HK1135655B - Security elements, method of producing and the use of the security elements, and data carriers for assembling the security elements - Google Patents

Description

Security element, method for the production and use thereof, and data carrier equipped with the same

The invention relates to an embossing lacquer (embossing lacquer) suitable for producing micro-optical arrangements, in particular micro-optical security elements; methods of manufacturing such micro-optical arrangements and security elements; a micro-optical security element; use of a micro-optical security element for product protection; data carriers with such micro-optical security elements, such as value documents; and the production of a value document having such a micro-optical security element.

Data carriers such as value or identification documents, banknotes (banknotes), contracts, checks and other items of value (for example branded goods) are usually provided with security elements for protection, which can verify the authenticity of the data carrier and at the same time serve to protect against unauthorized copying. The security element may be shaped, for example, in the form of: security threads embedded in banknotes, cover films (cover foil) for holed banknotes, applied security strips, or self-supporting transfer elements (e.g. labels that are attached to value documents after their manufacture). A further variant is for example a tear line of the product package.

Security elements with optically variable elements which convey different image impressions to viewers at different viewing angles have a special effect here, since optically variable elements cannot be reproduced even with high-quality color copiers. To this end, the security element can be equipped with security features in the form of optically diffractive active microstructures or nanostructures, for example with conventional embossed holograms or other hologram-like diffractive structures, as described, for example, in publications EP 0330733a1 or EP 0064067a 1.

It is also known to use a lens system as a security feature. Security threads made of transparent material embossed with a grid comprising a plurality of parallel cylindrical lenses on their surface are described, for example, in the publications EP 0238043a2 or DE 3609090a 1. The thickness of the security thread is chosen to correspond approximately to the focal length of the cylindrical lens. The printed image is applied in precise registration on the reverse side, designed taking into account the optical properties of the cylindrical lens.

So-called moir (moire) magnification arrangements are sometimes also used as authenticity features (authenticity features). Such moir é magnification arrangements are disclosed in publications WO 2006/087138a1 or DE 102005028162a 1. The security element disclosed in WO 2006/087138a1 has at least a first and a second authenticity feature. The first authenticity feature comprises a first arrangement having a plurality of focusing elements (focusing elements) present in a first grid (grid), and a second arrangement having a plurality of microstructures present in a second grid. The first and second arrangements are arranged relative to each other such that the microstructure of the second arrangement is seen to be magnified when viewed through the focusing elements of the first arrangement.

This amplification effect is also known as moir é magnification. The basic mode of operation of The moir é magnification arrangement is described in The article "The moir é modifier", M.C. Hutley, R.Hunt, R.F. Stevens and P.Savander, Pure appl.Opt.3(1994), pages 133-142. Very briefly, moir é magnification thus refers to the phenomenon that occurs when a grid comprising identical image objects is viewed through a lenticular screen at about the same pitch. This produces a moir pattern, as in the case of any pair of similar grids, but in this case each moir stripe appears as a magnified and rotated image of the image grid repeating unit.

The focusing elements of the micro-optical authenticity features are embossed by an embossing lacquer. The microstructure to be viewed through the focusing element may have any desired form. According to WO 2006/087138a1, they are made from colorless embossing lacquers and are coated to be reflective, or are made from colored embossing lacquers. The complete microstructure can therefore be identified in each case by means of a focusing element (referred to below as microlens), the microlens and the microstructure having to have approximately the same dimensions. Further, the closer the microstructure is located to the focal point of the lens, the stronger the magnifying effect of the microlens. Since the larger the curvature of the lens, the smaller the focal length, in order to obtain good magnification, either a large distance between the lens and the microstructure (small curvature of the lens) or a highly curved lens (short distance between the lens and the microstructure) must be used.

The relationship between the dimensions of the microstructures, the diameter of the lens and the focal length results in a large curvature of the lens and a relatively high thickness of the micro-optical authenticity feature and thus of the security element.

It is difficult to manufacture focusing elements or microlenses by embossing, since considerable embossing depth and curvature are necessary. Moreover, in the case of highly curved microlenses, the size of the microstructures to be replicated is limited.

Another problem lies in the fact that: the thicker the security element, the more difficult it is to introduce into a document of value, such as a banknote. Thick security elements appear to be fragile and prone to breakage when the value document is bent or folded.

In addition, the high-thickness embossing layer tends to scatter light uncontrollably, so that the microstructure pattern (motif) to be observed through the thick microlenses can be illuminated and the brightness of the microstructure pattern is reduced.

Another difficulty is the resolution of the pattern of the microstructure arrangement. The microstructure must be on the order of the microlens. If complex microstructures such as letters, numbers, logos or even images are to be represented, the resolution must be a few micrometers, preferably significantly below the micrometer scale, i.e. in the nanometer range. Such resolution is not generally available with classical printing methods that are sometimes used to produce microstructured patterns in conventional micro-optical authenticity features. An alternative method of printing is to produce a microstructure pattern by embossing of an embossing lacquer, as is done according to WO 2006/087138a 1. However, this alternative is generally only satisfactory in the case of colorless embossing lacquers. The colored embossing lacquer can be colored by pigments or soluble dyes. Both of these possible approaches have drawbacks. Soluble dyes tend to bleed with the solvent and sometimes exhibit significant migration. Pigments generally contain particles whose particle size is too large to follow the very finely structured embossing structure completely. This produces a microstructure pattern with pigment defects that are clearly visible when magnified.

Starting from this prior art, the invention is based on the following objects: a security element with micro-optical authenticity features is provided which has a reduced thickness compared to prior art security elements known, for example, from EP 0238043a2 and WO 2006/087138a1 and which can be easily incorporated into documents of value, such as banknotes.

Another object is to provide a security element with micro-optical authenticity features, which has a colorless, colored or color-variable microstructure.

It is also an object of the present invention to provide a security element with micro-optical authenticity features, which has a high resolution, preferably in the nanometer range, colorless, colored or color-variable microstructure.

Furthermore, it is an object of the present invention to provide a security element with micro-optical authenticity features, which security element has an improved protection against forgery.

It is also an object of the invention to provide a method of manufacturing such a security element.

It is also an object of the present invention to provide an embossing lacquer with which such a security element can be manufactured.

It is a further object of the present invention to provide a value document having such a security element with micro-optical authenticity features and the use of the security element with micro-optical authenticity features in product protection.

These objects are achieved by the embossing lacquer according to claim 1, the security element with at least one micro-optical authenticity feature according to claim 28, the method of manufacturing a security element with at least one micro-optical authenticity feature according to claim 36, the use of the security element with at least one micro-optical authenticity feature according to claim 37 in product protection, and the data carrier according to claim 38.

Embodiments of the invention are described in the respective dependent claims.

The invention relates in particular to security elements having micro-optical authenticity features whose structure is known substantially from WO 2006/087138a 1. With regard to the different embodiments of the security element, in particular with regard to the lattice arrangement of the focusing elements (microlenses) and the microstructures (graphical elements), with regard to the geometry of the microlenses and the microstructures, with regard to the structure of the security element, i.e. the layers employed and the sequence of the layers, and with regard to the effects achieved (e.g. colour and kinetic effects), reference is made expressly to WO 2006/087138a1, the disclosure of which is incorporated in the disclosure of the present application in this respect. The security element of the publication incorporated by reference has a first micro-optical authenticity feature and a second authenticity feature that can be verified by machine and/or vision. The subject matter of the invention also includes security elements without such a second authenticity feature, i.e. security elements with only one micro-optical authenticity feature or a plurality of micro-optical authenticity features, which optionally also have further authenticity features different from the second authenticity features of the publications incorporated by reference.

The manufacture of the security elements of the invention, in particular the microlenses and microstructures, can likewise be achieved by the technique disclosed in WO 2006/087138a 1. Alternatively, microlenses and microstructures can also be produced by the method disclosed in the german patent application with the application number 102006029852.7. In this respect, the disclosure of this application is incorporated into the disclosure of the present application. Also, the related method will be described more specifically below.

For a detailed description of the mode of operation and the advantageous arrangement of the micro-graphical elements and the micro-lenses, reference is also made to the pending german patent application with the application number 102005062132.5, the disclosure of which is also incorporated in the disclosure of the present application in this respect.

Conventional micro-optical authenticity features, such as the focusing elements or microlenses of the authenticity feature disclosed in WO 2006/087138a1, are embossed with conventional embossing lacquers. The refractive index of conventional embossing lacquers is about 1.5.

The inventive security elements with micro-optical authenticity features (hereinafter "micro-optical security elements") differ from the conventional micro-optical security elements up to now in that special embossing lacquers are used to produce the focusing elements and/or microstructures.

Embossing lacquers, in particular those used for the production of focusing elements, have a high refractive index. This high refractive index is achieved by the inventive embossing lacquer with a binder of an organic compound having a high refractive index, which organic compound undergoes a polymerization reaction under the influence of radiation (in particular UV radiation) or an electron beam and is crosslinked or cured to a polymer having a high refractive index. The high refractive index for the purposes of the present invention is a refractive index of greater than 1.5, preferably greater than 1.6, particularly preferably greater than 1.7. The refractive indices in each case were at 589nm and 20 ℃ unless otherwise stated.

High refractive index compounds are known. Flexible focal length lenses (lenses) and contact lenses made of high refractive index plastics have also been provided. The increased refractive index allows thinner contact lenses and lenses to be manufactured that have similar optical properties as thicker contact lenses and lenses made from lower index plastics, and thereby achieve contact lenses that are more comfortable to wear or lighter lenses.

US patent No. 6709107 discloses an ophthalmic lens consisting of two layers made of polymer materials having different refractive indices. The first polymeric material has a refractive index of at least 1.6 and is, for example, a polythiourethane (polythiourethane) or an episulfide polymer. The second polymeric material has a lower refractive index and is, for example, poly (allyl carbonate), polyurethane, polythiourethane, and/or polycarbonate.

Polythiourethanes have been used for the early manufacture of high refractive index optical lenses/glasses (see Internet site "http:// www.brunobock.org").

According to the invention, high refractive index compounds are now used to produce micro-optical authenticity features, i.e. the arrangement of the focusing elements and the arrangement of the microstructures.

For this purpose, essentially all organic compounds and combinations of organic compounds which can be processed into embossable lacquer systems or can otherwise be brought into the desired form (embossing lacquer) and which, upon irradiation, in particular UV or electron irradiation, undergo a polymerization reaction and crosslink or cure to a high refractive index polymeric material, i.e. a polymer, a copolymer or a mixture of polymers and/or copolymers, can be used.

Polymers, copolymers, and mixtures of polymers and/or copolymers of high refractive index will be referred to hereinafter as "high refractive index polymeric materials". The embossing lacquer which forms a high refractive index polymer upon irradiation will be referred to hereinafter as "high refractive index embossing lacquer".

The organic compound itself forming the high refractive index polymer has a high refractive index. Such compounds contain polarizable elements in their molecules. The polarizability of an element (i.e., an atom) is a measure of the deformability of the electron cloud around the atom. For example, iodine has a polarizability greater than that of bromine or chlorine. Polarizable elements for the purposes of the present invention are elements having a polarizability greater than carbon, in particular halogens such as iodine, bromine, chlorine and sulfur. The polarizable elements impart an increased polarizability and thus an increased refractive index to the compounds or their molecules.

The relevant radiation-curing compounds contain at least one polarizable element in their molecule, i.e. in the monomer. They may also contain a plurality of polarizable elements in each monomer, where the polarizable elements may be the same or different. It is generally considered that the more polarizable elements the monomer contains and the higher polarizable degree of the elements the monomer contains, the higher the refractive index.

Radiation-curing compounds that undergo polymerization reactions with one another constitute a radiation-curing compound system.

Radiation-curable compound systems have the same type of compound molecules, such as ethylenically unsaturated compounds, which polymerize through their unsaturated bonds (self-crosslinking agents); alternatively, the radiation-curable compound system has different types of compound molecules, i.e. a first compound can react to crosslink with a second compound (a bi-or multi-functional crosslinker).

Furthermore, the molecules of the radiation-curing compound system may have the same chemical composition (chemical identity) or different chemical compositions. For example, they may be the same acrylate molecule or differently substituted acrylate molecules. In the former case homopolymers are produced, while in the latter case copolymers are produced. Copolymers are also produced in the case of two or more radiation-curable compound systems. The higher the functionality of the monomer, the stronger the crosslinking of the resulting polymeric material. Molecules of different functionality can be employed in each radiation-curable compound system, but the average functionality must be greater than 1 in self-crosslinking compound systems and greater than 2 in compound systems crosslinked by curing agents.

The high refractive index embossing lacquer may contain one or more radiation-curable compound systems.

The type of polymerization reaction that the radiation-curable compound system undergoes to form the high refractive index polymeric material is essentially unimportant. Compound systems which undergo polymerization, compound systems which undergo polyaddition and compound systems which undergo polycondensation can all be used.

The compounds of the radiation-curable compound system can be used as monomers, or prepolymers, or mixtures thereof.

High refractive index compounds (i.e., compounds having a high refractive index) may also be used in combination with radiation-curable compounds having a lower refractive index, provided that the polymeric material formed by the polymerization reaction is a high refractive index polymeric material.

The radiation-curable compound system or systems constitute the binder of the high refractive index embossing lacquer. The high refractive index embossing lacquer contains only the radiation-curable organic compound or, in general, also other components in addition to the radiation-curable organic compound. The further components may be additives commonly used in embossing lacquers, such as additives for viscosity control, additives for flow control or release (release), waxes, defoamers, diluents, optionally reactive diluents. Further additives are optional photoinitiators, or additives to enhance the coloration and/or refractive index. Photoinitiators are generally necessary in UV curing, but not in electron beam curing.

The curing of the embossing lacquer can be initiated both cationically and radically, and in UV curing also depends on the photoinitiator chosen, which in turn depends on the choice of monomers or prepolymers. The photoinitiator should preferably be active in both the short-wave UV spectrum and the long-wave UV spectrum. The activity in the short-wave spectral range is generally important for good surface curing and the activity in the long-wave spectral range is important for good through-curing. It is therefore generally advisable to employ photoinitiator systems which comprise at least two photoinitiators having an activity in different spectral ranges.

Preferred radiation-curing compound systems are, for example, acrylates which can be polymerized by their unsaturated compounds, or epoxides which can be polymerized by their epoxide groups, or episulfides which can be polymerized by their episulfide groups. Acrylates, epoxides and episulfides, each having a functionality greater than 1, are self-crosslinking radiation-curable compound systems.

Preferred acrylates are, for example, phenylthioethyl acrylate (PTEA) with a refractive index of 1.557, obtainable from BIMAX, bis (4-methacryloylthiophenyl) sulfide (MPSMA), obtainable from Sumitomo Seika Co., Japan, bis (4-vinylthiophenyl) sulfide (MPV), obtainable from Sumitomo Seika Co., Japan, with a refractive index of 1.695.

(structural formula of PTEA)

(structural formula of MPSMA)

(structural formula of MPV)

Further preferred acrylates are pentabromophenyl methacrylate or 2, 6-dichlorostyrene.

A preferred epoxide is bis [4- (2, 3-epoxypropylthio) phenyl ] sulfide (MPG) having a refractive index of 1.669.

(structural formula of MPG)

The preferred episulfide is the disulfide disclosed in U.S. patent No. 6709107.

Preferred radiation-curing compound systems containing curing agents for crosslinking contain further compounds such as isocyanates, ethylenically unsaturated compounds, epoxides or episulfides. Preferred ethylenically unsaturated compounds are, for example, simple olefins, allyl ethers, vinyl acetate, alkyl vinyl ethers, conjugated dienes, styrene and acrylates. Isocyanates, ethylenically unsaturated compounds, epoxides and episulfides as curing agents are advantageously crosslinked with mercaptans and/or polythiols. The average functionality of the starting compound is greater than 2.

Polythiols lead to particularly fast curing systems for both epoxides and episulfides, for isocyanates, and for unsaturated monomers/oligomers. The crosslinking reaction may be initiated using UV light and an electron beam. The degree of crosslinking and thus the hardness of the polymeric material can be adjusted by the functionality of the individual components. The molecular weight is adjusted in particular by polythiols or thiols. Polythiols and thiols are known chain regulators for regulating the molecular weight of different polymers.

The polymerization of mercaptans and polythiols with isocyanates, olefinically unsaturated compounds, epoxides and episulfides is a polyaddition reaction. The reaction of mercaptans and polythiols with ethylenically unsaturated compounds is known as thiol-ene reaction (thiol-ene reaction). The initiator to be used may be a standard photoinitiator generating free radicals, or a dehydrogenation initiator may be used. Thiol groups can even be excited and cleaved directly by radiation, thereby generating sulfur-centered radicals (thio radicals) and hydrogen radicals which initiate radical chain reactions.

Curing of the isocyanate with the thiol is preferably effected by free-radical initiators, or by bases which can be activated by UV radiation (e.g. alpha-aminoacetophenones) or amines which can be activated by UV radiation.

Preferred mercaptans are pentaerythritol-tetra-3-mercaptopropionate (PETMP), 2-ethyl-2- (hydroxymethyl) -1, 3-propanediol trithioglycolate, trimethylolpropane Trimercaptoacetate (TMPMA), ethylene Glycol Dimercaptoacetate (GDMA), and ethoxylated trimethylolpropane-tris (3-mercaptopropionate) (ETTMP).

The refractive index of the high refractive index polymeric material may be further enhanced according to the present invention by adding high refractive index inorganic particles to the high refractive index embossing lacquer.

Suitable inorganic materials for increasing the refractive index are metal oxides, metal suboxides, metal fluorides, metal oxyhalides, metal sulfides, metal chalcogenides, metal nitrides, metal oxynitrides, metal carbides and mixtures thereof, in particular silicon oxide (SiO)₂) Zinc sulfide (ZnS), zinc oxide (ZnO), zirconium oxide (ZrO)₂) Titanium dioxide (TiO)₂) Carbon, indium oxide (In)₂O₃) Indium Tin Oxide (ITO), tantalum pentoxide (Ta)₂O₅) Chromium oxide (Cr)₂O₃) Cerium oxide (CeO)₂) Yttrium oxide (Y)₂O₃) Europium oxide (Eu)₂O₃) Iron oxide (e.g. Fe)₃O₄And Fe₂O₃) Hafnium nitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO)₂) Lanthanum oxide (La)₂O₃) Magnesium oxide (MgO), neodymium oxide (Nd)₂O₃) Praseodymium oxide (Pr)₆O₁₁) Samarium oxide (Sm)₂O₃) Antimony trioxide (Sb)₂O₃) Silicon monoxide (SiO), selenium trioxide (Se)₂O₃) Tin oxide (SnO)₂) Tungsten trioxide (WO)₃) Alumina (Al)₂O₃) Zinc sulfide (ZnS) and mixtures thereof. TiO is particularly preferable₂、ZrO₂、Fe₂O₃、Fe₃O₄、Cr₂O₃、ZnO、Al₂O₃And ZnS. It is particularly preferred to use a mixture of different refractive index enhancing particles.

According to the invention, the high refractive index organic material is used in the form of so-called "nanoparticles". Nanoparticles can be obtained, for example, from byk (nanobyk) and Clariant. The smaller the nanoparticle, the finer the structure that can be formed with the embossing lacquer, and the more preferred the nanoparticle. Nanoparticles in the order of 5nm are most preferred, but nanoparticles in the order of 10nm, 20nm and even 50nm are still very suitable.

When such nanoparticles are added to conventional plastics with a refractive index of about 1.5, this results in strong light scattering because of the highly different refractive index between the nanoparticles and the plastic material. However, in the high refractive index embossing varnish of the present invention, the difference in refractive index between the polymer material and the nanoparticles is small, which results in good optical transparency of the polymer material containing the nanoparticles.

Nanoparticles are also used to color the high refractive index embossing lacquer of the present invention. The use of such nanopigments makes it possible to produce very advantageously coloured microstructures with very fine resolution. High refractive index embossing lacquers containing nanopigments can of course be used to make focusing elements to obtain colored focusing elements, especially when the nanopigments have a high refractive index. Suitable nanopigments are, for example, conductive carbon blacks available in primary particle sizes of 18nm to 23nm ("Printex" and "hiback" from Degussa).

The nanoparticles, such as nanopigments, should be dispersed as homogeneously as possible in the high refractive index embossing lacquer. A particularly uniform distribution can be achieved when the nanoparticles are functionalized with reactive groups and form a nanocomposite with the polymer material via said reactive groups. Changli Lu, Zhanchen Cui, Zuo Li, Bai Yang and Jianong Shen in Journal of Materials Chemistry, 2003, 13(3), 526-530 describe such nanocomposites. The material described here is a nano-ZnS/polyurethane composite material, which is prepared by immobilization of ZnS nanoparticles functionalized with thiophenol and mercaptoethanol in a polyurethane matrix. The films made from the materials have refractive indices up to 1.848 (at 632.8 nm).

A further particularly preferred way of coloring the high refractive index embossing lacquer according to the invention is to polymerize a suitable dye into the high refractive index embossing lacquer. Dichroic dyes that can polymerize upon crosslinking without negatively changing their color are available from Rolic. Such dyes can also be synthesized starting from so-called reactive dyes for dyeing fibers. The reactive dyes contain, in addition to a chromophore component, a special reactive component via which the reactive dye can be covalently bonded to the fibre by reaction with the functional groups of the fibre. In the coloring of the high refractive index embossing lacquer according to the invention, the reactive groups of the reactive dyes do not react with the functional groups of the fibers, but for example with the OH groups or SH groups of the radiation-curing compounds or the reactive diluents of the high refractive index embossing lacquer according to the invention. Since the dyes polymerize and are thus fixed in the high refractive index polymeric material formed, they do not exhibit the drawbacks of migration of the pigments and lack of resistance to solvents, as do dyes conventionally used for coloring embossing paints. Reactive dyes with a high refractive index are particularly advantageous. The coloring with a reactive dye may be performed instead of the coloring with a nanopigment, or the coloring may be performed with a reactive dye in addition to the coloring by using a nanopigment.

In the case of UV curing and the use of photoinitiator systems, the wavelengths of the radiation-curing compound and optionally of the pigment, dye, and radiation source must be coordinated with one another to achieve good curing. The BASF company shows on RadTech 2005 of baselona a computer program that can predict the possibility of certain combinations to cure UV paints under certain conditions.

Some exemplary formulations of high refractive index UV-curable embossing lacquers will be given below:

radical cure weight%

Pentabromophenyl methacrylate (n ═ 1.71) 45

Phenylthioethyl acrylate (n ═ 1.56) 45

S, S' -Thiodi-4, 1-phenylene-bis (Thiomethylacrylate) (Sigma-Aldrich) 5

Irgacure 907(Ciba) 5

Pentabromophenyl methacrylate (n ═ 1.71) 45

Phenylthioethyl acrylate (n ═ 1.56) 45

PETIA: pentaerythritol triacrylate, pentaerythritol tetraacrylate 5

(mixture, Cytec)

Irgacure 907(Ciba) 5

Pentabromophenyl methacrylate (n ═ 1.71) 40

2, 6-dichlorostyrene (n ═ 1.57) (Sigma-Aldrich) 30

Phenylthioethyl acrylate (n ═ 1.56) (BIMAX) 20

S, S' -Thiodi-4, 1-phenylene-bis (Thiomethylacrylate) (Sigma-Aldrich) 5

Irgacure 1700(Ciba) 5

Pentabromophenyl methacrylate (n ═ 1.71) 40

2, 6-dichlorostyrene (n ═ 1.57) (Sigma-Aldrich) 30

Phenylthioethyl acrylate (n ═ 1.56) (BIMAX) 20

PETIA: pentaerythritol triacrylate, pentaerythritol tetraacrylate 5

(mixture, Cytec)

Irgacure 1700(Ciba) 5

S, S' -Thiodi-4, 1-phenylene-bis (Thiomethylacrylate) (Sigma-Aldrich) 50

Phenylthioethyl acrylate (BIMAX) 45

Irgacure 1700(Ciba) 5

S, S' -Thiodi-4, 1-phenylene-bis (Thiomethylacrylate) (Sigma-Aldrich) 35

Phenylthioethyl acrylate (BIMAX) 40

ZnS nanoparticles (optionally functionalized) 20

Irgacure 1700(Ciba) 5

Cationic curing

Bis [4- (2, 3-epoxypropylthio) phenyl ] sulfide (www.sumitomoseika.co.jp) 80

DVE-3(Rahn or Cytec) 16

Cyracure UVI-6992 (photoinitiator from DOW) 4

Both the high refractive index embossing lacquer according to the invention can be used to produce an arrangement of focusing elements and the high refractive index embossing lacquer according to the invention can be used to produce an arrangement of authenticity feature microstructures. For the focusing element, a high refractive index is particularly necessary; whereas for the microstructure, essential is mainly the fine resolution obtainable by the nanopigments (preferably polymerized thereto) and the dyes polymerized thereto.

The inventive micro-optical security element is equipped with focusing elements and/or microstructures consisting of the inventive embossing lacquer.

The embossing lacquer of the invention can be used for manufacturing security elements with the thickness of 20-50 mu m, and the thickness of the carrier film is 5-25 mu m. In a preferred embodiment, the grid pitch of the arrangement of focusing elements and the grid pitch of the arrangement of microstructures is in the range of about 3 μm to about 50 μm, preferably about 5 μm to about 35 μm, and particularly preferably about 10 μm to about 20 μm. The diameter of the focusing elements is typically of the order of about 10 μm to 30 μm, and the diameter of the individual microstructure elements is preferably of the same size.

For the manufacture of microlenses and microstructures, different methods are used. In particular, using classical techniques of semiconductor technology (photolithography, electron beam lithography), appropriate structures in the resist material can be exposed, refined, electroformed and used to make embossing tools for film embossing. Particularly suitable for the production of large surfaces are known methods of embossing into thermoplastic films or films coated with radiation-curing lacquers. Alternatively, a technique of applying a microlens arrangement by an ink-jet printing method or a self-organizing process of microparticles on a surface is also known.

Using classical methods of semiconductor technology, it is in particular possible to manufacture microstructures having any desired shape and profile.

Another method for producing microstructures for the microstructure arrangement of the present invention is so-called microcontact printing (μ CP). The method can achieve a resolution of less than 1 μm and is thus suitable for the production of small, high-resolution, printed microstructures. In this method, microstructures are fabricated by semiconductor patterning techniques (photolithography, electron beam lithography, etching and lift-off, nanolithography, etc.), followed by molding using an elastomer (e.g., PDMS). This produces a flexible, finely structured stamp (stamp) or printing cylinder suitable for transferring extremely thin ink layers when using special printing inks and surface treating the printing substrate. Printed microstructures with high resolution can be produced by applying suitable inks using the thus produced printing cylinders.

Alternatively, the microstructures and/or microlenses may be applied to the carrier by a micro-gravure printing process. In the method, a mould is used whose surface has an arrangement of elevations and depressions in the form of the desired microstructures or the desired microlenses, the depressions of which are filled with a curable, coloured or colourless embossing lacquer, the carrier is pretreated in order to fix the coloured or colourless lacquer well, the surface of the mould is brought into contact with the carrier and the lacquer in contact with the carrier is cured in the depressions of the mould so as to be connected to the carrier, the surface of the mould is removed from the carrier so that the cured embossing lacquer connected to the carrier emerges from the depressions of the mould.

It should be noted here that the micro-optical arrangements produced from the high refractive index embossing lacquers according to the invention can advantageously be equipped with overprint lacquers (overprint lacquers). Such a layer arranged on the micro-optical arrangement protects the micro-optical arrangement from counterfeiting, since it is no longer possible to cast the micro-optical arrangement. The use of the embossing lacquer according to the invention for producing a micro-optical arrangement also has an advantageous effect in the formation of an overprint lacquer, since, for example, the thin lenses of small curvature according to the invention can also be fitted with further layers (overprint lacquer) more easily and more reliably than has hitherto been possible according to the prior art.

Some exemplary security elements of the present invention will be described below with reference to the accompanying drawings. The embodiments are to be considered in all respects as illustrative and not restrictive. For clarity, the figures are not drawn to scale to true size. In particular the lens curvatures shown in the figures and the distances between the lenses and the microstructures do not represent the actual lens curvatures and the distances between the lenses and the microstructures that can be realized in practice according to the invention.

Shown in the drawings are:

FIG. 1 is a schematic view of a banknote with an embedded security thread and an attached transfer element;

FIG. 2 is a schematic cross-sectional view of the layer structure of the security thread of the present invention;

FIG. 3 is a security element of the present invention having a monochrome graphic image, wherein (a) shows a very diagrammatic perspective view from obliquely above, (b) shows a cross-section of the security element;

fig. 4 is a security element of the invention having a multicoloured graphical image, wherein (a) shows a schematic plan view and (b) shows a cross-section of the security element;

FIG. 5 is a schematic view similar to FIG. 4 of a security element of the present invention having a graphic image of mixed colors;

fig. 6 shows (a) and (b) steps of manufacturing microstructures of the microstructure arrangement for the security element of the invention;

figure 7 shows a cross-section through a microstructure arrangement of a security element of the invention; and

fig. 8 shows a cross-section of a security element of the invention with a microstructure that can be produced according to the exemplary embodiment of fig. 6.

The invention will now be explained in more detail by means of an example of a banknote. To this end, fig. 1 shows a schematic view of a banknote 10 with two security elements 12 and 16. The first security element is a security thread 12 which emerges at some window regions 14 on the surface of the banknote 10 and is embedded in the interior of the banknote 10 in the intervening region. The second security element is formed by an attachment transfer element 16 of any desired shape.

Fig. 2 schematically shows a cross-section of the layer structure of the security thread 12. The security thread 12 comprises a support 20 in the form of a transparent plastic film (e.g. a PET film about 20 μm thick). A grid-like arrangement of microlenses 22 is provided on the upper side of the carrier film 20, the microlenses 22 forming a grating (grating) of preselected symmetry on the surface of the carrier film.

On the underside of the carrier film 20, an arrangement of microstructures, i.e. a pattern layer 24, is provided, which contains a similar grid-like arrangement of identical micropattern elements 28. The arrangement of the micropattern elements 28 also forms a two-dimensional grating having a preselected symmetry.

As shown in fig. 2, the grating of the micro-graphic element 28 differs slightly from the grating of the micro-lens 22 in its symmetry and/or the size of its grating parameters by the offset of the micro-graphic element 28 relative to the micro-lens 22. This produces a moir é magnification effect. If the micro-graphic elements 28 are printed precisely in the grid pitch of the microlenses 22, an alternating image effect can be achieved. For example, so-called "animated" images may thus be produced, in which the microstructures are visible to a viewer only from a certain viewing direction and cannot be recognized from all other angles. The grating period and diameter of the micro-graphic elements 28 are of the same order of magnitude as the grating period and diameter of the micro-lenses 22 and cannot be discerned with the naked eye.

Figure 2 shows a security element in which the micro-graphic elements 28 are applied by micro-gravure printing. A support layer 30 of a transparent UV-curable lacquer is thus provided on the side of the carrier opposite the microlenses 22. Alternatively, the support layer 30 may also be prepared from a UV-or electron beam-cured embossing lacquer pigmented with nanopigments or reactive dyes according to the invention. The same applies to the micropattern elements 28. However, at least the arrangement of the microlenses 22 is made of the high refractive index embossing lacquer of the present invention, so that the microlenses 22 can have a small curvature and the security thread 12 has a small thickness of about 20 μm. The security thread 12 can therefore absolutely be introduced into the banknote without problems. It is thus provided, for example, with a heat-seal finish (sealfinish) 32.

Fig. 3 shows a security element according to the invention with a monochrome graphic image, which is shaped as a cover film 60 for a holed banknote. Fig. 3(a) shows a very diagrammatic perspective view from obliquely above, and fig. 3(b) is a cross-section through the security element.

The security element 60 has a transparent carrier 62, an arrangement of microlenses 64, a support layer 66 and coloured microstructured elements (micropattern elements) 68. The micro-graphic element 68 is shown in fig. 3(a), where the figure is simplified to a simple letter "a". Alternatively, the micro-graphic elements may also be in the form of complex logos or images that require very high resolution. In this case, not only the lenses 64 but preferably also the micro-graphic elements 68 are made of the embossing lacquer according to the invention, so that the embossing lacquer for the micro-graphic elements 68 is colored according to the invention with nanopigments or reactive dyes.

In the embodiment shown, the micro-graphic elements 68 are embedded in the overprint varnish 65 and thereby protected from counterfeiting.

As mentioned above, it is basically also conceivable to provide the first micro-optical arrangement (focusing element) with a cover-light lacquer in addition to the second micro-optical arrangement (microstructure) or to provide the first micro-optical arrangement (focusing element) with a cover-light lacquer instead of providing the second micro-optical arrangement (microstructure). Advantageously, this also makes the focusing element (in the case of the embodiment shown in fig. 3, the microlens 64) safe from counterfeiting. However, for the sake of clarity, this application does not include any drawing of the cover-tone paint showing the first micro-optical arrangement.

If desired, additional functional layers may be applied, such as a metallic or color-shifting coating 63 shown in phantom in FIG. 3(b), which contains negative image elements in the form of uncoated localized regions 61. Such coatings with interstices can be produced easily, for example, using the washing method known from publication WO 99/13157 a1 or unpublished german patent application No. 102007001791.1. With regard to the method of producing the partial region 61, the disclosures of WO 99/13157 a1 and DE 102007001791.1 are incorporated into the disclosure of the present application.

The security element 80 shown in fig. 4 according to a further exemplary embodiment of the present invention has a multicoloured graphical image. The arrangement of microstructure elements 82 shown in figure 4(a) contains microstructure elements 82-1 and 82-2 of different colours, which are again shown only with the letter "a" in the figure for simplicity of drawing. The microstructured elements can also be complex drawings, which however require a fine resolution to be ensured by the coloured embossing lacquers according to the invention with nanopigments or reactive dyes. Fig. 4(b) shows a cross-section of the security element.

Fig. 5 shows a further design of a security element 90 according to the invention, the security element 90 having a microstructure with mixed colors. In the exemplary embodiment shown, adjacent microstructure elements 92-R, 92-G, 92-B are applied with the red, green, and blue embossing lacquers of the present invention, respectively, at a structured depth and line width. Due to the small size of the microstructure elements 92, e.g., about 35 μm or less, the individual colors are not distinguishable when viewed and the viewer perceives a mixed color. When different mixed colors are produced in different regions of the security element, a moir é magnification arrangement with a gradation, color transformation effect or color contrast variation can be produced.

Alternatively, color shifting effects may also be produced when microstructures 92 are provided with vapor deposited thin film structures. Instead of a film structure, it is also possible to provide ink in certain areas with the special effect of a color change.

By suitable arrangement of the microstructure elements 92-R, 92-G, 92-B, a continuous color gradation from red to green can also be achieved.

Fig. 6(a) and 6(b) show the security element of the invention in a stage of manufacture in which the microstructuring of the high refractive index embossing lacquer is not produced by micro-intaglio printing as in the previous embodiment, but by conventional printing and embossing techniques. Thus, there is no support layer between the transparent carrier substrate 74 and the layer consisting of the high refractive index embossing lacquer 72. The high refractive index embossing lacquer is pigmented according to the invention with nanopigments or reactive dyes. The manufacturing is realized by the following steps: the colored embossing lacquer 72 is first applied to a transparent carrier substrate 74 by conventional printing methods. The microstructuring of the embossing lacquer is then achieved by known embossing techniques. The embossing lacquer layer 72 is thereby structured into thin, i.e. almost colourless, areas 75 and microstructure-forming thicker areas 76, resulting in a coloured microimage or a high resolution microstructure arrangement (fig. 6 (b)).

The arrangement comprising the carrier film 74 and the microstructures 76 shown in fig. 6 is then combined with an arrangement of focusing elements, which arrangement of focusing elements is likewise made of a high-refractive index embossing lacquer according to the invention, into a micro-optical security element.

Fig. 7 shows a microstructure arrangement similar to that of fig. 6, but the embossed lacquer layer 272 is configured such that the microstructures 276 of the microstructure arrangement have different contour heights or depths, so that a specific thickness of the embossed lacquer layer according to the invention achieves different color saturation and thus different contrast. In this way, microstructures can be realized which can also be used as shading continuous change dot-pattern (halftone) images, for example.

An additional method of making an embossed microstructure is illustrated in more detail in fig. 8. In this exemplary embodiment, embossing is performed in a transparent pigmented embossing lacquer 42 (e.g., a transparent pigmented UV lacquer) applied to a transparent carrier substrate 45 (e.g., a PET film). The embossed microstructures 46 may then be present in the form of, for example, characters or patterns. On the other side of the carrier substrate 45, a lens arrangement 48 having a plurality of microlenses 49 is embossed in a radiation-curing embossing lacquer according to the invention, for example a UV lacquer.

A layer 44 of reflective metal or opaque (e.g. white) ink is applied under the embossed lacquer layer 42. When embossing lacquers and covering colours of different colours are used, production can be carried out in this way, in particular with subtractive and additive colour effects.

To transfer the security element 40 onto security paper or to improve the adhesion of the security element designed as a security thread, an activatable adhesive 43 may further be applied to the metal or ink layer 44.

According to the invention, a security element with micro-optical authenticity features is used to guarantee the authenticity of any desired product. For example, in product packaging, the micro-optical authenticity feature may be included in the tear line.

Another subject of the invention is an item of value, such as a branded article, a document of value, a banknote or the like, provided with a security element according to the invention.

Claims (40)

1. A security element for marking the authenticity of a value item with at least one micro-optical authenticity feature comprising a first micro-optical arrangement having a plurality of focusing elements present in a first grid, and a second micro-optical arrangement having a plurality of microstructures present in a second grid, the first and second arrangements being arranged such that the microstructures of the second arrangement are seen to be magnified when viewed through the focusing elements of the first arrangement, the security element being characterized in that the first and/or the second micro-optical arrangement is made of a high refractive index embossing lacquer containing at least one binder having at least one radiation-curable compound system consisting of one or more organic compounds, at least part of the organic compounds of said radiation-curable compound system consisting of molecules having at least one polarizable element, such that upon radiation curing a polymeric material is formed having a refractive index greater than 1.5.

2. Security element according to claim 1, characterized in that the polarizing element is at least one element selected from the group consisting of S, Cl, Br, I and mixtures thereof.

3. Security element according to claim 1, characterized in that the radiation-curing compound system is a UV-curing compound system.

4. The security element according to claim 1, characterized in that the embossing lacquer contains a polymerization initiator.

5. Security element according to claim 1, characterized in that the radiation-curing compound system is a compound system which is cured by means of an electron beam.

6. Security element according to claim 1, characterized in that the radiation-curing compound system is capable of free-radical polymerization or cationic polymerization.

7. Security element according to claim 1, characterized in that the compounds of the radiation-curing compound system are used as monomers and/or prepolymers.

8. A security element according to claim 1, characterized in that a polymeric material with a refractive index of more than 1.6 is formed upon curing.

9. A security element according to claim 8, characterized in that a polymeric material with a refractive index of more than 1.7 is formed upon curing.

10. Security element according to claim 1, characterized in that the compounds of the radiation-curing compound system are self-crosslinking compounds.

11. Security element according to claim 10, characterized in that the self-crosslinking compound of the radiation-curing compound system consists of molecules having the same or different chemical composition.

12. Security element according to claim 10, characterized in that the self-crosslinking compound of the compound system is or comprises at least one acrylate.

13. Security element according to claim 10, characterized in that the self-crosslinking compound of the compound system is or comprises at least one epoxide.

14. Security element according to claim 10, characterized in that the self-crosslinking compound of the compound system is or contains at least one episulfide compound.

15. Security element according to claim 1, characterized in that the radiation-curing compound system has a first compound and a second compound which is capable of reacting with the first compound to crosslink.

16. Security element according to claim 15, characterized in that the first compound of the radiation-curing compound system and/or the second compound of the radiation-curing compound system consist of molecules having the same chemical composition or different chemical compositions.

17. Security element according to claim 15, characterized in that the second compound is a thiol and/or a polythiol or that the second compound contains a thiol and/or a polythiol.

18. Security element according to claim 15, characterized in that the first compound is an isocyanate.

19. Security element according to claim 15, characterized in that the first compound is or contains an ethylenically unsaturated compound.

20. Security element according to claim 15, characterized in that the first compound is or comprises an epoxide.

21. Security element according to claim 15, characterized in that the first compound is or comprises an episulfide.

22. Security element according to one of claims 1 to 21, characterised in that all compounds of the radiation-curable compound system consist of molecules with at least one polarizable element.

23. Security element according to one of claims 1 to 21, characterised in that at least part of the compounds of the radiation-curable compound system consists of molecules with at least two polarizable elements.

24. Security element according to claim 23, characterized in that at least part of the compounds of the radiation-curing compound system consists of molecules with more than two polarizable elements.

25. A security element according to any one of claims 1 to 21, characterized in that the embossing lacquer contains refractive index enhancing nanoparticles.

26. Security element according to claim 25, characterized in that the nanoparticles are nanopigments.

27. The security element according to claim 25, characterized in that the nanoparticles are polymerized into the embossing lacquer.

28. Security element according to any one of claims 1 to 21, characterized in that the embossing lacquer contains a reactive dye.

29. Security element according to any one of claims 1 to 21, characterized in that the embossing lacquer further contains additional components customary in embossing lacquers.

30. A security element according to any one of claims 1 to 21, characterized in that it has at least one further authenticity feature which can be verified by machine and/or visually.

31. A security element according to any one of claims 1 to 21, characterised in that the first and second grids of the micro-optical authenticity feature have a fixed geometric relationship.

32. A security element according to any one of claims 1 to 21, characterised in that the microstructures of the second arrangement of micro-optical authenticity features are present in the form of micro-characters or micro-patterns.

33. A security element according to any one of claims 1 to 21, characterized in that the microstructures and/or the focusing elements are provided in a colour.

34. A security element according to claim 33, characterized in that the microstructures are composed of microstructure elements of different colors.

35. Security element according to one of claims 1 to 21, characterised in that its total thickness is between 20 μm and 50 μm.

36. A security element according to any of claims 1 to 21, characterized in that it is a transfer element or a security thread.

37. Method for manufacturing a security element according to any one of claims 1 to 36, characterized in that the microstructures and/or the focusing elements are applied by the following technique: semiconductor technology, or micro-contact printing (μ CP) or micro-gravure printing.

38. Use of a security element according to any one of claims 1 to 36 for marking the authenticity of a product.

39. Data carrier, characterized in that it is equipped with a security element according to any one of claims 1 to 36.

40. A data carrier as claimed in claim 39, characterized in that the data carrier is a value document.