WO2007071937A2

WO2007071937A2 - Method of manufacturing security substrates

Info

Publication number: WO2007071937A2
Application number: PCT/GB2006/004697
Authority: WO
Inventors: Simon Marchant; David Bray; Paul Howland
Original assignee: De La Rue International Limited
Priority date: 2005-12-20
Filing date: 2006-12-15
Publication date: 2007-06-28
Also published as: GB2433470B; GB2433470A; RU2386541C2; WO2007071937A3; RU2008129760A; DE112006003410T5; GB0625090D0; CA2629286A1; GB0525888D0

Abstract

The present invention relates to improvements in methods of manufacturing security substrates having security features. The method comprises the steps of manufacturing an elongate fibrous tape and fabricating at least one security feature in or on the tape. A base substrate is formed by depositing fibres onto a support surface and the tape is incorporated within the base substrate to form the security substrate during the formation of the base substrate.

Description

iMPROVEMENTS IN METHODS OF MMIUPACTURING SECURITY SUBSTRATES

The present invention relates to improvements in methods of manufacturing security substrates having security features. More specifically the present invention relates to a method of incorporating a security feature into a fibrous substrate, such as paper, by manufacturing a paper tape provided with a security feature and incorporating the paper tape during the forming process of the base substrate.

It is generally known to include elongate elements in paper or other substrates, usually as a security feature. Such elements can be threads, strips or ribbons of, for example, plastics film, metal foil, metallised plastic, metal wire. These elongate elements are included in the thickness of the substrate to render imitation of documents produced therefrom more difficult. These elements help in the verification of the documents as they render the view of the documents in reflected light different from that in transmitted light. To increase the security provided by the inclusion of such an elongate element, it is also known to endow the element itself with one or more verifiable properties over and above its presence or absence. Such additional properties include magnetic properties, electrical conductivities, the ability to absorb x-rays, fluorescence, optically variable effects and thermochromic behaviour.

As a further security feature, it has been found to be particularly advantageous to provide windows in one side of the surface of the substrate, which expose such elongate elements at spaced locations. Examples of methods of manufacturing paper incorporating security elements with or without windows are described below. It should be noted that references to "windowed thread paper" include windowed paper incorporating any elongate security element.

EP-A-0059056 describes a method of manufacture of windowed thread paper on a cylinder mould paper-making machine. The technique involves embossing the cylinder mould cover to form raised regions and bringing an impermeable elongate security element into contact with the raised regions of the mould cover, prior to the contact entry point into a vat of aqueous paper stock. Where the impermeable security element makes intimate contact with the raised regions of the embossing, no fibre deposition can occur and windows are formed in the surface of the paper. After the paper is fully formed and couched from the cylinder mould cover, water is extracted from the wet fibre mat and the paper is passed through a drying process. In the finished paper the regions of the security element which are exposed in the windows are visible in reflected light on one side of the paper, which is commonly used for mainly banknotes .

EP-A-0229645 describes a method using two cylinder moulds to produce two separate plys of paper, with a security thread introduced in between the two layers . The option of incorporating holes in both layers by, for example, incorporating drainage restriction devices on the mould covers is disclosed in the specification. The resulting holes can be registered to produce windows on each side of the thread. This method has a major drawback in that the two cylinder moulds need to be exactly the same diameter and linked by a registration system which renders production of the paper extremely expensive. This document also fails to teach how to actually achieve registration.

Based on the desire to be able to display as much information or indicia as possible in the exposed regions, it has also been recognised that it would be highly advantageous to be able to expose the elongate element on both sides of the paper, or other substrate, in which it is embedded. EP-A-0059056 suggests that this could be achieved by using sufficiently large impervious projections on the cylinder mould. The disadvantage with the method described in this specification is that the holes produced by the drainage limiting devices need to be covered up and this means that rather wide threads have to be used, which increases the cost of the paper. Another disadvantage of this method is that the windows on each side necessarily coincide.

EP-A-1630285 describes an alternative method for manufacturing a paper substrate incorporating an elongate impermeable element which is exposed in windows in both surfaces of the substrate. This method involves a modification to the cylinder mould papermachine with the requirement of an additional moving belt under the conventional cylinder mould. Such a modification is non- ideal and increases the cost and complexity of the process.

GB-A-2397582 describes a further alternative method for manufacturing a paper substrate incorporating an elongate impermeable element which is exposed in windows on both surfaces of the substrate. In this method the security element comprises a plurality of wide regions separated by narrow regions, the wide regions being of a width which obstruct the deposition of fibres. The elongate element is brought into contact with a cylinder mould cover having window forming means such that the narrow regions form windows in the conventional manner as in EP-A-0059056 and the wide regions, by virtue of obstructing deposition, form windows in the opposing surface. The main limitation with this method is that the profile of the elongate element has to be tessellated. This tessellated profile increases the expense for producing the elongate element as single elements have to be produced using die-stamping or laser cutting rather than simply slitting from a wide web.

The use of watermarks is also common in many security documents. A multi-tonal watermark is typically created using a cylinder mould process and is formed by varying the density of paper fibres so that in some areas the fibres are denser and in others less dense than that of the base paper layer which separates the denser and less dense areas. When viewed in transmitted light the less dense areas are lighter and the denser areas darker than the base paper, and the contrasts can be seen very clearly.

A multi-tonal watermark is often a pictorial image such as a portrait and can be very detailed and complex which significantly reduces the risk of counterfeiting.

Cylinder-mould paper machines have been used for many years to manufacture security substrates comprising not only the aforementioned security elements and watermarks, but also a range of other security features. Whilst the use of the cylinder-mould paper machine has been successful in manufacturing security substrates of a sufficient high quality, the manufacturing process has to be tightly controlled and the paper machine run at slower speeds than would be typical for a plain substrate containing no security features. For example, in the production of cylinder-mould made watermarks, a relatively slow machine speed is essential to ensure that the watermark exhibits a full range of tones with a very high degree of clarity.

It has also been found that the production of paper with wide elongate security elements, up to 6mm wide but more commonly between 1 and 4mm wide, can limit the paper machine speed. This is to allow adequate dewatering around the security element, which prevents the security elements delaminating from the paper along the edge of any windows in the surface of the paper in which the thread is exposed, and to ensure adequate coverage of fibre on the back of the security element.

It is therefore one object of the present invention to provide an improved method of manufacturing fibrous security substrates comprising security features which are fabricated during the manufacturing process, such as watermarks and windowed security elements, which overcome the aforementioned disadvantages.

It is a second object of the present invention to provide an improved method of manufacturing fibrous security substrates which enable the generation of new security devices not achievable with known paper making processes. It is a third object of the present invention to provide an improved method of manufacturing fibrous security substrates which enable the incorporation of an elongate impermeable element which is exposed at windows in both surfaces of the fibrous security substrate.

The invention therefore comprises a method of manufacturing fibrous security substrates comprising the steps of manufacturing an elongate fibrous tape and fabricating at least one security feature in or on the tape, forming a base substrate by depositing fibres onto a support surface, wherein the tape is incorporated within the base substrate to form the security substrate during the formation of the base substrate.

The fabrication of the security feature occurs during the manufacture of the tape, preferably as an integral part of the tape manufacturing process.

The at least one security feature comprises a watermark, an elongate security element at least partly embedded with in the fibrous tape and/or perforations produced in the tape during the forming process providing a pattern, identifying indicia or the like.

The invention further comprises a security substrate formed by the aforesaid method and security documents formed from the said security substrate.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a flow chart illustrating the steps of the method of the present invention;

Figure 2 is a plan view of a first fibrous web for use in the method of the present invention;

Figures 3a and 3b are schematics of sections of cylinder mould paper making machines used in the method of the present invention;

Figure 4 is a plan view of one side of a security substrate made by the method of the present invention;

Figure 5 is a cross-sectional side elevation of the security substrate of Figure 4 on the line IV-IV of Figure 4;

Figures 6 to 8 and 10 to 13 are plan views of alternative security substrates incorporating different security features;

Figure 7a is a plan view of the security substrate of Figure 7 viewed in transmitted light;

Figure 9 is a cross-sectional side elevation of a further alternative security substrate;

Figure 14 is a schematic of a section of a cylinder mould paper making machine used in a further embodiment of the method of the present invention; , Figure 15 is cross sectional side elevation of a portion of the cylinder mould cover of the machine of Figure 14 on the line XV-XV;

Figure 16 is a cross sectional side elevation of a portion of the substrate produced on the machine of Figure 14 on the line XVI-XVI of Figures 17 and 18;

Figures 17 and 18 are plan views of the front and back of the security substrate of Figure 16;

Figures 19 and 20 are plan views of the front and back of an alternative substrate to that of Figure 16;

Figures 21 and 22 are front and rear elevations of a portion of tape used in the method of the present invention;

Figure 23 is a cross sectional side elevation of a section of the cylinder mould cover of the paper machine used to produce the tape of Figures 21 and 22; and

Figures 24 and 25 are plan views of the front and back of another alternative embodiment of a security substrate to that of Figure 16.

The method of the present invention is used to manufacture a security substrate 16, which comprises a base fibrous substrate 15, preferably paper, and a fibrous, preferably paper, tape 14 incorporating one or more security features 11 which are fabricated in the tape 14. Referring to Figures 1 and 2, in the first part of the method of the present invention a first paper web 10 is produced from which a plurality of paper tapes 14 are formed, each comprising one or more security features 11. At least one of the security features 11 is one which is fabricated in the tape 14 during its manufacture. This security feature 11 is one which may limit the production speed of the manufacturing process as compared to the speed of the process when producing a plain substrate without the feature 11. Examples of such security features include multi-tonal watermarks, single tone watermarks commonly known as electrotypes, patterned fibre free regions in the form of holes or perforations, and polymeric elongated elements (including embedded and partially embedded threads) . One or more further security features may be fabricated in the tape 14 post manufacture.

The security feature 11 may also be one where the paper fibres fully or partly define the security feature 11. In the case of watermarks, the fibres fully define the feature, whereas in the case of the polymeric elongate security element, the paper fibres 21 only partly define the feature, for example by forming the windows and bridges in a windowed element or by concealing an embedded element when viewed in reflection.

A number of security features 11 are preferably aligned in parallel strips 12 across the web 10. Figure 2 illustrates a series of aligned windowed polymeric security elements (threads) across the width of the web 10. An optional adhesive coating may be applied to the first paper web 10, using a conventional size bath in which the paper web 10 is submerged in an adhesive resin. A conventional size press may also be used, comprising a pair of rolls, into the nip of which an adhesive is applied through which the dry or partially dry web 10 is passed. Alternatively, the adhesive may be applied to the first paper web 10 using conventional coating methods such as gravure coating. An alternative to using an adhesive coating is to add thermosoftening fibres to the furnish used to make the paper web 10, such that on heat activation during the drying of the security substrate 16 the fibres from the tapes 14 (made from the paper web 10) fuse to the base substrate 15.

The first paper web 10 is then slit along lines 13 on either side of the security feature 11 to produce a series of tapes 14. It is not essential for the tapes 14 to have a linear edge and the edge of the tapes 14 could have a curved or geometric pattern. One method of achieving a curved or geometric pattern is by cutting the tapes 14 with a laser.

The paper web 10 is preferably made from cotton based paper stock but alternatively wood based pulp or synthetic fibres can be used. Paper tapes 14 of varying permeability may be employed in the current invention with the only strength requirement being that the final paper tape 14 has sufficient handling strength to be integrated into the base substrate.

Preferably the tape 14 is produced using a cylinder mould paper machine (similar to that shown in Figures 3a and 3b) , although other papermaking processes could be used such as the Fourdrinier process. The cylinder mould paper machine comprises a vat 20 containing a suspension of paper fibres 21 in which dips the major portion of a cylinder 22 arranged with its axis horizontal. The surface of the cylinder 22 comprises a cylinder mould cover 23, formed from a wire mesh. Liquid is drawn through the mesh as the cylinder 22 is rotated causing paper fibres to deposit on the mesh and form a sheet which is couched from the cylinder 22 by the couch roll 24 and conveyed away. The permeability of the paper can be adjusted by varying the mesh size of the cylinder mould cover 23. A substrate containing security features such as a watermark and a partially embedded polymeric thread would preferably be formed on a fine mesh with a typical mesh size being 70 (warps per inch) by 48 (wefts per inch) (70/48) . The fine mesh results in a uniform well consolidated low permeable sheet suitable to withstand the mechanical handling experienced by a banknote in general circulation. Typically a low permeable fibrous paper tape 14 suitable for use in the current invention will have a Bendtsen porosity in the range 0 to lOOmls/min.

Alternatively a high permeable paper web can be produced by using a coarse mesh size for example a typical mesh size would be 20 (warps per inch) by 20 (wefts per inch) 20/20. Paper produced from a coarse mesh comprises a plurality of discrete areas having a lower fibre density than the rest of the web. Water can more easily pass through the areas of lower fibre density resulting in a high permeable substrate. Other methods may be used to make high permeability paper, including the use of electrotypes to produce small regions of reduced grammage paper. Another method is to apply water jets through a cylinder rotating on the formed, but still wet, paper mat. The cylinder is partially blinded by a patterned stencil. Where the pattern is open, water passes through the cylinder and displaces the paper fibres causing low, or even zero, grammage regions that are more porous than adjacent regions. Such methods could result in specific regions of the tape having high permeability compared to other parts of the tape 14.

The base substrate 15 is subsequently produced, preferably also using a cylinder-mould process, and one or more of the tapes 14 is fed into the vat 20 of furnish 21 used to form the base substrate 15, in which rotates the major portion of a cylinder 22 on a horizontal axis. The surface of the cylinder 22 comprises a cylinder mould cover 23 formed from a wire mesh. Liquid is drawn through the mesh as the cylinder 22 is rotated causing fibres 21 to deposit on the mesh and form a continuous sheet of the base substrate 15 which is couched from the cylinder 22 by the couch roll 24 and conveyed away. The tape 14 can be brought into contact with the cylinder mould cover 23 either before the cylinder mould 22 enters the vat as shown in Figure 3b, or more preferably, as shown in Figure 3a, after the cylinder mould 22 has entered the vat. In the case of a low permeable paper tape, once the tape 14 has made contact with the cylinder mould cover 23, no more fibres deposit over the tape 14 resulting in it being exposed on the back surface 18 of the finished security substrate 16. The back surface 18 of the substrate 16 is the surface of the substrate 16 which is facing away from the cylinder mould cover 23 during its formation. The front surface 17 is the surface which is facing towards the cylinder mould cover 23 during formation of the substrate 16.

In an alternative embodiment the tape 14 may be formed from a paper web that is sufficiently permeable that the fibres continue to deposit over the tape 14 once it has made contact with the cylinder mould enabling the possibility of the tape 14 being wholly embedded.

The base substrate 15 can be produced at a production speed higher than the speeds used when the security feature 11 is formed directly in the substrate 15, because there are no complex processes required. The incorporation of a tape 14 in the substrate 15 is not detrimental to the machine speed because of the high compatibility between the fibrous tape 14 and the fibrous base substrate 15.

The security features 11 are incorporated into the paper web 10 using the same methods as for a typical banknote substrate. For example multi-tonal watermarks are introduced by embossing the wire mesh face-cloth attached to the cylinder mould. When the wire cloth is embossed with a detailed image, the fibres deposit with a lesser or greater thickness on the raised and depressed elements of the embossing respectively to form a fully three-dimensional watermark in the paper. An alternative security device is a single tone light element, commonly known as an electrotype. This is created by attaching a metallic electrotype element or a polymeric sealing compound to the cylinder mould cover, resulting in a significant decrease in drainage through the cover and reduced fibre deposition, forming a light mark in the paper.

A further security feature 11 which is suitable for use in the present invention is an array of patterned apertures in the form of holes and perforations. WO-A-0039391 describes a method of making single ply paper with fibre- free regions by blinding one or more selected areas of a cylinder mould cover, and then depositing a layer of paper fibres onto the cylinder mould cover around the blinded areas. The blinded areas are impermeable which substantially prevents the deposition of fibres. A similar method is described in WO-A-03054297. The blinded areas can be created by attaching a suitably shaped metallic or polymeric element to the cylinder mould cover.

The presence of apertures in the tape 14 enables the incorporation of a new security device in the finished security substrate 16 which is not currently achievable by known papermaking processes. Fibres from the substrate 15 fill at least one aperture in the tape 14 and form a fibrous layer on the surface of the tape 14 around the perimeter of the apertures such that the apertures are not well defined and poorly resolvable in reflected light, but are clearly visible in transmitted light.

In a further embodiment an elongated security element or thread can be incorporated in the tape 14. Such security elements may be wholly or partially embedded into the tape 14. It is usual to refer to partially embedded security elements as being windowed, as the security element is exposed at regular intervals on the surface of the substrate in which it is embedded, like a series of windows. A number of methods for producing security papers with so-called windowed security elements have been described one of which is described in EP-A-0059056. Paper is still regularly produced by the method described within EP-A-0059056 and sold commercially under the trade name Stardust^® by the De La Rue Group .

In a further embodiment of the present invention the fibrous tape 14 has an elongate element partially embedded therein and at least one discrete aperture extending through the fibrous tape 14 exposing at least a part of the elongate element, wherein at least one edge of the elongate element is exposed in the aperture (s) . A method for producing a paper web, with an elongate element exposed in an aperture, is disclosed in WO-A-4001130.

As the first part of the method of the present invention is only concerned with generating the webs 10 from which the tapes 14 are cut, and not the final security substrate 16, the polymeric security elements (or other security features 11) can be positioned very close together on the paper web 10. This highly efficient arrangement of the security features 11 further compensates for the paper machine being run at a reduced speed to successfully incorporate the security features 11. This avoids the usual trade-off that occurs when the security features 11 are incorporated during the production of the final substrate, i.e..between running at high speeds to increase production and low speeds to ensure the quality of the security feature 11. Experimental work has shown that where the edge of the tape 14 has a thinner fibrous layer than the main body of the tape 14 a higher level of adhesion to the base substrate 15 is observed than for a tape 14 with a uniform thickness. This is because, when the tape 14 is rewetted on insertion into the vat during the production of the base substrate 15, the fibres in the thin fibrous layer of the tape 14 have an increased freedom of movement compared to a thicker layer and can entangle and bond more efficiently with the base substrate 15.

A preferred method for manufacturing a paper tape 14 with a thin fibrous edge is to attach continuous thin wires circumferentially around the cylinder mould cover to mark the edge of each paper tape 14. The wire will result in a significant decrease in drainage and fibre deposition forming a light line 13 in the paper web 10 defining the edge of each tape 14. The paper is significantly thinner along these lines 13 and can be torn by a suitable roller and rewind arrangement. The tearing action, as opposed to a slitting action, results in a frayed fibrous edge which further enhances the bonding of the tape edge into the base substrate 15.

A further advantage of the present invention is that the production of the paper web 10 for the tape 14 is solely concerned with the generation of the security features 11. This allows paper fibres of a specific type or characteristic to be used in order to optimise the security feature 11. This is particularly useful for watermarks, where short fibres lead to improved watermark definition. However, whilst short fibres would normally result in a degradation in strength and durability of traditionally made paper, the proposed method enables the fibres in the base substrate 15 to be optimised for strength and durability whilst using short fibres in the tape 14. It is well-known in the papermaking art that the doublefold and tensile strength properties are generally improved by the addition of longer fibres or synthetic fibres and therefore for example the strength of the base substrate 15 could be optimised by using synthetic PVOH fibres as described in EP- A-0073448.

The resultant final security substrate 16 will contain a higher quality security feature 11 and exhibit a higher strength and durability compared to when the security feature 11 is incorporated directly into the paper during the production of the finished substrate.

In a further embodiment the paper tape 14 may be given different aesthetic properties to the base substrate 15. For example the tape 14 may be formed from red coloured fibres resulting in a red paper tape 14 comprising a security feature 11 as defined previously. In further examples the tape 14 could be fully or partly formed from phosphorescent or fluorescent fibres.

The tape 14 may go undergo a number of optional processing steps prior to being incorporated into the base substrate 15. In order to provide additional security, images may be printed onto the tape 14 using conventional security printing techniques such as gravure, screen printing, litho, intaglio etc. The surface of the tape 14 could be modified by embossing or applying tactile inks such that in the final substrate 16 the tape 14 can be identified by touch. The tape 14 may also be perforated to provide improved bonding with the base substrate 15 or to produce a decorative effect.

In order to ensure the tape 14 is fully bonded to the base substrate 15, a heat sealable or water soluble adhesive may be applied to one or both sides of the tape 14 by standard coating or printing processes. In the preferred embodiments where the tape 14 is to be incorporated into the base substrate 15 such that it surfaces on the back surface 18 of the finished security substrate 16, the adhesive may be applied only over the edge of the tape 14 on the side that surfaces to adhere the fibres from the base substrate 15 that overlap the edge of the tape 14.

There is no width or thickness restriction to the tape 14 of the present invention but preferably the width of the tape 14 is in the range 5-50mm and more preferably 10-30mm.

The thickness of the tape 14 is preferably between 20- 70% of the thickness of the base substrate 15 and more preferably between 40-70% of the thickness of the base substrate 15.

In a preferred embodiment a well consolidated low permeable paper tape 14 is arranged to enter the liquid in the vat 20 prior to contacting the cylinder mould cover 23, so that the surface of the cylinder mould cover 23 has already acquired a substantial coating of paper fibres 21 before the tape 14 makes contact, as shown in Figure 3a. Preferably between 20-70% and more preferably between 20-50% of the desired thickness of paper fibres 21 of the base substrate 15 have been deposited on the cylinder mould cover 23 before the tape 14 contacts the cylinder mould cover 23. As the cylinder 22 continues to rotate, few or no fibres 21 are deposited on the back surface of the tape 14, although fibres 21 continue to accumulate adjacent to the tape 14, with the result that the tape 14 is exposed on the back surface 18 of the finished security substrate 16.

The incorporation of the tape 14 as shown in Figure 3a, such that there is a substantial coating of fibres on the front surface of the tape 14, improves the durability of the finished security substrate 16.

In an alternative embodiment, as shown in Figure 3b, the fibrous tape 14 is arranged to contact the cylinder mould cover 23 prior to the cylinder mould 22 entering the liquid in the vat with the result that the tape 14 is exposed on the front surface 17 of the finished security substrate 16. In the case of a well consolidated low permeable tape 14 the restricted drainage results in few or no fibres 21 being deposited on the back surface of the tape 14, although fibres 21 will continue to accumulate adjacent to the tape 14, with the result that the tape 14 is also substantially exposed on the back surface 18 of the finished security substrate 16. In this case an additional paper layer may be applied to the back surface 18 of the security substrate 16 to cover the exposed back surface of the tape 14. The additional layer can be applied by a separate lamination process or produced parallel to the production of the main substrate on a short former and brought together in the wet section of the paper machine. In the case where a high permeable fibrous tape 14 contacts the mould cover prior to entry into the vat 20 the drainage will not be restricted and fibres 21 will be deposited on the back surface of the tape 14.

In yet another alternative embodiment a well consolidated low permeable fibrous tape 14 is incorporated into the base substrate 15 in the same manner as that described for elongate elements in EP-A-00059056. The technique involves embossing the cylinder mould cover 23 to form raised regions and bringing the tape 14 into contact with the raised regions of the mould cover 23, prior to the contact entry point into a vat of aqueous paper stock 21. Where the low permeable tape 14 makes intimate contact with the raised regions of the embossing, no fibre deposition can occur and windows are formed in the front surface of the base substrate 15. After the finished substrate 16 is fully formed and couched from the cylinder mould cover 23, water is extracted from the wet fibre mat and the finished substrate 16 is passed through a drying process. In the finished substrate 16 the regions of the tape 14 which are exposed in the windows are visible in reflected light when viewed from the front surface 17 of the substrate 16.

Figures 4 to 13 show a number of embodiments of different security documents produced from a security substrate 16 made by the method of the present invention.

Figures 4 and 5 show a^' document made from the finished security substrate 16 in which a tape 14 is embedded within the base substrate 15 such that one surface of the tape 14 is exposed at the back surface 18 of the finished security- substrate 16. In this example the tape 14 comprises a security feature 11 in the form of a multitonal pictorial watermark lla. The tape 14 is made from the same furnish as the base substrate 15 and therefore the finished security substrate 16 has a uniform appearance.

Figure 6 shows an alternative embodiment in which the tape 14, exposed at the back surface 18 of the finished security substrate 16, is made from a different coloured furnish to the base substrate 15 and is therefore clearly observable within the finished security substrate 16. In the example shown in figure 6 the tape 14 also comprises a plurality of security features 11, in the form of a multi- tonal watermark lla and a single tone light electrotype watermark lib.

In the embodiments shown in Figures 4 and 6 the tape 14 is preferably made from a well consolidated low permeable paper such that it restricts drainage during papermaking and is subsequently exposed on the back-surface of the finished security substrate 16. Alternatively if the tape 14 is made from a high permeable paper it will not significantly restrict drainage resulting in it being wholly embedded within the substrate. The use of an embedded paper tape 14 enables one or both of the watermarks lla, lib to be positioned in the middle of the document and therefore less susceptible to damage in circulation.

In Figure 7 the finished security substrate 16 comprises a well consolidated low permeable paper tape 14 which contains a security feature 11 in the form of a partially embedded security thread Hd that is exposed in windows 30. The tape 14 is incorporated into the base substrate as described with reference to Figure 3a with the windows 30 facing away from the mould cover 23 such that the tape surfaces on the back surface 18 of the finished security substrate 16, which is the surface shown in Figure 7. As the tape 14 surfaces on the back surface of the finished security substrate 16 the windows 30 are not covered by the fibres of the base substrate 15 and the optical characteristics of a traditional windowed thread Hd are maintained. Between the windows 30 are bridges 31 that cover the security thread Hd. The bridges 31 of paper have an increased grammage compared to the main body of the tape 14, and conversely the paper on either side of a windows 30 has an area 32 of reduced grammage compared to the main body of the paper sheet made from the base substrate 15. When viewed in transmission, as shown in Figure 7a, the thread Hd can be seen as a dark vertical strip running through a series of alternate horizontal dark and light tracks with the bridges 31 appearing darker than the main body of the document formed from just the base substrate 15. The areas 32 adjacent to the windows 30, with reduced grammage, appear lighter. The alternating dark and light regions make up what is known as a thread track.

The windowed security thread Hd can comprise a range of functional properties in order to enhance the security associated with a traditional windowed security thread and well known to those skilled in the art. Public security threads include those having demetallised designs, thin film interference structures, liquid crystal layers, thermochromic layers, photochromic layers, iridescent layers, multiple different coloured metal layers, holographic and diffractive structures and print layers. The use of security threads with covert properties is also applicable to the current invention and examples include those with magnetic properties, luminescent properties, conductivity or other machine detectable characteristics.

The tape 14 illustrated in Figure 7 can be made from the same furnish as the base substrate 15 with the finished security substrate 16 appearing substantially uniform apart from the windowed thread Hd. In an alternative embodiment the furnish of the tape 14 is of a different colour to the base substrate 15, as illustrated in Figure 8. When the document is viewed in reflection, from the same side as the surfacing tape 14, a coloured stripe is observed in the middle of which is a windowing polymeric thread. The colour of the tape provides additional security as well as attracting the attention of the general public to the security thread Hd. In alternative embodiments the tape 14 may be coloured by a conventional printing process prior to insertion into the base substrate 15. A conventional printing process enables a design to be applied to the tape 14 rather than an all-over colouring.

Small perforations may be added to the tape 14 on either side of the polymeric thread to enable drainage during papermaking and therefore allow fibres to form on the bottom surface of the tape 14 in the non-window regions.

In a further embodiment a coloured ink or coating which contains a component that becomes mobile when wetted could be applied to the tape 14. The tape 14 is rewetted when it is inserted into the vat 20 during the production of the base substrate 15. On rewetting the tape 14 the mobile component of the ink migrates through the tape 14. The extent of the migration of the mobile component will be dependent on the thickness of the paper of the tape 14 and therefore regions of different paper thicknesses will appear to have a different colour or shade of colour.

A cross-section of a tape 14 incorporating a polymeric security thread Hd exposed in windows 30 on one surface is shown in Figure 9. A layer 33 of coloured ink containing a mobile and non-mobile component is applied to the opposite surface of the tape 14. In one example the tape 14 could be printed with an orange ink containing a non-mobile green component and a mobile red component. On rewetting the tape 14 the red component will migrate through the tape 14 and will be visible at a higher concentration in the low grammage light regions of the thread track compared to the high grammage thread bridges 31. The final document will comprise a thread track with two alternating colours along the track.

Figure 10 shows an example of a secure document comprising a well consolidated low permeable tape 14 in which the tape 14 comprises a first security feature 11 in the form of patterned holes lie, which provide identifying information, and a second security feature in the form of a traditional multi-tonal watermark 11a. The holes lie in the tape 14 can be created during the original papermaking process by blinding or sealing the cylinder mould cover 23. Alternatively the holes Hc can be created by perforating the tape 14 after it has been formed, prior to incorporating it into the base substrate 15. Examples of methods of perforating the tape include stamping, die-cutting and laser cutting.

In another preferred embodiment, the security feature 11 of the tape 14 comprises identifying information in the form of patterned holes lie such as stars, and the tape 14 is made from a low permeable paper produced from a different coloured furnish to the base substrate 15. The holes lie are formed during the paper making process for the tape 14 by blinding the cylinder mould cover 23 on which the paper fibres 21 are deposited. If the base substrate 15 is substantially white and the tape 14 is a shade of blue, then on viewing the base substrate 15 in reflection, from the exposed tape 14 side, a blue strip will be observed comprising white stars. However, because the white fibres from the base substrate 15 fill the holes lie of the tape 14 and form a fibrous layer on the tape around the perimeter of the holes lie, the edge of the holes lie appear blurred and poorly defined when viewed in reflection. The fact that the presence of the white fibres around each hole lie can be identified with the naked eye against the blue background of the tape 14 provides an additional security benefit. A counterfeiter simply printing white stars on a blue background cannot replicate this blurred fibrous edge. In contrast, on viewing the document in transmission, as shown in Figure 11, a sharp image of the stars can be clearly seen against the background of the coloured tape. The fact that the tape 14_, is of a- different colour to the base substrate 15 provides additional security and substantially increases the contrast for the patterned holes/perforations lie when viewed in transmissive light.

Alternatively, the tape 14 can be made from the same colour furnish as the base substrate 15, but differ in another characteristic such as porosity, opacity or density. In this case the identifying information formed from the outline of the holes 11 will be virtually invisible in reflected light, but easily distinguishable in transmitted light.

In yet a further embodiment, the paper tape 14 comprises an array of small circular perforations lie arranged to form the numeral 5 as shown in Figure 12. In this example the tape 14 is made from a low permeable paper produced from a furnish with a lower opacity than the base substrate 15. The perforations lie are formed during the paper making process for the tape 14 by blinding the cylinder mould cover 23 on which the paper fibres 21 are deposited. The patterned tape 14 is subsequently incorporated into the base substrate 15 as described with reference to Figure 3a. Some fibres from the base substrate 15 form in the perforated regions lie of the tape 14 and slightly overlap the edges of the perforations such that when viewed in reflection the perforated regions lie are not clearly defined and a virtually imperceptible "blurred" image of the number "5" is present, as shown in Figure 12. However on viewing in transmission, the presence of the tape 14 is immediately noticeable due to the difference in opacity compared to the base substrate 15 and the perforated regions lie of the tape 15 are clearly defined within" the tape 15 as sharp circles defining the numeral "5", as shown in Figure 13.

An additional benefit of the perforations lie in a low permeable tape 14 is that it increases the adhesion of the tape 14 to the base substrate 15 due to the fact there are substrate fibres present on both sides of the tape 14. Without the perforations lie the fibres from the base substrate 15 would only be attached to one surface of the tape 14, i.e. the surface that is not exposed on the back 18 of the security substrate 16. However with the perforations lie present, the fibres from the base substrate 15 fill the perforations lie and become attached to the tape 14 on the opposite side of the tape 14. A preferred embodiment to enhance adhesion between a low permeable tape 14 and a fibrous base substrate 15 comprises a series of perforations along one or both long edges of the tape 14. Alternatively there could be a series of perforations along the middle of the tape, or an array of perforations covering the whole surface of the tape 14. Experimental work has shown that the adhesion of the tape 14 to the base substrate 15 is optimised if the perforations are of a size in the 0.5 - 2mm wide by 0.5 - 4mm long and the space between the perforations is in the range l-3mm.

A further advantage of the embodiments utilising a perforated tape 14 is that the perforations lie assist in the dewatering of the security substrate 16 on papermaking machines without sophisticated double felt presses.

In a further embodiment of the current invention the tape 14, made from a low permeable paper, comprises a first security feature 11 in the form of one or more holes lie. The holes lie in the tape 14 can be created during the original papermaking process by blinding or sealing the cylinder mould cover 23. The tape 14 is then incorporated into the base substrate 15 in combination with a conventional elongate impermeable element 40 such that the elongate impermeable element 40 contacts the cylinder mould cover 23 through the holes lie in the tape 14 and thereby the regions 41 of the elongate impermeable element 40, coincident with the holes lie in the tape 14, surface on the front side 17 of the finished substrate 16 forming windows. The regions 42 of the elongate polymeric element 40 not coincident with the holes lie in the tape 14 and positioned on the surface of the tape 14 away from the mould cover 23 will surface on the back side 18 of the base substrate 15 as no fibres will deposit over the low permeable paper tape 14. In this manner the elongate impermeable element 40 is exposed in one or more windows on both the front and back side 17, 18 of the finished substrate 16.

Figures 14 to 18 illustrate an embodiment of the present invention which enables the incorporation of an elongate impermeable element 40 such that it is exposed at windows in both surfaces 17,18 of the finished substrate 16. A fibrous tape 14 made from a low permeable paper comprises a first security feature 11 in the form of a series of holes lie positioned along the tape 14. The holes lie are formed during the paper making process for the tape 14 by blinding the cylinder mould cover 23 on which the paper fibres are deposited. The tape 14 is incorporated into the base substrate 15 as shown in Figure 14. In this example the tape 14 and the base substrate 15 are made from the same furnish 21. The tape 14 is combined with an elongate impermeable element 40 immediately before the tape 14 contacts the cylinder mould 22. The elongate impermeable element 40 and tape 14 are brought together such that the elongate element 40 contacts the tape 14 on the side of the tape 14 away from the cylinder mould cover 23. The elongate impermeable element 40 is positioned such that it lies across one or more of the holes lie in the tape 14. The combined structure is then brought into contact with the cylinder mould cover 23 (Figure 15) prior to the cylinder mould 22 entering the liquid in the vat 20 with the result that the tape 14 is exposed on the front surface 17 of the finished security substrate 16 (Figure 16) . Furthermore the regions 41 of the elongate impermeable element 40 lying across the holes lie in the tape 14 also contacts the cylinder mould cover 23 and likewise are exposed on the front surface 17 of the finished security substrate 16. In the case of a well consolidated low permeable tape 14 the restricted drainage results in few or no fibres 21 being deposited on the back surface of the tape 14, although fibres 21 will continue to accumulate adjacent to the tape 14, with the result that the tape 14 is substantially exposed on the back surface 18 of the finished security substrate 16. Fibres forming the base substrate 15 will continue to form in the holes lie in the tape 14.

If the elongate impermeable element 40 is sufficiently narrow not to interfere with fibre deposition then fibres 21 will also from over regions 41 of the impermeable elongate element 40 such that it is only exposed on the front side 17 of the final substrate 16 (Figure 16) . This results in the elongate impermeable element 40 being exposed in alternate windows on the front and back of the finished substrate 16 as shown in Figure 17 (Front) and Figure 18 (Back) . In order to allow fibre deposition the impermeable elongate element 40 will preferably have a width less than 3mm, and more preferably less than 2mm.

Alternatively if the elongate element 40 is sufficiently large to interfere with fibre deposition as they are too wide to be bridged by the fibres 21, regions 41 of the impermeable element 40 will be exposed on both the front and back surface 17, 18 of the final substrate 16 (Figures 19 and 20) . In this case the impermeable elongate element 40 preferably has a width greater than 3mm and even more preferably greater than 6mm.

For the embodiments described with reference to Figures 14 to 20 the tape 14 and the elongate impermeable element 40 may be delivered into the papermachine in a number of ways . In one method the tape 14 and the elongate impermeable element 40 will be delivered on separate rolls with guide reels being used to ensure they are brought into contact at the correct point. Alternatively the tape 14 and the elongate impermeable element 40 may be brought into contact in a separate step prior to the papermaking process and delivered into the papermachine from the same roll. Although not essential an adhesive layer can be used to bond the tape 14 to the elongate impermeable element 40, this adhesive bond could be formed prior to entry into the papermachine, for example using an adhesive lamination process, or during the papermaking process using a moisture or heat activated adhesive.

In a preferred embodiment the elongate impermeable element 40 is incorporated into the fibrous tape 14 during its fabrication. This can be achieved using the method of making fibrous substrates described in WO-A-04001130. The tape 14, illustrated in Figures 21 and 22 viewed from the front surface 45 and back surface 46, comprises a partially embedded elongate impermeable element 40 and one or more holes lie which expose both surfaces of regions 43 of the elongate impermeable element 40. The tape 14 also comprises traditional windows 30, as described in EP-A-0059056, in which only one surface of regions 44 of the security element 40 are exposed.

The method of manufacturing the low permeable tape 14 illustrated in Figures 21 and 22 is shown in Figure 23. A porous support surface, for example in the form of a cylinder mould cover 23, is produced in a known way. The mould cover 23 has a plurality of drainage restriction regions 47. These can, for example, be provided by fixing a blinding material to the mould cover 23. The blinding material is typically a metal which is welded to the cylinder mould cover 23. Other suitable blind materials are wax, polymer or any other material which can be securely attached to the cylinder mould cover 23 to prevent drainage of water from fibrous stock 21 and hence fibre deposition. These drainage restriction regions define the shape of the holes lie formed in the tape 14. The cylinder mould cover 23 also comprises embossed raised regions 48 which are used to generate the conventional windows 30. The elongate impermeable element 40 is brought into contact with both the raised regions 48 and 5 drainage restricted regions 47 on the mould cover 23 prior to the contact entry point into a vat 20 of aqueous paper stock. Where the elongate impermeable element 40 makes intimate contact with the raised regions 48 of the embossing, no fibre deposition can occur and windows 30 are

10 formed in the front surface 47 of the paper tape 14 that was in contact with the mould cover 23. Assuming that the impermeable elongate element 40 is not sufficiently wide to prevent fibre deposition, fibres 21 will be deposited over the impermeable element 40 in contact with the raised

15 regions 48 such that it will not be exposed on the back surface 48 of the paper tape 14. In the drainage restricted regions 47 there is little or no covering of fibres 21. However in the flat freely draining regions full fibre coverage is obtained. Thus when the substrate used to form

20 the paper tape 14 is removed from the cylinder mould 23 the elongate impermeable element 40 is exposed from both sides of the tape 14 in the holes lie corresponding to the drainage restrictive regions and exposed from one surface of the paper tape 14 in the windows 30 corresponding to the

25 raised embossed raised regions 48. In the regions between the windows 30 and the holes lie the elongate element 40 is wholly embedded within the tape 14.

The low permeable tape 14, illustrated in Figures 21 30 and 22, is then incorporated into the base substrate 15 as ■ . described with reference to Figure 3b, prior to the cylinder mould 22 entering the liquid in the vat 20, with the conventional windows 30 facing away from the mould cover 23. The tape 14 is exposed on the front surface 17 of the finished security substrate 16. Furthermore the regions 43 of the elongate element 40 lying across the holes lie in the tape 14 also contact the cylinder mould 23 and likewise are exposed on the front surface 17 of the finished security substrate 16 (Figure 24) . If the elongate impermeable element 40 is sufficiently narrow not to interfere with fibre deposition then fibres 21 will also from over regions 43 of the impermeable elongate element 40 such that it is only exposed on the front side 17 of the final substrate 16. Fibres forming the base substrate 15 will continue to form in the holes lie in the tape 14. As the tape 14 is of low permeability it is also exposed on the back surface 18 of the finished security substrate 16 and therefore the conventional windows 30 are not covered by the fibres of the base substrate 15 and therefore regions 44 of the security element 40 are exposed on the back surface 18 (Figure 25) .

The inventive method, for the incorporation of an elongate impermeable element 40 into a base substrate 15 such that it windows on both surfaces, described in the various embodiments in Figures 14 to 25, allows total control of the degree and position of exposure of the elongate impermeable element 40 within the security substrate 16. For example the elongate impermeable element 40 can be exposed on both surfaces of the final substrate 16 in an alternating manner (Figures 15 to 18), or coincident manner (Figures 19 and 20) , or where the elongate impermeable element 40 can be exposed in a plurality of windows 30 on one surface and only a single window 30 on the second surface (Figures 24 and 25) . Thus, substrates 16 made according to the present invention are advantageous in that it is possible to increase the exposure of the elongate element 40, not just on one surface of the substrate 16, but two sides, which means that it can be used to its best extent. This is important because such elongate impermeable elements 40 can be expensive to provide.

The elongate impermeable elements 40 are preferably made of clear polyester, although other materials may be used, such as polyethylene or polypropylene, and may have a constant or variable width. The elongate impermeable elements 40 typically have a layer of adhesive, which help the embedment within the tape and/or final substrate 16.

The elongate elements 40 can incorporate a wide variety of known security features which may include the following:-

- a metallic layer, indicia or designs, which appear dark, when the substrate is viewed in transmitted light, compared to the lighter, partly light- transmitting, substrate. When viewed in reflected light, the shiny metallic parts will be clearly seen in the windows;

- de-metallised indicia or designs, which may comprise areas of substantially removed metal to take advantage of the transparency of the base film and provide a large area of transparent window; holographic or diffractive designs, which may comprise areas of full metal and half-tone screens to provide partial transparency and/or no metal;

- front to back print registration, in which features are printed which would clearly exhibit Moire patterns from both front and back if a counterfeit were attempted. Alternatively, such patterns could be produced on a transparent film prior to insertion of the element into the paper as a security feature itself. The exact reproduction of such patterns are very difficult to mimic;

- luminescent, iridescent, thermochromic, liquid crystal or magnetic materials;

designs or indicia created by printed inks;

- dichroic materials which can have different colours when viewed in transmission and refection, for example as described in GB-A-1552853. These materials are particularly useful where the windows on the front and back of the substrate coincide to form an aperture (as shown in Figure

16);

thin film interference devices, as described in EP-A-227423 or liquid crystal polymer films or liquid crystal pigmented inks, such as described in EP-A-435029 or EP-A-863815. The elongate impermeable elements 40 may be oriented, which means that each side of the element 40 may carry different information, materials or optical effects. Examples include : -

holographic or diffractive materials on a first side of the element, with a thin film interference device on a second side;

liquid crystal film over a black or dark background on a first side and plain metal on a second side;

- different coloured metals on each side, e.g. aluminium on the first side and another metal on the second side. Alternatively one or more coloured transparent lacquers over a metal layer could be used to create a variety of colours;

a magnetic micrometallised thread, such as described in GB-A-2375078;

- repeating indicia or security features located in either window or bridge regions on one or both sides of the substrate.

Many other options are available and with such a large exposed area of the element available, it is possible to ""'' combine many security or decorative features together on one element 40. In all of the embodiments described, if the finished security substrate 16 undergoes further standard security printing processes, then the colour and/or design of the tape 14 can be correlated to the design of the final printed document. Standard security printing processes include one or all of the following; wet or dry lithographic printing, intaglio printing, letterpress printing, flexographic printing, screen printing, and/or gravure printing. The printed designs are preferably printed both on the substrate 15 and the exposed regions of the paper tape 14. The patterns and designs on the security tape 14 and document may be registered with each other, which makes it very difficult to counterfeit.

Claims

CLAIMS :

1. A method of manufacturing fibrous security substrates comprising the steps of manufacturing an elongate fibrous tape and fabricating at least one security feature in or on the tape, forming a base substrate by depositing fibres onto a support surface, wherein the tape is incorporated within the base substrate to form the security substrate during the formation of the base substrate.

2. A method as claimed in claim 1 in which the at least one security feature is fabricated during the manufacture of the tape.

3. A method as claimed in claim 1 in which at least further security feature is fabricated after the manufacture of the tape.

4. A method as claimed in any one of the preceding claims in which the security feature is one which limits the production speed of the manufacturing process as compared to the speed of the process for producing a plain substrate without the security feature.

5. A method as claimed in claim 1 in which the at least one security feature comprises a watermark.

6. A method as claimed in claim 1 in which the at least one security feature comprises an elongate security element, at least partially embedded within the fibrous tape.

7. A method as claimed in claim 1 in which the at least one security feature comprises identifying indicia provided by perforations in the tape.

8. A method as claimed in any one of the preceding claims in which the tape incorporates a plurality of security features which may be the same or different.

9. A method as claimed in any one of the preceding claims in which the tape is formed by a cylinder mould process.

10. A method as claimed in any one of the preceding claims in which the base substrate is formed by a cylinder mould process.

11. A method as claimed in any one of the preceding claims in which the tape and base substrate are made from paper.

12. A method as claimed in any one of the preceding claims in which a furnish from which the tape is made is substantially the same as that from which the base substrate is made so that the tape is not readily distinguishable from the base substrate.

13. A method as claimed in any one of claims 1 to 11 in which a furnish from which the tape is made is different from that from which the base substrate is made, so that the tape has a contrasting appearance to the base substrate.

14. A method as claimed in any one of the preceding claims in which a plurality of fibrous tapes are slit from a web containing a plurality of parallel security features.

15. A method as claimed in any one of the preceding claims in which an adhesive is applied to the fibrous tape prior to its incorporation within the base substrate.

16. A method as claimed in any one of claims 1 to 14 in which the fibrous tape includes thermo—softening fibres.

17. A method as claimed in any one of the preceding claims in which edges of the fibrous tapes are thinner than a main body of the tape.

19. A method as claimed in claim 17 in which the thinner edges are formed by attaching wires to the support surface to mark the edges of each tape.

20. A method as claimed in any one of the preceding claims further comprising the step of printing onto the tape prior to its incorporation within the base substrate.

21. A method as claimed in any one of the preceding claims further comprising the step of modifying the surface of the tape to provide a tactile element prior to its incorporation within the base substrate.

22. A method as claimed in any one of the preceding claims in which the tape is wholly embedded within the base substrate.

23. A method as claimed in any one of claims 1 to 21 in which the tape is partially embedded within the base substrate and exposed at windows in at least one surface of the base substrate.

24. A method as claimed in any one of claims 1 to 2ΛΛr& in which the tape is partially embedded within the base substrate such that one surface of the tape is exposed.

25. A method as claimed in any one of the preceding claims in which the tape is coated or printed with a coating or ink which includes a component which becomes mobile when wetted.

26. A method as claimed in any one of the preceding claims in which a plurality of tapes are formed from a web of tape substrate, a plurality of wires being attached to a support surface on which the tape substrate is being formed to decrease drainage and fibre deposition and form a light line defining edges of the tapes such the tapes are separable from each other by a tearing action along these lines, said tapes having a frayed fibrous edge.

27. A method as claimed in any one of the preceding claims further comprising the step of incorporating an elongate impermeable element into the base substrate adjacent the tape.

28. A method as claimed in claim 27 in which the tape includes holes through which the impermeable element contacts a support surface of a paper making machine during the formation of the base substrate.

29. A method as claimed in claim 27 or claim 28 in which the tape and elongate impermeable element are combined prior to incorporation in the base substrate.

30. A method as claimed in any one of claims 27 to 29 in which the tape and elongate element are bonded prior to incorporation within the base substrate.

31. A method as claimed in any one of claims 27 to 30 in which the elongate element is incorporated into the fibrous tape during its fabrication, said tape including at least one hole which exposes both sides of at least one portion of the elongate element .

32. A method as claimed in claim 31 in which the tape further comprises windows in which only one surface of at least one portion of the elongate security element is exposed.

33. A method as claimed in any one of claims 27 to 32 in which the elongate element includes more security features.

34. A security substrate formed by the method of any one of the preceding claims.

35. A security document made from a security substrate of claim 34.

36. A security document as claimed in claim 35 comprising a banknote, document of value, share certificate, passport or the like.

37. A method as substantially hereinbefore described with reference to and as shown in the accompanying drawings.