Matrix comprising zero-order diffractive pigments

[0001] The present invention relates to pigments exhibiting a colored effect after rotation and / or tilting, in particular pigments with a colored effect, in which the colored effect is based on zero order diffraction, methods of their preparation and their use.

[0002] Physical color: it is known to obtain physical color either by means of a surface mesh with first and higher order diffraction or by means of a flat dielectric layer system or Fabry-Perot type layer system (interference filters) which are disclosed in US3858977. It is also known that physical colors can be obtained by joining very fine grids of sub wavelengths with one or more dielectric and / or metal systems on them. As described in US4484797, in a so-called zero-order diffraction filter (ZOD filter) or in a zero-order diffraction device (ZOD device), zero-order diffraction is used to produce very clearly marked color effects. The main features and advantages of ZOD devices are:

- iridescent optical effect which changes with the tilting angle θ and / or the rotation angle Φ,

- the optical effect is easily recognizable by untrained people,

- the optical effect can be read by the machine,

- strong color effect, even in diffused lighting conditions,

- cheap mass production technique available,

- very difficult to counterfeit, because the optical effect depends on the material properties, the deposition of the material with a high refractive index at 2 different levels in combination with an extremely fine mesh with a sub-wavelength. Copying only the mesh or material layers will not have the desired effect.

[0003] ZOD devices: As shown in Fig. 1.1, a typical ZOD structure consists of a material with a low refractive index (LRI) (white, n1 in the range 1.1-1.7) in which material segments (HRI layer) with a high refractive index (black, n2> n1 + 0.25) are regularly arranged on the periodic microstructure, e.g. parallel or crossed grid lines. More generally, either the waveguide layer is modulated by diffractive microstructures or the microstructure is placed on top or underneath this layer. The material above and below the waveguide can have a different refractive index and can even be air. For zero-order diffraction to occur, a number of parameters must be set, including microstructure period A, microstructure depth t, waveguide layer thickness c, fill factor or duty cycle ί.ί. = ρ / Λ and microstructure profile or shape (rectangular, sinusoidal, triangular or more complex). The period of microstructures is smaller than the wavelength of light for which the filter is intended. When illuminated with white light, this ZOD structure directly directly reflects a particular spectral area or color in a very effective way, which comes from the resonance effect in the HRI waveguide layer with a sub-length mesh structure. This layer acts as a leaky waveguide. Hence, ZOD filters are sometimes called resonance meshes. Part of the incident light at an angle θ is directly transmitted, and part bends and is captured in the waveguide layer. Some of the captured light bends again and interferes with the transmitted part. At a certain wavelength and angular orientation Φ of the periodic microstructure, resonance occurs, which leads to total destructive interference. No such light is transmitted. In contrast to devices with first or higher order diffraction in ZOD devices or ZOD filters, the light is reflected in the angle of view, which is equal to the angle of incidence θ. As long as the materials used show no absorption, the through spectra complement the reflection spectra. For more details on zero order diffraction filters, see MT Gale "Zero-Order Grating Microstructures" in RL van Renesse, Optical Document Security, 2nd Edition, pp. 267-287. The reflected and transmitted color depends on the orientation of the grid relative to the observer. As shown in Fig. 1.2, the color changes around a surface normal ("color hop"). Depending on the symmetry of the grid, different angles of rotation can be obtained. In linear grids, the spectra are identical if the ZOD grid is rotated by 180^about, but there is a strong color change after a turn of 90^about

Symmetrical color jumps at 60 can be easily created in 2-dimensional meshes^about and 90^about, but other values ​​are also possible. At specific wavelengths 100% reflection is theoretically possible. In practice, values ​​up to 80-90% are observed. [0004] Preparation of ZOD filters: It is known to produce ZOD filters as laminated films in "roller to roller" processes with thermally vaporized ZnS as a HRI layer deposited on film substrates that have undergone microstructure by shallow hot extrusion.

[0005] The use of ZOD filters: As described above, it is known to use manufactured films as security elements for protecting passports and documents, as well as in banknotes. ZOD filters are considered the natural successor to the now widely used holograms in security applications. The main reason is that ZOD filters are more difficult to counterfeit, but they use the same basic production technologies as for holograms. ZOD filters are also more visible to the human eye and can be easily checked with simple machines.

[0006] Color-shifted pigments: It is known that color-shifted pigments can be produced by multilayer deposition of alternating layers with high and low light reflection or a Fabry-Perot type interference layer system. The color shift comes from the interference effects of thin films in multi-layer systems.

[0007] US5135812 describes methods for producing such pigments based on vacuum deposition. An optically variable thin film coating is formed on one side of the flexible web of material. The coating is separated from the web to form optically variable thin film flakes that are placed in ink and ink carriers to obtain optically variable inks. This is considered to be disadvantageous in the sense that the pigments thus obtained do not exhibit a pronounced color effect upon rotation. Furthermore, at least five layers should be deposited, which is rather expensive and leads to thick pigments. Such pigments typically have a thickness of 1 μm.

[0008] WO98 / 530012A1 describes alternative methods for producing pigments with such multilayer systems based on the deposition of gas or liquid phase layers. The document describes multi-layer interference pigments that are obtained by curing and by hydrolysis of an aqueous solution of a titanium compound that can be thermally hydrolysed on a continuous web. The resulting layer is separated from the web and breaks to form flakes. The flakes thus obtained are coated alternately with a metal oxide hydrate with a high refractive index and a metal oxide hydrate with a low refractive index by hydrolysis of the corresponding water-soluble metal compounds after drying or without indirect drying in a wet process.

so obtained colored after

Again, it is considered unfavorable that pigments do not show a pronounced turnover effect. In addition, to achieve moderate color effects when tilted, at least five layers should be deposited, resulting in thick pigments.

[0009] Diffraction pigments: WO03 / 011980A1 describes flakes of diffraction pigments, including single-layer or multi-layer flakes. The petals comprise a layer that has a reflective surface and a diffractive structure formed on the reflective layer, wherein, in order to increase the intensity of the color contrast of the high-order diffracted light beam, the pitch and amplitude of the structure are selected to reduce the intensity of the zero-order diffracted light beam. The document mentions methods for producing such pigments by vacuum deposition. Since the color effect of such pigments is based on first or second order diffraction, only the typical rainbow color effect of holograms can be realized.

[0010] WO04 / 024836 describes pigments with first and higher order diffraction which, like a prism, split light into spectral components and which contain a magnetic layer to selectively set pigments. This document does not disclose or consider zero-order diffraction pigments.

[0011] WO03 / 102084 describes all dielectric optical diffraction pigments having first and higher order diffraction.

[0012] FR2888491 discloses photoprotective compositions containing diffraction pigments with a mesh period less than or equal to 270 nm.

[0013] Hence, there is a need for pigments exhibiting a rotating and / or tilting color effect and for suitable manufacturing processes. In addition, there is a need for physical-colored pigments that are thinner compared to prior art pigments. The latter makes it possible to use more printing and coating techniques for depositing lacquers containing pigments compared to lacquers containing pigments having a physical color according to the prior art.

[0014] Hence, the object of the present invention is to alleviate at least some of these drawbacks of the prior art. The object of the present invention is in particular to provide new pigments exhibiting a rotating and / or tilting color effect and to provide production methods for obtaining such pigments. It is a further object of the present invention to provide thinner pigments compared to prior art pigments.

[0015] These objects are achieved by means of a matrix comprising the pigment as defined in claim 1 and by the production method as defined in claim 5. Further aspects of the invention are disclosed in the description and independent claims, and preferred solutions are disclosed in the description and dependent claims.

[0016] The present invention will be described in more detail below. It is understood that the various solutions, preferences and scopes developed / disclosed in this description may be arbitrarily combined. In addition, depending on the specific solution, the selected terms, solutions or ranges may not apply.

[0017] Unless otherwise stated, the following terms will be used in this description:

Zero order diffraction pigments ("ZOD pigments") are pigments exhibiting a color effect (i.e. a color change) upon rotation and / or tilting, said color effect based on zero order diffraction.

[0018] A material is considered "susceptible to shallow extrusion" if it retains the structure of the extrusion tool on its surface after being subjected to the shallow extrusion step.

[0019] A "periodic microstructure" is a periodic structure that has a period of 100 nm to 600 nm.

[0020] The term "pigment" is known in the art. It relates to solid particles, each particle having a color and / or a colored effect. Said particles preferably have a maximum diameter of less than 100 microns (μη), especially less than 20 μη. Such particles are preferably in the form of flakes, which means that they are thin compared to their length and width.

[0021] The term "high refractive index layer" ("HRI layer") is known in the art. The HRI layer can be made e.g. from ZnS, TiO2, Cr2O3, AlN, Al2O3, HfO2, Nb2O5, Si3N4, Ta2O5, V2O5, WO3 or ZrO2 or similar inorganic materials or from high index polymers such as HRI721 and HRI751 (optimate) .

[0022] The present invention will be better understood with reference to the figures.

Figure 1.1 schematically shows a side view of a known ZOD device. Black means HRI material, while white means material with a low refractive index. A is the period, t means the depth of the microstructure, p means the width of the top line of the microstructure, Φ means the angle of rotation, θ means the angle of view, and ac means the thickness of the layer

HRI.

Fig. 1.2 is a schematic drawing of the device

ZOD in top view, describing the color hop on the rotation relative to the normal to the surface for the linear grid. Green light is reflected, for example, at a certain angle of view, if the grid lines are perpendicular to the direction of reflection (left part). Rotating the ZOD device by 90^about changes color from green to red. The grid lines are now collinear with the reflection direction (right part). Other grid symmetries give different angles of rotation.

Figure 1.3a shows alternative ZOD pigment mesh shapes: sinusoidal shape (above) and triangular shape (below). The connections of these two shapes and the connections with rectangular shapes also show zero order diffraction.

Fig. 1.3b shows the possible asymmetrical shapes of the ZOD pigment mesh: asymmetrical triangular shape (above) and asymmetrical rectangular shape (below).

Fig. 1.4 shows ZOD pigments (black mesh) embedded in paste, liquid, powder or polymer.

Fig. 1.5 shows ZOD (black mesh) pigments coated with a polymer, sugar, etc. to form a small powder particle mixed with other powder particles (light gray color).

Fig. 2.1 schematically shows the method of producing ZOD pigments described herein.

Fig. 2.2 schematically illustrates the alternative method of producing ZOD pigments described herein, it being possible to arrange the first 3 steps in different orders. The geometry of the knife separators during shallow extrusion can be different, e.g. rectangular. Instead of strengthening, the function of the separator will also provide a lowering, however, the height of the knife blade is greater than the total thickness of the dielectric layer system.

[0023] More generally, in a first aspect, the invention relates to a matrix comprising a pigment, in particular a zero-order pigment ("ZOD pigment"), wherein said pigment consists of solid particles, each of said particles having color and a color effect and each of the listed particles consists of an optical waveguide layer (HRI layer), where said layer is made of a material with a refractive index, which is greater than the average refractive index of the adjacent matrix material by at least 0.25, while said layer has a resonant mesh structure with a zero order diffraction with a period of 100-600 nm (but excluding a period less than or equal to 270 nm), mesh depth 30-300 nm, and said layer has a thickness of 50-500 nm.

[0024] In a preferred embodiment, the zero order diffraction grating structure has a period that is smaller than the wavelength of light that will be reflected at the zero order of reflection.

[0025] In a further preferred embodiment, the zero-order diffraction structure has a mesh depth of 150 nm or less.

[0026] In a further preferred embodiment, the particles of said pigment have a thickness of 100 nm to 2 microns and a lateral size of 1-100 microns. The shape of each particle can be any, with a rectangular, triangular, hexagonal or pentagonal shape being preferred. Although ZOD effects on a large surface area (> 2 mm²) are known (see e.g. document US04484797), the effect of the size of ZOD has not been studied to date. It has been surprisingly found that ZOD effects already appear if the grid extends laterally by at least 3 grid periods, because appropriate calculations and experiments are difficult. Thus, ZOD color effects are possible over a large surface area, but color pigments based on zero order diffraction with a lateral size of at least 1 micrometer can be produced. The reflection spectrum of such color pigments depends, in addition to the parameters mentioned above, on the size and shape of the pigment. Without being bound by theory, it is believed that, e.g., pigments with a grid period of 300-500 nm or less and a lateral size of 1-2 micrometers have wider reflection maxima than pigments with the same grid, but with a lateral size of 10 micrometers or more.

[0027] In one embodiment of the invention, the following parameters must be met. The grid period must be less than the wavelength of the bent light. Typical grid periods Λ are in the range 100-600 nm (excluding a period less than or equal to 270 nm), especially 300-500 nm. Typical mesh depths t are 30-300 nm, preferably 150 nm or less. For dielectric materials, the useful thickness c strongly depends on the mesh and material properties, but typical thicknesses are in the range of 30-250 nm. A suitable range for the fill factor ff = p / A is 0.3-0.8, preferably 0.4-0.7. The reflection profile is also affected by the grid profile. Possible grid profiles are rectangular, curved (e.g. sinusoidal), triangular or combinations of these three basic shapes. Preferable examples of mesh shapes are shown in Figs. 1.1 and 1.3.

[0028] In a preferred embodiment, the above ZOD pigments are composed of particles that have an anisotropic lateral shape, in particular an elongated lateral shape. Generally, ZOD devices change their color at different polar angles (theta), which gives ZOD pigments an opalescent appearance when applied to the surface, similar to the color shift effects observed with interference pigments with a well-defined color shift (document US5135812). In addition, ZOD devices with linear, one-dimensional grids show a different color change on a 90-degree turn^about around normal to the surface. In ZOD pigments that are deposited with any orientation, the color hop can no longer be observed by the human eye and only the dependence on the polar angle theta remains. However, if the pigment shape is strongly anisotropic, e.g. rectangular, and the deposition method promotes alignment in one direction, the embedded color pigments will still exhibit a color hopping effect, which means that the surface will change color as it rotates around normal to the surface.

Suitable pigments contain rod-shaped particles, in particular rectangular particles, with a width to length ratio in the range from 1: 2 to 1:10, in particular 1: 5 (e.g. 10 x 50 microns). This can be achieved by depositing e.g. long, narrow, rectangular pigments on the surface in a wet coating process with or without a polymeric binder. Suitable techniques include printing, in particular flexographic printing, jet printing or screen printing, pour coating or dip coating and spray coating. It has been found advantageously that if the dried layer has a thickness of less than 2 times the dimension of the side of the pigment, this results in a layer which is a maximum of several micrometers thick.

[0029] In a further preferred embodiment, one or more of the above ZOD pigments are embedded in an organic or inorganic droplet and fixed in the droplet. As shown in Fig. 1.5, these droplets are used as powder, paste or gel fillers, and are also incorporated into a liquid or plastic. For pharmaceutical or food applications, the ZOD pigments described herein could be sugar-coated or embedded in sugars.

[0030] In a further embodiment, the invention relates to ZOD pigments consisting of a layer made of a material with a refractive index that is higher than the refractive index of an adjacent material, while the layer has a diffraction grating structure with a period that is less than the wavelength of light that will be reflected at zero order reflection, preferably in the range 100-600 nm, but excluding a period less than or equal to 270 nm. Typical grid depths are from 30 to 300 nm, preferably 150 nm or less, with the layer acting as an optical waveguide and the thickness of the waveguide layer being between 50 and 500 nm.

[0031] In a further preferred embodiment, the invention relates to a matrix, in particular a coating, enamel or varnish, comprising the ZOD pigments described above. A suitable matrix has an average optical refractive index at least 0.25 lower than the refractive index of the HRI layer of the ZOD pigment (cf. Fig. 1.4).

[0032] In a second aspect, the invention relates to methods, in particular mass production methods, for producing the matrix described herein, wherein for the production of said particles said process comprises the steps of i) depositing and optionally subjecting microstructure to a first layer on a substrate which is soluble in the first solvent ii) producing a layer of said pigment in one or more deposition steps and optionally in one or more microstructuring steps where all the additional layers are insoluble in said first solvent, iii) dissolving said first layer and iv) optionally subjecting the resulting pigments to one or ZOD pigments coatings with high selection stages in terms of size and / or shape can be used, at least one microstructuring step takes place wi) or ii). In the context of the present invention, the microstructure steps are those process steps that give the microstructure of one of the layers produced, and a typical example are shallow extrusion steps. In the context of the present invention, mass-scale production processes are those processes that result in large amounts of ZOD pigments, and typical examples are roller-to-roller processes.

[0033] Similarly to the (discussed above) pigments with interference layer arrangement obtain by flaking the refractive index after microstructure and deposition on an elastic web. This can be done by vacuum deposition and shallow extrusion methods over a large surface area in "roller to roller" ("R2R") processes. Equipment used in roller-to-roller processes is known in the art and can also be used in the processes for producing ZOD pigments described herein. Thus, in a preferred embodiment, all the steps of the method of producing ZOD filters are adapted to suit such an R2R process. Such R2R processes are considered advantageous due to the relatively low production costs and high production speed.

[0034] In one embodiment, the first method of producing a ZOD pigment will comprise the following steps (compare Fig. 2.2):

1. Shallow hot or cold extrusion of a periodic microstructure ("mesh") in a deformable polymeric film or a deformable layer on a polymeric film ("carrier film"). Suitable polymeric film materials ("carrier films") are thermoplastic polymers. The carrier foil can be made e.g. from acrylonitrile-butadiene-styrene ABS, PC polycarbonate, PE polyethylene, PEI polyetherimide, PEK polyether ketone ketone, PEN polyethylene terephthalate, PET polyethylene terephthalate, PI polyimide, PMMA poly methacrylate, POM polyoxymethylene, polypropylene polypropylene, polypropylene polypropylene polypropylene Suitable materials for the polymeric, deformable layer are PVA polyvinyl alcohol, PVP polyvinylpyrrolidone and other suitable thermoplastic and film-coated polymers. The main mesh forming tool used for shallow extrusion can be metallic foil or, for example, Ni or steel foil or sheet or plate or roller, with or without a surface finish with Cr. It can also be made of MoC or WC, etc.

2. Deposition of at least one HRI layer, typically by thermal vapor deposition, plasma deposition, spraying or gravure printing. The thickness of each layer is less than 1 micrometer, typically 50-500 nm. Metallic layers can also be deposited by thermal vapor deposition, plasma deposition or spraying. The thickness of these layers is typically in the range of 5-150 nm.

3. Pigments can be mechanically peeled off by dissolving the shallow extrusion layer. Pigments can be dissolved in the liquid after deposition.

4. Pigments can be selected in size and shape to further narrow the size distribution. Several sizes can be produced at once with this technique.

5. ZOD or HRI pigments are then embedded in paste, powder or spread in liquid or paste to make them processable.

[0035] In a preferred embodiment, the main mesh device has small mesh patches with rims that are in the shape of ZOD pigments. The mesh edges are sufficiently either increased or lowered so that each mesh on the main unit is well separated. The intermediate area serves as a knife to separate pigments. Since the color effect of ZOD pigments may depend on the size, close control of the pigment shape is necessary for reproducible results and narrow color spectra. This size adjustment can be achieved using the main mesh device described here, because the shape of ZOD pigments is adjusted at the stage in which the mesh is produced.

[0036] In a preferred embodiment, a separating layer is deposited on the shallow extruded film or layer or on the main tool, preferably on the main tool. The release layer serves as a release layer for shallow embossing or the HRI layer. Possible examples of separation layers are Teflon, DLC, silanes, etc.

[0037] Suitable steps and materials are described in detail below, with reference to Fig. 2.1, schematically showing these steps.

[0038] Step a): A shallow extruded first layer is deposited on the flexible substrate, which may dissolve in the first solvent. This can be done, for example, by pour coating or "roller to roller" cascading, or by gravure printing. The deposition rate using these techniques can be up to several hundred meters per minute on flexible substrates in the form of a web with a web width of one meter. Suitable materials for flexible substrates are polymeric films, e.g. PET, PEN, PP, PMMA, PS, MOPP, PE, PC and PVC. The thickness of the flexible substrates may vary widely, but is preferably 5-500 μη, particularly preferably 12-250 μη. Such materials are commercially available or can be obtained by known methods. Suitable first layer materials are polymers that can be extruded shallow and are soluble in a solvent, e.g. in polyester or nitrocellulose derivatives. Examples of water soluble and shallow extrudable polymers are polyvinylpyridine PVP or polyvinyl alcohol PVA. The thickness d1 of the first layer is typically from 50 nm to 10 μη, preferably from 100 nm to 3 μη, and particularly preferably from 300 nm to 2000 nm.

Suitable solvents for this process step can be selected according to the choice of first layer material, environmentally friendly solvents being preferred and water, ethanol, isopropanol and mixtures thereof are typically used.

[0039] Step b1): Then, in the first layer, the batch microstructure is extruded shallowly and this can be done, for example, by means of shallow hot or cold extrusion, roller-to-roller type, where the roller surface has a periodic microstructure. This is typically done by placing a nickel adjusting pad around the shaft. The periodic microstructure is specified above. The edge knife structures defining the shape of the pigment described in the first method can be used.

[0040] Step c1): A second layer is then deposited on the first layer, which is insoluble in the first solvent and transparent at least in the visible spectrum, where "transparent" means that the average transmittance is> 75%, preferably> 90%. The thickness d2 of this second layer must be greater than the depth t of the grid. This ensures long-lasting flake-like substrates. The d2 value is preferably in the range from 100 nm to 2000 nm. Deposition can be carried out by vacuum methods such as e.g. vapor deposition, atomization or chemical vapor deposition (CVD). Suitable materials for this second layer are polymers such as PPX poly-p-xylene alkylene or inorganic metal oxides or metal halides e.g. MgF2, Al2O3 or SiO2. Other deposition options are wet deposition techniques such as pour coating or roller-to-roller cascade coating, or intaglio printing. Examples of materials that can be wet coated and which are insoluble in aqueous solutions are NC nitrocellulose or PS polystyrene. If the second layer is deposited by vacuum deposition, then the second surface of the second layer, which is not in contact with the first layer, may have a wavelength grid structure. This is shown in Fig. 2.1a). Depending on the material used and the thickness of the layer, the profile and depth of the mesh may or may not differ on both surfaces. If wet coating techniques are used, this second surface will in most cases not be correlated with the first surface (not shown in Fig. 2.1a).

[0041] Step d1): Then the second layer is separated from the flexible substrate by contacting the first layer with the first solvent. Such contact can result in partial or complete dissolution of the first layer. During the dissolution stage, the second layer breaks down into flakes.

[0042] In a preferred embodiment, step d1) can be carried out by a "roller to roller" method.

[0043] In a preferred embodiment, step d1) can be assisted by ultrasonic treatment (US).

[0044] Step b2): A second layer, which can be shallowly extruded and which is insoluble in the above-defined first solvent, is deposited on the above-mentioned first layer. The preferred d2 value is in the range from 100 to 2000 nm. The same deposition techniques can be used as for the first layer.

The second layer can be deposited from an aqueous dispersion containing microspheres. Preferred materials are e.g.

latex or PS microspheres.

[0045] Step c2): Next, shallow extrusion takes place in the second layer of the batch microstructure. This can be done as described in connection with b1, e.g. by shallow roller-to-roller hot stamping. If the second layer is made of polymeric microspheres, then the shallow hot extrusion, which is preferably carried out at a temperature above the glass transition temperature of the polymeric material, leads to melting or welding of the layer. Thus, after shallow hot extrusion, such a layer is insoluble in water although it has been deposited from an aqueous solution. Depending on the elastic and plastic properties of the material of the first and second layers, the batch microstructure is extruded shallowly in the upper surface of the second layer or in both surfaces.

[0046] Step d2): The second layer is separated from the flexible substrate and, as described in (d1) above, flake-shaped substrates are formed.

[0047] In a preferred embodiment of this third method, the deposition of said first and said second layer takes place simultaneously, e.g. by pour coating or cascading coating.

[0048] In a preferred embodiment of both methods, the size and shape of the flakes can be influenced by production (e.g., shallow extrusion) in the first, second or both layers of predetermined points or picking lines. These picking points may be, for example, parallel lines in the x and y direction. The thickness of the lines is preferably small, i.e. less than 3 pm, and especially less than

1.5 μη. The distance between the lines is preferably from 1 to 100 pm, and particularly preferably from 2 to 20 pm. Pigments have been found to favor linear pigments during the coating process. This linear alignment is necessary after

ZOD traded products Such points / lines have an asymmetrical shape in the pigment setting.

realizations of the color effect coated with such pigments can be produced before, after or simultaneously with the shallow extrusion of the ZOD microstructure. In a preferred embodiment, the breaking points are extruded shallowly together with the microcrescent structure. In this solution, the shallow extrusion tool contains the ZOD microstructure and the ZOD pigment structure. Therefore, no additional equipment is needed.

[0049] In many applications, pigments are deposited in a polymer matrix with a refractive index of 1.5 at 550 nm. For such applications, the waveguide layer must be made of a material with a refractive index of at least> 1.75. [0050] In a third aspect, the invention relates to the use of a matrix as described herein and paint, coating or ink comprising a matrix as described herein. Such a matrix can advantageously be used in areas such as identification, authentication and security, marking and marketing, as well as decoration, paints, cosmetic and pharmaceutical compositions.

[0051] Examples of applications are security features in banknotes, credit cards, passports and anti-counterfeiting and security marking. Other possible applications are car paints or coatings or packaging.

[0052] ZOD pigments, especially when embedded in paste, coatings and devices for liquids, powders or polymers, can be used in pharmaceutical compositions (e.g. tablets), food, colored coatings for cars, plastics, metals, paper, etc.

[0053] ZOD pigments coated with a polymer, sugar, etc. for making a small powder particle, mixed in other powder particles, are useful in pharmaceutical tablets, food or sunscreen, etc.

[0054] To further illustrate the invention, the following examples are given, these examples being given without intending to limit the scope of the invention.

Example 1: A water-soluble PVA layer (1000 nm thick) is applied to a PET film (23 micrometers thick). Then ZOD microstructure is deposited in this PVA layer with a R2R nickel pad at 100^aboutC. Next, a ZnS layer (190 nm thick) is deposited in the evaporation chamber. Pigments are obtained from the coated film by dissolving the PVA layer in water at room temperature, whereby the hard ZnS layer crumbles into small particles with a diameter of several micrometers. The size of these particles can be further reduced by US treatment, and the size distribution can be reduced by centrifugation or sieving. The pigments obtained show a pronounced color effect.

Example 2: The procedure of Example 1 is followed, except that the Ni washer is also used for predetermined breaking lines 10 * 50 microns thick. The pigments obtained have a pronounced color effect and no US treatment or steps to improve the size distribution are necessary.