GB2311303A

GB2311303A - Reinforced paper incorporating a security element

Info

Publication number: GB2311303A
Application number: GB9605629A
Authority: GB
Inventors: Malcolm Robert Murray Knight; Duncan Hamilton Reid; Stephen David Ridyard
Original assignee: Portals Ltd
Current assignee: Portals Ltd
Priority date: 1996-03-18
Filing date: 1996-03-18
Publication date: 1997-09-24
Anticipated expiration: 2016-03-18
Also published as: GB2311303B; GB9605629D0

Abstract

Security paper is made incorporating an elongate security element (17) and a reinforcing strip (21) which is formed with meshes therein and is embedded in the paper. The security element may be exposed at windows in the paper or may be totally covered. The element (17) and strip (21) may be fed to the cylinder mould either separately (as shown), together or in a pre-bonded state. The strip (21) may be partially soluble, provided with an adhesive coating or made of hot-melt adhesive to enhance bonding with the paper fibres.

Description

REINFORCED WINDOWED PAPER INCORPORATING A SECURITY ELEMENT The invention is directed at improvements in windowed paper incorporating an elongate security element, and to a method of making reinforced windowed paper incorporating an elongate security element.

It is generally known to include, as a security feature, elongate security elements such as threads, strips or ribbons of, for example, plastics film, metal foil, metallised plastics or metal wire, in the thickness of security paper to render imitation of documents produced from that paper more difficult. 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 conductivity, the ability to absorb x-rays and fluoresence.

As a further security feature, it has been found to be particularly advantageous to provide windows in the surface of the paper which expose such elongate elements at spaced locations. Examples of methods of manufacturing such 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 0059056 describes a method for manufacture of windowed thread paper on a cylinder mould papermaking machine. The technique involves embossing the cylinder mould cover and bringing an elongate element into contact with the raised regions of the embossing prior to the contact entry point into a vat of aqueous stock. Where the elongate element makes intimate contact with the raised regions of the embossing, no fibre deposition can occur. After the paper is fully formed and couched from the cylinder mould cover, these contact points are present as exposed regions which ultimately form windows in the finished banknote paper.

WO 93/08327 describes a method of manufacturing windowed thread paper on a Fourdrinier papermaking machine. A rotating embedment means with a modified profile or embossing is used to drive an elongate element into draining stock on a fourdrinier wire.

The profile of the embedment means is such that raised portions are provided which remain in contact with the elongate element during the embedment process. Thus fibres are prevented from collecting between the element and embedment means such that the elongate element is subsequently exposed in windowed regions of paper.

EP 0070172 describes a method of forming paper involving the use of a security device in the form of a strip having first regions which are relatively impermeable and second regions which permit drainage of the liquid from the papermaking stock through the strip such that the impermeable regions inhibit deposition of fibre and thus become exposed in the finished sheet.

GB 1365876 describes the incorporation into security paper as a security device of a porous plastic mesh which may be coloured and which is subsequently detectable by both visual and tactile means.

FR 2702228 describes the manufacture of a security document with a water-soluble ribbon bearing markings visible in reflected light. The ribbon is invisible when viewed in transmitted light.

EP 0625431 describes the manufacture of paper on a multi-ply machine incorporating security strips of a width exceeding 2mm. This specification states that, in the absence of multi-ply techniques, the use of security strips of width approximately 1.5-2.0mm produces defects (holes) on the back of the sheet, i.e. the side away from the mould cover without, however, the same defects occurring on the side of the paper facing the mould cover. According to this specification, defects on the front side of the paper, i.e. the side facing the mould cover, only occur when the width of the security strip is increased to approximately 4-5mm. The technique also describes the use of liquid permeable areas in the edge of the area of the security strip for use on even wider security strips. These liquid permeable edge regions provide anchorage for the security strip in the paper.

The use of elongate security elements in the security paper made by the known techniques can lead to a relative weakness in the mechanical strength of the finished paper or banknote. This is particularly relevant to the wider threads being used nowadays of 1.6mm upwards. When a banknote is folded in the vicinity of the elongate element, there is a tendency for the fold to occur directly alongside the elongate security element which is itself relatively rigid.

Thus the edge of the element tends to act as a stress concentration point. The fibre is in places locally thinner against the edge of the element than in the general body of the sheet. Thus when the sheet is folded, the effect of stress concentration and thin fibre can lead to a weakness and tendency to tear down the side of the elongate security element. Similarly, when a tensile force is applied substantially at right angles to the elongate security element, the localised regions of thin fibre will tend to make the note tear preferentially in the vicinity of the elongate security element.

The use of meshes as support and strengthening for security paper is well known in the industry.

GB 3453 describes the use of an open mesh fabric as support across the width of the note. US 1921504 defines a method of incorporating a textile mesh into secure documents for reinforcement on a Fourdrinier machine. However, none of these methods is suitable for reinforcing paper incorporating security threads.

It is therefore an object of the present invention to provide a reinforced paper incorporating a security element and a method of making same.

The invention therefore provides a reinforced fibrous sheet comprising an elongate security element and a reinforcing strip of material having openings therein substantially embedded in the sheet between the elongate element and one surface of the sheet.

The invention also provides a method of making a reinforced fibrous sheet generally incorporating a continuous elongate security element comprising the steps of continuously depositing fibres onto a support surface to form a sheet, continuously introducing an elongate element and a reinforcing strip of a material having openings therein such that the elongate element is at least partially embedded within the sheet and the reinforcing strip lies between the elongate element and one surface of the sheet.

The use of a reinforcing strip leads to the mechanical reinforcement of the known weak areas of banknotes and other security documents formed from the paper and enhances resistance to tearing due to prolonged/repeated folding and also a transverse tensile force.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a schematic section through a cylinderstyle mould papermaking machine for use in the method according to the present invention; Fig. 2 is a schematic section similar to that of Fig. 1, but showing an alternative point of introduction of the reinforcing strip; Fig. 3 is an enlarged cross-section of a piece of paper made by the method of the present invention; Fig. 4 is a plan view of windowed thread paper of the prior art; and Fig. 5 is a further schematic section similar to that of Figs. 1 and 2 showing yet another alternative point of introduction of the reinforcing strip and elongate element.

As seen in Fig. 1 a cylinder mould papermaking machine 10, which can be used in the method of the present invention, comprises a vat 11 containing an aqueous fibre stock 12 consisting of a suspension of papermaking fibres. The paper may be made from natural or synthetic fibres or a mixture of both. A cylinder mould 13, arranged with its axis in the horizontal plane, is positioned so that the major portion dips into the vat 11. The surface of the cylinder mould 13 is provided by a wire mesh known as the cylinder mould cover. Generally there are several layers of mesh employed, the outermost being finest.

Liquid is drawn through the mesh as the cylinder mould 13 is rotated causing papermaking fibres to deposit on the mesh and form a sheet 14 which is couched from the cylinder mould 13 by couch roll 15 and is conveyed away on the couch fabric 16. When making windowed paper, the surface of the cover of the cylinder mould 13 is provided with raised portions as described in EP 0059056.

An elongate security element 17 is continuously implanted in the paper. The security element 17 can be of any type, including threads or strips that are metallised, demetallised, holographic, microprinted, dichroic etc. The element 17 is supplied from a bobbin 18 and passes over a guide 19, such as a roller, into contact with the cylinder mould 13. For the windowed paper the element 17 is led into the vat 11 so as to contact each raised portion before the raised portion enters the vat 11, i.e. whilst still above the water level 20 so that the elongate element 17 is laying over the raised portion as fibres begin to deposit. Fibres are progressively deposited over the element 17 and also below the level of the element 17 except at the raised portions. For non-windowed paper the element 17 is led into the vat 11 after fibres have been deposited on the cylinder mould.

A reinforcing strip 21 is also continuously implanted in the paper. The reinforcing strip 21 has openings therein and may be in the form of a mesh tape, or perforated strip or other appropriate construction. The reinforced strip 21 used in accordance with the invention preferably have widths of 10-20mm, although those having greater and smaller widths may also be used. The strip 21 is preferably in tape form and is unwound from a spool 22 and transported over a suitable guide 23 to preferably be run into the vat 11 below the water level 20 behind the elongate element 17, i.e. on the opposite side of the element 17 to the cylinder mould 13. As some fibres have already covered the elongate element 17 and the fibrous stock 12 may drain through the reinforcing strip 21, fibre is deposited both between the reinforcing strip 21 and the elongate element 17 and behind the reinforcing strip 21 so that it is wholly buried. Thus the reinforcing strip 21 is substantially incorporated within the body of the paper sheet 14 and surrounded by paper fibres.

The reinforcing strip 21 may alternatively be introduced into the vat 11 together with the security element 17 as shown in Fig. 2. As a further alternative, the thread 17 and strip 21 may be intimately bonded prior to insertion into the paper and inserted in the manner represented by numeral 17 in Fig. 1. There is then no need for a separate reinforcing strip represented by numeral 21 in Fig. 1.

It should be noted that other methods of making paper may be used in the present invention using other types of papermaking machines such as a fourdrinier machine. The means of introduction of the security element 17 and reinforcing mesh tape 21 may vary on such other machines.

The construction of a final paper sheet 14 according to the invention, containing windows, can be seen in Fig. 3 on a exaggerated scale. Where the security element 17 was in contact with a raised portion on the cylinder mould 13, the element 17 lies exposed on one surface of the paper 14 (i.e. the mould side). These exposed areas form the windows 24 and the areas between the windows 24 are bridges 25 where complete coverage of the element 17 with paper fibre has been effected. The strip 21 is completely embedded in the paper 14 between the element 17 and the non-windowed surface 26 of the paper.

Suitable mesh tapes for use as the reinforcing strip in this invention are: Smith & Nephew Tape R769 Net 909 Bondina Fabric 1703 polyamide MT 1235 MT 1236 MT 1237 The mesh tape may be wholly insoluble or partially soluble. The latter may be made from polyvinyl alcohol which, under the action of heat/moisture in the paper forming and/or drying processes will soften on the outside and allow a more intimate bond with the paper fibre. Alternately the mesh may be treated with a coating or by other means, or include minute hairs or the like to promote adhesion to the paper fibre. A further option is the use of meshes formed from hot-melt adhesives which are available as sheets, nets or mesh webs. Examples of such materials are Xiroweb thermoplastic bonding adhesive webs from Sarnatech-Xiro AG; the webs or films comprise copolyamide, terpolymers based on polyethylene vinylacetate, modified polyethylene, polypropylene, modified polyolefins, polyester and composite films thereof. Where such films are supplied as continuous impermeable sheets, they must be perforated and slit to the necessary mesh width prior to the papermaking processes described herein.

The thickness of the mesh tape or other type of strip and the dimensions of its openings are preferably such that, in the finished paper, they provide a tactile effect.

In addition to the mechanical reinforcement of paper made by this method, there are other surprising and wholly unexpected technical benefits. Contrary to the comments made in DE 4314380, which states that defects/holes only occur on the front side of the paper sheet when the width of the security strip is increased to approximately 4-Smm, it has been found that defects/holes can occur on the front side at width ranges substantially below this value. It has been observed that paper fibre is correctly deposited in the bridge 25 and inter-note regions around the cut line 26 between notes (see Fig. 4) on the cylinder mould 13 and that fibre coverage is complete when the wet paper is couched off the cylinder mould 13.

However, when the paper on its carrier couch fabric 16 is passed through a conventional single felt press section with the felt on the underside of the paper, i.e. the opposite side to the windows in which the security element is exposed, damage to the fibre coverage on the front side can occur in the bridge 25 and inter-note regions to produce holes 27, i.e.

unwanted exposure of the security element in these regions. The effect is associated with a relatively high moisture content in the paper proceding the press section.

It has been found that the use of reinforcing strips 21 in accordance with the present invention substantially reduces this tendency. High pressures are generated within the moist fibre coverage over the security strip at the press nip; since the water squeezed out of the fibrous coverage by this pressure cannot pass through the impermeable security strip, it is transported along the strip and sideways across the strip to the edges of the strip where it can be forced through the paper and into the supporting press felt.

The effect of this action is to disrupt the fibre coverage over the security strip. To a significant extent, the unwanted holes 27 in the bridge 25 internote regions on the front surface appear to be due to adhesion of the disrupted region of pressed fibre to the press roll surface as the paper on its carrier fabric is removed at the outgoing nip. It has been found that the presence of a reinforcing strip 21 inhibits the propensity of the paper fibre to follow the path of the press roll at this point and thus plays a significant role in keeping the paper sheet 14 consolidated. This effect was entirely unexpected prior to the experimental trials leading to the present invention.

A further unexpected technical benefit is that in the absence of a reinforcing strip, the passage of water forced through the paper adjacent to the security strip displaces fibre and produces very thin paper or holes alongside the strip. These thin regions or holes are visually unacceptable as well as constituting regions of mechanical weakness. It has been found that the use of reinforcing strips as described herein prevents the formation of such thin regions or holes by inhibiting the fibre displacement that otherwise occurs during the pressing operation.

For the purposes of restricting the formation of thin fibre coverage or holes over or alongside the thread during pressing, the reinforcing strip may be made from a material, e.g. a suitable grade of polyvinyl alcohol, such that the strip is wholly or substantially dissolved and incorporated within the body of the sheet during the drying operation, in a manner similar to that described for dissolving security strips in US 4552617. However, the benefits of subsequent mechanical reinforcement of the finished document against damage due to folding/tearing are then not available when such dissolving meshes are used.

Thus the use of a reinforcing strip 21 not only assists the finished product resist damage due to mechanical flexing etc., it has the additional highly valuable benefit in consolidating the sheet through the manufacturing process. A third benefit is that the reinforcing mesh 21 provides a distinct tactile effect to the finished document which is a valuable addition to the overall public security.

As mentioned previously, the reinforcing strip 21 may comprise a perforated strip. Such perforations may be produced mechanically by punching, using laser drills, electrical sparking or other known means.

Such perforated film is in common use in other fields e.g. for wrapping bread.

As well as providing mechanical reinforcement to windowed thread paper, the invention is also of value in providing reinforcement to paper where the security element is wholly enclosed within the sheet; the reinforcing strip may be introduced behind the embedded security element as shown in Fig. 5, or the security element may be bonded to the reinforcing strip.

The use of reinforcing strip as described in this specification is particularly beneficial for paper incorporating security elements in the width range 1.0-4.0mm, although it is also beneficial to security elements of width outside this range.

Apart from the benefits of mechanical reinforcement and reduction of elimination of the production of thin regions of paper or holes during the pressing operation described above, the inclusion of a reinforcing strip into the paper may optionally also increase the security content of the document by selecting a strip with openings of suitable size and construction such that the presence of the strip in the finished document produced from the paper is detectable visually and/or by tactile means. These means are available to the general public without any special training or instruction. Optionally, the mesh may be coloured and/or luminescent to further increase the security content of the document and make the presence of the strip more apparent.

Claims

CLAIMS:

1. A reinforced fibrous sheet comprising an elongate security element and a reinforcing strip of material having openings therein substantially embedded in the sheet between the elongate element and one surface of the sheet.

2. A reinforced fibrous sheet as claimed in claim 1 in which the elongate security element is substantially exposed at windows in an opposing surface of the sheet at a plurality of spaced locations.

3. A reinforced fibrous sheet as claimed in claim 1 or claim 2 in which the width of the reinforcing strip is in the range of 10 to 20mm.

4. A reinforced fibrous sheet as claimed in any one of claims 1 to 3 in which the width of the elongate element lies in the range of 1 to 4mm.

5. A reinforced fibrous sheet as claimed in any one of the preceding claims in which the papermaking fibres are natural, synthetic or a mixture thereof.

6. A reinforced fibrous sheet as claimed in any one of the preceding claims in which the reinforcing strip is at least partially soluble.

7. A reinforced fibrous sheet as claimed in any one of the preceding claims in which the reinforcing strip is coated, treated or configured to promote its adhesion to the sheet.

8. A reinforced fibrous sheet as claimed in any one of the preceding claims in which the reinforcing strip and elongate security element are bonded together.

9. A reinforced fibrous sheet as claimed in any one of the preceding claims in which the thickness and mesh opening size of the reinforcing strip are such that it provides a tactile effect in the finished sheet.

10. A reinforced fibrous sheet as claimed in any one of the preceding claims in which the reinforcing strip is coloured and/or luminescent.

11. A method of making a reinforced fibrous sheet generally incorporating a continuous elongate security element comprising the steps of continuously depositing fibres onto a support surface to form a sheet, continuously introducing an elongate element and a reinforcing strip of a material having openings therein such that the elongate element is at least partially embedded within the sheet and the reinforcing strip lies between the elongate element and one surface of the sheet.

12. A method as claimed in claim 11 in which the security element is at least substantially exposed at windows in one surface of the sheet at a plurality of spaced locations, said support surface having spaced portions into contact with which the elongate element is introduced before any significant deposition of fibres has occurred.

13. A method as claimed in claim 11 or claim 12 in which the reinforcing strip and security element are introduced simultaneously.

14. A method as claimed in any one of claims 11 to 13 in which the reinforcing strip and security element are bonded together before introduction.

15. A method as claimed in claim 11 or claim 12 in which the security element is introduced before the reinforcing strip such that it is first at least partially embedded within the deposited fibres.

16. A method as claimed in any one of claims 11 to 15 in which the width of the reinforcing strip lies in the range of 10 to 20mm.

17. A method as claimed in any one of claims 11 to 16 in which the width of the elongate element lies in the range of 1 to 4mm.

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

19. A reinforced fibrous sheet substantially as hereinbefore described with reference to and as shown in the accompanying drawings.