CA1124012A - High dry hide tio.sub.2 slurries - Google Patents

Abstract

27,123 TITLE
HIGH DRY HIDE TiO2 SLURRIES

ABSTRACT OF THE DISCLOSURE
High dry hide titanium dioxide pigment slurries are prepared from in-process material which is treated with low amounts of aluminum oxide.

Description

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 . ~ ., -~, .; ~

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 ~ ' , ~Z~2 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 - 2a -' 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 .

z 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 , ~

~4~2 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%

Table I

2 3 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 k ' 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 . _ .
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-energy 5 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:

, `

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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Claims (8)

27,123 WHAT IS CLAIMED IS:

1. In an 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, the improvement comprising using undried, unmilled hydroclassified fines as the source of the titanium dioxide wherein said fines pass through a 325 mesh screen and are coated with about 0.3 to 3 percent by weight of hydrous aluminum oxide.

2. The slurry of Claim 1 wherein up to about 60 percent of the fines is replaced by dried and milled titanium dioxide pigment.

3. The slurry of Claim 1 wherein the fines are formed by the combustion of titaniferous salts.

4. The slurry of Claim 3 wherein the combustion of titaniferous salts is performed in the presence of aluminum chloride so as to burn in up to about 2 percent by weight aluminum oxide.

5. The slurry of Claim 1 wherein the fines are derived from the hydrolysis of a titanium iron sulfate solution.

6. The slurry of Claim 5 wherein the resultant hydrolysate is calcined in the presence of an aluminum salt so as to burn in up to about 2 percent by weight aluminum oxide.

7. The slurry of Claim 1 wherein the solids content is about 60 to 65 percent by weight.

8. The slurry of Claim 1 wherein the fines, which are in the form of a dilute slurry, are concentrated by filtration or evaporation of the water.