Note: Descriptions are shown in the official language in which they were submitted.
The present invention concerns a procedure for dispersing talc. In
particular, the present invention concerns a procedure with ~hich
gran~l1ated, finely divided talc can be advantageously dispersed to
become a suspension which fulfills the requirements of paper coating
paste, at the same time retaining the advantages of granulated talc
regarding its handling, and in which standard blunging apparatus can
be used.
Granulating finely ground talc is a method commonly used in order
to improve the processability of a bulk-type talc product. In the
granulation process, the moistened talc is compressed with fairly
great force into small non-dusting briquettes. However, the talc
particles whlch have been pressed too close to each otller and are
mutually suitab].y oriented become combined by actlon o~ a van der
Waals force like those in the original talc c.rystal. The energy
threshold of talc is ~.l kcal/mol (17.2 kJ/mol) and the critical
distance, 3 A (R.F. GIESE, JR: Interlayer Bonding in Talc and
Pyrophyl]ite, 1974). In conventional granulation, and in storage
silos, these values are o~ten exceeded, with the consequence that
upon granulation the particle size distribution of the suspended
talc is coarser than before granulation.
In paper coating paste, the pigment must boe completely dispersed.
Success in this respect implies that the aggregated particles are
separated. It is in fact necessary, in suspending finely divided
talc, to use especia].ly powerful dispersing agents. The energy re-
quirements in the coating talc suspending process are twice those in
suspending coa~ing kaolin (J-E, TEIRFOLK, INSKO p. 82-80 VI).
. ", ~
The viscosity~and rheologlcal properties of the suspension to be
used in paper coating paste must be stab]e. No agglomeration or
sedimentation must take place, not even during prolonged storage.
,..''~'
7~
The present Inventlon provldes a procedure In whlch the
use of expenslve, high-power speclal mlxers can be avolded.
The present Inventlon thus provl,des a method in whlch
the talc Is suspended In the presence of at least one hydrophlllc
mlneral substance.
Accordlng to the present Inventlon there Is provlded a
procedure for dlspenslng talc 1n whlch the talc Is suspended In
the presence of at least one hydrophlllc mlneral substance, the
quantlty of talc belng between 10-60% by welght of the quantlty
of the suspenslon, and the quantlty of sald hydrophlllc mlneral
belng between 5-55~ by welght o~ the quan~lty of suspenslon.
Sultably the hydrophlllc mlneral substance Is kaolln, calclum
carbonate or gypsum.
In the procedure of the Inventlon, the talc may be
elther flnely dlvlded powdery talc or granulated talc. The orlg-
lnal graln slze of the granulated flnely dlvlded talc Is 1-5
~ m on the average. To the granulatlng water have been added
0.5-1.5% by wel~ht, of the talc dry welght, e.g. of pH-regulatlng
hydrophlllzlng and defoamlng auxlllary substances, such as e.g.
NaOH, polyalkylene glycol and/or Its derlvatlves, and approprlate
tensldes. To the aqueous suspenslon prepared of hydrophlllc mln-
eral materlal(s) or of mlxtures of such, the above-mentloned aux-
lllary substances are added at 0.1-0.5% by welght, referred to
the total quantlty of plgments. In vlew of malntalnlng the
effectlvlty of the addltives, the temperature must not rlse above
50C In the suspendlng operatlon.
~0
The hydrophlllclty of a mlneral Is caused by the dlf-
ference between the surface energy of sald mlneral and that of
the water surface: the smaller thls dlfference, the hlgher the
hydrophlllclty of the mlneral.
The surface energy of normal water Is 72 mJ/m2
The surface energy of kaolIn Is 65 mJ/m2
The surfacé energy of calclum carbonate Is 70 mJ/m2
The surface energy of gypsum Is about 70 mJ/m2
The surface energy of talc Is 45 mJ/m2
The dlfferences between the surface energles of the
mlnerals are due to dlfferen~ crystal strUctures and chemlcal
composltlon. Talc Is by nature strongly hydrophoblc. The cther
mlnerals mentloned are easlly wettable. A talc/water suspenslon
prepared wlthout auxlllary substances
- 2~ -
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1 is thixotropic, but it becomes dilatant later as the air escapes
from the suspension. The stability of ViSCQsity is poor, and the
rheological properties change with the slow wetting of the talc.
The viscosity of a suspension with more than 60% dry matter content
produced without additives is far too high in view of its use.
For hydrophilic minera] substance, the contents of which in the
suspension should be S- ~ % of the weight of the ultimate suspension,
one may use for instance kaolin, calcium carbonate or gypsum suited
for paper coating. The effect of the mineral substance in dispersing
finely divided, granulated talc is based on the following:
- the refining effect with which the particles in the suspension
scatter the talc agglomerates;
- different surface energy: by interposing themselves in the inters-
tices of talc particles, they decrease the hydrophobicity of the
pigment and inhibit the reagglomeration of talc particles under
pressure.
In a suspension prepared as described, one obtains the original
particle size distribution and a high dry matter content: 60-70%,
advantageously 65-68%. Complete wetting of the pigments is achieved,
and the handling properties of the suspension are good. The auxili-
ary substances that are used are suited for making a coating paste,and the suspension is stable also in prolonged storage. Dispersing
as taught by t~e invention can be carried out in standard blungers,
and the processability advantages afforded by the talc granulation
can be preserved.
Example l
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Finely divided, granulated talc, with average grain size 2.2jum,
and to the granulating water of which was added polyalkylene glycol
(Pluriol PE 6400) at 0.8% of the dry weight of talc, was dispersed
in a suspension made of SPS kaolin to the suspension water of which
had been added 0.3 parts by weight of a dispersing agent (Polysalz S),
1 0.02 parts by weight of sodium hydroxide and 0.02 parts by weight of
defoaming agent (Nopco 8034), (all percentages referring to the total
pigment weight). The ultimate dry matter content of the suspension
was 65%, thereof 50% talc and 50% kaolin. The suspension process took
place in a Kady Mill apparatus. On dilution to 63% by weight, the sus-
pension had a viscosity of 100 mPas/50 r/min. The viscosity and
rheological properties did not change during storage for 24 hours.
The suspension was used to coat LWC paper, with good results.
Example 2
Finely divided, granulated talc with average grain size 2.2 ~m, and
to the granulating water of which was added polyalkylene glycol
(PluriolR PE 6400) at 1.2% of the dry weight of talc, was dispersed
in a suspension prepared of SPS kaolin and to the suspension water
of which had been added 0.3 parts by weight of a dispersing agent
(Polysalz S), 0.02 parts by weight of sodium hydroxide ~all these
referred to the total pigment weight). The ultimate dry matter con-
tent of the suspension was 60.0%, thereof 50% talc and 50% kaolin.
The suspension process took place in the laboratory with a Diaf
apparatus. The viscosity of the suspension was 75 mPas/20 r/min.
The viscosity and rheological properties did not change in 24-hr
storage.
When merely finely divided talc was suspended to 60% suspension
density, the required suspending time was doubled. The suspension
had viscosity 80 mPas/20 r/min. The viscosity and the rheological
properties changed substantially during storage for 24 hrs. The sus-
pension was unstable.
Example 3
__ _ ____
Fine-grained granulated talc with 2.5 lum average grain si~e was
dispersed in a suspension prepared of calcium carbonate with 1.7 ~m
average grain size, to the suspension water of which had been added,
among others, 1.2 % polyalkylene glycol (Pluriol PE 6400) at 1.2%
by weight, and sodium hydroxide at 0.02% by weight of the talc dry
7~93
1 weight. Dispersion was carried out in the laboratory with a Diaf
apparatus. The ultimate dry matter content of the suspension was 60%.
The grain size of the dry matter of the suspension with different
carbonate/talc proportions was as follows:
TalcCarbonate Average grain size
Calculated Measured Difference
95% 5% 2.47 2.30 7,4%
10 90% 10% 2.42 2.20 10%
70% 30% 2.26 2.lO 7,6%
50% 50% 2.10 1.90 10,5%
The grain sizes were measured with a Sedigraph apparatus. In the
experiments, nearly 10% smaller grain sizes were achieved than might
be expected, calculating from the original grain size of the plgments.
This is believed to be due to the scatterlng of the talc agglomerates.
Example 4
___ _ _ __
Fine-grained granulated talc with average grain size 2.2 ~m was
dispersed with a Diaf apparatus in a suspension prepared of gypsum
(CoCoatR) meant for paper coating, to the suspension water of which
was added polyethylene glycol (PluriolR 6400~ 0.8% by weight and
sodium hydroxide 0.02% by weight~ of the weight of talc. The ultimate
solid matter content of the suspension was about 60%. With mixing
proportions 5-30% gypsum 95-70% talc, it was easy to obtain a well
dispersed stable suspension in which no sedimentation took place, nor
any substantial change of viscosity, during storage for two days.
Example 5
Finely divided granulated talc with average grain size 2.2 ym and to
the granulating water of which was added polyalkylene glycol (Pluriol
Pe 6400) at 0.8% of the talc dry weight, was dispersed in a suspension
prepared of SPS kaolin, to the suspension water of which had been added
0.3 parts by weight of dispersing agent (Polysalz S), 0.02 parts by
6 ~ 7493
weight of sodium hydroxide ~all referred to the total pigment weight).
The ultimate dry matter content of the suspension was about 64% and it
contained 70-95% talc and 30-5% kaolin. Suspension was carried out in
the laboratory with a Diaf apparatus. The viscosity and rheological
properties did not change at storage for 24 hrs. The viscosity at
different mixing proportions was:
Talc KaolinDry matter, % Viscosity,
mPas/20 r/min
1095 5 63.9 450
64.1 550
63.9 420
When only finely divided talc was suspended to 64% dry matter content,
the viscosity of the suspension was about double the above-mentioned
values.
