Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Patent
1993-02-24
1994-09-06
Group, Karl
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
106415, 106418, 106459, C04B 1400
Patent
active
053444884
DESCRIPTION:
BRIEF SUMMARY
The invention relates to pigments based on plate-like substrates covered with an iron oxide or iron oxide-containing mixture on which zinc oxide is deposited.
Pigments of this type are known, for example, from EP 0,256,417. These pigments are prepared by adding an aqueous zinc nitrate solution to an aqueous suspension of muscovite platelets coated with iron oxide and titanium dioxide and maintaining the reaction solution obtained at a pH of, for example, 8-9 and an elevated temperature of, for example, 80.degree. C. for, for example, 80 minutes. The coated pigments are separated off, dried and ignited at 650.degree. C. for, for example, one hour.
Pigments of this type have favourable properties, such as, for example, high gloss, high brightness, good skin compatibility, antibacterial action and high absorption in the UV and have therefore been proposed for industrial applications and in particular also for cosmetic applications. A disadvantage is that conventional ZnO/mica pigments tend to agglomerate, which constitutes a problem, since plate-like pigments cannot be dispersed like conventional pigments by subjecting them to high shearing forces, since this leads to a destruction of the platelet structure. Furthermore, it would be desirable to provide pigments which, in addition to the excellent properties of an external ZnO topcoat--good skin compatibility, antibacterial action, favourable optical absorption properties--have a surface colour; conventional ZnO/mica pigments have this desirable combination of properties only very insufficiently.
Furthermore, the processes previously used for preparing ZnO/mica pigment have in many cases disadvantages; thus, for example, in the process described in EP 0,256,417, a zinc nitrate solution is used, which is undesirable for reasons of environmental protection.
One object of the present invention was to provide ZnO pigments, based on plate-like substrates, which do not have, or have only to a small extent, the disadvantages of conventional pigments. A further object of the present invention was to provide preparation processes which are superior to conventional processes. Further objects of the present invention are obvious to one skilled in the art from the detailed description which follows and the examples.
It has now been found that these objects can be achieved by the pigments according to the invention and the preparation process according to the invention.
Accordingly, the invention relates to pigments based on plate-like substrates which, if desired, are covered with one or more layers comprising metal oxides or metal oxide mixtures, zinc oxide being deposited on the surface of the substrates with the formation of a not entirely continuous layer.
The invention furthermore relates to a process for the preparation of these pigments, characterised in that the plate-like substrates, which are covered with one or more layers comprising metal oxides or metal oxide mixtures, are suspended in water, in that an acid aqueous solution of zinc chloride or zinc sulfate is added to this suspension at a pH favourable for the deposition of zinc oxide, this pH being kept substantially constant by simultaneous addition of a base, and in that the product is separated off, washed, dried and, if desired, ignited.
The invention furthermore relates to the use of the pigments according to the invention for pigmenting plastics, coatings or cosmetics.
The pigments according to the invention are based on plate-like and preferably transparent or semi-transparent substrates consisting of, for example, layered silicates, such as mica, talc, kaolin, glass or other comparable minerals. Apart from these, metal platelets such as, for example, aluminium platelets or plate-like metal oxides, such as, for example, plate-like iron oxide or bismuth oxychloride are also suitable. The plate-like substrates typically have a thickness between 0.1 and 5 .mu.m and in particular between 0.2 and 4.5 .mu.m. The expansion in the other two dimensions is usually between 1 and 250 .mu.m and in particular bet
REFERENCES:
patent: 4956019 (1990-09-01), Noguchi et al.
Nedorost et al., "Nacreous silver pigment with a rutile structure", Chemical Abstracts, vol. 100, No. 2 (May 28, 1984), Abstract No. 177278f, pp. 137-138.
Bruckner Hans D.
Reynders Peter
Gallo Chris
Group Karl
Merck Patent Gesellschaft mit beschrankter Haftung
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