CN111497492B

CN111497492B - Embossing method for embossing microstructures or nanostructures

Info

Publication number: CN111497492B
Application number: CN202010122837.9A
Authority: CN
Inventors: A.劳赫; F.西弗斯; G.基弗索尔; B.塞斯; C.富瑟; A.普雷奇; M.拉姆; M.海姆; W.霍夫米勒; H.扎什卡
Original assignee: Giesecke and Devrient GmbH
Current assignee: Giesecke and Devrient GmbH
Priority date: 2015-11-27
Filing date: 2016-11-18
Publication date: 2022-03-08
Anticipated expiration: 2036-11-18
Also published as: WO2017088964A3; CN108472981A; EP3792073A1; CN108472981B; EP3380334A2; EP3380334B1; EP3792072A1; CN111497492A; EP3792073B1; WO2017088964A2; DE102015015407A1

Abstract

The invention relates to a method for embossing structures having dimensions in the micrometer or nanometer range into a paint layer (6) consisting of a paint, wherein the paint layer (6) is arranged on one side of a film web (5) and can be hardened by means of ultraviolet radiation. The film web (5) is first pressed in the transport direction with the side on which the not yet hardened paint layer is present, by means of a pressure roller (2), against an embossing cylinder (1) on the surface of which structures in the micrometer or nanometer range to be embossed are located. In this case, structures in the micrometer or nanometer range are formed in the lacquer layer. The paint layer (6) is then hardened by means of ultraviolet radiation from a source for ultraviolet radiation. According to the invention, the film web (5) is guided to the impression cylinder (1) from above or at least from an oblique top.

Description

Embossing method for embossing microstructures or nanostructures

The present application is a divisional application of a prior application entitled "imprint method for imprinting microstructures or nanostructures" filed as 2016, 11, 18, and having an application number of 201680079437.6.

Technical Field

The invention relates to a method for embossing structures having dimensions in the micrometer or nanometer range into a paint layer consisting of a paint, wherein the paint layer is arranged on one side of a film web and can be hardened by means of ultraviolet radiation. First, the film web is pressed in the transport direction with the side on which the not yet hardened paint layer is present, by means of a pressure roller, against an embossing cylinder, on the surface of which structures in the micrometer or nanometer range to be embossed are located. In this case, structures in the micrometer or nanometer range are formed in the lacquer layer. The paint layer is then hardened by ultraviolet radiation from a source for ultraviolet radiation.

Background

Such methods have been known for many years, in which the film web is guided to the embossing cylinder from below or at least obliquely from below. A portion of the paint of the layer of paint which has not yet been hardened ends up in the transport direction just before the point where the layer of paint contacts the impression cylinder and constitutes a so-called "paint wedge". However, such lacquer wedges are unevenly distributed in the methods known from the prior art, wherein both the thickness of the wedge and its distribution in the direction of the axis of rotation of the impression cylinder are continuously and unpredictably variable. The geometry and the distribution of the paint wedges are thus random, which is particularly disadvantageous in that an uneven distribution of the paint layer in the film web is formed. The structures in the micrometer range or nanometer range are thus embossed in the unevenly distributed paint layer, wherein after embossing and subsequent hardening of the paint layer by means of UV radiation, a paint layer is also formed which is not of the same thickness and is unevenly distributed in the horizontal direction, in each case based on the film web, with structures in the micrometer range or nanometer range being embossed.

Disclosure of Invention

The object of the invention is therefore to improve the method in such a way that the disadvantages of the prior art are overcome.

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

According to the invention, the film web is guided from above or at least obliquely above to the impression cylinder. Surprisingly, the portion of the not yet hardened lacquer layer of the lacquer layer which accumulates in the transport direction just before the point at which the lacquer layer contacts the impression cylinder results in a larger wetted surface on the surface of the impression cylinder. Furthermore, in contrast to the paint wedges of the prior art method, the paint wedges of the method according to the invention are not unevenly distributed and their geometry and distribution are not randomly formed. A lacquer layer is thus obtained on the film web, not only before, but also during and after embossing with structures in the micrometer or nanometer range, with a predictable and uniform thickness and greater width, and with predictable and unchanging positions on the film web. This leads particularly advantageously to end products having stable and predictable properties and to a lower reject rate, that is to say to end products which are less flawed or embossed in compliance with regulations, for example security threads or security strips having diffractive or mirror-like structures in or on banknotes.

The reason for the larger wetted surface on the surface of the impression cylinder in the method according to the invention is that gravity guides the lacquer layer, in addition to the direction of movement of the film web, to the point where the film web contacts the impression cylinder. In contrast, in the prior art method, the lacquer layer is pulled away from the impression cylinder by gravity.

A further advantage of the invention is that, by means of the larger wetted surface on the surface of the impression cylinder, the time for air to escape from the impression structure on the surface of the impression cylinder is increased, so that the paint layer can be imprinted at a higher film web speed and with a constant number of bubbles in the imprinted paint layer, or alternatively in contrast thereto with a constant film web speed but with a reduced number of bubbles in the imprinted paint layer.

In the embossing method according to the invention, the pressure roller presses with high mechanical pressure on the embossing cylinder, so that a clearly discernible quantity of the lacquer layer is pressed. This means that the width of the lacquer layer after embossing is no longer the same as the width of the lacquer layer before the embossing cylinder, but is wider. For example, the width of the lacquer before embossing is 620mm and 720mm after embossing.

Another object of the invention is to provide a method for embossing a film web with a constant number of air bubbles in the embossed paint layer, or with a reduced number of air bubbles in the embossed paint layer, with the same or even higher speed of the film web, so-called "bubble-free" embossing.

The invention therefore relates to a further method according to the preamble of the independent claim, in which the lacquer of the lacquer layer in the region of the embossing cylinder and/or in the lacquer wedge has a low viscosity for rapid, bubble-free embossing. The reduction in viscosity of the lacquer may be achieved by heating the lacquer. For example, a certain lacquer can be printed without bubbles at a film web speed of 20m/min at a lacquer temperature of 20 ℃ and at a film web speed of 45m/min at a lacquer temperature of 60 ℃. The heating of the lacquer therefore particularly preferably results in more than twice the film web speed and thus in an increase in the economy of the embossing process.

The method according to the invention for bubble-free embossing by reducing the viscosity or by heating the lacquer can be carried out independently of the direction of introduction of the film web into the embossing cylinder, i.e. not only when the film web is fed (or fed) to the embossing cylinder from above or at least obliquely from above according to the invention, but also when the film web is fed to the embossing cylinder from below or at least obliquely from below as is known from the prior art.

The speed of the film web, the viscosity or temperature of the lacquer layer, the quantity of lacquer applied to the film web and the pressure of the pressure roller can influence the width of the lacquer layer after the embossing process.

However, bubble-free embossing has only a very small variation range for the variation of the parameters temperature and speed of the film web, i.e. small variations of these parameters have a large influence on the width of the embossed paint layer. For example, the width of the lacquer before embossing is 620mm and after embossing it should be 720 mm. A web speed change of 1m/min already has a significant influence on the post-embossed lacquer layer width. A web speed of about 5m/min to 10m/min, which is clearly too low, results in the paint being squeezed beyond the edges of the film web, and a slightly too high speed of about 3m/min results in air bubbles.

This also means, in particular, that the width of the imprinted lacquer layer can be kept constant at a predetermined value by varying the speed of the film web. If the width of the imprinted lacquer layer increases beyond a predetermined value, the web speed must be increased, and if the width of the imprinted lacquer layer decreases beyond a predetermined value, the web speed must be reduced.

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

The invention therefore relates to a further method according to the preamble of the independent claim, in which additional structures or microstructures are introduced at least partially, preferably completely, into the surface of the satin zone (Velinbereich) on the edge of the embossing cylinder, in which there are no structures to be embossed in the micrometer range or nanometer range for the embossed end product. Although the satin area is no longer transferred defect-free into the paint layer on the film web, the part of the film web which is embossed by the satin area is inherently a trim and is cut off and treated so that the structure or microstructure in this area has no effect on the subsequent end product.

The additional structures or microstructures, on the one hand, have a higher demand for lacquer due to their larger surface, so that the undulating region of the width of the lacquer layer after embossing is reduced.

In addition, the additional structure or microstructure also makes it possible to distinguish the edges of the transparent lacquer that are not discernible per se, i.e. the edges of the lacquer layer on the left or right outer edge of the lacquer layer on the film web, by the additional structure or microstructure leading to an increase in scattering or absorption or to a discernible change in the reflection of the light incident on the lacquer layer. For example, the additional structure can be designed in the form of a chessboard pattern, the individual areas each having a size of 10 μm, which visually leads to a sanding of the lacquer compared to an unstructured smooth surface. The additional structures can also consist of micro-mirrors or diffractive structures, which lead to roughening of the painted surface or to a directionally dependent specular 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 whether the width corresponds to a predetermined value, can be carried out independently of the direction of introduction of the film web into the embossing cylinder, i.e. not only when the film web is fed to the embossing cylinder from above or at least from above at an angle, but also when the film web is fed to the embossing cylinder from below or at least from below at an angle, as is known from the prior art.

In a preferred embodiment, the position of the edge of the film web after embossing is determined by an optical system, which is formed, for example, by at least one optical grating or at least one camera system.

In this case, the grating is arranged in the transport direction of the film web after the impression cylinder above the paint layer of the film web, wherein the grating is arranged above the paint layer of the film web in such a way that the grating monitors the region outside the paint edge or on the other side of the paint edge, in which the paint layer is not to be arranged on the film web. When the web speed is set correctly, the light emitted by the grating thus impinges on a smooth, mirror-like surface of the film web without lacquer layer, so that the detector of the grating shows a first value. If the web speed is set too low, the width of the paint layer after embossing exceeds a predetermined amount and the paint edges move in the direction of the outer edges of the film web. The light emitted by the grating impinges on the surface which is embossed with additional structures or microstructures and which is roughened, for example, with a lacquer layer. Thus, less light is reflected back to the detector of the grating than in the case of a smooth, mirror-like surface of a film web without a lacquer layer, so that the detector of the grating displays a second value which is different from the first value. For the adjustment, the second value is a signal, i.e., the web speed is increased in this way until the detector of the raster again indicates the first value.

In addition or alternatively, a second grating can be arranged such that it monitors the region inside or on the side of the paint edge, in which the paint layer is to be arranged on the film web. The detector of the grating thus displays a second value of the surface of the lacquer layer which is impressed by the additional structure or microstructure and is, for example, roughened. If the detector of the grating displays a first value for a smooth mirror-like surface of the film web without a lacquer layer, the width of the lacquer layer is too small and the web speed must be reduced until the detector of the grating again displays a second value.

Instead of a point detection of the position of the lacquer edge by one or two light barriers, a detection along a line perpendicular to the lacquer edge can also be carried out. This is done, for example, by means of a camera system which analyzes images along a line perpendicular to the edge of the lacquer. Such an analysis advantageously also allows an analysis of the trend and thus an intervention of prospective nature. In this case, the sensor or camera system must be triggered, for example, by a signal of an additional double wedge mark or by a rotary encoder on the platen.

The film web is made, for example, of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polypropylene (PP) or Polycarbonate (PC) and has a thickness of preferably 8 μm to 36 μm for security threads or films, a thickness of at most 100 μm for banknotes made of polymers or film-laminated banknotes, or a thickness of at most 200 μm for card bodies.

The thickness of the lacquer layer is preferably a thickness of from 0.5 μm up to 20 μm, particularly preferably from 4 μm up to 15 μm and very particularly preferably from 4 μm to 8 μm. The lacquer layer is preferably applied to the film web by means of a flexographic printing process (flexodrucksverfahren).

According to a preferred embodiment, the film web is deflected by a deflection roller and guided onto the impression cylinder, the deflection roller being arranged upstream of the pressure roller in the transport direction. The film web can again be guided away from the impression cylinder by means of a second deflection roller. The first deflection roller and, if appropriate, the second deflection roller make it possible for the lacquer layer to wrap around the impression cylinder over a larger circumferential surface.

According to the invention, the term "from above" means that the film is guided vertically or at least approximately vertically from above or in the direction of gravity or approximately in the direction of gravity onto the impression cylinder. According to the invention, the term "at least obliquely from above" means that the film is guided onto the impression cylinder from above at an angle in the range from more than horizontal to approximately vertical, wherein the film is guided onto the impression cylinder in particular not horizontally.

Such structures with dimensions in the micrometer or nanometer range are used in particular for improving the security protection of documents of value, in particular banknotes, stocks, bonds, certificates, vouchers, checks, high-quality admission tickets, but also for other paper which is at risk of counterfeiting, such as passports and other documents for identification, and cards, such as credit or debit cards, including also product security elements, such as labels, stamps, packaging, etc. Structures having dimensions in the micro-or nano-range are, for example, diffractive structures, micro-mirrors, frosted structures or moth-eye structures.

Of course, the features mentioned above and those yet to be explained below can be used not only in the combinations indicated, but also in other combinations without leaving the scope of protection of the present invention, as long as these combinations are included in the scope of protection.

The advantages of the invention are illustrated by the following examples and supplementary figures. These examples represent preferred embodiments, to which, however, the invention is not in any way restricted. Moreover, the illustrations in the figures are strongly schematic and do not reflect the reality for a better understanding. In particular, the proportions shown in the figures are not to scale with actual relationships present, but are merely intended to clarify the views. Further, for ease of understanding, the embodiments described in the following embodiments are reduced to essential core information. In practice, more complex patterns or images can be used.

Drawings

In the schematic diagram:

figure 1 shows a side view of an embossing method according to the prior art,

figure 2 shows a side view of the embossing method according to the invention,

figure 3 shows a plan view of the edge region of the paint layer on the embossed film web with the paint edges detected by two rasters,

figure 4 shows a side view of the object shown in figure 3,

fig. 5 shows a top view of the edge region of the paint layer on the embossed film web with the paint edge detected by the camera system.

Detailed Description

Fig. 1 shows a side view of an imprinting method known from the prior art. The lacquer layer 6 is located on the film web 5, wherein the film web is guided in the direction of movement 7 from obliquely below onto the embossing device. The embossing device is formed here by an embossing cylinder 1, a pressure roller 2 of roller-shaped design, an ultraviolet radiation source 4 and two deflection rollers 3, into the surface of which embossing cylinder 1 structures to be embossed are introduced having dimensions in the micrometer or nanometer range. The film web 5 is deflected by the first deflection roller 3 in such a way that the lacquer layer 6 comes into contact with the impression cylinder. A part of the not yet hardened paint layer accumulates in front of or at the linear contact point and forms an unevenly formed paint wedge 8 in this case. The film web 5 with the paint layer 6 is then pressed by the pressure roller 2 onto the impression cylinder 1 and structures having dimensions in the micrometer or nanometer range are formed in the paint layer 6. The lacquer layer 6 is then hardened by electromagnetic radiation in the ultraviolet wavelength range of the source 4 and guided away from the impression cylinder 1 by the second deflection roller 3 and to the 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 guided to the embossing device from obliquely above. The film web 5 is deflected by the first deflection roller 3 in such a way that the lacquer layer 6 comes into contact with the impression cylinder. A part of the not yet hardened paint layer accumulates in the vicinity of or at the linear contact point and forms the paint wedge 9 described above and particularly advantageously uniformly shaped here. The film web 5 with the paint layer 6 is then pressed by the pressure roller 2 onto the impression cylinder 1 and structures having dimensions in the micrometer or nanometer range are formed into the paint layer 6. The lacquer layer 6 is then hardened by electromagnetic radiation in the ultraviolet wavelength range of the source 4 and guided away from the impression cylinder 1 by the second deflection roller 3 and to the subsequent processing steps.

Fig. 3 shows a plan view of the edge region of the paint layer on the embossed film web with the paint edges detected by two rasters. Fig. 4 shows a side view of the object shown in fig. 3 along a section plane LL.

The first raster 18 is formed by a light source 18.1 and a detector 18.2, the first raster 18 being arranged in the transport direction of the film web 5 after the impression cylinder 1 above the paint layer 6 of the film web 5, so that the first raster 18 monitors along the line 16 the region 13 outside the paint edge 15 or on the other side of the paint edge 15, in which no paint layer is arranged on the film web 5. When the web speed is set correctly, the light emitted by the light source 18.1 thus impinges on a smooth, mirror-like surface of the film web without lacquer layer, so that the detector 18.2 shows a first value.

The second light barrier 19 is formed by a light source 19.1 and a detector 19.2, and the second light barrier 19 is arranged such that the second light barrier 19 monitors the region 14 within the paint edge 15 or on the side of the paint edge 15 along the line 17, in which the paint layer 6 is arranged on the film web 5. The additional structure or microstructure in the satin area of the embossing cylinder is in the region 12, which is embossed into the lacquer layer 6 only in the region 14. The detector 19.2 shows a second value of the lacquer layer 6, which is different from the first value, as a result of the additional structure or microstructure embossed and, for example, roughened surface 14.

Fig. 5 shows a top view of the edge region of the paint layer on the embossed film web with the paint edge detected by the camera system. In this case, the detection takes place along a line 20 perpendicular to the lacquer edge 15. This detection takes place, for example, by means of a camera system which analyzes the images along the line 20 by determining the gloss values of the respective surfaces.

Claims

1. A method for controlling the transport speed of a film web during embossing of structures having dimensions in the micrometer or nanometer range into a transparent lacquer layer on the film web moving in the transport direction, wherein the transparent lacquer layer is arranged on one side of the film web and can be hardened by means of ultraviolet radiation, wherein the film web is first pressed with the side on which the transparent lacquer layer is present that has not yet been hardened in the transport direction by means of a pressure roller onto an embossing cylinder of the structures in the micrometer or nanometer range to be embossed on its surface, such that the structures in the micrometer or nanometer range are shaped in the transparent lacquer layer, and wherein subsequently the transparent lacquer layer is hardened by means of ultraviolet radiation from a source for ultraviolet radiation,

it is characterized in that the preparation method is characterized in that,

at least partially, additional structures are introduced on the surface of the regions of the edges of the embossing cylinder in which the structures in the micrometer range or nanometer range to be embossed are absent, said additional structures, when introduced on the paint layer edges at the outer edges of the paint layer, being able to cause a discernible change in the reflection of light impinging on the paint layer edges,

determining whether the embossed paint layer width defined by the paint edge remains at a predetermined value as a function of the discernible change, wherein the paint layer width is maintained at the predetermined value by changing the transport speed of the film web when the paint layer width is not maintained at the predetermined value.

2. A method as claimed in claim 1, characterized in that the additional structures are introduced over the entire surface of the regions of the edge of the embossing cylinder in which the structures in the micrometer range or nanometer range are not to be embossed.

3. A method according to claim 1 or 2, wherein the additional structure is a microstructure.

4. A method as claimed in claim 1, characterized in that the position of the edge of the lacquer layer on the film web after embossing is determined by means of an optical system.

5. A method as claimed in claim 4, characterized in that the optical system comprises a grating for emitting light to the paint arrises and a detector for detecting light reflected back to the grating, said detector showing a first value when said additional structure is not detected and a second value different from the first value when said additional structure is detected.

6. A method as claimed in claim 5, characterized in that the raster monitors the side region of the paint edge on which the paint layer is to be applied to the film web, wherein when the detector indicates the second value, this indicates that the embossed paint layer width is maintained at a predetermined value.

7. A method as set forth in claim 6 wherein, when the detector indicates the first value, the speed of conveyance of the film web is reduced until the detector again indicates the second value.

8. A method as claimed in claim 5, characterized in that the raster monitors the side region of the paint edge in which no paint is to be applied to the film web, wherein when the detector indicates the first value, this indicates that the embossed paint width is maintained at a predetermined value.

9. The method of claim 8, wherein when the detector indicates the second value, the speed of the film web is increased until the detector again indicates the first value.

10. A method according to claim 1, wherein said additional structure is designed in the form of a chess board pattern.

11. Method according to claim 1, characterized in that the additional structure is constituted by a micro mirror or a diffractive structure.