GB2578620A

GB2578620A - A security device

Info

Publication number: GB2578620A
Application number: GB1817857.4A
Authority: GB
Inventors: Donald Spinks Gary
Original assignee: Security Fibres Uk Ltd
Current assignee: Security Fibres Uk Ltd
Priority date: 2018-11-01
Filing date: 2018-11-01
Publication date: 2020-05-20
Also published as: GB201817857D0; WO2020089625A1

Abstract

A security device 1 comprising a substrate 2 having a first surface 3 and second surface. At least the first surface is provided with a plurality of printed regions 4. The printed regions are only visible under ultra violet light. The printed regions comprise fluorescent inks which glow, emitting a coloured light when they are excited by ultra violet radiation. The inks are provided in varying tonal densities such that when the printed regions are viewed under ultra violet light they produce a continuous spectrum of colours having diffuse boarders between the different colours giving a rainbow effect. The substrate may be in the form of a fibre or planchette.

Description

A security device

Field of the Invention

The present invention concerns improvements in and relating to security documents.

More particularly, this invention concerns a security device for a security document arid a method of manufacturing a security device for a security document.

Background of the Invention

Security documents, for example banknotes, passports, lottery tickets, some certificates and other items of potentially high value, are targets for counterfeiters, who seek to produce counterfeit copies of the security documents and thus illegally benefit from the high value of the genuine items. Security documents typically include various security devices or features that are difficult for a counterfeiter to simulate; such devices include holograms, security planchettes, and security fibres. In order to increase the burden for the counterfeiter, security documents have traditionally included fine detailing in their design.

In order to be effective, a security device must exhibit characteristics that are easily identified by a user seeking to verify the authenticity of the security document concerned whilst increasing the burden for a potential counterfeiter. To that end, many security devices exhibit a fluorescent response.

An 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 -2 -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 printed regions. The dye can be a dye that is responsive to ultra violet (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. W02004/025028A1 (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 W02004/025028 Al. The "fibres" are intended for incorporation into paper products as a form of counterfeit protection. Each fibre has -3 -a plurality of printed 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 printed. 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.

Summary of the Invention

The present invention provides, in a first aspect, a security device for inclusion in a security document, the security device comprising one or more of: a substrate having a first surface and a second surface; a first printed region provided on at least one of the first or second surfaces, said first printed region having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a first colour; and a second printed region provided on at least one of the first or second surfaces, said second printed region having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a second colour.

The first and second printed regions may be arranged on the at least first or second surface such that the coloured light emitted by the fluorescing printed regions mixes to produce light of further, different, colours. It may be that the colours so produced varying over a portion of at least one of the first or second surfaces. Thus, when said at least one of the first or second surface is viewed under ultra-violet light a pattern comprising a plurality of different colours may be observed.

Security devices that produce a plurality of coloured regions as a result of additive mixing, under ultra-violet light may be challenging to counterfeit. It may be that the particular arrangement of fluorescent printed regions and their varying tone densities enables the emission of a graduated pattern of colours with diffuse borders, which is difficult to reproduce. -4 -

According to a second aspect of the invention a method of manufacturing a security device is provided. The method comprising one or more of the following: providing a substrate having a first surface and a second surface; providing a first printed region of varying tone density on at least the first surface or second surface of the substrate by printing a first ink that fluoresces under ultra violet light emitting coloured light of a first colour; providing a second printed region of varying lone density on aL least the first surface or second surface of the substrate by printing a second ink that fluoresces under ultra violet light emitting coloured light of a second colour; and cutting the substrate to create a security device including at least a portion of said pattern The first and second printed regions may be arranged on the at least first or second surface of the substrate such that the coloured light emitted by the fluorescing printed regions mixes to produce light of different colours at different regions of at least one of the first or second surfaces thereby producing a repeating pattern of colour across said at least one of the first or second surface of the substrate.

According to a third aspect of the invention, there is provided a security document comprising a security device according to the first aspect and/or fourth aspect of the invention.

According to a fourth aspect of the invention, there is provided a security device for inclusion in a security document, the security device comprising one or more of: a substrate having a first surface and a second surface, a plurality of printed regions provided on at least one of the first or second surfaces.

The printed regions may fluoresce under ultra violet light emitting coloured light. The printed regions may have varying tone density across each of said printed regions. The printed regions may be arranged on the at least first or second surface such that the coloured light emitted by the fluorescing printed regions mixes to produce different coloured light at different points on at least one of the first or second surfaces. -5 -

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure 1 shows a first embodiment of the invention where the security device is a planchette; Figure 2 is a schematic showing how fluorescent inks can be provided in an overlapping manner on the substrate surface to produce pattern of colours shown in the fourth embodiment; Figure 3 is a schematic showing the pattern of colours produced when the overlapping fluorescent inks according to an embodiment of the present invention; Figure 4 is a plan view of a second embodiment of the invention, where the security device is fibre; Figure 5 is a plan view of a third embodiment of the invention where the security device is a star shaped planchette; Figure 6 shows a fourth embodiment of the invention where the security device is a triangle shaped planchette; Figure 7 shows a security document comprising the security device of the third embodiment of the invention, (a) is the security document as viewed under visible light and (b) is the security document as viewed under ultra violet light; Figure 8 is a flowchart showing steps in the manufacture of the example security device of Figure 3; and -6 -Figure 9 is a flowchart showing the steps of manufacture of the example security document of Figure 8.

Detailed Description

A first aspect of the invention provides a security device for inclusion in a security document, the security device comprising a substrate having a first surface and a second surface. A first. printed region may be provided on at least one of the first or second surfaces. Said first printed region may have varying tone density and/or may be printed in an ink which fluoresces under ultra violet light to emit light in a first colour. A second printed region may be provided on at least one of the first or second surfaces. Said second printed region may have varying tone density and/or may be printed in an ink which fluoresces under ultra violet light to emit light in a second colour. It may be that the first and second printed regions are arranged on the at least first or second surface such that the coloured light emitted by the fluorescing printed regions mixes to produce light of further, different, colours. It may be that the colours so produced vary over a portion of at least one of the first or second surfaces. Thus, security devices in accordance with the present invention may use tonal variation in printed regions to produce a striking visible effect that is difficult to counterfeit. Moreover, use of tonal variation may allow a wide variety of differently coloured light to be produced using only two colours. Additionally or alternatively, security devices in accordance with the present invention may facilitate an efficient manufacturing process as a wide variety of colours can be produced with only two print stations (one print station for each colour).

It may be that only a single colour is applied in each printed region. This may allow for improved repeatability of the visual effect as a different print station (e.g. roller) may be used to apply each colour. This is in contrast with 'split duct' printing where inking rollers are charged along their length with different colours so that inks merge with their neighbour to produce a graphic 'spectrum' effect. The tendency for the inks to merge may cause a loss in purity of the individual colours which is particularly detrimental for fluorescent effects. -7 -

The security device may further comprise a third printed region provided on at least one of the first or second surfaces. The third printed region may have varying tone density. The third printed region may be printed in an ink which fluoresces under ultra violet light to emit light in a third colour. The first, second and third printed regions may be arranged on the at least first or second surface such that the coloured light emitted by the first, second and third fluorescing printed regions mixes to produce lighL of further, different, colours. IL may be LhaL Lhe colours so produced vary over a portion of at least one of the first or second surfaces. Using a third colour may facilitate the production of a wider range of visual effects, thereby increasing the difficulty of counterfeiting. Additionally or alternatively, security devices in accordance with the present invention may facilitate an efficient manufacturing process as all colours (e.g. a full colour spectrum) can be produced with only three print stations (one print station for each colour).

The varying tone density may be provided by halftone printing. Halftone printing is a known reprographic technique whereby dots of different size, pattern and/or spacing are used to give an appearance of different tones. The tone density of each printed region may vary in a smooth (i.e. non-discontinuous) manner across the region. Thus the resulting colour pattern may have diffuse boundaries between different colours.

The tone density of each region may vary between 0% and 100%. The tone density may vary in one or more gradations or discrete steps, for example in ten degree gradations (e.g. having densities of 10%, 20%, 30% etc). Thus the resulting colour pattern may have discrete boundaries between different colours. There may be two or more gradations in each printed region, for example three or more gradations, for example five or more gradations. The tone density may increase with distance across a region, decrease with distance across a region or vary (both increasing and decreasing at different points) across a region.

The first, second and third (if present) printed regions may be arranged such that the coloured light emitted by the fluorescing printed regions mixes to produce further, differently coloured light, the colour so produced varying in a continuous spectrum across a portion of at least one of the first or second surfaces. It may be that a -8 -graduated spectrum or 'rainbow' effect pattern is produced. The differently coloured light (which may give the appearance of differently coloured regions when the device is viewed under ultra violet light) may appear in the same order in a repeating pattern. The printed regions may be arranged such that the coloured light emitted by the fluorescing printed regions mixes to produce white light at one or more points on at least one of the first or second surfaces.

The first and second surfaces of the substrate may be opposing surfaces.

The printed regions may be arranged on the first and/or second surface of the substrate such that they at least partially overlap. The printed regions may be arranged on the first and/or second surface of the substrate such that they completely overlap. The first, second and/or third (if present) printed regions may be provided on the same one of the first or second surface. The first, second and/or third (if present) printed regions may be provided on only one of the first or second surface. The first, second and/or third (if present) printed regions may be provided on both the first surface and second surface of the substrate.

The printed regions may be provided using an ink that fluoresces under ultra violet light to produce one of red, blue or green light. Each of the first, second and third (if present) printed regions may be produced using an ink that fluoresces to produce a different one of red, blue or green light. Each of the first, second and third (if present) printed regions may be produced using an ink comprising a mixture of two or more differently coloured pigments (for example red, green and blue pigments) that fluoresce to produce light having a colour resulting from the mixture of said different colours. Each of the first, second and third (if present) printed regions may be provided using an ink of a single colour. As an alternative to red, blue and green inks, cyan, magenta and yellow inks may be used. Where red, green and blue inks are used, additive mixing of the light from each printed region may allow white light to be produced. Where cyan, magenta and yellow inks are used subtractive mixing of the light from each printed region may allow black light to be produced. -9 -

The printed regions may be provided using inks that have an excitation wavelength of 365 nm.

The printed regions maybe provided using inks that comprise microencapsulated fluorescent organic or organometallic dyes. The microencapsulated inks may each comprise a fluorescent dye of more than one colour. The printed regions maybe provided using inks LhaL have a lighLfasmess of a I. leasL 3 on We blue wool scale.

The substrate may be transparent. The substrate may be paper. The substrate may be tissue paper. The substrate may be without optical brighteners. The substrate may be paper of a high porosity, high wet strength tissue paper with a nominal basis weight of between 23 and 28 g/m2. The substrate may be paper of a high porosity, high wet strength tissue paper with a nominal basis weight of 25 g/m2.

The security device may further comprise a layer of varnish on at least the printed regions. The security device may further comprise a layer of varnish on at least one or more of the printed regions.

The security device may be a particulate, for example a fibre, planchette or starlight. The security device may be at least 1 mm in length. The security device may be not more than 10 mm in length.

A second aspect of the invention provides a method of manufacturing a security device, the method comprising providing a substrate having a first surface and a second surface. The method may comprise providing a first printed region of varying tone density on at least the first surface or second surface of the substrate by printing a first ink. The first ink may fluoresce under ultra violet light emitting coloured light of a first colour. The method may comprise providing a second printed region of varying tone density on at least the first surface or second surface of the substrate by printing a second ink. The second ink may fluoresces under ultra violet light emitting coloured light of a second colour. The first and second printed regions may be arranged on the at least first or second surface of the substrate such that the coloured light emitted by the fluorescing printed regions mixes to produce light of different colours at different regions thereby producing a pattern, for example a repeating pattern, of colour across said at least one of the first or second surface of the substrate. The method may comprise cutting the substrate to create a security device including at least a portion of said pattern. Thus the method may comprise producing a substrate sheet having a plurality of instances of said repeating pattern, and then subdividing said sheet La provide a par ticulate for use in the production of a security document.

The method may further comprise the step of providing a third printed region of varying tone density on at least the first surface or second surface of the substrate by printing a third ink. The third ink may fluoresce under ultra violet light emitting coloured light of a third colour. The third printed region may be arranged on the at least first or second surface of the substrate such that the coloured light emitted by the first, second and third fluorescing printed regions mixes to produce light of different colours at different regions of at least one of the first or second surfaces thereby producing a repeating pattern of colour across said at least one of the first or second surface of the substrate.

The method may comprise using halftone printing to provide a tone density that varies across a printed region.

The first and second printed regions may be arranged on the at least first or second surface such that the colour so varies to provide a rainbow effect pattern. The first and second regions may be arranged such that the coloured light emitted by the fluorescing printed regions mixes to produce white light at one or more points on the at least one or more surfaces of the substrate. The first and/or second printed region may have at least two different tone densities.

The first, second and/or third (if present) printed region may be a region that fluoresces under ultra violet light to produce red light. The first, second and/or third (if present) printed region may be a region that that fluoresces under ultra violet light to produce blue light. The first, second and/or third (if present) printed region may be a region that fluoresces under ultra violet light to produce green light. Each of the first, second and/or third (if present) printed regions may fluoresce to produce a different one of red, green or blue light.

The first, second and/or third (if present) printed regions may be provided on the first and/or second surface of the substrate such that there are regions where inks from two or three printed regions at least partially overlap, for example completely overlap. The first, second and/or third (if present) printed regions may be provided on the first and/or second surface of the substrate such that there are regions where inks from two different regions do not overlap. The first, second and/or third (if present) printed regions may be provided on the first and/or second surface of the substrate such that there are regions where only two of the inks overlap.

The first, second and/or third (if present) printed regions may be provided on the first and/or second surface of the substrate such that for every one region that two regions overlap, there are two printed regions in which the inks do not overlap. The first, second and/or third (if present) printed regions may be provided on the first and/or second surface of the substrate such that for every one region that three regions overlap, there are three printed regions in which the inks do not overlap. The first, second and/or third (if present) printed regions may be provided on the first and/or second surface of the substrate such that there are regions where each one of the inks overlaps with one of each of the other inks.

The step of providing printed regions on both the first and second surface of the substrate may comprise printing on one of the front or the rear sides of the substrate and allowing the ink to soak through to the other side of the substrate. The step of providing printed regions on both the first and second surface of the substrate may comprise individually printing on the first surface of the substrate and printing on the second surface of the substrate.

The method may further comprise the step of applying a layer of varnish on at least the printed regions.

-12 -According to a third aspect of the invention, there is provided a security document comprising the security device according the first aspect of the invention. The security document may be bank note, a passport, identity papers or fiduciary papers.

According to a fourth aspect of the invention, there is provided a security device for inclusion in in a security document. The security device comprising a substrate having a first surface and a second surface. The security document may comprise a plurality of printed regions provided on at least one of the first or second surfaces, wherein said printed regions fluoresce under ultra violet light emitting coloured light and may have varying tone density across each of said printed regions. The printed regions may be arranged on the at least first or second surface such that the coloured light emitted by the fluorescing printed regions mixes to produce different coloured light at different points on at least one of the first or second surfaces.

The plurality of printed regions may include at least two printed regions. The plurality of the printed regions may include at least three printed regions.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention.

For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

In a first example embodiment of the invention (Figure 1), there is provided a security device 1, namely a planchette, for a security document. The security device 1 comprises a substrate 2. The substrate 2 having a first surface 3 and an opposing second surface (not shown). Provided on the substrate 2 are plurality of coloured stripes 4. The coloured stripes 4 are visible only under ultra violet light. The coloured stripes 4 are produce using three printed inks which fluoresce to produce red, blue and green light respectively. The inks are provided in the coloured stripes 4 using a halftone printing process. When viewed under ultra violet light, coloured stripes 4 fluoresce to produce a continuous spectrum of colours having diffuse boarders between the different colours (or a graduated rainbow as shown in Figure 3).

-13 -Figure 2 shows a schematic example pattern of fluorescent inks applied to coloured stripes 4 to produce a graduated rainbow. Coloured stripe regions 4 comprises three halftone printed "layers" 12, 13, 14 (halftone printing represented as blocks in Figure 2). The halftone printed layers comprise a strip of ink that is provided on the substrate at graded tonal densities either increasing or decreasing along the strip as required to achieve the various colours of Lhe graduated rainbow parer n. The first halftone printed layer 12 fluoresces under ultra violet light to produce red light. A second halftone printed layer 13 fluoresces under ultra violet light to produce blue light. And a third halftone printed layer 14 fluoresces under ultra violet light to produce green light. Coloured stripes 4 comprise printed regions where two halftone printed layers of any of 12 and 13, 13 and 14, or 14 and 12 overlap. When those regions are viewed under ultra violet light the red and blue, blue and green, green and red colours produced additively mix to produce magenta 9, cyan 10, or yellow 11 coloured light respectively (Figure 3). Coloured stripes 4 also comprise regions where printed layers 12, 13 and 14 do not overlap at all. When those regions are viewed under ultra violet light, the region where layer 12 does not overlap 6 produces red light, the region where layer 14 does not overlap 8 produces green light. As a result of the tonal variation and overlap of these colours, coloured stripes 4 produce a continuous spectrum of colours of when viewed under ultra violet light. Depending on whether the different gradations of tonal density are discrete or continuously varying, the boundaries between the different colours may be discrete (discontinuous) or diffuse (continuous). In an alternative embodiment, coloured stripes 4 comprise a further region where all three of the fluorescent inks overlap and each carry equal tonal weights; such that when this region is viewed under ultra violet light, the colours additively mix to produce white light (not shown).

In an alternative embodiment, the first halftone printed region 6 fluoresces under ultra violet light to produce magenta light. The second halftone printed region 7 fluoresces under ultra violet light to produce cyan light. And the third halftone printed region 8 fluoresces under ultra violet light to produce yellow light. Coloured stripes 4 also comprise printed regions where two halftone printed regions of any of 6 -14 -and 7, 7 and 8, or 8 and 6 partially overlap. When those regions are viewed under ultra violet light the magenta and cyan, cyan and yellow, yellow and magenta colours produced subtractively mix to produce blue 9, green 10, or red 11 coloured light respectively (Figure 3). As a result of the tonal overlap of these colours, coloured stripes 4 produce a continuous spectrum of colours of diffuse boundaries when viewed under ultra violet light. In an alternative embodiment, coloured stripes 4 comprises a further region where all three of the fluorescent inks overlap and each carry equal tonal weights; such that when this region is viewed under ultra violet light, the colours subtractively mix to produce black light (not shown).

In one embodiment, the inks are provided on the first surface 3 of the substrate to produce coloured stripes 4. In an alternative embodiment, the inks are provided on the first surface 3 and the second opposing surface to produce coloured stripes 4.

In a second example embodiment of the invention (Figure 4), there is provided a security device 20, namely a fibre, for a security document. The security device 20 comprises a substrate 22. The substrate 22 having a first surface 23 and an opposing second surface (not shown). Provided on the substrate 22 are a plurality of coloured stripes 24. The coloured stripes are visible only under ultra violet light. The coloured stripes 24 comprise printed regions that comprise three inks which fluoresce to produce red, blue and green light respectively. The inks are provided in the coloured stripes 24 using a halftone printing process. When viewed under ultra violet light, printed regions 24 fluoresce to produce a continuous spectrum of colours having diffuse boarders between the different colours. In one embodiment, the inks are provided on coloured stripes 24 in the same manner as outlined for coloured stripes 4.

Figure 5 shows a further embodiment of the invention where the security device is a planchette 70. The planchette 70 is in the form of a star. The planchette 70 includes elongate coloured stripes 74, produced by halftone printing and partially overlapping fluorescent inks that produce red, blue and green inks under ultra violet light. The coloured striped 74 produce a continuous spectrum of colours under ultra violet light.

-15 -Each of coloured stripes 74 extends diagonally across planchette 70 and are only visible under ultra violet light. The planchette 70 is small, typically having a maximum dimension of between 2mm and 5mm.

In one embodiment, the colours are visible when ultra violet light having a wavelength between 245 nm and 365 nm is shone at the planchette.

A large number of planchettes, such as the planchette 70, can be cut from a single sheet of paper. The printed stripes 74 are printed onto the paper prior to the planchettes 70 being cut. The printed coloured stripes 74 may be printed on both sides of the planchette 70 and overlap at certain points.

The planchettes in accordance with the present invention are intended to be incorporated into a paper product, such as a bank note, as a counterfeit protection device.

In one form of the invention, the planchettes are made from a material with a different density and structure to the base paper with which it is to be used. This allows the planchette to be seen in the so-called "look through" of the paper. The effect is similar to viewing a watermark.

The star 70 shown in Figure 5 is, of course, only one of many possible shapes for a planchette in accordance with the present invention. For example, the planchette may take any shape such as a triangle 80 (Figure 6) or the shapes of national symbols, such as a fern for New Zealand or a maple leaf for Canada.

The substrate (2, 22, 72) is a thin and porous paper and printing on a single side of the substrate (2, 22, 72) with an appropriate amount of ink means that the ink soaks through the substrate (2, 22, 72) and so both sides of the substrate have been printed on. In an alternative embodiment, each side of the substrate (2, 22, 72) is printed individually.

-16 -According to one embodiment of the invention, the inks are microencapsulated organic or organometallic dyes that have a wool scale lightfastness of at least 3.

The printed regions may also be coated with a varnish. The varnish protects the printed regions against abrasion and improves the affinity of security device in the finished paper. In one embodiment, the varnish is a 4% solution of Solvitose NX in acrylic wa Ler based binder.

The substrates (2, 22, 72) from which the security devices are produced, in the embodiments of the invention as described above, are 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.

Paper products in accordance with the present invention are made by mixing slurry paper pulp with the security devices of the present invention. The security devices 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 devices in the pulp become an integral part of the web or sheet of paper. The printed 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 (Figure 7, (a)).

The security devices, for example a plurality of fibre 20, are incorporated into paper pulp used to manufacture a security paper, in this example banknote 50 (Fig. 7).

Under visible light (Fig. 7(a)), the fibres 20 are unremarkable, blending in with other cellulose fibres that make up the paper of the banknote 50. However, under ultraviolet light, the fibres 20 fluoresce, forming a pattern continuous spectrum of colours in the banknote 50 (shown schematically for ease of illustration by the dotted pattern in Fig. 7(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.

-17 -Fibres 20 are manufactured by the process shown in Fig. 8. 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 (c), which contain three inks containing pigments that fluorescent in red, blue or green when illuminated under UV light. The printing machine prints regions 23, 24 and 25 forming multiple copies across the paper substrate 22. The printed paper substrate passes to cutting machine 90, where it is cut into fibres 20. The cut fibres 20 are deposited into a bin 100 for transpor L. to a paper mill.

At the paper mill, the banknote of Fig. 7 is manufactured by the method shown in Fig 9. Security fibres 20, produced by the method of Fig. 8, 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 printed 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.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for -18 -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. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may Lherefore be absent, in miler embodirriems.

Claims

-19 -Claims 1. A security device for inclusion in a security document, the security device comprising: a substrate having a first surface and a second surface; a first printed region provided on at least one of the first or second surfaces, said first. printed region having varying Lone density and being printed in an ink which fluoresces under ultra violet light to emit light in a first colour; and a second printed region provided on at least one of the first or second surfaces, said second printed region having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a second colour; and the first and second printed regions are arranged on the at least first or second surface such that the coloured light emitted by the fluorescing printed regions mixes to produce light of further, different, colours, the colours so produced varying over a portion of at least one of the first or second surfaces.
2. The security device according to claim 1, further comprising a third printed region provided on at least one of the first or second surfaces, said third printed region having varying tone density and being printed in an ink which fluoresces under ultra violet light to emit light in a third colour; and the third printed region is arranged on the at least first or second surface such that the coloured light emitted by the first, second and third fluorescing printed regions mixes to produce light of further, different, colours, the colours so produced varying over a portion of at least one of the first or second surfaces.
3. A security device according to claim 1 or claim 2, wherein the printed regions are arranged such that the colour so produced varies in a continuous spectrum over a portion of at least one of the first or second surfaces.
4. A security device according to any preceding claim, wherein the printed regions are arranged such that the coloured light emitted by the fluorescing printed regions mixes to produce white light at one or more points on at least one of the -20 -first or second surfaces.
5. A security device according to any preceding claim, wherein the first printed region is printed in an ink that fluoresces under ultra violet light to produce one of red light, blue light, green light or a mixture thereof.
6. A security device according Lc.) claim 5, wherein We second printed region is printed in in an ink that fluoresces under ultra violet light to produce a different one of red light, blue light, green light or a different mixture thereof.
7. A security device according to claim 6 when dependent on claim 2, wherein the third printed region is printed in in an ink that fluoresces under ultra violet light to produce a different one of red light, blue light, green light or a different mixture thereof.
8. A security device according to any preceding claim, wherein the printed regions are provided on the same one of the first or second surfaces.
9. A security device according to any preceding claim, wherein the printed regions are provided on only one of the first or second surfaces.
10. A security device according to any of claims 1 to 8, wherein the printed regions are provided on the first and second surface of the substrate.
11. A security device according to any preceding claim, wherein the device is a particulate, for example a planchette, a fibre or a starlight.
12. A security device according to any preceding claim, wherein the first and second surfaces are opposing surfaces.
-21 - 13. A security device according to any preceding claim, wherein the printed regions at least partially overlap.
14. A security device according to claim 13, wherein the printed regions are arranged such that they completely overlap.
15. A security device according Lo any preceding claim wherein the printed regions are provided using inks that comprise microencapsulated fluorescent organic or organometallic dyes, having a lightfastness of at least 3 on the blue wool scale. 10
16. A method of manufacturing a security device, the method comprising: providing a substrate having a first surface and a second surface; providing a first printed region of varying tone density on at least the first surface or second surface of the substrate by printing a first ink that fluoresces under ultra violet light emitting coloured light of a first colour; providing a second printed region of varying tone density on at least the first surface or second surface of the substrate by printing a second ink that fluoresces under ultra violet light emitting coloured light of a second colour; the first and second printed regions being arranged on the at least first or second surface of the substrate such that the coloured light emitted by the fluorescing printed regions mixes to produce light of different colours at different regions of at least one of the first or second surfaces thereby producing a repeating pattern of colour across said at least one of the first or second surface of the substrate; and cutting the substrate to create a security device including at least a portion of said pattern.
17. A method according to claim 16, further comprising the step of providing a third printed region of varying tone density on at least the first surface or second surface of the substrate by printing a third ink that fluoresces under ultra violet light emitting coloured light of a third colour; -22 -the third printed region being arranged on the at least first or second surface of the substrate such that the coloured light emitted by the first, second and third fluorescing printed regions mixes to produce light of different colours at different regions of at least one of the first or second surfaces thereby producing a repeating pattern of colour across said at least one of the first or second surface of the substrate.
18. The method according to claim 16 or claim 17, comprising using halftone printing to provide at least one of said printed regions of varying tone density. 10
19. A method according to any of claims 16 to 18, wherein the printed regions are arranged on the at least first or second surface such that the colour so produced varies to provide a rainbow effect pattern.
20. A method according to any of claims 16 to 19, wherein the printed regions are arranged such that the coloured light emitted by the fluorescing printed regions mixes to produce white light at one or more points on at least one of the first or second surfaces.
21. The method according to any of claims 16 to 20, wherein the inks are inks that fluoresce under ultra-violet light to emit one of red, blue and green light, or a mixture thereof.
22. The method according any of claims 16 to 21, further comprising the step of providing a layer of varnish on at least the printed regions.
23. A security document comprising the security device of claims 1 to 15.
24. The security document of claim 23, wherein the document is a bank note, a cheque, a passport, identity papers, or fiduciary papers.-23 -
25. A security device for inclusion in a security document, the security device comprising: a substrate having a first surface and a second surface, a plurality of printed regions provided on at least one of the first or second surfaces, wherein said printed regions fluoresce under ultra violet light emitting coloured light and have varying tone density across each of said printed regions. Lhe primed regions are arranged on Lhe aL least firsi, or second surface such alai. the coloured light emitted by the fluorescing printed regions mixes to produce differently coloured light at a plurality of different points on at least one of the first or second surfaces.
26. The security device according to any preceding claim, wherein the plurality of printed regions includes at least three printed regions.