Patent Application
20060127649
This invention relates a security paper for producing value documents, such as bank notes or the like, which comprises a creasable, multilayer substrate comprising at least one paper layer and at least one film, and to a method for producing such a security paper.
Value documents according to the invention are bank notes, check forms, shares, certificates, postage stamps, air tickets, labels for product protection and the like. The simplifying designation “security paper” or “value document” will hereinafter therefore always include documents of the stated type.
Bank notes are normally manufactured from so-called security papers consisting of cotton fibers and having special security features, such as a security thread at least partly incorporated into the paper, and a watermark. The period of circulation of a bank note depends on how much it is stressed. Certain denominations are preferably used in trade and thus have a shorter period of circulation due to the stronger load through environmental influences. The main cause for a restricted period of circulation of bank notes is seen to be early soiling. Since bank note paper is very porous, it has a large surface area or high surface roughness. Even if the resulting projections and cavities are in orders of magnitude that cannot be resolved by the human eye, they offer ideal conditions for dirt deposits in comparison with a smooth surface.
It has therefore been suggested in WO 98/15418 to manufacture bank notes completely from a plastic substrate. However, in this case the usual and time-tested security elements such as portrait watermark and windowed security thread must be forgone, as well as the special properties such as sound and feel of bank note paper. Also, the steel gravure printing usual in the bank note sector, which serves as an additional tactile authenticity mark due to the relief arising from the inking, leads only to a flat, hardly noticeable relief on plastic substrates. Moreover, pure plastic bank notes are very sensitive to heat, so that plastic substrates have a strong tendency to shrink particularly in countries with unfavorable climatic conditions. In particular with regard to falsification security, plastic bank notes have the decisive disadvantage that the substrate is readily available and can be procured by anyone.
WO 96/28610 has suggested lacquering, i.e. coating, paper bank notes as an alternative. This does reduce the soiling problem but cannot increase the mechanical stability of a substrate.
Multilayer substrates comprising a film core coated on both sides with paper plies have also been proposed. The strength of this laminate is increased in comparison with a pure paper substrate, but the soiling problem with the exterior paper layers is not solved. So as not to excessively increase the total thickness of such bank notes, the paper plies must moreover be designed very thin, so that the usual security features such as security thread or watermark can no longer be optimally incorporated.
The problem of the invention is therefore to produce a security paper that is dirt-repellant, has increased mechanical strength and therefore a high period of circulation, and has increased falsification security.
The solution to this problem results from the disclosure herein.
According to the invention the security paper comprises or consists of a creasable multilayer substrate comprising at least one paper layer and one film, the film being equipped with at least one security feature.
The multilayer substrate is a creasable structure which has the bending and folding properties of a sheet and is not rigid and barely flexible like a card. In particular, the substrate is to have the feel and sound of paper as far as possible.
In the simplest case the substrate consists of two layers, namely a paper layer and a film at least partly applied to one side of the paper layer. Neither the paper layer nor the film layer is necessarily formed all over. To maximize the protective properties of the film, the film will preferably cover the paper layer all over. This also applies to other multilayer substrates with more than two layers.
It is preferable to use a layer structure in which a paper layer is covered on both sides with film, preferably all over. That is, the substrate has a paper core whose surfaces are covered with film at least partly, preferably all over.
The type of paper layer need not fulfill any conditions, so that usual papers made of annual fibers, in particular cotton fibers or cellulose fibers, can be used, as well as papers consisting at least partly of synthetic fibers, preferably polyamide fibers.
The paper layer normally has a weight of from 50 to 100 g/m2, preferably from 80 to 90 g/m2. Any suitable weight can of course be used depending on the mode of application.
The paper layer can be of single-ply or multi-ply construction. In case of multi-ply paper layers, the paper layers can consist of the same or different paper types and be in turn combined with plastic films. Hereinafter “paper layer” will refer to both the single-ply and the multi-ply variants.
Furthermore there is the possibility to provide the paper layer all over or as single partial areas. A film can e.g. cover an interrupted paper layer or several separate partial areas of paper.
The paper layer is preferably produced on a cylinder paper machine.
The paper layer can additionally be equipped with security features to impede imitation of the security paper.
The security features can be applied to the paper layer or incorporated within the volume of the paper layer.
If the security features are to be incorporated within the volume of the security paper, the features in question are preferably already incorporated into the paper pulp during papermaking.
As a classic security feature, in particular a watermark is incorporated into the paper layer. Alternatively or additionally, security threads can be incorporated into the paper. A so-called windowed security thread, which appears on the front and/or back of the paper layer, must be regarded as particularly suitable for improving security. It is also conceivable to incorporate the security thread into the laminate in such a way that it comes to lie completely visibly between the paper layer and the film. Said security thread is incorporated for example during production of the laminate and can be fixed on the paper ply by composite adhesive and the film.
A security feature incorporated within the paper volume can be a feature substance with a visually and/or machine detectable physical property. The substance can have for example magnetic, electroconductive, luminescent, light-diffractive, light-polarizing, photochromic, thermochromic or light-interfering properties, and can be uniformly distributed all over or incorporated in the form of patterns. The luminescent feature substances can be for example luminescent substances that are excitable with UV light and emit in the visual spectral range. In the case of a machine check, however, luminescent substances also emitting in the invisible spectral range, preferably the IR spectral range, can be used.
Besides security features incorporated within the volume, security features can also be applied to the paper surface preferably as a print. One side or of course both surfaces of the paper layer can be equipped with security features.
Said security features can firstly be the abovementioned visually and/or machine detectable ones. Secondly, it is particularly suitable to use intaglio printing, which produces on the print substrate during the printing operation a typical relief which is readily palpable. If coated with a very thin film, the relief is palpable in the paper despite the film. Intaglio printing can be done with ink and/or as blind embossing.
Likewise, optically variable security elements can be provided on the paper. Optically variable elements or printing inks that show a viewing angle-dependent interplay of colors due to light diffraction or light interference need a background as smooth as possible for good visibility of this effect, so that when they are applied to paper it must often be pretreated with a primer layer first. Security elements of this kind are for example holograms, Kinegrams® or other diffraction structures, filmlike liquid crystal or interference layer structures, but also printing inks containing interference layer or liquid crystal pigments or other special-effect pigments, such as lustrous metallic effect coloring pigments. Simple metal layers or metallic effect prints are also conceivable.
The security features applied to at least one surface of the paper can also be present in the form of a coding. This is expedient in particular in the case of printed security elements.
By using a plurality of feature substances and/or varying the concentration of one or more feature substances in corresponding printing inks it is very easy to produce any desired codings on the security paper, for example in the form of a bar code. Said coding can constitute for example an independent additional security feature or serve as a comparative feature for other data already provided on the security paper. Thus, information visually visible on the bank note, such as denomination, the name of a person shown in the portrait, or the like, can be encrypted and stored on the paper invisible to the eye in the form of the coding. In a machine check the coding is read, decrypted and checked for identity with the corresponding, visually visible information.
Further, there is the possibility of writing information into the paper by laser. Depending on the intensity of laser energy, different gray, brown and black shades can be produced with which in particular portraits can be represented. Alternatively, microwriting can be done, in which the individual letters have maximum dimensions of 100 μm.
At least partially covering the paper layer with a film prevents open access to the security features applied to or incorporated in the paper layer, so that falsification security is considerably increased.
Either only one surface of the paper layer or both surfaces can be equipped with film. The paper layer is preferably covered completely by the film to obtain optimal surface protection.
The film is a plastic film, preferably of polyethylene terephthalate PET or oriented polypropylene OPP. Any other suitable plastic substrate is of course also usable. Depending on the application, the films can have a matted or glossy finish. A special variant of the matt/gloss effect on a film can be produced e.g. by coating a glossy film in certain areas with a photoresist, then etching the film surface, and subsequently removing the photoresist. The film is still glossy in the area of the originally applied photoresist, while the surface appears slightly etched and therefore dull in the areas without photoresist.
The film has a thickness of preferably 1 to 20 μm, particularly preferably 6 to 15 μm. Depending on the application, films only 6 μm thick can also be used. In this case the typical properties of a paper sheet, such as creasability and foldability, can be particularly effective.
The films serve to improve the mechanical strength of the security paper, among other things. To increase this further, in particular also to improve edge tear ability, the films used can have different stretch. In particular the films applied to different sides of the paper layer considerably increase edge tear resistance when they have different stretch.
Besides the ability to increase mechanical stability and dirt repellence of a security paper, the films can also decisively contribute to improved falsification security if equipped accordingly with security features.
The films can, like the paper layer, be equipped with security features that are applied to the film surface and/or incorporated within the volume of the film.
A security feature incorporated within the film volume can be a feature substance with a visually and/or machine detectable physical property. The substance can have for example magnetic, electroconductive, luminescent, light-diffractive, light-polarizing, photochromic, thermochromic, or light-interfering properties, and can be uniformly distributed all over or incorporated in the form of patterns. The luminescent additives can be for example luminescent substances that are excitable with UV light and emit in the visual spectral range. In the case of a machine check, however, luminescent substances also emitting in the invisible spectral range, preferably the IR spectral range, can be used.
In the case of security features applied to the surface of the film, the security feature can come to lie on the side facing away from the paper and/or the side facing the paper. With a three-layer substrate, the security feature would therefore be present on one surface of the film either on the outer side of the substrate or on the inner side thereof. In particular security features that enter into a less firm bond with the film preferably come to lie on the inner side of the laminate, so that the poor accessibility impedes forgery.
The security features applied to the surface of the film can be the abovementioned visually and/or machine detectable security features.
Likewise, optically variable security elements can be provided on the film. Optically variable elements or printing inks showing a viewing angle-dependent interplay of colors due to light diffraction or light interference need a background as smooth as possible for good visibility of this effect, as particularly films offer. Security elements of this kind are for example holograms, Kinegrams® or other diffraction structures, filmlike liquid crystal or interference layer structures, but also printing inks containing interference layer or liquid crystal pigments or other special-effect pigments, such as lustrous metallic effect coloring pigments. Simple metal layers or metallic effect prints are also conceivable.
The security features applied to the film can also be present in the form of a coding, as already described in detail in connection with the paper layer.
A security feature that can be applied to the surface of the film can also be e.g. a special print.
A particularly suitable special print is an intaglio print, in which a readily palpable relief surface is produced. The print can be done firstly on the fully laminated multilayer substrate, so that the finished laminate can thus be processed and printed like a conventional security paper. Intaglio printing can be done with ink and/or as blind embossing.
Secondly the film can be printed separately before it is incorporated into the laminate, and only be applied to the paper layer after the printing operation.
As explained in connection with the paper layer, information can also be written into the film by laser.
Of the optically variable elements or printing inks, in particular metallizations of the film are suitable, possibly in combination with diffraction structures. The metallization can be of opaque or semitransparent design, the semitransparency being obtained by very thin metal layers or by rasterization of the metal layer. “Semitransparency” refers here to translucency, i.e. the metallization normally has a light transmission of under 90%, preferably between 80% and 20%. There is further the possibility of using or combining different colored metallizations. Aluminum and/or copper are particularly suitable for metallization. The metallization directly applied to the film shows the decisive advantage of extremely high brilliance. This can be explained by the extremely smooth surface of the film, which allows particularly directional reflections in the security feature. In contrast, such metallizations on paper always appear duller, since the unevenness in the paper causes disturbances in the reflection.
These highly reflective metallizations of the film are preferably produced only partially by the so-called washing method, as described in WO 99/13157, to which reference is expressly made.
If the metallizations are additionally provided with e.g. embossed diffraction structures, this results in extremely brilliant holographic effects which cannot be produced in conventional fashion.
Such security features are particularly safe from forgery if the film is applied to the paper such that the security features come to lie on the inner side of the laminate and are thus not accessible from outside.
In a further preferred embodiment, the film is provided at least partly with a microperforation, so that the film is preferably destroyed upon mechanical tampering. The microperforation is substantially invisible in particular within the laminate. The perforation can be provided only in a partial area of the film, but also extend over the whole film surface. Any pattern can of course be produced by means of the perforation, it being preferable to use perforated lines which make the film tear particularly easily upon attempted tampering. Alternatively, information, e.g. letters or portraits, can be perforated instead of lines.
The perforations are preferably made in the film before lamination of the film onto the paper layer. This has the advantage that inclusions of air and thus folds and warps of the film are avoided during lamination. The perforation can be realized by means of heatable needle rollers, which results in holes in the order of magnitude of a few μm. Perforations of considerably smaller dimensions, namely at most 1 μm in diameter, can be obtained by laser or corona treatment. Sharp-edged embossing is also possible for producing perforations.
In a further variant, the perforations can also be made on the film already applied to the paper layer. The perforation can optionally be additionally present in the paper layer.
The form of the produced holes is arbitrary and can have for example circular or linear dimensions.
The film can be applied to the paper layer by different methods, such as extrusion of the film directly onto the paper web or lamination.
The films are preferably cold-laminated onto the paper ply. An adhesive is applied to the film, partly dried and optionally activated by temperatures of preferably at most 80 to 90° C. The film is in particular not partly melted or excessively loaded by heat. This has the advantage that stretches of the films, if any, are not destroyed but are still present after lamination.
Lamination, preferably cold lamination, ensures a firm, inseparable bond between paper and cover layer.
The laminating process is carried out via roller lamination so that very thin films with a thickness of few μm can also be laminated onto the paper layer without problems, such as bubbles or warps.
The choice of security features of the paper or the film and also the combination thereof is possible without restriction.
The paper layer and the film are inseparably interconnected preferably with an adhesive. The adhesive is preferably a water- or UV-crosslinking adhesive. It is particularly preferable to use a wet adhesive, in particular a polyurethane adhesive.
The adhesive can also be processed in very large quantities without damaging the properties of the laminate. The processing of large quantities has the advantage that security features can be incorporated into the adhesive very easily and in sufficient quantity.
The adhesive is preferably applied in quantities of from 6 to 9 g/m2 and side of paper or film.
Like the paper layer and film, the adhesive can be equipped with security features. The security features expediently used here are ones that can also be incorporated within the volume of the paper or film. The security features can be feature substances with a visually and/or machine detectable physical property. The substances can have for example magnetic, electroconductive, luminescent, light-diffractive, light-polarizing, photochromic, thermochromic or light-interfering properties, and can be uniformly distributed all over or be incorporated in the form of patterns. Fluorescent substances or so-called ColorShift flakes with a thin-film structure are particularly suitable.
The adhesive layer can be varied in its optical properties depending on the application case. The adhesive can e.g. be of transparent to opaque design. Furthermore, it is possible to adapt the color of the adhesive to the application case.
The adhesive can be applied in either one layer or several layers. The film is preferably equipped with the adhesive and then the adhesive-coated film applied to the paper layer. The adhesive layers can be processed either all over or in sections as long as a firm bond in the laminate is obtained.
For example, the first adhesive layer with a first feature substance can be applied to the film all over, while a second adhesive layer with a second feature substance is applied to the first adhesive layer only in sections e.g. in the form of a coding. Likewise, the single pieces of information incorporated into different adhesive layers can complement each other to form total information.
Alternatively, different-colored adhesives can be processed, so that the adhesive layer has a rainbow pattern in a thus equipped value document. Such a rainbow pattern can be produced e.g. by gravure printing with three differently inked cylinders.
The adhesive moreover has an advantageous effect on other security elements, in particular on the optical appearance of watermarks and security threads in the paper layer. The contrast in the light/dark areas of the watermark appears much more clearly in comparison with conventional watermarks in uncoated paper. The normally used gaps in the metallic coatings of security threads can also be recognized much more easily in transmitted light.
This contrast-enhancing effect is possibly due to the fact that the adhesive penetrating into the paper layer changes the refractive index. This is merely a tentative explanation and not a scientifically confirmed fact.
Since it is possible to equip paper and/or film and/or adhesive with security features, it is also possible to combine the security features present in the individual layers such that they complement each other to form total information or else are incorporated in register. Likewise, special color effects can result, for example.
Thus, parts of a coding, such as some of the bars of a bar code, can be printed on the paper layer and the other part incorporated within the volume of the film. Likewise, writing or picture information can be divided up into single areas, the single areas being incorporated into different layers, possibly even with different security features.
In a special variant, the complementing of security features in different layers to form total information can also be used for self-authentication. In particular in the embodiments where the film and the paper layer do not completely overlap, the film and the paper layer can e.g. be provided with respective printed patterns that complement each other to form a total pattern when they overlap.
By overlapping watermarks in the paper web with colored films it is thus also possible to produce watermarks appearing colored.
Watermarks in the paper can also be combined with the above-described metallization. If watermarks with particularly bright places are used, so-called highlight watermarks, and they are overlapped e.g. with a semitransparent metal stripe located on the film, only the metal stripe can be recognized in reflection but the watermark can be recognized through the metal in transmission. These reflection/transmission effects are suitable in particular as easily recognizable human features.
The present creasable multilayer substrate avoids the disadvantages stated in the prior art. In particular, by combining paper and film the substrate unites the positive properties of both substrate types. Firstly, the mechanical strength and dimensional stability of the substrate are ensured. Shrinkage of the film is excluded with the help of the paper layer, while the paper is given additional support by the film. In particular the edge tear strength is considerably improved. Exact adaptation of paper layer, film and adhesive moreover ensures firm cohesion of the individual layers, so that splittability is considerably reduced or even impossible. On the other hand, the film prevents excessive soiling of the paper surface, thereby increasing the period of circulation. The film coating moreover leads to increased falsification security, since the security features in the paper, but also partly the security features in the film, come to lie inside the substrate and are thus no longer accessible from outside, and are optionally also disposed in a complex mutual relationship. Further, coating the paper with adhesive and film leads to an improved quality of single security features, as explained above with reference to the watermark and security thread. Despite the many advantages based on film properties, the advantages provided by paper need not be forgone. Thus, despite the film coating the properties of feel and sound normally desired in security paper remain largely unchanged.
Further advantages and embodiments will be explained in more detail with reference to the figures. It is pointed out that the figures show the layer structure of the inventive security paper only schematically. The proportions shown in the figures do not necessarily correspond to the relations existing in reality and serve primarily to improve clearness.
As shown in
However, a plurality of feature substances that are singly detectable can also be provided. An additional coding can be produced via the mixing ratio of the feature substances.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102-43-653.3 | Sep 2002 | DE | national |
This application is a National Phase of International Application Serial No. PCT/EP03/10427, filed Sep. 18, 2003.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP03/10427 | 9/18/2003 | WO | 11/14/2005 |
