Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BASF Aktiengesellschaft 950283 O.Z. 0050/47376
Humidity-resistant bluish luster pigments
5 The present invention relates to novel, humidity-resistant bluish
luster pigments based on titania-coated platelets heated in a
reducing atmosphere, obtainable by reaction of the reduced
platelets with a silane of the general formula I
RaSiXb
where:
R is a Cl-C10-alkyl radical substituted in the ~-position by a
glycidoxy group, by an amino group, by a hydroxyl group or by
a monoalkylamino group or an alkoxy radical whose alkyl
chains may each contain up to 10 carbon atoms and may be
interrupted by from 1 to 5 ether oxygen atoms or imino
groups, the radicals R for a > 1 being identical or
different;
X is a Cl-C4-alkoxy;
25 a is 1 or 2; and
b is 2 or 3, subject to the proviso that a + b = 4.
The invention also relates to a process for producing these
30 pigments and to their use for coloring paints, inks, including
printing inks, plastics, glasses, ceramic products and decorative
cosmetic preparations.
Reduced titania-coated mica pigments whose TiO2 coating includes
35 reduced titanium species (oxidation state of the titanium < 4 to
2) or has been completely converted into these reduced species
have been known for some time as "dark" pearl luster pigments for
the blue to black spectrum. Particularly bluish luster pigments
are described in EP-A-332 071 and DE-A-195 11 697, which was
40 unpublished at the priority date of the present invention. These
pigments are notable for good hiding, high color strength and
high luster and are particularly interesting for automotive
finishes. Frequently, however, they lack satisfactory humidity
resistance.
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DE-A-43 21 005 discloses unreduced, TiO2-coated mica pigments
rendered suitable for use in waterborne paint systems by coating
with a layer of the oxides of silicon, aluminum and cerium and in
some cases also zirconium and the hydrolysis product of a
5 zirconium aluminate, of a metal acid ester or of an
organofunctional silane as organic coupling reagent.
It is an object of the present invention to provide
humidity-resistant bluish luster pigments which are based on
10 reduced titania-coated silicate platelets and have advantageous
application properties.
We have found that this object is achieved by the luster pigments
1~ defined at the beginning.
The invention also relates to the thereby defined process for
producing these luster pigments.
20 The invention further provides the use of the above-defined
bluish luster pigments for coloring paints, inks, including
printing inks, plastics, glasses, ceramic products and decorative
cosmetic preparations.
25 Suitable platelet-shaped silicatic substrate materials for the
bluish luster pigments of the present invention include in
particular light-colored or white micas, particularly preferably
flakes of preferably wet-ground muscovite. It is of course also
possible to use other natural micas, such as phlogopite or
30 biotite, artificial micas, talc and glass flakes.
The silicatic platelets are coated with a layer which consists
essentially of titanium dioxide and may contain minor proportions
35 (generally < 5 % by weight) of further, preferably colorless,
metal oxides such as zirconium dioxide, tin dioxide, aluminum
oxide and silicon dioxide.
These pigments are generally known and commercially available
40 under the names Iriodin~ (E. Merck, Darmstadt), Flonac~ ~Kemira
Oy, Pori, Finland) or Mearlin~ (Mearl Corporation, Ossining, New
York).
The size of the silicate platelets is not critical per se and can
45 be adapted to the particular application. Typically, the
platelets have average largest diameters of from about 1 to 200
~m, in particular from about 5 to 100 ~m, and thicknesses of from
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about 0.1 to 1 ~m, in particular about 0.5 ~m. Their specific free
surface area (BET) is customarily within the range from 1 to 15
m2/g, in particular from 3 to 12 m2/g.
5 The thickness of the TiO2 layer determines the reflection color of
the substrate material and is preferably within the range from 50
to 100 nm (silver) or from 300 to 340 nm (bluei optical layer
thicknesses).
To produce the luster pigments of the invention, the
titania-coated silicate platelets serving as substrate material
have been heated in a reducing gas atmosphere.
15 Examples of suitable reducing gases include ammonia gas,
hydrogen, volatile hydrocarbons (especially Cl C4-alkanes) and
mixtures thereof. All the gases are preferably used in a mixture
with inert gases such as nitrogen (cf. DE-A-195 11 697,
unpublished at the priority date of the present invention, and
20 the references cited therein, which include EP-A-322 071).
Preferred reducing gases are ammonia gas and mixtures of ammonia
gas with volatile hydrocarbons such as methane, ethane and/or
propane, for which a volume ratio of from about 95:5 to 70:30 is
25 advisable. The proportion of the particularly preferred reducing
gas/inert gas mixtures which is accounted for bv nitrogen is
preferably, respectively, up to 90 % by volume and within the
range from 10 to 60 % by volume.
30 Suitable temperatures for the reduction are preferably within the
range from 750 to 850~C when ammonia gas is used and preferably
> 800 to 900~C when ammonia gas/hydrocarbon mixtures are used.
35 The reduction leads to the formation of reduced titanium species
(lower titanium oxides such as Ti305, Ti2C3 down to Tio, titanium
oxynitrides and also titanium nitride), which, owing to their
blue absorption color, combine with the silvery- or
blue-reflecting substrate platelets to produce particularly
intensive bluish luster pigments.
The reduced titania-coated mica pigments are common knowledge and
are also commercially obtainable under the name of Paliocrom~
(BASF, Ludwigshafen).
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The humidity-resistant bluish luster pigments of the invention
are advantageously obtainable by the manufacturing process of the
invention by reacting the reduced titania-coated silicate
platelets with a silane of the formula I
RaSiXb I.
Here suitable radicals R are alkyl radicals which generally
10 contain from 1 to 10, preferably 2 to 4, carbon atoms and are
substituted in the ~-position by one of the following groups: a
glycidoxy group, an amino group, a hydroxyl group or a
monoalkylamino group or an alkoxy group, whose alkyl chains may
each contain up to 10 (preferably up to 4) carbon atoms and may
15 be interrupted by from 1 to 5 ether oxygen atoms or imino groups.
Of these substituents, mono-(C1-C4-alkyl)amino groups with or
without a substitution by an ether oxygen atom or an imino group
in the alkyl radical are preferred, the glycidoxy group is
20 particularly preferred and the amino group is very particularly
preferred.
If the silane I contains more than one alkyl radical R (a = 2),
these alkyl radicals R can be identical or different. Preferably,
25 however, only one radical R is present (a = 1).
The radicals X are identical alkoxy radicals, which generally
contain up to 4, preferably up to 2, carbon atoms.
Suitable silanes I contain at least 2 alkoxy radicals (b = 2),
but preferably 3 alkoxy radicals (b = 3).
Since, according to the invention, the reaction of the reduced
35 silicate platelets preferably takes place with silane decomposed
in the gas phase, particularly suitable silanes of the formula I
have a sufficiently high vapor pressure at temperatures < 500~C,
preferably ~ 400~C, permitting simple vaporization.
40 Particularly preferred silanes conform to the formula Ia
R'SiX'3 Ia
45 where R' is a propyl radical having a terminal amino group or a
terminal glycidoxy group and X' is methoxy or ethoxy.
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Examples of very particularly preferred silanes are
3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane and
3-glycidoxypropyltrimethoxysilane.
5 Examples of further suitable silanes are
N-(2-aminoethyl)-3-aminopropyltrimethoxysilane,
2-aminoethyltriethoxysilane, 4-aminobutyltriethoxysilane and
di(3-aminopropyl)diethoxysilane.
It lS also posslble to use mlxtures of the silanes I, of course.
Even very small quantities of silane I are sufficient to render
the pigments of the invention humidity-resistant. It is customary
15 to use from 0.5 to 7 g, preferably from 2 to 5 g, of silane per
100 g of pigment.
The inventive reaction of the reduced silicate platelets with the
silane I can be carried out wet-chemically at room temperature in
20 aqueous suspension. It is of course also possible to carry out
the reaction at higher temperatures of up to 95~C, but this is
generally not necessary.
If desired, the aqueous suspension of the silicate platelets may
25 have added to it a nonionic surfactant to further coat the
surface of the silicate platelets and provide particularly
low-dusting pigments. Examples of surfactants which are preferred
here are poly-C2-C3-alkylene glycols, especially polyethylene
glycols having an average molecular weight from 200 to 800 and
30 polypropylene glycols having an average molecular weight from 400
to 1000, but also mixed polyethylene/polypropylene glycols.
Suitable surfactant quantities are customarily in the range from
2 to 10 g per 100 g of pigment.
An advantageous way of carrying out the process is to charge a
stirred reaction vessel with an aqueous suspension of the reduced
silicate platelets and to add an aqueous solution of the silane,
which optionally may also comprise the surfactant, or else neat
40 silane with stirring.
The pigment which is being reacted with the silane is
advantageously isolated by spray drying. However, it is also
possible to filter the pigment off and dry it in a drying
45 cabinet. But in this case it is advisable first to exchange the
remaining water against a low boiling, water-miscible organic
solvent to forestall clumping of the pigment platelets during
CA 022l~2l~ l997-09-2~
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drying. Examples of suitable solvents are acetone and
Cl-C4-alcohols such as methanol and ethanol.
It is also possible to introduce the silicate platelets without
5 water into a solids mixer equipped with additional
deagglomerating means and spray an aqueous solution of the silane
and optionally of the surfactant onto the pigment platelets with
stirring and deagglomeration.
A preferred embodiment of the process of the invention comprises
reacting the reduced silicate platelets with gaseous (vaporized)
silane (chemical vapor deposition, CVD).
15 The CVD variant is preferably likewise carried out in the
presence of water (water vapor).
An advantageous reactor which can be used for this process
variant is a fluidized bed reactor in which the reduced silicate
20 platelets are fluidized with an inert gas, preferably nitrogen,
and optionally heated to a temperature of up to 300~C, preferably
within the range from 150 to 300~C. The vaporized silane and the
water vapor are then introduced by means of inert carrier gas
streams (various subsidiary streams of fluidizing gas) from
25 upstream vaporizer vessels via separate nozzles.
A particularly suitable apparatus for the CVD variant is a solids
mixer equipped with additional deagglomerating means and upstream
vaporizers (e.g., thin-film evaporators) for silane and water
30 which are likewise flushed by an inert gas passing through them.
Examples of preferred solids mixers are mixers having plough
share stirrers and vertical shaft mixers, each equipped with a
stator/rotor beater.
The vaporizer temperatures naturally depend on the boiling point
of the substance to be vaporized. Other factors are the flow rate
of the inert gas stream directed through the vaporizer and the
desired silane concentration in the reactor. In the case of
40 3-aminopropyltriethoxysilane, for example, suitable vaporizer
temperatures range from about 70 to 150~C when a fluidized bed
reactor is used and from about 150 to 300~C when the reaction is
carried out in a solids mixer (at carrier gas streams from about
~00 to 200 l/h).
CA 022l~2l~ l997-09-2
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When a fluidized bed reactor is used, the concentration of the
vaporized silane is advantageously ' 3 % by volume, preferably
within the range from 0.001 to 0.5 % by volume, based on the
total quantity of gas in the reactor. If the reaction is carried
5 out in the presence of water vapor, at least the amount of water
vapor which is stoichiometrically necessary to hydrolyze the
silane should be used, but preference is given to an excess from
10 to 100 times.
10 When the reaction is carried out in a solids mixer, the silane
concentration in the carrier gas stream is generally within the
range from 0.1 to 6 g/l, preferably within the range from 0.5 to
4 g/1. If water vapor is added, an excess of from 1 to 10 times
is preferred here. And it is advisable, after the silane
15 vaporization has ended, to add further water vapor to ensure a
complete hydrolysis of any adsorbed silane to reactive silanol
intermediate.
20 Customary reaction times for the CVD process variant typically
range from 2 to 10 h when a solids mixer is used and up to 20 h
when a fluidized bed reactor is used.
The bluish luster pigments of the invention are notable for
25 advantageous application properties, especially high humidity
resistances, and it is especially the pigments which have been
reacted with the silane in a solids mixer which also show
excellent dispersibility in varnishes.
30 They are advantageously useful for many purposes, such as
coloring of plastics, glasses, ceramic products, decorative
cosmetic preparations, inks, including printing inks, especially
varnishes, especially to prepare automotive finishes.
35 For these applications, the pigments of the invention can also be
advantageously used in admixture with transparent and hiding
white, color and black pigments.
CA 022l~2l~ l997-09-2
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Examples
A) Preparation of luster pigments of the invention
Example 1
In an approximately 50 l capacity Lodige mixer equipped with a
plough share stirrer, a stator/rotor beater, 3 separate gas feed
10 lines and 2 upstream thin-film evaporators, 4 kg of a silverily
reflecting titania-coated mica pigment which have been reduced
with ammonia gas at 800~C were reacted with
3-aminopropyltriethoxysilane in the presence of water vapor and
nitrogen. A 300 l/h stream of nitrogen was passed through the
15 silane vaporizer, which was heated to 170~C, and a 160 l/h stream
of nitrogen was passed through the water vaporizer, which was
heated to 85~C. In this way, 218 g of silane and 52 g of water
were introduced into the reactor over 65 min. On completion of
the silane vaporization, water vapor was subsequently introduced
20 for a further 80 min, so that a total of 117 g of water were
added.
The pigment obtained had a carbon content of 0.8 % by weight.
Classification < 50 !lm left an oversize of 2 % by weight.
Example 2
In the mixer of Example 1, 4 kg of the mica pigment of Example 1
30 were reacted with 3-aminopropyltriethoxysilane in the presence of
water vapor and nitrogen. Two 200 l/h streams of nitrogen
introduced 120 g of silane from the vaporizer heated to 240~C and
16 g of water from the vaporizer heated to 110~C, over 10 min. On
completion of the silane vaporization, water vapor was
35 subsequently introduced for a further 50 min, so that a total of
95 g of water were added.
The pigment obtained had a carbon content of 0.5 % by weight.
Classification < 50 ~m left an oversize of 0.7 % by weight.
Example 3
In a fluidized bed reactor made of glass with a diameter of 16 cm
and a height of 100 cm, equipped with a glass frit bottom, filter
45 socks suspended from the top and cleaned by a nitrogen jet and
two gas inlet nozzles mounted on the side above the frit bottom,
600 g of the mica pigment of Example 1 were heated to 200~C under
CA 022l~2l~ l997-09-2~
BASF Aktiengesellschaft 950283 O.Z. 0050/47376
fluidization with a total of 1700 l/h of nitrogen. ~art of the
fluidizing gas (400 1/h of nitrogen) was passed through an
upstream 3-aminopropyltriethoxysilane vaporizer heated to 80~C,
while a further portion of the fluidizing gas (300 l/h of
5 nitrogen) was passed through an upstream water vaporizer heated
to 40~C. In total, 35 g (37 ml) of silane were introduced.
The pigment obtained had a carbon content of 0.5 % by weight.
Classification < 50 ~m left an oversize of 0.5 % by weight.
Example 4
In the fluidized bed reactor of Example 3, 600 g of the mica
15 pigment of Example 1 were heated to 200~C under fluidization with
a total of 1800 l/h of nitrogen, 400 l/h of which was passed
through an upstream 3-aminopropyltriethoxysilane vaporizer heated
to 100~C, while 400 l/h of nitrogen were passed through an
upstream water vaporizer heated to 40~C. In total, 70 g (74 ml) of
20 silane were introduced.
The pigment obtained had a carbon content of l.1 % by weight.
Classification < 50 ~m left an oversize of 0.3 % by weight.
25 Example 5
In a stirred vessel, a suspension of 100 kg of the mica pigment
of Example 1 in 850 l of water was admixed with a solution of
30 5 kg of 3-aminopropyltriethoxysilane in 50 l of water. The water
was then removed by spray drying, the suspension at a pressure of
4.5 bar, a tower inlet temperature of 320~C and a tower outlet
temperature of 110~C at a rate of 130 kg/h.
35 The pigment obtained gave rise to an oversize of 0.6 % by weight
in a < 50 ~m classification.
Example 6
~ A suspension of 20 g of the mica pigment of Example 1 in 200 ml
of water was admixed with 0.4 g of 3-aminopropyltrimethoxysilane
~y stirring. The water was then removed by spray drying in a
laboratory unit, the suspension being sprayed at a tower inlet
temperature of 230~C and a tower outlet temperature of 95~C at a
45 rate of 0.5 kg/h.
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The pigment obtained had a carbon content of 0.3 % by weight.
Classification < 50 ~m left an oversize of 0.5 % by weight.
Example 7
Example 6 was repeated to react 20 g of the mica pigment of
Example 1 with 0.4 g of 3-glycidoxypropyltrimethoxysilane.
10 The pigment obtained had a carbon content of 0.5 % by weight.
Example 8
In a 250 1 capacity Lodige mixer equipped with a plough share
15 stirrer and a stator/rotor beater, 44.2 kg of the mica pigment of
Example 1 were sprayed with a mixture of 3.3 kg of
3-aminopropyltriethoxysilane, 2.4 kg of a polypropylene glycol
having an average molecular weight of 600 and 0.2 kg of water
with stirring and deagglomeration.
The pigment obtained had a carbon content of 1.0 % by weight.
B) Evaluation of luster pigments of the invention
To evaluate the humidity resistance of the pigments in paint, the
first step was to prepare the painted test panels as follows: for
each pigment, 4 g were stirred into 96 g of a polyester mix
varnish having a solids content of 21 % by weight and dispersed
30 using a propeller stirrer at 1500 rpm for 15 min. Thereafter each
base coating was adjusted to a spray viscosity of 18 sec in DIM
cup 4 (DIN 53 211) and sprayed both onto an unprimed aluminum
panel and onto an automotive body panel (paint build: bonded
substrate (zinc phosphated steel)/cathodic
35 electrocoating/polyester-acetobutyrate primer). Following a short
flashoff time, a one-component clear varnish based on
acrylate/melamine resin (47 % by weight solids, adjusted to
23 sec DIN 4) was applied on top, wet on wet. After 30 minutes
flashoff at room temperature, each panel was baked at 130~C for
40 30 min.
The humidity behavior was subsequently evaluated according to the
Cleveland Humidity Test (DIN ISO 6270) and the water immersion
test (ISO 2812-2; May 1982).
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11
In the humidity test, the painted panels were placed in a
Cleveland Condensing Humidity Cabinet (Condensation Tester Q C-T
from The Q-Panel Company; Cleveland, Ohio, USA). The fully
deionized water bath was adjusted to 70~C and the panels were
5 continuously bedewed for 24 h at l00 % relative humidity.
In the water immersion test, the painted panels were placed for
24 h in a water bath heated to 80~C following 24 hour aging at
room temperature.
On completion of the exposure, the panels were each dried off and
without delay evaluated for a color change against the gray scale
of EN 20105-A02. On this scale, coatings without a change in
15 color are rated 5 and coatings which have turned white all over
are rated l.
In the same way, the luster change was evaluated against the
relative evaluation scale of ISO 4628/l. On this scale, which
20 likewise ranges from 0 to 5, a rating of 0 means no loss of
luster and a rating of 5 means very pronounced loss of luster.
The results of these investigations are reported in the table
below, which also shows the results, by way of comparison (C),
25 for a starting pigment prior to reaction with the silane.
Table
30 Pigment Cleveland Humidity Test Water Immersion Test
of Example Color change Luster change Color change Luster change
1 4 1 5
2 5 0 5 0
3 5 0 4-5
4 5 0 4-5 2
0 5 2
6 5 1 4 2
7 5 1 4-5 2
8 5 1 4
C 2 4-5 2 4
CA 0221~21~ 1997-09-2
