GB2559364A

GB2559364A - A method of manufacturing a security sheet

Info

Publication number: GB2559364A
Application number: GB1701729.4A
Authority: GB
Inventors: Horvath Adam
Original assignee: Portals de la Rue Ltd
Current assignee: Portals Paper Ltd
Priority date: 2017-02-02
Filing date: 2017-02-02
Publication date: 2018-08-08
Also published as: GB201701729D0

Abstract

Security fibers 30 are applied to a surface of a wet fibrous substrate 16 on a support 11, before the sheet is dried 21. Also claimed is a security element (41, figure 2) comprising security fibres 30 at least partially embedded in a fibrous substrate 16. The concentration, size or type of fibres 30 varies along the substrate 16. The substrate 16 is preferably produced using a rotating cylinder mould 12. The security fibres 30 are preferably applied 31 using a contact roller or nozzle arrangement. The security element (41, figure 2) is preferably machine readable. The security sheet is preferably coated. The apparatus is also claimed. The sheets are used in identification documents, passports, banknotes, passbooks, certificates, licences, shares and cheques.

Description

(71) Applicant(s):

Portals De La Rue Limited

Overton Mill, Station Road, Overton, Hampshire, RG25 3SE, United Kingdom (72) Inventor(s):

Adam Horvath (74) Agent and/or Address for Service:

Boult Wade Tennant

Verulam Gardens, 70 Gray's Inn Road, LONDON, WC1X 8BT, United Kingdom (51) INT CL:

D21H 21/42 (2006.01) B42D 25/355 (2014.01) B42D 25/40 (2014.01) (56) Documents Cited:

CN 103174060 B CN 102373653 B

US 20090188638 A1 (58) Field of Search:

INT CL B42D, D21H Other: EPODOC; WPI (54) Title of the Invention: A method of manufacturing a security sheet Abstract Title: Manufacturing fibrous sheet containing security fibre (57) Security fibers 30 are applied to a surface of a wet fibrous substrate 16 on a support 11, before the sheet is dried 21. Also claimed is a security element (41, figure 2) comprising security fibres 30 at least partially embedded in a fibrous substrate 16. The concentration, size or type of fibres 30 varies along the substrate 16. The substrate 16 is preferably produced using a rotating cylinder mould 12. The security fibres 30 are preferably applied 31 using a contact roller or nozzle arrangement. The security element (41, figure 2) is preferably machine readable. The security sheet is preferably coated. The apparatus is also claimed. The sheets are used in identification documents, passports, banknotes, passbooks, certificates, licences, shares and cheques.

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- 1 A METHOD OF MANUFACTURING A SECURITY SHEET

The present invention relates to a method of manufacturing a security sheet comprising a plurality of security fibres, an apparatus for performing the method and a security sheet formed by the method.

Security documents, such as passports, banknotes, passbooks, identification documents, certificates, licences, share certificates and cheques, commonly comprise a security sheet formed from a fibrous substrate layer and one or more security features for preventing and/or deterring counterfeiting. The security features are usually at least partially embedded in the thickness of the fibrous substrate layer or located on at least one surface of the fibrous substrate layer. Exemplary security features include watermarks (conventional/tonal or electrotype), security threads, security fibres, security particles, planchettes, holograms, print and/or inks, colour changing inks or other optically variable elements, ultraviolet (UV) visible features and any other security features known in the art. Security fibres are a particularly suitable security feature as their properties can be selected such that they are invisible to the naked eye when viewed in reflected visible light and visible to the naked eye when viewed in light outside the visible spectrum (e.g. UV light). Therefore they form a covert security feature and their presence can therefore be easily detected by a security document inspector.

Security fibres are typically randomly distributed throughout the thickness of the security sheet and an exemplary method for incorporating security fibres into a security sheet is disclosed in WO-A-2016/063049. A fibrous substrate layer is formed by the deposition of fibrous stock on a cylinder mould cover rotating in a vat of aqueous fibrous stock. The fibrous substrate layer is subsequently couched from the cylinder mould cover by a couch roll and transferred to a drying section on a belt (e.g. a formex), where water is removed from it and the security sheet subsequently formed. The security fibres may be embedded within the fibrous substrate layer by being randomly distributed and mixed in the vat of aqueous fibrous stock such that, during formation on the cylinder mould cover, they are randomly distributed throughout the entire thickness and width of the fibrous substrate layer. Alternatively, the security fibres may be pumped through an injector adjacent to the cylinder mould cover and onto the fibrous stock before the fibrous substrate layer is fully formed. Further fibrous stock is subsequently deposited over the security fibres such that the security fibres are located in a central region within the thickness of the fibrous substrate layer. However, in WO-A-2016/063049 the security fibres are only deposited in restricted regions, such as across the entire width of the fibrous substrate layer or in bands.

- 2 US-A-2003/0104176 discloses a security paper with at least two types of luminescent mottled fibres forming in a code. The code is defined by a geometric arrangement of subareas of the mottled fibres and/or by the presence or absence of mottled fibres of a specific type. In a similar manner to WO-A-2016/063049, the mottled fibres are applied to the fibrous stock on a cylinder mould cover within the vat of aqueous fibrous stock by a special exit nozzle. In order to form the code, one or more nozzles apply the mottled fibres either continuously to form subareas of mottled fibres with the geometric arrangement or intermittently in accordance with the code. However, in the method of USA-2003/0104176 and WO-A-2016/063049 the security fibres may disperse beyond the desired subareas due to the turbulent flow of the security fibres in the aqueous fibrous stock in the vat prior to contact with the fibrous stock on the cylinder mould cover. As a result, the edges of the subareas may not be clearly defined and, therefore, the code may be difficult to identify and/or may not be aesthetically pleasing. Furthermore, subareas with complex shapes are difficult to form due to the unclearly defined edges.

An object of the present invention may be to provide a method of incorporating security fibres into a security sheet in clearly defined and/or complex shapes, preferably thereby rendering the counterfeiting of the security sheet more difficult and/or making the security sheet more aesthetically pleasing. A further object may be to enable the application of the security fibres to the surface of the security sheet in a resilient manner rather than only within the thickness of the security sheet.

The present invention therefore provides a method of manufacturing a security sheet comprising: depositing a fibrous stock on a support surface to form a wet fibrous substrate layer; applying security fibres to at least one surface of the wet fibrous substrate layer; and drying the wet fibrous substrate layer; wherein the security fibres are applied to the wet fibrous substrate layer after the wet fibrous substrate layer has formed on the support surface and before the wet fibrous substrate layer is dried.

The invention further provides an apparatus for manufacturing a security sheet comprising: at least one support surface configured to receive a deposition of a fibrous stock thereon, form a wet fibrous substrate layer from the deposited fibrous stock thereon and transfer the formed wet fibrous substrate layer to a drying section for drying; and at least one application device configured to apply security fibres to at least one surface of the wet fibrous substrate layer and located adjacent the at least one support surface between where the wet fibrous substrate layer is formed and the drying section.

-3Preferably the wet fibrous substrate layer is dried in a drying section and the security fibres are applied to the wet fibrous substrate layer before being dried in the drying section. Further preferably the drying section comprises a press section forming a nip at which pressure is applied to dry the wet fibrous substrate layer and the security fibres are applied to the wet fibrous substrate layer before entering the nip. Yet further preferably the security fibres are applied when the fibrous substrate layer comprises at least 60% water by volume or at least 80% water by volume.

The support surface preferably comprises a cylinder mould cover of a cylinder mould rotating in a vat of fibrous stock. The fibrous substrate stock is preferably deposited on the cylinder mould cover to form the wet fibrous substrate layer and the security fibres are applied to the wet fibrous substrate layer after the wet fibrous substrate layer has exited the fibrous stock in the vat. The support surface may comprise a cylinder rotating in a machine direction. The fibrous stock is preferably deposited onto the cylinder by spraying to form the wet fibrous substrate layer and the security fibres are applied to the wet fibrous substrate layer downstream of the spraying in the machine direction. A second support surface may extend from the first support surface to at least the drying section. A third support surface may comprise a cylinder and/or a belt configured to receive fibrous substrate sprayed thereon by at least one spraying device.

The security fibres are preferably applied to the wet fibrous substrate layer by at least one application device, the at least one application device comprising: a roller in contact with the wet fibrous substrate layer and comprising at least one formation element for depositing at least one dose of security fibres onto the wet fibrous substrate layer; and/or a nozzle arrangement for ejecting at least one dose of security fibres onto the wet fibrous substrate layer.

In preferred embodiments the security fibres are applied as at least one security element. The nozzle arrangement may comprise a plurality of nozzle openings configured for applying security fibres as a single security element. The security fibres are preferably applied such that the concentration, size and/or type of the security fibres varies across the at least one security element. The security fibres may be applied such that the at least one security element comprises a substantially continuous gradation in the concentration of the security fibres. The security fibres may be applied such that the at least one security element comprises at least two adjacent regions of security fibres of different concentrations, sizes and/or types, the concentration, size and/or type of security fibres in

-4each region being substantially the same. The outer perimeter of the at least one security element preferably comprises at least one of a logo, symbol, indicium, image, alphanumeric character and/or any shape conveying information to a reader. The security fibres are preferably applied as a plurality of security elements having differing compositions and/or shapes. In preferred embodiments the at least one security element forms machine readable information. The security fibres are preferably applied continuously such that at least one security element extends between edges of the security sheet and/or the security fibres are applied discretely such that at least one security element is separated from another security element formed on the wet fibrous substrate layer.

The method preferably comprises applying a vacuum to a surface of the wet fibrous substrate layer opposing the surface of the wet fibrous substrate layer to which the security fibres are applied. Preferably the security fibres are applied as a suspension of security fibres in a liquid. Preferably a coating is applied over the security fibres at the surface of the wet or dried fibrous substrate layer. The security fibres are preferably visible in reflected light incident on the surface of the security sheet in visible light or light falling outside of the visible spectrum. The method may further comprise cutting the dried fibrous substrate layer into a plurality of security sheets.

The present invention further provides a security sheet formed according to the aforementioned method and/or using the aforementioned apparatus. The security sheet may comprise at least one fibrous substrate layer and at least one security element formed by security fibres at least partially embedded in the fibrous substrate layer. The security fibres are preferably located at at least one surface of the fibrous substrate layer and/or within the thickness of the fibrous substrate layer.

The present invention further provides security sheet comprising at least one fibrous substrate layer and at least one security element formed by security fibres at least partially embedded in the fibrous substrate layer, wherein the concentration, size and/or type of the security fibres varies across the at least one security element.

The at least one security element may comprise a substantially continuous gradation in the concentration of the security fibres. The at least one security element may comprise at least two adjacent regions of security fibres of different concentrations, sizes and/or types, further wherein the concentration, size and/or type of security fibres in each region is substantially the same. A first region may comprise security fibres that are visible

-5to the human eye when viewed in reflected visible light. An adjacent second region may comprise security fibres that are not visible to the human eye when viewed in reflected visible light. The security fibres of the second region may be visible when viewed in reflected light outside of the visible spectrum. The number or volume of security fibres in at least one first region may be at least approximately 110%, at least approximately 120%, at least approximately 150%, at least approximately 200% and/or at least approximately 400% of the number or volume of security fibres in an adjacent at least one second region. Each may region form at least 10%, at least 25% and/or at least 50% of: the surface area of the security element; the volume of fibrous substrate and security fibres falling within the boundaries of the shape of the security element; and/or the total number of security fibres in the security element. The security sheet may comprise a plurality of security elements, wherein the composition of security fibres and/or shape of at least one security element is different to that of at least one other security element.

The security fibres of the present invention may comprise one or more physical entities carrying one or more security features of a suitable composition. The security fibres may be of any type and/or size suitable which are visible to the human eye and/or machine readable. A mix of different types and sizes of security fibres may be provided to improve the different security elements and thus the security sheet may be more difficult to counterfeit.

The term “security fibres” is known in the art and generally refers to predominantly fibrous and elongate (i.e. substantially one dimensional shaped) elements which are distinguishable by the human eye and/or a machine from the fibrous substrate layer forming the body of the security paper. Therefore, each security fibre may comprise an elongate body (e.g. a discrete filament) configured to produce a security effect. The security effect may enable the security fibre to be distinguished from the fibrous substrate in visible light or light falling outside of the visible spectrum to the naked eye or a machine. Each security fibre may be of a different composition to the fibres of the fibrous substrate.

EP-B-2342085, which is incorporated herein by reference, discloses particularly suitable security fibres. Security fibres are usually made from synthetic or natural materials such as paper, silks, polyester, nylon, rayon and/or other artificial fibres. The security fibres preferably have a length in the range 1 to 10 mm, more preferably in the range 1 to 6 mm and more preferably in the range 1 to 3 mm. The width of the security fibres is preferably from 20 to 100 pm and more preferably approximately 50 pm. The linear density of the security fibres, particularly if formed from nylon, viscose or rayon, is preferably in a range 5

-6x 10⁷ to 30 χ 1Ο⁷ kg/m (5 to 30 dtex) and more preferably in a range 9 x 10⁷ to 28 x 10⁷kg/m (9 to 28 dtex).

The security fibres of the present invention may be configured to produce an effect visible to the naked eye in reflected and/or transmitted visible light, such as by being coloured, metallic, pearlescent, iridescent and the like. The security fibres may be configured to produce an effect invisible to the naked eye in reflected and/or transmitted visible light and visible to the naked eye in reflected and/or transmitted light falling outside of the visible spectrum, such as photochromic, luminescent, fluorescent (i.e. UV absorbing), infrared transmitting and/or the like. The security fibres may be dyed, printed upon and/or coated with suitable chemical compositions to achieve such effects. For example, as in EP-B-2342085, the security fibres may be formed of paper strips comprising printed regions of different colours and unprinted regions. In addition or alternatively, the security fibres may be machine readable, but not readily visible to the naked eye when viewed in reflected light incident on the security fibres and/or transmitted light. For example, the security fibres may be magnetic or electrically conductive fibres which can be detected by electrical or magnetic detection means, such as those as disclosed in WO-A9826379.

In a particularly preferred embodiment the security fibres comprise reclaimed fibres such that the fibrous substrate and security fibres have the same base material (e.g. cotton or cellulose). However, the security fibres differ from the fibrous substrate by virtue of being configured to produce an effect forming an additional security feature that is not formed by the fibrous substrate. The reclaimed fibres may comprise fibres that are rejected from the fibrous stock prior to entry into the vat for forming the fibrous substrate. For example, the reclaimed fibres may be rejected by virtue of falling outside of the range of lengths suitable for the fibrous stock. In particular, the reclaimed fibres may have a greater length than the fibres forming the fibrous stock. The reclaimed fibres may be dyed with a UV absorbing material.

Coloured security fibres may be visible to the naked eye when viewed in reflected light in the visible light spectrum. In this specification the term visible light spectrum refers to electromagnetic waves having a wavelength of between approximately 400nm and approximately 700nm. If the security fibres are, for example, fluorescent, it may only be visible in ultraviolet light (i.e. having a wavelength of between approximately 40nm and approximately 400nm). Furthermore or alternatively, the security fibres may only be visible

-Ί in the infrared spectrum (i.e. having a wavelength of between approximately 700nm and approximately 1000nm).

In addition, or alternatively, the security fibres may be substantially hydrophilic or hydrophobic such that, when exposed to liquid ink (either applied directly to the security fibres or to the fibrous substrate layer adjacent the security fibres) the ink is attracted to, or repelled by, the security fibres. As a result, the security fibres will disrupt the printing where they are exposed on a surface being printed. A hydrophilic or hydrophobic coating may be applied to security fibres by immersion, spraying or other similar processes. For example, the security fibres may include a coating of hydrophobic varnish, such as is disclosed in EP-B-2342085.

The security fibres may comprise a plurality of different types and/or compositions of security fibres such that they produce different effects. One example of a machine readable fibre suitable for the current invention is described in US5903340.

By way of example only, embodiments of a method of manufacture, apparatus and security sheet in accordance with the present invention are now described with reference to, and as shown in, the accompanying drawings, in which:

Figure 1 is a cross-sectional side elevation of a section of a paper-making machine for use in a method of manufacturing according to the present invention;

Figure 2 is a plan view of a security sheet formed by the machine illustrated in Figure 1;

Figure 3 is a plan view of a further embodiment of a security sheet formed by the machine illustrated in Figure 1;

Figure 4 is a perspective view of a roller of the machine of Figure 1 for depositing security fibres in the shape of at least one security element on the security sheet illustrated in Figure 3;

Figure 5 is a cross-sectional side elevation of a further embodiment of a section of a paper-making machine for use in a method of manufacturing according to the present invention;

Figure 6 is a plan view of a further embodiment of a security sheet formed by the machines illustrated in Figure 1 and 5;

Figure 7 is a plan view of a further embodiment of a security sheet formed by the machines illustrated in Figure 1 and 5;

Figure 8 is a perspective view of an embodiment of a nozzle arrangement of the machines of Figure 1 and 5; and

-8Figure 9 is a plan view of a further embodiment of a security sheet formed by the machines illustrated in Figure 1 and 5.

Figure 1 illustrates a section of an apparatus 10, in this case a cylinder mould papermaking machine, suitable for manufacturing a security sheet 40 in accordance with the present invention. The apparatus 10 comprises a first support surface 11, which may comprise a cylinder mould cover 12 of a cylinder mould 13 rotating in a vat 14 of fibrous stock 15. The first support surface 11 is porous and may comprise a wire mesh. As the cylinder mould 13 rotates in a machine direction 45, the liquid within the fibrous stock 15 passes through the first support surface 11. The fibrous stock 15 is deposited on the first support surface 11 and a fibrous substrate layer 16 is thereby formed. The apparatus 10 may comprise a vacuum within the cylinder mould 13 to assist in drawing the liquid through the first support surface 11 and drawing the fibres within the fibrous stock 15 onto the first support surface 11. Once the formed fibrous substrate layer 16 exits an upper surface 17 of the fibrous stock 15 in the vat 14, the vacuum may at least partially dry the fibrous substrate layer 16 by removing liquid from it.

The fibrous stock 15 may be a liquid, a suspension or aqueous and may comprise a plurality of fibres suspended in liquid, preferably water. The wet fibrous substrate layer 16 is “wet” by virtue of containing such a substantial quantity of liquid in addition to the fibres, as described in further detail below. The fibres may comprise a range of fibre types, including synthetic or natural fibres, or a mixture of both. The actual preparation of the fibres is unrestricted by the invention, and will depend upon the effect desired in the fibrous substrate layer 16. As a general consideration, security sheets 40 used for security documents need to be hard wearing, resilient, and self-supporting, and so an appropriate fibre mix is preferably selected. The fibres may comprise cellulose, cotton, polyvinyl alcohol (PVOH) or the like.

As the fibrous substrate layer 16 is formed, it is couched from the first support surface 11 as a continuous wet web, for example by a couch roll 18. The couch roll 18 rotates in contact with the first support surface 11 and is used to transfer the wet fibrous substrate layer 16 from the first support surface 11 to a second support surface 20. The second support surface 20 may comprise a belt, felt and/or formex and also moves in the machine direction 45. In the present disclosure the second support surface 20 may comprise a plurality of discrete belts, felts and/or formexes and is considered to comprise any surface for supporting the fibrous substrate layer 16 downstream of the first support surface 11 and cylinder mould 13. The second support surface 20 may transport the wet

-9fibrous substrate layer 16 from the couch roll 18 and/or cylinder mould 13 to a drying section 21. The second support surface 20 may be supported therebetween by at least one support device 22, which may comprise at least one roller as illustrated. At least one support device 22 may comprise a suction roll 25 containing an internal vacuum source for drawing liquid from the wet fibrous substrate layer 16 as it passes over the suction roll 25.

In the drying section 21, the wet fibrous substrate layer 16 undergoes a drying process to extract liquid from it. Preferably the majority of the liquid in the wet fibrous substrate layer 16 present upon exiting the vat 14 of fibrous stock 15 is extracted in the drying section 21. The drying section 21 may comprise at least one press section 23 for applying pressure at a nip to the wet fibrous substrate layer 16 to remove water therefrom. As illustrated, each press section 23 may comprise at least two adjacent rollers 24 forming a nip through which the second support surface 20 and wet fibrous substrate layer 16 pass and are compressed.

After the drying section 21 any other further processing steps may be performed. For example, a surface sizing agent (e.g. PVOH) coating may be applied to the fibrous substrate layer 16, the fibrous substrate layer 16 may undergo further pressing and drying (e.g. contactless drying) and the dried fibrous substrate layer 16 may be rolled into one or more reels. After the further processing steps the dried fibrous substrate layer 16 is initially cut along cutting lines to form a plurality of interim sheets. Preferably the dried security sheet 40 has a grammage of between approximately 80 and 200 gsm and more preferably of between approximately 100 and 150 gsm. Each interim sheet and/or the dried fibrous substrate layer 16 may be cut into a plurality of security sheets 40, examples of which are shown in Figures 2 and 3. The security sheets 40 may subsequently be incorporated into a security document by further processing. For example, the dried fibrous substrate layer 16 may be cut across its width into three interim sheets, which may each be cut into five bank notes across their widths. The print of the bank notes may be applied to the interim sheets before cutting into the individual banknotes.

In accordance with the present invention a plurality of security fibres 30 are applied to at least one surface of the wet fibrous substrate layer 16, preferably in the form of at least one security element 41. As illustrated in Figures 2 and 3, each resulting security sheet 40 may comprise at least one security element 41, each formed continuously and/or discretely by the security fibres 30. Each at least one security element 41 may comprise any suitable shape and may have an outer perimeter in the shape of a logo, symbol, indicium, image, alphanumeric character and/or any shape conveying information to a

- 10reader. For example, at least one security element 41 may have the shape of the denomination of a banknote formed from the security sheet 40. In preferred embodiments the security fibres 30 are visible when viewed in reflected light incident upon at least one surface of the security sheet 40. The security fibres 30 may be visible to the naked eye in reflected and/or transmitted light, or invisible to the naked eye in reflected and/or transmitted visible light but visible to the naked eye in reflected and/or transmitted light falling outside of the visible spectrum.

The wet fibrous substrate layer 16 may begin to lose water and dry as soon as it exits the fibrous stock 15, whether by evaporation, the vacuum in the cylinder mould 13 or the vacuum in any suction roll 25. However, the security fibres 30 are applied when the fibrous substrate layer 16 is sufficiently wet and workable such that the security fibres 30 are fully integrated within, and embedded between the fibres of, the surface of the fibrous substrate layer 16. In particular, the security fibres 30 may be mixed with the fibres at the surface of the fibrous substrate layer 16. As a result, the security fibres 30 and fibrous substrate layer 16 are securely combined together. If the security fibres 30 are applied to the dry fibrous substrate layer 16 (i.e. downstream of the drying section 21) it will generally be located on its surface rather than embedded in it, therefore resulting in a less resilient connection. Therefore, the security fibres 30 are applied to the fibrous substrate layer 16 after it has formed on the first support surface 11 and preferably once it has exited (i.e. downstream of) the upper surface 17 of the aqueous fibrous stock 15 contained in the vat 14. The security fibres 30 are applied to the fibrous substrate layer 16 before (i.e. upstream of) the drying section 21 and, particularly, before the press section 23 (particularly before its nip). In preferred embodiments the security fibres 30 are applied to the wet fibrous substrate layer 16 when it has a liquid content of at least approximately 60% by volume or at least approximately 80% by volume. The liquid content may be measured according to ISO 287:2009.

The security fibres 30 are applied by at least one application device 31, which is located between the point at which the wet fibrous substrate layer 16 has formed and the drying section 21. Preferred locations of the at least one application device 31 are illustrated in Figure 1. At least one application device 31 may be located on the opposing side of the wet fibrous substrate layer 16 to a vacuum source and the first and/or second support surface 11,20 may be porous to allow material to be drawn through them by the vacuum. For example, at least one application device 31 may be positioned at a first location 32, which is adjacent the first support surface 11 and between the point at which the wet fibrous substrate layer 16 is formed, for example above the upper surface 17, and

- 11 the couch roll 18, particularly the point at which the wet fibrous substrate layer 16 is lifted from the first support surface 11. At least one application device 31 may be positioned at a second location 33, which is adjacent the second support surface 20 and a suction roll 25 forming a support device 22. The vacuum from within the cylinder mould 13 and/or suction roll 25 may draw the security fibres 30 onto the wet fibrous substrate layer 16, thereby assisting in embedding the security fibres 30 in between the fibres of the wet fibrous substrate layer 16.

At least one application device 31 may be positioned at a third location 34, which is adjacent a substantially horizontal portion of the second support surface 20. As illustrated the second support surface 20 may run between two support devices 22 at substantially equal heights to form the horizontal portion. A vacuum device may be located on the opposing side of the horizontal portion of the second support surface 20 to the at least one application device 31 at the third location 34. The vacuum device draws the security fibres 30 onto the wet fibrous substrate layer 16 in a similar manner to the suction roll 25 and/or cylinder mould 13.

Advantageously the at least one application device 31 may be located above the cylinder mould 13 and second support surface 20 at the top of the apparatus 10, such as at the second and/or third location 33, 34. These locations may provide adequate space for the movement and installation of the at least one application device 31. Furthermore, by positioning the at least one application device 31 at the first location 32, the security fibres 30 may be applied to a first surface of the wet fibrous substrate layer 16 and, by positioning the at least one application device 31 at the second and/or third location 33, 34, the security fibres 30 may be applied to an opposing second surface of the wet fibrous substrate layer 16.

The at least one application device 31 may comprise any arrangement suitable for applying the security fibres 30 to a surface of the wet fibrous substrate layer 16 and embedding the security fibres 30 in between the fibres of the wet fibrous substrate layer 16. The at least one application device 31 may comprise a roller 35 in contact with the wet fibrous substrate layer 16, as illustrated at the second and third locations 33, 34 in Figure 1. The roller 35 rotates as the wet fibrous substrate layer 16 is transported through the apparatus 10 on the moving first or second support surface 11,20. As illustrated in further detail in Figure 4, the roller 35 comprises a cylinder 36 and a plurality of formation elements 37. Each formation element 37 is configured for receiving security fibres 30 and delivering security fibres 30 to the wet fibrous substrate layer 16. The at least one formation element

- 12 37 may have the same shape as the at least one security element 41 such that the security fibres 30 are applied in the shape of the at least one security element 41.

At least one formation element 37 may comprise a recess in the surface of the roller 35 for receiving a volume or dose of security fibres 30. The recess may be filled with security fibres 30 and upon contact with the wet fibrous substrate layer 16 the security fibres 30 may be transferred from the recess onto the surface of the wet fibrous substrate layer 16. Alternatively, at least one formation element 37 may comprise an aperture through the outer surface of the roller 35. The security fibres 30 may be directed from within the roller 35 onto the wet fibrous substrate layer 16 through the aperture. For example, security fibres 30 may be directed from a reservoir through the aperture or into the recess by one or more nozzles, spraying devices, tubes, brushes, further rollers or the like.

The at least one application device 31 may comprise a nozzle arrangement 38 for ejecting at least one dose of security fibres 30 onto the surface of the wet fibrous substrate layer 16, as illustrated at the first location 32 in Figure 1. An exemplary nozzle arrangement 38 is illustrated in Figure 7 and is discussed in further detail below. The nozzle arrangement 38 may comprise at least one nozzle 60 having at least one nozzle opening 61 located adjacent to the wet fibrous substrate layer 16. Preferable the at least one nozzle opening 61 and/or nozzle 60 is located no more than approximately 10mm from the surface of the wet fibrous substrate layer 16. The at least one nozzle opening 61 may have the same shape as the at least one security element 41 such that the security fibres 30 are applied in the shape of the at least one security element 41. The nozzle arrangement 38 may comprise a pump and at least one conduit for pumping the security fibres 30 from a reservoir and through the at least one nozzle opening 61. A controller may be configured to control the dosing of security fibres 30 through the nozzle arrangement 38.

The nozzle arrangement 38 may comprise positioning means configured to change the position and/or orientation of the at least one nozzle opening 61 relative to the first and/or second support surface 11,20 as they move in the machine direction 45. As a result, the nozzle arrangement 38 may be configured to apply a plurality of security elements 41 to each security sheet 40 and/or to apply at least one security element 41 requiring a plurality of doses of security fibres 30. In particular, the nozzle arrangement 38 may be configured to move the at least one nozzle opening 61 parallel or perpendicular to the machine direction 45. For example, the nozzle arrangement 38 may comprise at least one robotic arm controlled by at least one actuator and the at least one nozzle 60 may be

- 13located at an end of the at least one robotic arm. The at least one robotic arm may be a multi-axis articulating robotic arm. The nozzle arrangement 38 may comprise a dolly supporting the at least one nozzle 60, such as in the form of fixed tubes or at least one robotic arm. The dolly may be configured to move parallel or perpendicular to the machine direction 45.

The at least one application device 31 may apply the security fibres 30 continuously such that, as illustrated in Figure 2, each security sheet 40 comprises at least one security element 41 extending continuously across the wet fibrous substrate layer 16 between edges of areas thereof that will form a plurality of security sheets 40. For example, the at least one security element 41 may comprise a stripe, which may be a rhombus as illustrated or in any other suitable shape. To form at least one continuous security element 41 the at least one application device 31 may comprise a nozzle arrangement 38 configured to eject a continuous dose of security fibres 30 onto the wet fibrous substrate layer 16. Alternatively, the at least one application device 31 may comprise at least one formation element 37 extending entirely around the circumference of the roller 35. If the nozzles 60 of the nozzle arrangement 38 move perpendicular or parallel to the machine direction 45, or the at least one formation element 37 is suitably shaped, the at least one continuous security element 41 may comprise a complex shape. For example the at least one security element 41 may have a sinusoidal, square or any other periodic waveform and the amplitude and/or frequency of the waveform may form a code.

The at least one application device 31 may apply the security fibres 30 discretely such that, as illustrated in Figure 3, each security sheet 40 comprises at least one security element 41 formed from the security fibres 30 and having a discrete shape. The discrete shape may be located at one or more edges, but each security element 41 may be separated from at least one other security element 41 on the wet fibrous substrate layer 16 and/or the security sheet 40. To form at least one discrete security element 41 the at least one application device 31 may comprise a nozzle arrangement 38 configured to eject discrete doses having a predetermined volume of security fibres 30 onto the wet fibrous substrate layer 16. Alternatively, the at least one application device 31 may comprise at least one formation element 37 separated from another at least one formation element 37 around the circumference of the roller 35, as illustrated in Figure 4.

The security fibres 30 may be applied to the wet fibrous substrate layer 16 as a suspension in liquid and the liquid may be driven from the fibrous substrate layer 16 in the drying section 21. For example, the security fibres 30 may be suspended in water or the

- 14like. If the security fibres 30 comprise natural fibres, the liquid may comprise in addition to water additional components such as carboxymethylcellulose (CMC) and/or a water soluble resin for example polyamine polyamide epichlorohydrin (PAAE). If the security fibres comprise synthetic fibres, the liquid may comprise CMC or a flocculating agent such as Teepol PB, supplied by Teepol (RTM). As a result, when the suspension is applied via the at least one formation element 37 (whether a recess or an aperture) and/or the nozzle arrangement 38 the security fibres 30 can be easily controlled due to its higher mass. In particular, the security fibres 30 will not be dispersed by any air flow, thereby creating at least one security element 41 with clearly defined edges. Furthermore, the mass of the liquid assists in driving the security fibres 30 in between the fibres of the wet fibrous substrate layer 16. In a particular example, the concentration of the fibres in the suspension is approximately 0.1%, approximately 0.05% or approximately 0.01%. The concentration is calculated using the dry weight of the fibres in grammes as a percentage of the liquid volume in cm³. For example, to achieve 0.05% concentration, 500g of security fibres 30 may be added to 10000cm³ of liquid. The 10000cm³ of liquid may contain 5ml CMC.

The pressure, volume and velocity of application of at least one dose of the security fibres 30 may be controlled and selected to ensure that the wet fibrous substrate 16 is not damaged during the application and ensure that the security fibres 30 are firmly embedded in the wet fibrous substrate 16. Furthermore, they may be controlled to ensure that the application is sufficiently quick to ensure that the at least one security element 41 is formed with clearly defined edges even though the wet fibrous substrate 16 is moving in the machine direction 45. Typically the first and second support surfaces 11,20 travel in the machine direction 45 at a relatively slow velocity compared to other manufacturing processes, such as less than 2 metres per second, and therefore clearly defined edges may be obtained at relatively low velocities. However, if the at least one application device 31 comprises a nozzle arrangement 38 configured to move at least one nozzle 60 relative to the machine direction 45, the edges may be sharper if the nozzles 60 are operated to travel at the same velocity as the first and/or second support surfaces 11,20 in the machine direction 45 during the dosing.

When the apparatus 10 is operated according to the methods described above, the resulting security sheet 40 comprises at least one security element 41 of security fibres 30 with clearly defined edges because the security fibres 30 are applied in a controlled manner, rather than in an uncontrolled dispersion in the vat 14 of fibrous stock 15 as in the prior art methods. In the present disclosure a “clearly defined” edge refers to a security element 41 having a discrete end, or highly distinct decrease to substantially zero

- 15concentration, of security fibres 30. This is contrary to indistinct or blurry edges in which the decrease in concentration is continuous and unclear. Furthermore, the at least one security element 41 may comprise a complex shape because it has clearly defined edges and because the security fibres 30 can be applied as a shaped security element 41 via the at least one application device 31. The security sheet 40 may therefore be more difficult to counterfeit, since the formation of complex shapes and clearly defined edges requires increased counterfeiting skill and any undefined edges would easily identify a counterfeit. Furthermore, the at least one security element 41 may be relatively resilient due to the embedding of the security fibres 30 in the fibrous substrate layer 16, which is a result of the security fibres 30 being applied to the fibrous substrate layer 16 whilst it is still wet.

Various alternatives to those described above also fall within the scope of the present invention and may provide yet further benefits. In particular, as illustrated in Figure 5, an apparatus 50 may be configured to manufacture a security sheet 40 comprising a plurality of layers of fibrous substrate. The apparatus 50 of Figure 5 may be similar to the apparatus 10 of Figure 1, with the addition of a further layer forming arrangement 51. The same reference numerals are shown in Figure 5 to indicate the same features from Figures 1 to 4. In particular, the fibrous substrate layer 16 is formed as described above, a further fibrous substrate layer 52 is formed by the further layer forming arrangement 51 and the two layers are combined prior to the drying section 21. The further fibrous substrate layer 52 may have a lower grammage than the fibrous substrate layer 16 and preferably has a grammage of between approximately 18 and 24 gsm. The fibrous substrate layer 16 preferably has a grammage of between approximately 55 and 180 gsm, and more preferably between approximately 75 and 130 gsm.

The further layer forming arrangement 51 may be a short former as illustrated and may comprise a further cylinder 53 rotating in the machine direction 45 in a further vat 54. The further cylinder 53 may comprise a porous outer surface, such as a wire mesh, and forms a third support surface 55. In a similar manner to the cylinder mould 13 described above, the further fibrous substrate layer 52 may be formed by the deposition of fibres from a reservoir of fibrous stock in the further vat 54 on the further cylinder 53. However, as illustrated, fibrous stock 57 (having a similar composition to the fibrous stock 15 in the vat 14) may be applied to the further cylinder 53 by spraying from at least one spraying device 49. A vacuum may be generated within the further cylinder 53 to draw the spray of fibrous stock 57 onto it. Therefore, as the further cylinder 53 rotates the further fibrous substrate layer 52 is formed thereon.

- 16The further fibrous substrate layer 52 is subsequently transferred onto a moving belt 56, which may also be a felt and/or formex, extending from the further cylinder 53 to the cylinder mould 13 and couch roll 18. The fibrous substrate layer 52 is transferred on the underside of the belt 56 towards the cylinder mould 13. One or more vacuum boxes (not shown) may be located above the belt 56 to draw the further fibrous substrate layer 52 onto the belt 56 from the further cylinder 53 and keep the further fibrous substrate layer 52 on the underside of the belt 56 until it reaches the couch roll 18. The third support surface 55 may also comprise the belt 56 and in the present disclosure generally refers to the one or more surfaces upon which the further fibrous substrate layer 52 is formed and transferred to the first and/or second support surface 11,20 for combination with the fibrous substrate layer 16. The third support surface 55 may therefore comprise a plurality of belts, felts, formexes and cylinders. The belt 56 feeds the further fibrous substrate layer 52 into the fibrous substrate layer 16 at the point where the fibrous substrate layer 16 is couched from the cylinder mould 13 onto the couch roll 18. The fibrous substrate layers 16, 52 are thereby combined prior to drying.

Security fibres 30 may be applied to the further fibrous substrate layer 52 between its formation in the further layer forming arrangement 51 and its combination with the fibrous substrate layer 16. In particular, at least one application device 31 may be located adjacent to the third support surface 55 and further fibrous substrate layer 52 downstream of the spraying or at least one spraying device 49 in the machine direction 45. A suitable fourth location 58 for at least one application device 31 is adjacent the further cylinder 53 before the further fibrous substrate layer 52 is transferred to the belt 56. The vacuum from within the further cylinder 53 may draw the security fibres 30 onto the wet further fibrous substrate layer 52, thereby assisting in embedding the security fibres 30 in between the fibres of the wet further fibrous substrate layer 52. A suitable fifth location 59 is adjacent the belt 56 between where the further fibrous substrate layer 52 has been transferred onto it and the cylinder mould 13.

The fibrous substrate layers 16, 52 are combined, any further security fibres 30 are applied and the fibrous substrate layers 16, 52 are passed through the drying section 21, passed through further processing sections and cut as described above. The resulting security sheet 40 may not comprise substantially distinguishable layers due to the combination of the fibrous substrate layers 16, 52 whilst they are still wet. Security fibres 30 applied at the fourth location 58 is located at a first surface of the security sheet 40 and security fibres 30 applied at the second or third location 33, 34 is located at an opposing second surface of the security sheet 40. Security fibres 30 applied at the first or fifth

- 17location 32, 59 is located within the thickness of the security sheet 40 and separated from the first and second surfaces. Therefore, an advantage of using multiple layers to form the security sheet 40 is that the security fibres 30 can be hidden from the outer surfaces of the security sheet 40. It may therefore only be visible in transmitted light or upon splitting the security sheet 40 through the plane of the paper. Furthermore, the security sheet 40 formed from multiple layers may be relatively more resilient and hard wearing.

The security sheet 40 may further comprise a coating applied to over at least part of at least one of its surfaces and over at least part of the security fibres 30. Preferably the coating is applied before the drying section 21 such that the security fibres 30 are held on the surface of the fibrous substrate layer(s) 16, 52 during the drying step. The coating may be a polymer coating. The coating may provide additional support to keep the security fibres 30 in place, particularly upon contact with the rollers 24 of the press section 23, and also increase the resilience of the area of the security sheet 40 comprising the security fibres 30.

Each at least one security element 41 may comprise a plurality of regions of different concentrations, sizes and/or types of security fibres 30. In particular, as illustrated in Figure 6, at least one first region 80 may comprise security fibres 30 of substantially the same concentration, size and/or type that is/are different to that of the security fibres 30 of at least one second region 81 adjacent to the at least one first region 80. The security element 41 may comprise further regions 82 of yet further different concentrations, sizes and/or types of security fibres 30. The at least one first, second and further regions 80, 81, 82 may be directly adjacent to one another such that they are not spaced apart and may be arranged to form together a complete security element 41 (i.e. a complete logo, symbol, indicium, image, alphanumeric character and/or any shape conveying information to a reader).

As illustrated in Figure 6, the at least one first region 80 may comprise a high concentration of security fibres 30 and the adjacent at least one second region 81 may comprise a substantially lower concentration of security fibres 30. In particular, the difference in the concentration may be substantially the same across a plurality of security sheets 40 rather than simply being a result of random variations in concentration of the security fibres 30 in a single security sheet 40. As a result, the first and second regions 80, 81 are clearly distinguishable from one another. The “concentration” of security fibres 30 may refer to: the volume of space of the fibrous substrate layers 16, 52 occupied by security fibres 30 within the boundaries of the shape of the security element 41; and/or the

- 18number of security fibres 30 therein. The number or volume of security fibres 30 in the at least one first region 80 may be at least approximately 110%, at least approximately 120%, at least approximately 150%, at least approximately 200% and/or at least approximately 400% of the number or volume of security fibres 30 in the adjacent at least one second region 81. Each region 80, 81,82 may form at least 10%, at least 25% and/or at least 50% of: the surface area of each security element 41 (i.e. the area occupied by the perimeter of the security element 41 visible or located at the surface of the fibrous substrate layer 16, 52); the volume of fibrous substrate and security fibres 30 falling within the boundaries of the shape of the security element 41; and/or of the total number of security fibres 30 in the security element 41.

At least one region 80, 81,83 may be of a type that is only visible in light falling outside of the visible spectrum (e.g. by being UV responsive) such that the complete security element 41 can only be distinguished when viewed in light falling outside of the visible spectrum. Adjacent regions 80, 81,82 may each have security fibres 30 of different colours in reflected visible light and/or of different sizes.

The apparatus 10, 50 may comprise a plurality of different application devices 31, which may each apply different compositions of security fibres 30 to at least one of the fibrous substrate layers 16, 52. Therefore, the security sheet 40 may comprise a plurality of security elements 41 of differing compositions and/or shapes, each having differing concentrations, sizes and/or types of security fibres 30.

During the application of the security fibres 30 the at least one application device 31 may vary the concentration of the security fibres 30 applied as the at least one security element 41, either by varying the rate of application of security fibres 30 or by varying the concentration of the suspension of security fibres 30 during application. In particular, the at least one application device 31 may comprise a reservoir of security fibres 30, or a highly concentrated liquid suspension of security fibres 30, and a reservoir of liquid. During the application of a dose the liquid and security fibres 30 are combined continuously in controlled quantities and the ratio of liquid to security fibres 30 may be thereby be varied during a single dose. As a result, the concentration of security fibres 30 across at least one security element 41 can be controllably varied.

Alternatively, for example, a dose of varying (e.g. continuously increasing or decreasing) concentration may be sprayed through the nozzle arrangement 38 as the nozzles 60 move relative to the fibrous substrate layers 16, 52, such as by the nozzle

- 19arrangement 38 remaining stationary whilst the first, second or third support surface 11,20, 55 move or by the nozzle arrangement 38 moving in a direction and/or velocity different to the first, second or third support surface 11,20, 55. As a result, as illustrated in Figure 7, the at least one security element 41 visibly comprises a substantially continuous gradation in the concentration of the security fibres 30 rather than discrete regions 80, 81,82 of different concentrations. The higher concentration may be visible as darker areas and the lower concentration may be visible as relatively lighter areas.

In an embodiment of the at least one application device 31, as illustrated in Figure 7, the nozzle arrangement 38 may comprise a plurality of nozzles 60 and nozzle openings 61 configured to form a single security element 41 (i.e. a continuous body of security fibres 30). Each nozzle 60 and nozzle opening 61 may be located adjacent to at least one other nozzle 60 and nozzle opening 61. In the illustrated embodiment each nozzle 60 comprises a tube 62 extending from a mount 63, although the nozzle arrangement 38 may comprise any other suitable arrangement in which a plurality of nozzle openings 61 are adjacent one another. The nozzles 60 are arranged to form the shape of a security element 41 and the illustrated arrangement is for forming a pound sign on a security sheet 40 as shown in Figure 3. Such a nozzle arrangement 38 may result in sharper edges of the security element 41 compared to those formed by a nozzle arrangement 38 with a single nozzle opening 61 forming an entire security element 41. This is because the volume of security fibres 30 applied can be more accurately controlled through a plurality of smaller nozzle openings 61, rather than ensuring an equal application of security fibres 30 across the entire area of a larger nozzle opening 61. Furthermore, different concentrations of suspension, sizes and/or types of security fibres 30 can be applied through each nozzle 60 such that the security element 41 comprises variations of the concentration, sizes and/or types of security fibres 30 across it.

Alternatively, the at least one first region 80 may be formed by applying security fibres 30 upstream in the manufacturing process (e.g. at the first, fourth or fifth locations 32, 58, 59) and the at least one further region 81,82 may be formed by applying security fibres 30 to partially overlap or lie adjacent to the at least one first region 80 downstream in the manufacturing process (e.g. at the second or third locations 33, 34).

Figure 8 illustrates a further embodiment of the security sheet 40 wherein at least one second region 81 comprises at least one shadow element 65 of security fibres 30 located adjacent or overlapping with at least one first region 80 and forming a “shadow effect” of the at least one security element 41. When viewed in transmitted or reflected light coincident upon the surface of the security sheet 40, each shadow element 65 appears as a shadow of the first region 80. In particular, each shadow element 65 replicates at least part of the shape of each security element 41. The security fibres 30 of the at least one shadow element 65 are of a different composition to that of the at least one security element 41, such as by being lighter or darker in colour, having different sized security fibres 30 and/or by being different types of security fibres 30. In a particularly preferred embodiment the at least one first region 80 comprises security fibres 30 visible in reflected visible light and the at least one shadow element 65 comprises security fibres 30 that are not visible in reflected visible light, but are UV or infrared absorbing. Therefore, when the security sheet 40 is viewed under UV or infrared light the at least one shadow element 65 is visible to an inspector and the authenticity of the security sheet 40 may be verified. The shadow element 65 may be applied adjacent or underneath the first region 80 in any manner described above.

In yet a further embodiment the at least one application device 31 may comprise a mixing chamber from which at least one dose of security fibres 30 may be applied to the fibrous substrate layer 16, 52 (e.g. by virtue of being located upstream of the nozzle opening 61 of the nozzle arrangement 38). A plurality of different concentrations, sizes and/or types of security fibres 30 may be supplied to the mixing chamber in a controlled manner. As a result, the at least one application device 31 may be operable to apply at least two security elements 41 of having security fibres 30 of different compositions by controlling the supply of the security fibres 30 to the mixing chamber in between doses.

The security sheet 40 formed according to the present invention further improves the machine readability of the security fibres 30 and at least one security element 41. In prior art methods security fibres 30 are randomly distributed throughout the paper in unrestricted areas. Their distribution can be measured under laboratory conditions by sampling the number of security fibres 30 in different areas. However, this is a time consuming process and is generally used for quality control purposes to ensure a random distribution rather than verifying the authenticity of a document. In accordance with the present invention the at least one security element 41 may comprise machine readable information. In particular, the physical properties of the security fibres 30, such as a UV, infrared, magnetic or electric response, of the at least one security element 41 and/or security sheet 40 may be measured by a machine and compared to known properties. Any deviation from the known properties may indicate a counterfeit. For example, the physical properties may be due to the shape of the at least one security element 41. Alternatively, the known properties may be variations formed by the at least one security element 41

- 21 comprising a differing concentration of security fibres 30 as discussed above. Alternatively, the security sheet 40 may comprise a plurality of separated security elements 41 and known variations may be formed by differing spacing, compositions, shapes, sizes and the like of the plurality of security elements 41. In a particular embodiment the plurality of security elements 41 form a code by virtue of the spacing and/or size of each security element 41. In the present disclosure a “code” may be a covert pattern or the like conveying information that is not immediately distinguishable by the human eye, for example by requiring decoding before it can be understood.

The security sheet 40 can additionally comprise various other security features. One such security feature is a cylinder mould watermark, in which some regions of the watermark are more dense, or thicker, than the rest of the security sheet 40 and/or some regions of the watermarks are less dense, or thinner, than the rest of the security sheet 40. Another security feature is an electrotype watermark, in which the some regions of the electrotype watermark are less dense than the rest of the security sheet 40. Such an electrotyping process is well known in papermaking and has been described in US-B1901049 and US-B-2009185. The watermarks may be applied via embossings or impermeable electrotype elements (e.g. thin metal or resin elements) applied to the cylinder mould cover 12. Printing may also be applied to the security sheet 40 using any known printing techniques, such as dye-sublimation, screen, flexography, lithography, intaglio, gravure, dye diffusion, laser, inkjet toner, letterpress and toner transfer. Security threads and patches are another suitable security feature which may be applied to a surface of the fibrous substrate layers 16, 52 or embedded therein in any known manner, such as by being partially embedded therein, being fully embedded therein and/or being exposed at windows in the surface of the fibrous substrate layers 16, 52.

The security sheet 40 may form a security document of any suitable type, such as an identity document or document of value. Examples include cards, identity cards, banknotes, driving licences, cheques, booklets, passports, passbooks, identification documents, certificates, licences and cheque books. Personalised information, relating to the owner of the security document, may be printed or otherwise applied thereon.

Claims

CLAIMS:

1. A method of manufacturing a security sheet comprising:

depositing a fibrous stock on a support surface to form a wet fibrous substrate layer; applying security fibres to at least one surface of the wet fibrous substrate layer;

and drying the wet fibrous substrate layer;

wherein the security fibres are applied to the wet fibrous substrate layer after the wet fibrous substrate layer has formed on the support surface and before the wet fibrous substrate layer is dried.

2. A method as claimed in claim 1 wherein the wet fibrous substrate layer is dried in a drying section and the security fibres are applied to the wet fibrous substrate layer before being dried in the drying section.

3. A method as claimed in claim 2 wherein the drying section comprises a press section forming a nip at which pressure is applied to dry the wet fibrous substrate layer and the security fibres are applied to the wet fibrous substrate layer before entering the nip.

4. A method as claimed in any one of the preceding claims wherein the security fibres are applied when the fibrous substrate layer comprises at least 60% water by volume or at least 80% water by volume.

5. A method as claimed in any one of the preceding claims wherein the support surface comprises a cylinder mould cover of a cylinder mould rotating in a vat of fibrous stock, the fibrous substrate stock is deposited on the cylinder mould cover to form the wet fibrous substrate layer and the security fibres are applied to the wet fibrous substrate layer after the wet fibrous substrate layer has exited the fibrous stock in the vat.

6. A method as claimed in any one of the preceding claims wherein the support surface comprises a cylinder rotating in a machine direction, the fibrous stock is deposited onto the cylinder by spraying to form the wet fibrous substrate layer and the security fibres are applied to the wet fibrous substrate layer downstream of the spraying in the machine direction.

7. A method as claimed in any one of the preceding claims wherein the security fibres are applied to the wet fibrous substrate layer by at least one application device, the at least one application device comprising:

-23a roller in contact with the wet fibrous substrate layer and comprising at least one formation element for depositing at least one dose of security fibres onto the wet fibrous substrate layer; and/or a nozzle arrangement for ejecting at least one dose of security fibres onto the wet fibrous substrate layer.

8. A method as claimed in any one of the preceding claims wherein the security fibres are applied as at least one security element.

9. A method as claims in claim 7 and claim 8 wherein the nozzle arrangement comprises a plurality of nozzle openings configured for applying security fibres as a single security element.

10. A method as claimed in claim 8 or claim 9 wherein the security fibres are applied such that the concentration, size and/or type of the security fibres varies across the at least one security element.

11. A method as claimed in claim 10 wherein the security fibres are applied such that the at least one security element comprises a substantially continuous gradation in the concentration of the security fibres.

12. A method as claimed in claim 10 wherein the security fibres are applied such that the at least one security element comprises at least two adjacent regions of security fibres of different concentrations, sizes and/or types, the concentration, size and/or type of security fibres in each region being substantially the same.

13. A method as claimed in any one of claims 8 to 12 wherein the outer perimeter of the at least one security element comprises at least one of a logo, symbol, indicium, image, alphanumeric character and/or any shape conveying information to a reader.

14. A method as claimed in any one of claims 8 to 13 wherein the security fibres are applied as a plurality of security elements having differing compositions and/or shapes.

15. A method as claimed in any one of claims 8 to 14 wherein the at least one security element forms machine readable information.

-2416. A method as claimed in any one of claims 8 to 15 wherein the security fibres are applied continuously such that at least one security element extends between edges of the security sheet and/or the security fibres are applied discretely such that at least one security element is separated from another security element formed on the wet fibrous substrate layer.

17. A method as claimed in any one of the preceding claims further comprising applying a vacuum to a surface of the wet fibrous substrate layer opposing the surface of the wet fibrous substrate layer to which the security fibres are applied.

18. A method as claimed in any one of the preceding claims wherein the security fibres are applied as a suspension of security fibres in a liquid.

19. A method as claimed in any one of the preceding claims wherein a coating is applied over the security fibres at the surface of the wet or dried fibrous substrate layer.

20. A method as claimed in any one of the preceding claims wherein the security fibres are visible in reflected light incident on the surface of the security sheet in visible light or light falling outside of the visible spectrum.

21. A method as claimed in any of the preceding claims wherein the method comprises cutting the dried fibrous substrate layer into a plurality of security sheets.

22. An apparatus for manufacturing a security sheet comprising:

at least one support surface configured to receive a deposition of a fibrous stock thereon, form a wet fibrous substrate layer from the deposited fibrous stock thereon and transfer the formed wet fibrous substrate layer to a drying section for drying; and at least one application device configured to apply security fibres to at least one surface of the wet fibrous substrate layer and located adjacent the at least one support surface between where the wet fibrous substrate layer is formed and the drying section.

23. An apparatus as claimed in claim 22 wherein a first support surface comprises a cylinder mould cover of a cylinder mould rotating in a vat of fibrous stock.

24. An apparatus as claimed in claim 23 wherein a second support surface extends from the first support surface to at least the drying section.

-2525. An apparatus as claimed in any one of claims 22 to 24 wherein a third support surface comprises a cylinder and/or a belt configured to receive fibrous substrate sprayed thereon by at least one spraying device.

26. An apparatus as claimed in any one of claims 22 to 25 configured to perform the method of any one of claims 1 to 21.

27. A security sheet formed according to the method of any one of claim 1 to 21 comprising at least one fibrous substrate layer and at least one security element formed by security fibres at least partially embedded in the fibrous substrate layer.

28. A security sheet as claimed in claim 27 wherein the security fibres are located at at least one surface of the fibrous substrate layer.

29. A security sheet as claimed in claim 27 or claim 28 wherein the security fibres are located within the thickness of the fibrous substrate layer.

30. A security sheet comprising at least one fibrous substrate layer and at least one security element formed by security fibres at least partially embedded in the fibrous substrate layer, wherein the concentration, size and/or type of the security fibres varies across the at least one security element.

31. A security sheet as claimed in claim 30 wherein the at least one security element comprises a substantially continuous gradation in the concentration of the security fibres.

32. A security sheet as claimed in claim 30 wherein the at least one security element comprises at least two adjacent regions of security fibres of different concentrations, sizes and/or types, further wherein the concentration, size and/or type of security fibres in each region is substantially the same.

33. A security sheet as claimed in claim 32 wherein a first region comprises security fibres that are visible to the human eye when viewed in reflected visible light and an adjacent second region comprises security fibres that are not visible to the human eye when viewed in reflected visible light, the security fibres of the second region being visible when viewed in reflected light outside of the visible spectrum.

-2634. A security sheet as claimed in claim 32 wherein the number or volume of security fibres in at least one first region is at least approximately 110%, at least approximately 120%, at least approximately 150%, at least approximately 200% and/or at least approximately 400% of the number or volume of security fibres in an adjacent at least one second region.

35. A security sheet as claimed in any one of claims 32 to 34 wherein each region forms at least 10%, at least 25% and/or at least 50% of:

the surface area of the security element;

the volume of fibrous substrate and security fibres falling within the boundaries of 10 the shape of the security element; and/or the total number of security fibres in the security element.

36. A security sheet as claimed in any one of claims 30 to 35 comprising a plurality of security elements, wherein the composition of security fibres and/or shape of at least one

15 security element is different to that of at least one other security element.

Intellectual

Property

Office

-27Application No: GB1701729.4 Examiner: Mr Robert Black