Red-tinged bismuth vanadate pigments

Details Red-tinged bismuth vanadate pigments Red-tinged bismuth vanadate pigments

2001-03-12

2002-09-03

Green, Anthony J. (Department: 1755)

Compositions: coating or plastic

Materials or ingredients

Pigment, filler, or aggregate compositions, e.g., stone,...

C106S451000, C106S461000, C106S466000, C524S406000, C524S408000

Reexamination Certificate

active

06444025

ABSTRACT:

The present invention relates to red-tinged bismuth vanadate pigments, to a process for the preparation thereof and to the use thereof in pigmenting high molecular weight organic materials such as surface-coatings, plastics and printing inks.
There is a great need to replace the conventional heavy-metal-containing yellow pigments, such as lead chromate and cadmium sulfide, with pigments that are free from toxicological concern.
Bismuth vanadate pigments constitute a new class of yellow pigments that are free from toxicological concern. Hitherto, however, only green-tinged bismuth vanadate pigments have been of major industrial interest, because the red-tinged pigments are generally too dull and weak in colour. Red-tinged bismuth vanadate pigments having good properties in terms of application technology are described in DE-A 19 529 837 and EP-A 839 874. In the case of the former, the pigments are iron-containing bismuth vanadate pigments, the colour space of which (based on the L*C*h system of the Commission Internationale de l'Eclairage) is, however, limited to brightness values L* of <78, to colour angles (hue) h of from 78 to 85 and to chroma values C* of >85.
EP-A 839 874 describes bismuth vanadate pigments that can additionally contain phosphate and likewise have only low brightness values of <75.
Elements that are free from toxicological concern include, for example, zirconium. Bismuth vanadate pigments that contain zirconium are, for example, known from U.S. Pat. No. 5,399,197. However, those pigments are green-tinged yellow bismuth vanadate pigments.
Although EP-B 492 244 mentions green- and red-tinged yellow zirconium-containing bismuth vanadate pigments, the implementation examples describe only green-tinged yellow pigments. Furthermore, the person skilled in the art will infer from Example 6 that, with a zirconium content of 0.05 part relative to 1 part of bismuth, it is possible to obtain only a very pale yellow pigment.
The incorporation of molybdates, such as calcium molybdate, into the bismuth vanadate pigments is also free from toxicological concern. EP-A 239 526 describes molybdenum-containing bismuth vanadate pigments which are also, however, only green-tinged yellow.
For individual and especially for combination colourations there is a need to extend the colour space with further bismuth vanadate pigments. In particular, pigments are required that, without loss of colour strength, have greater colour angles and brightness values than the known red-tinged bismuth vanadate pigments.
The aim of the present invention was therefore to provide further red-tinged bismuth vanadate pigments that are free from toxicological concern, that extend the previously obtainable colour space and colour angle, and that have improved colouristic properties and improved properties in terms of application technology.
The invention accordingly relates to zirconium-containing red-tinged bismuth vanadate pigments of formula I,
BiV
b
O
x
.Ca
c
(MoO
4
)
d
.Zr
e
Si
f
O
y
.F
z
  I
wherein the variables have the following meanings:
b 0.8 to 1.5; preferably 1.1 to 1.5 and very especially 1.25 to 1.5;
c 0 to 0.3;
d 0 to 0.3;
e 0.01 to 0.3;
f 0 to 0.3;
x (3/2+5 b/2);
y (2e+2 f);
z 0 to 1.0; especially 0.05 to 0.7 and very especially 0.3 to 0.5.
Preference is given to red-tinged bismuth vanadate pigments of formula I according to the invention having brightness values L* in the range from 79 to 91, preferably from 81 to 87, or/and colour shade angles h of from 82 to 91, preferably from 84 to 89.
Special preference is given to zirconium-containing red-tinged bismuth vanadate pigments of formula I wherein the variables have the following meanings:
b 0.8 to 1.5; preferably 1.1 to 1.5, and very especially 1.25 to 1.5;
c 0 to 0.3;
d 0 to 0.3;
e 0.01 to 0.3;
f 0;
x (3/2+5b/2);
y (2e+2 f);
z 0 to 1.0, especially 0.05 to 0.7, and very especially 0.3 to 0.5;
and also to red-tinged bismuth vanadate pigments of formula I wherein the variables have the following meanings:
b 0.8 to 1.5, especially 1.1 to 1.5, and very especially 1.25 to 1.5;
c 0.01 to 0.3;
d 0.01 to 0.3;
e 0.01 to 0.3;
f 0.01 to 0.3;
x (3/2+5b/2);
y (2e+2 f);
z 0 to 1.0, especially 0.05 to 0.7, and very especially 0.3 to 0.5.
Special preference is also given to zirconium-containing red-tinged bismuth vanadate pigments of general formula I wherein the variables have the following meanings:
b 0.8 to 1.5, especially 1.1 to 1.5, and very especially 1.25 to 1.5;
c 0;
d 0;
e 0.01 to 0.3;
f 0 to 0.3;
x (3/2+5b/2);
y (2e+2 f);
z 0 to 1.0, especially 0.05 to 0.7, and very especially 0.3 to 0.5.
Special preference is furthermore given to zirconium-containing red-tinged bismuth vanadate pigments of formula I wherein the variables have the following meanings:
b 0.8 to 1.5, especially 1.1 to 1.5, and very especially 1.25 to 1.5;
c 0;
d 0;
e 0.01 to 0.3;
f 0;
x (3/2+5b/2);
y (2e+2 f);
z 0 to 1.0, especially 0.05 to 0.7, and very especially 0.3 to 0.5.
The pigments of formula I according to the invention may be solid solutions, which have different crystalline modifications according to their chemical composition.
The present invention relates also to a process for the preparation of pigments of formula I according to the invention, which comprises treating an aqueous mixture comprising bismuth, vanadium and zirconium salts and, if desired, salts of elements selected from the group consisting of calcium, molybdenum, silicon and fluorine, for from 2 to 30 hours in a pH range of from 4.5 to 8.
The sequence in which the salts are mixed with one another is generally immaterial.
A preferred embodiment of the present invention relates to a process for the preparation of pigments of formula I according to the invention, which comprises mixing
(a1) a solution of a bismuth salt, a zirconium salt and a calcium salt with a solution of a vanadate salt, a molybdate salt and a silicate salt, or
(a2) a solution of a bismuth salt, a zirconium salt and a calcium salt with a solution of a vanadate salt and a molybdate salt, or
(a3) a solution of a bismuth salt and a zirconium salt with a solution of a vanadate salt and a silicate salt, or
(a4) a solution of a bismuth salt and a zirconium salt with a solution of a vanadate salt, and
(b) then maintaining the resulting mixture for from 2 to 30 hours in a pH range of from 4.5 to 8.
In the process steps (a1), (a2), (a3) or (a4), the required starting materials are usually mixed together in the form of their ions in solutions. The particles precipitated do not generally exhibit pigment properties but are usually X-ray amorphous and often gel-like.
In process step (b), the particles, which are generally precipitated in amorphous form, are crystallised. Advantageously, the particles obtained after process steps (a1), (a2), (a3) or (a4) are not isolated, for example by means of filtration and washing, but are directly crystallised.
The process steps (a1), (a2), (a3) or (a4) are preferably carried out by blending a bismuth salt solution comprising, if desired, a calcium salt and a zirconium salt, or a zirconium salt alone, with a vanadate solution comprising, if desired, a molybdate and a silicate, or a silicate alone.
In a further embodiment of the process according to the invention, the process steps (a1), (a2), (a3) or (a4) can, however, also be carried out by blending the individual salt solutions with one another simultaneously or successively.
A further embodiment of the present process relates also to the process steps (a1), (a2), (a3) or (a4) wherein the bismuth salt solution and the vanadate solution are introduced in parallel.
Generally, stirring is carried out during or after parallel introduction, especially during introduction.
In process step (b), the mixture obtained in process steps (a1) to (a4) is adjusted to a pH range of from pH 4 to 8.5, preferably from 5 to 8, by addition of a base, especially an inorganic base.
In a variant of process step (b), the pH can also be adjusted stepwise, for example to a pH in the range from 2 to 4.5, especi

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