Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
1999-02-01
2001-05-29
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S436000, C106S437000, C106S439000, C106S440000, C106S479000, C106S480000
Reexamination Certificate
active
06238471
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to multilayer interference pigments having a blue mass tone.
Colored interference pigments are already known. They contain either colorant additives or coloring metal oxides, the latter possibly also forming the layer which produces interference colors. The play of colors brought about by this means is limited in nature. In particular, pigments with blue or bluish colors have not to date been obtainable in a satisfactory shade. The selection of desired colors is also restricted, in addition, because colorants may greatly reduce the chemical and thermostability of the interference pigments.
U.S. Pat. No. 3,951,679 describes colored pigments based on mica which is coated with metal oxide layers and may additionally carry a colored coating of Prussian Blue. The layer of Prussian Blue is formed by the reaction of an iron compound that has been deposited on the substrate with a water-soluble hexacyanoferrate. This pigment has the disadvantage that the Prussian Blue decomposes at a temperature of 200 to 300° C.
U.S. Pat. No. 4,968,351 describes a pearl luster pigment which is colored by means of an adsorbed colorant, a color lake being applied to the colorant layer in order to intensify the adsorption of the colorant. A disadvantage of this pigment is that on contact with organic solvents the organic colorant is separated from the interference pigment. Moreover, the organic colorant impairs the weathering stability of the pigment. U.S. Pat. No. 5,169,442 describes a blue-green pigment consisting of a substrate comprising mica coated with metal oxide and of a top layer formed from a mixed oxide of magnesium oxide, calcium oxide, cobalt oxide and titanium dioxide. The mass tone of this pigment, however, is not pure blue.
SUMMARY OF THE INVENTION
It is the object of the object of the invention to provide interference pigments having a blue mass tone which possess the light stability, chemical stability and weathering stability of customary commercial interference pigments.
This object is achieved in accordance with the invention in a first embodiment by multilayer interference pigments having a blue mass tone, also referred to as “mass colour” (see Plastics Technical Dictionary, p. 196, by Wittfoht) comprised of a platelet-shaped carrier material and a coating which is formed from
(i) a first layer of a colorless, transparent metal oxide of high refractive index,
(ii) a second layer of colorless, transparent metal oxide of low refractive index and
(iii) a third, outer layer of cobalt aluminate, cobalt-containing glass, tungsten bronzes or cobalt oxide.
This object is additionally achieved in accordance with the invention in a second embodiment by multilayer interference pigments having a blue mass tone, comprised of a platelet-shaped carrier material and a coating which is formed from
(i) a first layer of cobalt aluminate, cobalt-containing glass, tungsten bronzes or cobalt oxide,
(ii) a second layer of colorless, transparent metal oxide of low refractive index and
(iii) a third, outer layer of a colorless, transparent metal oxide of high refractive index.
This object is also achieved in accordance with the invention by a process for preparing the pigments according to the invention, in which
the platelet-shaped carrier material is suspended in water and the suspension is heated at 50 to 100° C., a water-soluble metal compound is added at a pH which is appropriate for hydrolysis, so that a metal oxide hydrate of high refractive index is precipitated onto the suspended particles, the pH required for the precipitation of the respective metal oxide hydrate being established and kept constant by simultaneous addition of acid or base,
subsequently the pH is adjusted with a base to 4 to 10 and a water-soluble metal compound is added, so that a metal-oxide hydrate of low refractive index is precipitated onto the suspended particles, the pH being kept constant by simultaneous addition of acid or base, and
subsequently the resulting product is washed, dried at from 60 to 180° C. and calcined at from 500 to 1100° C.,
then the product is suspended in water and is coated at a pH of from 3 to 10 with cobalt and aluminium oxide hydrate by addition and hydrolysis of the corresponding water-soluble metal compounds, the pH being kept constant by simultaneous addition of a base, and
and subsequently the product is washed, dried and from 60 to 180° C. and calcined at from 500 to 1100° C.
This object is also achieved in accordance with the invention by a process for preparing the pigments according to the invention, in which
the platelet-shaped carrier material is suspended in water and the suspension is heated to 50 to 100° C. and is coated at a pH of from 3 to 10 with cobalt and aluminium oxide hydrate by addition and hydrolysis of the corresponding water-soluble metal compounds, the pH being kept constant by simultaneous addition of base,
subsequently the pH is adjusted with a base to 4 to 10 and a water-soluble metal compound is added, so that a metal-oxide hydrate of low refractive index is precipitated onto the suspended particles, the pH being kept constant by simultaneous addition of acid or base, and
then a water-soluble metal compound is added at a pH suitable for hydrolysis, so that a metal oxide hydrate of high refractive index is precipitated onto the suspended particles, the pH required for the precipitate of the respective metal oxide hydrate being established and kept constant by simultaneous addition of acid or base, and
subsequently the product is washed, dried at from 60 to 180° C. and calcined at from 500 to 1100° C.
The invention also relates to the use of the pigments according to the invention for pigmenting paints.
For this purpose they can be employed as mixtures with customary commercial pigments, examples being inorganic and organic absorption pigments, metal-effect pigments (see Special Effect Pigments, Ed. Urich Zoril, p. 13) and LCP (Liquid Crystal Polymer) pigments (see U.S. Pat. No. 5,824,733).
Suitable carrier materials for the pigments according to the invention are natural or synthetic, platelet-shaped materials which have no inherent color. Preferred carrier materials are phyllosilicates, metal oxide platelets and glass flakes and ceramic flakes. Particular preference is given to mica, talc, kaolin, synthetic mica, and aluminium oxide and silicon dioxide platelets.
The silicon dioxide platelets are produced in accordance with International Application WO 93/08 237 on a continuous belt by solidification and hydrolysis of a waterglass solution.
The size of the carrier materials is not critical and can be matched to the particular intended use. In general, the platelet-shaped carrier materials have a thickness of between 0.05 and 5 &mgr;m, in particular between 0.2 and 2.0 &mgr;m. The extent in the two other dimensions is usually between 2 and 100 &mgr;m and, in particular, between 5 and 50 &mgr;m.
The thickness of the individual layers of the pigment is essential for the optical properties of the pigment. For a pigment with intense interference colors, the thickness of the individual layers must be adapted to one another. Furthermore it is possible, through an appropriate choice of layer thicknesses, to achieve a particularly strong variation in color as a function of the viewing angle. This is achieved, for example, by the precipitation of a thick SiO
2
layer (layer thickness>100 nm), giving pigments having a strongly pronounced angular dependence of the interference colors. Adjustment of the layer thicknesses to produce a given desired effect can be achieved with routine experimentation as is conventional in the art.
The thicknesses of the individual layers of the pigments according to the invention are preferably within the following ranges:
Metal oxide of high refractive index:
70-110
nm
Metal oxide of low refractive index:
60-110
nm
Color-imparting layer:
50-90
nm
This gives rise, for example, to the following preferred proportions for the individual constituents of one pigment according to the invention:
25-40%
Bruckner Hans-Dieter
Vogt Reiner
Bell Mark L.
DiVerdi Michael J.
Merck Patent Gesellschaft mit beschrankter Haftung
Millen White Zelano & Branigan P.C.
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