Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
1999-04-19
2001-08-28
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S417000, C106S418000
Reexamination Certificate
active
06280520
ABSTRACT:
The invention relates to a multilayer interference pigment consisting of alternating layers of a material of low refractive index and a material of high refractive index or of a metal on an absorbing platelet-shaped substrate which is opaque or semi-opaque.
BACKGROUND OF THE INVENTION
Multilayer pigments with alternating layers of a material of high refractive index and a material of low refractive index are known. The majority of them comprise metal oxides. Alternatively, the material of high refractive index can be replaced by a semi-transparent metal layer. The metal oxide layers are prepared either by a wet technique, by precipitating the metal oxide hydrates from a metal salt solution onto a carrier material, or by vapor deposition or sputtering in a vacuum. For instance, U.S. Pat. No. 4,434,010 describes a multilayer interference pigment consisting of a central layer of a reflective material (aluminum) and alternating layers of two transparent, dielectric materials of high and low refractive index, for example titanium dioxide and silicon dioxide, on either side of the central aluminum layer. In a further embodiment of the pigment, the layers following the centralaluminum layer are formed by magnesium fluoride and chromium. This pigment is used to print securities.
JP H7-759 (A) describes a multilayer interference pigment having a metallic luster It consists of a substrate coated with alternating layers of titanium dioxide and silicon dioxide. The substrate is formed from flakes of aluminum gold or silver, or from flakes of mica and glass which are coated with metals.
All types of pigment having an opaque metal layer as the central layer have the disadvantage that all wavelengths are reflected at this reflection layer, with the effect that, although a high luster is obtained, the actual interference color is overridden at the same time.
EP 0 753 545 describes goniochromatic luster pigments based on titanium dioxide-coated mica pigments whose TiO
2
coating is partly reduced. Owing to the titanium suboxides, titanium oxynitrides and titanium nitrides formed during the reduction, the titanium dioxide layer has a blue to violet coloration.
All of the multilayer interference pigments referred to are based on a transparent substrate or on an opaque, reflective metal layer as the middle layer. All pigments with a multilayer structure on a transparent substrate, examples being mica, SiO
2
flakes and TiO
2
flakes, have the disadvantage that, in the case of coating materials, it is often necessary to add absorption pigments to these pigments in order to obtain an adequate hiding power. When absorption pigments are mixed in, however, the color flop of the interference pigment is greatly attenuated.
All pigments with a multilayer structure on a central metal layer have the disadvantage that all wavelengths are reflected at this reflection layer. In order to reduce this effect, these high-hiding pigments as well are admixed with absorption pigments, as the result of which there is likewise an attenuation of the color flop.
DE 197 07 805, unpublished at the priority date of the present invention, discloses multilayer interference pigments having an absorbing middle layer, which are prepared by vapor deposition or sputtering of the individual layers onto a continuous belt which is provided with a detachment layer. These pigments have the disadvantage that, during the detachment of the dried film from the belt, and because of the subsequent comminution, particles having open broken edges are produced. Since these broken edges form scattering centers for the incident light, the luster of the pigment is reduced, which may lead to a disappearance of the interference effect.
SUMMARY OF THE INVENTION
An object of the invention is to provide an interference pigment having strong interference colors, a high angular dependency of the interference colors, and a high hiding power.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
Objects are achieved in accordance with the invention by a pearl luster pigment based on multiply coated, platelet-shaped, non-metallic substrates which are opaque or semi-opaque and have at least
a) one first layer comprising a metal oxide of high refractive index or a metal,
b) one second layer comprising a metal oxide of low refractive index,
c) one third layer comprising a metal oxide of high refractive index or a metal, and, if desired,
d) one subsequent coat.
Further objects are achieved in accordance with the invention by a process for preparing the pigments of the invention by suspending the substrate in water and coating it alternately with a metal oxide hydrate of high refractive index and a metal oxide hydrate of low refractive index, by addition and hydrolysis of the corresponding, water-soluble metal compounds, the pH required for the precipitation of the respective metal oxide hydrate being established and kept constant by simultaneous addition of acid or base, and subsequently separating the coated carrier material from the aqueous suspension, drying it and, if desired, calcining it.
The invention additionally provides for the use of the pigments of the invention for pigmenting paints, printing inks, plastics, glazes for ceramics and glass, and cosmetics.
The invention additionally provides for the use of the pigments of the invention for pigmenting securities and document papers, and packaging, and for the laser marking of polymeric materials and papers.
For this purpose they can be employed as mixtures with customary commercial pigments, examples being organic and inorganic absorption pigments, metal-effect pigments, and LCP pigments.
The material of high refractive index used comprises metal oxides or mixtures of metal oxides with or without absorbing properties, and also metals.
Preference is given to TiO
2
, ZrO
2
, Fe
2
O
3
, Fe
3
O
4
, Cr
2
O
3
, ZnO or (SnSb)O
2
, or thin metal layers, for example of nickel or aluminum.
The material of low refractive index used comprises metal oxides, for example Al
2
O
3
or SiO
2
, or mixtures thereof.
The thickness of the layers of the materials of high and low refractive index affect the optical properties of the pigment. When a product having strong interference colors is preferred, the thickness of the layers with respect to one another must be established. If n is the refractive index of a layer and d is its thickness, the interference color of a thin layer is given by the product of n and d, i.e. the optical thickness. The colors of such a film which are produced in reflected light with perpendicular light incidence result from an intensification of the light of wavelength
λ
=
4
2
N
-
1
·
n
d
and by attenuation of light of wavelengths
λ
=
2
N
·
n
d
,
where N, the order of interference, is a positive integer. The variation in color which takes place as the film thickness increases is a consequence of the intensification or attenuation of certain light wavelengths through interference. For example, a 115 nm thick film of titanium dioxide with the refractive index 1.94 has an optical thickness of 115×1.94=223 nm, and light of the wavelength 2×223 nm=446 nm (blue) is attenuated on reflection, so that the reflected light is yellow. In the case of multilayer pigments, the interference color is determined by the intensification of certain wavelengths, and if two or more layers in a multilayer pigment have the same optical thickness, the color of the reflected light becomes fuller and more intense as the number of layers increases. In addition to this, it is possible through an appropriate choice of layer thicknesses to achieve a particularly strong variation of the color as a function of the viewing angle. A pronounced color flop is developed, which may be desirable for the pigments according to the invention.
The thickness of the individual layers in the case of metal oxide materials of high refractive
Andes Stephanie
Bruckner Dieter
Fuchs-Pohl Gerald
Kuntz Matthias
Pfaff Gerhard
Faison Veronica F.
Koslow C. Melissa
Merck Patent GmbH
Millen White Zelano & Branigan
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