Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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3-16646/- CGC 1291
Bismuth Vanadate Process
Bismuth vanadates have been identified as pigmentary, yellow compounds
applicable for coloring plastics and paints (see U.S. Patents 4,115,141
and 4,115,142). A variety of precipitation and solid state reactions have
also been disclosed for preparing such bismuth vanadates and related
compounds. For example, prior to discovery of the indicated pigmentary
properties, Gottlieb et al., Thermal Analysis, Proceedings Fourth ICTA,
Budapest, 1, pp. 675-679 (l974) describe synthesis of bismuth vanadates
by solid state preparations wherein lntimately mixed bismuth and vanadium
oxides are heated at 800C for 16 hours, or by precipitation methods
wherein solutions of sodium vanadate and bismuth nitrate are reacted at
controlled concentrations, temperatures, time and pH. Correspondingly,
Roth et al., American Mineral, vol. 48, pp. 1348-1356 (1~63~ disclose
solid state approaches involving heating of the mixed oxides.
In addition, the approach of the above noted U.S. patents involves first
preclpitating a gel-like precursor from soluble bismuth and vanadium
compounds, and then converting the precursor into the crystalline,
pigmentary form either by a heat treatment at 200-500C or by an aqueous
aftertreatment carried out under specified conditions.
Alternate approaches are disclosed in German Offenlegungs-
schriFt 3,315,580, German ~ffenlegungss-chrift 3,315,581, U.S.
Patent 3,843,554 and U.S. Patent 4,063,956. In addition, U.S.
Patent 4,316,746 describes bismuth vanadate/molybdate and bismuth
vanadate/tungstenate pig~ents which consist, in the case of bismuth
vanadatelmolybdate, of a crystalline phase having a scheelitsllke
structure, while in the case of bismuth vanadate/tungstenate a two-phase
product is present.
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A bismuth vanadate/molybdate or bismuth vanadate/tungstenate was also
proposed in ~.S. Patent 4,455,174 and German Offenlegungs-
schrift 3,221,338 as a further alternative yellow pigment. These are
multiphase products which consist of a bismuth vanadate phase and a
bismuth/molybdate and/or a bismuth/tungstenate phase and which are
prepared by a process in which a solution containing a bismuth salt, a
vanadate and a molybdate is acidified, then treated with an alkaline
solution optionally containing the tungsten compound, whereupon the
solids are recovered, washed and optionally dried and heat treated at
300-800C.
Finally, greenish-yellow pigments based on BiVOI~ and containing Ca, Ba,
Mg or Zn were also proposed in U.S. Patent 4,251,283. They are obtained
by calcination, in the presence of air, of a mixture of BiPOI~, V20s and
of a corresponding oxide Me~, in whlch Me is Ca, ~a, Mg or Zn, at a
temperature of between 500 and 800C.
These diverse processes have, however, exhibited certain disadvantages. A
key disadvantage of the solid state processes is noted in the calcined
mass wherein a dull yellow brown color or a dirty green color is fre~
quently encountered. Such a reduction ~n the desired bright yellow color
has, in turn, a significant impact on the use of these materials in
pigment-related applications. Although the use of oxidizing agen-ts in
certain of the prior art processes has served to minimize this effect,
many of the oxidizing agents produce noxious off-gases. A further
disadvantage of certain of these processes :Ls the need for a mult:Lplicity
of steps including precipitation, calcining, and the like.
Acco}dingly, it is the primary advantage of the invention to develop animproved solid state process for the preparation of pigmentary-quality
bismuth vanadate compounds.
It is a further ob~ect to provide such a process which substantially
eliminates the adverse color effects on the desired bright yellow color
of these compounds.
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Various other objects and advantages of this invention will become
apparent from the following descriptive material.
It has now been surprisingly found that by subjecting the calcined
bismuth vanadate compounds to a procedure where the compound is wet
ground in the presence of an alkaline material or is treated with the
alkaline material subsequent to wet grinding, the disadvantages of the
prior art approaches have been substantially eliminated. Thus, the
off-color is believed to be attributable to the presence of the excess
vanadium frequently utilized in order to insure complete bismuth reaction
and/or to the presence of lower valent vanadium, namely trivalent and
quadrivalent vanaditlm. The instant process thus serves to convert these
contaminants to the soluble and readily removable alkali vanadate form in
order to obtain desired color. In addition, the process allows Eor the
use of low cost raw materials and for relatively simple operation
particularly in the combined alkaline-wet grinding procedure. Finally,
the process is applicable to a wide variety of bismuth vanadate com-
pounds, including bismuth vanadate and bismuth vanadates containing a
broad range of bismuth and vanadium replacement ions. The key end result
is the preparation of bright yellow plgmentary bismuth vanadate com-
pounds.
Accordingly, the present invention relates to a process for the prepara-
tion of bismuth vanadate and bismuth vanadate-containing compounds
wherein the precursor materials are calcined at elevated temperatures,
the improvement comprising the steps o~ wet grinding the calcined
product, contacting the calcined product with suf~icien~ alkaline
material to provide a pH level of 7.0-13.0 and recovering the treated
product, said wet grinding of the calcined product being conducted either
in the presence of said alkaline material or prior to said contacting
with said alkaline material.
The bismuth vanadate compounds applicable for preparation according to
the instant process comprise bismuth vanadate and single phased bismuth
vanadate compounds resulting from the incorporatlon of various precursor
materials or the solubilization o~ various ADO~ compounds therein. These
compounds may be depicted by the general ~ormula
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AD04
wherein A represents trivalent bismuth alone or cation combina-
tions of bismuth and at least one other cation,
and D represents pentavalent vanadium alone or cation combinations
of vanadium and at least one other non-A cation, at least one of A
or D being a cation combination. The applicable cations are com-
patible with the pigmentary properties of the resulting product.
Typical bismuth replacement cations include alkaline
earth metals and ~inc, while typical vanadium replacement cations
include molybdenum and tungsten.
A sub-group within the above noted formula corresponds
to the formula
(Bi,E)(v,G)o4
wherein E is an alkaline earth metal, zinc or mixtures thereof,
and G is molybdenum, tungsten or mixtures thereof, the molar ratio
oE E:Bi being between 0.1 and 0.4 and the molar ratio of G:V
between 0 and 0.4. Molar ratios of 0.1-0.3 for each are prefer-
red. The (Bi,E) and (V,G) notations are to be understood as mean-
ing that bismuth is partly replaced by one or more E cations and
that vanadium can be partly replaced by one or more G cations.
The latter compounds are more fully described in the
European Patent Applica-tion No. 0239,526.
The pre-calcining and calcining operations are well-
known to those skilled in the art, as particularly identified in
certain of the aforementioned publications. The applicable pro-
cesses include solid state reactions at elevated temperatures
starting from the corresponding metal oxides. As noted, the usual
method is to calcine mixtures of oxides, or any salt which yields
the corresponding oxide by thermal decomposition, e.g., carbon-
ates, nitrates, oxalates, hydroxides, etc., in the proper
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ratios for the desired composition. Calcining temperatures vary from
about 300 to about 950C. The optimum temperature depends upon the
particular composition being prepared. Higher temperatures are preferred
in order to facilitate reaction and to assure a homogeneous product. A
critical upper limit for calcining temperatures is imposed by the
formatlon of a liquid phase.
The time of calcination is not crltical; times of 1 to 100 hours may beused, but from 4 to 48 hours are preferred. Longer times are required at
lower temperatures. Calcining times may be shortened and homogeneity of
the products improved by regrinding between periods of heatlng.
The improved process steps of the invention involve subjecting the
calcined product to wet grinding in the presence of an alkallne material
or wet grinding followed by alkallne treatment. Thus, subsequent to
calcining, the product i5 discharged and cooled to room temperature. Wet
milling will generally be conducted in a pebble, ball, microball or sand
mill for a period of time sufficient to achieve pigmentary particle size.
The alkaline material is added as an aqueous solution to provlde the wet
milling environment, The alkaline material will generally be introduced
at the onset of the milling operation, although it may also be added in
solution during milling such that it is in contact with the calcined
material for sufficient time to form the alkali vanadate.
An operable but less preferred approach involves s~irring the milled
material in an alkaline solution at room temperature for a sufficient
period of time for salt formation.
Applicable alkaline materials lnclude alkali metal hydroxides and
carbonates, preferably sodium and potassium materials, and alkaline earth
metal hydroxides, carbonates and oxides, preferably magnesium materials.
The alkaline materials are added in sufficient amount to provide a pH
value of from about 7.0-13.0 to the pigment-containing slurry, and
preferably a pH value of 9.5-12Ø
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Finishing operations for the resulting material will include filtration,
washing to remove soluble salts and drying, for example, at 100-110C.
Subsequent dry grinding may also be an option.
The resulting bismuth vanadate compounds exhibit quality pigmentary
properties, particularly the desired bright yellow color and high tinting
capability. They are highly suited for pigmenting a wide variety of high
molecular weight organic materials, including resins, oils and organic
polymers. They can be incorporated into lacquers, paints and printing
inks.
To improve certain pigment properties, the prepared compounds can
additionally by treated with texture-improving agents, for example with
long-chain aliphatic alcohols, esters, acids or salts thereof, amines,
amides, wa~es or resinous substances, such as abietic acid, hydrogenation
products, esters or salts thereof, further with nonionic, anionic or
cationic surface-active agents.
The following examples further illustrate the embodiments of the inven-tion. In these examples, all parts given are by weight unless otherwise
indicated.
Example 1: Bismuth oxide (46.6 g) and vanadium pentoxide (18.2 g) are wet
milled, dried and heated at 778C for four hours. The resulting calcined
material is thereafter introduced into a pebble mill together with
sufficient sodium hydroxide solution to provide a pH in the area oE 9.5
to the system and milling is conducted until pigmentary particle size is
attained. The resulting product is then washed and dried. The product
exhibits a bright yellow color.
Pigmentary qualities are determined utilizing rubout in an acrylic
lacquer and subsequent color readings utilizing a colorimeter. In each
case, 22.8 parts of dry pigment and 100 parts of above lacquer are
prepared as an ink dispersion, referred to as the masstone ink, and drawn
down. In order to assess color strength, 11.4 parts of pigment and 11.4
parts of pigmentary titanium dioxide are blended, a corresponding ink
dispersion (referred to as tint) is prepared and drawn down. The results
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noted below are obtained utili~ing L, a, b colorimeter measurements
wherein "L" refers to lightness, "a" refers to red-green ratio with "+a"
denoting redness and "-a" denoting greeness, and "b" re~ers to yellow-
blue ratio with "~b" denoting yellowness and "-b" denoting blueness.
Masstone Tint
L 82.2 88.3
a - 8.6 -ll.0
b ~50.1 ~42.9
These data thus indicate the quality pigmentary properties of the
resulting pigment.
Example 2: The following pigments are prepared according to the generalprocedure of Example 1.
Parts (in g)
Ex. 2b Ex. 2c Ex. 2d
. _
Bismuth subnitrate 40.15
(basic bismuth nitrate)
Bismuth oxide - 46.6 46.6
Vanadium pentoxide 9.10 18.2 18.2
Molybdic oxide 3.7 7.5 3.75
Calcining temp. (C) 667 778 778
Calcinlng time (hours) 4 4 4
pH value 9.5 9.5 9.5
Color of the bright bright bright
rssulting pigmentyellow yellow yeliow
Summarizing, it is seen that this invention provides an improved process
for preparing pigmentary bismuth vanadate compounds. Variations may be
made in procedures, proportions and materials without departing from the
scope of the invention as defined by the following claims.
