EP1466756A2

EP1466756A2 - Improvement of the strength of paper sheets

Info

Publication number: EP1466756A2
Application number: EP04251941A
Authority: EP
Inventors: Paul Howland; Nicholas George Pearson
Original assignee: De la Rue International Ltd
Current assignee: De la Rue International Ltd
Priority date: 2003-04-03
Filing date: 2004-03-31
Publication date: 2004-10-13
Also published as: EP1466756A3; GB0407159D0; GB2400076B; GB0307755D0; GB2400076A

Abstract

The invention relates to improvements in paper, and in particular to the use of watermarks and security elements for strengthening paper sheets and documents made therefrom. The invention therefore provides a sheet having at least four corners and at least four sides joined at said corners, wherein corner reinforcing watermarks are provided at each of said corners. An elongate security element is at least partially embedded within the sheet along and close to an edge of each of at least a pair of opposing sides.

Description

The invention relates to improvements in sheets, and in particular to the combined use of watermarks and security elements for strengthening sheets and documents made therefrom.
Folded or bent corners (dog-ears) on banknotes present a significant problem for many banks, as they can cause problems in cash handling machines and can result in an artificially short note life. Many machines will reject such notes from circulation. One major European central bank has indicated that 80% of the rejections from their machines are due to such corner folds. Notes with folded corners can also be problematic in ATMs and cash dispensers and other note handling equipment. This is becoming a more significant problem as the use of such machines is becoming more and more widespread.
Efforts have been made to resolve this problem by providing note handling equipment with apparatus for flattening banknotes to enable a dog-eared or curled document to be fed without jamming. Such a system is described in US-A-5,265,856.
Another problem which occurs with banknotes in particular results from the tendency of users to roll and fold notes for storage or keeping in wallets and purses. This gives rise to damage at the middle of the edges of the notes and similar problems arise in ATMs and other note handling equipment as occurs with dog-ears and corners.
One solution for improving the life of a banknote has been proposed in WO 03/029003 which includes using a lacquer to reinforce the edge regions of a note, applying a film material to, or embedding, in the paper, or incorporating fibres in the so-called endangered regions of the paper.
It is therefore an object of the present invention to find a way of reducing the occurrences of corner folds and/or middle edge damage.
The invention provides a sheet having corners sides joined at said corners, wherein corner reinforcing watermarks are provided at at least two of said corners and an elongate element is at least partially embedded within the sheet along and at or close to an edge of at least one side.
Thus whilst the corner reinforcing watermarks usefully provide resistance to corner folds, the security elements provide resistance to tears across the sheet. This combination of features can usefully be used to significantly prolong the life of a bank note or other security document.
The invention also provides a sheet having at corners and sides joined at said corners, wherein corner reinforcing watermarks are provided at at least two of said corners and an elongate element is at least partially embedded within the sheet along and at or close to an edge of at least one of the sides.
The invention will now be described, by way of example only, with reference to the accompanying drawings in which:-
Fig. 1 is a representation of a small sheet of paper, such as a banknote, having corner reinforcing watermarks;
Fig. 2 shows different watermarks used for tests;
Figs. 3, 4 and 5 show test results for various tests showing the improvement provided by the invention;
Figs. 6 to 8 show further alternative patterns for corner reinforcing watermarks;
Fig. 9 is a representation of a small sheet, such as a banknote, having edge reinforcing watermarks;
Figs. 10 to 15 are further alternative patterns for edge reinforcing watermarks;
Figs. 16 and 17 are representations of sections of cylinder mould covers used in the manufacture of a sheet of paper having corner reinforcing watermarks according to the invention; and
Fig. 18 is a representation of a small sheet having corner reinforcing watermarks and security threads;
Fig. 19 is a cross section of a portion of the sheet of Figure 18 on the line XX; and
Fig. 20 is a cross section of a portion of the sheet of Figure 18 on the line YY.

paper

It should be noted that, in this specification, "a sheet" can refer to a large sheet of paper which is cut into smaller sheets from which documents, such as banknotes are made; or one of such smaller sheet.
For clarity, the reference to "sides" means the elongate edges joined at the corners of the sheet, rather than the flat planar surface (or faces) of the sheet.
According to the invention watermarks 11 are provided in at least two, preferably adjacent corners of the sheet 10 during the manufacture of the paper. A watermark is created by well known techniques of varying the grammage of paper fibres so that in some areas the fibres are of higher grammage than the average grammage of the base paper layer, and in others they are of lower grammage. When viewed in transmitted light the areas of lower grammage are lighter and the areas of higher grammage are darker than the base paper, and the contrast between the light and dark areas can be very clearly seen.
Watermarks have been widely used as security features, as true watermarks are very hard to counterfeit particularly by photocopying techniques. They are also used as aesthetic features, e.g. in stationery, as complex patterns can be produced by watermark techniques. Traditionally watermarks have always tended to be located in the main body of the sheet or document in which they are produced so that they can clearly be seen. In the present invention, on the other hand, the watermarks are specifically located in the corners of the sheet. This has resulted in the surprising increase in stiffness of the corners which leads to a significant and unexpected reduction in corner folds (dog-ears).
In particular it has been found that watermarks that locally increase the grammage of the paper in the corner of the document significantly reduces its propensity to form dog-ears by increasing the stiffness in this area. One reason for this increase is because of the increase in the stiffness of the paper. It is well known, according to classical beam theory, that the stiffness of an object is proportional to the cube of its thickness, as described in "Pulp and Paper Technology and Treatments of Paper", 1978, page 74 by J d'A Clark, Freeman Publications Inc, San Francisco. Small increases in thickness do thus result in a significantly largely benefit in terms of stiffness. A typical stiffness measurement would be the L&W test as specified in ISO 2493.
Another particularly effective watermark pattern is one that results in lines of higher grammage areas approaching the edges of the paper at between 55° and 35° to the edge perpendicular, and more preferably at 45°.
In tests carried out using handmade paper made using a specially prepared hand sheet mould, which was embossed with seven different patterns, it was found that corner reinforcing watermarks could increase the stiffness of the paper by over 50% in the corners. The patterns tested are shown in Fig. 2. These are marked for convenience as patterns A, B, C, D, E, F, G and a blank control as H. The L&W stiffness was measured at 45° to the vertical on the finished note and the results for each of the patterns as shown in Figure 2.
Figure 4 shows the results for a test developed for this study. The test gives an angle to which a fold relaxes after it has been bent over with a known force. In this case, whether other factors are constant, the watermark increases the fold recovery angle because of the stiffness imparted by the watermark pattern. The results of the specific patterns of Figure 2 are shown in Figure 4.
A further experiment was carried out to determine the probability of forming corner folds (dog-ears) and the results of this test are shown in Figure 5. Again these results show the severity of the fold, shown as "dog-ear index" is least for the six strip pattern F. It was found that the pattern F was the most effective. This was where the watermark comprised a wide stripe pattern with the stripes at substantially 45° to the machine direction (the edges of the sheet 10). The preferred width of the stripes used in the tests was in the range of 1 to 2mm wide and most preferably 1.5mm wide. The second most effective pattern was A which had wavy lines of 2mm width.
The tests showed that the orientation of the elements making up the watermark design is important to give the optimum strength in the direction in which corner folds are likely to form, i.e. 45° to the machine direction.
It was found that the stiffness of the paper increased where the watermark was made from a positive pattern having the effect of adding bulk to selected areas as compared to the thickness of the base paper layer, as opposed to a negative pattern where the main portion was thinner than that of the base paper layer. Not only was the stiffness of the paper found to be increased in the paper made according to the invention, but in tests to measure fold recovery angle, it was found that the improvement in fold recovery was as much as 50% over paper without corner reinforcing watermarks.
Additional patterns which have proved to be effective in trials are illustrated in Figs. 6 to 8.
In a further embodiment of the present invention, watermarks 12 are created either at, or covering, the middle of each edge of the sheet 10, i.e. at North, South, East and West positions of the note when viewed face on. The problems identified previously relating to damage at the middle of each of the edges of banknotes have been found to be significantly reduced by providing such reinforcing watermarks at the middle of each edge, as shown in Fig. 6 because of the increased stiffness and improved fold recovery in these regions. Again, the watermarks 12 are preferably positive and the preferred form include corrugations and/or elements of the design perpendicular to the likely direction of folding or rolling, i.e. parallel to the edges of the sheet 10.
Notes which have both corner and centre edge reinforcing, for example a combination of the pattern shown in Figs. 1 and 9 are preferred, and one of each can be arranged with an adjacent visible watermark 15.
The individual reinforcing watermarks 11, 12 may be discrete, as illustrated in Figs. 1 and 9, or they may be joined together so that the watermark appears as a continuous frame around the whole sheet 10. Alternatively just some of the reinforcing watermarks 11, 12 may be joined, to provide an aesthetic pattern.
It should be noted that machine made paper is produced in continuous webs, which is subsequently cut to form individual sheets. Obviously the pattern of reinforcing watermarks 11, 12 produced on the web will need to be carefully designed to ensure that when the sheet 10 are cut, the watermarks 11, 12 are located at the corners and/or edges of the sheet 10.
In a further embodiment of this invention it has been discovered that the effective thickness of the paper in the document corners and at far edges can also be increased by embossing corrugations at the corner or the edges having the reinforcing watermarks 11,12 in patterns, which may or may not be similar to those of the reinforcing watermarks 11,12. Embossing can preferably be achieved by an intaglio process commonly used for printing security documents.
It has been found that when this combination of techniques was applied to banknotes, corner stiffness increases of up to 250% were achieved, as measured by the L&W stiffness tester. The embossings also provide a useful tactile security check.
Documents in general, and banknotes in particular, can be embossed using the intaglio process. Embossing without the application of ink is sometimes used with a view to producing tactile security features as found on the Dutch 10 Guilder notes issued in 1997. These notes have a series of chevron patterns down the short edges of the notes. Testing carried out on these notes have shown that no improvement in corner fold stiffness was achieved by these embossings. The reason for this is that they are not positioned correctly to achieve such an effect being too far from the paper edge and the lines being too narrow.
The embossings may be produced by an intaglio process, either with or without (blind) ink. The embossings preferably fill an area bounded by at least a length of 10mm on each of the adjacent sides of each corner. More preferably the whole of each corner area is filled. The embossings preferably consist of a plurality of stripes, each having a width between 0.5 and 3mm wide which are separated by gaps having a width lying in the range 0.5 to 3mm. The stripes may be straight, wavy or curved and are preferably parallel.
The stripes of the embossings are preferably at an angle of between 70° and 111°,relative to the line of a corner fold set at 45° to one of the edges, and more preferably at an angle of 90°.
Alternatively the embossings may be provided by uninked die stamping.
The advantages provided by the corner and edge reinforcing watermarks 11 are enhanced in this invention by providing an elongate security element 20 (also known as a thread) along one or more sides of the sheet. The security element 20 is preferably positioned as close to the edge of the sheet 10 as possible, without compromising the integrity of its embedment within the sheet 10. Preferably the distance is at least 1mm. It is also envisaged that the security elements 20 can abut the edge of the sheet.
The sheet 10 may have 2, 3 or 4 corner reinforcing watermarks, and 1 or 2 elongate elements 20. As shown in Fig. 18 each end of a pair of security elements 20 overlaps with a watermark 11, and one or both of the security elements 20 may be partially embedded, so that it/they are exposed in windows 21 at one or both surfaces of the sheet 10, according to well known techniques. Alternatively one or both security elements 20 may be wholly embedded within the sheet 10 by known techniques.
The lower of the two security elements 20 in Fig. 18 is wholly embedded within the sheet 10, whilst the upper one is partly exposed in windows 21. Where the security elements 20 overlap with the corner reinforcing watermarks 11, the less dense areas of the watermarks 11 may be used to reveal the security elements 20, whilst the denser areas form bridges 22 covering the security elements 20. This is shown in Figure 19, whereas the wholly embedded security elements 20 are shown in Figure 20.
In another embodiment a pair of reinforcing watermarks 11 are provided at a pair of adjacent corners (joined by one side - long or short) of the sheet 10, whilst the security element 20 is provided along the opposite sides of the sheet. In yet another embodiment, a security element 20 is provided along the same side as the corner reinforcing watermarks 11, and a third corner may or may not have a reinforcing watermark 11.
In summary, there may be 2, 3 or 4 corner reinforcing watermarks 11 and 1 or 2 security elements 20 or the same or different sides to the corner reinforcing watermarks 11.
The security elements 20 can incorporate any known security features, such as holographics, demetallised or metallised indicia, thermochromics, liquid crystals, magnetic coding, electronic chips, iridescents etc. In addition they may be formed from standard web of plastics material, a scrim of woven or punctured mesh or other such substrates/bases. Suitable plastics materials for the supporting substrate are polyester, polypropylene, BOPP etc.
The security elements 20 provide an enhancement by acting to prevent the initiation of tears in the sheets 10 and, if tears are initiated to prevent their propogation past the security elements 20. Although it is mainly envisaged that the security elements 20 will run along the longest edges of the sheet, it is possible to include security elements 20 along the shorter of any edges.
It is known that cross directional shrinkage of the paper during the papermaking process is greater at the edges of the paper web than in the centre. To allow for this shrinkage profile, while maintaining the dimensions of the document, the forming cloth may be embossed with the reinforcing watermarks overlapping (Figure 16) or adjacent (Figure 17) or at any desired position between.

Claims

A sheet having corners and sides joined at said corners, wherein corner reinforcing watermarks are provided at at least two of said corners and an elongate element is at least partially embedded within the sheet along and at or close to an edge of at least one of the sides.
A sheet having corners and sides joined at said corners, wherein edge reinforcing watermarks are provided at at least two of said sides and an elongate element is at least partially embedded within the sheet along and at or close to an edge of at least one of the sides.
A sheet as claimed in claim 1 or claim 2 in which an elongate element is at least partially embedded at or close to an edge of each of at least a pair of opposing sides.
A sheet as claimed in any one of the preceding claims in which the reinforcing watermarks are positive watermarks.
A sheet as claimed in any one of the preceding claims in which the reinforcing watermarks comprise a plurality of stripes.
A sheet as claimed in claim 5 in which the stripes are straight.
A sheet as claimed in claim 6 in which the stripes are undulating.
A sheet as claimed in any one of claims 5 to 7 in which the stripes of the corner reinforcing watermarks substantially extend at an angle of 45° to the sides of the sheet.
A sheet as claimed in any one of claims 5 to 8 in which the stripes of the edge reinforcing watermarks are substantially parallel to the sides of the sheet.
A sheet as claimed in any one of claims 5 to 9 in which the width of the stripes lie in the range of 1 to 2.5mm.
A sheet as claimed in claim 10 in which the width of the stripes lies in the range of 1.5mm to 2mm.
A sheet as claimed in claim 1 and claim 2 having corner and edge reinforcing watermarks.
A sheet as claimed in any one of the preceding claims in which the reinforcing watermarks are joined by watermark patterns.
A sheet as claimed in any one of the preceding claims in which embossings are provided overlying the reinforcing watermarks in a similar or dissimilar pattern thereto.
A sheet as claimed in claim 14 in which the embossings are provided by an intaglio process.
A sheet as claimed in claim 15 in which the intaglio embossings are uninked.
A sheet as claimed in claim 14 in which the embossings are provided by die stamping.
A sheet as claimed in any one of claims 14 to 17 in which the embossings fill an area bounded by at least a length of 10mm on each of the adjoining sides of each corner.
A sheet as claimed in any one of claims 14 to 18 in which the whole of each corner area of the sheet are filled with embossings.
A sheet as claimed in any one of claims 14 to 19 in which the embossings comprise a plurality of the stripes, each stripe having a width lying in the range of 0.5 to 3mm wide and the stripes being separated by gaps having a width lying in the range of 0.5 to 3mm.
A sheet as claimed in claim 20 in which the stripes of the embossings are substantially parallel to each other.
A sheet as claimed in claim 18 or claim 21 in which the stripes of the embossings are substantially straight.
A sheet as claimed in any one of claims 20 to 22 in which the stripes of the embossings are at an angle lying in the range of 70° to 110° relative to the line of corner fold set at 45° to one of the edges.
A sheet as claimed in claim 23 in which the stripes of the embossings are at an angle of substantially 90° relative to the line of corner fold set at 45° to one of the edges.
A sheet as claimed in any one of the preceding claims in which one pair of opposing sides of the sheet are longer than another pair, and the elongate elements are provided along the longer pair.
A sheet as claimed in any one of claims 1 to 24 in which one pair of opposing sides of the sheet are longer than another pair, and the security elements are provided along the shorter pair.
A sheet as claimed in any one of the preceding claims in which at least one of the security elements is wholly embedded within the sheet.
A sheet as claimed in any one of the preceding claims in which at least one security element is partially embedded within the sheet and exposed at at least one surface of the sheet in windows.
A sheet as claimed in claim 29 in which the windows are provided by less dense parts of the reinforcing watermarks.
A sheet as claimed in any one of the preceding claims in which the elongate elements are located at least 1mm from the closest edge of the sheet.
A security document made from a sheet according to any one of the preceding claims.
A security document made from a sheet according to any one of the preceding claims.