Method for producing pigments with a predetermined inner and / or outer contour using a crack-forming layer

Description

[0001] The invention relates to a process for producing pigments.

[0002] Data storage media, such as valuables or identification documents, as well as other valuable items such as branded goods, are often provided with effect pigments for security purposes. These pigments allow verification of the data storage medium's authenticity and also serve as protection against unauthorized reproduction. Effect pigments can, for example, be integrated into the data storage medium's substrate or applied to the data storage medium's substrate. Pigments with a predefined outer contour are a common form of such effect pigments.

[0003] Effect pigments can be produced, among other things, by coating a substrate, then removing the coating from the substrate and grinding it into small fragments. These fragments can be dispersed as pigments in a binder and then printed. Due to the manufacturing process, neither the shape nor the size of the pigments are precisely defined.

[0004] However, various methods are also known for creating pigments with a predetermined outer contour.

[0005] For example, WO 2005 / 017048 A2 proposes embossing the carrier material according to the desired pigment contour and applying the coating to the embossed carrier material. The coating is removed from the carrier layer and broken down into pigments by grinding and sieving, which can have a diameter of 5 to 100 µm. In EP 2 062 947 A1, which proposes an improved embossed structure to define the pigment contour, the removed layer is also broken down into pigments.

[0006] In alternative solutions, the pigment layers are structured into pigments by lasering or etching.

[0007] The fragments of pigments with a uniform outer contour that still occur must still be sieved out - for example based on their size.

[0008] The invention is based on the object of providing a flexible but cost-effective production process for pigments, which in particular allows the production of pigments with a narrow pigment size distribution.

[0009] This object is achieved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

[0010] A fundamental concept of the present invention is to use a crack-forming layer in the pigment production process. In particular, crack formation can be used to structure the individual pigments.

[0011] In the process for producing pigments, a first layer is created on a substrate, the first layer is structured, and the pigments are removed from the substrate. In this case, the first layer is a crack-forming layer, so the first layer is structured by the formation of cracks. Before the pigments are removed from the substrate, a pigment layer is applied to the first layer structured by the cracks.

[0012] This avoids structuring of the pigments in a later process step, for example, by cracking the pigment layer during or after the pigments are removed from the substrate. The size distribution of the produced pigments is determined by the crack formation process.

[0013] The pigments comprise at least the pigment layer and optionally also the first layer. The pigment layer itself can comprise several sublayers, such as one or more of the following sublayers: reflector layer, in particular metallic or high-refractive index, dielectric, absorber layer, in particular metallic or high-refractive index, liquid crystal layer, magnetic layer, and / or embossing lacquer layer.

[0014] The pigment layer is already structured into a multitude of pigment sections by applying it to the structured first layer (and into the cracks).

[0015] The first layer is preferably adapted to the pigment layer. The thickness of the crack-forming layer is, in particular, greater than the thickness of the pigment layer. The width of the cracks to be formed is adapted to accommodate the pigment layer within the cracks.

[0016] The applied pigment layer lies particularly with pigment sections on pigment islands of the first layer and with pigment residues - in the cracks of the first layer - on the substrate.

[0017] The first layer forms the cracks independently, particularly during solidification, such as drying or curing, of the first layer. The cracks therefore occur independently of the substrate. Properties of the (carrier) substrate, such as its flexibility or similar, do not cause the cracks to form. The volume of the first layer decreases during solidification, causing the cracks to form. This volume change is also referred to as shrinkage. The first layer can be a layer with high shrinkage upon drying. Alternatively, solidification (and thus shrinkage) is triggered by curing, particularly radiation curing, such as UV curing.

[0018] Another advantage is that the crack formation already supports the dissolution step. During crack formation, no ideally linear or smooth edges are created in the first layer. The crack formation creates pigment islands in the first layer, which have at least one undercut and / or an enlarged sidewall area. The pigment islands have torn sidewall areas, which therefore have a correspondingly larger area than a linear sidewall. The pigment islands also have undercuts - particularly in the area of the sidewall areas. This means that they are no longer fully bonded to the substrate, but have already been partially detached from the substrate. The mechanical force theoretically required for the dissolution step is thus slightly reduced. More important is the advantage that - due to the larger surface area and the undercut - a solvent can dissolve the soluble layer more effectively.In particular, the solvent reaches the soluble partial layer of the substrate despite pigment residues in the cracks.

[0019] Of the total area of the first layer, the cracks have a surface area of at least 2%, preferably at least 3% and more preferably at least 5%; in particular, the surface area of the cracks is less than 15%, preferably less than 12%, more preferably less than 10%. The surface area of the cracks can preferably be 2-15%, preferably 3-12% and more preferably 5-10%. The surface area of the pigment islands is correspondingly less than 98%, preferably less than 97% and more preferably less than 95%, in particular more than 85%, preferably more than 88% and more preferably more than 90%. As a rule, the cracks are more than 100 nm wide, preferably more than 200 nm wide, more preferably more than 500 nm wide.

[0020] The crack-forming layer can preferably be applied by printing (either in specific areas or over the entire surface). Other coating methods, such as doctoring, spraying, etc., can be used alternatively.

[0021] Preferably, the first layer and / or a process parameter in the context of crack formation is selected such that pigments of a predetermined size are produced, in particular with sizes within a target size distribution.

[0022] To support the formation of specific pigment shapes, the first layer can be applied in regions, particularly in stripes, rectangular or square, and / or nuclei for crack formation can be provided. Nuclei for crack formation can be created, particularly in the form of partial depressions. The nuclei are therefore smaller (in depth and length) than the resulting cracks. The nuclei can be present in the substrate or in the first layer. They are formed and arranged in such a way that the shape of the pigments is determined by the nuclei. Alternatively or additionally, the first layer is applied in several regions, such as stripes, rectangles or squares, so that a large number of pigments are created in each region. The shape of the application region determines the shape of the pigments (through the crack formation starting at the edge of the region), e.g.striped or rectangular (or square) area => rectangular (or square) pigments.

[0023] In initial embodiments, a soluble layer is dissolved for the step of dissolving the pigments from the substrate. The pigment layer (and the first layer) is already structured into pigments (or into pigment sections of the pigment layer and pigment islands of the first layer), so that the pigments are detached from the substrate without mechanical stress—i.e., without the formation of further fragments. A partial layer of the substrate on which the first layer lies can be dissolved. A soluble lacquer layer can advantageously be used as the partial layer. Alternatively, the first layer itself is dissolved.

[0024] The soluble layer is particularly preferably water-soluble. Other solvents, such as organic solvents, could be used alternatively. However, organic solvents are more expensive and often incompatible with all (conceivable or used) pigment layers (or sublayers).

[0025] In second embodiments for the dissolution step, an intermediate substrate is used to lift the pigments from the substrate and thus dissolve them. The intermediate substrate stabilizes the pigments against mechanical stress during dissolution. The pigment layer is brought into contact with an intermediate substrate so that the already structured pigment layer adheres in sections to the intermediate substrate. A suitable adhesive layer can be applied to a carrier layer of the intermediate substrate or to the pigment layer. The adhesive layer, in turn, should be soluble, in particular water-soluble. By separating the intermediate substrate and the substrate, the pigments are dissolved from the substrate.

[0026] An intermediate product for the production of pigments, in particular according to one of the processes described above, comprises a substrate, a first layer, and a pigment layer. The first layer, which has formed cracks as a crack-forming layer, is arranged on the substrate. The pigment layer is arranged on the first layer, which is structured by the cracks, and is thereby structured into a plurality of pigments that can be detached from the substrate.

[0027] The present process allows pigments with sizes from a given size distribution to be produced without further intermediate steps.

[0028] The intermediate substrate comprises at least one intermediate substrate layer. Typically, the intermediate substrate comprises the intermediate substrate layer and an adhesive layer. The adhesive layer of the intermediate substrate is designed such that the pigment layer adheres more strongly to the adhesive layer of the intermediate substrate than to the substrate. The adhesive layer is a soluble, particularly water-soluble, layer.

[0029] The pigments resulting from the pigment layer can be called flat pigments or platelet-shaped pigments.

[0030] Of course, the pigments are intended for printing. The pigments—in particular detached from the substrate and / or the intermediate substrate—are processed into a printing ink. A printing ink containing the pigments is printed. Printing is preferably carried out by screen printing, in particular by zonal doctor blade coating. Alternatively, the pigment can be printed by gravure printing and optionally by flexographic printing. The printing ink comprises the pigments and at least one solvent and optionally a binder. In particular, if the pigments produced have a pigment size of less than 15 µm, preferably less than 10 µm, the printing ink can be used in an offset printing process.

[0031] The (effect) pigment can be used to protect data storage devices, such as valuables or identification documents, but also other valuable items, such as branded goods. The (effect) pigments allow for verification of authenticity and simultaneously serve as protection against unauthorized reproduction. The (effect) pigments can, for example, be integrated into a substrate or applied, in particular printed, to a substrate.

[0032] The pigment has a size or lateral dimension of less than 200 µm, in particular less than 60 µm, particularly preferably less than 30 µm. Pigments with sizes between 1 µm and 200 µm are conceivable, preferably between 10 µm and 100 µm, particularly preferably between 20 µm and 60 µm. The thickness of the pigments is in the range from 30 nm to 4 µm (or up to 2 µm), preferably between 100 nm and 1 µm.

[0033] A metal layer, for example made of aluminum, chromium, copper, iron, nickel, cobalt, silver, gold, or alloys of the aforementioned metals, can be used as an optical effect layer of the pigment. The thickness of the metal layer is between 2 nm and 200 nm, preferably between 10 nm and 50 nm, particularly preferably between 15 nm and 30 nm.

[0034] The optical effect layer can be formed as a reflective or semitransparent layer; instead of a metal layer, a high-refractive-index layer (HRI layer) can be provided. The pigment preferably comprises a three-layer structure, which can be designed as a color-shifting and / or color-filtering structure. The pigment can be formed by the three-layer structure or comprise the three-layer structure as a supporting sublayer or as an optically active sublayer. The three-layer structures preferably consist of a semitransparent metal layer, a dielectric, and a reflective (or semitransparent) metal layer. Examples of dielectrics used include SiO2, ZnS, MgF2, or TiO2.

[0035] Particularly preferably, at least the optically active partial layers of the pigment are provided symmetrically to the pigment plane. Thus, the orientation of the pigment after the printing process is irrelevant. For example, the pigment can be formed by two identical semitransparent partial layers with a supporting spacer layer. Such pigments preferably have a metallic luster with a specific color spectrum when viewed from above, while displaying a spectrum complementary to this color spectrum when viewed through, particularly preferably gold when viewed from above and blue when viewed through. In another variant, a dielectric and a semitransparent layer are provided symmetrically around a shared reflective layer (above and below).

[0036] In order to allow the orientation of the pigments to be influenced by a magnetic field, a magnetic layer can be used, which can be formed, for example, from the metals iron, nickel, cobalt or iron oxide, in particular magnetite (Fe3O4), or from alloys containing these metals. Such alloys preferably contain other elements such as Si, Nd, B, Gd, Sm, Sr, Ba or Mn. Preferably, they are nickel-free magnetic alloys made of Fe, Cr and / or Al, as used, for example, in EP2402401A1. The magnetic layer is advantageously located inside the pigments. In a particularly advantageous variant, the magnetic partial layer is provided between two reflective partial layers, for example made of aluminum.Particularly preferably, the pigments have a central magnetic layer provided on both sides (symmetrically) with a three-layer structure, i.e., in particular, on both sides, from the inside out, comprising a reflective layer (preferably a reflective metallic layer), a spacer layer (preferably a dielectric layer), and an absorber layer (preferably a semitransparent metallic layer). The corresponding (double-sided) interference layer structure can alternatively be realized using only dielectric layers (such as TiO2 or SiO2).

[0037] Further embodiments and advantages of the invention are explained below with reference to the figures, in which a true-to-scale and true-to-proportion reproduction has been omitted in order to increase clarity.

[0038] They show: Fig. 1a - dLayer structure at different times during the production of pigments using a crack-inducing layer; Fig. 2a, respectively, different examples of cracks in a crack-inducing layer in plan view; Fig. 3 temporal progression of crack formation in a design with multiple stripes of the crack-inducing layer; Figs. 4 and 5 release of the pigments from the substrate with the aid of an intermediate substrate; and Fig. 6 use of nuclei for crack formation in a cross-section of the layer structure and for three different pigment forms in plan view.

[0039] The production of pigments with a narrow size distribution using crack templates is described below using various examples.

[0040] A crack template refers to a layer on a carrier film (e.g., PET) that exhibits a network of continuous cracks, so that the entire layer ultimately consists of individual islands. This crack template is metallized, with the metallization tearing away at the island edges due to the height difference, and the island size thus determines the pigment size. The pigment layer is structured by the crack formation.

[0041] Fig. 1a shows a carrier film 2, which comprises a carrier layer 21 and an optional release layer 22. On the carrier film 2 - as in Fig. 1b shown - a continuous crack-forming layer 3 is applied, in which cracks 32 form, so that pigment islands 31 are created.

[0042] A pigment layer 4 is - as in Fig. 1cshown—applied to the crack-forming layer 3. The pigment layer 4 comprises pigment sections 41 located on the pigment islands 31. Furthermore, the pigment layer comprises pigment residues 42—arranged in the cracks 32—that lie on the carrier film or its release layer 22. The pigment layer 4 can be or comprise a metallization. The pigment layer can comprise several sublayers, in particular, have symmetrical multilayer structures.

[0043] For example, the pigment may comprise as sublayers: one or more reflector sublayers, one or more dielectric sublayers and one or more absorber sublayers, for example in a structure with absorber-dielectric-reflector, dielectric-absorber-dielectric, dielectric-reflector-dielectric or absorber-dielectric-absorber.

[0044] In order to preserve the pigments, the crack template is either detachable from the film (the crack template detaches from the film but remains connected to the other pigment layers) or the crack template is itself water-soluble or soluble in another solvent, so that it dissolves - in this case after the separation of the substrates - and releases the pigment.

[0045] Two types of pigments can therefore be produced: Pigments consisting of a first pigment partial layer, such as a vapor-deposited metallization, and the crack-inducing layer; or pigments consisting only of the pigment layer, such as a vapor-deposited metal layer (without the crack-inducing layer).

[0046] Fig. 1dshows a plurality of pigments 10, 11. The pigments 10 comprise only the pigment layer 4, and therefore possibly also its sublayers. The pigments 11, on the other hand, comprise both the pigment layer 4, or its sublayers, and the crack-forming layer 3. The shape and size of the pigments 10, 11 correspond to the shape and size of the pigment islands 31 (or the pigment sections 41).

[0047] The crack-forming layer can contribute to the stability of the pigments or the crack-forming material can have functional properties (e.g. fluorescent dyes or magnetic particles).

[0048] There are various ways to produce the crack template.

[0049] In a first embodiment, a dispersion applied to the entire surface of a carrier film with a sufficiently high minimum film formation temperature (MFT > 50°C) forms cracks upon physical drying. The dispersion consists of particles of organic polymers (e.g., based on polyacrylates, polystyrenes, etc.) or inorganic (e.g., SiO2, TiO2, Al2O3, etc.) nature, or mixtures thereof, dispersed in water. To ensure the solubility of the crack template in water, water-soluble compounds (e.g., sugar molecules, starch, or polyethylene glycols, etc.) can be added.

[0050] In another embodiment, a crack template is produced using the sol-gel technique. This involves using alkoxides of metals and non-metals, which form sol particles through hydrolysis and condensation reactions. Ultimately, they form a gel, which, in thin layers, is prone to cracking upon drying.

[0051] In another embodiment, a brittle UV varnish with high shrinkage is applied over the entire surface of a carrier film. During radiation curing, cracks form throughout due to shrinkage.

[0052] This crack template can, for example, be metallized to retain the pigments. Ideally, the UV varnish is designed to dissolve spontaneously in water (water-soluble UV varnishes). For water-insoluble UV varnishes, a water-soluble intermediate layer is conceivable to dissolve the pigments from the starting film in water. A corresponding release layer 22 is then provided on the carrier film 2. The release layer 22 is soluble in a solvent, preferably in water as the solvent, alternatively in an organic solvent.

[0053] A backing film with adhesive can also release the pigments from the carrier film, whereby the adhesive is subsequently dissolved and thus releases the pigments. This variant will be discussed later with reference to Fig. 4 and 5 described in more detail.

[0054] Controlling crack formation is crucial for the size distribution and shape of the pigments and depends on the chosen manufacturing method for the crack template. For physically drying dispersions, the island size (=pigment size) is adjusted using known parameters such as minimum film formation temperature, layer thickness, particle size, additives, or drying conditions.

[0055] Fig. 2a shows an image of a crack template, with the cracks forming islands with a size range. The island size and thus the pigment size is < 100 µm, particularly in the range of 10 to 30 µm (areas from 100 to 900 µm 2 < ).

[0056] Furthermore, it is known that the first generation of cracks propagates vertically from the edge of the printed image inward, after which the second generation of cracks develops parallel to the edge of the printed image and thus between the first generation. The resulting ladder-like crack template leads to rectangular islands or pigments. Fig. 2b shows the image of a corresponding crack template, with slightly larger islands.

[0057] The pigment size here is also below 100 µm, but rather in the range of 20 to 60 µm (areas of 400 to 3600 µm2).

[0058] However, this effect diminishes with increasing distance from the edge of the print image. If only rectangular islands are desired, the film is printed in stripes.

[0059] Fig. 3shows three stripes of a crack-forming layer 3 on the carrier 2. For illustration, the phases of drying and crack formation are shown from top to bottom in the figure. The time arrow t symbolizes that a temporal progression from top to bottom is shown here. The wet crack-forming layer 3 is still free of cracks. The first cracks 32a form during drying from the edge of the stripes inwards. The first-generation cracks 32b then extend from edge to edge across the stripes. Cracks 32c then form parallel to the edge. The dry crack-forming layer comprises the almost rectangular pigment islands 31 and the cracks 32 arranged between them.

[0060] Hexagonal islands and thus pigments are also possible in other ways.

[0061] For crack templates based on UV varnishes, a predetermined breaking point can be introduced during radiation curing by means of suitable structures on an embossing tool. The embossing tool, for example, presses two notches into or through the UV varnish (see nanoimprinting), whereby, after radiation curing, a crack is initiated at the shortest distance between the two notches due to shrinkage. By arranging the notches in a specific way, the cracks can be precisely controlled in lines and grids.

[0062] Fig. 6 The top row shows a notch 62 in the crack-forming layer arranged on the carrier substrate 2. The notch 62 serves only as a nucleus for crack formation and can therefore be smaller, in particular narrower and shorter, than the subsequent crack 32. Likewise, it is sufficient if the notch 62 only partially extends into the crack-forming layer 3. The pigment layer is applied to the crack-forming layer, creating the pigment sections 41.

[0063] The variety of the arrangement of the notches relative to each other and the type of notches themselves result in a variety of shapes for the islands and therefore pigments.

[0064] In the second row of Fig. 6 Triangular edge notches 62a are used to create linear cracks 32, resulting in rectangular pigments 10a. The third row shows that square pigments 10b can be produced by arranging star-shaped notches 62b accordingly.

[0065] Of course, hexagonal pigments 10c can also be easily produced using this method by generating notches 62c similar to a trident star and cracks 32 at 120° angles to each other.

[0066] The pigment layer or one or more of the sublayers are typically deposited by vapor deposition, e.g., using PVD coating. This involves applying the previously described sublayers or sublayers of the sublayers. Alternatively, a sublayer, particularly a metallic layer, could also be applied using gravure or flexographic printing processes.

[0067] The substrate can also be reused for this process, optionally after the remaining sections have been removed. On the substrate with the relief structure, the first film, the crack-forming layer and pigment layer can be applied multiple times in succession. This saves material costs and process steps. List of reference symbols

[0068] 10, 10a, 10b, 10c, 11Pigment 2Starting substrate 21Support layer of the starting substrate 22Release layer of the starting substrate 3Crack-forming layer 31Pigment island 32, 32a, 32b, 32cCracks 4Pigment layer 41Pigment sections 42Remaining sections 5Intermediate substrate 51Carrier layer of the intermediate substrate 52Adhesive layer of the intermediate substrate 54Adhesive layer with pigment sections 55Free adhesive layer sections 62, 62a, 62b, 62c Germ cells for crack formation

Claims

1. Process for producing pigments (1), comprising the following steps: - creating a first layer (3) on a substrate (2); - structuring the first layer (3); and - detaching the pigments (10, 11) from the substrate (2) ; characterized in that the first layer (3) is a crack-forming layer, so the first layer is structured by the formation of cracks (32); and before the pigments (10, 11) are detached, a pigment layer (4) is applied to the first layer (3) structured by the cracks (32).

2. Process according to Claim 1, characterized in that the pigments (10, 11) comprise: - the pigment layer (4) or - the pigment layer (4) and the first layer (3).

3. Process according to Claim 1 or 2, characterized in that the pigment layer (4) is structured into a multiplicity of pigment portions (41) by the application to the structured first layer (3).

4. Process according to one of Claims 1 to 3, characterized in that the applied pigment layer (4) lies on the substrate with pigment portions (41) on pigment islands (31) of the first layer (3) and with pigment residues (42) in the cracks (32).

5. Process according to one of Claims 1 to 4, characterized in that the first layer (3) forms the cracks (32) itself, in particular in the course of a solidification, such as drying or hardening, of the first layer (3).

6. Process according to one of Claims 1 to 5, characterized in that the first layer (3) and / or a process parameter is adapted in the course of the crack formation in order to create pigments (10, 11) of a predefined size, in particular with sizes within a target size distribution.

7. Process according to one of Claims 1 to 6, characterized in that nucleation sites (62) for the crack formation in the form of partial depressions are created, in particular in the substrate (2) or the first layer (3), so the shape of the pigments is determined by the nucleation sites (62).

8. Process according to one of Claims 1 to 7, characterized in that the first layer (3) is applied in multiple strips.

9. Process according to one of Claims 1 to 8, characterized in that the pigment layer (4) comprises multiple sub-layers.

10. Process according to one of Claims 1 to 9, characterized in that a soluble layer (22, 3) is dissolved during the step of detaching the pigments (10, 11) from the substrate (2).

11. Process according to Claim 10, characterized in that the soluble layer is a sub-layer (22) of the substrate (2) or is the first layer (3).

12. Process according to Claim 10 or 11, characterized in that the soluble layer (22, 3) is water-soluble.

13. Process according to one of Claims 1 to 9, characterized in that the process comprises the following further steps: bringing the pigment layer (4) into contact with an intermediate substrate (5), with some portions of the structured pigment layer (4) adhering to the intermediate substrate (31); and separating the intermediate substrate (5) and the substrate (2), the pigments (10, 11) being detached by the step of separation from the substrate (2).

14. Process according to Claim 13, characterized in that at least the pigment layer (4) adheres to a soluble layer (52) of the intermediate substrate (5), the soluble layer being located in particular on a film layer (51) of the intermediate substrate (5).

15. Intermediate product for producing pigments (10, 11), in particular according to one of Claims 1 to 14, with a substrate (2) on which the following are arranged: - a first layer (3), the first layer (3) as a crack-forming layer having formed cracks (32); and - a pigment layer (4), which is located on the first layer (3) structured by the cracks (32) and as a result is structured into a multiplicity of pigments (10, 11), which can be detached from the substrate and are formed at least by the pigment layer (4) and optionally by the first layer (3).