WO2017088964A2

WO2017088964A2 - Embossing method for embossing microstructures or nanostructures

Info

Publication number: WO2017088964A2
Application number: PCT/EP2016/001922
Authority: WO
Inventors: Andreas Rauch; Frank Sievers; Georg Kiefersauer; Birgit Seiß; Christian Fuhse; Andreas Pretsch; Michael Rahm; Manfred Heim; Winfried HOFFMÜLLER; Herbert ZASCHKA
Original assignee: Giesecke & Devrient Gmbh
Priority date: 2015-11-27
Filing date: 2016-11-18
Publication date: 2017-06-01
Also published as: WO2017088964A3; EP3792072A1; DE102015015407A1; EP3792073B1; EP3380334A2; EP3380334B1; CN111497492B; CN108472981B; CN108472981A; CN111497492A; EP3792073A1

Abstract

The invention relates to a method for embossing structures with dimensions in the micrometer or nanometer range in a layer of varnish. The layer of varnish is applied to one side of a film web and can be hardened by means of ultraviolet radiation. The film web is located in the conveying direction initially on one side, on which the layer of varnish which is yet to harden is applied, pressed through a presser on a embossing cylinder on which surface the structures which are to be stamped in the micrometer or nanometer region are arranged. This forms the structures in the micrometer range or in the nanometer range in the layer of varnish. Subsequently, the layer of varnish is hardened by ultraviolet radiation of a source for ultraviolet radiation. According to the invention, the film web is guided to the stamping cylinder from above or at least obliquely from above.

Description

Embossing process for embossing micro- or nanostructures

The invention relates to a method for embossing structures with dimensions in the range of micrometers or nanometers in a lacquer layer of a lacquer, wherein the lacquer layer is applied to one side of a film web and curable by means of ultraviolet radiation. The film web is first pressed in the conveying direction with the side on which the not yet cured lacquer layer is located, by a impression roller to an embossing cylinder, on the surface of which the structures to be embossed are in the micro or nanometer range. In the process, the structures in the micrometer or nanometer range are formed into the lacquer layer. Subsequently, the resist layer is cured by ultraviolet radiation from a source of ultraviolet radiation.

Such a method has been used for many years, wherein the film web is guided from below or at least from obliquely down to the embossing cylinder. A part of the varnish of the uncured lacquer layer accumulates in the conveying direction immediately before the point where the varnish layer touches the embossing cylinder and forms a so-called "lacquer wedge." However, this lacquer wedge is in the process known from the prior art The geometric shape and distribution of the lacquer wedge is thus stochastic, resulting in a particularly disadvantageous uneven distribution of the lacquer layer on the film web. The structures in the micron or nanometer range are thus embossed into an unevenly distributed lacquer layer, wherein even after the embossing and subsequent curing of the lacquer layer by means of UV radiation, an uneven thickness and in the horizontal direction, based on each the film web, unevenly distributed lacquer layer with embossed structures in the micro or nanometer range results.

The invention is therefore the object of developing a generic method such that the disadvantages of the prior art are eliminated.

This object is solved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

According to the invention, the film web is guided from above or at least obliquely from above to the embossing cylinder. It has surprisingly been found that the part of the lacquer of the not yet hardened lacquer layer, which accumulates in the conveying direction immediately before the point at which the lacquer layer touches the embossing cylinder, leads to a larger wetted surface on the surface of the embossing cylinder. In addition, the paint wedge of the method according to the invention is not distributed unevenly in contrast to the paint wedge of the method of the prior art and its geometric shape and distribution are not stochastically pronounced. This results in the film web both before and during and after embossing with structures in the micro or nanometer range, a resist layer with predictable and uniform thickness and greater width and a predictable and constant position on the film web. This leads particularly advantageously to an end product with constant and predictable properties and to a lower reject rate, ie to less defective or non-compliant embossed end products such as security threads or security strips with diffractive or mirror-like structures in or on banknotes. The reason for the larger wetted surface on the surface of the embossing cylinder in the method according to the invention is that the gravitational force leads the lacquer layer in addition to the direction of movement of the film web to the point at which the film web contacts the embossing cylinder. In contrast, in the prior art method, the lacquer layer is pulled away from the embossing cylinder by the gravitational force.

Another advantage of the invention is that due to the larger wetted surface on the surface of the embossing cylinder, the time for the escape of air from the embossing structures on the surface of the embossing cylinder increases, so that the paint layer at a higher speed of the film web and the same number of air bubbles in the embossed lacquer layer or alternatively at the same speed of the film web, but reduced number of air bubbles can be embossed in the embossed lacquer layer.

In the embossing method according to the invention, the impression roller is pressed against the embossing cylinder with a high mechanical pressure, so that a clearly recognizable amount of lacquer of the lacquer layer is squeezed. This means that the width of the lacquer layer after embossing is no longer identical to the width of the lacquer layer before the embossing cylinder, but wider. For example, the width of the paint before embossing is 620 mm and after embossing 720 mm.

A further object of the invention is to enable a higher speed of the film web with a constant number of air bubbles in the embossed lacquer layer or an equal or higher speed of the film web with a reduced number of air bubbles in the embossed lacquer layer, a so-called "bubble-free" embossing. The invention thus relates to a further method according to the preamble of the main claim, wherein for a rapid air bubble-free embossing the paint of the paint layer in the region of the embossing cylinder and / or in the paint wedge has a low viscosity. A reduction in the viscosity of the paint can be achieved by heating the paint. For example, a particular paint can be embossed free of air bubbles at a temperature of the paint of 20 ° C with a speed of the film web of 20 m / min and at a temperature of the paint of 60 ° C at a speed of the film web of 45 m / min. A heating of the paint thus particularly preferably leads to a speed of the film web that is more than twice as fast, and thus to an increase in the economic efficiency of the embossing process.

The inventive method for air bubble-free embossing by reducing the viscosity or heating of the paint can be done regardless of the direction of feeding the film web to the embossing cylinder, ie both in an inventive feeding the film web from above or at least from obliquely above the embossing cylinder and at a known from the prior art feeding the film web from below or at least from obliquely down to the embossing cylinder.

An influence on the width of the lacquer layer after the embossing process can be taken by the speed of the film web, the viscosity or temperature of the lacquer of the lacquer layer, the amount of lacquer applied to the film web and the impression pressure.

Bubble-free embossing, however, has only a very small range of variation for a change in the parameters of temperature and speed of the film web, ie even small changes in these parameters have a large influence the width of the lacquer layer after embossing. For example, the width of the paint before embossing is 620 mm and should be 720 mm after embossing. Even a change in the web speed of 1 m / min has a significant influence on the width of the paint layer after embossing. A significantly too low web speed of 5 m / min to 10 m / min causes the paint is squeezed beyond the edge of the film web, a slightly too high speed by about

3 m / min leads to air bubbles.

This means, in particular, that the width of the lacquer layer after embossing can be kept constant at a predetermined value via a change in the speed of the film web. If the width of the lacquer layer increases beyond a predetermined value after embossing, the web speed must be increased and vice versa.

A further object of the invention is to control the width of the lacquer layer on the film web after embossing or adhering to a predetermined value of this width.

The invention thus relates to a further method according to the preamble of the main claim, wherein in the surface of the Velinbereichs at the edge of the embossing cylinder, in which there are no structures to be embossed in the micron or nanometer range for the embossed end products, at least partially, preferably over the entire surface additional structures or Microstructures are introduced. Although the vellum area is no longer transferred faultlessly into the lacquer layer on the film web, the part of the film web embossed by the vellum area is in any case scrap and is cut off and disposed of, so that structures or microstructures in this area have no influence on the final end products. On the one hand, the additional structures or microstructures have a higher paint requirement due to their larger surface area, so that the fluctuation range of the width of the paint layer after embossing is reduced. Furthermore, the additional structures or microstructures make the inherently unrecognizable lacquer edge of the transparent lacquer discernible, that is to say the edge of the lacquer layer on the foil web at the outer left or right edge of the lacquer layer, by increasing the scattering or absorption or a recognizable change the reflection of the light incident on the lacquer layer lead. For example, the additional structure may be configured in the form of a checkerboard pattern with a dimension of the individual fields of 10 μm each, which optically leads to a matting of the paint compared to an unstructured, smooth surface. The additional structures can also consist of micromirrors or diffractive structures, which lead to a matting of the surface of the paint or a direction-dependent reflection of the incident light.

The control according to the invention of the width of the lacquer layer on the film web after embossing or adhering to a predetermined value of this width can be effected independently of the direction of feeding the film web to the embossing cylinder, ie both when the film web is fed from above or at least from obliquely up to the embossing cylinder as well as in a known from the prior art feeding the film web from below or at least from obliquely down to the embossing cylinder.

The position of the paint edge on the film web after the embossing is determined according to a preferred embodiment via an optical system. which consists, for example, of at least one light barrier or a camera system.

In this case, a light barrier is arranged above the lacquer layer of the film web in the conveying direction of the film web after the embossing cylinder, the light barrier being arranged above the lacquer layer of the film web in such a way that it monitors the area outside or beyond the lacquer edge, in which no lacquer layer on the lacquer layer Film web should be arranged. The light emitted by the light barrier should thus strike the smooth, reflecting surface of the film web without lacquer layer if the web speed is set correctly so that the detector of the light barrier indicates a first value. If the web speed is set too low, after embossing the width of the lacquer layer increases beyond the predetermined level and the lacquer edge shifts in the direction of the outer edge of the film web. The light emitted by the light barrier then strikes the surface of the lacquer layer which is embossed and, for example, matted by the additional structures or microstructures. Thus, less light is reflected back to the detector of the light barrier than in the case of the smooth, reflecting surface of the film web without lacquer layer, so that the detector of the light barrier displays a second value which is different from the first value. This second value is the signal for the control to increase the web speed until the detector of the light barrier again displays the first value. Additionally or alternatively, a second light barrier can be arranged such that it monitors the area within or on this side of the paint edge in which the paint layer is to be arranged on the film web. The detector of this light barrier should thus have the second value of that embossed by the additional structures or microstructures and, for example Show matted surface of the paint layer. If it indicates the first value of the smooth, reflecting surface of the film web without lacquer layer, the width of the lacquer layer is too small and the web speed must be reduced until the detector of this light barrier again displays the second value.

Instead of a selective detection of the position of the paint edge via one or two light barriers, detection along a line perpendicular to the edge of the paint can also take place. This is done, for example, by means of a camera system that evaluates the image along the line perpendicular to the edge of the paint. Such an evaluation also advantageously allows the evaluation of trends and thus enables a predictive intervention. In this case, the sensor or the camera system must be triggered, for example by means of the signal of an additional double wedge mark or by means of a rotary encoder on the embossing cylinder.

A film web consists for example of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polypropylene (PP) or polycarbonate (PC) with a thickness for security threads or security films of preferably 8 μπι to 36 μιη, banknotes made of polymer or composite film banknotes to 100 μπι or for card body up to 200 μιη.

The thickness of the lacquer layer is preferably 0.5 μπι to 20 μπ, more preferably 4 μιη to 15 μιη and most preferably from 4 μιτι to 8 μιη. The lacquer layer is preferably applied to the film web by means of a flexographic printing process.

According to a preferred embodiment, it is provided that the film web is deflected by a deflecting roller and applied to the embossing cylinder. leads, wherein the guide roller is arranged in the conveying direction in front of the press. By a second guide roller, the film web can be led away again from the embossing cylinder. By the first and optionally second deflection roller is achieved that the lacquer layer wraps around the embossing cylinder over a larger peripheral surface.

From the top in the sense of this invention means that the film is fed perpendicularly or at least almost perpendicularly from above or in the direction of the weight force or almost in the direction of the weight force on the embossing cylinder. At least obliquely from above in the sense of this invention means that the film is fed at an angle in a range from more than horizontal to almost perpendicular from above onto the embossing cylinder, wherein the film is in particular not supplied horizontally to the embossing cylinder. Such structures with dimensions in the range of micrometers or nanometers are used in particular for increasing the protection against counterfeiting of value documents, in particular banknotes, stocks, bonds, certificates, vouchers, checks, high-quality admission tickets, but also other counterfeit-endangered documents, such as passports and other identity documents - Mente, as well as cards, such as credit or debit cards, and also product security elements, such as labels, seals, packaging and the like. The structures with dimensions in the range of microns or nanometers are, for example, diffractive structures, micromirrors, matt structures or moth-eye structures.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the specified combinations but also in other combinations, without the frame As far as this is covered by the scope of the claims.

The advantages of the invention will be explained with reference to the following exemplary embodiments and the additional figures. The embodiments represent preferred embodiments, to which, however, the invention should not be limited in any way. Furthermore, the representations in the figures of better understanding are highly schematized and do not reflect the realities. In particular, the proportions shown in the figures do not correspond to the conditions present in reality and serve exclusively to improve the clarity. Furthermore, the embodiments described in the following exemplary embodiments are reduced to the essential core information for the sake of clarity. In practice, much more complex patterns or images can be used.

1 shows a side view of a stamping method according to the prior art,

2 is a side view of an inventive embossing method,

3 shows in plan view the edge region of a lacquer layer on a film web after embossing for a detection of the lacquer edge by two

Photocells, the object of Fig. 3 in side view, 5 shows a top view of the edge region of a lacquer layer on a film web after embossing for a detection of the lacquer edge by a camera system.

Fig. 1 shows a side view of a known from the prior art embossing method. On a film web 5 is a lacquer layer 6, wherein the film web is fed in the direction of movement 7 obliquely from below to an embossing device. The embossing device consists in this case of a stamping cylinder 1, in the surface to be embossed structures are introduced with dimensions in the range of microns or nanometers, a roller-shaped designed impression roller 2, a source 4 for ultraviolet radiation and two guide rollers 3. The film web 5 is through the first deflecting roller 3 deflected such that the lacquer layer 6 comes into contact with the embossing cylinder. Immediately before or at this line-shaped contact point, a part of the not yet cured lacquer layer accumulates, forming the unevenly shaped paint wedge 8. Subsequently, the film web 5 together with lacquer layer 6 is pressed by the impression roller 2 against the embossing cylinder 1 and the structures with dimensions in Area of micro or nanometers molded into the lacquer layer 6. Thereafter, the lacquer layer 6 is cured by electromagnetic radiation in the ultraviolet wavelength range of the source 4 and guided by a second guide roller 3 from the embossing cylinder 1 and fed to subsequent processing steps.

Fig. 2 shows a side view of the embossing method according to the invention, in which, in contrast to the embossing method of Fig. 1, the film web 5 is fed from obliquely above the embossing device. The film web 5 is deflected by the first guide roller 3 such that the lacquer layer 6 comes into contact with the embossing cylinder. Immediately before or at this line-shaped contact point, a part of the not yet cured lacquer layer accumulates Subsequently, the film web 5 together with the lacquer layer 6 is pressed by the impression roller 2 against the embossing cylinder 1 and the structures with dimensions in the range of micrometers or nanometers are molded into the lacquer layer 6. Thereafter, the lacquer layer 6 is cured by electromagnetic radiation in the ultraviolet wavelength range of the source 4 and led away via a second guide roller 3 from the embossing cylinder 1 and fed to subsequent processing steps. FIG. 3 shows in plan view the edge region of a lacquer layer on a film web after embossing for a detection of the lacquer edge by means of two light barriers. FIG. 4 shows the article from FIG. 3 in a side view along the sectional plane LL. A first light barrier 18, consisting of a light source 18.1 and a detector 18.2, is arranged over the lacquer layer 6 of the film web 5 in the conveying direction of the film web 5 after the embossing cylinder 1, so that they along a line 16 the area 13 outside or beyond the paint edge 15 monitors, in which no lacquer layer on the film web 5 should be arranged. The light emitted by the light source 18.1 thus hits the smooth, reflecting surface of the film web without lacquer layer, when the web speed is set correctly, so that the detector 18.2 indicates a first value. A second light barrier 19, consisting of a light source 19.1 and a detector 19.2, is arranged such that it monitors along a line 17 the area 14 within or on this side of the paint edge 15, in which the paint layer 6 is to be arranged on the film web 5. In area 12, the additional structures or microstructures are in the vein area of the embossing cylinder, which are embossed only in the area 14 in the lacquer layer 6. The detector 19.2 displays the second value by the additional structures or microstructures embossed and, for example, matted surface 14 of the lacquer layer 6, which is different from the first value.

5 shows in plan view the edge region of a lacquer layer on a film web after embossing for a detection of the lacquer edge by a camera system. In this case, detection takes place along a line 20 perpendicular to the coating edge 15. This detection takes place, for example, by means of a camera system which evaluates the image along the line 20 by determining the gloss values of the corresponding surfaces.

Claims

P a n t a n s p r e c h e

A method for embossing structures having dimensions in the range of micrometers or nanometers in a lacquer layer of a lacquer, wherein the lacquer layer is applied to one side of a film web and curable by means of ultraviolet radiation, wherein the film web in the conveying direction first with the side on which the not yet cured lacquer layer is pressed by a impression roller to an embossing cylinder, on the surface of which the structures to be embossed are located in the micrometer or nanometer range, that the structures in the micrometer or nanometer range are molded into the lacquer layer, and then the lacquer layer is hardened by an ultraviolet radiation of a source of ultraviolet radiation, characterized in that the film web is guided from above or at least obliquely from above to the embossing cylinder, so that a part of the lacquer of the not yet cured lacquer layer in the conveying direction immediately before the bodyaccumulated at the lacquer layer touches the embossing cylinder, resulting in a larger wetted surface on the surface of the embossing cylinder.

A method according to claim 1, characterized in that the film web is deflected by a deflecting roller and guided on the embossing cylinder, wherein the deflecting roller is arranged in the conveying direction in front of the impression roller.

Method for embossing structures having dimensions in the range of micrometers or nanometers into a lacquer layer, wherein the lacquer layer is applied to one side of a film web and is curable by means of ultraviolet radiation, the film web being fed in the transport direction. It is only with the side on which the not yet hardened lacquer layer is located that the impression is pressed through a impression roller to an embossing cylinder on the surface of which the structures to be embossed are located in the micro- or nanometer range. or nanometer range in the lacquer layer, and then the lacquer layer is cured by an ultraviolet radiation of a source of ultraviolet radiation, characterized in that for an air bubble-free embossing the lacquer of the lacquer layer in the region of the embossing cylinder and / or at the location in the direction of transport the lacquer layer touches the embossing cylinder and a part of the lacquer of the not yet hardened lacquer layer accumulates, has a low viscosity.

A method according to claim 3, characterized in that a reduction in the viscosity of the paint is achieved by heating the paint.

Method for embossing structures with dimensions in the range of micrometers or nanometers into a lacquer layer, wherein the lacquer layer is applied to one side of a film web and curable by means of ultraviolet radiation, wherein the film web in the conveying direction first with the side on which still unhardened lacquer layer is pressed by a impression roller to an embossing cylinder, on the surface of which are to be embossed structures in the micro or nanometer range, is pressed, that the structures in the micron or nanometer range in the lacquer layer, and then the lacquer layer through an ultraviolet radiation of a source of ultraviolet radiation is hardened, characterized in that on the surface of a vein area at the edge of the embossing cylinder in which no structures to be embossed in the micro or nanometer range are located. find, at least partially, preferably over the entire surface additional structures or microstructures are introduced.

6. The method according to claim 3, characterized in that an edge of the lacquer layer on the film web at the outer left or right edge of the lacquer layer after the embossing is determined by an optical system.