Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2003-06-04
2004-08-17
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S403000, C106S404000, C106S417000
Reexamination Certificate
active
06776835
ABSTRACT:
The present invention relates to multilayer pigments based on platelet-shaped metal substrates coated with two or more metal oxide layers by a one-pot process in an exclusively aqueous medium. The invention further relates to the use of the multilayer pigments in paints, varnishes, printing inks, including security printing inks, plastics, ceramic materials and in cosmetic formulations.
Effect pigments are used in many sectors of industry, for example in automotive coatings, varnishes, inks, including printing inks, especially security printing inks, paints, plastics, glasses, ceramic products and cosmetic preparations.
Their optical effect is based on the directed reflection of light at predominantly sheetlike, mutually parallel-oriented, metallic or strongly refractive pigment particles. The latter are platelet-shaped and their optical properties are determined by reflection and interference.
Effect pigments providing an angle-dependent change of colour between a plurality of interference colours are by virtue of their colour play of particular interest for automotive coatings and for application in forge proof security documents. Such pigments based on multiply coated platelet-shaped metal substrates, especially aluminium platelets, are known.
U.S. Pat. No. 3,438,796 first described multilayer pigments based on a central highly reflective metal layer. Alternating SiO
2
and aluminium layers were deposited in a high vacuum deposition process, separated from the base film, ground and classified. The production process is such, however, that the chemical resistance of the pigment powders thus produced is very low, since the metal used is open to chemical attack at the edges. The coated aluminium pigments thus obtained are costly and the process is extremely unsuitable for practice on a large industrial scale.
U.S. Pat. No. 4,879,140 discloses a further process for producing aluminium pigments, which comprises vaporizing metal compounds in a microwave plasma in such a way that they form a film on predetermined surfaces in the chamber. This film can be mechanically removed, ground and suitably classified. This process is likewise subject to the cost and dimension disadvantages mentioned.
EP 0 668 329 A2 discloses polychromatic pigments comprising an aluminium substrate which is coated with silicon dioxide in a neutral, aqueous medium. The wet-chemical coating of the substrates is effected through hydrolytic decomposition of organic silicon compounds in an ammonia solution without a change in the pH. Thereafter, the CVD process can be used to apply further layers of, for example, metals to the SiO
2
coated aluminium substrates.
The patent applications EP 0 686 675 A1, EP 0 708 154 A2 and EP 0 741 170 A1 likewise each have aluminium pigments coated with metal oxide layers by means of the CVD process.
EP 0 826 745 A2 discloses aluminium-based metal pigments which are prepared by physical vapour deposition (PVD) and which are distinguished by the fact that all metal surfaces which are exposed following the comminution of a metal film produced by PVD, especially the fracture surfaces, are coated with a passivating protective layer.
The great disadvantage of all vapour deposition processes is the associated high cost.
EP 0 768 343 A2 claims lustre pigments produced by applying SiO
2
layers to metal substrates by hydrolytic decomposition of organic silicon compounds. The decomposition is supported by the presence of an organic solvent in which the organometallic starting components have a certain solubility. Owing to the use of organometallic components and of organic solvents, this process is not very economical and also necessitates high safety precautions.
U.S. Pat. No. 2,885,366 discloses the coating of aluminium platelets with silicon dioxide from water-glass solutions. Here, however, the oxide layer is applied only for the purpose of passivating the aluminium surface.
It is an object of the present invention to provide a multilayer pigment which is based on metal platelets and for which the base substrate is coated neither by CVD nor by PVD processes, but exclusively wet-chemically and without the use of flammable compounds. At the same time, the pigment shall be notable for its optical properties and/or the strong angle dependence of the interference colours and its advantageous application properties.
Surprisingly, there has now been found a multilayer pigment based on multiply coated platelet-shaped metal substrates where the substrate is coated with dielectrics in an aqueous medium by a one-pot process. The wet-chemically coated metal substrate is especially notable for its colour strength. Metal platelets such as aluminium, which react in water at various pH values with the evolution of hydrogen, can be converted into chemically inert multilayer pigments through suitable choice of the coating parameters.
The present invention accordingly provides multilayer pigments based on platelet-shaped metal pigments and produced by the exclusive wet-chemical coating of the metal pigments in a one-pot process wherein the metal pigments are initially suspended in water and coated with an amorphous glassy layer at pH 6-11 and then with one or more metal oxides or metal oxide mixtures at a pH<4.
The invention further provides for the use of the thus produced multilayer pigments in paints, varnishes, printing inks, including security printing inks, plastics, ceramic materials and cosmetic formulations. The invention likewise provides for the use of pigments of the invention as dopants in the laser marking of plastics.
Suitable base substrates for the multilayer pigments of the invention are platelets composed of metal or metal alloys, for example, iron, aluminium, tin, zinc, silver, copper, titanium, lanthanides, cobalt, nickel, and all commercially available metal powders known to the person skilled in the art which are substantially stable in water. It is further possible to use mixtures of the metals and metal alloys mentioned as base substrates. Preferred base substrates are aluminium platelets and also aluminium alloys.
The size of the base substrates is not critical per se and can be adapted to the particular intended application. In general, the platelet-shaped metal substrates will have a thickness between 0.1 and 5 &mgr;m, especially between 0.2 and 4.5 &mgr;m. The extent in the other two dimensions is customarily between 1 and 250 &mgr;m, preferably between 2 and 200 &mgr;m, especially between 5 and 50 &mgr;m.
The thickness of the individual metal oxide layers on the metal substrate is essential for the optical properties of the multilayer pigment. For a pigment to have intensive interference colours, the individual layers have to be accurately adjusted with regard to one another in thickness.
The colour variation with increasing film thickness is a consequence of the intensification or attenuation of certain wavelengths of the light through interference. When two or more layers in a multilayer pigment possess the same optical thickness, the colour of the reflected light intensifies with an increasing number of layers. In addition, suitable choice of the layer thicknesses is a way of obtaining particularly strong variation in colour as a function of the viewing angle. A pronounced colour flop develops. The thickness of the individual metal oxide layers depends on the field of application and is generally 10 to 1000 nm, preferably 15 to 800 nm, especially 20-600 nm, regardless of their refractive index.
The multilayer pigments of the invention generally comprise at least two metal oxide layers. Preferably, a layer of low refractive index is present in combination with a coloured or colourless metal oxide layer of high refractive index. The pigments may comprise up to 12 layers, with the proviso that the thickness of all the layers on the metal substrate should not exceed 3 &mgr;m. Preferably, the multilayer pigments of the invention contain not more than 7, especially not more than 5, metal oxide layers. Particular preference is given to pigments coated on the metal substrate
Andes Stephanie
Dietz Johann
George Sabine
Herbski Margarete
Kniess Helge
Koslow C. Melissa
Manlove Shalie
Merck Patent Gesellschaft mit beschränkter Haftung
Millen White Zelano & Branigan P.C.
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