method of Fig. 4, are drawn from store 110 and mixed with water and conventional cellulose fibres (from a second store 120) to form a pulp 130. A paper making machine 140 manufactures paper from pulp 130 using conventional methods. At step 150, further processing of the paper takes place, including printing of standard images and the like. The manufactured and printed paper is then cut (step 160) to form the paper product 170, in this case, banknotes .

Thus, paper products in accordance with the present invention are made by mixing slurry paper pulp with the security fibres of the present invention. The security fibres of the present invention form a hydrogen bond with the cellulose fibres in the paper pulp and when the pulp is formed into a continuous web of paper, the security fibres in the pulp become an integral part of the web or sheet of paper. The coloured regions of the fibres can only be seen under ultra-violet light, thereby providing a security feature that cannot be seen in normal light conditions.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable eguivalents, then such equivalents are herein incorporated as if individually set forth. For example, the substrate may be a plastics or cellulose-based material. The coloured region may comprise a more complex pattern than stripes, for example, a two-dimensional pattern or a combination of numbers and/or letters. The coloured region may be a representation of a flag or other recognisable image.

Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims.