EFFECT PIGMENT, MANUFACTURING METHOD, VALUABLE DOCUMENT AND PRINTING INK

Abstract

A platelet-shaped magnetic effect pigment for use in a printing ink, includes a layer construction with a magnetic layer and at least one optical functional layer. The magnetic layer is based on magnetic particles fixed within a solid matrix and having a largely uniform preferential magnetic direction deviating from the platelet plane.

Claims

1.-21. (canceled)

22. A platelet-shaped magnetic effect pigment for use in a printing ink, comprising a layer construction with a magnetic layer and at least one optical functional layer, wherein the magnetic layer is based on magnetic particles fixed within a solid matrix and having a largely uniform preferential magnetic direction deviating from the platelet plane.

23. The platelet-shaped magnetic effect pigment according to claim 22, wherein the largely uniform preferential magnetic direction of the magnetic particles fixed within the solid matrix is aligned substantially perpendicular to the platelet plane of the effect pigment.

24. The platelet-shaped magnetic effect pigment according to claim 22, wherein the magnetic particles have a size of less than 1000 nm.

25. The platelet-shaped magnetic effect pigment according to claim 22, wherein the magnetic particles have a uniaxial magnetic anisotropy, including a uniaxial magnetic crystal anisotropy or a uniaxial magnetic shape anisotropy.

26. The platelet-shaped magnetic effect pigment according to claim 25, wherein the material of the magnetic particles is selected from the group consisting of BaFe12O19, FePt, CoCrPt, CoPt, BiMn, α-Fe2O3 and Nd2Fe14B and the magnetic particles have a uniaxial magnetic crystal anisotropy, or wherein the material of the magnetic particles is selected from the group consisting of iron, cobalt, nickel and an alloy of one or several of the aforementioned elements and the magnetic particles have a uniaxial magnetic shape anisotropy.

27. The platelet-shaped magnetic effect pigment according to claim 22, wherein the magnetic particles are each based on needles obtainable by means of the glancing angle deposition (GLAD) technique or the oblique angle deposition (OAD) technique.

28. The platelet-shaped magnetic effect pigment according to claim 22, wherein the optical functional layer is a metallic layer, a color layer obtainable by printing technology, an interference layer construction based on a reflective layer, a dielectric layer and an absorbent layer, or a combination of two or several of the aforementioned elements, including a color layer obtainable by printing technology and arranged above a metallic layer.

29. The platelet-shaped magnetic effect pigment according to claim 22, wherein the effect pigment has a sandwich-like layer construction and the magnetic layer as a central layer is provided both on the front side and on the back side with respectively one optical functional layer, wherein the two optical functional layers independently of each other are selected from a reflective metallic layer, a color layer obtainable by printing technology, an interference layer construction based on a reflective layer, a dielectric layer and an absorbent layer, or a combination of two or more of the aforementioned elements, including a color layer obtainable by printing technology and arranged above a reflective metallic layer.

30. The platelet-shaped magnetic effect pigment according to claim 29, wherein the effect pigment has an asymmetric layer construction with two optical functional layers differing from each other, two optical functional layers differing from each other, which respectively are an interference layer construction based on a reflective layer, a dielectric layer and an absorbent layer and differ from each other with regard to the material or the layer thickness of the dielectric layer, and the effect pigment has the following layer sequence: absorbent layer-dielectric layer-reflective layer-magnetic layer-reflective layer-dielectric layer-absorbent layer.

31. The platelet-shaped magnetic effect pigment according to claim 29, wherein the effect pigment has a symmetric layer construction with two identical optical functional layers.

32. The platelet-shaped magnetic effect pigment according to claim 31, wherein the effect pigment has a symmetric layer construction, wherein the magnetic layer as a central layer is provided both on the front side and on the back side with respectively one optical functional layer, wherein the two optical functional layers respectively are an interference layer construction based on a reflective layer, a dielectric layer and an absorbent layer, and the effect pigment has the following layer sequence: absorbent layer-dielectric layer-reflective layer-magnetic layer-reflective layer-dielectric layer-absorbent layer.

33. The platelet-shaped magnetic effect pigment according to claim 28, wherein the optical functional layer is an interference layer construction based on a reflective layer, a dielectric layer and an absorbent layer and the effect pigment has the following layer sequence: absorbent layer-dielectric layer-reflective layer-dielectric layer-absorbent layer-magnetic layer.

34. The platelet-shaped magnetic effect pigment according to claim 30, wherein the effect pigment has an asymmetric layer construction, wherein the magnetic layer, on the front side, is provided with an interference layer construction based on a reflective layer, a dielectric layer and an absorbent layer and the magnetic layer, on the back side, is provided with a reflective metallic layer, so that the effect pigment has the following layer sequence: absorbent layer-dielectric layer-reflective layer-magnetic layer-reflective metallic layer.

35. A method for manufacturing a platelet-shaped magnetic effect pigment according to claim 22, comprising: a) providing a liquid medium with randomly oriented magnetic particles being mobile therein; b) aligning the magnetic particles by means of an external magnetic field; c) curing the liquid medium surrounding the magnetic particles into a solid matrix so that a magnetic layer is obtained which has magnetic particles fixed within the solid matrix and having a largely uniform preferential magnetic direction deviating from the plane of the magnetic layer; d) producing a layer construction having the magnetic layer and at least one optical functional layer; and e) crushing the layer construction obtained in step d) into individual platelet-shaped magnetic effect pigments.

36. A method for manufacturing a value document, comprising: printing the value document substrate with a first printing ink containing platelet-shaped magnetic effect pigments according to claim 22 in a first region; aligning the platelet-shaped magnetic effect pigments in the first printing ink printed in the first region by means of an external magnetic field; curing the first printing ink printed in the first region.

37. The method according to claim 36, comprising: printing the value document substrate with a first printing ink containing first platelet-shaped magnetic effect pigments in a first region; printing the value document substrate with a second printing ink containing second platelet-shaped magnetic effect pigments according to claim 22 in a second region adjacent to the first region, the second effect pigments being visually different from the first effect pigments; aligning the platelet-shaped magnetic effect pigments in the first and/or the second printing ink printed in the first region and in the second region, respectively, by means of an external magnetic field; curing the first and/or the second printing ink printed in the first region and in the second region, respectively.

38. The method according to claim 36, comprising: printing the value document substrate with a first printing ink containing platelet-shaped magnetic effect pigments in a first region; printing the value document substrate with a second printing ink containing conventional platelet-shaped magnetic effect pigments in a second region adjacent to the first region, the conventional platelet-shaped magnetic effect pigments having a preferential magnetic direction extending along the platelet plane; aligning the platelet-shaped magnetic effect pigments in the first and/or the second printing ink printed in the first region and in the second region, respectively, by means of an external magnetic field; curing the first and/or the second printing ink printed in the first region and in the second region, respectively, so that the two regions have a clearly distinguishable appearance due to the different alignment of the two types of effect pigments.

39. A value document obtainable by the method according to claim 36.

40. The value document according to claim 39, wherein the value document is a bank note or an identification document.

41. A printing ink comprising platelet-shaped magnetic effect pigments according to claim 22.

42. The printing ink according to claim 41, wherein the printing ink comprises a binding agent including a UV-curing binding agent, a binding agent curing by means of electron beams or a heat-curing binding agent.

Description

[0074] There are shown:

[0075] FIG. 1 a magnetic particle suitable for producing the platelet-shaped magnetic effect pigment of the invention;

[0076] FIG. 2 a liquid medium with randomly oriented magnetic particles being mobile therein, which is temporarily present during producing the magnetic layer of the effect pigment according to the invention;

[0077] FIG. 3 an example of a magnetic layer of an effect pigment according to the invention with magnetic particles aligned by means of an external magnetic field;

[0078] FIG. 4 an example of a layer construction (detail) starting from which platelet-shaped magnetic effect pigments according to the invention can be obtained by means of crushing;

[0079] FIG. 5 an example of a platelet-shaped magnetic effect pigment according to the invention; and

[0080] FIG. 6 a conventional platelet-shaped magnetic effect pigment according to the prior art, whose magnetic moment extends perpendicular to the normal vector of the thin films.

[0081] FIG. 6 shows a conventional platelet-shaped magnetic effect pigment 9 according to prior art whose magnetic moment extends perpendicular to the normal vector of the thin films. Such effect pigments 9 are commercially available under the trade name OVMI® from the company SICPA, have a platelet-shaped construction and are present in the form of a layer composite which includes two layers of optical effect layers, e.g. in each case a color-shifting layer system with absorber/dielectric/reflector construction, and a magnetic layer embedded in between. The optical effect layers each represent a color area. The side areas of the pigment 9 are more or less uncolored. The magnetization of the magnetic pigment 9 is referred to by the formula symbol “m”. If a magnetic field with a field strength having the formula symbol “H” is applied, the pigments 9 are aligned such that their magnetization is parallel to the field vector, if possible (see FIG. 6). As a consequence, the magnetic pigments 9 can rotate about axes parallel to their magnetization “m”. The use of such magnetic pigments 9, e.g. when printing a value document, thus leads to a substantially uniform alignment of the pigments 9 in one direction, while the alignment of the pigments 9 in another direction is substantially randomly distributed. Thus, when viewing a value document obtained in this way, it is not always a color area of the pigment 9 that points upwards in the direction of the viewer. This leads to a widening of the light reflection and to a decreased brilliance and sharpness of the optically variable effect.

[0082] FIG. 5 shows an example of a platelet-shaped magnetic effect pigment 8 according to the invention, whose magnetic moment “m” is aligned perpendicular to the platelet plane. If a magnetic field with a field strength having the formula symbol “H” is applied, the pigments 8 are aligned such that their magnetization is parallel to the field vector, if possible. Just as with the magnetic effect pigments 9 known in the prior art, a degree of freedom remains: the platelets can rotate about an axis parallel to their magnetic moment without changing their potential energy in the magnetic field. In contrast to the magnetic pigments 9 known in the prior art, however, the rotation in the case of the pigments 8 according to the invention has no significant influence on the reflecting properties of the pigments 8. Consequently, the reflecting properties can be better controlled. In the case of the magnetic pigments 9 known in the prior art, the viewer sees a plurality of small pigments, each with a substantially random brightness. The security elements obtained in this way consequently have a granular or a, so to speak, “noisy” optical texture. In comparison, homogeneously glossy areas can be produced by means of the pigments 8 according to the invention. In this way, so-called micro-mirror bulge effects can be achieved, for example.

[0083] The platelet-shaped magnetic effect pigment 8 according to the invention, shown in FIG. 5, has a sandwich-like layer construction with a specific magnetic layer as a central layer, which is provided with an optical functional layer both on the front side and on the back side. In the present example, the two optical functional layers are identical and are each formed by an interference layer construction with a reflective layer (e.g. an Al layer), a dielectric layer (e.g. an SiO.sub.2 layer) and an absorbent layer (e.g. a Cr layer). The effect pigment 8 thus has a symmetric layer construction with the layer sequence: absorbent layer-dielectric layer-reflective layer-magnetic layer-reflective layer-dielectric layer-absorbent layer.

[0084] With reference to FIGS. 1 to 4, the production of the platelet-shaped magnetic effect pigment 8 according to the invention is described below in accordance with FIG. 5. FIGS. 1 to 3 illustrate in particular the manufacture of the magnetic layer.

[0085] According to FIG. 1, magnetic particles 1 with a size of 100 nm are first provided, which in the example are based on α-Fe.sub.2O.sub.3 (hematite). The magnetic moment of the particle is indicated by an arrow in FIG. 1.

[0086] In a subsequent step, the magnetic particles 1 are introduced into a liquid UV-curing medium 2 as a surrounding medium (see FIG. 2). In this way, a layer based on a liquid medium with a large number of randomly aligned magnetic particles 1 is obtained first.

[0087] Subsequently, an external magnetic field is applied, the direction of the field lines corresponding to the desired magnetization direction. FIG. 3 shows the magnetic particles 1 aligned largely uniformly in the liquid medium 2 by means of the external magnetic field.

[0088] The liquid medium 2 is then cured by means of UV radiation, i.e. the magnetic particles 1 are fixed in their spatial orientation in this way.

[0089] The magnetic layer 3 obtained, consisting of a solid matrix with magnetic pigments embedded and spatially fixed therein, is provided, according to FIG. 4, with respectively one color-tilting interference layer construction both on the front side as well as on the back side by means of vapor deposition, which has a reflective layer 4 (or 4′), a dielectric layer 5 (or 5′) and an absorbent layer 6 (or 6′). FIG. 4 shows a section of the layer construction 7 obtained in this way, starting from which the platelet-shaped magnetic effect pigments 8 according to the invention can be obtained by means of crushing.

[0090] Further Notes:

[0091] Basically, the curing of the liquid medium 2 (see FIG. 3) does not necessarily have to be effected by means of UV curing, but, alternatively, curing by means of electron beams (EBC) would also be possible. Electron beam curing can be particularly interesting in the field of highly pigmented layers or when using the magnet-bearing layer as a laminating adhesive, because the UV transparency of the construction is not important here. The magnetic alignment has such a large force that the alignment can also take place in a matrix that is so highly viscous that the alignment of the individual magnetic particle no longer changes significantly without active external action. Therefore, the matrix could even be a 100% system of laminating adhesive.

[0092] When employing a cationic laminating adhesive system, the exposure could be effected first, followed by bringing together the substrates and immediately afterwards the alignment of the magnetic particles.

[0093] With radically curing systems, the alignment of the particles can be effected either shortly before curing or during curing, because here the cross-linking reaction normally is effected so quickly that later an alignment is no longer possible. Radically curing systems can be cross-linked e.g. by UV or EBC.

[0094] UV curing normally requires a suitable photoinitiator, which should advantageously be chosen such that the UV radiation that can sufficiently penetrate the layer can also excite the photoinitiator. There exists a large number of suitable photoinitiators. Typical type I initiators are e.g. the BAPO (bisacylphosphine oxide) types, e.g. Omnirad 819, the aminoketones (e.g. Omnirad 369, 379). Typical type II initiators are ITX and the benzophenones. These normally still require co-initiators, such as tertiary amines.

[0095] Radically curing systems continue to consist mostly of acrylic acid esters (on the one hand the prepolymers, on the other the reactive thinners). Manufacturers, such as the companies Allnex, Arkema, BASF, Miwon, offer numerous representatives of both product groups. To increase the reactivity, e.g. thiols can still be used. In addition, stabilizers may be required.

[0096] A suitable formulation is based on the following composition (percentages are to be understood by weight (wt %)):

TABLE-US-00001 CN111 (epoxidised soya bean oil acrylate) 35% DPGDA (reactive thinner) 15% Eb130 (reactive thinner, Allnex) 15% TMP(EO)9TA (reactive thinner) 13% Magnetic pigment 10% Dispersing additive  1% Ebecryl 116 (amine synergist)  6% Omnirad 2100 (photoinitiator, IGM)  2% Esacure KIP160 (photoinitiator, IGM)  3%

[0097] The above formulation could be applied e.g. to a UV lacquer with magnetic pigment. In particular for laminating adhesives, advantageously, softer raw materials with better adhesion to metals are expedient.

[0098] When employing acidic adhesion promoters for adhesion to metals, one can do without the amine synergist, circumstances permitting.