Note: Descriptions are shown in the official language in which they were submitted.
27,123
HIGH DRY HIDE TiO 5LURRIES
~ his invention relates to titanium dioxide slurries
of high solids content ~hich are prepared wholly or in part
from in-process material from either the sulfate or the chloride
process for making Ti02, which in-process material has not
been dried or milled and has a low amount of an aluminum
oxide coating. The resultant slurries have excellent resis-
tance to hard seetling, good viscosity stability after slurry
aging, and paint optical properties at least equal to those
of conventional high dry hide slurries made entirely with con-
ventionally prepared titanium dioxide pigments
Titanium dioxide is at present the premier whitepigment of commerce~ It is generally produced by either hydro~
lyzing an aqueous solution of a titanium salt, such as a sul-
fate, and calcining the hydrolysate at 750-1000C., or oxi-
dizing a titanium halide, e.g, titanium tetrachloride, atelevated temperatures of 800C. or higher~ followed by cooling
to a temperature below 600C. The product resulting from the
calcination or oxidation contains a substantial amount of
oversized, gritty TiO2 particles which are broken up by either
wet or dry grinding. Drying, following the wet grinding,
fre~uently causes cementation of agglo~erates requiring a
further milling treatment before a smooth textured pigment
product can be obtained. In the dry milling operation, suspend-
ing agents and dispersing aids are often introduced during
the milling to facilitate the reduction of the pigment to fine,
uniform-sized particles. An effective means for dry grinding
is a fluid energy mill in which the pigment particles are
conveyed by a gaseous fluid, such as air or steam, into the
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outer portion of an inwardly spiraling Vortex at high yelocity and in a mannerwhich will maintain the vortex at a high rotative speed and relatively lcw
inward speed whereby the pigment aggregates may be ~fractured.
Previously, titanium dioxide slurries were prepared by placing the
dry finished pigment in water with an appropriate dispersant. United S-tates
Patent 3,536,510 describes high solids content anatase slurries in which dry
mllled anatase TiO2 is dispersed in water using appropriate dispersants,
preferably alkanolamines. United States Patent 3,758,322 describes high solids
slurries in which grit-free deflocculated, non-hydrous oxide treated TiO2 is
used to make rutile slurries, using an appropriate dispersant. German Patent
1,908,611 relates to high solids oontent rutile Tio2 water mixtures using finish-
ed rutile TiO2-water mixtures dispersed with sodium polyphosphates.
It has now been discovered that high dry hide titanium dioxide
slurries may be prepared from in-process material, i.e. that which has not
been fluid energy milled and dried, if it is coated with low amounts of
aluminum oxide. ~his material may be used either alone or in combination
with conventionally prepared, dried and milled pigment to prcduoe the slurries
of the present invention.
Accordingly, the present invention relates to an improved aqueous
titanium dioxide pigment slurry having high hiding power, a solids content of
about 55 to 70 percent by weight, and an effective amount of a dispersing agent,
wherein the improvement o~mprises using undried, unmilled hydroclassified rines
as the souroe of the titanium dioxide wherein said fines pass through a 325
mesh screen and are coated with about 0.3 tG 3 percent by weight of hydrous
aluminum oxide.
The starting titanium dioxide material for use in the present
invention may be ob-tained by either the "chloride process" or the "sulfate
process". Preferably, the ccmbustion or calcination, depending upon the
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process, is perf,ormed in the presertce of an alu,minun salt such as aluminum
chloride such as to "burn in" up to about 2% by weight'alum mum oxide into
the titanium dioxide. This material exits ~te re~ctor or calciner and is
mixed with water to fonm a raw slurry having about 15 - 30% by weight solids
which cQntains a substantial ar~unt of oversized gritty TiO2 particles which
are then broken up by grinding in such as sand r~lls. The slurry is then
hydro-classified by passing it through a 325 mesh (United States Standard)
screert. Preferably, a vibratory double deck screen is used. It is this
material passing through the screen that is used to make the high dry hide
slurries of the present
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invention. This material is hereinafter referred to as the
'Ifines. "
The fines, which are still in slurry form, are then
coated with about 0.3 to 3% by weight of hydrous aluminum
oxide. If the aluminum oxide is used in less than about 0.3%
there is difficulty in filtration to subsequently obtain a
solids content in the desired 55 to 70% by weight range. If
more than about 3% is used, then the water retained makes it
difficult to subsequently reach the desired 55 to 70~ by
weight solids in the filter cake Generally, the aluminum
oxide is added in the form of a salt such as sodium aluminate
or related compounds. This coating step, generally with larger
amounts of hydrous oxide, is well known in the titanium dioxide
industry and may be performed in known manners.
The resultant low-aluminum oxide-coated titanium
dioxide slurry is then made into a high dry hidel high solids
content slurry by increasing the solids content to the de-
sired 55 to 70% by weight, preferably about 60-65%, and most
preferably about 62-6~%. Generally, this is done by filtration
or in a rotary evaporator with the addition of small amoun-ts
of standard organic dispersants for titanium dioxide. The
dispersants are used in effective amounts, generally about 0.3
to 2% by weight~
Alternatively and/or additionally, the solids content
may be increased by the addition of dry finished titanium
dioxide pigment which has a heavy hydrous oxide coa~ing, i.e.
about 12 to 15% by weight. When dry finished pigment is
used, it should be about 0 to 90% by weight of the solids of
the slurry, preferably about 0 to 60%, and most preferably
about 20 to 55~.
Dispersants found especially useful herein are organic
polyelectrolytes and others such as 2-amino-2-methyl-1-propanol,
triethanolamine, sorbitol, mannitol, and water soluble salts.
For example, sodium salts of polymeric carboxylic acids, such
as Tamol~ 731 and Tamo ~ 850, sold by Rohm & Haas; Daxa ~ 30,
sold by W. R. Grace; Nopcosant~ , sold by the Nopco Division
of Diamond-Shamrock Corporation; Polywet~ ND-l and ND-2 of
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Uniroyal, Inc. and Cyaname ~ P-35 of American Cyanamicl Co.,
have been used.
The following examples are pr~sented to further
illustrate the present invention:
Example 1
Preparation of Low A12O3 Treated TiO2 Slurry
Titanium dioxide pigmen-t was prepared by the
chloride process of combustion of titanium tetrachloride
through the hydro-classification step. The slurry material
10 passing through a 325 mesh U.S. standard sieve was found to
have about 30% by weight solids~ It was placed in a vessel
and the pH raised to about 9.2 with sodium hydroxide. After
heating to about 70C., sodium aluminate in a 1:1 mixture with
water was added to provide about~0.8% A12O3 based upon the
15 dry weight of TiO2, and allowed to age for about 30 minutes.
The pH was then adjusted to 7.0 + 0.2 by the addition of 20%
sulfuric acid, and the coated slurry aged for about 2 hours.
The slurry was then filtered and the filter cake
washed with hot water~ At this point the filter cake had
20 a solids content of about 50%~
The filter cake was reslurried by agitation and the
addition o~ 0.63% by weight based on the dry weight of TiO2
in the filter cake of 2-amino-2-methyl-1-propanol (AMP). Dry
finished pigment (flat latex type having about 14% hydrous
25 oxide coating) was then added to increase the solids content
to 64% by weight. A thixotrope (~ttage 1~ - 50) and a
bacteriocide (Vancide~ TH) were added at the rates of 0.62 and
0.5% by weight, respecti~ely, based upon the total slurry.
This finished high solids, low aluminum oxide coated slurry
30 was then processed through a 200 mesh Newark wire cloth sieve
to break up and/or remove any TiO2 agglomerates.
The resultant slurry had the following composition:
% of Total slurry
Reslurried Filter Cake 65.4
Dry TiO2 33.3
Dispersant 0.63
Thixotrope 0.62
Bacteriocide 0.05
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Exa~ples 2-4
The procedure of Example l was repea-ted to prepare
slurries having the compositions as sbwn in Table I below.
Each of the reslurried filter cakes was coated with 0.6%
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Table I
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Reslurried Filter Cake 55 2 55.2 55.2
Dry TiO2 43 7 43.8 43.7
lO Dispersant
AMP12 0.26 ---- 0.26
TSPP3 0.17 0.32
P-35 ---- ---- 0.17
Thixotrope 0.67 0.63 0.67
Bacteriocide 0.05
l) AMP is 2-amino-2-methyl-1-propanol
2) TSPP is tetrasodium pyrophosphate
3) P-35 is a sodium salt of a pol~acrylic acid
Example 5
The procedure of Example l was repeated except that
20 0.6% A12O3 was added to the fines slurry, the slurry was in-
creased to 66% by weight solids by means of a thin film
rotary evaporator and 0.3~ AMP dispersant was used to maintain
the slurry in a deflocculated state. No dry finished
titanium dioxide pigment was added to the slurry~
Exa~le 6
To determine the tinting strength of each of theabove slurries, as compared to a conventionally prepared slurry
from dry finished pigment having a 7.5% Al2O3 and 6.5% SiO2
coating, each was made into a paint using a typical acrylic
30 latex paint formulation. Each paint was based upon a poly-
acrylic latex (Rhoplex AC-490 of Rohm & Haas Co.) and contained
other conventional ingredients together with one of the
slurries above.
Each of the resultant paints was then tested for
35 tinting strength by combining 200 g. of each paint with
16 g. of dilute chromium oxide green pigment, sha~ing the
mixtures, allowing them to age overnight, forming drawdowns
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on Morest 017 charts using a 6" x 0.003" Bird film applicator,
and allowing the drawdowns to age overnight before evaluation.
The relative tinting strength of the paints was-
determined by measuring the green reflectance of the standard
(conventionally prepared slurry) and the test sample over the
white portion of the chart. The resultant reflectance values
are converted into K/S values by the Kubelka - Munk equation.
The tinting streng-th of the sample being tested is then deter-
mined by the formula:
Tinting Strength sample = K/S Standard x 100
K/S Sample
The results for the paints made from the slurries of
Examples 1-5, as compared to the standard, were as follows:
SampleTinting Strength
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Standard ----
Ex. 1 +2~
Ex. 2 equal
Ex. 3 ~4%
Ex. 4 +2%
Ex. 5 ~2%
Accordingly, paints having equivalent or better
tinting strength are obtained from the slurries of the present
invention while eliminating or decreasing the need for the
expensive and energy-intensive steps of drying and fluid-energy5 milling a highly coated titanium dioxide pigment.
Example 7
The procedure of Example 1 was repeated to prepare
a titanium dioxide pigment slurry except that prior to the
combustion of the titanium tetrachloride aluminum chloride
30 was added such that 1.2% by weight aluminum oxide, based on
the weight of resultant titanium dioxide, was "burned in" the
pigment. The remainder of Example 1 was per~ormed on this
material including the sodium aluminate addition.
The tinting strength of the resultant slurry was
35 evaluated according to the procedure of Example 6, in comparison
with a conventionally prepared slurry.
The results were:
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Sample Tinting Strength
Standard
Ex. 7
This example shows the further beneficial effects
in the present invention from the use of a base titanium
dioxide which was formed in the presence of low amounts of
aluminum oxide.
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