EP1527902B2 - Method for producing a web of material - Google Patents

Description

The present invention relates to a method and an apparatus for producing web-shaped materials with a relief structure and to methods for producing a security element and a security document.

Value documents such as banknotes, checks, identity cards and credit cards often have security elements with diffraction structures which have an optically variable effect. That is, as the viewing angle changes, the perceptible information and / or the color of the information changes. Since a copying machine can only reproduce the information and / or color visible under a certain viewing angle, such security elements offer a high degree of protection against counterfeiting. Due to the appealing visual effects and the high copy protection, such security elements are also widely used in the field of product security. The security elements are either applied directly to the object of value or the associated packaging.

In order to ensure an economical production of such security elements, the diffraction structures are usually converted into a relief structure, which is introduced into the surface of a stamping tool. With this embossing tool suitable layers can be embossed in continuous processes and thus provided with the diffraction structures.

The EP 1 310 381 A2 describes a method for producing such security elements with diffraction structures. Here, a film is coated with a UV-curable varnish that is pre-cured to the gel point. The diffraction structure is then embossed into this precured lacquer and the lacquer is further imprinted during the embossing process by UV irradiation hardened. After the embossing process, the paint with the relief structure is subjected to a post-curing.

The pre-cure to the gel point ensures that the paint already has a certain strength at the time of embossing. This has the disadvantage that the fine relief structures, the dimensions of which are usually in the range of the wavelength of visible light, can not be reproduced with sufficient contour sharpness. This loss of acutance leads to loss of brilliance on the finished optically variable element.

The invention is therefore based on the object to provide a method and a device that ensures a higher contour sharpness of the molded relief structure and thus allows the production of optically variable security elements with increased brilliance.

This object is solved by the features of the independent claims. Advantageous embodiments and modifications of the invention are the subject of the dependent claims.

When a varnish is cured, the liquid varnish is converted into the solid state by crosslinking polymerization. The conversion at which the liquid properties and the solid state properties have the same level is called the gel point. There, insoluble, so-called "gel particles" appear for the first time.

According to the invention, the relief structure is introduced into a radiation-curable lacquer layer, wherein the lacquer layer at the time of introduction has a degree of cure below the gel point.

The invention is based on the knowledge that below the gel point, the liquid properties of the coating predominate and thus the embossed structures can be imprinted 1: 1 without loss of acutance in the paint. This increases the brilliance of the finished product.

In the method according to the invention for producing sheet-like materials having a relief structure, in particular a diffraction structure, in a first step a substrate is coated at least in regions, preferably over the entire surface, with a radiation-curable coating layer. The radiation-curable lacquer can be applied by any printing method, preferably screen, gravure or flexographic printing processes are used. The flexographic printing process is used in particular when the radiation-curing lacquer is not applied over the entire surface but only in regions on the substrate. However, the paint can also be carried out with other coating systems, such as roll coaters, spray nozzles or paint spray systems. The thickness of the applied lacquer layer is on the order of 1 to 10 .mu.m, preferably in the range of 1 to 5 .mu.m, particularly preferably in the range of 2 to 4 .mu.m.

The substrate used is preferably a plastic film, in particular a transparent plastic film. A particularly preferred material is polyester, but also other plastics such as PE, PP, MOPP, PPS, PGEK, PEK, PGE, PSO, PAEK, LCP, PEN, PPT, PET, PA, PC, COC, POM, ABS and PVC , can be used. The thickness of the plastic film is in the order of 4 to 30 microns, preferably from 6 to 25 microns, more preferably from 12 to 23 microns.

This substrate can be pretreated before coating with the radiation-curing lacquer in further process steps. This can happen to be pure pretreatments, such as corona discharge, which affect the adhesion properties between substrate and paint. However, the substrate can also be provided, at least in regions, with other coatings which also adjust the release or adhesion properties or provide the web-like material with further security features. These may be, for example, layers with luminescent and / or magnetic and / or electrical and / or optically variable and / or thermochromic properties.

The radiation-curing coating itself may also contain such security features. Alternatively, the paint can also be dyed with any printing inks. Preferably, however, transparent paints are used. The radiation-curing lacquer used is preferably UV-curable lacquers. But it could also be used other radiation-curing paints. It is also possible to use lacquers with a plurality of photoinitiators which trigger the polymerization process when irradiated in different wavelength ranges. This can have various advantages, as will be explained in more detail below. A lacquer which can be used in the context of the process according to the invention can have, for example, the following composition: 26.5% polyester 6.6% Epoxy novolac acrylate in trimethylolpropane triacrylate / hydroxyethyl methacrylate 26.5% hexafunctional aliphatic urethane acrylate 5.31% Mixture of pentaerythritol tri- and tetracrylate 21.2% Trimethylethylolpropantriacrylat 6.6% tertiary amine 6.9% Darocure (initiator for the short-wave UV range) 0.2% BAPO (initiator for the short-wave UV range)

In a further step, the relief structure is introduced into the lacquer layer, wherein the lacquer layer at the time of introduction substantially has a degree of cure below the gel point.

For the introduction of the relief structure, the lacquer layer is preferably brought into contact with a stamping tool which has the relief structure on its surface. This stamping tool can be an embossing stamp of any shape. Preferably, an embossing cylinder is used whose entire cylinder surface is provided with the surface to be transferred relief structure. The production of this embossing cylinder can be done in different ways. In the case of diffractive structures, the diffractive motif is provided as a so-called master structure in a nickel foil. By means of this master structure, metal foils, in particular nickel foils, can be produced by recombination processes and subsequent molding, preferably galvanic molding, which are seamlessly provided with the master structure over their entire surface. These metal foils are welded, for example, with a laser and form the cylinder jacket of the embossing tool, which is mounted on a clamping cylinder.

At the time of introduction of the relief structure, ie at the time when the lacquer layer is brought into contact with the embossing tool, the lacquer layer is already pre-cured to a degree of cure below the gel point. This pre-hardening takes place directly before the embossing process. That is, the coated with the paint layer substrate leaves by means of a corresponding transport system, the means for precuring and is transported by a suitably dimensioned transport path directly into the device for the embossing process. It is important that between the pre-curing process and the embossing process, the film no UV radiation or is exposed to other curing radiation in order to avoid non-reproducible, unintentional precuring of the embossing lacquer. For this purpose, the film is guided in a light-tight shaft between commissioned work and embossing. The length of the transport path should be selected such that, given the web speed, the paint has enough time to run evenly over the surface to form a homogeneously smooth paint film.

The pre-hardening is preferably carried out from the paint side. This makes it possible to only harden the surface of the lacquer in order to reduce the tack of the lacquer in this surface area, so that adhesion of the lacquer to the embossing tool is avoided. Since only the surface of the varnish is cured, the varnish retains its fluidity in the volume and can therefore still take over the relief structure with the necessary contour sharpness.

Preferably, the paint is also cured during the embossing process in a so-called main curing step. That is, while the lacquer layer is in contact with the embossing tool, the lacquer layer is preferably cured through the substrate by exposure to radiation to a degree of cure> 50%, preferably between 80 and 98%.

In certain embodiments of the method according to the invention, it may also be necessary to postcure the lacquer layer after introduction of the relief structure, for example by further exposure to radiation. This postcuring has the advantage that reproducible coating properties are produced which facilitate the further processing of the substrate with the embossed lacquer layer and prevent blocking of the web material during winding.

For the mentioned curing steps - pre-, main-, post-curing - the same or different radiation can be used. This radiation can be any light or particle radiation. If electromagnetic radiation is used, preferably visible light or UV radiation is used. IR radiation, in particular heat radiation, however, is also possible. Suitable radiation sources are, in particular, mercury vapor lamps, also referred to as Hg lamps for short, which are distinguished by a high proportion of ultraviolet radiation. The respective required wavelength ranges can be realized by appropriate doping of the Hg lamps, for example with Ga, Fe, Ga / Pb. Depending on the paint used and its composition, however, other sources of radiation, such as fluorescent tubes or lasers, may be advantageous.

The radiated wavelength or the wavelength range of the radiation sources can be monitored at certain intervals or continuously, since the radiation sources age and the radiation spectrum can change. For better light output, the radiation sources can be equipped with reflectors, preferably parabolic or free surface reflectors.

The described method steps preferably take place in a continuous process. For the device used, this means that the individual devices for coating the substrate, the introduction of the relief structure and the different curing processes are arranged one behind the other and connected via a common transport system. In this case, preferably transport rollers are used, which guide the web-like material continuously through the individual devices of the device.

However, the device may include other means necessary for the control and regulation of the individual process parameters. Thus, it is advantageous, for example, to control the temperature of the radiation-curable varnish during the entire process in a controlled manner in order to ensure that the varnish has the optimum viscosity in every working step.

However, the device can also have other processing devices that are not directly required for the method according to the invention, but make sense in terms of further processing or the intended use of the sheet-like material. Thus, in front of the devices essential to the invention, the device preferably has devices for surface treatment of the substrate, which determine the later adhesion or detachment properties of the lacquer. This may be a corona discharge device or, if a coating is to be applied, a printing unit or a coating device.

In addition to the devices according to the invention further processing means, such as a printing unit, may be arranged. Such devices are particularly advantageous when placed on the introduced relief structure more preferably partial coatings are to be applied. Thus, a soluble printing ink in the form of a pattern can be printed in register with the relief structure. This soluble ink can be dissolved and removed after the full surface metallization of the sheet material. Since the overlying thin metal layer is also removed, noticeable recesses in the form of the previously applied with the soluble ink patterns that serve as additional security feature arise in the metal layer.

The relief structures according to the invention are preferably diffraction structures. In order that the information stored in the diffraction structures can be visually recognized well, the web-like material is provided with a metal layer or a dielectric layer over the whole area or in regions after the introduction of the relief structure. Of course, following the method steps according to the invention further security features can be applied to the web-shaped material.

The sheet material can then be used to make security items for any valuables, such as banknotes, ID documents, passports, ID or credit cards, or any product security product.

If the web-shaped material is used as transfer material, in particular hot embossing foil, then the layer sequence of the security element is prepared on the substrate in the reverse order, as it later comes to rest on the valuable article to be secured, and subsequently into the desired one by means of an adhesive or lacquer layer Transfer outlines to the object of value. The outline shape is defined by the shape of the applied adhesive or lacquer layer or a preferably heated transfer punch. In so-called hot stamping processes, only a part of the adhesive layer is activated by means of the transfer punch and thus anchored to the object of value. The remaining sheet material can then be easily removed. The substrate can also be removed after the transfer from the layer structure of the security element or remain as a protective layer as an integral part of the security element on the layer structure. The individual security elements may be on the substrate as separate individual elements be prepared in the outline to be transmitted. Alternatively, the layer sequence of the security elements is provided in continuous form on the substrate.

If the web-like material is used as label material or security thread material, then a firm bond between the substrate and the layer structure of the security element applied thereon must be provided. The web-shaped material is cut in this case in threads or desired security elements of any outline shape and applied to the object to be secured, preferably glued. The security threads are usually at least partially embedded in a security paper during papermaking.

Further embodiments and advantages of the invention will be explained with reference to FIGS. The figures show only schematically the essential aspects and do not represent a detailed illustration.

Fig. 1

eine Ausführungsform eines nicht erfindungsgemäßen Verfahrens

Fig. 2 und 3

verschiedene Ausführungsformen der erfindungsgemäßen Vorrichtung bzw. des erfindungsgemäßen Verfahrens.

Show it:

Fig. 1

an embodiment of a method not according to the invention

FIGS. 2 and 3

various embodiments of the device or the method according to the invention.

Fig. 1 shows the embodiment of a method not according to the invention. Here, a transparent plastic film is used as the substrate 1, to which a radiation-curable paint 2 is at least partially applied by means of a Lackauftragswerks 3, here a printing unit. Subsequently the still moist uncured paint 2 is transported via a transport system 4 to a corresponding embossing unit 5. In the example shown, the embossing unit 5 consists essentially of an embossing cylinder 6, on the surface of which the relief structure 7 to be transferred is arranged. When the lacquer 2 is brought into contact with the embossing cylinder 5, the relief structure 7 is transferred into the lacquer 2. In order to fix the relief structure 7 in the lacquer, a hardening device 8, which has at least one radiation source 9, is located in the immediate vicinity of the embossing unit 5. This radiation source 9 irradiates the paint 2 through the substrate 1, which must be at least partially transparent to this radiation. The radiation of the radiation source 9 cures the paint during the embossing process to a degree of cure of> 50%, preferably between 80 and 98%. This process forms the main hardening of the paint 2.

The embossing into the still wet lacquer layer 2 gives an excellent embossing quality, since the fine relief structures 7 of the embossing tool 6 are imaged 100%. Usually, however, the paint after the embossing process is still soft, so that the relief structure 7 can be damaged during transport by subsequent devices of the device. Because the embossed paint surface comes in the course of processing again and again with transport rollers and similar devices of the device in contact, which can impress the soft paint surface. Since this leads to a visible loss of brilliance on the finished product or security element, the lacquer 2 after the embossing process in a further curing device 10, preferably a further radiation source 11, post-cured. This is preferably arranged on the embossed lacquer side of the substrate 1, so that the embossed lacquer layer 2 is exposed to the corresponding radiation unhindered.

This method is particularly suitable for web-shaped materials in which the substrate 1 should have a good adhesion to the layer structure applied thereto. This is the case in particular with label materials and security threads. Because in this case, the paint 2 has a greater adhesion to the substrate 1 as the embossing tool 6, so that the risk of paint deposition on the embossing tool 6 is relatively low.

For the radiation sources 9 and 11 of the respective curing devices 8, 10, the same radiation sources can be used. The radiation sources used are preferably UV lamps.

Alternatively, however, different radiation sources for the different curing devices 8, 10 can be used. In this case, the paint 2 contains two different photoinitiators. The first photoinitiator responds to the radiation of the radiation sources 9 during the main curing of the lacquer 2 and there initiates the polymerization of the lacquer 2. On the other hand, the second photoinitiator responds only to radiation of the radiation source 11 which is used for the after-hardening of the lacquer 2. For example, the first photoinitiator may be especially sensitive to emission bands in the visible range, for example by emitting Ga or Fe doped Hg lamps. By contrast, the second photoinitiator, for example, can react to UV radiation with a short wavelength, so that a radiation source with a corresponding emission band is selected for the radiation source 11 in the post-curing device.

Fig. 2 shows an embodiment of the method and the device for carrying out the method according to the invention. The method and the apparatus shown here are largely identical to that in FIG Fig. 1 already explained method steps or facilities.

The method differs only in that a pre-hardening device 12 is arranged in front of the embossing unit 5, which preferably has at least one radiation source 13. For this purpose, a post-curing device 10 is dispensed with. This pre-hardening device 12 is located directly in front of the embossing unit 5, so that the pre-hardened lacquer layer 2 is transported into the embossing unit 5 in direct connection to the pre-hardening device 12. The pre-hardening device 12 is preferably arranged on the side of the substrate 1 coated with varnish, so that the radiation of the radiation source 13 hits the varnish unhindered. This has the advantage that for the radiation source 13 and radiation sources can be used, the radiation from the substrate 1 would be absorbed.

In the precuring device 12, the lacquer layer 2 is pre-cured to a degree of cure below the gel point. Preferably, only the paint surface is purposefully hardened by the pre-hardening process, so that it loses its stickiness. This has the advantage that the paint 2 does not adhere to the embossing cylinder 6. At the same time, the varnish 2 is still so soft in volume that the relief structure 7 can be transferred unimpeded 1: 1 into the varnish 2.

Analogous to that already with reference to Fig. 1 described embodiment, identical or different radiation sources can be used here for the radiation sources 9 and 13. Likewise, the paint 2 may contain corresponding photoinitiators, which are adapted to the particular radiation of the radiation sources 13 and 9 used.

Fig. 3 shows a further embodiment of the invention. It represents a combination of in the Fig. 1 and 2 As shown here, the paint is both pre- and post-cured. This has the advantage that the tackiness of the paint can be reduced by pre-curing in order to avoid contamination of the embossing cylinder 6. By post-curing in the post-curing device 10, the relief structure 7 is stabilized in the paint 2. In addition, the post-curing process produces reproducible coating properties that are necessary for further processing of the film, such as another printing process. Finally, the post-curing also prevents blocking of the web-like material during winding.

By splitting the lacquer hardening in at least two curing processes, the risk of embrittlement of the lacquer due to excessive exposure to radiation can be significantly reduced. Furthermore, there is a much greater flexibility in the choice of the receptors of the paints, which can be adapted much better in this way to the specific requirements of the security elements to be provided with valuables or the further processing steps. In this way, the processing speed can be increased.

According to a specific embodiment, it is also possible to use what are known as dual-cure paint formulations which, for complete curing, in addition to the radiation fraction (precuring and primary hardening or only precuring), are completely cured by the subsequent action of heat. In this case, the post-curing device 10 is equipped with a heat radiator.

Claims (30)

1. A method for manufacturing web-shaped materials having a relief structure (7), comprising the following steps of:

   coating a substrate (1) at least regionally with a radiation-curable lacquer layer,

   incorporating the relief structure (7) in the lacquer layer with an embosser (6) that has the relief structure (7) on its surface and that is brought into contact with the lacquer layer,

   wherein at the time of incorporation the lacquer layer substantially has a degree of cure below the gel point and before the incorporation of the relief structure (7) the lacquer layer is precured to a degree of cure below the gel point.
2. The method according to claim 1, characterized in that as the embossing tool (6) an embossing cylinder is employed.
3. The method according to claim 1, characterized in that the precuring takes place directly before the incorporation of the relief structure (7).
4. The method according to claim 3, characterized in that the precuring takes place from the lacquer side.
5. The method according to at least one of claims 1 to 4, characterized in that a lacquer (2) is employed that contains at least two photoinitiators.
6. The method according to at least one of claims 1 to 5, characterized in that a UV-curable lacquer (2) is employed.
7. The method according to at least one of claims 1 to 6, characterized in that the method has a main curing step, wherein the lacquer layer is cured by the action of radiation during the incorporation of the relief structure (7).
8. The method according to at least one of claims 1 to 7, characterized in that the lacquer layer is cured during the main curing to a degree of cure of >50%, preferably between 80 and 98%.
9. The method according to at least one of claims 1 to 8, characterized in that the main curing takes place through the substrate (1).
10. The method according to at least one of claims 1 to 9, characterized in that during the precuring the surface of the lacquer (2) is cured partially.
11. The method according to at least one of claims 1 to 10, characterized in that the lacquer layer is postcured by the action of radiation after the incorporation of the relief structure (7).
12. The method according to at least one of claims 7 to 11, characterized in that all curing steps take place with the same radiation, preferably UV or electron radiation.
13. The method according to at least one of claims 7 to 11, characterized in that for the different curing steps different radiations are employed.
14. The method according to at least one of claims 1 to 13, characterized in that the relief structure (7) constitutes a diffractive structure.
15. The method according to at least one of claims 1 to 15, characterized in that as the substrate (1) a preferably transparent plastic foil is employed.
16. The method according to at least one of claims 1 to 15, characterized in that as the substrate (1) a plastic foil is employed that has a thickness in the range of 10 to 30 µm, preferably 12 to 23 µm.
17. The method according to at least one of claims 1 to 15, characterized in that the substrate (1) absorbs UV radiation in the short-wave range up to around 400 nm.
18. The method according to at least one of claims 1 to 17, characterized in that the substrate (1) is pretreated before the application of the lacquer layer, in order to adjust the detachment and/or adhesion properties.
19. The method according to at least one of claims 1 to 18, characterized in that the web-shaped material after incorporation of the relief structure (7) is supplied all over or regionally with a metal layer or a dielectric layer.
20. The method according to at least one of claims 1 to 19, characterized in that the web-shaped material is supplied with further security features.
21. The method according to at least one of claims 1 to 20, characterized in that the web-shaped material is manufactured as a transfer material, a label material or a security thread material.
22. A method for manufacturing a security element, characterized in that it comprises the manufacture of a web-shaped material according to any of claims 1 to 21.
23. A method for manufacturing a security document, characterized in that it comprises the manufacture of a security element according to claim 22.
24. An apparatus for manufacturing web-shaped materials having a relief structure (7), such as a diffractive structure, with a device (3) for applying a lacquer (2) to a substrate (1), a device (12) for precuring the lacquer (2) to a degree of cure below the gel point, and an embosser (5) for incorporating the relief structure (7) in the lacquer (2), characterized in that the device (12) for precuring the lacquer is arranged directly upstream of the embosser (5) and the web-shaped materials are guided in a lightproof slot between the device (3) for applying the lacquer and the embosser (5), so that the lacquer (2) is not subjected to curing radiation between the precuring and the incorporation of the relief structure (7).
25. The apparatus according to claim 24, characterized in that the embosser (5) has an embossing cylinder (6).
26. The apparatus according to at least one of claims 24 or 25, characterized in that the apparatus has a device (8) for the main curing of the lacquer (2).
27. The apparatus according to claim 26, characterized in that the device (8) for the main curing is arranged in the embosser (5), so that the main curing takes place during the embossing procedure.
28. The apparatus according to at least one of claims 24 to 27, characterized in that the device (12) for precuring and the device (8) for the main curing are arranged on opposing sides of the substrate (1) coated with lacquer (2).
29. The apparatus according to at least one of the claims 24 to 28, characterized in that the device (12; 8) for precuring and/or main curing is a radiation source (13; 9).
30. The apparatus according to claim 29, characterized in that the radiation source (13; 9) is employed as an electron beam, a laser, a fluorescent tube, a mercury vapor lamp or a doped Hg lamp, preferably a Ga-, Fe- or Ga/Pb-doped Hg lamp.

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