The invention relates to methods for producing coloured materials with the use of metal nanoparticles of gold, copper or silver, to said coloured materials, and to the uses of same in various applications.

A flake including a layer of a diamagnetic material; and at least one additional layer is disclosed. The flake, such as a plurality of flakes, can be dispersed in a liquid medium to form a composition. The composition can be applied to a surface of a substrate to form a security device. A method of making the security device is also disclosed.

The invention relates to coated effect pigments, wherein the coating comprises a binder which is suitable for powder paints. They comprise a crystalline and an amorphous fraction which is determined by C.sup.13 NMR MAS relaxation measurements, the relaxation of the .sup.13C cores being fitted as a biexponential relaxation according to the formula (II) and the degree of crystallinity c being in a range between 40 to 85%, and relaxation having a short average relaxation time T.sub.1.sup.s and a long average relaxation time T.sub.1.sup.l, and T.sub.1.sup.l being in a range of from 65 to 130 s. The effect pigments coated according to the invention have at least one endothermic peak with a maximum from a range of T.sub.max=100 to 150° C. and an enthalpy ΔH associated with said peak from a range of 15 J/g to 80 J/g in DSC at a feed speed of 5° C./min, the enthalpy being calculated relative to the amount of the binder. The binders are applied to the effect pigment by way of spontaneous precipitation.

The present invention relates to semitransparent pearlescent pigments, to processes for producing them, and to the use of such pearlescent pigments, where the pearlescent pigments comprise monolithically constructed substrate platelets composed of a metal oxide having an average thickness of 1 to 40 nm and a form factor, expressed by the ratio of the mean size to the average thickness, of at least 80, which are enveloped by at least one substantially transparent coating A composed of at least one low-index metal oxide and/or metal oxide hydrate, having a refractive index of less than 1.8, and at least one interference layer in the form of a coating B composed of at least one high-index metal oxide, having a refractive index of at least 1.8.

An article including a reflector having a first surface and a second surface opposite the first surface; a first selective light modulator layer external to the first surface of the reflector; a second selective light modulator layer external to the second surface of the reflector; a first absorber layer external to the first selective light modulator layer; and a second absorber layer external to the second selective light modulator layer; wherein each of the first and second selective light modulator layers include a host material is disclosed herein. Methods of making the article are also disclosed.

Optical effect pigment comprising a plurality of layers and a magnetic element, the layers can be arranged in two stacks of asymmetric layers or in a single stack of layers and comprise at least an absorber layer and at least a dielectric layer and can further comprise a reflector layer. The magnetic element presents a magnetisation which is out-of-plane, i.e. predominantly perpendicular to the plane of the pigment, which allows a deposition on the printing substrate whereby the face of the pigment lying up or down on the substrate can be predetermined. Such effect pigment has applications in many fields and specifically in security printing, where due to controlled deposition for instance a double-stack pigment will produce a different optical effect on each of its faces.

The present invention provides a magnetic multilayer pigment flake and a magnetic coating composition that are relatively safe for human health and the environment. The pigment flake includes one or more magnetic layers of a magnetic alloy and one or more dielectric layers of a dielectric material. The magnetic alloy is an iron-chromium alloy or an iron-chromium-aluminum alloy, having a substantially nickel-free composition. The coating composition includes a plurality of the pigment flakes disposed in a binder medium.

The present invention relates to an effect pigment having optically active layers consisting of a flake of a highly reflective material with directly adjacent on one side or on both sides a layer of a semiconducting material having a bandgap of 0.1 to 3.5 eV. The effect pigment may be further coated with a coating which is optically non-active in the visible wavelength region.

The present invention is directed to effect pigments with solvochromic properties. These effect pigments have a structure comprising a substrate in platelet form and a coating applied to the substrate, wherein the coating comprises: optionally a layer (1) comprising or consisting of at least one of tin oxide, tin hydroxide and/or tin oxide hydrate, a layer (2) comprising at least one of metal oxide, metal hydroxide and/or metal oxide hydrate, and a layer (3) comprising at least one of metal oxide, metal hydroxide and/or metal oxide hydrate, wherein the layers (2) and (3) comprise in their metal oxide, metal hydroxide and/or metal oxide hydrate in a majority two different metal ions from the group consisting of Ti, Fe, Sn or Zr and a further spacer layer (4) being located in between layers (2) and (3), wherein layer (4) has a porous structure comprising cavities and connectors. The solvochromic properties denote to the effect pigment having a first interference color under ambient atmosphere which changes reversibly to a second interference color, when the effect pigment comes into contact with a solvent.

An optical device includes a reflector layer having a first surface, a second surface opposite the first surface; a third surface, and a fourth surface opposite the third surface; and a first selective light modulator layer external to the first surface of the reflector layer; in which at least one of the third surface and the fourth surface includes an azimuthal modulator layer. A method of making an optical device is also disclosed.