Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Process for the preparation of coated finely divided
inorganic solids and their use
The invention relates to a process for the preparation of
coated finely divided inorganic solids and to their use.
inorganic solids (e.g. inorganic pigments or fillers) are
incorporated inter alia as functional additives in the
form of powders or dispersions into synthetic polymers,
surface coatings,. paints/inks (e.g. printing inks),
fibres, paper (e.g. paper for lamination) ; adhesives,
ceramics (e.g. electroceramics and magnetic ceramics),
enamels, adsorbents, ion exchangers, grinding and
polishing agents, cooling lubricants and cooling
lubricant concentrates, refractory products, hard
concrete materials, medical products and cosmetics (e.g.
powders, ointments, toothpastes)- In order that the
inorganic solids are able to develop their desired
properties in such fields of application, very good and
uniform distribution of the finely divided inorganic
solids in the particular system in question is desirable.
Such uniform distribution is imperative in the case of
incorporation into polymers in particular.
In order to improve the processing properties of the
finely divided inorganic solids, DE 198 39 856 Al has
proposed embedding them into a matrix consisting of an
organic carrier material. The pulverulent intermediate
formed thereby consists of individual particles having a
size of < 1 m. Such a particle in tuna contains several
individual inorganic solids particles, which are embedded
in the organic matrix. Disadvantages of these additives
are the relatively high content of organic carrier
material and the relatively expensive process for the
preparation of these additives.
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In DE 100 05 685 Al, it is proposed to coat finely
divided barium sulfate with an organic substance, each
individual barium sulfate particle being coated with a
layer of organic substance. In this process, the filter
cake of barium sulfate can be processed to form a paste,
with which the organic substance is mixed. The mixture
is then dried. in a variant of the process, the filter
cake of barium sulfate is dried and then the organic
substance is added. Both processes have the disadvantage
that the distribution of the organic substance on the
barium sulfate particles is not uniform. in a further
process variant it is proposed to suspend the filter cake
of barium sulfate in water again, to add the organic
substance and then to dry the mixture- Although this
process results in better distribution of the organic
substance on the barium sulfate particles, it has the
disadvantage that a relatively large amount of water is
required for preparing the suspension, which water must
subsequently be removed again.
The object of the invention is to overcome the
disadvantages of the prior art and provide a process with
which finely divided inorganic solids can be modified
with an organic substance in such a manner that they can
readily be incorporated as additives into various systems
(e.g. polymers, surface coatings. paints/inks, paper,
ceramics, medical products or cosmetic products). In
particular, the organic substance is to be distributed
uniformly over the surface of the inorganic solids, and
the proportion of organic substance is to be less than
15 wt.%, preferably less than 10 wt.%, of the finished
additive (coated inorganic finely divided solids).
Furthermore, it is to be possible to carry out the
preparation process using a smaller amount of water than
in processes known hitherto in which the organic
substance is added to a suspension of finely divided
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inorganic solids in water. If required, it is also to be
possible to carry out the modification of the finely
divided inorganic solids with the organic substance
without using any water at all.
As such, the present invention relates to a process for the preparation of
coated
finely divided inorganic solids, characterised in that the surface of finely
divided
inorganic solids particles is coated with at least two different organic
additives,
at least one additive comprising a wetting agent, dispersing agent or
deflocculating agent and the proportion of additives being not more than 15
wt.% of
the coated solids,
the finely divided inorganic solids being in the form of an aqueous suspension
or in the form of a filter cake and the two different organic additives being
added to
the finely divided inorganic solids separately or in the form of a mixture,
the resulting suspension being dried, and
the coated finely divided inorganic solids having a mean particle size d50 of
from 0.001 to 20 pm.
Furthermore, the present invention also relates to a use of the coated finely
divided
inorganic solids prepared by the process as described above as an additive in
plastics, in the preparation of polymers, in surface coatings and paints/inks,
in paper
production, in ceramics, medical or cosmetic products.
The object is achieved by a process in which the surface
of finely divided inorganic solids particles is coated
with at least' two different organic additives, at least
one additive comprising a wetting agent, dispersing agent
or deflocculating agent and the proportion of additives
being not more than 15 wt.%, preferably not more than
10 wt.%, or 5 wt.*, and particularly preferably not more
than 3 wt.%, of the coated solids, the finely divided
inorganic solids being in the form of an aqueous
suspension or in the form of a filter cake (paste-like or
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in dough form) and the two different organic additives
being added to the finely divided inorganic solids
separately or in the form of a mixture, the resulting
suspension being dried and the coated finely divided
inorganic solids having a mean particle size d5o of from
0.001 to 20 m.
There are preferably used as the finely divided inorganic
solids, separately or in the form of a mixture, titanium
dioxide, barium sulfate, lithopone, zinc sulfide, zinc
oxide, calcium carbonate, calcium sulfate, iron oxide,
silicon dioxide, talcum, kaolin, mica, aluminium oxide,
aluminium hydroxide, metal titanates, coloured titanates
(e.g. chrome nickel titanates), zirconium oxide,
magnesium oxide, hydrotalcite, chalk, mixed-phase
pigments, anticorrosive pigments, inorganic flameproofing
pigments, black pigments (e.g. iron oxide black),
inorganic special-effect pigments, or metal nitrides,
carbides and borides.
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Wetting, dispersing or deflocculating agent is here to be
understood as meaning a surface-active substance which
facilitates the dispersion (= breaking up) of a
pulverulent substance in a liquid medium, by lowering the
S 'surface tension between two oppositely charged components
by reversal of the charge of the surface. As a result,
the agglomerates that are present are broken down in the
dispersion process, so that re-agglomeration
(= accumulation) or flocculation (= aggregation) is
prevented.
As wetting, dispersing or deflocculating agents (referred
to only as dispersing agents hereinbelow) there may be
used both ionic and non-ionic dispersing agents. The
following substances can preferably be employed; alkali
metal (especially Na and K) salts or ammonium salts of
organic acids (e.g. salts of poly(meth)acrylic acid),
alkali metal salts of acrylate or methacrylate copolymers
(having a preferred molecular weight of up to 15,000),
polyphosphates (inorganic or organic polyphosphates, e.g.
poly(meth)acrylate phosphates), generally
poly(meth)acrylates, polyethers, anionically modified
polyethers, fatty alcohol polyglycol ethers, modified
polyurethanes or anionically active aliphatic esters.
The added amount of dispersing agent is dependent on the
mean particle size of the inorganic solids. The finer
the inorganic solids, the greater the added amount of
dispersing agent. The added amount of dispersing agent
is preferably from 0.01 to 10 wt., particularly
preferably from 0.01 to S wt.%, or from 0.1 to 3 wt.~,
based on the finished coated product.
The second organic additive preferably comprises one or
more of the following substances: carboxylic acids,
soaps, metal soaps, alcohols (e.g. 1,1,1-trimethylol-
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propane), pentaerythritol, neopentyl glycol, polyglycols
(e.g. polyethylene glycol), polyethylene glycol ethers,
organic esters (e.g. neopentyl glycol dibenzoate),
silanes, siloxanes, silicone oils, organic sulfones of
the formula RSO2R, organic ketones (R- (C=O) -R) , organic
nitriles (RCN), organic sulfoxides (R2-S02) , organic
amides (R- (C=0) -IuZ?'R or R- (S=O) -ONR'R) , fatty acid esters
or fatty acid amides.
The added amount of the second organic additive is also
dependent on the mean particle size of the inorganic
solids. The finer the inorganic solids particles, the
greater the added amount of the second organic additive.
The added amount of the second organic additive is
preferably from 0.01 to 10 wt.%, particularly preferably
from 0.01 to 5 wt.%, or from 0.1 to 3 wt.%, based on the
finished coated product.
The dispersing agent can be added to the finely divided
inorganic solids separately or in admixture with the
second organic additive. In the case of separate
addition, the sequence of addition is in principle
unimportant. For practical reasons, however, it is
preferable in the case of separate addition first to add
the dispersing agent and then to add the second additive.
The finely divided inorganic solids may be in the form of
an aqueous suspension or in the form of a filter cake
(paste-like or in dough form), It is advantageous to use
a filter cake in the undried state (e.g. from current
production) because the inorganic particles are then not
completely agglomerated and the outlay in terms of
dispersion after addition of the dispersing agent and of
the second organic additive is thus minimised. If the
finely divided inorganic solids are in powder form, it is
e:cpedient to carry out wet grinding of the inorganic
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solids before preparing a suspension. The suspension or
filter cake preferably has a solids content of from 15 to
85 wt.%, particularly preferably from 25 to 80 wt.;; and
very particularly preferably from 50 to 80 wt.&.
Drying of the suspension provided with the additives can
be carried out by means of conventional drying units.
Spray driers,- grinding driers or vacuum driers are
preferably used. If required, the dried product can
to subsequently be ground, for example by means of a steam-
jet mill, air-jet mill or pinned disk mill.
Surprisingly, it has been found that, even with a very
high solids content, suspensions or filter cakes are
liquefied after addition of the dispersing agent and of
the second organic additive to such an extent that
optimum distribution of the additives on the particle
surface is ensured and the resulting suspension can be
pumped without difficulty, which reduces the outlay in
terms of the process considerably. Owing to the low
water content of such a "liquid" suspension, the outlay
in terms of drying is also reduced.
It is also possible to mix finely divided inorganic
solids in powder form with the dispersing agent and the
second organic additive in a mixer and then grind the
mixture, for example in a steam-jet mill, air-jet mill or
pinned disk mill.
The coated finely divided inorganic so'-ids preferably
have a mean particle size d5o of from 0.001 to 20 m,
particularly preferably from 0.005 to 5 m, very
particularly preferably from 0.01 to 2 m, or from 0.1
to 1 }lm.
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An advantage of the process according to the invention is
that the coated finely divided inorganic solids that are
obtained have excellent flowability and can very readily
be transported pneumatically. On account of these
properties, they can excellently be metered for addition
to polymer melts. If the coated finely divided inorganic
solids are in turn to be processed further in the form of
a suspension or slurry, they can be processed without a
high outlay in terms of dispersion to (also non-aqueous)
"liquid" dispersions having a high solids content, for
example from 30 to 80 wtA, preferably from 40 to
75 wt.t. It has additionally been found that such
suspensions have high stability to storage or, if solids
should settle out, can very readily be re-dispersed.
There is therefore no agglomeration of the particles.
If undesirable foam formation should occur during the
preparation of such a suspension (dispersion in water or
an organic solvent), the foam formation can be suppressed
by addition of an antifoam. The added amount of antifoam
is dependent on the nature of the inorganic solids and on
the nature and amount of the dispersing agent used and of
the second organic additive. The added amount may be up
to 3 wt.% but is generally.less than 1.5 wt.%, in each
case based on the solids content of the suspension.
The coated finely divided inorganic solids prepared by
the process according to the invention can be used, for
example, in plastics, especially in the preparation of
polymers (e.g. thermoplastic or thermosetting polymers),
in surface coatings, paints/inks (e.g. printing inks),
fibres, paper (e.g. paper for lamination), adhesives,
ceramics (e.g. electroceramics and magnetic ceramics),
enamels, adsorbents, ion exchangers, grinding and
polishing agents, cooling lubricants and cooling
lubricant concentrates, refractory products, hard
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concrete materials, medical products and cosmetics (e.g.
powders, ointments, toothpastes).
The coated finely divided inorganic solids prepared by
the process according to the invention are distributed in
polymers much better than finely divided inorganic solids
treated according to the prior art. This manifests
itself niter alia in the so-called pressure filter test.
The subject-matter of the invention is explained in
greater detail by means of Examples:
Preparation for Examples A and 1: Preparation of a BaSO1
paste
in known manner, barium sulfate was precipitated from
aqueous solution by reaction of barium ions with sulfate
ions. The precipitated BaSO4 was separated from the
mother liquor and washed. The resulting paste-like
filter cake consisted of 67 wt.s dry matter and 33 wt.%
water. The particle size dso of the- BaSO4 particles was
0.45 m.
Comparison Example A: Coating of the BaS04 surface with an
additive according to the prior art
200 1 of demineralised water were placed in a stirrer
vessel, and 120 kg of the prepared BaSO4 paste (contained
80 kg of BaSO4) were added, with stirring. 1330 ml of an
aqueous 1,1,1-trimethyloipropane solution, which
contained 600 g of 1,1,1-trimethylolpropane per litre of
solution, were then added in portions in the course of
30 minutes under the action of the shearing forces of a
dissolver (2000 rpm). 798 g (0.99 wt. %, based on the
finished product) of 1,1,1-trimethy?olpropane were thus
introduced. The mixture was dispersed for a further
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15 minutes. The resulting suspension had a solids
content of 325 g/1 (26.2 wt.%) and was spray-dried under
the following conditions:
inlet temperature 535 C, outlet temperature 135 C,
spraying plate 18,000 rpm, throughput 110 1/h.
The resulting pulverulent BaSO4 with a single-layer
coating had a moisture content of 0.15 wt.s and a mean
3.0 particle size dso of 0.54 m.
The suspension proved to be problematical before drying
in terms of its stirring and pumping properties. The
reason was the high viscosity of the suspension, as was
to be expected with a solids content of 26.2 wt.%.
Example 1: Coating of the BaSO4 surface with a dispersing
agent and a second organic additive
28 1 of demineralised water were placed in a stirrer
vessel, and 149 kg of the prepared BaSO4 paste (contained
99.8 kg of BaSO4) were added, with stirring. 400 g of a
40 % potassium polyacrylate copolymer solution in water
(having a mean molar mass of about 5000) were then added
in portions in the course of 30 minutes under the action
of the shearing forces of a dissolver (2000 rpm). 160 g
(0.16 wt.%, based on the finished product) of potassium
polyacrylate copolymer were thus introduced. The mixture
was dispersed for a further 15 minutes. 1642 ml of an
aqueous 1,1,1-trimethylolpropane solution, which
contained 600 g of 1,1,1-trimethylolpropane per litre of
solution, were then added in portions, with stirring.
985 g (0.98 wt.%, based on the finished product) of
1,1,1-trimethylolpropane were thus introduced. Stirring
was then carried out for a further 15 minutes. The
suspension so obtained had a solids content of 960 g/l
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(55.9 wt.%-) and was spray-dried as described in
Comparison Example A.
The coated BaSO4 powder so prepared had a moisture content
of 0.15 wt.% and a mean particle size dso of 0.48 gm.
Despite the very high solids content of 55.9 wtA, the
suspension had a surprisingly low viscosity before drying
and accordingly exhibited very good stirring and pumping
properties. The suspension could be dried without
difficulty.
Comparison Example B: Processing of the coated BaSO4 from
Comparison Example A in a polymer melt
in a twin-screw extruder, 27 kg of BaSO4 powder from
Comparison Example A were incorporated into 23 kg of
polyethylene terephthalate (PET from KoSa, type:
Polyclear 1101). The temperature of the heating zone was
265 C. The concentration of BaSO4 in the PET masterbatch
so prepared was 54 wtA.
Example 2: Processing of the coated BaS04 from Example 1
in a polymer melt
Analogously to Comparison Example 8, 27 kg of the BaSO4
powder from Example 1 prepared by the process according
to the invention were incorporated into 23 kg of
polyethylene terephtha ate (PET from KoSa, type:
Polyclear 1101).
Example 3: Comparison of the polymers from Example 2 and
Comparison Example B by means of the PP value
In order to check the distribution of the BaSO4 solids
particles in the polymer, pressure filter'tests were
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carried out on both the 54 % BaSO4/PET masterbatches. The
PF value obtained thereby is used as a measure of the
quality of masterbatches_ The lower the PF value, the
better the quality of, the masterbatches in terms of the
distribution of the inorganic solids particles in the
polymer. The masterbatches from Example 2 and Comparison
Example B were melted continuously in an extruder and fed
to a 14 gm screening cloth (filter area 6.16 cm2). The
temperature was 265 C in the 1st heating zone, 2700C in
the 2nd heating zone and 280 C in the 3rd, 4th and Sth
heating zones. The throughput was about 40 g/minute.
Measurement is complete when a pressure of 200 bar is
reached or after 60 minutes at the latest. The pressure
filter test values (PF value) are calculated by the
following formula:
PF = (P.-Pu)xFx100[barxcrnal QI
(txKxG)
wherein:
p = final pressure (bar)
Po = starting pressure (bar)
F = filter area (cma)
t - measuring time (min)
K = concentration Or pigment)
G = throughput (g/min)
In this manner, a PF value of 0.87 bar=cm2/g was found for
the masterbatch prepared in Comparison Example S and a PF
value of only 0.19 bar=crn2/g was found for the masterbatch
prepared in the Example according to the invention. This
low PF value clearly shows the superiority of the coated
finely divided inorganic solids prepared by the process
according to the invention when incorporated into
polymers.
