GB2618651A - A precursor for security fibres, a method of producing the precursor, a method of producing security fibres from the precursor a security fibre for use in a - Google Patents

Abstract

A security fibre comprises a transparent impermeable substrate; and a printed region 4 printed on only one side of the substrate printed with an ink invisible light and fluorescent in light outside the visible spectrum. The printed region is visible from each of the printed and unprinted sides of the substrate. There is also provided a precursor for a security fibre comprising an elongate, visible light transparent, ink impermeable web of indefinite length, on only one side of which is printed multiple regions 4 of ink. A method of manufacturing the precursor comprises providing a reel of transparent impermeable web (23, Fig.3A) of indefinite length; unreeling the web to move the web to a gravure printing stage; applying fluorescent inks to regions of the web, on only one side of the web, by means of the gravure printing roll (25, Fig.3A) to form the precursor; moving the printed web to a coiling stage, where the web is coiled into a reel (27, Fig.3A) of precursor. The regions may be divided into adjacent sub-regions 5, 6, 7, 8 each of which is a different ink which fluoresces a different colour when illuminated by ultraviolet (UV) light of 245-345 nm.

Description

A PRECURSOR FOR SECURITY FIBRES, A METHOD OF PRODUCING THE PRECURSOR, A METHOD OF PRODUCING SECURITY FIBRES FROM THE

PRECURSOR AND A SECURITY FIBRE FOR USE IN A SECURITY PAPER

Technical field

pool. Security fibres are typically used in banknote paper and security document paper and the like as anti-counterfeit feature, they are embedded in the paper at the papermaking stage typically by mixing into the paper slurry and these fibres typically are coated or printed with a material that is invisible under normal light but exhibits fluorescence under UV light.

[0002]. It is also known to produce UV activated multi colour security fibres for use as anti-counterfeit devices in banknote and security papers using a sheet fed production print and cutting process onto printed papers and films, or using tissue paper substrates.

Prior Art

[0003]. Previous known method of producing Security Fibres are detailed in EP 1791701B, EP2308686, EP 1546458B1, EP2342085B1. The security fibres detailed here are different to these previous methods and offer improvements in manufacturing method and performance.

p0041. Such previous security fibres contain 2 or more printed areas typically printed on both sides of a thin paper base, and use inks that are invisible under normal light and fluoresce in different colours (blue, green, yellow, red for example) under UV light to provide an observable security feature.

[0005]. It is also known to produce holographic micro particles for use an anti-counterfeit device in security papers that contain microscopic holographic features using reel to reel production process using surface relief embossing, reel to reel print and reel fed cutting. (EP 2359196B1 (WO 2010/046708).

[0006]. GB 2456612A and EP 208105B1 disclose a gravure printing process to produce an optical microstructure and print methods of produced surface relief carrying structures.

SUMMARY OF INVENTION

[0007]. According to a first aspect of the present invention there is provided a precursor for a security fibre comprising an elongate, visible light transparent, ink impermeable web of indefinite length, on only one side of which is printed multiple regions of ink, said ink being invisible in visible light but fluorescing when exposed to wavelengths of stimulant light beyond the visible spectrum.

[00os]. Preferably the web is formed from a transparent plastic or cellulose material which is either inherently impermeable to the ink used for printing or pre-treated to be impermeable. The web may also be formed from transparent calendared or super-calendared paper, calendared to render the paper or card substantially impermeable but effectively transparent.

[coos]. Each region may be separated from each adjacent region by a margin. Each region is preferably printed with a pattern of subregions each treated with a different ink so that each subregion will fluoresce in a different visible colour when exposed to stimulant light. Because each region is printed onto only one side of a transparent impermeable membrane the region is visible from each side of the membrane and appears to be exactly in register on each side of the membrane. This obviates the problems of printing onto two sides of the membrane in register as required in GB2392868. In the prior art of EP1791701 ink is printed onto one side of a permeable membrane (tissue paper) where ink is drawn through the permeable membrane to be visible on the opposite side. However, this results in a poorly defined diffuse print subregion and/or region as the ink is drawn through the paper via unpredictable capillary action. Tissue paper has poor tensile strength making it susceptible to breakage during printing. Tissue paper also has a low (poor) Young's modulus, making it elastic such that accurate printing is a challenge.

[mow] According to a second aspect of the present invention the printed precursor web is produced by at least a first gravure printing stage in which the unprinted visible light transparent web is fed from a delivery reel, on which the web is coiled, through a gap between a gravure roll and a backing roll where the gravure roll applies fluorescent ink from a reservoir to the single surface of the web to form the sub-regions and regions.

poonj The gravure roll stage may apply multiple sub-regions simultaneously, each having a differently coloured ink. Alternatively, multiple gravure roll stages may be used each applying a differently coloured ink sub-region until a complete set of regions is formed across the span of the web.

[00012] Preferably the margin of each region is of a width at least equal to the width of a sub-regions. More preferably the margin of each region is an integer multiple of the width of each sub-region. The width of each sub-region being substantially similar.

[00013] Preferably a sub-region margin of each sub-region has a width much less than the width of each sub-region and is printed during gravure printing with an ink density which decreases progressively towards the adjacent sub region. By means of this arrangement which can be achieved as a result of the precision with which an impermeable web can be printed, the effect of overlap between the sub-regions is minimised and unwanted colours and effects are avoided.

[00014] Preferably the printed precursor roll is coiled onto an output reel downstream of the gravure roll stage. The precursor web may be unwound and fed to a cutting station where a moving blade is displaced to pass adjacent a stationary blade over which the precursor web is passed, synchronised to cut through the margin of each region to form fibres, which are collected into a hopper.

[00015] The precursor web may be subject to a heat seal stage where the printed side of the web precursor is overprinted or laminated with a heat seal coating. Preferably the heat seal stage is applied between the printing stage and the stage of coiling the web precursor onto the output reel.

[0ools] According to a third aspect of the present invention there is provided a security fibre comprising an impermeable transparent substrate, said substrate printed onto one side only with a single region bearing at least one ink which is normally invisible in visible light but fluoresces when irradiated with non-visible light.

[00017] Visible light is light normally visible to the human eye.

[00018] Preferably the region is divided into sub-regions each printed with a different ink whereby each region fluoresces a different visible colour when irradiated. The sub regions are preferably straight lines or stripes. The region may be a rectangular stripe or may be of other geometric shapes including a parallelogram, hexagon or elongated hexagon. Alphanumeric or other complex shapes may be printed onto region. With prior art security fibres this would be impractical because of the difficulty of achieving registration on each side of the web or the imprecision inherent in the use of tissue paper. The dimensions of fibres are variable according to purpose but typically have a length greater than the width, with 6mm long by 2mm wide being very large. Commonly used dimensions are 4mm long and 0.3 mm wide. Any complex shape must be smaller than the least dimension of the fibre, ie less than 2mm and more commonly less than 0.3 mm in at least one dimension.

[00019] Preferably the printed fibre is coated with a transparent heat seal material overlying the printed region. More preferably the unprinted side of the fibre may be coated with a layer of heat seal. The material of the heat seal may be selected to enhance adhesion of the fibre into a security paper or bank note in order to enhance the durability of the fibre in the security paper or bank note.

[00020] This new patent extends the use of the manufacturing principles of holographic micro particles to of create a new type of multi coloured UV fluorescent security fibre made using efficient reel to reel manufacturing processes and providing a novel structure and novel characteristics shapes and improved properties for incorporating and adhering into typically banknote paper as security fibres. It is envisaged these articles can also be tailored for incorporation into plastic substrates used for banknotes with suitable choice of materials.

[00021] The basic manufacturing technique is based on reel to reel processing to use a transparent plastic or cellulose base film,( PET, cellulose acetate) , print patterns or stripes of fluorescent colours on one side of the film that can be also be visualised also from the opposite film side due to the transparency of the film.

[00022] These new security fibres can be added to other types of security substrates such as rock paper and polypropylene as used for plastic banknotes.

[00023] EP 2359196E1 discusses production process knowledge and machinery for holographic micro particles which is based on continuous running webs in reel to reel rotary processes with a final rotary cutting process for converting web materials to micro particles meant for covert microscopic examination of a scale typically 0.3mm. The present invention extends this to larger particles shapes typically as parallelograms, typically 0.3 mm x 4 mm or similar, substantially rectangular or quadrilateral thin platelets, to use as security fibres.

[00024] These new security fibres are manufactured uses a transparent base, preferably one side printed with multi colour UV fluorescent inks in a graphical pattern or in a preferred method as a set of parallel lines, size typically 1 mm to 2 mm wide. The second side displays the UV fluorescent colour under UV light by transmission.

[00025] Preferably in one preferred form the geometry of line as and web input and rotary to create security fibres in parallelogram shapes where the UV fluorescent print lines run parallel to the small edges of the parallelogram. This adding a new novel shape base security feature into the new security fibres by alignment print to a non-rectangular shape, requiring precise equipment geometry and is not possible using sheet fed work.

[00026] In one preferred embodiment, during printing, the master reels contain either an additional print working or an full face coating using a heat seal material designed to melt during the papermaking process to give the new security fibres an improved good bond to the paper fibres to prevent them being shed from the paper reels or banknotes during flexing.

[00027] In a preferred method the heat-seal coating is applied to both faces of the security fibres for improved bonding. Typically, the heat-seal coating would vary from 1 um (1 gsm) to 10 gsm in thickness, a preferred thickness being around =3 micron (3 gsm) for good bonding and would be gravure coated.

[00028] In an additional feature printed micro print small feature can be additionally added to the fibre, such as graphical shapes or micro text, typically 0.1 to 1 mm letter height, typically 0.5 mm. In a preferred construction the micro print runs in lines parallel to the small side of the parallelograms in stripes along the master reels, is visually visible (visible or invisible fluorescent inks) and located either away from the UV fluorescent lines, typically adjacent, or under the fluorescent lines such that from the second side of the fibre particle to UV fluorescence can be further verified by visualizing the micro print against the fluorescent. This can also be used to display custom graphics in the fluorescent colour esign, such as a national flag shape and colours.

[00029] It is preferred to use a patterned fluorescent UV print rather than a line or stripe, where the print pattern across the stripes is modified and print density modulated to reduce the unwanted visual effect of any overlap between fluorescent lines and to conceal any brightness variation due to small cutting wander in cut position to fibre. We this envisage the stripe or lines being replaced by a graded stripe or line, such that the deposited ink density is highest in the centre of the line and reduces at the edges of the UV ink printed lines such that any overlap between 2 lines contains typically 25% or 50% ink densities to avoid building up bright lines where the UV inks overlap which is not desirable.

[00030] A preferred but not exclusive printing process is gravure print. Ink density reduction may be achieved at the edges of lines by using 2 or more gravure cell depths in the lines, typically a larger cell depth in the line centre block and a reduced cell depths and so reduce ink coverage in the 2 edge portions (typically 20 to 50% of the line such that any print overlap areas are less visually apparent. This can also be achieved with conventional print technique such as half tone the edges of the print lines where overlap may occur.

[00031] Additional covert ink security features may be used in the new security fibres such as IR excited visible replay up converter materials (Stokes) features and magnetically detectable coatings.

[00032] Variable widths of fluorescent line printing may be used to allow concealment of cutting variations in cutting of fibres. So, for a multi-colour UV fluorescent security fibre the UV fluorescent print would consist of a number of equal width printed lines of different colour UV fluorescents except for the end lines, bordering the next fibre, which may be enlarged in width to allow for edge cutting down the centre of the line. The end lines may be enlarged by a factor of 2 more to allow for fibre cutting along the centre of line to separate adjacent fibre particles.

[00033] In a further embodiment of this the edge lines for cutting and creating fibre borders may be additionally enlarged ( say 3 or 5 x other lines widths) to allow for more process variation by adjusting ( reducing) either the print density or UV fluorescent doping density so that the enlarged edge lines on the fibre maintained the same apparent visual impact as the narrow lines within the body of the fibre by balancing the additional lines width with a reduced brightness to achieve an equal visual effect for an observer.

[00034] In another preferred embodiment two master reels of the new form of security fibres may be laminated together to encapsulate a magnetically detectable coating or a metallised coating. In this case each master reel substrate would be printed with a white opaque UV dull coating, then printed with UV fluorescent workings, then over-coated with a suitable heat seal on the outside side for paper bonding and coated with a suitable magnetic coating on a side designated to be the inner surface. The film would then be laminated to itself during a film-to-film lamination to encapsulate using typically a crosslinking adhesive. This structure may then provide a standard looking white fibre with UV fluorescent features encapsulating either a magnetically detectable layer or a metallic layer or patterned layer for additional security than could be visualized by transmission through the final paper article. This may then be converted to provide a multi colour UV fluorescent fibre containing additionally an encapsulated and protected magnetically verifiable layer or metallised layer.

[00035] EP 2359196B1 ( WO 2010/046708) teaches a manufacturing processes and structures for holographic micro taggants for incorporation into security papers as a covert security taggant feature. The present invention extends these methods further to manufacture novel security fibres, usually as multi colour fluorescent fibres using inks that replay a colour under ultra violet light, typically 245-345 nm but which are colourless under normal lighting. Printed small alpha numeric graphics and fluorescent UV features may be provided.

[00036] A security fibre production process based on continuous running webs in reel-to-reel rotary processes with a final rotary cutting process for converting web materials to fibre shapes, as small thin hexagonal discs, or substantially rectangular or quadrilateral thin platelets is disclosed.

[00037] Additional coatings may be provided on the fibres to aid adhesion into the security paper. Such coatings may provide heat activated adhesives to enhance adhesion to paper fibres and give better bonding to paper fibres in the banknotes. Ideally this heat activated adhesive can be printed on one or both sides of the fibre or incorporated as a print working designed to activate during drying of the paper slurry.

[00038] We envisage reel to reel production of security fibres carrying UV fluorescent print in one or several colours and optionally additional coatings or print. Additional coatings may be one or more of; a magnetic coating for authentication, or additional optical coatings or micro print images for application in security papers.

[00039] The manufacturing principles and processes that are based on reel-based web processing, reel to reel rotary processes, reel to reel coatings and gravure print and the principle of reel to micro particle conversion.

[0oozto] Patterning effects (print, shapes) may be provided on security fibres by means of the micro particles, using print and coatings to enable carrying additional micro printed graphic features.

[00041] Optical or magnetic detection functionality in coated/ printed layers (such as multi colour UV fluorescent, IR up converters or encapsulated magnetically active layers).

[00042] Typical film input materials may be used in manufacturing using transparent filmic substrates such as typical plastic, polyethylene terphane, polypropylene and cellulose based films and also very thin translucent thin papers.

[00043] Two sided imaged fibres may be made by lamination and incorporating an additional encapsulated feature such as a magnetic detectable layer with holographic images carrying graphics on both sides of a particle made in this case by a lamination technique so that both side of the security device read correctly.

[00044] The concept of adding printed information to paper or plastic based metallised security fibres micro particles. One way of doing this would be printing a mask or ink pattern (raised ink leaving 'margins') and allowing the unprinted areas to be etched away to give a de-metallised pattern.

[00045] The patent describes our conversion process to create the security fibre using a web to micro particles based on a web-based reel input rotary cutting technique. [00046] GB 2456612A and EP 208105B1 describes gravure print methods to produce surface relief carrying structures to facilitate the present invention.

[00047] The present invention provides a security fibre production process which operates on a reel to reel continuous process basis using reels of filmic material as the input.

[00048] The new security fibres use a filmic transparent substrate such as PET, polypropylene or a cellulose base film clear film such as cellulose acetate or translucent film. The use of transparent reel-based substrates allows printing of the security fibres fluorescent inks on only one side with the second side of the fibre visualizing the fluorescent pattern by transmission. This allows simple line registration.

[00049] The films are printed with fluorescent inks, invisible in normal light, visible under UV light typically using gravure printing methods, although other print methods can be used.

[00050] Advantageously for multi colour fibre applications the print is laid down in a series of parallel lines.

[00051] Additional printed graphic can be used for additional security -in a visible colour to give a micro print security feature.

[00052] It is useful typically addition print working and / or use full cover coatings to add an additional lacquer or ink with heat-sealable thermal activated properties forming coating on the security fibre that activates during paper making to give a good bond to the paper fibres.

[00053] Typically, in the print working an additional visible line working would be incorporate in the web to aid film guiding.

[00054] Typically the process would flood coat a single colour UV fluorescent or print lines or structured lines of multiple UV fluorescent inks ( 2 to several) together with workings of tinted or clear heat seal coating.

[00055] Typically print lines (stripes) would abut.

[00056] In one advantageous cases the printed lines would overlap slightly with the use of print cylinders designed to give less ink density at the edge of lines to reduce the ink density at the overlap of lines to reduce the visual impact density of any overlap areas of fluorescent ink and also to reduce the effect of side to side variations in register movements potentially leaving overlapping fluorescent ink showing a different colour leaving unprinted gap as these can cause film damage when winding.

[00057] The lines or stripes may be printed with variable ink density, putting down a lighter ink density at the edge the lines in overlap areas with the next line to reduce the intensity of overlap area. Another advantageous structure of the line workings is to reduce edge density by using a half tone effect at the edge of lines. One method of doing this in a gravure printing process is to use cylinders with one cell depth of the centre of a line to give 100% coverage and using a second less volume cell depth or at the outer edges of the line to reduce the ink density in overlap areas and give a fade off effect to reduce the visibility of print overlap.

[00058] It is useful with multi-colour fluorescent fibres to print several lines of fluorescent ink of different colours and then use cylinders and half toning to provide a fade off effect where the end of the fibre needs cutting to conceal variations in cutting position that could lead to variations in relative fluorescent intensity.

[00059] Typically, at the overlap of two lines the edge ink density would reduce to around 30-50%, though other values are possible.

[00060] Typically for the end of a fibre where cutting was required the density would fade off in stages to 20-30% across the cut line to minimize visibility of the variation, though different values are possible.

[00061] It is helpful in the present process to full coverage print the web film so as not to leave gaps as an uneven filmic surface with gaps between lines as this could cause winding problems.

[00062] In the present process the film is single sided coated and relies on the transparency of the film to be visible from the second side.

[00063] The creating of the security fibres is done using a modified rotary cutter with web based continuous process input. Entirely different from previous sheet-based techniques.

[00064] The new security fibres have unique and different shapes from previous typically rectangular fibres.

[00065] The shape of HSI fibres can vary -in one embodiment the fibres can be planar structures shaped as quadrilateral structures, specifically typically parallelograms, with a shape defined by the relativity of web advance on the input web and rotation of cutting blades.

[00066] Typical size for HSI security fibres would be a planar structure typically 10 micron to 200 micron thick typical m 4 mm long x 0.3 mm wide on a 30 to 50 micron film thickness with angled end faces at 5 to 45 degrees on the parallelogram, not rectangular. Size range typical in length 0.5 mm to 15 mm usual around 4 to 6 mm, in width 0.05 mm to 6 mm, usual about 0.1mm to 2 mm.

[00067] The fibre shape may be based on a hexagon or elongated planar hexagon, of similar dimensions to above.

[00068] The shape of the UV fluorescent security fibres are advantageous in that the shape of the security fibre can add an additional level of variation and security. Previous techniques manufactured rectangular security fibres only.

[00069] This process may advantageously print an additional visible working for registration. [00070] This process may incorporate heat activated binder coatings into the security fibre either as a print line or working as an all over coating to enhance adhesion to the paper fibres during papermaking.

[00071] This process produces security fibres shaped as any one of thin planar parallelograms, rectangles or elongated hexagonal shapes.

[00072] Variable fibre shapes are possible with this process.

[00073] This process generates of a flat film profile using all over printing and coating of the film to give a flat film for subsequent winding and coating coated preferably with a heat sealable coating on one or both sides to enhance adhesion to the paper fibres during papermaking.

[00074] This new process combines the use of surface relief microstructures coupled with gravure print to make accurately defined security fibres.

[00075] So we also envisage as one optional embodiment...

[00076] A security fibre for use as an anti-counterfeit feature in security paper, consisting of a transparent substrate comprising a first layer of a surface relief structure of a substantially rectangular shaped surface relief a structure of peaks and troughs and a second gravure printed layer consisting of a plurality of colour fluorescent ink lines characterised such that the gravure print cylinder lines abutted each other and also exceeded the width of the raised areas of the surface relief thus only transferring ink onto the raised areas of the surface leaving the lower areas of the surface relief unprinted, so giving a pattern of clean edge lines on the proud areas of the pattern and leaving the lower areas of the surface relief unprinted uncoated gaps to conceal production variations.

[00077] It is also known that in the security fibre field it is useful not to have fluorescent inks overlapping as this produces a mixed colour at the interface and can show cutting inaccuracy at the ends.

[00078] A security fibre consisting of a transparent substrate one side printed with coloured stripes, invisible under normal light and visible under UV light wherein the coloured print lines abut each other but the sub regions (lines) themselves are reduced in colour density at their edges ( half toned or using different gravure cell depths) so that less colour is laid down at the overlap or edges of the printed lines. This is useful in reducing visibility overlap effects in the centre of a fibre between adjacent colours and also for reducing the visual effect of any cutting inaccuracy at the edge of a fibre.

[00079] A dual colour 4 mm fluorescent fibre printing for example 2 mm lines of fluorescent ink, where the 1 mm centre was 100% colour but over each 0.5 mm edge the colour density dropped from 100% to 20 % density to reduce the visual effect of any print misalignment and to hide the visual effect of any cutting mis-alignment which may see the fluorescent colours balance seem unbalanced.

[00080] We also envisage process reel to reel using conventional hot or UV embossing from a nickel former to create the surface relief pattern lines. Which is then printed by gravure print using print lines that abut each other but are defined by the upper regions of the semi rectangular structure.

[00081] It would additionally also be possible to create a surface relief using a gravure print roller laying down thick lines of linear coating. For example, for UV curing or using a rapidly dried high solids coating, doing the opposite of normal gravure print to freeze the surface relief rather than allow it to flow out to create a microstructure.

[00082] A security fibre wherein the fibre consists of a metallised film. The metallised film may be patterned by selective demetallisation. Both surfaces would be one of white printed or clear printed and then both surfaces coated with stripes of fluorescent ink to give a new type of security fibre feature with a multicoloured UV fluorescent and transparency feature wherein the metallised zone remains opaque and a demetallized feature can be seen in transmission.

[00083] The security fibre may be all over microprinted. The microprinted security fibre may be subsequently overlaid with multi colour fluorescent lines.

[0ooset] The security fibre may include patterning effects (print, shapes) using micro particles, print and coatings to enable micro printed graphic features.

[00085] A security fibre having an additional coated or printed layer, which may or may not be coloured and which may include using a material designed to soften during the papermaking process acting as a heat-seal adhesive element designed to increase bonding into paper fibres during papermaking. Ideally this can be printed on one or both sides of the fibre or incorporated as a print working.

[00086] Manufacturing a security fibre precursor and a security fibre using a transparent filmic substrate such as; polyethylene terphane, polypropylene and cellulose based clear films and also very thin translucent calendared papers.

[00087] A laminated security fibre formed from two similar layers, each layer comprising a transparent filmic substrate onto only one side of which are printed regions and sub-regions of a fluorescent material. The layers being bonded together to encapsulate an additional feature. The additional feature may be a magnetic layer, eg a ferromagnetic layer, to be detectable by suitable instrumentation when embedded in the security paper. The laminated security fibre may have holographic image carrying graphics printed on both layers so that the image can be read correctly from both sides of the security fibre.

mow Paper or plastic based metallised security fibre micro particles may be manufactured using a printing a mask or ink pattern (raised ink leaving 'margins). The unprinted areas may be etched away to give a de-metallised pattern. The resulting demetallized pattern presenting printed information which confirms the authenticity of the security fibres and the security paper.

[00089] Optically active features may be added to the surface of the security fibre suitable for 'carrying additional optical taggants for visual authentication under assisted special lighting, so as well as UV sources (eg red, green UV responses) the security fibre responds to IR sources.

[00090] Advantageously for multi colour fibre applications the print is laid down in a series of parallel lines.

[00091] Advantageously micro print line structures may be utilised designed to be decoded/visualized by matched overlays using a moire pattern line interference principle to generate hidden images.

[00092] It is useful typically addition print working and/or use full cover coatings to add an additional lacquer or ink with heat-sealable thermal activated properties forming coating on the security fibre that activates during paper making to give a good bond to the paper fibres.

[00093] Typically the process would flood coat a single colour UV fluorescent or print lines or structured lines of multiple UV fluorescent inks ( two to several) together with workings of tinted or clear heat seal coating.

[00094] Typically print lines abut.

[00095] In one advantageous case the printed lines would overlap slightly. This can be achieved with the use of print cylinders designed to give less ink density at the edge of lines. This reduces the ink density at an overlap of lines to reduce the visual impact density of any overlap areas of fluorescent ink and also to reduce the effect of side-to-side variations in register movements. Conventionally overlapping fluorescent ink can show a an unwanted colour. Side-to-side register movements may leave an unprinted gap which can cause film damage when winding the web onto the reel after printing.

[00096] It is advantageous to print the lines with variable ink density, putting down a lighter ink density at the edge the lines in overlap areas with the next line to reduce the intensity of overlap area.

[00097]. Edge density may be advantageously reduced by using a half tone effect at the edge of lines to reduce the density. One method of doing this in a gravure printing process is to use cylinders with one cell depth of the centre of a line to give 100% coverage and using a second less volume cell depth or at the outer edges of the line to reduce the ink density in overlap areas and give a fade off effect to reduce the visibility of print overlap.

[00098]. It is useful with multi-colour fluorescent fibres to print several lines of fluorescent of different colours and then use cylinders and half toning to provide a fade off effect where the end of the fibre needs cutting to conceal variations in cutting position that could lead to variations in relative fluorescent intensity.

[00099]. Typically, at the overlap of two lines the edge ink density would reduce to around 30-50%, though other values are possible. Typically for the end of a fibre where cutting was required the density would fade off in stages to 20-30% across the cut line to minimize visibility of the variation, though different values are possible..

[000100]. Another method to obtain clear fibre separation for cutting is also envisaged as using variable widths of fluorescent line printing to allow concealment of cutting variations in cutting of fibres. So for a multi-colour UV fluorescent security fibre the UV fluorescent print would consist of a number of equal width printed lines of different colour UV fluorescents except for the end lines bordering the adjacent fibre which would be enlarged in width to allow for edge cutting down this border line of the two fibres. These end lines would be enlarged by a factor of two or more to allow for fibre cutting along the centre of line to separate adjacent fibre particles.

[occoon In a further embodiment of this use of the enlarged edge lines for cutting and creating fibre borders the edge lines could be additionally enlarged ( say 3 or 5 x other lines widths) to allow for more process variation on cutting tolerance by adjusting (reducing) either the print density or UV fluorescent doping density so that the enlarged edge lines on the fibre maintained the same apparent visual impact as the narrow lines within the body of the fibre by balancing the additional lines width with a reduced brightness to achieve an equal visual effect for an observer. This would help provide additional tolerance and concealment for cutting variations.

[000102]. It is helpful in the process to full coverage print the film so as not to leave gaps as an uneven filmic surface with gaps between lines as this could cause winding problems.

[000103]. The process envisages creating of the security fibres is done using a modified rotary cutter with web based continuous process input.

[000104]. The shape of HSI fibres can vary -in one embodiment the fibre can be a planar shape such as a quadrilateral preferably a parallelogram.

[000105]. The shape and dimensions of the parallelogram is defined by the relativity of web advance on the input web and rotation of cutting blades and input angle of the materials.

[000106]. Typical size for HSI security fibres would be a planar structure typically 10 micron to 300 micron thick shapes as a quadrilateral, preferably a parallelogram typical m 4 mm long x 0.3 mm wide on a 30 to 50 micron film thickness with angled end faces at 5 to 45 degrees on the parallelogram, not rectangular. Size range typical in length 0.5 mm to 15 mm usually around 2 to 8 mm" in width 0.05mm to 6 mm, usual about 0.1mm to 2 mm.

[000107]. In other configurations the fibre shape could be based on a hexagon or elongated planar hexagon, of similar dimensions to above.

[000108]. The shape of each security fibre is generally a parallelogram and not rectangular. [000109]. A preferable feature is to align printed UV fluorescent ink stripes to one side of the parallelogram to providing an additional level of authentication and uniqueness defined by the shape and alignment of print to the non-rectangular shape.

Achieving this relies on a precise set of of input angle, roller speed and stationary blades on a rotary cuter and is there for machine geometry, speed and cutter specific and both easily verifiable and hard to replicate.

BRIEF DESCRIPTION OF FIGURES

[000110]. An embodiment of a security fibre and method of production in accordance with the present invention will now be described, by way of example only, with reference to the accompanying figures, in which: Figure 1 is a plan view of a security fibre; Figure 2A is a sectional view of a security fibre; Figure 2B is a sectional view of a variant of the security fibre; Figure 3A is a diagrammatic view of a reel to reel printing stage for printing regions onto a web of transparent impermeable substrate as a stage in the process of forming the fibres; and Figure 3B is a diagrammatic view of a cutting stage downstream of the printing stage, wherein the printed web is cut into fibres; Figure 4A is a plan view of a variant of the security fibre; and Figure 4B is a diagram illustrating relative colour brightness and corresponding ink density of adjacent differently coloured regions.

DESCRIPTION

[000111]. The figures are diagrammatic and not to scale.

[000112]. Figure 1 shows a preferred embodiment of a security fibre 1 having dimensions 35 micron thick, 4 mm long and 0.3 mm wide. The fibre has a parallelogram shape. A region 4 of the fibre is printed with four sub-regions 5, 6, 7, 8 of fluorescent ink which is invisible when illuminated only by a visible light spectrum light source. The fluorescent inks each fluoresce when exposed to a UV light source such that sub region 5 fluoresces red, sub-region 6 fluoresces yellow, sub-region 7 fluoresces green and sub-region 8 fluoresces blue. An additional security microprint 3 comprises alphanumeric text approximately 0.08mm height, is printed onto the sub region 7 parallel to the left end of the fibre. The ink printed region 4 is printed onto an impermeable transparent substrate 13. Only one side of the substrate 13 is printed as can be better seen in figure 2A.

[000113]. Figure 2 A shows a cross section of the security fibre in Figure 1, showing the transparent impermeable filmic substrate 13 onto which fluorescent inks are deposited to form printed region 4 comprising the sub-regions 5,6,7,8. An additional top heat seal coating 15 is printed to overly the printed top surface of the fibre including any unprinted margins. A bottom heat seal coating 16 is printed across the whole of the unprinted bottom surface of the fibre. The heat seal coatings are or at least become visible and UV light transparent during use. When exposed to visible light the fibre is substantially transparent and therefore invisible, however when exposed to UV light of appropriate frequency, the UV light passes unhindered through the heat seal coating and transparent substrate 13, to stimulate the fluorescent inks to emit visible light of frequencies corresponding to red, yellow, blue and green. The emitted light passes back through the transparent substrate and seal coating and is thus naked eye visible to an observer 12 at either side of the fibre. The heat seal coating is selected to protect the region 4 and to facilitate bonding of the fibre into a security paper when mixed with the paper pulp.

[000114]. Figure 2B shows a cross section through a second embodiment of the security fibre 17. A region is printed onto a transparent substrate formed of three sub-regions 5,6,7. In the first embodiment the sub regions are printed with a uniform thickness and density across their whole width and abut each adjacent region. The regions of the second embodiment have a uniform thickness across a central region of each stripe or line and the thickness of each strip is reduced at the edges next to adjacent sub-regions. When printed the thinning edge regions overlap ensuring that the whole of the region of the security fibre is printed and minimising the effect of mixing inks at the edges of the sub-regions. The second embodiment may also be coated with a heat seal over the top and bottom of the security fibre.

[000115]. Figure 3A shows the reel to reel rotary manufacturing process. An input reel 24 of unprinted transparent impermeable web is unwound to feed through a gravure printing stage comprising a gravure role 25 and a backing role 26. The gravure role 26 draws fluorescent inks from a reservoir to print onto one surface of the web 23.

[owns]. The printed web is then moved downstream to a be coiled at a coiling stage into an output reel 27. In a variant of the process the top and printed bottom surfaces of the web may be coated with a heat sealant in a stage between the gravure printing stage and the coiling stage.

[000117]. Figure 3B shows a cutting process diagram wherein a precursor security fibre reel 27 is moved to the cutting stage and unwound at station 31, so the web 29 can be fed towards a cutting stage. The cutting stage comprises a stationary blade 31 over which the precursor web is fed. A rotating blade spins around an axis parallel to the plane of the web 29 at a speed synchronised with the forward movement of the web in order to cut the security fibres from the leading edge of the web 29 by cutting through the margins of the regions. The geometry of each of the stationary blade and rotating blade, and the relative speed of the rotating blade and web can be selected to determine the profile of the security fibres. As shown the cut security fibres 34 can be collected directly into a hopper [mons]. Figure 4 shows a method using variable widths of fluorescent line printing to allow concealment of cutting variations in cutting of fibres. Figure 4 shows 2 adjacent fibres 35 and the cut line 37. So for a multi-colour UV fluorescent security fibre 35 the UV fluorescent print would consist of a number of equal width printed lines of different colour UV fluorescents 39 marked R,Y,G except for the end lines 36 marked B bordering the adjacent fibre which would be enlarged in width 36 to allow for edge cutting variation down this border cut line 37 of the two fibres. The end fluorescent line 36, 38 spans adjacent fibres and is of larger width than the interior print lines to allow cutting variation and is of reduced ink density or reduced UV fluorescent doping in the ink to balance the visual effects between these wider lines 36,38 and narrower internal lines 39. These end lines 36 would be enlarged by a factor of 2 to 4 or more to allow for fibre cutting along the centre of line to separate adjacent fibre particles with their brightness appropriately reduced to maintain a visual balance of brightness 38 for an observer.

Clauses defining the invention [000119]. Clause 1.A security fibre suitable for incorporation in high security papers or other substrates containing one or multiple colour print workings printed on one side of a transparent or translucent substrate for authentication under UV fluorescent light or visible light or both characterised that the fibre shape is a non rectangular.

j000lzoi. Clause 2. As clause 1 where the fibre shape is a quadrilateral.

[000121]. Clause 3. As clause 1 or 2 characterised that the security fibre shape is a planar parallelogram.

j000122i. Clause 4. As any of clause 1 to 3 characterised that the colour print workings are not visible in normal light and are only visible under a UV light source replaying different colours such as red, yellow, green, blue.

[000123]. Clause 5. As any of clause 1 to 4 characterised that the print working s are lines or stripe further characterised hat the lines or stripe are aligned parallel to the small side of the parallelogram such that where the UV fluorescent print lines to run parallel to the small edges of the parallelogram.

[000124]. Clause 6. As any of clause 1-5 characterised such that one of the print workings or an additional print working or all over coating has the properties of a heat seal coating to achieve greater bonding to paper fibres by melting and bonding to paper fibres during the papermaking process.

[000125]. Clause 7. As clause 6 further characterised that the heat seal coating is applied to both faces of the security fibre.

[000126]. Clause 8. As any preceding clause where manufacturing technique is based on reel to reel processing [000127]. Clause 9. As any preceding clause where the base film is a transparent plastic or cellulose base film,( PET, cellulose acetate) , allowing print patterns or stripes of fluorescent colours on one side of the film that can be also be visualised from the opposite film side due to the transparency of the film, including and also very thin translucent thin papers.

[000128]. Clause 10. As any preceding clause where the parallelogram or quadrilateral size is in the range small side, typically 0.1-2mm, large side 1.5 mm to 10 mm o...

[000129]. Clause 11. As any preceding clause where one side is printed with multi colour UV fluorescent inks in a graphical pattern or in a preferred method as a set of parallel lines, and where second side displays the UV fluorescent colour under UV light by transmission.

[000130]. Clause 12. As any preceding clause where the security fibre further includes a visible micro print [000131]. Clause 13. As any preceding clause where a patterned fluorescent UV print rather than a line or stripe, where the print pattern across the stripes is modified and print density modulated to reduce the unwanted visual effect of any overlap between fluorescent lines and to conceal any brightness variation due to small cutting wander in cut position to fibre such that We that the stripes or lines are replaced by a graded stripe or line, such that the deposited ink density is highest in the centre of the line and reduces at the edges of the UV ink printed lines such that any overlap between 2 lines contains typically 25% or 50% ink densities [000132]. Clause 14 As any preceding clause such that the printed lines are produced by a gravure print process and reduced ink density at the edges of lines by using 2 or more gravure cell depths in the lines, typically a larger cell depth in the line centre bock and a reduced cell depths and so reduce ink coverage in the 2 edge portions ( typically 20 to 50% of the line such that any print overlap areas are less visually apparent.

[000133]. Clause 15 As any preceding clause where the print density reduction at the egd of lines is achieved with conventional print technique such as half tone the edges of the print lines where overlap may occur.

[000134]. Clause 16. As any preceding clause where additional ink covert security features are also incorporated in the new security fibres such as IR up converter ( Stokes) features and magnetic coatings.

[000135]. Clause 17. As any preceding clause where the security fibre is constructed from two layers laminated together to encapsulate a magnetically detectable coating, where there is an printed with an opaque UV dull coating, then printed with UV fluorescent workings, then overcoated with a suitable heat seal and during lamination to one or both reel would be applied a suitable magnetic coating which would be encapsulated using typically a crosslinking adhesive. To provide would then be converted to provide a multi colour UV fluorescent fibre containing additionally an encapsulated and protected magnetically verifiable layer.

[000136]. Clause 18. As any preceding clause wherein the security fibres are manufactured using a web to micro particles based on a web principle using a rotary cutting technique the based reel input input angle, speed and shape of the rotary tool to control length and width and interior angles of the parrallelograms with a shape defined by the relativity of web advance on the input web and rotation of cutting blade in order to provide distinctive shapes and sizes as a additional security features.

[000137]. Clause 19. As any preceding clause where the multi colour UV fluorescent or visible the print is laid down in a series of parallel lines.

[000138]. Clause 20. As any preceding clause where a structure replaces replace the lines being printed with lines consisting of variable ink density, putting down a lighter ink density at the edge the lines in overlap areas with the next line to reduce the intensity of overlap area.

[000139]. Clause 21. As clause 20 a security fibre wherein printed lines would overlap slightly with the use of print cylinders designed to give less ink density at the edge of lines to reduce the ink density at the overlap of lines to reduce the visual impact density of any over lap areas of fluorescent ink and also to reduce the effect of side to side variations in register movements.

[000140]. Clause 22. As any preceding clause to generate variable print density using a gravure printing process is to use cylinders with one cell depth of the centre of a line to give 100% coverage and using a second less volume cell depth or at the outer edges of the line to reduce the ink density in overlap areas and give a fade off effect to reduce the visibility of print overlap.

[00ow]. Clause 23.As any of clause 20 to 22 where the edge density line workings is to reduce edge density by using a half tone effect at the edge of lines to reduce the density.

[000142]. Clause 24. As in clause 23 additional printed graphic micro print is incorporated for additional security -in a visible colour to give a micro print security feature.

[000143]. Clause 25. A security fibre according to any one of the preceding clauses where the dimension of security fibres is a planar structure typically 10 micron to 200 micron thick typical m 4 mm long x 0.3 mm wide on a 30 to 50 micron film thickness with angled end faces at 5 to 45 degrees on the parallelogram, not rectangular. Size range typical in length 0.5 mm to 15 mm usual around 4 to 6 mm" in width 0.05mm to 6 mm, usual about 0.1mm to 2 mm.

[000144]. Clause 26. As according to any preceding clause using surface relief structures to control print alignment created by gravure print or surf ace relief embossing as security fibre for use as an anti-counterfeit feature in security paper, consisting of a transparent substrate comprising a first layer of a surface relief structure of a substantially rectangular shaped surface relief a structure of peaks and troughs and a second gravure printed layer consisting of a plurality of colour fluorescent ink lines characterised such that the gravure print cylinder lines abutted each other and also exceeded the width of the raised areas of the surface relief thus only transferring ink onto the raised areas of the surface leaving the lower areas of the surface relief unprinted, so giving a pattern of clean edge lines on the proud areas of the pattern and leaving the lower areas of the surface relief unprinted uncoated gaps to conceal production variations.

[000145]. Clause 27. As in clause 1 and 25 a security fibre of a transparent substrate one side printed with coloured stripes, invisible under normal light and visible under uv light wherein the coloured print lines abut each other but the lines themselves are reduced in colour density at their edges ( half toned or using different gravure cell depths) so that less colour is laid down at the over lap or edges of the printed lines to aid is useful in reducing visibility overlap effects in the centre of a fibre between adjacent colours and also for reducing the visual effect of any cutting inaccuracy at the edge of a fibre.

[000146]. Clause 28. A security fibre wherein the fibre consists of a metallised film ideally patterned by selective demetallisation. Both surface would be white printed and then both surface coated with stripes of fluorescent ink to give a new type of security fibre feature with a multicoloured uv fluorescent and transparency feature wherein in the metallised zone remains opaque and a demetallized feature can be seen in transmission.

[000147]. Clause 29. A security fibre as in any preceding clause manufactured by a process of reel to reel printing and coating follows by a process of reel to fibre cutting as described herein whereby the shape and size of the security fibre can be varied by adjusting the parameters of the cutting process as web speed, rotation cut speed and input web angle relative to cutter.

[000148]. Clause 30. A security fibre according to clause 29 wherein the shape of the security fibre is a parallelogram.

mom% Clause 31. Any article containing the security fibres as in any of the above claims.

Claims (34)

1. Claims 1. A precursor for a security fibre comprising an elongate, visible light transparent, ink impermeable web of indefinite length, on only one side of which is printed multiple regions of ink, said ink being invisible in visible light but fluorescing when exposed to wavelengths of stimulant light beyond the visible spectrum.
2. 2. A precursor according to claim 1 wherein the web is formed from one of; PET, polypropylene or a cellulose base film clear film, cellulose acetate or translucent film, calendared paper or super calendared paper.
3. 3. A precursor according to claim 1 or claim 2 wherein each region is sub divided into sub-regions, each sub-region being printed with a different ink to fluoresce to a different colour.
4. 4. A precursor according to any one of claims 1-3 wherein the edges of the sub-regions abut.
5. 5. A precursor according to any one of claims 1-4 wherein adjacent edge portions of the sub-regions are printed to have a relatively reduced thickness or concentration of ink and are printed to overlap with the edge portions of adjacent sub-regions.
6. 6. A precursor according to any one of the preceding claims wherein at least one of the printed surfaces of the precursor and the opposite unprinted surface is coated with a heat seal layer.
7. 7. A precursor according to any one of the preceding claims wherein at least a part of the region is printed with micro print features.
8. 8. A precursor according to any one of the preceding claims wherein the region has non-rectangular polygonal profile.
9. 9. A precursor according to any one of the preceding claims wherein a first layer of web is laminated onto a second layer of web such that the regions are in register.
10. 10. A precursor according to claim 9 wherein the first and second layer envelop an intermediate layer of metallic and/or magnetic material.
11. 11. A precursor according to claim 10 wherein the intermediate layer is a metallic layer and is partially demetallized.
12. 12. A precursor according to one of claims 9 to 11 wherein the printed regions and metallized regions interact to produce moire patterns.
13. 13. A method of manufacturing a precursor according to any one of claims 1-12 for a security fibre comprising; providing a reel of transparent impermeable web of indefinite length; unreeling the web to move the web to a gravure printing stage where the web is moved between a gravure print roll and a backing roll; applying fluorescent inks to regions of the web, on only one side of the web, by means of the gravure printing roll to form the precursor; moving the printed web to a coiling stage, where the web is coiled into a reel of precursor.
14. 14. A method according to claim 13 comprising a heat seal coating stage, wherein a coating of heat seal is applied to at least one side of the printed web downstream of the gravure printing stage.
15. 15. A method of manufacturing a precursor according to one of claims 13 or 14 comprising the step of laminating two layers of the printed web together with the regions in register.
16. 16. A method according to claim 15 wherein an intermediate metallised or magnetic layer is laminated between the two layers.
17. 17. A method of processing a reel of precursor according to any one of claims 1-12 into security fibres wherein a reel of precursor is uncoiled and moved continuously towards a cutting station, said cutting station comprising a stationary blade and a blade mounted for rotation past the stationary blade, continuously rotating the rotary blade past the stationary blade as the precursor moves into the cutting station and controlling the speed of the cursor and the speed of the rotary blade to cut through the margins of the regions of the precursor to cut security fibres from the precursor.
18. 18. A method according to claim 17 wherein the precursor is cut with a stationary blade and the rotary blade geometry arranged to cut a non-rectangular polygonal profile around each region.
19. 19. A method according to one of claims 17 or 18 wherein the step of cutting the security fibres from the precursor moves the security fibres to fall into a hopper arranged beneath the cutting station.
20. 20. A security fibre comprising: a transparent impermeable substrate; a printed region printed on only one side of the substrate printed with an ink invisible in visible light and fluorescent in light outside the visible spectrum, whereby the printed region is visible from each of the printed and unprinted sides of the substrate.
21. 21. A security fibre according to claim 18 wherein the printed region comprises at least two adjacent sub-regions, wherein each subregion is printed with a different ink to fluoresce a different colour.
22. 22. A security fibre according to claim 21 wherein each sub-region is a line or stripe, each stripe is printed to have an edge portion next to the adjacent sub-region, and a main portion wherein the edge portion has a reduced thickness or concentration of fluorescent ink relative to the main portion of the stripe.
23. 23. A security fibre according to claim 22 wherein the edge portions of adjacent stripes overlap.
24. 24. A security fibre according to any one of claims 20-24 wherein microprint graphical features are printed onto the region.
25. 25. A security fibre according to claim 24 wherein the microprint graphical features are alphanumeric features.
26. 26. A security fibre according to one of claims 24 or 25 wherein the microprint graphical features are printed in visible ink.
27. 27. A security fibre according to any one of claims 20 to 27 having a visibly non-rectangular planar polygonal profile.
28. 28. A security fibre according to any one of claims 20 to 27 wherein the security fibre is formed from first and second similar layers of transparent substrate laminated together with the regions in register.
29. 29. A security fibre according to claim 28 wherein the security fibre incorporates an intermediate metallised or magnetic layer enveloped by the first and second layers.
30. 30. A security fibre according to one of claims 28 or claim 29 wherein the printing on the region and the metallised layers interact to form a moir pattern.
31. 31. A security fibre according to any one of claims 20 to 30 wherein at least one side of the fibre is coated with a heat seal coating.
32. 32. A security fibre according to claim 31 wherein the heat seal coating enhances bonding into a security paper.
33. 33. A security fibre according to any one of claims 20-32 in combination with a security paper or a banknote.
34. 34. A method of manufacturing a security paper or a banknote comprising mixing security fibres according to any one of claims 20 to 32 into a paper pulp prior to processing the pulp into paper.