U.S. patent application number 09/388578 was filed with the patent office on 2002-05-16 for bismuth vanadate pigments comprising at least one metal fluoride coating.
Invention is credited to MRONGA, NORBERT, REISACHER, HANSULRICH, SEEGER, OLIVER, ZICKGRAF, REINHARD.
Application Number | 20020056402 09/388578 |
Document ID | / |
Family ID | 7879674 |
Filed Date | 2002-05-16 |
United States Patent
Application |
20020056402 |
Kind Code |
A1 |
SEEGER, OLIVER ; et
al. |
May 16, 2002 |
BISMUTH VANADATE PIGMENTS COMPRISING AT LEAST ONE METAL FLUORIDE
COATING
Abstract
Bismuth vanadate pigments comprising at least one coating
containing calcium fluoride, bismuth oxyfluoride or a lanthanide
fluoride or oxyfluoride or a mixture thereof are useful for
coloring paints, printing inks and plastics.
Inventors: |
SEEGER, OLIVER; (MANNHEIM,
DE) ; REISACHER, HANSULRICH; (MAXDORF, DE) ;
MRONGA, NORBERT; (DOSSENHEIM, DE) ; ZICKGRAF,
REINHARD; (WALDSEE, DE) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Family ID: |
7879674 |
Appl. No.: |
09/388578 |
Filed: |
September 2, 1999 |
Current U.S.
Class: |
106/479 ;
428/403 |
Current CPC
Class: |
C09C 1/0006 20130101;
C01P 2006/66 20130101; C09C 1/0015 20130101; C09C 3/063 20130101;
C01P 2006/62 20130101; Y10T 428/2991 20150115; C01P 2006/65
20130101; C01P 2002/52 20130101; Y10T 428/2993 20150115; C09C
2200/401 20130101 |
Class at
Publication: |
106/479 ;
428/403 |
International
Class: |
C04B 014/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 3, 1998 |
DE |
19840156.6 |
Claims
We claim:
1. Bismuth vanadate pigments comprising at least one coating
containing calcium fluoride, bismuth oxyfluoride or a lanthanide
fluoride or oxyfluoride or a mixture thereof.
2. Bismuth vanadate pigments as claimed in claim 1, further
comprising at least one coating containing a metal oxide.
3. Bismuth vanadate pigments as claimed in claim 1, further
comprising at least one coating containing an oxide or an oxide
hydrate of an alkaline earth metal, aluminum, silicon, tin,
titanium, zirconium, hafnium, niobium, tantalum, zinc or a
lanthanide metal or a mixed oxide of these metals or a mixture
thereof.
4. Bismuth vanadate pigments as claimed in claim 1, further
comprising at least one coating containing a metal phosphate.
5. Bismuth vanadate pigments as claimed in claim 1, further
comprising at least one coating containing an alkaline earth metal
phosphate, aluminum phosphate or zinc phosphate or a mixture
thereof.
6. Bismuth vanadate pigments as claimed in claim 1, further
comprising at least one coating containing a metal oxide and at
least one coating containing a metal phosphate.
7. Bismuth vanadate pigments as claimed in claim 1, further
comprising at least one coating containing a metal oxide and at
least one coating containing an alkaline earth metal phosphate,
aluminum phosphate or zinc phosphate or a mixture thereof.
8. A method of coloring paints, printing inks and plastics, which
comprises incorporating the bismuth vanadate pigments of claim 1
into said paints, printing inks and plastics.
Description
[0001] The present invention relates to bismuth vanadate pigments
comprising at least one coating containing calcium fluoride,
bismuth oxyfluoride or a lanthanide fluoride or oxyfluoride or a
mixture thereof.
[0002] This invention further relates to the use of these bismuth
vanadate pigments for coloring paints, printing inks and
plastics.
[0003] Bismuth vanadate pigments are well known. As well as the
pure BiVO.sub.4 pigment, there are a number of BiVO.sub.4 pigments
in which some of the metal and/or oxygen atoms are replaced by
other metals and/or nonmetals. These pigments are useful nontoxic
yellow pigments and are particularly suitable for coloring paints
and plastics. To improve their application properties, especially
their thermal stability, their weatherfastness and their resistance
to chemicals, bismuth vanadate pigments are frequently provided
with protective coats of metal oxides (including silicates) and/or
protective coats of phosphates with or without fluoride.
[0004] For instance, U.S. Pat. No. 4,063,956 discloses coating
monoclinic bismuth vanadate with a first metal oxide hydrate layer
(e.g., aluminum oxide hydroxide) and a second dense layer of
amorphous silicon dioxide. In U.S. Pat. No. 4,115,141, bismuth
vanadate is stabilized by coating with silicon dioxide or aluminum
phosphate.
[0005] Combined oxide coatings are also described in U.S. Pat. No.
4,455,174, where bismuth vanadate pigments of the composition
BiVO.sub.4.x Bi.sub.2MoO.sub.6.y Bi.sub.2WO.sub.6 (x=0.6-2.25,
y=0-0.1) are coated first with zirconium dioxide and then with
silicon dioxide. In U.S. Pat. No. 4,752,460, doped tetragonal
bismuth vanadate pigments of the type (Bi,A) (V,D)O.sub.4 (A=Mg,
Ca, Sr, Ba, Zn; D=Mo and/or W; molar ratio of A:Bi=0.1-0.4 and
D:V=0-0.4) are coated first with silicon dioxide and then with
aluminum oxide.
[0006] U.S. Pat. No. 5,123,965 describes coating doped tetragonal
bismuth vanadate pigments with aluminum phosphate, calcium
phosphate, titanium phosphate and mixtures of zinc phosphate and
the phosphate of aluminum, of magnesium, of zirconium, of titanium
or of calcium. Fluoride ions may be present during the coating with
aluminum phosphate.
[0007] Fluoridic metal oxide coatings based on silicon dioxide,
magnesium silicate and magnesium fluoride are finally known from
EP-A-271 813, where bismuth vanadate pigments of the formula
BiVO.sub.4.x Bi.sub.2MoO.sub.6 (x=0.2-0.25) are coated with this
mixed layer and additionally with a wax layer.
[0008] However, the known coatings do not always lead to bismuth
vanadate pigments having satisfactory properties.
[0009] It is an object of the present invention to provide bismuth
vanadate pigments having good application properties, especially
good stabilities, for example good weatherfastness.
[0010] We have found that this object is achieved by bismuth
vanadate pigments comprising at least one coating containing
calcium fluoride, bismuth oxyfluoride or a lanthanide fluoride or
oxyfluoride or a mixture thereof.
[0011] This invention also provides for the use of these bismuth
vanadate pigments for coloring paints, printing inks and
plastics.
[0012] The bismuth vanadate pigments of the invention may be based
on any known bismuth vanadate pigment, including those mentioned
above. Further examples of suitable base pigments are the doped
bismuth vanadate pigments described in EP-A-640 566 and DE-A-195 29
837.
[0013] The bismuth vanadate pigments of the invention are coated at
least with a metal fluoride layer consisting essentially of calcium
fluoride, bismuth oxyfluoride or a lanthanide fluoride or
oxyfluoride, preferably lanthanum fluoride, lanthanum oxyfluoride,
cerium fluoride, cerium oxyfluoride, yttrium fluoride or yttrium
oxyfluoride. The fluorides (and/or oxyfluorides) mentioned may be
present together in one and the same layer, but the separate
application of layers each containing only one fluoride is
preferred.
[0014] Particular preference is given to calcium fluoride layers
and bismuth oxyfluoride layers, although calcium fluoride layers
are preferably combined with further stabilizing coatings.
[0015] Thus, the metal fluoride coating of the invention may with
advantage be combined with metal oxide coatings and/or metal
phosphate coatings, in which case combinations of metal fluoride
layers and metal oxide layers are preferred. In general, the layers
are applied sequentially, but a certain degree of intermixing of
the layers cannot be ruled out, especially in the case of the same
layer type (fluoride, oxide or phosphate). Preferably, the metal
fluoride coating(s) is or are applied to the bismuth vanadate
pigment as the innermost layer in the case of multiple coating.
However, the sequence of coats may also be changed.
[0016] Preferred materials for the metal oxide coatings are oxides
and oxide hydrates of alkaline earth metals, especially magnesium,
calcium, strontium and barium, of aluminum, silicon, tin, titanium,
zirconium, hafnium, niobium, tantalum, zinc and of lanthanide
metals, especially lanthanum, cerium and yttrium. Mixed oxides of
these metals, especially the metal silicates, are particularly
suitable. These compounds may likewise be present together in one
and the same layer.
[0017] Examples of particularly preferred oxides are aluminum
oxide, aluminum oxide hydrate, cerium dioxide and silicon dioxide
and also the calcium silicates CaSiO.sub.3 and Ca.sub.2SiO.sub.5,
of which CaSiO.sub.3 and silicon dioxide are most preferred. Where
a metal oxide layer is present as outer layer, a silicon dioxide
layer is particularly favorable.
[0018] Preferred materials for the metal phosphate coatings are the
phosphates, especially the orthophosphates, of alkaline earth
metals, especially magnesium and calcium, of zinc and of aluminum,
which may also be present mixed in one and the same layer, this
being preferred for the alkaline earth metals and zinc.
[0019] The bismuth vanadate pigments of the invention may have any
number of coats. The number of coats is preferably within the range
from one to four. Examples of particularly preferred coats are
single coats of bismuth oxyfluoride and combination coats of
calcium fluoride, calcium metasilicate and silicon dioxide or of
bismuth oxyfluoride, calcium fluoride, calcium metasilicate and
silicon dioxide. Further suitable combinations may be found in the
Examples.
[0020] Depending on the particle size and the specific surface area
of the bismuth vanadate used, the stabilized bismuth vanadate
pigments of the invention generally contain from 2 to 40% by
weight, preferably from 4 to 20% by weight of coating material,
based on the weight of the coated pigment. The fluoride content is
generally within the range from 0.05 to 10% by weight, preferably
within the range from 1 to 5% by weight, based on the weight of the
coated pigment.
[0021] The bismuth vanadate pigments of the invention are notable
for their high stability, especially their very good
weatherfastness and low photochromism. Photochromism is the
reversible transformation of a compound into another of different
color (absorption spectrum) due to visible or ultraviolet light.
The measure of photochromism employed herein is the CIELAB .DELTA.E
total color difference. The bismuth vanadate pigments of the
invention also have excellent acid stability when coated with a
bismuth oxyfluoride layer.
[0022] However, the bismuth vanadate pigments of the invention are
not just convincing with regard to their stability, but
surprisingly also have excellent color properties, especially high
chroma and lightness.
[0023] To prepare the bismuth vanadate pigments of the invention,
the coatings are advantageously precipitated wet-chemically onto
the selected base pigment.
[0024] To deposit the metal fluoride layer, a suspension of the
substrate (which can be an uncoated bismuth vanadate pigment or a
bismuth vanadate pigment already coated with metal oxide or metal
phosphate), a solution of a calcium, bismuth or lanthanide metal
salt and a solution comprising fluoride ions are thoroughly mixed,
preference being given to the use of aqueous solutions and
suspensions.
[0025] Processwise it is possible to proceed in various ways: The
substrate suspension can be introduced as initial charge and the
calcium, bismuth or lanthanide metal salt solution and the fluoride
ion solution added at the same time. However, it is also possible
to introduce the fluoride ion solution as initial charge together
with the substrate suspension and to add the calcium, bismuth or
lanthanide metal salt solution, or vice versa to introduce the
calcium, bismuth or lanthanide metal salt solution as initial
charge together with the substrate suspension and to add the
fluoride ion solution.
[0026] The pH of the mixture during the addition of the calcium,
bismuth or lanthanide metal salt solution and/or the fluoride ion
solution is advantageously maintained within the range from 2 to
11, preferably within the range from 5 to 9.
[0027] The temperature during the precipitation can be within the
range from room temperature to the boiling point of the mixture
(reflux temperature). A temperature within the range from 20 to
80.degree. C. is preferred.
[0028] When coating with metal oxide layers is desired, it is
possible to proceed in a conventional manner by mixing the
substrate suspension (uncoated or precoated bismuth vanadate
pigment) with a preferably aqueous solution of a salt of the
respective metal and precipitating the oxide or oxide hydrate onto
the substrate while maintaining a pH which is customarily within
the range from 3 to 10, preferably within the range from 5 to
9.
[0029] Metal phosphate layers can be similarly deposited in a
likewise known manner by mixing the substrate suspension with the
corresponding metal salt solution(s) and a phosphate ion solution
while maintaining a pH within the range from 3 to 10 in general,
but preferably within the range from 5 to 9.
[0030] To prepare the metal salt solutions required for the
precipitation reactions, it is possible in principle to use any
salt of the metals with inorganic or organic acids which is soluble
in water (by addition of an acid, if necessary). Examples of
preferred metal salts are calcium nitrate, calcium sulfate, calcium
chloride, magnesium nitrate, magnesium sulfate, magnesium chloride,
aluminum sulfate, aluminum nitrate, sodium aluminate, aluminum
acetate, alkali metal silicates such as sodium silicate and
potassium silicate, zinc nitrate, zinc sulfate, zinc chloride,
bismuth nitrate, cerium nitrate, cerium ammonium nitrate, cerium
sulfate, cerium chloride, lanthanum nitrate, lanthanum sulfate,
lanthanum chloride, yttrium nitrate, yttrium sulfate and yttrium
chloride.
[0031] The fluoride ion solutions are preferably prepared from
alkali metal fluorides, ammonium fluorides or complex
fluoride-containing salts. Examples of particularly suitable
fluorides are: sodium fluoride, potassium fluoride, potassium
hydrogendifluoride, ammonium fluoride, ammonium hydrogenfluoride,
sodium tetrafluoroborate and ammonium tetrafluoroborate.
[0032] Examples of preferred phosphate ion solutions are solutions
of alkali metal phosphates and hydrogenphosphates, especially
sodium phosphate and potassium phosphate, and especially phosphoric
acid.
[0033] After the last layer has been deposited, or on completion of
the last addition, the suspension is generally stirred for from 1
to 5 h. The coated bismuth vanadate pigment may then, optionally
after cooling to room temperature, be isolated in a conventional
manner by filtration, washing and drying.
[0034] If desired, the coated bismuth vanadate pigment may be
subjected to a grinding operation. Preference is given to a
wet-grinding operation, which is preferably inserted after the
washing of the pigment.
[0035] Tinctorially particularly useful bismuth vanadate pigments
of high chroma and lightness are obtained on subjecting the pigment
to a thermal treatment.
[0036] The point in time at which the thermal treatment is carried
out is generally immaterial. It is possible to heat-treat either
the uncoated base pigment in a conventional manner following its
synthesis or the coated pigment after drying.
[0037] To heat-treat the dried coated pigment, it is generally
heated to >300.degree. C., preferably to 350-700.degree. C., for
0.5-20 h.
[0038] The heat-treated coated pigment is advantageously then
subjected to a wet-grinding operation. In this case, there is of
course no need to grind the pigment after coating.
[0039] If desired, the bismuth vanadate pigments according to the
invention may be additionally coated with organic additives in
order, for example, that their dispersibility in paint systems may
be improved.
[0040] Bismuth vanadate pigments of the invention are very useful
for coloring paints, printing inks and plastics.
EXAMPLES
[0041] Preparation and assessment of bismuth vanadate pigments of
the invention
[0042] The tinctorial properties and the photochromism were
assessed on paint films prepared as follows. A mixture of 15 g of
each pigment and 35 g of alkyd-melamine baking varnish was shaken
on a Skandex machine for 60 min with 70 g of glass beads (1 mm in
diameter), then hidingly applied to sheet aluminum bearing a black
and white coating, flashed off and baked at 130.degree. C. for 30
min.
[0043] To evaluate the photochromism, the paint films were each
half-covered with a metal stencil and then irradiated for 2 h with
an NXe 1500B xenon lamp (from Original, Hanau). The .DELTA.E values
were determined by measuring the irradiated and nonirradiated parts
of the paint films using a Zeiss RFC 16 spectrophotometer after
storage of the sample in the dark for 30 minutes.
[0044] The weatherfastnesses were evaluated in the masstone by
means of accelerated weathering for 80 days in a Xenotest 1200 with
turnaround run (from Heraeus) in accordance with DIN 53387. The
evaluation was undertaken in accordance with DIN EN 20105-A02 (gray
scale for assessing change in color). The assessment scale ranges
from 0 (miserable weatherfastness) to 5 (excellent
weatherfastness).
[0045] To determine the CIELAB values of hue H [.degree.], chroma
C* and lightness L* , the paint films obtained were measured using
the abovementioned spectrophotometer. The values obtained are
tabulated below.
Example 1
[0046] a) To a mixture of 1000 g of water, 418 g of aqueous sodium
vanadate solution (7% by weight of vanadium) and 5.5 g of 85%
strength by weight phosphoric acid were added with stirring 1130 g
of aqueous bismuth nitrate solution (11.05% by weight of bismuth)
over 30 min. The pH of the mixture was then adjusted with 30%
strength by weight sodium hydroxide solution to 4.5 over 1 h and
then with 5% strength by weight sodium hydroxide solution to 5 over
10 min.
[0047] The resulting suspension was then heated to 95.degree. C.
while maintaining pH 5. After about 40 min, the suspension turned
deep yellow, and the pH rose briskly to 8.1. The suspension was
stirred at 95.degree. C. to constant pH.
[0048] After cooling down to room temperature, the product was
filtered off, washed salt-free and kept in the form of a press cake
(solids content: from 20 to 30% by weight; in the present case:
23.8% by weight) until needed for further processing.
[0049] The bismuth vanadate pigment obtained had a bismuth content
of 63.0% by weight and a vanadium content of 14.9% by weight.
[0050] b) The bismuth vanadate pigment obtained in a) was, after
drying, heat-treated at 450.degree. C. for 1 h. Thereafter the
pigment was subjected to a wet-grinding operation in the presence
of water to an average particle size of 0.8 .mu.m and dried at
100.degree. C. in a through-circulation drying cabinet.
[0051] The uncoated bismuth vanadate pigment obtained scored a
rating of 3 in the accelerated weathering test; its photochromism
.DELTA.E was 2.5.
Example 2
[0052] A suspension in 875 ml of water of 1100 g of a bismuth
vanadate press cake prepared similarly to Example 1a) (solids
content 23.8% by weight) was admixed at room temperature with a
solution of 28.7 g of potassium fluoride in 325 ml of water and a
solution of 116 g of calcium nitrate tetrahydrate in 1 l of water
which were added dropwise concurrently over 2.5 h with stirring. On
completion of the addition of the solutions the suspension pH was
5.8.
[0053] The suspension was heated to 80.degree. C. and 1050 ml of
sodium silicate solution (15 g of Si/l) were added over 1.5 h. The
pH rose to 8.2.
[0054] After stirring at 80.degree. C. for one hour and subsequent
cooling down to room temperature, the coated pigment was filtered
off, washed with water, dried at 110.degree. C. in a
through-circulation drying cabinet and heat-treated at 400.degree.
C. for 1 h. Thereafter the pigment was subjected to a wet-grinding
operation to an average particle size of 0.8 .mu.m and dried at
100.degree. C. in a through-circulation drying cabinet.
[0055] The resulting CaF.sub.2/CaSiO.sub.3/SiO.sub.2 coated bismuth
vanadate pigment had a calcium content of 4.7% by weight, a silicon
content of 4.3% by weight and a fluoride content of 2.7% by weight
and scored a rating of 5 in the accelerated weathering test; its
photochromism .DELTA.E was 0.6.
Example 3
[0056] To a suspension in 450 ml of water of 117 g of a bismuth
vanadate pigment prepared similarly to Example 1b) were added 10.8
g of potassium fluoride. The stirred suspension was heated to
80.degree. C. and brought to pH 6 by addition of 10% strength by
weight nitric acid and 55 g of aqueous bismuth nitrate solution
(23.7% by weight of bismuth) were added over 45 min, during which
the pH was maintained at 6 by the simultaneous addition of 30%
strength by weight sodium hydroxide solution.
[0057] After stirring at 80.degree. C. for one hour and
subsequently cooling down to room temperature, the coated pigment
was filtered off, washed with water, subjected to a wet-grinding
operation to an average particle size of 0.8 .mu.m and dried in a
through-circulation drying cabinet at 100.degree. C.
[0058] The resulting BiOF coated bismuth vanadate pigment had a
fluoride content of 0.84% by weight and scored a rating of 4-5 in
the accelerated weathering test; its photochromism .DELTA.E was
0.7.
Example 4
[0059] A suspension in 220 ml of water of 272 g of a bismuth
vanadate press cake prepared similarly to Example 1a) (solids
content 27.5% by weight) was admixed at room temperature with a
solution of 8.2 g of potassium fluoride in 325 ml of water and a
solution of 33 g of calcium nitrate tetrahydrate in 325 l of water
which were added dropwise over 2 h with stirring. On completion of
the addition of the solutions the suspension pH was 5.8.
[0060] The suspension was refluxed for two hours and then cooled
down to 80.degree. C., at which point 79 ml of a 6.75% strength by
weight aqueous zinc nitrate solution and 78 ml of 3.4% strength by
weight phosphoric acid were added in parallel over 30 min, during
which the pH was maintained at 5.8 by simultaneous addition of 10%
strength by weight aqueous sodium carbonate solution.
[0061] After stirring at 80.degree. C. for one hour and subsequent
cooling down to room temperature, the coated pigment was filtered
off, washed with water, dried at 110.degree. C. in a
through-circulation drying cabinet and heat-treated at 400.degree.
C. for 1 h. Thereafter the pigment was subjected to a wet-grinding
operation to an average particle size of 0.8 .mu.m and dried at
110.degree. C. in a through-circulation drying cabinet.
[0062] The resulting CaF.sub.2/(Ca,Zn).sub.3(PO.sub.4).sub.2 coated
bismuth vanadate pigment had a calcium content of 4.1% by weight, a
zinc content of 2.1% by weight, a phosphorus content of 1.0% by
weight and a fluoride content of 3.0% by weight and scored a rating
of 4-5 in the accelerated weathering test; its photochromism
.DELTA.E was 1.1.
Example 5
[0063] A suspension in 220 ml of water of 270 g of a bismuth
vanadate press cake prepared similarly to Example 1a) (solids
content 27.5% by weight) was admixed at room temperature with a
solution of 8.2 g of potassium fluoride in 325 ml of water and a
solution of 33 g of calcium nitrate tetrahydrate in 325 ml of water
which were added dropwise concurrently over 2 h with stirring. On
completion of the addition of the solutions the suspension pH was
5.8.
[0064] The suspension was heated to reflux temperature and 150 ml
of sodium silicate solution (15 g of Si/l) were added over 1.5 h.
The pH rose to 6.4.
[0065] The suspension was subsequently stirred at 80.degree. C. for
half an hour and brought to pH 5.8 by addition of 25% strength by
weight nitric acid, at which point 79 ml of a 6.75% strength by
weight aqueous zinc nitrate solution and 78 ml of 3.4% strength by
weight phosphoric acid were added in parallel over 30 min, during
which the pH was maintained at 5.8 by simultaneous addition of 10%
strength by weight aqueous sodium carbonate solution.
[0066] After stirring at 80.degree. C. for one hour and subsequent
cooling down to room temperature, the coated pigment was filtered
off, washed with water, dried at 110.degree. C. in a
through-circulation drying cabinet and heat-treated at 450.degree.
C. for 1 h. Thereafter the pigment was subjected to a wet-grinding
operation to an average particle size of 0.8 .mu.m and dried at
100.degree. C. in a through-circulation drying cabinet.
[0067] The resulting
CaF.sub.2/CaSiO.sub.3/SiO.sub.2/Zn.sub.3(PO.sub.4).su- b.2 coated
bismuth vanadate pigment had a calcium content of 2.8% by weight, a
zinc content of 1.8% by weight, a phosphorus content of 0.8% by
weight and a fluoride content of 2.8% by weight and scored a rating
of 4-5 in the accelerated weathering test; its photochromism
.DELTA.E was 1.1.
Example 6
[0068] 100 g of a bismuth vanadate pigment prepared similarly to
Example 1b) were suspended in 725 ml of water, the suspension was
heated to 80.degree. C. with stirring, and 110 g of a 7.5% strength
by weight aqueous aluminum nitrate solution were added over 40 min,
during which the pH was maintained at 6.2 by simultaneous addition
of 10% strength by weight aqueous sodium carbonate solution.
[0069] After cooling to 70.degree. C., a solution of 10.9 g of
potassium fluoride in 440 ml of water and a solution of 44.4 g of
calcium nitrate tetrahydrate in 440 ml of water were added dropwise
in parallel with stirring over 90 min. On completion of the
addition of the solutions the suspension pH was 6.2.
[0070] Following renewed heating to 80.degree. C., 106 g of a 6.75%
strength by weight aqueous zinc nitrate solution and 104 g of 3.4%
strength by weight phosphoric acid were added in parallel over 35
min, during which the pH was maintained at 5.8 by simultaneous
addition of 10% strength by weight aqueous sodium carbonate
solution.
[0071] After stirring at 80.degree. C. for half an hour and
subsequent cooling down to room temperature, the coated pigment was
filtered off, washed with water, subjected to a wet-grinding
operation to an average particle size of 0.8 .mu.m and dried at
110.degree. C. in a through-circulation drying cabinet.
[0072] The resulting
AlO(OH)/CaF.sub.2/(Ca,Zn).sub.3(PO.sub.4).sub.2 coated bismuth
vanadate pigment had an aluminum content of 0.9% by weight, a
calcium content of 3.7% by weight, a zinc content of 1.9% by
weight, a phosphorus content of 1.0% by weight and a fluoride
content of 3.0% by weight and scored a rating of 4-5 in the
accelerated weathering test; its photochromism .DELTA.E was
1.1.
Example 7
[0073] 276 g of a bismuth vanadate press cake prepared similarly to
Example 1a) (solids content 27.1% by weight) were suspended in 300
ml of water, the suspension was heated with stirring to reflux
temperature, and 300 ml of sodium silicate solution (15 g of Si/l)
were added over 1 h, during which the pH was maintained at 8.8 by
simultaneous addition of 25% strength by weight nitric acid.
[0074] After refluxing with stirring for one hour and subsequent
cooling to 55.degree. C., a solution of 8.2 g of potassium fluoride
in 325 ml of water and a solution of 33.2 g of calcium nitrate
tetrahydrate in 325 ml of water were added dropwise in parallel
with stirring over 75 min. On completion of the addition of the
solutions the suspension pH was 5.5.
[0075] After stirring at 55.degree. C. for one hour and cooling
down to room temperature, the coated pigment was filtered off,
washed with water, dried at 110.degree. C. in a through-circulation
drying cabinet and heat-treated at 450.degree. C. for 1 h.
Thereafter the pigment was subjected to a wet-grinding operation to
an average particle size of 0,8 .mu.m and dried at 100.degree. C.
in a through-circulation drying cabinet.
[0076] The resulting SiO.sub.2/CaF.sub.2 coated bismuth vanadate
pigment had a calcium content of 2.8% by weight, a silicon content
of 4.4% by weight and a fluoride content of 2.6% by weight and
scored a rating of 4-5 in the accelerated weathering test; its
photochromism .DELTA.E was 1.2.
Example 8
[0077] To a suspension in 300 ml of water of 276 g of a bismuth
vanadate press cake prepared similarly to Example 1a) (solids
content 27.1% by weight) were added a solution of 0.8 g of
potassium fluoride in 50 ml of water, a solution of 3.3 g of
calcium nitrate tetrahydrate in 50 ml of water and 300 ml sodium
silicate solution (15 g of Si/l) dropwise in parallel at room
temperature with stirring over 60 min, during which the pH was
maintained at 8.8 by simultaneous addition of 25% strength by
weight nitric acid.
[0078] After heating to reflux temperature, stirring at that
temperature for one hour and cooling down to room temperature, the
coated pigment was filtered off, washed with water, dried at
110.degree. C. in a through-circulation drying cabinet and
heat-treated at 450.degree. C. for 1 h. Thereafter the pigment was
subjected to a wet-grinding operation to an average particle size
of 0.8 .mu.m and dried at 100.degree. C. in a through-circulation
drying cabinet.
[0079] The resulting CaF.sub.2/CaSiO.sub.3/SiO.sub.2 coated bismuth
vanadate pigment had a calcium content of 0.74% by weight, a
silicon content of 4.6% by weight and a fluoride content of 0.1% by
weight and scored a rating of 4-5 in the accelerated weathering
test; its photochromism .DELTA.E was 1.1.
Example 9
[0080] a) To a mixture of 1000 g of water, 411 g of aqueous sodium
vanadate solution (7% by weight of vanadium) and 10 g of 85%
strength by weight phosphoric acid were added with stirring
initially over 60 min 488 g of aqueous bismuth nitrate solution
(24% by weight of bismuth) and then 2.2 g of calcium hydroxide and
2.3 g of zinc oxide.
[0081] The pH of the mixture was then adjusted with 30% strength by
weight sodium hydroxide solution to 4.5 over 2 h and subsequently
with 5% strength by weight sodium hydroxide solution to 4.7 over 6
min.
[0082] The resulting suspension was then heated to 95.degree. C.
while maintaining pH 4.7. After about 2 h, the suspension turned
deep yellow, and the pH rose briskly to 7.9. The suspension was
stirred at 95.degree. C. to constant pH.
[0083] After cooling down to room temperature, the product was
filtered, washed salt-free and kept in the form of a press cake
(solids content: from 20 to 35% by weight; in the present case:
28.2% by weight) until needed for further processing.
[0084] The doped bismuth vanadate pigment obtained had a bismuth
content of 61.0% by weight, a vanadium content of 14.8% by weight,
a calcium content of 0.6% by weight, a zinc content of 0.9% by
weight and a phosphorus content of 0.8% by weight.
[0085] b) The doped bismuth vanadate pigment obtained in a) was
after drying heat-treated at 450.degree. C. for 1 h. Thereafter the
pigment was subjected to a wet-grinding operation in the presence
of water to an average particle size of 0.8 .mu.m and dried at
100.degree. C. in a through-circulation drying cabinet.
[0086] The uncoated bismuth vanadate pigment obtained scored a
rating of 3-4 in the accelerated weathering test.
Example 10
[0087] A suspension in 700 ml of water of 647 g of a doped bismuth
vanadate press cake prepared similarly to Example 9a) (solids
content 30.9% by weight) was admixed at room temperature with a
solution of 21.9 g of potassium fluoride in 325 ml of water and a
solution of 89 g of calcium nitrate tetrahydrate in 900 ml of water
which were added dropwise over 75 min with stirring. On completion
of the addition of the solutions the suspension pH was 7.1.
[0088] The suspension was heated to reflux temperature and 800 ml
of sodium silicate solution (15 g of Si/l) were added over 1 h. The
pH rose to 8.2.
[0089] After stirring at that temperature for half an hour and
subsequent cooling down to room temperature, the coated pigment was
filtered off, washed with water, dried at 110.degree. C. in a
through-circulation drying cabinet and heat-treated at 450.degree.
C. for 1 h. Thereafter the pigment was subjected to a wet-grinding
operation to an average particle size of 0.8 .mu.m and dried at
100.degree. C. in a through-circulation drying cabinet.
[0090] The resulting CaF.sub.2/CaSiO.sub.3/SiO.sub.2 coated doped
bismuth vanadate pigment had a calcium content of 5.3% by weight, a
silicon content of 4.0% by weight and a fluoride content of 2.5% by
weight and scored a rating of 5 in the accelerated weathering
test.
Example 11
[0091] A suspension in 1200 ml of water of 647 g of a doped bismuth
vanadate press cake prepared similarly to Example 9a) (solids
content 30.9% by weight) was admixed at room temperature with a
solution of 4.4 g of potassium fluoride in 325 ml of water and a
solution of 8.7 g of calcium nitrate tetrahydrate in 325 ml of
water which were added dropwise over 60 min with stirring. On
completion of the addition of the solutions the suspension pH was
7.0.
[0092] The suspension was heated to reflux temperature and 360 ml
of sodium silicate solution (15 g of Si/l) were added over 50 min.
The pH rose to 7.9.
[0093] Then 219 g of a 7.5% strength by weight aqueous aluminum
nitrate solution were added over 45 min, during which the pH was
maintained at 6.1 by simultaneous addition of 10% strength by
weight aqueous sodium carbonate solution.
[0094] After half an hour's stirring at reflux temperature, 164 g
of a 5.2% strength by weight aqueous calcium nitrate solution and
157 g of 3.4% strength by weight phosphoric acid were added over 45
min, during which the pH was maintained at 5.8 by simultaneous
addition of 10% strength by weight aqueous sodium carbonate
solution.
[0095] After renewed half an hour's stirring at reflux temperature,
212 g of a 6.75% strength by weight zinc nitrate solution and 207 g
of 3.4% strength by weight phosphoric acid were finally added,
during which the pH was in turn maintained at 5.8 by simultaneous
addition of 10% strength by weight aqueous sodium carbonate
solution.
[0096] After a concluding half an hour's stirring at reflux
temperature and cooling down to room temperature, the coated
pigment was filtered off, washed with water, dried at 110.degree.
C. in a through-circulation drying cabinet and heat-treated at
500.degree. C. for 1 h. Thereafter the pigment was subjected to a
wet-grinding operation to an average particle size of 0.8 .mu.m and
dried at 100.degree. C. in a through-circulation drying
cabinet.
[0097] The resulting
CaF.sub.2/SiO.sub.2/AlO(OH)/Ca.sub.3(PO.sub.4).sub.2/-
Zn.sub.3(PO.sub.4).sub.2 coated doped bismuth vanadate pigment had
a calcium content of 2.1% by weight, a silicon content of 1.4% by
weight, an aluminum content of 0.9% by weight, a zinc content of
2.9% by weight, a phosphorus content of 2.1% by weight and a
fluoride content of 0.6% by weight and scored a rating of 4-5 in
the accelerated weathering test.
Example 12
[0098] 403 g of a doped bismuth vanadate press cake prepared
similarly to Example 9a) (solids content 24.8% by weight) were
suspended in 400 ml of water, the suspension was heated to
80.degree. C. with stirring, and 103 g of a 5.2% by weight aqueous
calcium nitrate solution and 98 g of a 3.4% strength by weight
phosphoric acid were added dropwise in parallel over 30 min, during
which the pH was maintained at 5.8 by simultaneous addition of a
10% strength by weight aqueous sodium carbonate solution.
[0099] After half an hour's stirring and subsequent cooling to
55.degree. C., a solution of 7.8 g of potassium fluoride in 325 ml
of water and a solution of 33 g of calcium nitrate tetrahydrate in
325 ml of water were added dropwise in parallel over 45 min. On
completion of the addition of the solutions the pH was 7.1.
[0100] The suspension was heated to reflux temperature and 300 ml
of sodium silicate solution (15 g of Si/l) were added over 1 h. The
pH rose to 8.3.
[0101] After a concluding half an hour's stirring at reflux
temperature and cooling down to room temperature, the coated
pigment was filtered off, washed with water, dried at 110.degree.
C. in a through-circulation drying cabinet and heat-treated at
450.degree. C. for 1 h. Thereafter the pigment was subjected to a
wet-grinding operation to an average particle size of 0.8 .mu.m and
dried at 100.degree. C. in a through-circulation drying
cabinet.
[0102] The resulting
Ca.sub.3(PO.sub.4).sub.2/CaF.sub.2/CaSiO.sub.3/SiO.su- b.2 coated
doped bismuth vanadate pigment had a calcium content of 5.8% by
weight, a silicon content of 3.4% by weight, a phosphorus content
of 1.5% by weight and a fluoride content of 2.0% by weight and
scored a rating of 5 in the accelerated weathering test.
Example 13
[0103] 50 g of a doped bismuth vanadate pigment prepared similarly
to Example 9a) and then dried were heat-treated at 500.degree. C.
for 1 h. The cooled pigment was then subjected to a wet-grinding
operation in 365 ml of water in the presence of glass balls (0.8 mm
in diameter) and then, after removal of the glass balls, admixed
with a further 400 ml of water.
[0104] To this suspension were added 0.78 g of potassium fluoride.
After a pH of 6 had been set by addition of 10% strength by weight
nitric acid, 11.6 g of bismuth nitrate solution (23.8% by weight of
bismuth) were added at room temperature over 20 min, during which
the pH was maintained at 6 by simultaneous addition of 10% strength
by weight aqueous sodium carbonate solution.
[0105] After stirring for one hour a solution of 2.73 g of
potassium fluoride in 150 ml of water and a solution of 11.1 g of
calcium nitrate tetrahydrate in 150 ml of water were added dropwise
in parallel at room temperature with stirring over 30 min. On
completion of the addition of the solutions the suspension pH was
5.4.
[0106] The suspension was heated to 80.degree. C. and 100 ml of
sodium silicate solution (15 g of Si/l) were added over 1 h. The pH
rose to 8.2.
[0107] After subsequent stirring at 80.degree. C. for one hour and
cooling down to room temperature, the coated pigment was filtered
off, washed with water, subjected to a wet-grinding operation to an
average particle size of 0.8 .mu.m and dried in a
through-circulation drying cabinet at 100.degree. C.
[0108] The resulting BiOF/CaF.sub.2/CaSiO.sub.3/SiO.sub.2 coated
doped bismuth vanadate pigment had a calcium content of 2.7% by
weight, a silicon content of 2.1% by weight and a fluoride content
of 1.6% by weight and scored a rating of 4-5 in the accelerated
weathering test.
1TABLE Colorimetric data of bismuth vanadate pigments prepared
Example Hue [.degree. C.] C* L* 1a 92.9 87.7 81.7 1b 93.5 98.2 87.7
2 93.6 99.1 88.9 3 93.5 99.3 88.3 4 93.4 99.3 88.9 5 93.4 98.8 88.4
6 93.4 100.1 88.9 7 93.4 98.7 88.3 8 93.0 99.9 89.0 9a 91.3 88.2
82.0 9b 92.6 97.7 87.2 10 92.6 100.1 88.7 11 92.4 100.0 87.7 12
92.5 100.0 88.4 13 92.9 100.3 88.4
* * * * *