Patent Application
20140238628
The present invention relates to a method for manufacturing a security paper, as well as a microlens thread for introduction into a paper web with such a method.
For protection, value documents, such as banknotes, stocks, bonds, certificates, vouchers, checks, valuable admission tickets and other papers that are at risk of counterfeiting, such as passports or other identification documents, are often provided with security elements that permit the authenticity of the value document to be verified, and that simultaneously serve as protection against unauthorized reproduction. The security elements can be developed, for example, in the form of a security thread that is completely or partially embedded in a banknote.
In recent years, security threads having microlenses have come into use on the banknote market. These microlens threads differ significantly from metalized threads and offer attractive optical properties. The microlens threads are furnished, on the side facing the viewer, with microlenses whose focusing effect is created by light refraction on an approximately spherically curved surface. In the focal plane of the microlenses, micropatterns are located that are arranged such that, through the coaction of the microlenses and the micropatterns, it is possible to depict for the viewer a magnified image having special motion effects.
In order not to impair the focusing effect of the microlenses and thus the optical effect of the microlens thread, the lens side of the thread is not provided with adhesive before the embedding in a paper web, as is the case in conventional security threads, such as hologram threads. However, the dispensation with adhesive on the top of the thread (lens side) often leads to a reduced stability of the banknotes produced, and in some cases even to a wrinkling on the banknote back.
Proceeding from this, the object of the present invention is to avoid the disadvantages of the background art and especially to specify a method for manufacturing a security paper that facilitates a secure embedding of a microlens thread in the paper, and that simultaneously ensures, in the window regions in which the microlens thread emerges at the surface of the paper, an attractive visual appearance of the microlens thread.
This object is solved by the features of the independent claims. Developments of the present invention are the subject of the dependent claims.
According to the present invention, in a generic method, it is provided that
In a preferred method variant, it is provided that
A registered introduction of the microlens thread can especially occur according to one of the methods described in document WO 2004/050991 A1. In this respect the disclosure of this document is incorporated in the present application by reference.
In some designs, the microlens thread can include a motif having a motif jump. As described in greater detail in document WO 2008/145333 A2, in manufacturing a microlens thread, normally an endless security element foil is first manufactured as roll material, wherein, when conventional manufacturing methods are used, breaking points always occur, especially gaps or a misalignment in the appearance of the security elements. These breaking points come from the fact that the pre-products for the embossing dies used in manufacturing are generally manufactured as flat plates that are fitted on an impression or embossing cylinder. The image patterns that adjoin on both sides do not, as a general rule, match at the junctions and, after printing or embossing, lead, in the appearance of the finished security elements, to a motif jump of the kind cited. According to an advantageous embodiment of the present invention, a microlens thread that includes a motif having a motif jump is introduced into the paper web in register, such that the motif jump comes to lie in one of the ridge regions of the paper web. The motif jump then remains hidden from the viewer.
Motif jumps potentially also occur multiple times within an embossing cylinder. For example, in the event that the patterns are composed from small segments by means of recombination, seams having motif jumps result. In general, due to the method, motif jumps are created both in the grid of the micropatterns and in the grid of the microlenses. Here, it is usually attempted to bring the two seams into overlap at manufacture, such that the impression of only one motif jump is created for the viewer.
In a modification of the described method, immediately before entering into the paper web, the microlens thread is selectively printed on with an adhesive layer in those regions of its top that, at sheet formation, come to lie below ridge regions of the paper web.
In a further preferred method variant, it is provided that
Also in this variant, the microlens thread can include a motif having a motif jump, and the microlens thread be introduced in register, such that the motif jump comes to lie in one of the ridge regions of the paper web and is thus hidden for the viewer.
According to a modification of the method, immediately before entering into the paper web, the microlens thread is selectively provided with openings in those regions of its top that, at sheet formation, come to lie below ridge regions of the paper web.
The openings are advantageously produced by punching or laser cutting. If the openings are produced only immediately before the entry of the microlens thread into the paper web, then they are preferably produced by laser cutting.
In all designs, the paper web is expediently formed having the predetermined ridge pattern in a paper machine, and the endless microlens thread enters into the paper machine.
According to a further preferred method variant, it is provided that, in step M), a microlens thread is provided whose top exhibits fractional regions having microlenses and microlens-free fractional regions, the microlens-free fractional regions being smaller than the width of the ridge regions of the ridge pattern in the paper web, and the microlens-free fractional regions being coated with adhesive before the introduction into the paper web. The microlens thread is especially introduced into the paper web not in register such that, in every window region, microlenses can be seen at least in some regions, and a portion of the adhesive-coated fractional regions always come to lie below ridge regions of the paper web.
According to a further preferred method variant, it is provided that, in step M), a microlens thread is provided that, on the one hand, exhibits fractional regions having microlenses, which fractional regions are coated with adhesive before the introduction into the paper web, and which are smaller than the width of the ridge regions of the ridge pattern in the paper web, and on the other hand, exhibits fractional regions having microlenses that are not coated with adhesive before the introduction into the paper web. The microlens thread is especially introduced into the paper web not in register, such that, in every window region, microlenses that exhibit no adhesive coating can be seen at least in some regions, and a portion of the adhesive-coated fractional regions always come to lie below ridge regions of the paper web.
In all described method variants, the microlens thread is advantageously contiguously provided on its bottom with an adhesive layer before the introduction into the paper web.
The present invention also includes a microlens thread for introduction into a paper web, especially with the method just described. The microlens thread includes a top and an opposing bottom, the top exhibiting fractional regions having microlenses, and exhibiting microlens-free fractional regions that are coated with adhesive.
The fractional regions having microlenses and the microlens-free fractional regions advantageously form, on the top of the thread, alternating strips that each completely occupy the width of the microlens thread, and that each exhibit, in the longitudinal direction of the microlens thread, a dimension between 1 mm and 30 mm, preferably between 3 mm and 12 mm.
The fractional regions having microlenses and the microlens-free fractional regions can usually be present in the form of rectangles. However, it would also be possible for the fractional regions having microlenses and the microlens-free fractional regions to be present in the form of diagonals. Especially in wider threads, it is possible to produce diagonal paper ridges.
The bottom of the microlens thread is preferably contiguously coated with adhesive.
Further exemplary embodiments and advantages of the present invention are explained below by reference to the drawings, in which a depiction to scale and proportion was dispensed with in order to improve their clarity.
Shown are:
The invention will now be explained using a banknote as an example. For this,
In a first exemplary embodiment of the present invention, the microlens thread 12 illustrated in
The microlens thread 12 includes a support 20 in the form of a transparent plastic foil, for example a PET foil about 20 μm thick. The top 30 of the microlens thread 12 exhibits a grid-shaped arrangement of microlenses 22 that form, on the surface of the support foil, a lattice having a prechosen symmetry. The spherically or aspherically designed microlenses 22 preferably exhibit a diameter between 5 μm and 50 μm, and especially a diameter between merely 10 μm and 35 μm, and are thus not perceptible with the naked eye. It is understood that, in other designs, also larger or smaller dimensions may be considered. Also the use of cylindrical lenses is similarly possible.
On the bottom 32 of the microlens thread 12 is arranged a motif layer 26 that includes a likewise grid-shaped arrangement of micromotif elements 28. Also the arrangement of the micromotif elements 28 forms a lattice having a prechosen symmetry, with a desired magnification effect, characteristic motion effects and/or tilt effects being produced due to the coordination of the lattice of the microlenses 22 and the arrangement of the micromotif elements 28. The micromotif elements are not perceptible with the naked eye. Now, reference is additionally made to WO 2009/000528 A1, in which it is explained that the micropatterns can also consist of image fragments that are not arranged repeatingly. The microlens thread 12 typically includes further layers 24, such as protective, cover or further functional layers, which, however, are not significant for the present invention and are thus not described in greater detail.
Due to the manufacture with embossing cylinders, the motif perceived by the viewer will usually exhibit a motif jump, as described in greater detail in document WO 2008/145333 A2.
Now, to manufacture a security paper, a paper web 50 having a predetermined ridge pattern 18 (
As schematically depicted in
Said microlens thread 12 coated in this way with adhesive 40, 42 is now introduced in register into the paper web 50, such that the adhesive-coated regions 46 of the microlens thread coincide with the ridge regions 16 of the paper web 50, as shown in
Such an introduction in register can especially occur according to one of the methods described in document WO 2004/050991 A1. For example, the microlens thread 12 can be introduced into the paper web by means of a biased coil. A first sensor detects the position of the coated regions 46 shortly before the introduction into the paper web, a second sensor the position of the ridges 16 formed in the paper web immediately after sheet formation. The positions detected by the two sensors are analyzed and used to control the magnitude of the bias. When the bias is increased, the microlens thread 12 is stretched more strongly, and when the bias is lowered, the stretching is reduced. In this way, the microlens thread 12, with its coated and uncoated regions 44, 46, can be aligned in perfect register with the window and ridge regions 14, 16.
For the registered thread embedding, the procedure is preferably such that the thread bears a register mark that is recognized particularly well by a detection system. The thread embedding is then controlled at the thread by means of tensile stress in such a way that the register mark of the thread has a fixed local reference to the register mark of the paper, usually a watermark. Here, the regions in which the thread exhibits adhesive on the top then have a fixed, known local reference to the register mark of the thread. Similarly, the ridge regions in the paper have a fixed local relationship to the register mark in the paper.
Through said approach it is ensured that the ridge regions 16 of the paper web 50 are glued to the microlens thread 12, such that a secure embedding of the microlens thread 12, without wrinkling and without lifting up or tearing out the paper ridges at manufacture, is ensured. Likewise, stability of the paper ridges to circulation stresses is significantly improved. At the same time, the microlenses 22 of the uncoated regions 44 that are visible in the window regions 14 remain free of adhesive, such that the optical properties of the microlenses 22 are not impaired. The microlens thread 12 thus displays, after its embedding in the paper web 50, the desired clear visual appearance in the window regions 14.
In advantageous embodiments, the uncoated regions 44 and the coated regions 46 exhibit the same size as the window regions 14 and the ridge regions 16, respectively. In some embodiments, it is also provided that the coated regions 46 are smaller, for example no more than 10% or no more than 50% smaller, than the ridge regions 16. How much shorter the glue-coated portion should be compared with the paper ridges of the thread also depends strongly on the register tolerance when embedding the thread in register. With, for example, ±1 mm register tolerance when introducing the thread in register, the glue-free regions of the thread should be 2 mm shorter than the paper ridges. Even if, in each case, only a portion of the microlens thread 12 is glued to the ridge regions 16, a significantly improved embedding results compared with the background art.
Also designs in which the uncoated regions 44 are somewhat smaller than the window regions 14 may be considered. However, the focusing effect of adhesive-coated microlenses 22 in the window regions 14 is reduced or canceled, such that the uncoated regions 44 are preferably not more than 10%, particularly preferably not more than 5% smaller than the window regions 14.
A further advantage of the introduction of the microlens thread 12 in register consists in that any motif jumps 34 in the motif image can be hidden under a paper ridge 16 of the security paper 50, as shown in
In a modification of the described method sequence, the microlens thread 12 is not introduced into the paper web 50 in register, but rather is, immediately before the entry into the paper machine, printed on with an adhesive pattern 48 in such a way that the coated regions 46 come to lie in the depressed sections of the cylinder mold, in which the paper ridges 16 form. For this, a sensor, for example, can detect the position of the ridges 16 formed in the paper web at sheet formation, and the detected position can be used to control the printing positions for the adhesive pattern 48. Also in this way, the uncoated and coated regions 44, 46 can be aligned in perfect register with the window and ridge regions 14, 16.
A further variant of the present invention will now be explained with reference to
In the variant in
The microlens thread 60 is now introduced into the paper web 50 in register, such that the regions 66 of the microlens thread 60 that are provided with openings coincide with the ridge regions 16 of the paper web 50, as already described in principle in connection with
In this variant of the present invention, due to the provision of the openings 62, it is achieved that, at paper formation, under the ridge regions 16, paper fibers or other components of the substrate 50 can penetrate through the openings 62 to create a connection between the ridge regions 16 and the substrate material 52 under the microlens thread 60 (
The openings 62 can, for example, be punched or produced through laser cutting. Every region 66 can include one or also multiple openings 62. For illustration,
In a modification of the described method sequence, the microlens thread 60 is not introduced into the paper web 50 in register, but rather, it is provided only immediately before the entry into the paper machine, through laser impingement, with the opening pattern 68, in such a way that the regions 66 having openings 62 come to lie in the depressed sections of the cylinder mold, in which the paper ridges 16 form. For this, for example, a sensor can detect the position of the ridges 16 formed in the paper web, and the detected position can be used to control the laser beam. Also in this way, the opening pattern 68 can be aligned in perfect register with the window and ridge regions 14, 16.
In a further variant of the present invention that is illustrated in
Here, the adhesive-coated, microlens-free fractional regions 76 are developed to be smaller than the width of the window regions 14 of the ridge pattern 18. In this way, it is ensured that, when the microlens thread 70 is not introduced into a security paper 50 in register, microlenses 22 can be seen in every window region 14, at least in some regions (
In this way, on the one hand, a visually attractive appearance is obtained, and on the other hand, an embedding that is improved over the background art can be achieved also without an introduction of the microlens thread 70 in register, since a portion of the adhesive-coated fractional regions 76 will always come to lie below ridge regions 16 of the paper web, as illustrated in
According to a modification of the above-mentioned variant of the present invention illustrated in
According to a further modification of the above-mentioned variant of the present invention illustrated in
The adhesive or glue used in the present invention can be, for example, a heat seal coating. Furthermore, the adhesive can exhibit security features, for example dyes or color pigments and luminescent substances.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 112 554.3 | Sep 2011 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/003695 | 9/4/2012 | WO | 00 | 3/5/2014 |
