The present invention relates to a method of πanufacturing bank- 5 notes, and also to banknotes.

The object of the inventive banknote manufacturing method and the inventive banknote is to prevent the forging of banknotes.

10 Banknotes have been forged throu out the ages, the most usual method being to print forged banknotes. Various methods have been developed over the years to produce banknotes which will be recognizable as genuine when checked. Examples of such techniques include the inclusion of watermarks, the dispersion of coloured fibres in the banknotes, the

15 use of dyes which fluoresce when irradiated with ultraviolet light, magnetic pigments, the use of radioactive isotopes, security prints in the form of so-called guioches, etc.

It can be said that methods of producing a banknote which can be 20 dete-πr-ined as genuine or a forgery when carefully checked have been sufficiently developed. Many of these methods, however, require the use of special equipment or require the banknote to be studied care¬ fully and thoroughly.

25 One problem that has arisen in recent times is caused by another technique, namely the copying technique, which has been developed rapidly and to a level such that colour copying on cαramercially available colour copiers achieves a banknote copy of very high quality. In fact, the quality achieved in a modern colour copier is so high

30 that a banknote provided with a complicated colour pattern can be copied with such excellence that a person who looks at the banknote will not suspect the banknote of being a forged banknote. In recent years, a large number of forged banknotes produced on normal, commer¬ cially available colour copiers have been discovered in subsequent

35 checks.

The existing problem is actually not one of providing the banknotes with a refined proof of being genuine, but instead lies in the fact

that the banknotes are not checked at all, or only summarily, by the person receiving a banknote when the banknote is tendered as a standard form of payment. Thus, it would appear that despite all refined proof of being genuine, a forged banknote needs to deviate markedly from a genuine banknote in order for the person receiving the banknote to notice that the banknote offered deviates from the genuine article, even when making a quick check, therewith calling for a closer check.

Apparently, a banknote which is produced on a modern colour copier is sufficiently similar to a genuine banknote to enable the banknotes to be printed in large numbers and used as a means for payment.

The present invention solves the problem created by colour copiers by proposing a banknote which cannot be reproduced by a colour copier without the produced copy being readily identifiable as a forgery, when taking a quick look at the banknote.

The present invention thus relates to a method for producing a banknote in which the banknote is produced from paper pulp and provided with a fibre-thinned region, similar to the region of a so-called watermark, and is characterized in that a reinforcement in the form of a material having a higher mechanical strength than the paper fibres is introduced in at least one region of the banknote during its manufacture; in that the paper fibres in at least one part of said region are thinned- out to an extent such that together with the reinforcement they form an optical window through which the irradiating beams of a colour copier are trarismitted forwards and backwards; and in that one or more signs or figures are printed in the region of said optical window within said window and preferably only on one side of the banknote, these signs or figures being asymmetrical so that when copying one side of the banknote the sign or figure printed on the opposite surface of the banknote will appear on the copy in a mirror- image form.

The present invention also relates to a banknote of the kind having the characteristic features set forth in Claim 8.

The invention will now be described in more detail with reference to an exemplifying embodiment thereof and also with reference to the accompanying drawing, in which

- Figure l is a schematic illustration of a paper machine with which the invention is applied; Figure 2 shows part of a cylindrical wire;

Figure 3 is a cross-sectional view of a banknote shown in exag¬ gerated scale; - Figure 4 is a top view of a banknote; and

Figures 5 and 6 illustrate an optical window.

When manufacturing a banknote from paper pulp in accordance with the present invention, the same technique is used as that by means of which watermarks are produced, wherein the banknote is provided with one or more regions in which the fibres are thinned out.

According to the present invention, there is -introduced into the banknote a reinforcement which is comprised of a material that has a higher mechanical strength than the paper fibres in at least one region of the banknote during its manufacture, wherein at least a part of this region of the paper fibres is thinned out to an extent such that said fibres together with the reinforcement form an optical window through which the irradiation beams of a colour copying process are transmitted forwards and backwards.

The optical window can be said to be a watermark with extreme fibre thinning in c-αmparison with what is normal in the case of watermarks. In addition, one or more characters or figures are printed on the banknote in the region of the optical window preferably on one side of the banknote, these signs or figures being asymmetrical so that when copying one side of a banknote the sign or figure printed on the opposite of the banknote will appear on the copy in mirror-image form.

Figure 1 illustrates schematically a paper machine 1 of the kind which is equipped with a cylindrical wire which functions to draw water from the paper pulp 3 that comes into contact with the cylinder wire. The thus dewatered paper pulp is stripped from the wire 2 as a

continuous web 4 which passes to a station in which it is processed to a finished paper in a known manner.

According to the invention, the aforesaid rei-nforcement is introduced in conjunction with stripping the paper web from the wire 2. Although this can be accαπ-plished in different ways and at different stages, it is preferably effected by storing a continuous web of reinforcement material 5 on a reel 6 and moving the reinforcement web down into the paper pulp and over the wire 2, so that the reinforcement web will meet the wire when paper pulp has already been deposited thereon but when additional paper pulp will be deposited on top of the reinforce¬ ment web, thus embodying the reinforcement web in the paper.

As before mentioned, the re forcemeπt shall be stronger and of greater mechanical strength than a thinned region of paper fibre. Furthermore, the reinforcement shall be sufficiently transparent to light for the light in a copying machine to be transmitted reciprocatingly through the optical window.

According to one preferred embodiment of the invention, the reinforce¬ ment is comprised of a fibre glass net or a plastic net. Plastic film may also be used.

Since an optical window is required only over a part of the surface of the banknote, it is proposed in accordance with one preferred embodiment of the invention that the reinforcement web is given a smaller width than the banknote, said web 5 being placed in the transport direction 7 of the paper web.

However, the web 5 may have the sane, or essentially the same width as the banknote. This provides the advantage of reinforcing the whole of the banknote.

Figure 4 illustrates a narrower web (shown in broken lines 8, 9) embodied in a banknote 10.

An optical window is produced by greatly thi-nning out the paper fibres. This is achieved in a similar manner to the process of

producing watermarks, i.e. by providing the wire 2 with promontories 11, 12, which may be formed from foam rufcfoer or some other suitable material. Figure 2 shows only a part of the wire periphery. The amount of paper pulp deposited on the wire at these promontories 11, 12 will be smaller than the amount of paper pulp deposited between said promontories. Consequently, the paper fibres in the finished paper will be thinned-out in those regions which correspond to the positions of the promontories. The promontories 11, 12 may, of course, have a form which corresponds to the form of the desired thinned region.

Figure 3 illustrates schematically part of a banknote 10 in cross- section, the reference numeral 13 identifying paper and the reference numeral 14 identifying the reinforcement. The reinforcement is shown in broken lines. The fibre-thinned regions are referenced 22.

Figure 4 illustrates different examples of optical windows, all of which are located in the region where the banknote is reinforced by means of the reinforcement 14, in accordance with the invention.

According to one preferred eir-bodiment, a clear varnish or the like is applied to the banknote over the optical window or windows 15-21, prior to printing the banknote. This clear varnish covering improves the transparency of the optical windows.

When a character, sign or a figure is printed on one side of the optical window of the banknote, this print will be reproduced on a copy made from the banknote. When, for instance, the sign "SE" is printed on the rear side of the banknote, in accordance with Figure 5, this sign will appear on the front side of the banknote copy as a mi-rror-image of the sign, as shown in Figure 6.

Provided that the optical window or optical windows is/are sufficiently large, a person studying the banknote will immediately obtain a very strong impression that the banknote is not genuine. In actual fact, even a very quick look at the banknote will tell people who are not used to studying banknotes closely that something is wrong. This is particularly true when the sign or signs printed on the rear side of

the banknote is/are alphanumerical signs, since people are quite used to seeing such signs.

The sign or figure used is not of particular interest, the essential criterion being that the sign or the figure concerned will immediately and subconsciously alert the attention of the viewer.

This makes it very easy for a person to discover that a banknote copy is not a genuine banknote. Naturally, the banknote shall also be provided with conventional security devices, such as those mentioned in the aforegoing, in order for a closer study to establish whether the banknote is genuine or not.

The presence of a highly-transparent optical window will mean that a banknote with which the forger has attempted to "fool" the copier by, for instance, taping over the window and replacing this part of the banknote with a part that corresponds to an apparently genuine bank¬ note, will have a different appearance, since an optical window has a certain, or significant degree of transparency. In other words, it is extremely difficult, if not impossible, to forge the inventive banknote with the aid of colour copiers.

According to one highly preferred embodiment, banknotes of different denominations are produced such that each of the denominations will have a unique combination of the number and/or the shape of the optical windows. This is illustrated in Figure 4 with the windows 19-21 or the windows 16-18. For instance, the number of windows 19-21 may be different for different banknote denαminations. Furthermore, the shapes of the windows may be different for different banknote de- nσmi-nations, the windows 15-18 exemplifying different shapes.

This enables the deriomination of the banknote to be quickly seen or felt. This is highly advantageous when studying banknotes optically, since the permeability to light is much greater in the optical windows than in the remaining part of the banknote. The present invention thus provides a simple and positive method of reading banknotes optically.

-According to another preferred e-τibodiment of the invention, the fibres are thinned in those regions where optical windows are to be produced, to a degree such that the finished paper will have a measur¬ ably t_hinner thickness at the region of the optical windows in than over the remainder of the banknote. This feature can be used in two ways. For example, the thickness of the banknote can be measured mechanically with known thickness measuring techniques, and therewith determine the der tiination of the banknote. This is particularly advantageous when each de-rKimination has a unique combination of optical windows with regard to size and/or shape. It is also, however, beneficial to the partially sighted or blind person when the difference in thickness is sufficiently great to enable the person concerned to feel the combination or the number of optical windows with their fingertips and therewith determine the denomination and genuineness of the banknote.

It is said in the aforegoing that the reinforcement is preferably comprised of fibre glass net. It will be obvious to the skilled person, however, that other materials can be vised to reinforce the paper to an extent which will compensate for the reduction in strength caused by thinning the fibres. The invention is therefore not re¬ stricted to any particular type of reinforcement.

It has earlier been mentioned that clear varnish can be used to make the optical windows more transparent. However, wax or some other suitable substance can be used instead, to provide the same effect.

The present invention shall not therefore be considered restricted to the aforedescribed and illustrated exemplifying embodiments thereof, since modifications can be made within the scope of the following Claims.