Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2000-11-13
2002-07-16
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S403000, C106S404000, C106S461000, C106S482000, C423S263000
Reexamination Certificate
active
06419736
ABSTRACT:
The present invention relates to sulfide and oxysulfide pigments which are based on platelet-shaped substrates coated with a sulfide or oxysulfide of a rare earth metal and/or of yttrium, and to their preparation and use, especially in car finishes, paints, inks, plastics and cosmetic formulations.
Rare earth metal sulfide and yttrium sulfide pigments without carriers, and their use in plastics, coating materials and cosmetics, are known from EP 0 203 838 B1. EP 0 545 746 B1 describes pigments comprising both a composition based on a sesquisulfide of a rare earth metal or of yttrium and a dopant.
In EP 0 620 254 B1 a pigment based on a rare earth metal sulfide or on yttrium sulfide is used as a carrier which is coated with a transparent oxide, preferably a metal oxide.
These known rare earth metal sulfide and yttrium sulfide pigments, although they can be employed to good effect as absorption pigments for numerous purposes, cannot be regarded as pearl lustre pigments owing to the absence of interference capacity and to deficient lustre.
It was therefore the object of the invention to provide rare earth metal sulfide or oxysulfide and yttrium sulfide or oxysulfide pigments having good opacity and strong colour shades, covering a relatively broad colour spectrum, and at the same time having the interference and lustre properties of pearl lustre pigments.
It has surprisingly now been found that, by coating platelet-shaped substrates with sulfides or oxysulfides of the rare earth metals (lanthanides) and of yttrium, pigments having advantageous coloristic properties are obtained.
On the platelet-shaped substrates it is possible to apply uniform sulfide or oxysulfide layers of rare earth metals and of yttrium which have a high lustre, give the pigment an attractive powder colour, and may possibly generate the interference colours of thin platelets.
The invention therefore provides sulfide and oxysulfide pigments which are based on platelet-shaped substrates, characterized in that the substrates are coated with a sulfide or oxysulfide of a rare earth metal and/or of yttrium.
The invention additionally provides a process for preparing the pigments of the invention and for the use of these pigments in formulations such as paints, varnishes, printing inks, plastics and cosmetics.
The substrates are coated with a sulfide of the rare earth metals or of yttrium having the formula M
2
S
3
, in which M is at least one element chosen from the group formed by the lanthanides of atomic numbers from 57 to 71 inclusive and yttrium. Preferably, M
2
S
3
is a sesquisulfide of cubic &ggr;-Ce
2
S
3
or &ggr;-La
2
S
3
. However, sulfide mixtures, such as &ggr;-Ce
2
S
3
and &ggr;-La
2
S
3
, or mixed sulfides, such as LaYS
3
, are also suitable. The coatings may additionally consist of oxysulfides of the formula M
2
S
3−x
O
x
(2.5<×<0.05)
A suitable platelet-shaped base substrate is any platelet-shaped material known to the person skilled in the art which is stable under the conditions of coating. Particular mention may be made here of natural and synthetic mica, kaolin, talc, vermiculite, TiO
2
, SiO
2
and Al
2
C
3
flakes, glass flakes, graphite, metal flakes, bismuth oxychloride, platelet-shaped iron oxide, LCPs (liquid crystal polymer pigments), holo-graphic pigments and other platelet-shaped materials.
Preference is given to mica, such as muscovite or phlogopite, for example. The platelet-shaped substrate employed can, however, also comprise materials which already possess a metal oxide coating, especially mica or SiO
2
flakes with one or more coats of, for example, TiO
2
, ZrO
2
, SnO
2
, Al
2
O
3
, SiO
2
, ZnO or mixtures of these metal oxides.
Other suitable substrate materials are thin metal flakes, which in some cases—as in the case of Al flakes, for example—are enveloped by a layer of a stabilizing compound of low refractive index, such as silica. Apart from Al flakes, other metal flakes employed include those of Ag, Ti, Cu/Zn and other metals.
The size of these platelet-shaped substrates is not critical per se, and it is therefore possible to use particles of the size appropriate for the intended application. In general, the substrate will be employed in particle sizes of from about 1 to 200 &mgr;m, in particular from about 5 to 100 &mgr;m. The thickness of the particles is generally from about 0.1 to 5 &mgr;m, in particular about 0.5 &mgr;m.
The starting materials used as substrates are known and can be prepared by known techniques. Mica particles of the desired size order can be obtained by wet or dry milling of mica followed by classification. Metal oxide-coated materials, especially metal oxide-coated mica flakes, can either be obtained commercially—for example, as Iriodin® pearl lustre pigment from Merck KGaA, Darmstadt, Germany—or can be prepared by known techniques. Such techniques are described, for example, in the following patents and patent applications: U.S. Pat. No. 3,087,828, U.S. Pat. No. 3,087,829, DE 19 59 998, DE 20 09 566, DE 22 14 545, DE 22 44 298, DE 23 13 331, DE 25 22 572, DE 31 37 808, DE 31 37 809, DE 31 51 343, DE 31 51 354, DE 31 51 355, DE 32 11 602, DE 32 35 107, WO 93/08237 and EP 0 763 573.
The pigments of the invention are prepared by adding a salt solution of a rare earth metal and/or of yttrium and optionally oxalic acid to an aqueous suspension of a platelet-shaped substrate, the pH of the suspension being optionally kept substantially constant, by simultaneous addition of a base, within a range which brings about hydrolysis of the added salt, and the pigment coated in this way with an oxide or oxide hydrate or oxalate is separated off, washed, dried, preferably at 80-150° C. for from 10 minutes to 1.5 hours, and calcined, preferably at 400-900° C. Finally, the product is calcined in an H
2
S gas stream or in a CS
2
or H
2
S/CS
2
gas stream under inert gas for from 10 minutes to 2 hours at temperatures from 550 to 1200° C., preferably from 800 to 1000° C., in the course of which the oxalate or oxide of the rare earth metal and/or yttrium is converted to the sulfide or oxysulfide.
It is also possible to carry out the reaction with H
2
S or CS
2
in a fluidized-bed reactor (CVD process).
In order to conduct the CVD variant it is advisable, as is generally the case for CVD processes, to use a fluidized-bed reactor or tube furnace. The substrate particles to be coated are heated in the reactor, for example with fluidization by means of an inert fluidizing gas such as N
2
or argon, to the desired reaction temperature (generally from 400 to 900° C., preferably from 650 to 850° C.). The elemental sulfur or H
2
S and/or CS
2
is then introduced from separate nozzles with the aid of inert streams of carrier gas (advantageously substreams of the fluidizing gas) from upstream evaporator vessels, the sulfur concentration being held judiciously at from
0
.
5
to 5% by volume, preferably≦2% by volume, based on the total amount of gas in the reactor.
In addition to compounds containing sulfur, particularly preferred sulfur donors include hydrogen sulfide and elemental sulfur.
If elemental sulfur is used, the procedure adopted is judiciously to render finely ground sulfur powder inert for about 1 to 4 h and then to heat it in the absence of oxygen to the reaction temperature, generally 400-1200° C., preferably 400-900° C. and, in particular, 600-850° C.
By depositing rare earth metal oxide or oxide hydrate layers or yttrium oxide or oxide hydrate layers in the presence of one or more dopants, selected, for example, from the group of alkaline earth metals and/or alkali metals, onto the platelet-shaped substrates, it is possible to produce particularly smooth, stable, defined and strongly coloured rare earth metal sulfide layers or yttrium sulfide layers, respectively. The dopant is in the form of an inclusion in the crystalline lattice of the sulfide layer M
2
S
3
or the oxysulfide layer M
2
S
3−x
O
x
. The dopant can be selected alone or in mixtures from the salts of alkali metals and/or alkaline earth metals; preference is given to t
Kuntz Matthias
Pfaff Gerhard
Riddle Rodney
Schoen Sabine
Vogt Reiner
Bell Mark L.
Hailey Patricia L.
Merck Patent Gesellschaft mit beschrankter Haftung
Millen White Zelano & Branigan P.C.
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