JPH0124732B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high solids content titanium dioxide slurry made in whole or in part from in-process material from either a sulfate or chloride process for producing _TiO2 . The intermediate product is not dried or milled and has a low amount of aluminum oxide coating. The resulting slurry exhibits resistance to hard sediment formation, good viscosity stability after slurry ripening, and a conventional high dry hiding slurry made entirely using conventionally produced titanium dioxide pigments. have paint optical properties at least equal to those of the paint slurries (hide slurries). Titanium dioxide is currently the main white pigment commercially available. It generally hydrolyzes aqueous solutions of titanium salts such as sulfates and produces the hydrolyzate.
It is produced by calcination at 750-1000°C or by oxidation of titanium halides, such as titanium tetrachloride, at temperatures as high as 800°C or higher, followed by cooling to temperatures below 600°C. The product resulting from calcination or oxidation contains a substantial amount of oversized coarse TiO ₂ particles that are ground by wet or dry milling. Drying followed by wet milling often causes cementation of the agglomerates, so further milling may be required to later obtain a smooth textured pigment product. In dry milling operations, suspending agents and dispersing aids are often introduced during milling to facilitate particle size reduction of the pigment to fine, uniformly sized particles. An effective means for dry milling is a fluid energy mill, in which the pigment particles are moved by a gaseous fluid such as air or steam into the outer part of a volute that spirals inwardly at high speed and at high rotational speed. It is conveyed in such a way as to maintain the swirl at a speed and a relatively low internal velocity so that the pigment agglomerates can be broken up. Previously, titanium dioxide slurries were prepared by placing the dried finished pigment in water with suitable dispersants. According to US Pat. No. 3,536,510,
A high solids content anatase slurry is described in which dry milled anatase TiO ₂ is dispersed in water using a suitable dispersant, preferably an alkanolamine. US Patent No.
No. 3,758,322 describes the use of grit-free methods for preparing rutile slurries using suitable dispersants.
A high solids slurry is described in which deflocculated, hydrous-free, oxide-treated TiO ₂ is used. West German Patent No. 1908611 describes finished rutile TiO ₂ − dispersed using sodium polyphosphate.
High solids content rutile using water mixtures
Concerning _TiO2 water mixture. It has been found that a highly dry hiding titanium dioxide slurry can be produced from an intermediate product, i.e., not fluid energy milled and not dried, if it is coated with a low amount of aluminum oxide. Ta. This material can be used alone or in combination with conventionally prepared, dried and milled pigments to produce the slurry of the present invention. The starting titanium dioxide material for use in the present invention can be obtained by either the chloride method or the sulfate method. Depending on the method, the combustion or calcination is carried out in the presence of an aluminum salt, such as aluminum chloride, to bake up to about 2% by weight of aluminum oxide into the titanium dioxide. This material is present in a reactor or calciner and mixed with water to form a crude slurry having a solids content of about 15-30% by weight, which crude slurry contains a substantial amount of oversized coarse _TiO2 particles. The particles are then ground, for example by grinding in a sand mill. The slurry is then wet classified by passing it through a 325 mesh (US standard) screen. Preferably, a vibrating double deck screen is used. It is this material that passes through the screen that is used to make the highly dry opaque slurry of the present invention. This material is hereinafter referred to as "fines". The "fines", still in slurry form, are then coated with about 0.3-3% by weight of hydrous aluminum oxide. If less than about 0.3% aluminum oxide is used, there are later difficulties in obtaining the desired solids content in the range of 55-70% by weight. If more than 3% is used, the retained water will be added to the desired 55% of the filter cake afterward.
- Difficult to reach 70% solids by weight. Generally, aluminum oxide is added in the form of a salt such as sodium aluminate or related compounds.
This coating step, which generally has a higher amount of hydroxide, is well known in the titanium dioxide industry and can be carried out in known manner. The resulting low aluminum oxide coated titanium dioxide slurry is then reduced to a desired solids content of 55-70% by weight, preferably about 60-65%.
Most preferably, it is increased to about 62-64% to produce a high dry hiding, high solids content slurry. Generally this is carried out in a rotary evaporator or by filtration with the addition of small amounts of standard organic dispersants for the titanium dioxide. Dispersants are used in effective amounts, generally from about 0.3 to 2% by weight. The solids content of the slurry can be adjusted by adding a large amount of dried finished titanium dioxide pigment with a hydrous oxide coating, i.e. about 12-15% by weight, instead of or in addition to the filtration or evaporation concentration operations described above. It can be increased by If dry finished pigment is used, it should range up to about 90%, preferably up to about 60%, most preferably about 20-55% by weight of the slurry solids. Dispersants found to be particularly useful in the present invention are organic polyelectrolytes and others such as 2-amino-2-methyl-1-propanol, triethanolamine, sorbitol, mannitol, and water-soluble salts. . For example, Tamol 731 and Tamol 850 sold by Rohm and Haas;
Daxad 30, sold by Earl Grace, Nopcosant, sold by Diamond-Shamrock Corporation
Polywet ND-1 and ND-2 from Uniroyal, Inc. and American Cyanamid.
Cyanamer from Cyanamid Co.
P-35 was used. The invention is further illustrated by the following examples. Example 1 Preparation of a TiO ₂ Slurry with Low Al ₂ O ₃ Treatment A titanium dioxide pigment was prepared by a chloride process consisting of combustion of titanium tetrachloride by a wet classification process. Slurry material passing through a 325 mesh US standard sieve was found to have approximately 30% solids by weight. It was placed in a container and the PH was raised to about 9.2 with sodium hydroxide. After heating to about 70℃,
Sodium aluminate in a 1:1 mixture with water was added to give about 0.8% Al ₂ O ₃ on a dry basis on TiO ₂ and aged for about 30 minutes. Then the pH is 20
% sulfuric acid to 7.0±0.2 and the coated slurry was aged for about 2 hours. The slurry was then removed and the filter cake was washed with hot water. At this point, the filter cake had a solids content of approximately 50%. Stir the filter cake and add 0.63% by weight of _TiO2 based on the dry weight of TiO2 in the filter cake.
Amino-2-methyl-1-propanol (AMP)
was reslurried by adding . Dry finished pigment (flat latex type with approximately 14% hydrous aluminum oxide coating) was then added to increase the solids content to 64% by weight.
Thixotrope [Attage1--50]
and bacteriocide (Vancide TH) were added at a rate of 0.62 and 0.5% by weight, respectively, based on the total slurry. The finished high solids, low oxide aluminum coating slurry was then processed through a 200 mesh Newark wire cloth sieve to break up and/or remove TiO ₂ agglomerates. The resulting slurry had the following composition: % of total slurry Re-slurried filter cake 65.4 Dry TiO ₂ 33.3 Dispersant 0.63 Thixotrope 0.62 Bactericide 0.05 Examples 2-4 The method of Example 1 was repeated. A slurry having the composition shown in the table was prepared. Each of the reslurried filter cakes was coated _with 0.6% _Al2O3 .

Table Example 5 Adding 0.6% Al ₂ O ₃ to a fines slurry, increasing the slurry to 66% solids by weight by thin film rotary evaporator, and using 0.3% AMP dispersant. The method of Example 1 was repeated except that the slurry was kept in a peptized state. No dried finished titanium dioxide pigment was added to the slurry. Example 6 Each of the above slurries compared to a slurry obtained by dispersing a dry finished pigment with a 7.5% Al ₂ O ₃ and 6.5% SiO ₂ coating in water with the addition of conventional additives such as dispersants and thixotropes. Each was made into a paint using a typical acrylic latex paint process to determine tinting strength. Each paint was based on a polyacrylic latex (Rhoplex AC-490 from Rohm and Haas) and contained one of the slurries described above as well as other conventional ingredients. Each of the resulting paints was then prepared using a 6"
Morest 017 using applicator
Draw downs were formed on charts and the color strength was measured after the draw downs were aged overnight. The relative tinting strength of the paint was determined by measuring the green reflectance of a standard (a conventionally prepared slurry) and a test sample on the white part of the chart. The resulting reflectance value is calculated using the Kubelka−Munk equation (Kubelka−Munk
It was converted into a K/S value using the equation). Next, the coloring strength of the sample to be tested was determined using the following formula. Coloring power of sample = K/S standard/K/S sample x 100 The results for the paints made from the slurries of Examples 1-5 in comparison with the standard were as follows: Sample Coloring power ... ... Example 1 +2% 〃 2 Equal 〃 3 +4% 〃 4 +2% 〃 5 +2% Therefore, the expensive and intense energy-intensive process of drying and fluid energy milling of highly coated titanium dioxide pigments Paints with equal or better tinting strength, with no or less need for paint, were obtained from the slurry of the present invention. Example 7 The method of Example 1 is repeated, except that prior to combustion of the titanium tetrachloride, aluminum chloride is added so that 1.2% by weight aluminum oxide, based on the weight of the resulting titanium dioxide, is baked into the pigment. A titanium dioxide pigment slurry was produced.
The remainder of Example 1 was carried out on this material, including the addition of sodium aluminate. The coloring strength of the resulting slurry was evaluated in accordance with the method of Example 6 by comparing it with a slurry produced by a conventional method. The results were as follows: Sample Tinting Strength Standard...Example 7 +7% This example demonstrates the further advantages of the present invention from the use of the base titanium dioxide formed in the presence of low amounts of aluminum oxide. It shows a great effect.

Claims (1)

Claims: 1. As a source of titanium dioxide in an aqueous titanium dioxide pigment slurry having high hiding power, a solids content of about 55-70% by weight and an effective amount of dispersant;
Undried, mill-ground, wet-classified,
An improved aqueous titanium dioxide pigment slurry characterized by the use of fines that pass through a 325 mesh screen and are coated with about 0.3 to 3% by weight of hydrous aluminum oxide. 2. The slurry of claim 1, wherein up to about 60% of the fines are replaced by dried and milled titanium dioxide pigment. 3 The fine particles are titaniferous salts.
2. A slurry as claimed in claim 1 formed by combustion of salts. 4. The combustion of the titanium-containing salt contributes approximately 2% by weight to the combustion product.
4. The slurry of claim 3, wherein the slurry is made in the presence of aluminum chloride to bake the aluminum oxide. 5. The slurry of claim 1, wherein the fines are derived from hydrolysis of a titanium iron sulfate solution. 6. The slurry of claim 5, wherein the resulting hydrolyzate is calcined in the presence of an aluminum salt so as to bake up to about 2% by weight of aluminum oxide into the calcined product. 7. The slurry of claim 1, wherein the solids content is about 60-65% by weight. 8. A slurry according to claim 1, wherein the fines in the form of a dilute slurry are concentrated by evaporation of filtration or water.