EP2169650A1 - Safety marking for securing valuable objects - Google Patents

Abstract

The laser-sensitive core-shell particle (50) has a core and a shell surrounding the core. The shell of the core-shell particle is surrounded by an ablation conveying function layer, which reduces a binding force between the core-shell-particle and binding agent by irradiation of the core-shell particle. Independent claims are included for the following. (1) a method for manufacturing a laser-sensitive core-shell particle; (2) a laser-markable safety feature of a laser-markable safety element for a safety paper which is used for manufacturing safety and value documents such as notes, cheques, identification cards or documents, and for a data carrier, particularly branded articles; (3) a laser-markable safety element with a substrate; and (4) a method for manufacturing a laser-markable safety element.

Description

The invention relates to a laser-sensitive core-shell particle for embedding in a binder-containing marker, a method for producing such a core-shell particle, a laser-markable security feature for securing valuables, a laser-markable security element for hedging valuables, a method for producing a laser-marked security element and a security paper and a data carrier with such a security feature or such a security element.

Data carriers, such as valuables or identity documents, or other valuables, 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. Such security elements may be designed, for example, in the form of a security thread embedded in a banknote, a tear-open thread for product packaging, an applied security strip or a self-supporting transfer element, such as a patch or a label which is applied to a value document after its manufacture.

For individual marking of the security elements, laser inscribers, for example based on CO ₂ lasers Nd: YAG lasers or UV lasers, are used. Depending on the wavelength of the marking laser used, however, there are restrictions with regard to the usable laser-markable markers. For example, currently used luminescent materials and many IR absorbers absorbing in the range below 1000 nm or above 1300 nm are not markable with Nd: YAG lasers.

A wider range of laser markable markers can be provided by taking into consideration markers in which laser-sensitive core-shell particles are embedded with a core and a shell surrounding the core, with only one of the core and shell materials radiating absorbed by the laser inscription.

The publication EP 1 826 728 A2 proposes for this purpose a security element with a laser-markable marker material with core-shell particles, in which one of the materials of core and shell absorbs the radiation of a marking laser and the other of the materials of core and shell does not absorb the radiation of the marking laser. Under certain circumstances, however, the laser marking of such markers, the ablation of the core-shell particles from the marker material only incomplete, so that an incomplete marking of the security element, ie the marker arises.

Based on this, the present invention seeks to provide a security feature for securing valuables of the type mentioned, which avoids the disadvantages of the prior art. In particular, the most complete removal of the core-shell particles from the marker is to be ensured in the laser marking.

This object is achieved by the laser-sensitive core-shell particle having the features of the independent claim. A method for producing such a core-shell particle, a security feature, a security element, a method for producing a laser-marked security element, a security paper and a data carrier with a Such security feature or such a security element are given in the independent claims. Further developments of the invention are the subject of the dependent claims.

According to the invention, a generic laser-sensitive core-shell particle comprises a core and a shell surrounding the core, wherein one of the core and shell materials absorbs the radiation of a marking laser and the other of the core and shell materials does not absorb the radiation of the marker laser is executed. The shell of the core-shell particle is surrounded by an ablation-promoting functional layer, which reduces the bond strength between the core-shell particle and the embedding binder upon irradiation of the embedded in a binder-containing marker core-shell particle with the marking laser to the promote laser-induced removal of the core-shell particle from the marker. In the context of the present invention, the term "shell" also includes a shell constructed from several layers.

In a preferred embodiment, the marker, in which the laser-sensitive core-shell particles is embedded, designed for use in security printing, which may be in particular be applied in offset, flexographic, screen or stitch printing ink, coating or paint.

In a first variant of the invention, the core of the core-shell particle contains an absorber tuned to the wavelength of the irradiated laser radiation, in particular an IR absorber. The shell of the core-shell particle can in this variant a colored and / or luminescent substance, in particular a colored and / or luminescent pigment or a contained in the irradiated laser radiation non-absorbing absorber. Alternatively, the shell of the core-shell particle contains an absorber tuned to the wavelength of the irradiated laser radiation, in particular an IR absorber. In this variant, the core of the core-shell particle may contain a colored and / or luminescent substance, in particular a colored and / or luminescent pigment, or an absorber which does not absorb in the region of the irradiated laser radiation. In general, suitable dyes are suitable for the non-colorants and luminescent substances used in addition to pigments, the conceptual difference between pigments and dyes being known to the person skilled in the art.

Advantageously, the functional layer of the core-shell particle is formed from a low melting point material having a melting temperature in the range of 100 ° C to 250 ° C, preferably 100 ° C to 220 ° C. As a low-melting material for the functional layer but can also be a low-melting compound having a melting temperature below 100 ° C, for example, carnauba wax having a melting temperature between 80 ° C and 87 ° C or hard paraffin with a melting temperature between 50 ° C and 60 ° C.

According to a further variant of the invention, the functional layer of the core-shell particle is formed from a material having a highly temperature-variable viscosity, strongly temperature-variable hydrophilicity or strongly temperature-variable hydrophobicity. Preferably, a hydrophilic shell of the core-shell particle can be surrounded with a hydrophilic surfactant layer as a functional layer. Upon irradiation with the marking laser, heat is generated in the absorbent portion of the core-shell particle which is transferred to the surfactant layer. The heat applied to the surfactant layer leads to an increase in temperature which makes the surfactant layer hydrophobic. To current understanding is due to the repulsion of hydrophilic shell and hydrophobic surfactant layer repulsion, which promotes the removal of the core-shell particle from the marker.

In a further variant of the invention, the functional layer has materials with hydrophilic groups in order to ensure improved wetting of the functional layer in the embedding binder of a marker.

In principle, materials can also be used for the functional layer, which have a combination of the properties described above, ie, for. As a low-melting material with strong temperature variable viscosity, which z. B. in some waxes or hard paraffins is the case.

Also advantageously, the functional layer of the core-shell particle may be formed from a vaporizable or sublimable material having an evaporation or sublimation temperature of less than 250 ° C, preferably less than 200 ° C, more preferably less than 150 ° C , In this case, the heat development of the core or the shell of the core-shell particle can be utilized during the marking process with the marking laser. The temperature-sensitive functional layer is rendered gaseous by the heat radiating from either the core or the shell and escapes substantially from the marker. Such temperature-sensitive materials may be sublimable colored pigments, luminescent pigments, dyes, liquids with a boiling point in the desired temperature range or evaporable polymeric coatings.

In a further variant of the invention, the core-shell particle is surrounded by a functional layer which contains a predetermined breaking point which breaks at a sufficiently large excitation energy. To characterize a sufficiently large excitation energy is e.g. a setpoint temperature in question. By a temperature increase in the functional layer, which is caused by the absorbed radiation of the marking laser in the core or in the shell of the core-shell particle, such a predetermined breaking point can break and promote the removal of the core-shell particle from the marker.

To stabilize the core-shell particle, an inorganic or organic layer can be arranged between the core and the shell and / or between the shell and the functional layer.

Furthermore, it is provided in a preferred variant of the invention that the functional layer contains a colored and / or luminescent substance, in particular a colored and / or luminescent pigment. The colorants / luminescent substances or colorant / luminescent pigments described above or below with reference to the core or the shell of the core-shell particle according to the invention can also be contained in the functional layer.

The invention also encompasses a method for producing a laser-sensitive core-shell particle in which either a laser-absorbing material is encapsulated with a non-laser-absorbing material and surrounded with the ablation-promoting functional layer, or a non-laser-absorbing material is encapsulated with a laser-absorbing material and combined with the ablation-promoting Function layer is surrounded. In the context of the present invention, "encapsulating" is quite general the coating of a first material with a second material understood, so for example, the coating of the core of the core-shell particle with a shell.

According to the invention, a laser-markable security feature for safeguarding valuables contains a laser-markable marker with core-shell particles which are each surrounded by an ablation-promoting functional layer according to one of the described embodiments.

A laser-markable security element advantageously comprises such a laser-markable security feature, which is arranged on a substrate.

Also advantageously, an auxiliary layer may be disposed between the substrate and the laser-markable security feature that reduces the bond strength between the core-shell particles of the laser-markable marker and the substrate.

The auxiliary layer between the substrate and the laser-markable security feature may in particular have an adhesion to the laser-markable security feature that is less than the adhesion between the auxiliary layer and the substrate.

Alternatively, the auxiliary layer may be formed of a low melting point material having a melting temperature of less than 250 ° C, preferably less than 150 ° C, and more preferably less than 100 ° C.

It is also possible that the auxiliary layer contains an absorber, in particular an IR absorber. Upon irradiation with the marking laser, according to current understanding, either the (IR) absorbers in the auxiliary layer are ablated, wherein absorbent core-shell particles arranged above these (IR) absorbers are entrained in the marking substance, or at least the adhesion between the auxiliary layer and the laser markable security feature comprising the core-shell particles is reduced. Also caused by the absorber in the auxiliary layer softening of the auxiliary layer, for. B. by supplying the laser energy absorbed by the absorber, leads to an improved removal of the core-shell particles from the security feature.

The invention further comprises a method for producing a laser-marked security element, in which the described laser-markable security feature is applied to a substrate and irradiated with radiation of the marking laser in a marking area in order to remove the core-shell particles from the marking substance in the marking area.

Prior to applying the laser markable security feature, an auxiliary layer according to any of the described embodiments can be applied to the substrate which reduces the bond strength between the core-shell particles of the laser-markable marker and the substrate. The auxiliary layer can advantageously be applied to the substrate by means of flexographic printing, screen printing or offset printing.

To produce the laser-marked security element, the laser-markable security feature is preferably exposed to laser radiation in the near-infrared (NIR), in particular at wavelengths of about 1.06 μm. to Marking can then be used with Nd: YAG lasers or related laser types, such as Nd: glass or Nd: YVO ₄ lasers. Alternatively, the marker can be marked by laser radiation in the ultraviolet spectral range.

A security paper for the production of security or value documents, such as banknotes, checks, identity cards, certificates or the like, is preferably provided with a laser-markable security feature of the type described above or with a laser-markable security element of the type described above. The security paper may comprise a carrier substrate made of paper or plastic. In principle, it should be noted that the substrate material used for the application of the security feature or security element is any type of paper, in particular cotton paper. Of course, it is also possible to use paper which contains a proportion of polymeric material in the range of 0 <x <100% by weight.

Furthermore, it is conceivable in principle, although not currently preferred that the substrate material of the data carrier, a plastic film, for. B. a polyester film is. The film may also be monoaxially or biaxially stretched. The stretching of the film, inter alia, leads to it receiving polarizing properties that can be used as another security feature.

It may also be expedient if the substrate material is a multilayer composite which has at least one layer of paper or a paper-like material. Such a composite is characterized by an extremely high stability, which is for the durability of the substrate or disk of great advantage.

It is also conceivable, however, to use a multilayered, paper-free composite material as the substrate material, which is very advantageous, above all, for identity cards and credit cards. These materials can be used with particular advantage in particular climatic regions of the earth.

All materials used as substrate material may have additives that serve as a mark of authenticity. It is primarily to think of luminescent, which are preferably transparent in the visible wavelength range and in the non-visible wavelength range by a suitable tool, for. B. a UV or IR radiation emitting radiation source can be excited to produce a visible or at least detectable with auxiliary luminescence. Other security features can be used with advantage, as long as they do not affect the viewing of the security element according to the invention or at least not significantly.

The invention further comprises a data carrier, in particular a brand article, value document or the like, which is equipped with a security feature of the type described above or a security element of the type described above.

Further embodiments and advantages of the invention are explained below with reference to the figures. For better clarity, a scale or proportion accurate representation is omitted in the figures.

Fig. 1

eine schematische Darstellung einer Banknote mit einem erfindungsgemäßen Sicherheitselement,

Fig. 2

schematisch in (a) bis (e) eine mit einem erfindungsgemäßen Markierungsstoff versehene Fläche vor, während und nach der Lasermarkierung; schematisch in (f) ein lasermarkiertes Sicherheitselement,

Fig. 3

eine Ausgestaltung von Kern-Hülle-Teilchen nach einem weiteren Ausführungsbeispiel der Erfindung, und

Fig. 4

eine schematische Darstellung einer Schichtenfolge eines markierten Sicherheitselementes im Querschnitt.

Show it:

Fig. 1

a schematic representation of a banknote with a security element according to the invention,

Fig. 2

schematically in (a) to (e) a surface provided with a marker according to the invention before, during and after the laser marking; schematically in (f) a laser-marked security element,

Fig. 3

an embodiment of core-shell particles according to a further embodiment of the invention, and

Fig. 4

a schematic representation of a layer sequence of a marked security element in cross section.

The invention will now be explained using the example of a banknote. Fig.1 shows a schematic representation of a banknote 10, which is equipped with a laser-marked security element 12 according to the invention.

For marking with a marking laser, for example an Nd: YAG laser with a wavelength of 1.064 μm, the security element 12 contains at least one laser-markable marking substance 30 with a colored or a luminescent pigment. By means of the laser marking, the colored or luminescent pigment is removed from the marking substance 30, so that a color-visible region or marking region 42 differing in its luminescence properties is created in the security element 12.

In a first, in Fig. 2 (a) illustrated embodiment of the invention contains the color / coating of the marker 30, a binder 28, in the Core-shell particles 20 are embedded. The core-shell particles 20 comprise a core 22 containing an infrared absorber and a shell 24 made of a colorant or luminescent substance, in particular a colored pigment, which does not absorb the radiation of the marking laser emitting in the infrared spectral range.

In order to promote the laser-induced removal of the core-shell particles 20 from the marker 30, the shell 24 is surrounded by an ablation-promoting functional layer 26 which upon irradiation of the core-shell particles 20 embedded in the binder-containing marker 30, the bond strength between the core Sheath particles 20 and the embedding binder 28 are reduced.

Without wishing to be bound by any particular explanation, it is presently believed that the shell 24 of the core-shell particles 20 has a highly rugged surface (not shown) such that the core-shell particles would be devoid of the additional functional layer provided by the invention anchored with a high bond strength in the surrounding binder 28. The bond strength between the bare core-shell particles 22, 24 and the binder 28 may be so high that the forces acting between the binder 28 and the shell 24 of the bare core-shell particles (adhesion forces) may be greater than those Forces that exert similar molecules in the material of the sheath 24 of the core-shell particles (cohesive forces).

In addition, since the binders 28 commonly used in security printing have high elasticity, the binder matrix is excited to oscillate by the strong bonding to the core-shell particles during laser marking. The laser irradiation can be so to a physical separation of core 22 and shell 24 of the bare core-shell particles, so that the shell 24 is not or not completely removed from the binder matrix 28. The sheath 24 then at least partially remains in the binder matrix 28 and results in undesirable, incomplete laser ablation of the bare core-sheath particles.

By the present invention provided additional functional layer 26, the influence of the binder is reduced according to current understanding and the adhesion of the binder 28 to the core-shell particle 20 is reduced. It should be emphasized that the explanatory approaches and mechanisms of increased ability to ablate proposed in this application are plausible explanations according to current knowledge, but do not claim to be complete or correct. In particular, the knowledge or even the correctness of the proposed explanatory approaches for the execution of the invention is not required.

Coming back to the presentation of the Fig. 2 (a) In the embodiment of the invention shown there, the functional layer 26 is formed from a low-melting material having a melting temperature in the range of 50 ° C. to 250 ° C. Suitable low-melting materials are both organic compounds and inorganic compounds. Organic compounds are, for example, carnauba wax with a melting point between 80 ° C and 87 ° C, hard paraffin (paraffinum durum) with a melting point between 50 ° C and 60 ° C, stearin with a melting point between 60 ° C and 70 ° C, white Beeswax (Cera alba) having a melting temperature between 62 ° C and 65 ° C or other saturated higher fatty acids and polyethylene having a melting temperature between 90 ° C and 125 ° C and copolymeric compounds such as acrylonitrile-butadiene-styrene copolymer (ABS) with a melting temperature between 85 ° C and 100 ° C and styrene-acrylonitrile (SAN) with a melting temperature of about 250 ° C.

Suitable inorganic compounds for the functional layer 26 are, for example, MgCl * 6H ₂ O having a melting temperature of 117 ° C., Mg (NO ₃ ) ₂ * 6H ₂ O having a melting point of 89 ° C., CH ₃ COONa * 3H ₂ O having a melting temperature of 58 ° C or MgCl ₂ * 6H ₂ O / Mg (NO ₂ ) ² * 6H ₂ O with a melting temperature of 58 ° C.

The coating of the shell 24 of the core-shell particle 20 can be carried out in the emulsion polymerization or spray-coating process or using plasma technologies. Before providing the core-shell particles 20 with the ablation-promoting functional layer 26, the functional layer 26 is below the melting temperature in a solid state of matter. The functional layer 26 is connected to the sheath 24, and the sheath 24 is fixedly connected to the core 22.

In Fig. 2 (b) is a plan view of the coated with the laser-markable marker 30 surface of the security element 12 shown schematically before the laser marking. The generally colorless and non-absorbing at the wavelength of the marking laser binder 28 is optically little or no apparent. The color of the marker 30 is determined either by the IR absorber contained in the core 22, depending on the wavelength of illumination used, or by the fluorescent and colorant pigments preferably contained in the envelope 24. Depending on the application, the core and the shell of the core-shell particles 20 together can determine the visual impression of the not yet laser-marked marking substance 30.

The FIGS. 2 (c) to (e) illustrate, in an idealized representation, the ablation process of the core-shell particles 20 according to the invention from the marking substance according to the current understanding, wherein a wax layer 26 is assumed as the functional layer for the illustration.

First is in Fig. 2 (c) the marker 30 after the start of the irradiation 32 is shown with a marking laser. The radiation 32, which at the in Fig. 2 illustrated embodiment of the invention from an Nd: YAG laser and has a wavelength of 1064 nm, is of the binder 28, the sheath 24 of the core-shell particle 20 and in the embodiment of the wax layer 26 ( Fig. 2 (a) ) is not absorbed. However, the radiation 32 is absorbed by the IR absorber contained in the core 22 of the core-shell particle 20, and the received laser energy is converted to heat.

The heat generated in the core 22 is transferred via the shell 24 to the wax layer 26. Due to the resulting increase in temperature, the melting point of the wax is exceeded and the wax layer 26 begins to melt. The wax layer liquefies when it exceeds the melting point and expands to a certain extent, as in Fig. 2 (c) represented by the reference numeral 27, in the binder 28 into.

By liquefaction and expansion of the wax layer 26, 27, a low bond strength between the core 22, 24 interior of the core-shell particle and the surrounding binder matrix 28 is achieved so that the core 22 and shell 24 of the core-shell particle, as in FIG Fig. 2 (d) shown, can be easily removed from the marker 30 (reference numeral 34). The cause of the lighter ablation, as currently understood, may be considered a "cohesive failure" within the wax layer 26, 27 in which, due to the heating, the interaction of the wax layer molecules is weakened, so that a part of the wax layer molecules interacts with the binder molecules via adhesive forces and remains in the binder matrix, while another, smaller part of the wax layer molecules binds to the shell 24 of the core shell via adhesive forces Particle interacts and is removed by the supplied laser energy together with the core and shell of the core-shell particle from the marker 30. The Fig. 2 (d) is thus idealized insofar as in the representation there the entire molten wax layer 27 remains in the marking substance 30, while in practice part of the wax layer 26 will remain on the core-shell particle.

After being released from the marker 30, the core-shell particles 22, 24 are aspirated with a suitable suction device and thus permanently removed from the surface of the marking region. Fig. 2 (e) shows the laser-marked marker 40 after leaching of the core-shell particles. The laser-marked marker 40 includes the binder 28 and the remaining portion of the expanded wax layer 27. The core 22 and sheath 24 are completely removed from the marker 30.

In Fig. 2 (f) is that in Fig. 1 shown on the banknote 10 security element 12 shown in more detail after the laser marking. The laser-marked security element 12 contains first areas in which the laser-markable marking substance 30 was not exposed to radiation of the marking laser, and second areas 42 in which the core-shell particles were removed from the marking substance 30 and in which the laser-marked marking substance 40 is now present , As in Fig. 2 (f) As shown, the second region with the laser-marked marker 40 typically forms one colorless marking area 42 within the first areas, the visual impression of which is imprinted by the absorbent core 22 and / or the colored and fluorescent pigments of the shell 24 of the core-shell particles. In the embodiment of Fig. 2 (f) the marking area 42 forms the numerical sequence "50" corresponding to the denomination of the in Fig.1 banknote 10 corresponds.

Before the laser marking, the wax layer 26 can, as in Fig. 2 (a) shown, the sheath 24 completely surrounded or can surround them only in some areas and only around the sheath 24 flow around during melting. A particularly efficient melting of the wax layer 26 can be achieved if not only the core 22, but also the wax layer 26 contains IR-absorbing materials.

Between core 22 and shell 24 and / or between shell 24 and the ablation-promoting functional layer 26 may optionally be arranged an inorganic or organic layer for stabilizing the core-shell particle 20.

In Fig. 3 For example, a core-shell particle 50 with absorbent sheath 54 is illustrated in accordance with another embodiment of the invention. The core 52 and the functional layer 56 are formed in this embodiment in the region of the wavelength of the radiation of the marking laser non-absorbent, while the shell 54 of the core-shell particle 50 contains an IR absorber. The core 52 of the core-shell particle 50 may contain a colored and fluorescent pigment. At the in Fig. 3 illustrated arrangement of the core 52, shell 54 and functional layer 56, the heat generated by the radiation of the marking laser in the sheath 54 is transferred by the shortest route to the ablation-promoting functional layer 56, without a non-absorbent layer being disposed between the absorbent core and the functional layer.

The functional layer can also be formed from a material with a highly temperature-variable viscosity, strongly temperature-variable hydrophilicity or strongly temperature-variable hydrophobicity, instead of by a low-melting material. Suitable materials for the functional layer 56 are, for example, surfactants. The heat generated by the marking laser in the envelope 54 changes the viscosity and / or hydrophilicity / hydrophobicity of the functional layer.

If, for example, a hydrophilic shell 54 is surrounded by a hydrophilic functional layer 56 of surfactants, the surfactants in the functional layer 56 become hydrophobic upon irradiation with the marking laser due to the radiation absorbed by the shell 54 and the heat transferred to the functional layer, so that repulsion of the hydrophilic shell 54 enters from the hydrophobic functional layer 56. This promotes the removal of the core-shell particles 50 from the marker 30 (not shown). Unlike the in Fig. 2 In the case of such a functional layer 56, according to the current understanding, the adhesion forces between the functional layer 56 and the sheath 54 are reduced without a reduction in the cohesion forces within the functional layer 56 having to occur. Such a mechanism can therefore be considered as an "adhesion break" in laser marking.

In another embodiment, the functional layer 56 is made of a vaporizable or sublimable material having a Evaporation or sublimation temperature is formed in a range between 120 ° C and 200 ° C. The heat transferred from the absorbent sheath 54 gasses the temperature-sensitive material in the functional layer 56 and escapes from the marker 30. Suitable temperature-sensitive materials are sublimable colored pigments, liquids having a boiling point in the desired temperature range, or vaporizable polymeric coatings. In the case of a vaporizable liquid, the core 52 and the shell 54 may be surrounded by another layer and float in the vaporizable liquid forming the functional layer 56.

In another embodiment, the functional layer 56 and the shell 54 of the core-shell particle are formed from the same or different vaporizable or sublimable materials. Also core-shell particles of this embodiment can be ablated very well with laser radiation from the marker 30 / remove.

As evaporation-capable or sublimable materials, it is possible in particular to use for the shell of the core-shell particle or the functional layer: anthraquinone derivatives, anthracene derivatives, azo dyes, azomethine dyes, stilbene dyes, quinophthalone dyes, coumarins, β-naphthol: Pigment Orange 5, monoazo pigments: Pigment Yellow 1, 3.13, 74.111, anthraquinone: Pigment Red 177 and naphthol AS: Red 146.

Further examples of sublimated dyes are:
Yellow: PTY-52, Macrotex Yellow, Phoron Brilliant Yellow 6GL;
Red: MS Red G, Macrotex Red Violet R, Ceres Red 7B, Samaron Red HBSL, Sk Rubinee SGL;
Blue: Kayaset Blue 714, Waxoline Blue AP-FW, Phoron Brilliant Blue sR, MS Blue 100, Direct Blue No.1.

The coating of the core 52 or the shell 54 can be effected in a sol-gel process, by means of emulsion polymerization, spray-coating processes or plasma technologies.

According to a further embodiment, in the functional layer 56 surrounding the shell 54 of the core-shell particle 50, a predetermined breaking point is included, which breaks at a set temperature. Suitable predetermined breaking points can be achieved in the functional layer 56 by using particularly brittle materials. In laser marking, the functional layer 56 breaks down due to the vibrations of the infrared absorber at the predetermined breaking point and thus ensures the necessary freedom of movement for the release of the core 52 and the sheath 54 Cause for easier removal of core and shell in the fraction of the functional layer 56 is looking for.

It is understood that with respect to the core-shell particles 50 of the Fig. 3 functional layers described also for the core-shell particles 20 of the Fig. 2 can be used.

As in the Fig. 2 and 3 As illustrated, a laser-sensitive core-shell particle 20, 50 may be prepared by either encapsulating a laser-absorbent material as the core 22 with a non-laser-absorbent material as the cladding 24 and surrounding it with a functional layer 26, or by using a non-laser-absorbent material as the core 52 with a laser absorbing Material encapsulated as a shell 54 and surrounded with a functional layer 56.

• Lösen von 0,5 g der Kern-Hülle-Kombinationen 22, 24 in 50 g Paraffin mit einem Schmelzpunkt zwischen 80 °C und 100 °C bei 100 °C,
• Mischen dieser Lösung in einem bei 90 °C thermostatisierten Mikromischer mit entionisiertem Wasser der Temperatur 90 °C im Verhältnis 1:5, wobei HPLC-Pumpen (HPLC: High Performance Liquid Chromatography) verwendet werden, die mit 90 °C heißem Wasser vorgeheizt sind,
• Pumpen der auf diese Weise gebildeten Paraffin-in-Wasser-Dispersion direkt in eine gerührte Vorlage aus 11 Eiswasser, wobei sich die Paraffintröpfchen mit den darin eingebetteten Kern-Hülle-Kombinationen 22, 24 unter Ausbildung eines Bodensatzes verfestigen.

The wrapping of the core 22 and the shell 24 with the low-melting material paraffin can be carried out, for example, according to the following method:

• Dissolving 0.5 g of the core-shell combinations 22, 24 in 50 g of paraffin having a melting point between 80 ° C and 100 ° C at 100 ° C,
• Mixing this solution in a 90 ° C thermostated micromixer with deionized water of temperature 90 ° C in the ratio 1: 5, using HPLC (High Performance Liquid Chromatography) pumps preheated with 90 ° C hot water,
• Pumping the thus formed paraffin-in-water dispersion directly into a stirred pad of 11 ice water, wherein the paraffin droplets solidify with the embedded therein core-shell combinations 22, 24 to form a sediment.

A laser-markable security feature for securing valuables can be produced by embedding the core-shell particles 20, 50 in a laser-markable binder-containing marker, in particular a spot, flexographic or screen printing ink.

In Fig. 4 is a layer sequence of an inventive, already marked security element 60 shown schematically in cross section. In this case, an auxiliary layer 64 and a laser-markable marking substance 30 of the type described above were first applied to a substrate 62. The auxiliary layer 64 reduces the bond strength between the core-shell particles 20, 50 of the laser-markable marker 30 and the substrate 62. The auxiliary layer 64 can, as in Fig. 4 be arranged over the entire surface or even partially on the substrate 62. It may not be visually visible, visually visible, for example colorful, or provided with additional marking substances, for example luminescent pigments.

In order to reduce the bond strength between the core-shell particles and the substrate, the auxiliary layer 64 may have an adhesion to the laser-markable marking substance 30 that is less than the adhesion between the auxiliary layer 64 and the substrate 62 Auxiliary layer 64, for example, a surface tension of 32 mN / m, and the marker 30, in which the core-shell particles 20, 50 are embedded, a surface tension of 36 mN / m.

Alternatively, the auxiliary layer 64 may be formed of a low melting point material having a melting temperature between 50 ° C and 250 ° C. Preferably carnauba wax with a melting temperature between 80 ° C and 87 ° C can be used.

The auxiliary layer 64 may also include a binder and low melting point materials that have a specific gravity and surface tension less than the specific gravity and surface tension of a binder of the auxiliary layer 64. Upon heat transfer from the absorbent portions of the core-shell particles 20, 50 to the low melting point materials in the auxiliary layer 64 then tend to float and attach to the interface between the auxiliary layer 64 and the marker 30.

In another alternative, the security element 60 may include an auxiliary layer 64 containing an IR absorber. The IR absorber, whose absorption properties are tuned to the wavelength of the marking laser, heats up on irradiation with the marking laser and can lead to a detachment of the parts of the marking substance 30, which are arranged immediately above the irradiated areas of the auxiliary layer 64, or at least the Reduce adhesion between the auxiliary layer 64 and the marker 30 and thereby facilitate the ablation of the core-shell particles.

In a substrate 62 formed of paper, the auxiliary layer 64 may also reduce the specific surface area of the substrate 62 by closing the capillary on the surface of the substrate 62. By reducing the specific surface area, the substrate 62 is smoothed so that the adhesion between the substrate 62 and the marker 30 and thereby the physical anchoring of the label to the substrate is reduced.

The auxiliary layer 64 may be applied to the substrate 62 prior to application of the marker 30 to the substrate, for example via a flexographic printing process, screen printing process, or offset printing process.

After the auxiliary layer 64 and the marking substance 30 have been applied, the laser-markable security feature formed in the marking region 42 is exposed to radiation from a marking laser in order to remove the core-shell particles 20 or 50 from the marking substance 30 there. This results in a laser-marked security element 60 having a marking region 42 in which core-shell particles are dissolved out of the marking substance 30, as shown in FIG.

Claims (15)

A laser-sensitive core-shell particle for embedding in a binder-containing marker, in particular for security printing, comprising a core and a shell surrounding the core, one of the core and shell materials absorbing the radiation of a marker laser and the other of the core and shell materials the radiation of the marking laser is designed to be non-absorbent, characterized in that the shell of the core-shell particle is surrounded by an ablation-promoting functional layer which, upon irradiation of the embedded in a binder-containing marker core-shell particle with the marking laser, the bond strength between the core Sheath particles and the embedding binder to promote laser-induced removal of the core-shell particle from the marker. The laser-sensitive core-shell particle according to claim 1, characterized in that the core of the core-shell particle contains an absorber absorbing the radiation of the marking laser, in particular an IR absorber, and preferably that the shell of the core-shell particle is a colored one and / or luminescent substance, in particular a colored and / or luminescent pigment. The laser-sensitive core-shell particle according to claim 1, characterized in that the shell of the core-shell particle contains an absorber absorbing the radiation of the marking laser, in particular an IR absorber, and that preferably the core of the core-shell particle is a colored one and / or luminescent substance, in particular a colored and / or luminescent pigment. Laser-sensitive core-shell particle according to at least one of claims 1 to 3, characterized in that the functional layer is formed from a low-melting material having a melting temperature in the range of 100 ° C to 250 ° C. Laser-sensitive core-shell particle according to at least one of claims 1 to 4, characterized in that the functional layer is formed from a material having a highly temperature-variable viscosity, strongly temperature-variable hydrophilicity or strongly temperature-variable hydrophobicity. A laser-sensitive core-shell particle according to at least one of claims 1 to 3, characterized in that the functional layer is made of a vaporizable or sublimable material having an evaporation or sublimation temperature of less than 250 ° C, preferably less than 200 ° C, especially is preferably formed by less than 150 ° C. Laser-sensitive core-shell particles according to at least one of claims 1 to 3, characterized in that the shell of the core-shell particles is surrounded by a functional layer containing a predetermined breaking point, which breaks at a sufficiently large excitation energy, in particular at a desired temperature. Laser-sensitive core-shell particle according to at least one of Claims 1 to 7, characterized in that an inorganic or organic layer for stabilizing the core-shell particle is arranged between the core and the shell and / or between the shell and the functional layer. A process for producing a laser-sensitive core-shell particle according to at least one of claims 1 to 8, wherein either a laser absorbing material is encapsulated with a non-laser absorbing material and surrounded with the functional layer, or a non-laser absorbing material is encapsulated with a laser absorbing material and coated with the Function layer is surrounded. Laser-markable security feature for safeguarding valuables, characterized in that the security feature contains a laser-markable, binder-containing marker with core-shell particles according to at least one of claims 1 to 8, and in particular as a paint, lacquer or coating. Laser-markable security element for securing valuables, characterized in that a laser-markable security feature according to claim 10 is arranged on a substrate. Laser-markable security element according to claim 11, characterized in that an auxiliary layer between the substrate and the laser-markable security feature is arranged, which reduces the bond strength between the core-shell particles of the laser-markable marker and the substrate, wherein the auxiliary layer preferably has an adhesion to the laser-markable security feature which is less than the adhesion between the auxiliary layer and the substrate. Laser-markable security element according to claim 12, characterized in that the auxiliary layer of a low-melting material having a melting temperature of less than 250 ° C, preferably from less than 150 ° C, more preferably less than 100 ° C is formed, and / or that the auxiliary layer contains an (IR) absorber. A method for producing a laser-marked security element for securing valuables, in which a laser-markable security feature according to claim 10 is applied to a substrate and exposed in a marking area with radiation of a marking laser to remove the core-shell particles from the laser-markable marker in the marking region , wherein preferably before the application of the laser-markable security feature, an auxiliary layer is applied to the substrate, which reduces the bond strength between the core-shell particles of the laser-markable marking substance and the substrate. Security paper for the production of security and value documents, such as banknotes, checks, identity cards, certificates or the like, or data carriers, in particular branded articles, value documents and the like, comprising a security feature according to claim 10, a security element according to at least one of claims 11 to 13, or a producible according to claim 14 security element is equipped.

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