Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Patent
1998-01-09
1999-10-26
Bell, Mark L.
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
106415, 106418, 106437, 106439, 428402, 428403, 428404, C09C 136
Patent
active
059720980
DESCRIPTION:
BRIEF SUMMARY
The invention relates to very thin pearlescent pigments based on plateletlike titanium dioxide coated with iron oxide.
Pearlescent (pearl lustre) pigments containing iron oxide have been described in several instances and have been successfully used for many years. Both pigments in which iron oxide is precipitated together with titanium dioxide onto the substrate and pigments in which the precipitations are carried out in succession are described. During subsequent calcining, iron oxide diffuses into the TiO.sub.2 layer and pseudo-brookite (Fe.sub.2 TiO.sub.5) is formed. Mica is used exclusively as the substrate.
U.S. Pat. No. 3,087,828 reports that gold-colored mica pigments which assume a reddish colour shade on calcining are obtained by deposition of an Fe.sub.2 O.sub.3 layer onto a TiO.sub.2 layer.
U.S. Pat. No. 3,874,890 describes a process for the preparation of gold-colored pearlescent pigments in which a mica pigment coated with TiO.sub.2 and/or ZrO.sub.2 is first coated with iron(II) hydroxide, which is then oxidized to Fe.sub.2 O.sub.3.
U.S. Pat. No. 4,744,832 describes a pearlescent pigment based on plateletlike substrates, in particular mica, coated with metal oxides, the metal oxide layer comprising both titanium and iron and the pigment having a multilayer build-up, a layer of pseudo-brookite and an iron oxide layer following a first layer of TiO.sub.2 in the rutile form.
Mica pigments are widely used in the printing and coating industry, in cosmetics and in plastics processing. They are distinguished by interference colors and a high gloss. However, mica pigments are unsuitable for the formation of extremely thin layers, because mica, as the substrate for the metal oxide layers of the pigment, already has a thickness of 200 to 1200 nm. Another disadvantage is that the thickness of the mica platelets within a certain fraction, which is determined by the platelet size, sometimes varies significantly around a mean value. Furthermore, mica is a naturally occurring mineral which is contaminated by foreign ions. Processing steps which are very expensive industrially and time-consuming are, moreover, necessary. These include, above all, grinding and grading.
Pearlescent pigments which are based on thick mica platelets and are covered with metal oxides have a significant scatter content because of the thickness of the edge, especially at finer particle size distributions below 20 .mu.m.
Thin glass platelets which are obtained by milling a glass melt with subsequent grinding have been proposed as a substitute for mica. Interference pigments based on such materials indeed show color effects which are superior to those of conventional pigments based on mica. A disadvantage is, however, that the glass platelets have a very large average thickness of about 10-15 .mu.m and a very wide thickness distribution (typically between 4 and 20 .mu.m), while the thickness of interference pigments typically is not greater than 3 .mu.m.
EP 0,384,596 describes a process in which hydrated alkali metal silicate is charged with a jet of air at temperatures of 480-500.degree. C., bubbles with low wall thicknesses forming; the bubbles are then comminuted and plateletlike alkali metal silicate substrates having a thickness of less than 3 .mu.m are obtained. However, the process is expensive and the thickness distribution of the resulting platelets is relatively wide.
DE 11 36 042 describes a continuous belt process for the preparation of plateletlike or spangle-like oxides or hydrated oxides of metals of group IV and V and of the iron group of the Periodic Table. In this process, if appropriate, a separating layer of, for example, silicone varnish is first applied to a continuous belt to facilitate later detachment of the metal oxide layer. A liquid film of a solution of a hydrolyzable compound of the metal to be converted into the desired oxide is then applied and the film is dried and then detached with a vibrating device. The layer thickness of the resulting platelets is stated as 0.2 to 2 .mu.m, without concrete example
REFERENCES:
patent: 3395203 (1968-07-01), Morita et al.
patent: 3767443 (1973-10-01), Clark et al.
patent: 4344987 (1982-08-01), Ostertag et al.
patent: 4744832 (1988-05-01), Franz et al.
patent: 5009711 (1991-04-01), Emmert et al.
Derwent abstract 87-039671 of JP 61 295 234 A, Dec. 1986.
Derwent Publications, AN 87-039671 (Dec. 26, 1986).
Andes Stefanie
Brenner Gunter
Bruckner Dieter
Heyland Andrea
Hock Sabine
Bell Mark L.
Hertzog Scott L.
Merck Patent GmbH
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