EP2760676B1 - Method for producing a microstructure support - Google Patents

Description

The invention relates to a method for producing a microstructure on a support, to a microstructure support obtainable by the process, to microoptical representational arrangements comprising the microstructure support according to the invention, and to articles having a microstructure support according to the invention or a microoptical representation arrangement according to the invention.

Data carriers, such as security documents or identity documents, and other items such as branded articles, are often provided with security elements for the purpose of security, which permit verification of the authenticity of the data carrier and at the same time serve as protection against unauthorized reproduction. The security elements can be embodied, for example, in the form of a security thread embedded in a banknote, a covering film for a banknote with a hole, an applied security strip or a self-supporting transfer element which is applied to a value document after its manufacture.

Security elements with optically variable elements, which give the viewer a different image impression at different viewing angles, play a special role since such optically variable elements can not be reproduced even with very high-quality color copying machines. For this purpose, the security elements can be equipped with security features in the form of diffraction-optically effective microstructures or nanostructures, for example with conventional embossed holograms or other hologram-like diffraction structures.

More recently, so-called micro-optical representation arrangements are used as security features. A typical and well-known micro-optical representation arrangement is, for example, a moiré magnification arrangement. The basic mode of operation of such moiré magnification arrangements is described in the article " The moire magnifier ", MC Hutley, R. Hunt, RF Stevens and P. Savander, Pure Appl. Opt. 3 (1994), pp. 133-142 , described. The so-called moiré magnification is a phenomenon that occurs when viewing a grid of identical image objects through a lenticular of approximately the same pitch. As with any pair of similar rasters, this results in a moiré pattern consisting of a periodic arrangement of enlarged and possibly rotated images of the elements of the image raster.

The grating period and the diameter of the image objects are of the same order of magnitude as those of the microlenses of the lenticular grid. With the naked eye the image objects should not be recognizable. The smaller the structures are formed, the greater the security against counterfeiting.

Due to the small size of the structures, all methods for producing the image objects (micromotif elements), in which application methods such as printing methods play a significant role in the achievable dimensions, are less suitable because the achievable minimum size of the micromotif elements is limited by the resolution of the application method. Microstructures or micromotif elements are therefore preferably produced using embossed structures. Embossing can be generated in very high resolution.

Particularly conspicuous, memorable and tamper-proof are micro-optical representations with contrast-rich colored microstructures. The microstructure elements of microstructure supports are therefore preferably colored. For the coloring of embossed microstructures several methods are known.

The WO 2009/083146 discloses a method for producing a microstructure in which an embossed structure is produced and either only the elevations or only the depressions of the embossed structure are covered or filled with an imprint material. The imprint material must be selected correspondingly highly viscous, to adhere only to the elevations of the embossed structure, or chosen correspondingly low viscosity, to fill only the recesses of the embossed structure. In order to achieve the desired selective application, the viscosity of the printing material and the transfer conditions must be precisely matched, which is complicated. Frequently, the application is not as selective as desired, which may limit the achievable contrast.

From the WO 2009/121578 For example, a method for producing a microoptical representation arrangement is known in which a stamping structure is produced in a substrate and the stamping recesses are filled with paint. The color in the wells forms the micromotif elements while the excess of color is being doctored off. However, scraping as a purely mechanical process does not make it possible to completely remove the color outside the pits. It remains a Tonungsfilm, that is a very small, but usually noticeable remainder of color, back, which limits the maximum achievable contrast.

In the WO 2011/057739 discloses a method which is intended to avoid a retention of such a Tonungsfilms. In the process is on the surface of the microstructure support has a protective layer that does not cover the microwell-equipped surface area, then a paint that both fills the microwells and forms a layer on top of the protective layer, and finally removes the protective layer along with the unwanted color layer. However, this variant of the method does not remove the undesirable color on the bumps between the individual microwells.

In the event that the Tonungsfilm on the surveys between the individual microwells is to be removed to achieve the best possible contrast, beats the WO 2011/057739 a multi-step approach. First, the microwells must be filled with a release layer, then a protective layer is applied over the entire surface, removed the protective layer together with the release layer in the microwells, finally applied a coat of paint, scraped the ink layer in the undesirable areas as far as possible, and finally the protective layer together with removed the unwanted areas of the color layer.

A simple method for producing colored microstructures in which color is located exclusively in the depressions of the embossed structure, while all areas outside the depressions are free of color, is not yet known.

It is therefore an object of the present invention to obviate the drawbacks of the prior art and to provide a simple, reliable method for producing high contrast color microstructures suitable for microoptical display arrangements. In order to achieve the high contrast, color should be used exclusively in the area of the microstructure elements, ie in the area of the embossing recesses, while avoiding a toning film in all other areas.

The object is achieved by the method for producing a microstructure on a support with the features as stated in claim 1. Further objects of the present invention are a microstructure support, a micro-optical representation arrangement, and objects with the microstructure support or the micro-optical representation arrangement, in each case having the features as indicated in the other independent claims. Advantageous embodiments of the invention are specified in the respective dependent claims.

In the method according to the invention for producing a microstructure on a carrier, an embossing structure with elevations and depressions is first formed in at least a partial region of a carrier foil, wherein the depressions are arranged in the form of the microstructure, and then the depressions are provided with a composition filled in the desired color. This can be done as for example in the publications WO 2009/121578 and WO 2009/083146 disclosed. In the method disclosed in the latter document, the depressions are typically not completely filled, and only a thin toning film is present on the elevations of the microstructure, whereas in the method according to FIG WO 2009/121578 the wells are completely filled and on the surveys a relatively thick paint layer is present, which still needs to be removed. Typically, the excess color is doctored off, leaving after toning still a Tonungsfilm. Toning films are not or at least not completely removable by mechanical means such as doctoring.

The term "color" is to be understood in the broadest sense. Also white, black and gray are colors in the sense of the present invention. Colored compositions can also be transparent or translucent. It is essential that the materials are visually distinguishable to a viewer.

The carrier used is preferably a transparent plastic film, in particular a PET film, wherein layer thicknesses between about 6 μm and 60 μm are preferred. The microstructures are preferably formed with a structure depth between about 1 .mu.m and about 20 .mu.m, more preferably between about 1 .mu.m and about 10 .mu.m. The micromotif elements are preferably produced with a lateral dimension between about 5 μm and about 50 μm, more preferably between about 10 μm and about 35 μm.

To fill the microstructures, i. of the microstructure pits to form the colored micromotif elements, free-radically or cationically radiation-curable compositions in the desired color are used. The invention takes advantage of the fact that the radical polymerization is inhibited by oxygen, and the cationic polymerization by moisture, that is, by vapor or gaseous water, is inhibited. It has long been known that radically radiation-curable compositions such as UV varnishes and UV-curable inks should be cured under inert gas to avoid premature chain terminations by formation of peroxide radicals. Similarly, in the cationic polymerization, the irradiation zone should be kept very dry, for example by rinsing with a dried gas.

The problem with prior art methods is the creation of an unavoidable toning film which provides the maximum achievable contrast Reduced undesirable in colored microstructures. The invention solves the problem by forming the colored microstructures by means of radically radiation-curable colored compositions or cationic radiation-curable colored compositions and targeted utilization of the inhibition of the polymerization reactions by oxygen or moisture.

As mentioned several times above, after filling the embossed microstructure recesses with a colored composition, if appropriate after doctoring off excesses of the composition, there is a carrier material which has an undesired toning film on the surface areas which are raised in relation to the depressions. This toning film has a very small layer thickness compared to the layer thickness of the colored compositions in the microwells. For comparison: typical layer thicknesses of the colored compositions in the microwells are from about 1 μm to about 20 μm (approximately corresponding to the maximum structure depth of the depressions), while the toning film has a thickness of about 0.1 μm. Oxygen diffuses across the surface into the coating, with the rate of diffusion being, of course, the same in the region of the microwells and outside the microwells. At a time when oxygen is already present in the entire layer thickness of the toning film, in the microwells the oxygen is only present in a corresponding layer thickness of the composition, i. only in a thin surface area.

If the composition is then irradiated with radiation of a suitable wavelength, curing is inhibited in the areas of high oxygen content, ie the curing takes place slowly. With suitable coordination of radiation intensity and time duration, there is for each radiation-curable system a period in which, although the surface-distant part of the radiation-curable composition is already hardened in the microwells, the near-surface part of the layer thickness of the toning film, and of course the entire toning film, is hardly hardened. During this period, the uncured composition can still be detached from the support material or in the areas of the microwells from the cured part of the composition.

The process according to the invention is preferably carried out inline, i. Curing takes place immediately after filling the microwells, and optionally, doctoring off the excess of the radiation-curable composition. With a very long time between application of the radiation-curable composition and its cure, oxygen (or moisture in cationic curing systems) may penetrate too deep into the composition in the microwells. If intermediate storage before curing is desired or necessary, it is therefore recommended to temporarily store in the absence of oxygen or moisture. Otherwise, however, the time factor between application of the radiation-curable composition and its cure is not critical because of the considerable difference in thickness between the toning film and the thickness of the composition in the microwells.

Of course, the above for oxygen and radically curing compositions is fully analogous to moisture and cationic curable compositions.

As a rule, it is sufficient for the desired inhibition of the curing according to the invention to carry out the curing in normal ambient air. To enhance the effect, of course, the oxygen content of the Air or the moisture content of the air can be increased specifically to achieve a faster and stronger penetration of the Tonungsfilms with oxygen or water. This can be advantageous, in particular in the case of very high-viscosity systems in which the diffusion rate is slow. The process conditions which are advantageous for a hardening inhibited according to the invention, such as the duration and intensity of the irradiation, and, if appropriate, intensification of the inhibition by increasing the oxygen or moisture content, depend on the radiation-curable composition chosen. Advantageous conditions can be determined by a person skilled in the art for each system with the aid of less orienting tests.

The radiation-curable compositions suitable for the process according to the invention are not limited in any particular way. In principle, all pigmentable compositions which can be cured radically or cationically by radiation, such as, for example, UV radiation, X-radiation, electron radiation or else IR radiation, are suitable. The compositions should be at least to some extent soluble in water or an organic solvent in the uncured state or only weakly crosslinked state, but in the substantially crosslinked state should no longer be soluble in this solvent. Corresponding paints and printing inks are known to a person skilled in the art. Particularly preferred for the present invention are radically curing UV lacquers, i. UV lacquers with oxygen inhibition.

Suitable examples are UV flexographic inks from the series UVAFLEX Y (Zeller + Gmelin) and also compositions of 40% by weight Ebecryl 294/25 HD (Cytec), 38% by weight HDDA (= hexanediol diacrylate), 15% by weight wheel -Color L3 Process Cyan (Kromachem), 7% by weight Lucirin TPO-L (BASF). Suitably such compositions do not contain amine synergists, which are typically used against oxygen inhibition.

In the case of irradiation with UV radiation, the choice of the radiator is advantageously matched to the lacquer or the printing ink and the photoinitiator used. While undoped Hg emitters are well suited for surface hardening, doped emitters (e.g., Fe doping or Ga doping) are better for curing in the off-chip part in the microwells and thus more suitable for the process of the present invention.

• Eine Möglichkeit besteht darin, eine Substanz aufzubringen, die den Tonungsfilm löst oder zumindest anlöst, und den gelösten Tonungsfilm bzw. den gelösten Teil des Tonungsfilms dann gemeinsam mit der Ablösesubstanz mittels mechanischer Mittel wie Abrakeln oder Abwischen zu entfernen. Je nach Art der strahlenhärtbaren Zusammensetzung kann eine derartige Ablösesubstanz beispielsweise Wasser oder ein organisches Lösungsmittel oder ein Gemisch organischer Lösungsmittel oder auch ein Gemisch aus Wasser und mindestens einem organischen Lösungsmittel sein. Die Ablösesubstanz kann übliche Hilfsstoffe, beispielsweise Tenside, Entschäumer, Entlüfter oder Verdicker enthalten. Geeignet sind auch kommerzielle Reinigungsmittel.

In order to remove the undesired toning film, ie the non-hardened or only slightly cured radiation-curable composition, there are several possibilities according to the invention:

• One possibility is to apply a substance which dissolves or at least dissolves the toning film, and then to remove the dissolved toning film or the dissolved part of the Tonungsfilms together with the release substance by mechanical means such as doctoring or wiping. Depending on the nature of the radiation-curable composition, such a release substance may be, for example, water or an organic solvent or a mixture of organic solvents or else a mixture of water and at least one organic solvent. The release substance may contain conventional auxiliaries, for example surfactants, defoamers, deaerators or thickeners. Also suitable are commercial cleaning agents.

The release substance may for example be printed or sprayed on or applied in any other suitable manner. Advantageously, they are allowed to act for a short time, for example about 0.2 seconds to about 10 seconds. If the entire toning film could not be removed by applying and removing the peeling agent once, the step of applying and removing the peeling substance is repeated once or several times if necessary. If a release substance with excipients, for example a commercial cleaning agent, was used, it is advisable to wash before further processing with a solvent and / or water.

Further suitable release substances are solvent-based paints which dry physically (ie, dry by evaporation of the solvent) or crosslink only very slowly under the process conditions. Such paints can be applied as the abovementioned solvents and solvent mixtures and after a suitable exposure time with the dissolved Tonungsfilm or the dissolved part of the Tonungsfilms be doctored off again or wiped off. The treatment can be repeated.

A particularly suitable paint formulation is a two-component polyurethane paint formulation, which is preferably thickened with nitrocellulose. In order to achieve a relatively high viscosity at a low solids content, high molecular weight types are preferred. In addition, for a good cleaning action and a strong attack on the low-cured Tonungsfilm and to avoid side reactions of the isocyanates ester-soluble types are preferred.

The solvent of the release lacquer formulation should preferably consist mainly of middle boilers and optionally high boilers (for example methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), propyl acetate, butyl acetate, methoxypropyl acetate), thus at the time of the doctoring or Wiping off the release lacquer formulation will still provide sufficient solvent to guarantee good removal of the lacquer formulation. Very low-boiling solvents evaporate quickly, so that the release substance is no longer sufficient fluid after a short time to be removed by mechanical means can. Solvent-free paints are preferred.

Preferred materials for both the embossed structure material and the colored composition for filling the microwells are UV lacquers. Therefore, for reasons of good compatibility with the paint of the embossed structure and the colored lacquer for filling the microwells, UV lacquers are also preferred as the release substance. The paints may be solvent-based or solvent-free. Solvent-free paints are preferred in that their composition does not change even with a longer exposure time. In the absence of a solvent, no solvent can evaporate. UV lacquers are used in particular as a release substance if the entire toning film is to be removed in one step, or, in the case of a multi-step removal process, in the last step.

The release substances are preferably colorless in order to eliminate the risk of a possible unwanted introduction of additional color.

After the single-stage or multi-stage "washing off" of the toning film, the toning-film-free microstructure support, depending on the system used, is dried by removal of the solvents or by radiation curing.

In addition or as an alternative to "washing off" the toning film, it is also possible to use a method for "peeling off" the toning film. For example, clearcoats and laminating adhesives are suitable for a stripping process. The clearcoats or laminating adhesives must contain one or more solvents capable of dissolving the toning film. After a suitable exposure time, a film is laminated on and the composite of clear coat and film or of laminating adhesive and film is peeled off together with the dissolved part of the toning film. The process can be repeated as many times as necessary. Of course, care must be taken to use a clearcoat or laminating adhesive that does not adhere well to the microstructure support and to the already cured portion of the colored compositions in the microwells to ensure proper stripping.

If the clearcoat used forms a sufficiently stable film during drying, it can optionally also be stripped off without a laminated film. If the lamination of a supporting film is required, an additional laminating adhesive can be used to better bond between clearcoat and film. The detachment from the microstructure support can be done for example by separation winding.

Of course, it is also possible to combine different methods of removing the toning film, for example, first to wash off a portion of the toning film with a commercial cleaning agent and then to remove the remainder of the toning film with the aid of a clearcoat.

Of course, in the abovementioned stripping methods, not only the toning film is removed, but also part of the colored composition in the microwells, namely a surface area which corresponds approximately to the layer thickness of the Tonungsfilms. However, due to the considerable difference in thickness between the toning film and microstructure elements, this has no significant effect on the appearance of the microstructure elements. After removal of the toning film, it is preferred to post-cure the microstructure elements, ie the colored composition in the microwells.

The microstructure support obtainable by the process of the invention is readily distinguishable from prior art microstructure supports by the absence of a toning film. It can have only one microstructure or else several different microstructures, and optionally contain further embossed structures, for example hologram structures, in microstructure-free surface areas.

The microstructure supports obtained by the method according to the invention can be combined with a microoptical viewing device to form a microoptical representation arrangement. The microstructure support then forms the micromotiv layer of the microoptical representation. Micro-optical representational arrangements are in particular micro-optical magnification arrangements such as moiré magnification arrangements, magnification arrangements of the moiré type and modulo magnification arrangements, as described in the publications DE 10 2005 062132 . WO 2007/076952 . DE 10 2007 029 203 . WO 2009/000529 . WO 2005/000527 and WO 2009/000528 are described, the relevant disclosure of which is hereby incorporated by reference. All of these micro-optical magnification arrangements contain a motif image with microstructures which, when viewed with a suitably coordinated viewing grid, reconstructs a predetermined target image. As in the above Describing more in detail, it is possible to generate a multiplicity of visually attractive enlargement and movement effects which lead to a high recognition value and high security against forgery of security elements and value documents equipped therewith. Arrangements are, for example, arrangements of spherical or aspherical microlenses, micro-mirrors, or perforated or slit masks. The microstructure supports according to the invention can generally provide the micro-motifs to be considered in any desired micro-optical representation arrangements.

The production of a micro-optical representation arrangement is described for example in the document WO 2009/121578 the content of which is hereby incorporated by reference. Of course, in the context of the present invention, other methods of manufacture known to a person skilled in the art are also possible. For example, microstructure carriers and microoptical viewing devices need not necessarily be manufactured separately, but the microstructure carrier may also be integrated into the microoptical viewing device. For example, a carrier material may have microlenses embossed on one surface, while the microstructure carrier according to the invention is formed on the opposite surface.

Furthermore, the microstructure support according to the invention can also be combined on both sides with microoptical viewing devices, or a plurality of microstructure supports can be arranged in several levels in a microoptical display arrangement.

The microstructure supports or micro-optical representational arrangements according to the invention are particularly advantageous for the production of security elements such as security threads, security strips, or transfer elements. Such security elements can have further functional layers, ie layers that have any properties that can be detected visually or by machine.

The security elements according to the invention can be used to authenticate goods of any kind. Preferably, they are used to authenticate value documents, for example banknotes, checks or identity cards. They can be arranged on a surface of the value document or partially embedded in the value document. With particular advantage they are used in value documents hole hole hole. In such a case, the security element can be viewed from both sides, whereby possibly different motives can be recognized.

Fig. 1

eine schematische Darstellung einer Banknote mit Sicherheitselementen in Form eines Fenstersicherheitsfadens und eines aufgeklebten Transferelements,

Fig. 2

eine schematische Darstellung des Aufbaus einer mikrooptischen Darstellungsanordnung,

Fig. 3

ein beispielhaftes Herstellungsverfahren einer mikrooptischen Darstellungsanordnung, schematisch dargestellt anhand von Schnitten durch eine mikrooptische Betrachtungseinrichtung und einen Mikrostrukturträger, wobei

Fig. 3c

einen erfindungsgemäßen Mikrostrukturträger zeigt, und

Fig. 3d

einen Mikrostrukturträger gemäß Fig. 3c vor Entfernung des Tonungsfilms zeigt,

Fig. 4a

eine schematische Darstellung eines Verfahrens zur Entfernung des Tonungsfilms bei einem erfindungsgemäßen Mikrostrukturträger,

Fig. 4b

eine schematische Darstellung eines alternativen Verfahrens zur Entfernung des Tonungsfilms bei einem erfindungsgemäßen Mikrostrukturträger,

Fig. 5a, b

eine schematische Darstellung eines weiteren alternativen Verfahrens zur Entfernung des Tonungsfilms bei einem erfindungsgemäßen Mikrostrukturträger,

Fig. 6

eine schematische Darstellung eines erfindungsgemäßen Mikrostrukturträgers im Schnitt, und

Fig. 7

eine schematische Darstellung eines Herstellungsverfahrens eines erfindungsgemäßen Mikrostrukturträgers unter Verwendung eines zu dem Verfahren in Fig. 3 alternativen Mikrostrukturfüllungsverfahrens.

The invention will be further illustrated by means of figures. It should be noted that the figures are not to scale and not in proportion. In addition, only those essential to understanding the described method features or layers are shown. It is understood that additional features or layers may be present. Like reference numerals designate like or corresponding elements. Show it:

Fig. 1

a schematic representation of a banknote with security elements in the form of a window security thread and a glued transfer element,

Fig. 2

a schematic representation of the structure of a micro-optical representation arrangement,

Fig. 3

an exemplary manufacturing method of a micro-optical representation arrangement, schematically illustrated by sections through a micro-optical viewing device and a microstructure support, wherein

Fig. 3c

shows a microstructure according to the invention, and

Fig. 3d

a microstructure according to Fig. 3c before removal of the toning film shows

Fig. 4a

a schematic representation of a method for removing the Tonungsfilms in a microstructure according to the invention,

Fig. 4b

a schematic representation of an alternative method for removing the Tonungsfilms in a microstructure support according to the invention,

Fig. 5a, b

a schematic representation of a further alternative method for removing the Tonungsfilms in a microstructure support according to the invention,

Fig. 6

a schematic representation of a microstructure support according to the invention in section, and

Fig. 7

a schematic representation of a manufacturing method of a microstructure support according to the invention using a to the procedure in Fig. 3 alternative microstructure filling method.

It is emphasized that the following statements are to be understood as illustrative and not restrictive.

Fig. 1 shows a schematic representation of a banknote 7, which is equipped with two security elements 8 and 9 according to the present invention. The security element 8 is a security thread which protrudes in certain window areas 8 'on the surface of the banknote 7, while it is embedded in the intervening areas inside the banknote. The security element 9 is a glued transfer element of any shape. Alternatively, it can also be a security element in the form of a cover film, which is arranged in or above a window area or a through opening of the banknote. The security elements 8 and 9 can each contain micro-optical representation arrangements with a microstructure support produced according to the invention. Such microoptical display arrangements can be designed in particular as a moiré magnification arrangement, as a moiré-type microoptical magnification arrangement or as a modulo magnification arrangement.

Fig. 2 schematically shows the structure of a micro-optical representation arrangement 6, for example, for the security elements 8 or 9 in Fig. 1 , Shown here are as well as in all other figures, only necessary for the explanation of the principle of operation parts of the structure. The micro-optical representation arrangement 6 has a microlens carrier 5 in the form of a transparent plastic film, for example an approximately 20 μm thick polyethylene terephthalate (PET) film. A main surface of the microlens carrier 5 is provided with a grid-like arrangement of microlenses 51, which form a two-dimensional Bravais grid with a preselected symmetry. The Bravais lattice may, for example, have a hexagonal lattice symmetry, but because of the higher security against forgery, preference is given to a lower symmetry and thus a more general shape, in particular the symmetry of a parallelogram lattice.

The spacing of adjacent microlenses 51 is preferably as small as possible in order to ensure the highest possible area coverage and thus a high-contrast representation. The spherically or aspherically configured microlenses 51 preferably have a diameter of between 5 μm and 50 μm, and in particular a diameter of only between 10 μm and 35 μm, and are therefore not visible to the naked eye. Of course, the micro-optic display assembly 6 may also have other micro-optic viewing elements than microlenses.

On the underside of the transparent microlens carrier 5 is a motif layer which also contains a grid-like arrangement of identical micromotif elements 11. The arrangement of the micromotif elements or microstructure elements 11 also forms a two-dimensional Bravais lattice with a preselected symmetry, for example with hexagonal lattice symmetry or the symmetry of a parallelogram lattice. The micro-motive layer 3 is formed by a microstructure support according to the invention, it being possible for the microstructure support and the microlens support to be identical, ie the support film 5 can be provided with microlenses 51 on one surface and microstructure elements 11 on the other surface. The microstructure elements 11 together form the microstructure 1.

As in Fig. 2 is indicated by the slight offset of the micromotif elements or microstructure elements 11 with respect to the microlenses 51, the Bravais lattice of the microstructure elements 11 differs slightly in its orientation and / or in the size of its lattice parameters from the Bravais lattice of the microlenses 51 to the desired one Moiré magnification effect to produce. The grating period and the diameter of the microstructure elements 11 are in the same order of magnitude as that of the microlenses 51, ie in the range of 1 .mu.m to 50 .mu.m, in particular in the range of 10 .mu.m to 35 .mu.m, so that even the microstructure elements 11 are not visible to the naked eye recognize.

The optical thickness of the carrier material 5 and the focal length of the microlenses 51 are coordinated so that the microstructure elements 11 are located approximately at the distance of the lens focal length, as indicated by the dashed lines. When viewed from above through the microlenses 51, a viewer sees a slightly different subarea of the microstructure elements 11, so that the multiplicity of microlenses 51 overall produces an enlarged image of the microstructure elements 11. The resulting moiré magnification depends on the relative difference of the lattice parameters of the Bravais gratings used. For a more detailed description of the operation and advantageous arrangements of the motif grid and the microlens grid (or other micro-viewing elements) is to the publications DE 10 2005 062132 and WO 2007/076952 referenced, the disclosure of which is included in the disclosure of the present invention.

However, the above statements should not be understood as meaning that the microstructure supports produced according to the invention are in any way limited to use in moiré magnification arrangements are. Rather, the microstructure supports produced according to the invention are generally applicable to microoptical representational arrangements, and with particular advantage in particular to modulo-mapping magnification arrangements, as described in the applications WO 2009/000528 and WO 2009/000527 are described.

Fig. 3 FIG. 3 illustrates an exemplary manufacturing method for a microoptical display arrangement, schematically illustrated by sections through a microoptical viewing device and a microstructure carrier, wherein FIG Fig. 3c shows a microstructure according to the invention, and Fig. 3d shows a microstructure carrier in the state before removal of the Tonungsfilms.

How out Fig. 3a 1, a microlens carrier 5 is first produced by coating a microlens carrier film 52 on a first main surface 53 in a subregion 55 with an embossing lacquer, into which microlenses 51 are embossed. Alternatively, the microlenses 51 can also be imprinted directly into the main surface 53 of the microlens carrier film 52. In the subregions 56, 57 of the first main surface 53 there are no microlenses. However, other embossing structures can be provided here, for example a hologram embossing.

Fig. 3b 2 shows a precursor 2 of a microstructure carrier 3 according to the invention. The carrier 2 consists of a microstructure carrier film 21, on which a microstructure embossing lacquer 22 is applied, and has a first main surface 23 and a second main surface 24. In the first main surface 23, a microstructure is impressed in a portion 27, which consists of recesses 26 and elevations 25. The sections 28, 29 have in the embodiment no microstructure, but may have a different embossing, such as a hologram embossing.

To produce a microstructure support 3 according to the invention, a colored radiation-curable composition 12 is applied to the first main surface 23 of the support 2, for example a free-radically curing UV lacquer. The composition 12 fills the recesses 26 of the microstructure and any excess of radiation-curable composition 12 covers the major surface 23 of the support 2 and is removed prior to further processing, for example by means of a gravure doctor blade. Subsequently, the radiation-curable composition is cured in the microwells 26 by irradiation with a suitable wavelength, wherein a microstructure support 3 should be obtained, as in Fig. 3c is shown. The microstructure support 3 has a microstructure in a partial area 37 with microstructure elements 11 made of radiation-cured colored composition 12, while the partial areas 38, 39 do not contain a microstructure. In the sub-areas 38,39 and on the elevations 25 is, as from Fig. 3c it can also be seen that no radiation-curable composition 12, ie, the first main surface 23 of the microstructure support 3 is completely free of radiation-curable composition 12.

This aspired and in Fig. 3c shown state, however, is not achievable by the above procedure. The above-mentioned procedure, ie filling the microwells 26 by applying a composition 12 and scraping off the excess, rather leads to a microstructure support 4, as in Fig. 3d is shown. Namely, it is not possible to completely remove the excess of colored radiation-curable composition 12, which is on the main surface 23, by means of mechanical means such as doctoring or wiping. Rather, it remains in practice on the entire surface a very thin film 40, a so-called Tonungsfilm that reduces the achievable contrast of a micro-optical representation. The toning film 40 is in Fig. 3d shown greatly exaggerated. The thickness d1 of the toning film 40 constitutes only about 1/20 to about 1/10 of the thickness d3 of the ink fountain 12 in the microwells 26, that is, the total layer thickness d2 hardly differs from the thickness d3. Nevertheless, the toning film 40 is perceived by a viewer as disturbing in both the microstructured portion 47 and the microstructured portions 48, 49.

Such Tonungsfilme could not be removed with previously used methods and had to be accepted. According to the invention, however, it has been found that such Tonungsfilme are quite removable, namely taking advantage of two conditions: on the one hand the large difference in thickness between Tonungsschicht and color filling of the microstructures, and on the other hand, the oxygen inhibition of radical polymerizations or the moisture inhibition of cationic polymerizations. According to the invention, therefore, either a colored, free-radically radiation-curable composition or a colored, cationic radiation-curable composition is used as the color filling of the microstructures, and the radiation curing is carried out in the presence of oxygen or in the presence of moisture (water). The oxygen content of the air or the humidity are usually sufficient for a satisfactory inhibition. If necessary, additional oxygen or additional gaseous water can be supplied during the radiation curing.

Oxygen molecules and water molecules penetrate through the surface 41 into the radiation-curable composition 12, wherein in the composition 12 a concentration gradient of oxygen molecules or water molecules is formed. The regions of the composition 12 that are close to the surface 41 very quickly have a high content of oxygen molecules or water molecules, while the content of oxygen molecules or water molecules increases only slowly in the surface-distant regions. Due to the extremely small layer thickness d1 of the toning film 40, virtually the entire toning film 40 can be referred to as "near the surface", while the remaining regions of the composition 12, ie the regions of the thickness d3 in the recesses 26, are more surface-distant.

When oxygen (or moisture) diffuses from the surface 41 into the composition 12, as in FIG Fig. 3d indicated by the arrows, there is a time at which the diffusing molecules have penetrated the layer thickness d1, but are still hardly diffused into the region d3. At this time, the radiation curing is carried out according to the invention (in Fig. 3d indicated by the irradiation arrows hxv). When a radiation-transparent carrier material is used, it is unimportant whether it is irradiated from the main surface 23 or from the main surface 24. In the region of the layer thickness d1, the radiation hardening is inhibited and proceeds slowly, while it is much faster in the region of the layer thickness d3. Therefore, when the radiation curing in the area d3 is already substantially completed, the area d1 is hardly hardened yet, and thus the composition 12 in the area d1 can still be peeled off. According to the invention, this region of the composition 12 is removed, as in connection with FIGS FIGS. 4 . 5 and 6 will be described.

After removal of the toning film 40, the resulting microstructure support 3 according to the invention is combined with a microlens support 5 to form a security element 8, as shown in FIGS FIGS. 3e to 3g is shown. In the illustrated exemplary embodiment, the microstructure carrier 3 and the microlens carrier 5 are adhesively bonded to one another at their main surfaces 23 and 54 by means of a laminating adhesive 15 such that the lenses 51 form a microoptical viewing device for the microstructure elements 11, as in FIG Fig. 3f shown. The microstructure carrier film 21 can finally be removed from the microstructure embossing lacquer 22 or, alternatively, remain on the film composite.

At the in Fig. 3g illustrated security element 8, the microstructure carrier film 21 is peeled off. The security element 8 has in the subregion 61 a micro-optical representation arrangement 6 with the microstructure support produced according to the invention. The subregions 62, 63 without microoptical representation arrangement 6 can be equipped with further security features.

The FIGS. 4 and 5 show exemplary variants for removing the Tonungsfilms 40 of the invention from a microstructure support 4 to obtain a microstructure support 3 according to the invention, as in Fig. 6 is shown. In the FIGS. 4 and 5 In each case, the state after irradiation of the colored radiation-curable composition 12 is shown, ie the state in which the radiation-curable composition 12 is already substantially hardened in the thickness range d3, but is still substantially uncured in the thickness range d1.

On the surface 41 is now, as in Fig. 4a represented a release substance 42 and applied to the underlying composition 12th is allowed to act to dissolve the region of the layer thickness d1 in the release substance 42 or at least to dissolve the uppermost region. The release substance 42 is a substance in which the composition 12 is still at least to a certain extent soluble in the still substantially uncured state, and is preferably readily soluble. The nature of the release substance 42 therefore, in this exemplary embodiment and of course also generally, depends on the radiation-curable composition 12 chosen, as well as the exposure time to the toning film 40.

Suitable release substances 42 are, for example, water, organic solvents and solvent mixtures, commercial cleaners, solvent-based paints and solvent-free paints. After the exposure time, the applied release substance 42 is removed together with the dissolved substance 12 by mechanical means, for example by doctor blade doctoring or by wiping. If the toning film 40 could not be completely removed, ie the composition 12 could not be dissolved in the area of the entire layer thickness d1, the process is repeated and, if necessary, repeated several times until the entire toning film 40 has been removed. Of course, it is preferable to remove the toning film 40 in a peeling step.

Even with the mechanical removal of the release substance 42, a certain minimal residue remains on the microstructure support 4, which can not be removed mechanically. However, since a large excess of peeling substance 42 is used and most of it can be removed mechanically, the proportion of radiation-curable composition 12 which possibly remains on the microstructure support 3 along with remnants of the release substance 42 is extremely small and no longer disturbing. For example , the (wet) coating weight of the applied with a gravure printing unit releasing substance 42 at about 4 g / m ² to about 20 g / m ^2, while the (uncured or hardly cured) Tonungsfilm 40 has a basis weight in the order of about 0.1 g / m ² . Of course, the release substance 42 itself should be colorless, so as not to cause a disturbing contrast reduction by the release substance itself.

Fig. 4b shows an alternative process variant in which a clearcoat, such as a UV coating, which may be solvent-containing or solvent-free, is used as a release substance 42. The clearcoat dissolves the not yet or hardly crosslinked surface area of the composition 12, preferably a range of the layer thickness d1. After drying the clearcoat, the dissolved portion of the radiation-curable composition 12 may be stripped together with the clearcoat film 42, as long as the clearcoat forms a sufficiently stable film. In the embodiment, the radiation-curable composition is stripped throughout the uncured area of thickness d1, so that the steps of applying the release substance, dissolving the colored composition, and peeling need not be repeated.

The microstructure support 3 according to the invention, as obtained in Fig. 6 is shown. In the exemplary embodiment, the microstructure support 3 consists of the microstructure support film 21, the microstructure embossing lacquer 22 and recesses filled with radiation-hardened colored composition 12 in the microstructure embossing lacquer 22. The filled microwells now form microstructure elements 11 in the color of the radiation-cured composition, the microstructure elements 11 together forming the microstructure 1 represent. How out Fig. 6 it can be seen, the microstructure support 3 according to the invention has no toning film 40.

A further variant of the method according to the invention for removing the toning film 40 is shown in FIG Fig. 5 shown. At the in Fig. 5 illustrated embodiment, a laminating adhesive is used as the release substance 42, which can dissolve the radiation-curable composition 12 in the uncured or hardly cured state. After dissolving the Tonungsfilms 40 or at least a portion of the Tonungsfilms 40 in the laminating adhesive 42 is laminated to the laminating adhesive, a carrier film 43, and then as in Fig. 5b the toning film 40 is drawn off together with the laminating adhesive 42 and the carrier film 43, for example by means of a separation winding. In the embodiment, the entire toning film can be peeled off at once. How out Fig. 5b it can be seen, the surface 23 of the microstructure support 3 is free of a Tonungsfilm, even in the region of the elevations 25 of the microstructure. Again, however, if only part of the toning film 40 can be released and peeled off during the first application of the release substance 42, the removal operation is preferably repeated until the entire toning film is removed.

At the release substance 42 in Fig. 5 It can also be a clear coat as in Fig. 4b which, however, does not form a sufficiently stable film to be removed intact. Then a lamination of a supporting film 43 is required, wherein between release substance 42 and film 43, an additional laminating adhesive can be provided.

When the toning film 40 is removed in several steps, different release substances 42 can also be used in the individual steps. This may be indicated in particular when different radiation-curable compositions 12 are also used. Such a case occurs in particular when the microwells 26 differ to be colored. In any case, however, an inventive microstructure support 3 is obtained, as shown schematically in FIG Fig. 6 is shown.

The inventive method for removing a Tonungsfilms is also applicable when the micro-wells of the microstructure are only partially filled with a colored radiation-curable composition, for example, when a low-viscosity colored composition is used to produce the microstructure, as it is in principle in the WO 2009/083146 is disclosed. Of course, in the present invention, a low-viscosity, free-radically radiation-curable or cationic-radiation-curable composition is used. This case is schematic in Fig. 7 shown. In this case, the carrier 2 'corresponds to Fig. 7a the carrier 2 of Fig. 3b , the microstructure support 4 'of Fig. 7c the microstructure support 4 of Fig. 3d , the microstructure support 4 'of Fig. 7d the microstructure support 4 of Fig. 4a , and Fig. 7b shows the desired microstructure support 3 ', the microstructure support 3 of Fig. 3c respectively. Fig. 6 equivalent. In Fig. 7 For example, the references used heretofore will be further used as "primed" reference numerals, with corresponding elements denoted by the corresponding "primed" reference numerals (eg, microstructure support 3 'instead of microstructure support 3).

In the analogous method, the embossed microstructure of a carrier 2 '( Fig. 7a ) is filled with a colored radiation-curable composition 12 ', whereby a microstructure support 4' is obtained, the microwells 26 'of which are substantially filled with the radiation-curable composition 12' ( Fig. 7c ). The colored radiation-curable composition 12 'is in the embodiment, however, not only in the microwells 26', but also on the elevations 25 'and the rest raised surface areas of the embossing lacquer layer 22 '. This toning film 40 'in turn has a very small thickness compared to the thickness of the colored radiation-curable composition 12' in the recesses 26 '. It does not necessarily have to be a coherent movie. Upon irradiation of the radiation-curable composition in the presence of oxygen (radically curing radiation-curable composition) or moisture (cationically-curable radiation-curable composition), again, the near-surface portions of the colored, radiation-curable composition 12 'are cured only slowly because of the oxygen or water diffused through the surface 41'.

If a release substance 42 is applied to the superficially substantially uncured radiation-curable composition 12 '( Fig. 7d ), the near-surface areas, ie substantially the Tonungsfilm 40 ', can be removed as it is in connection with the FIGS. 4 and 5 has been described. The microstructure support 3 'is then obtained, which contains the colored radiation-cured composition 12' only in the depressions of the microstructure ( Fig. 7b ).

Claims (15)

1. A method for producing a microstructure (1) on a carrier (2), having

   (a) forming an embossed structure with elevations (25) and depressions (26) at least in a partial region of a first main area (23) of a carrier foil (21), wherein the depressions are arranged in the shape of the microstructure (1),

   (b) coating the first main area (23) at least in the partial region having the embossed structure with a colored, radically or cationically radiation-curable composition (12), such that a colored coating is created, having a greater layer depth (d₂, d₃) in the depressions (26) than in the not depressed regions (d₁),

   (c) if required, reducing the layer thickness of the radiation-curable composition by mechanical means, wherein the radiation-curable composition is removed in the not depressed regions up to a mechanically irremovable toning film (40),

   (d) irradiating the radiation-curable composition with radiation of a suitable wavelength in the presence of oxygen or moisture for a duration of time which is not sufficient in order to cure the toning film subjected to oxygen or moisture, but which is sufficient to cure at least the largest part of the radiation-curable composition in the depressions,

   (e) removing the toning film by

   (e1) coating the carrier foil with a detaching substance (42) at least in the region coated with the radiation-curable composition, the radiation-curable composition being soluble in said detaching substance before its curing,

   (e2) detaching the toning film or a portion of the toning film together with the detaching substance, and

   (e3) if required, repeating the steps (e1) and (e2) with the same or a different detaching substance up to the complete removal of the toning film.
2. The method according to claim 1, characterized in that

   - in step (e1) an organic solvent or a mixture of organic solvents or water or a mixture of water and at least one organic solvent is utilized as detaching substance, which can optionally contain conventional accessory substances such as surfactants and/or defoamers and/or de-aerating agents and/or thickeners, and

   - in step (e2) the toning film or the loosened portion of the toning film is detached together with the detaching substance by mechanical means, wherein

   - when the detaching substance contains accessory substances, the steps (e1) and (e2) are preferably repeated with a detaching substance without accessory substances.
3. The method according to claim 1, characterized in that

   - in step (e1) a lacquer on solvent basis is utilized as detaching substance, and

   - in step (e2) the toning film or the loosened portion of the toning film is detached by mechanical means together with the lacquer on solvent basis.
4. The method according to claim 1, characterized in that

   - in step (e1) a solvent-containing or solvent-free UV lacquer is utilized as detaching substance, and

   - in step (e2) the toning film or the loosened portion of the toning film is detached together with the UV lacquer by mechanical means.
5. The method according to claim 1, characterized in that

   - in step (e1) a physically drying clear lacquer on solvent basis is utilized as detaching substance, and

   - in step (e2) the toning film or a portion of the toning film is stripped together with the clear lacquer film after the drying of the clear lacquer.
6. The method according to claim 1, characterized in that

   - in step (e1) a laminating adhesive is utilized as detaching substance,

   - a foil is laminated onto the laminating adhesive, and

   - in step (e2) the toning film or a portion of the toning film is stripped together with the laminating adhesive and the foil.
7. The method according to any of the claims 1 to 6, characterized in that

   - a radically curing UV lacquer is utilized as colored radiation-curable composition, and for curing is irradiated with UV light in the presence of oxygen,
   or

   - a cationically curing UV lacquer is utilized as colored radiation-curable composition, and for curing is irradiated with UV light in the presence of moisture.
8. The method according to any of the claims 1 to 7, characterized in that in step (d) the content of oxygen or of gaseous water of the surrounding atmosphere is increased in order to intensify the inhibition of the curing of the radiation-curable composition in targeted fashion.
9. The method according to any of the claims 1 to 8, characterized in that after removing the toning film, the formed microstructure carrier is dried by removing remaining solvent or postcured by irradiation.
10. A microstructure carrier having
    a carrier foil with elevations and depressions at least in a partial region of a first main area of the carrier foil, wherein the depressions are arranged in the form of a microstructure and contain a colored radiation-cured composition,
    characterized in that the microstructure can be obtained by a method according to any of the claims 1 to 9.
11. The microstructure carrier according to claim 10, characterized in that besides the microstructure, the microstructure carrier has at least one further embossed structure, optionally likewise forming a microstructure.
12. A micro-optic representation arrangement for representing a motif formed by a plurality of micromotif elements, having

    - a carrier with a microstructure in the form of depressions embossed into the carrier which contain a colored radiation-cured composition and which form micromotif elements, and

    - a micro-optic viewing device for the motif,
    characterized in that the carrier with the microstructure is a microstructure carrier that can be obtained by a method according to any of the claims 1 to 9 or a microstructure carrier according to claim 10 or 11.
13. The micro-optic representation arrangement according to claim 11, characterized in that the micro-optic representation arrangement is a moiré magnification arrangement, a magnification arrangement of the moiré type or a modulo magnification arrangement.
14. An object having a microstructure carrier according to claim 10 or 11 or a microstructure carrier that can be obtained by a method according to any of the claims 1 to 9 and/or a micro-optic representation arrangement according to claim 12 or 13.
15. The object according to claim 14, characterized in that the object is a security element or a data carrier.

Images