EP0486065B1 - Security paper and process for making the same - Google Patents

Abstract

The invention relates to a security document having an integral security element, preferably an optically variable element in the form of hologram, diffraction or interference structures applied to the paper surface, and to a process for making such a security document. The security document is characterised in that the optically variable element is embedded in the security document, the paper surface forming one plane with the surface of the optically variable element.

Description

The invention relates to a security with an embedded security element, preferably an optically variable element in the form of hologram, diffraction or interference structures applied to the paper surface. The invention further relates to methods for producing such a security.

To protect against counterfeiting with color copiers, securities are increasingly being equipped with optically variable security elements, in particular holograms. The protection against counterfeiting is based on the insufficient reproduction of the optical properties of such elements by the color copier.

Various methods are known for applying the optically variable elements to the security; they can usually be divided into three categories: gluing, transfer printing and embossing.

When gluing, adhesive labels, which are initially pre-punched on silicone paper, for example, are transferred to the paper substrate. The adhesive labels have at least one layer structure, which is composed of a pressure-sensitive adhesive layer, a self-supporting film of an optically active layer (for example with a diffraction grating) and an overlying protective layer. The thickness of an adhesive label is typically around 50 micrometers, with the major part of the thickness being attributable to the carrier film.

In transfer printing, also called hot stamping, the optically variable element is prefabricated on a transfer belt and transferred to the substrate in a subsequent step. The structure transferred to the paper typically has a thickness in the range of a few micrometers. In the case of holograms, the usual layer structure of the element consists of a hot-melt adhesive layer, an embossed lacquer layer, an aluminum vapor deposition layer and a transparent protective covering layer. This layer structure is initially on the transfer film, and is attached to the film with a release layer (for example a wax layer). For the transfer, the tape with the hot-melt adhesive layer is placed on the substrate; the hot-melt adhesive layer is activated by pressing on a heated stamp, so that the element connects to the substrate. At the same time, the separating layer melts, causing the hologram to detach from the transfer belt. The transfer principle is the most frequently used method today and in particular is also usually used to apply holograms to plastic credit cards.

The embossing process is particularly suitable for diffraction elements such as holograms and optical gratings. Here, a layer of a curable lacquer is applied to a substrate, which is preferably provided with an extremely thin and reflective metal surface. The diffractive relief structure is embossed into the lacquer layer with an embossing stamp. After the lacquer has hardened, the structure is covered with a protective lacquer. The finished element has a layer structure consisting of the successive layers of lacquer with a metal layer and relief structure and the protective lacquer layer.

Each of the known processes and the products manufactured with them have their specific advantages and disadvantages. Adhesive labels, for example, are technically simple to produce and can be transferred to the intended substrates without any problems. Extremely disadvantageous for an application in the securities sector with adhesive labels, however, is the possibility of detaching the elements as a whole from the substrate and transferring them to counterfeit products. For this reason, the transfer and embossing elements are preferred for security applications.

The transfer and embossing elements largely meet the counterfeit protection requirements required in the securities sector, but there are a number of technical problems in the production of securities with these elements.

It has to be taken into account that securities usually have a high-quality security image, in most cases these images are applied using steel intaglio printing. Gravure printing and related processes require a relatively high surface roughness of the substrate in order for the printing inks to bond well to the substrate. Rough surfaces are unsuitable for the application of the less stable optically variable elements. The sensitive hologram structures are in fact very negatively influenced in their quality by rough surface structures.

It should also be noted that the entire surface of the security is subjected to a very high pressure load during gravure printing. Any optical elements that may have been applied before printing are hereby usually reduced in their optical effect and can be caused by the roughness of the paper which is characterized by the paper substrate even damaged or completely destroyed.

In the production of securities with optically variable elements, this problem either equips the security with the printed image first and applies the hologram in one of the subsequent work steps, or the application of the elements is broken down into individual steps, taking the measures not endangered by the steel intaglio printing process before printing and the others only after printing. With such a procedure, it was previously consciously accepted that the direct coupling with the printing process on the one hand made it impossible to prefabricate unprinted securities with optically variable elements (no production on stock), and on the other hand to apply the optically variable elements per printing line special machines (transfer machines etc.) are required. The special machines required per printing line not only increase the costs and the space required for the machine park, but due to the different production capacity at the end of the printing line each create a bottleneck that can only be compensated for with increased additional machine expenditure.

From EP-A-0 338 378 such a system for manufacturing paper products is known which has both a printed image and an optical diffraction element. In a continuous process, the paper is first printed in known printing units. A radiation-curable lacquer is then applied in a single operation, analogous to the embossing process described, and provided with a diffraction structure. In subsequent operations, the diffraction structure is vaporized with a reflective metal layer and provided with a protective lacquer.

In other known systems, the hologram application process is divided into two. Following the paper production, the lacquer is applied to the paper surface in a first sub-step. After printing on the paper, the optical grid is embossed in the next sub-step.

A variant of this two-part process is described in US Pat. No. 4,420,515. A metal layer and an overlying adhesive layer are first applied to a plastic transfer belt with a prepared surface; these two layers form the substructure of the future security element. In the first sub-step, the two layers are laminated onto the substrate, the substructure of the element assuming the surface quality of the transfer tape under the action of heat and pressure during the lamination process. In the second sub-step, a printed image and an optically acting relief structure are applied to the substrate.

As already indicated, the forced sequence of printing and application of the optically active layers or the application of the optically active structures leads to a number of serious disadvantages.

Another disadvantage of the known methods is their difficult integration into the organizational process of security printers. For security reasons, it is practically inevitable in the production of securities that the printing process, in particular the printing of the serial number, represents the last processing process before the delivery of the securities. It is therefore customary in securities printing houses to prefabricate paper with the associated security features such as watermarks, security thread and any optical elements and then to print on it.

It is also not possible to maintain this production sequence in the known methods.

From GB-A-2103 669 a security paper is also known, in which security elements are introduced. For this purpose, the elements located on a carrier tape are introduced into the resulting paper mass together with the carrier tape during the manufacturing process of the security paper. In this process, the water-soluble or porous carrier tape is embedded in the resulting paper together with the security element. However, this method has the disadvantage that the carrier tape now lying in the paper in the area of the security element leads to a thickening of the security paper.

The invention is therefore based on the object of specifying a security with a security element, in particular an optically variable element and method for its production, in which a subsequent printing of the security, in particular in steel intaglio printing, is possible without the optically variable element being damaged and which prevents the thickening of the security paper from occurring in the immediate vicinity of the security element.

The application of the optically variable elements to the security is to be integrated into the paper production in such a way that it is possible to work with comparatively fast-working reel machines. Finally, the application of the optically variable elements should be integrated into existing production processes in such a way that existing machines have to be changed as little as possible.

According to the invention, this object is achieved by the features mentioned in the characterizing part of claims 1, 5 and 11. Advantageous further developments are the subject of dependent claims.

The invention is based on the knowledge that optically variable elements and paper are two materials with extremely different properties and that, depending on the intended function, different requirements are placed on the two materials. Paper, in particular security, has, among other properties, a certain "grip", and the paper can also accept and bind printing inks. These properties are achieved by choosing special types of paper, preferably rag paper, and by setting a predetermined surface roughness and structure. In contrast, optically variable elements must have optical properties with the highest possible efficiency. For this, however, the physical laws primarily require surface structures that are characterized by a more smooth and flat surface.

When the optical elements are applied to paper, there is therefore always the risk that the surface roughness of the paper will be imprinted in the sometimes very sensitive layers of the surface element and thus damage, impair or even destroy them. As a rule, a balance between the different surface qualities is necessary to prevent such an impairment.

In contrast to the previous procedure, in which the optically variable elements were only ever imprinted, glued or transferred onto the security after the actual production, the invention teaches that the optically variable element should already be connected to the security during paper production, specifically in the state in which the security is still relatively damp, soft and has not yet been squeezed or calendered. In contrast to the dried and hardened state of the paper, it is possible in this phase to also press a pressure-sensitive, optically variable element into the paper mass without causing any damage. The still high water content in this phase of production has a pressure-equalizing effect and enables the element to be embedded evenly in the paper pulp.

In contrast to the subsequent application of the optically variable elements, the surface roughness of the paper does not characterize the sensitive layers of the element, but conversely there is an adaptation of the still compliant paper fibers to the smooth undersurface of the optically variable elements on their other side supported by the smooth surfaces of the calender rolls.

As a result, the optically variable element is embedded in the paper substance, the paper surface being flush with the surface of the optically variable element. Subsequent printing is also possible in the areas of the optically variable element, since the high pressures which occur do not lead to an excessive load on the optically variable element embedded in the surface of the security.

It is particularly advantageous for the implementation of the method according to the invention if the optically variable elements are in tape form, similar to the known security threads. In contrast to these security threads, the carrier material with the optically active structure is placed on the paper layer formed after the sheet formation has been completed or is almost complete. In this sense, the tape is either brought outside the pulp to the circular screen after the paper layer has completely formed, ie it is placed on the paper fiber layer after leaving the circular screen or the tape is brought to the circular screen by means of nozzles in the pulp after e.g. . B. 90% of the final paper thickness is present, so that the material thickness of element plus paper corresponds approximately to the paper thickness in the adjacent areas. The subsequent process steps, such as. B. calendering, gluing, drying, etc., correspond to the usual procedure. Through them the carrier tape is firmly anchored in the security. The paper-side layer of the carrier tape is preferably to be provided with an adhesive layer which cures when the paper dries. Depending on the embodiment, ie bandwidth, rigidity, time of application etc., the specialist selects the most suitable one from the range of adhesives commercially available. Both pressure-sensitive adhesives and water-soluble adhesives or hot-melt adhesives appear particularly suitable. If necessary, it is also possible to support the adhesive curing by means of an appropriate UV or infrared radiation.

In the event that an endless carrier tape is not to be used, individual optically variable elements in the form of adhesive labels can also be provided. These adhesive labels are preferably attached to an endless transfer belt which is later, i. H. after anchoring the labels, in the paper mass is peeled off again.

Since the hologram application can still be carried out at the roll stage of the paper, high processing speeds are possible.

The independence of the printing process and hologram application results in a further advantage that the process sequence customary in the securities printing plants can be followed. So the paper with all its security elements such as watermark, security thread, optically variable element etc. can be prefabricated and, if necessary, stored. As usual, the particularly safety-critical printing process represents the last process step.

The methods for producing the security according to claim 1 are of course not limited to securities that have sensitive optically variable elements. Other security elements, such as. B. security threads with micro or negative printing can be introduced in the manner described in securities. Because such security elements Because of their high resistance compared to optically variable elements, they place less demands on the paper material and the treatment, so they can be fed in at any point during paper production. It can e.g. B. can be brought up to the circular screen after 85% paper accumulation, so that the element is well protected embedded in the remaining 15% that surround it at the end of papermaking or just before the final paper thickness is available.

Fig. 1

einen Querschnitt durch ein Wertpapier mit eingelassenem Hologrammelement und

Fig. 2 - 9

schematische Darstellungen einer Rundsiebpapiermaschine zur erfindungsgemäßen Aufbringung der optisch variablen Elemente.

Embodiments of the invention are described below with reference to the accompanying drawing, for example. In it show:

Fig. 1

a cross section through a security with embedded hologram element and

Fig. 2-9

schematic representations of a circular screen paper machine for applying the optically variable elements according to the invention.

1 shows a section of a security 10 with an embedded security element, preferably an optically variable element 12. The optically variable element is embedded seamlessly in the form of a strip in the paper mass, its surface being flush with the paper surface. The surface of the optically variable element, which preferably has a hologram structure 14, is visible over the entire surface, so that the optical effects can be checked easily, which is not always the case with the known "window security threads", since there the tiny areas that do Make thread material visible, optically not very effective.

The optically variable element is in the form of a thin self-supporting film strip 16. The band 16, as indicated in FIG. 2, is fed to the paper machine in such a way that it rests on the paper fiber layer 26 that has already been formed. The tape 16 is inserted between the take-off felt 22 and the paper fiber layer 26 leaving the circular screen 18. The tape 16 is drawn off from a supply roll 17.

The paper layer is formed on the circular screen 18 in a known manner by withdrawing liquid from the pulp 24 through the interior 20 of the circular screen 18, the paper fibers being deposited on the circular screen.

The introduction of the tape 16 between the felt 22 and the paper layer 26 enables particularly good guidance and precise placement of the tape 16. However, as shown in FIG. 3, the carrier tape with the optically variable elements can also be placed on the other side of the paper layer 26, that is to say, for example, inserted into the gap between the rollers 25 and the paper layer 26.

Another possible variant of thread insertion is shown in FIG. 4, in particular for narrow threads. In this case, the belt 16 carrying the optically variable element is placed on the circular sieve before the paper production. This option is particularly suitable for threads whose width is in the area of the paper fiber length or less, since no fibers are deposited on the thread itself, but those that deposit on the wire in the immediate vicinity of the thread Overlap the thread so that a paper base has nevertheless formed in the area of the thread when leaving the pulp.

In a preferred embodiment, the side of the tape 16 facing the paper web is provided with an adhesive layer, as a result of which the tape is more firmly fixed on the paper surface. The adhesive layer can be designed both as a water-soluble wet adhesive and as a hot-melt adhesive. When the paper web dries, the adhesive is activated and / or cured. The element is thus firmly anchored in the paper.

The feeding of the safety element is described here for reasons of clarity on a machine with only one circular screen. However, it is not a problem to transfer this method to a machine with two layers of production. In this case, the thread is fed to the screen, which produces the majority of the paper thickness.

5 to 9 show different ways in which the carrier tape 16 can be brought within the pulp 24 to the rotary screen 18 after z. B. 90% of the final paper thickness is available.

The hologram thread 16 is, as can be seen from FIG. 5, applied to the paper 26 with a nozzle 30, similar to a conventional security thread, the nozzle 30 being immersed so far in the pulp 24 that a point is reached where sufficient Paper is formed. No more paper is deposited in front of the belt 16 if the belt 16 is sufficiently wide or if the paper has essentially reached its final thickness, since the thread in its contact area prevents the water permeability of the paper and sieve. With this method, too Hologram thread 16 z. B. coated with a hot glue. It is then firmly attached to the paper in the hot dryer section of the paper machine. It is disadvantageous that the adhesive (such as, for example, hot glue) may initially only have a minimal adhesive force when it is introduced, since otherwise the tape 16 would stick in the insertion nozzle 30. The tape 16 is initially held only by the "self-adhesive force" of the moist paper 26, that is to say by adhesion. The processes described below are therefore more suitable for wider, thicker and stiffer carrier materials.

FIG. 6 shows a method which enables a hologram thread 16 to be applied, which is coated with a strong pressure-sensitive adhesive and, as is customary in such cases, is provided with a silicone paper 35 which protects the coated side. This double band of hologram carrier tape 16 and silicone paper 35 is, as before, drawn off from a supply roll 17 and brought to the circular screen 18 via deflection rolls. At the same point there is the pull-off device 32 for the silicone paper 35, which essentially consists of a deflection roller which feeds the pulled-off silicone paper to a storage roll 31.

When using weaker pressure sensitive adhesives, similar to scotch tape, it is sufficient to cover the side of the tape 16 coated with adhesive during the feeding to the circular screen 18, so that in this case only the hologram thread 16 is on the dispenser roll 17. 7 shows such a method, in which a self-contained silicone-coated carrier tape 40 is used as the protective cover. This tape runs through a distance defined by the deflection rollers 41 to 43, wherein it covers the adhesive upper side of the hologram tape 16 in the area between the deflection rollers 44 and 41. On this prevents paper fibers or other substances contained in the pulp from settling on the adhesive coating and thereby impairing the adhesion to the wet sheet material.

As shown in FIG. 8, the methods shown in FIGS. 6 and 7 can be combined in order to facilitate the threading of a hologram tape 16 coated with pressure-sensitive adhesive with silicone paper 35. Here, the silicone paper 35 is pulled off from the belt 16 directly after the dispenser roll 17 via the deflection roll 33 and fed to a storage roll 34. The now exposed adhesive coating of the tape 16 is protected by a circumferential silicone-coated film 40 during the further transport to the wet paper web, quite analogously to the method described above.

The procedure shown in FIG. 9 offers a further alternative to the previously mentioned methods for introducing pressure-sensitive adhesive-coated hologram tapes. In this case, the hologram band 16 is coated with adhesive 50 immediately before it is introduced into the paper machine and is transported to the circular sieve according to the known method with the aid of a circulating silicon band 40.

With regard to the adhesives that can be used, it should be noted that in addition to hot and pressure-sensitive adhesives, other adhesives, such as, for. B. multi-component adhesive, or adhesives that are activated in water can be used. It is also advantageous to use adhesive mixtures in which the tapes are first attached and then firmly attached to the paper in later production steps (for example when drying and calendering under the influence of heat).

After placing the hologram tape on the paper layer, it runs in the usual way through the further treatment stations of the paper machine, during calendering the tape is pressed into the still soft paper layer in the manner shown in Fig. 1, the paper fibers of the smooth surface of the Customize elements.

In the event that an endless belt is not applied, but individual elements, the transfer belt must be removed again after the elements have been anchored in the paper. This is preferably done after the paper web has dried, but in any case before the sizing station. The same procedure is necessary if endless belts are to be applied in the transfer process or if thin foils with low intrinsic stability are to be fixed on the paper surface.

After the quality check, the paper web is ready for printing, it can either be wound up on a winder and stored or it can be fed directly into a printing machine.

The method according to the invention is not limited to a circular screening machine. In the case of a Fourdrinier machine, the hologram tape can be fed from the wire shortly before or shortly after leaving the paper fiber layer in the same way as was explained in connection with a rotary wire machine.

Claims (16)

1. A paper of value having an embedded security element, preferably an optically variable element in the form of hologram, diffraction or interference structures applied to the paper surface, the security element (12) being embedded in the paper of value (10) under the surface layer of glue and the surface forming an uninterrupted, smooth, ridgeless plane, characterized in that the security element exists as a thin self-supporting film strip (16).
2. The paper of value of claim 1, characterized in that the film strip has a width of a few millimeters to a few centimeters.
3. The paper of value of either of the above claims, characterized in that the optically variable element is a hologram.
4. The paper of value of claim 3, characterized in that the hologram has a thickness of 10 to 50 micrometers.
5. A method for producing a paper web for papers of value having an optically variable element in the form of an element applied to the surface with a hologram, diffraction or interference structure according to one or more of claims 1 to 4, characterized by the following steps:

   a) providing a transfer band to which the optically variable element or elements are applied;

   b) feeding the transfer band to the wet paper web during production of the paper directly before or directly after the paper web is taken from the vat of the paper machine,

   c) calendering the paper web in the paper machine together with the transfer band lying on the surface of the paper web,

   d) drying and hardening the paper web,

   e) removing the transfer band from the paper web and gluing the paper web to produce an interrupted smooth surface.
6. The method of claim 5, characterized in that the optically variable elements exist on the transfer band in the form of labels.
7. The method of claim 5 or 6, characterized in that the labels are coated with an adhesive on the paper side.
8. The method of claim 7, characterized in that the adhesive is a hot-melt adhesive.
9. The method of one or more of claims 5 to 8, characterized in that the transfer band is introduced into a cylinder machine between the felt web and the paper web running off the forming vat.
10. The method of one or more of claims 5 to 8, characterized in that the transfer band is applied to the side of the paper web facing away from the wet felt before the calender rollers.
11. A method for producing a paper web for papers of value having an optically variable element with a hologram, diffraction or interference structure according to one or more of claims 1 to 4, characterized by the following steps:

    a) providing an optically variable element in the form of a thin self-supporting film strip (16),

    b) optionally coating the film strip with adhesive on the side facing the paper web,

    c) feeding the film strip (16) to the forming paper web,

    d) calendering the paper web in the paper machine together with the thin self-supporting film strip (16) lying on the surface of the paper web,

    e) drying, hardening and gluing the paper web to produce an uninterrupted smooth surface.
12. The method of claim 11, characterized in that the thin self-supporting film strip is already coated on the dispensing roller with silicone paper protecting the adhesive layer, which is removed directly before contact with the wet paper web.
13. The method of claim 11, characterized in that the thin self-supporting film strip (16) is transported to the paper web with the aid of a circulating silicone-coated carrier web which covers the side coated with adhesive.
14. The method of claim 13, characterized in that the thin self-supporting film strip is provided with protective silicone paper which is removed directly after the dispensing roller.
15. The method of claim 13, characterized in that the adhesive is applied to the thin self-supporting film strip directly before it is introduced into the paper machine.
16. The method of claim 11, characterized in that the thin self-supporting film strip is fed as soon as at least 90% of the paper thickness exists.

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