Nontoxic yellow/orange pigment compositions, well suited for the coloration of a wide variety of substrates, for example paints, varnishes, plastics, ceramics, etc., comprise a major amount of a zirconium oxide and an additive amount of cerium, praseodymium and/or terbium values, such rare earth values being in the form of the oxides thereof.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to novel pigments based on zirconium oxide, 
to a process for the preparation thereof and to the coloration of a wide 
variety of substrates utilizing such novel pigments. 
2. Description of the Prior Art 
Inorganic pigment colorants are today widely used in many industries, 
especially in those of paints, plastics and ceramics. For such 
applications, the properties of, inter alia, thermal and/or chemical 
stability, dispersibility (ability of the product to disperse properly in 
a given medium), intrinsic color, coloring power and opacifying power, 
constitute a number of particularly important criteria to be taken into 
consideration in the selection of a suitable pigment. 
Unfortunately, the majority of inorganic pigments which are suitable for 
applications such as the above and which are currently actually employed 
on an industrial scale generally comprise metals (especially cadmium, 
lead, chromium or cobalt), the use of which is becoming increasingly 
strictly controlled, indeed banned, by government legislation and 
regulation in many countries due to their reputedly very high toxicity. 
This is particularly the case in respect of yellow pigments based on 
cadmium sulfides or lead chromite. 
Thus, serious need continues to exist in this art for novel replacement 
inorganic pigments that are economically viable, suitable for use on an 
industrial scale and which otherwise avoid the above disadvantages and 
drawbacks to date characterizing the state of this art. 
SUMMARY OF THE INVENTION 
Accordingly, a major object of the present invention is the provision of 
novel pigments, yellow/orange in coloration, which are devoid of the above 
indicated high-toxicity problem. 
Briefly, the present invention features, in a first embodiment thereof, 
novel yellow colored pigments based on a zirconium oxide of essentially 
monoclinic form and comprising an additive amount of cerium values. 
This invention also features, in a second embodiment thereof, novel 
orange-yellow pigments based on a zirconium oxide of essentially 
monoclinic form, comprising an additive amount of praseodymium values, and 
having a chromaticity coordinate a (measured according to the standard 
described below) of at least 10. 
The present invention also features, in a third embodiment thereof, novel 
orange-yellow pigments based on a zirconium oxide and comprising an 
additive amount of terbium values. 
In a fourth embodiment of this invention, novel orange-yellow pigments are 
provided, based on a zirconium oxide and comprising additive amounts of 
both cerium and praseodymium values. 
The present invention also features a process for the preparation of the 
aforesaid novel pigments, comprising intimately admixing the oxides of 
zirconium and of those additives indicated above, or precursors thereof, 
and then calcining the admixture thus formulated.

DETAILED DESCRIPTION OF BEST MODE AND PREFERRED EMBODIMENTS OF THE 
INVENTION 
More particularly according to the present invention, the subject novel 
pigments are based on zirconium dioxide ZrO.sub.2 which constitutes the 
major component thereof. These novel pigments additionally comprise at 
least one additive selected from among cerium, praseodymium and terbium, 
as described above. The additives are present in the pigment essentially 
in the form of the oxides thereof. The total content of additive is 
generally at most 20%, preferably at most 10% and more preferably at most 
5%, expressed by weight of additive oxide. Moreover, the minimum content 
is generally at least 0.5% and more particularly at least 1%. 
It should be appreciated that the pigments of the invention include all 
those which are obtained by combining two or more of the above additives. 
In the case of the third embodiment, namely, the pigments based on 
zirconium and terbium, such pigments can additionally comprise cerium 
and/or praseodymium values. 
In the event of a cerium/praseodymium pairing, the cerium preferably 
constitutes at least 50% and more preferably at least 90% by weight of the 
cerium/praseodymium couple. The cerium permits obtaining, in this case, 
pigments in which the zirconium oxide is present solely in the monoclinic 
form. 
In a preferred embodiment of the invention, the additive(s) is/are at least 
partially and preferably entirely enclosed or confined within the lattice 
of the zirconium oxide such that the pigment constitutes a solid solution. 
In this instance, the pigment exhibits a high phase purity because the 
presence of a phase of the oxide of the additive is not observed. 
The crystalline state of the zirconium dioxide can vary according to the 
level of additive present in the pigment. In the case of the first, second 
and fourth embodiments of the invention, the zirconium oxide exists 
essentially in the monoclinic state. For the third embodiment, the 
zirconium oxide can develop from a 100% monoclinic structure to a 100% 
tetragonal structure and, more particularly, to an 80% tetragonal and 20% 
monoclinic structure. For the first, second and fourth embodiments and 
according to a specific variant of the third embodiment, the content of 
zirconium oxide in the tetragonal state is at most 30% by volume and more 
particularly at most 20%. The amount of the various phases is measured 
according to the technique of Evans et al, British Ceram. Trans. J., 83, 
pp. 39-43 (1984). It will be appreciated that the higher the content of 
tetragonal phase, the more the coloration shifts towards yellow. 
The pigments of the invention can also comprise a stabilizing agent of the 
crystalline structure of the zirconium oxide. These stabilizing agents are 
well known to this art and typically comprise rare earth metals. Exemplary 
thereof is yttrium. It will of course be appreciated that the rare earth 
metals described above as additives to the pigment inherently serve as 
stabilizing agents for the zirconium dioxide. In addition to the 
aforementioned rare earth metals, other rare earth metals can therefore 
comprise the pigment compositions of the invention, as stabilizing agents 
therefor. By "rare earth" metals are intended, in addition to yttrium, the 
elements of the Periodic Table having atomic numbers of from 57 to 71, 
inclusive. 
When yttrium is employed in the third embodiment of the invention, the 
zirconium oxide can be stabilized in the cubic form, to obtain a product 
which is 100% in the cubic form. This structure imparts a pale-yellow 
color to the pigment. 
Lastly, as regards the chromaticity coordinates of the compositions of the 
invention, the compositions according to the second embodiment preferably 
have an a coordinate of at least 15; likewise as regards the compositions 
according to the fourth embodiment in the event that the cerium content is 
at most 50%. Finally, in the context of the third embodiment, the 
coordinate a is preferably at least 10. 
The process for the preparation of the pigments of the invention will now 
be described. 
This process essentially consists of two stages. In the first, a mixture 
comprising the oxides of zirconium and of the additives or stabilizing 
agents indicated above, or precursors of such oxides, is formulated. 
Exemplary oxide precursors include the salts of organic or inorganic 
acids, such as nitrates, chlorides, sulfates, acetates or oxalates. The 
amounts of oxides or of precursors are adjusted such as to correspond to 
the stoichiometry of the desired final product. 
It will also be appreciated that, in the formulation of the mixture, no 
compounds capable of supplying silicon, for example silica, are 
introduced. Nor are any compounds introduced that, in the subsequent 
reaction, would produce a significant amount of zircon (zirconium 
silicate). Stated differently, the operation is carried out under 
conditions such that the zirconium will be present in the pigment 
substantially in the form of zirconium oxide. The procedure is preferably 
carried out in the absence of flux. 
As regards the starting material zirconium dioxide, an oxide is preferred 
having a mean particle size of at least 5 .mu.m. In the case of a 
stabilized zirconium oxide, a product which is particularly well suited is 
that described in FR-A-2,595,680. For the additives, it is advantageous to 
use mixed oxides or salts such as, for example, (Ce,Pr)O.sub.2. In this 
event, a more intense color is obtained. 
In a second stage, the mixture is calcined. This calcination generally is 
carried out under air. The temperature is generally at least 1,550.degree. 
C. and more particularly ranges from 1,600.degree. to 1,700.degree. C. The 
duration of the calcination is approximately 1 to 12 hours and preferably 
at least 3 hours. 
Upon completion of the calcination, the product can be ground and/or 
deagglomerated according to any known means to adjust the particle size to 
the desired value according to the application intended for the pigment. 
The pigments according to the invention are well suited for the 
coloration/pigmentation of a very wide variety of substrates, such as 
plastics, paints and ceramics. 
Thus, they can be used for the coloration of plastics which can be of 
thermoplastic or thermosetting type. 
Exemplary such thermoplastic resins suitable for coloration according to 
the invention include poly(vinyl chloride), poly(vinyl alcohol), 
polystyrene, styrene/butadiene, styrene/acrylonitrile or 
acrylonitrile/butadiene/styrene (A.B.S.) copolymers, acrylic polymers, 
especially poly(methyl methacrylate), polyolefins such as polyethylene, 
polypropylene, polybutene or polymethylpentene, cellulose derivatives such 
as, for example, cellulose acetate, cellulose acetobutyrate or ethyl 
cellulose, or polyamides including polyamide or nylon 66. 
Exemplary thermosetting resins for which the pigments according to the 
invention are also suitable include the phenoplasts, aminoplasts, 
especially urea/formaldehyde or melamine/formaldehyde copolymers, epoxy 
resins and thermosetting polyesters. 
The pigments of the invention can also be used for the coloration of 
special polymers, such as fluorinated polymers, in particular 
polytetrafluoroethylene (P.T.F.E.), polycarbonates, silicone elastomers or 
polyimides. 
In the specific application for the coloration of plastics, the pigments of 
the invention can be used directly in the form of powders. They can also, 
preferably, be employed in a predispersed form, for example as a premix 
with a portion of the resin, in the form of a concentrated paste or of a 
liquid. This permits introduction thereof at any stage in the manufacture 
of the resin, a particularly significant advantage of the pigments 
according to this invention. 
Thus, the pigments according to the invention can be incorporated or 
formulated into plastics such as those indicated above in a proportion by 
weight typically ranging either from 0.01% to 5% (for the final product) 
or from 40% to 70% in the case of a concentrate. 
The pigments of the invention are also useful in the field of paints and 
varnishes and, more particularly, are advantageously incorporated in the 
following resins: alkyd resins, the most well known of which being 
glycerophthalic resins; modified long- or short-oil resins; acrylic resins 
prepared from esters of acrylic acid (methyl or ethyl) and from esters of 
methacrylic acid, optionally copolymerized with ethyl, 2-ethylhexyl or 
butyl acrylate; vinyl resins such as, for example, poly(vinyl acetate), 
poly(vinyl chloride), poly(vinyl butyral), poly(vinyl formal), and vinyl 
chloride and vinyl acetate or vinylidene chloride copolymers; aminoplastic 
or phenolic resins, usually modified; polyester resins; polyurethane 
resins; epoxy resins; silicone resins; etc. 
Generally, the pigments are incorporated in a proportion of 5% to 30% by 
weight of the paint and of 0.1% to 5% by weight of the varnish. 
The pigments of the invention are also suitable for the coloration of 
ceramics, such as, for example, porcelain, earthenware and stoneware, 
either by coloring the entire mass of the ceramic (physical admixing of 
the ceramic powder with the pigment) or by coloring solely the face 
surface thereof by means of glazes (glassy coating compositions) 
containing the pigment. 
In this application, the amount of pigments used typically ranges from 1% 
to 30% by weight with respect either to the total mass of the ceramic, or 
with respect to the glaze alone. 
In addition, the pigments according to the invention are also suitable for 
applications in the rubber industry, especially in floor coatings, in the 
paper and printing inks industry and in the field of cosmetics, as well as 
in many other fields such as, for example, and without limitation, dyes, 
leather finishing and laminated coatings for kitchens and other work 
surfaces. 
Thus, the present invention also features colored compositions and 
substrates, especially of the plastic, paint, varnish, rubber, ceramic, 
glaze, paper, ink, cosmetic, dye and laminated coating type, which 
comprise the novel pigments described above. 
In order to further illustrate the present invention and the advantages 
thereof, the following specific examples are given, it being understood 
that same are intended only as illustrative and in nowise limitative. 
EXAMPLE 1 
This example describes the preparation of pigments according to the 
invention based on terbium. 
The oxides Tb.sub.4 O.sub.7 and ZrO.sub.2 (Rh one-Poulenc) were mixed in an 
agate crucible, the percentage by mass of terbium oxide being varied. The 
mixture was calcined in a muffle furnace under air at 1,600.degree. C. for 
3 hours (increase and decrease adjusted to 200.degree. C./h). 
The characteristics of the products obtained are reported in Table 1 below. 
The intrinsic coloration of the pigments according to the invention was 
quantified by means of the chromaticity coordinates L, a and b given in 
the CIE system 1976 (L, a, b) as defined by the Commission Internationale 
d'Eclairage [International Commission on Illumination] and listed in the 
Recueil des Normes Fran.cedilla.aises (AFNOR) [French Standards 
Compendium], colorimetric color No. X08-12 (1983). They were determined 
using a colorimeter marketed by Pacific Scientific. The nature of the 
illuminant was D65. The observation surface was a circular pellet having a 
surface area of 12.5 cm.sup.3. The observation conditions corresponded to 
viewing under an aperture angle of 10.degree.. In the measurements 
reported, the specular component was excluded. 
L provides a measurement of the reflectance (light/dark shade) and thus 
varies from 100 (white) to 0 (black). 
a and b are the values of the coloration tendencies: 
positive a=red 
negative a=green 
positive b=yellow 
negative b=blue 
L therefore represents the variation from black to white, a the variation 
from green to red and b the variation from yellow to blue. 
The structure was determined by analysis of the X-ray diffraction spectra. 
TABLE 1 
______________________________________ 
Tests Structure L a b 
______________________________________ 
ZrO.sub.2 + 1% Tb.sub.4 O.sub.7 
100% monoclinic 
79.8 12.9 50.2 
ZrO.sub.2 + 5% Tb.sub.4 O.sub.7 
20% tetragonal 
74.5 20.6 61.8 
80% monoclinic 
ZrO.sub.2 + 10% Tb.sub.4 O.sub.7 
60% tetragonal 
76 18.5 52.3 
40% monoclinic 
ZrO.sub.2 + 15% Tb.sub.4 O.sub.7 
80% tetragonal 
76.9 18.0 50.6 
20% monoclinic 
______________________________________ 
EXAMPLE 2 
The procedure of Example 1 was repeated, under the same conditions, but 
varying the nature and the proportions of additives. The results obtained 
are reported in Table 2 below: 
TABLE 2 
__________________________________________________________________________ 
Pr.sub.6 O.sub.11 / 
Pr.sub.6 O.sub.11 / 
Tb.sub.4 O.sub.7 
Tb.sub.4 O.sub.7 
Tb.sub.4 O.sub.7 / 
Tb.sub.4 O.sub.7 / 
Tests Pr.sub.6 O.sub.11 
Tb.sub.4 O.sub.7 
CeO.sub.2 
CeO.sub.2 
CeO.sub.2 
CeO.sub.2 
Pr.sub.6 O.sub.11 /CeO.sub.2 
__________________________________________________________________________ 
Proportions (50/50) 
(50/50) 
(50/50) 
(75/25) 
(66/33) 
(1/3;1/3: 
1/3) 
% by weight 
5 5 5 5 5 5 5 
L 71.2 69.1 73.0 70.9 
69.9 68.6 69.5 
a 17.7 21.2 18.3 26.3 
25.4 27.6 23.3 
b 57.5 56.0 58.4 59.9 
57.9 59.0 57.3 
Structure 
Mono + 
Mono + 
Mono + 
Mono 
Mono + 
Mono + 
Mono + 
Tetra Tetra 
trace Tetra 
trace 
trace 
(&lt;20%) + 
(&lt;20%) 
Tetra (&lt;20%) 
Tetra 
Tetra 
Pr.sub.6 O.sub.11 
__________________________________________________________________________ 
EXAMPLE 3 
The procedure of Example 1 was repeated, under the same conditions, but 
starting from a mixed oxide (Ce.sub.0.95 Pr.sub.0.05)O.sub.2 for the 
product based on cerium and praseodymium. The contents of additive were 5% 
by weight. 
The results obtained are reported in Table 3: 
TABLE 3 
______________________________________ 
Tests Ce/Pr Ce/Pr CeO.sub.2 /Tb.sub.4 O.sub.7 
______________________________________ 
Proportions 
(95/5) (98/2) (95/5) 
L 82.2 86.5 84.7 
a 7.4 2.4 6.4 
b 53.2 40.2 42.7 
Structure Mono Mono Mono 
______________________________________ 
The combination of the above examples evidences that the pigments of the 
invention extend over a wide range of coloration, these examples relating 
to products extending, for the colorimetric coordinates, from the point 
a=2.4, b=40.2 to the point a=26.3, b=59.9. 
EXAMPLE 4 
This example describes the application of the pigment of Example 1 
containing 5% of Tb.sub.4 O.sub.7 in a glaze. 
A slip having the following composition was prepared: 
Frit, Ferro F 87, 80 g. This frit contained 27% of SiO.sub.2 and 9% of PbO 
(by weight). 
______________________________________ 
Pigment 5 g 
Gum arabic 0.24 g 
Deionized water 50 ml 
______________________________________ 
The materials constituting the slip were ground in a 250-ml corundum jar 
equipped with beads and with a planetary grinder for 1 hour. The ground 
mixture was sieved at 100 .mu.m. 
The glaze thus obtained was applied by spraying a white earthenware shard 
with a spray gun. The mass of glaze deposited was 20 g/dm.sup.2. 
Firing was carried out for 30 minutes at 950.degree. C. after an increase 
in temperature of 6 hours. 
The colorimetric results were as follows: 
TABLE 4 
______________________________________ 
L a b 
______________________________________ 
Pigment 74.5 20.6 61.8 
Tile 71.8 23.8 70.9 
______________________________________ 
While the invention has been described in terms of various preferred 
embodiments, the skilled artisan will appreciate that various 
modifications, substitutions, omissions, and changes may be made without 
departing from the spirit thereof. Accordingly, it is intended that the 
scope of the present invention be limited solely by the scope of the 
following claims, including equivalents thereof.