Low sheen opacifying pigments and manufacture thereof by calcination of kaolin clay

Flux calcined kaolin clay especially useful as a pigment for low sheen paints is obtained by mixing hydrous kaolin with an aqueous solution of alkaline flux, spray drying, pulverizing, calcining and repulverizing.

BACKGROUND OF THE INVENTION 
It is normal practice to produce kaolin pigments by calcination of purified 
fine particle size hydrous kaolin clay. Calcination of kaolin at 
temperatures up to about 1100.degree. C. cements particles together and 
produces products of improved whiteness and opacity. Such pigments are 
widely used by the paper, plastics, rubber and paint industries. A seminal 
patent is commonly assigned U.S. Pat. No. 3,586,523, Fanselow et al, the 
disclosure of which is incorporated herein by cross-reference. This patent 
is directed to producing low abrasion fine particle size opacifying 
calcined kaolin clay, such as the pigments supplied under the registered 
trademarks ANSILEX and ANSILEX 93. Such pigments have an average particle 
size of about 0.8 microns. When used in paints, the fine calcined pigments 
obtained by practice of the Fanselow et al patent also provide tint 
strength and high sheen. 
For flat paints, the low angle sheen as measured by 85 degree gloss is 
generally less than 10. For better flat paints, the 85 degree sheen is 4 
or below. To achieve low sheen the particle size of the calcined clays is 
increased by changing the particle size distribution of the feed such that 
the feed is coarser than used by Fanselow et al. While a sheen of 4 is 
achievable by calcining a coarser feed, the hiding and tint strength 
properties are compromised (reduced). It is extremely difficult to balance 
the properties of a paint formulation since 85 degree sheen and 
opacity/tint strength move in opposite direction to their particle size. 
Thus, as particle size in the optically efficient range increases, 
opacification decreases. The following commonly assigned patent, U.S. Pat. 
No. 4,525,818, Kostanzek, discloses means to produce certain coarse 
calcined kaolin clay pigments especially useful as primary extenders in 
paint. The calcined clay pigments have an average particle size of about 3 
to 4 microns. 
Practice of our invention utilizes fluxing compounds during calcination of 
the kaolin, the compounds being added to hydrous kaolin before 
calcination. Reference is made to U.S. Pat. No. 2,307,239, Rowland, which 
is a pioneer patent in the field of calcined kaolin pigments. This patent 
broadly discloses addition of various alkali and alkaline earth compounds 
to clay before calcination. A preferred compound is sodium chloride. U.S. 
Pat. No. 3,853,573, Ferrigno, discloses pigmentary compositions produced 
by combining a fluxing agent composed of one or a combination of metal 
oxides with calcined kaolin, with optional hydrous kaolin, and an 
inorganic binder. Dry addition of flux is practiced by Rowland and 
Ferrigno; no attempt is made to coarsen the clay in the optically 
efficient particle size range. In a thesis, "The Kaolin to Mullite 
Reaction Series," Wilfred Anthony Martinez, Rutgers University, 1979, 
various "mineralizers" were added to both a fine particle size kaolin and 
a relatively coarse particle size hydrous kaolin, primarily to explore the 
effect on the crystallinity. Dry addition of mineralizer was practiced in 
all experimental work. There is no attempt to control the coarsening of 
kaolin clay during calcination throughout the optically active size. The 
phrase "controlled coarsening" as used herein refers to increasing the 
percentage of coarsened particles throughout the particle size range of 
0.5 to 2 microns. 
So-called "flash" or "shock" calcination is used to produce relatively 
coarse kaolin derived pigments. Reference is made to U.S. Pat. No. 
3,021,195, Podschus et al. Special calciners must be used and multi-stage 
thermal treatment is used. The rotary calciners or Nichols furnaces 
generally used by the kaolin industry cannot be readily reconstructed to 
function as shock calciners. While the calcined pigments are relatively 
coarse, average size about 1.4 microns, and sheen is low, the pigments 
tend to be more yellow than other calcined clay pigments. 
SUMMARY OF THE INVENTION 
Our invention overcomes this difficulty by controlled coarsening through 
calcination of hydrous fine size kaolin with controlled low dosages of 
fluxing agents. The controlled coarsening allows the calcined pigments to 
attain unusually low sheen while other important properties such as hiding 
and tint are not compromised. 
The new products can be made with conventional rotary calcination kilns 
without new capital. This does not require use of flash calcination 
process to produce low-sheen pigments. The experimental products made by 
our invention have higher whiteness and less yellowness than commercial 
flash calcined low sheen pigments. 
An essential feature of the process is that the fluxing agent must be water 
soluble and is added to the hydrous kaolin with mixing in the presence of 
water. Dry mixing of flux with clay before calcination, as taught in the 
prior art, does not result in controlled coarsening throughout the desired 
range of 0.5 to 2 microns. Further, dry mixing results in large amounts of 
oversize (grit) which may render the product of limited if any commercial 
use. 
DETAILED DESCRIPTION OF THE INVENTION 
The fluxing agent may be mixed with kaolin clay in the presence of water at 
various points during the processing of hydrous kaolin but is preferably 
added to a dispersed slurry of hydrous kaolin in solution form just prior 
to spray drying. The spray dried pigment is pulverized and calcined at 
temperatures between 500 to 1200.degree. C. but preferably between 800 to 
1070.degree. C. See Fanselow et al, supra. The calcined product is 
pulverized before use in formulating paints, paper coating colors, 
plastics, rubber and other applications. The dosage of fluxing agent and 
the type of fluxing agent required are dependent on the hydrous kaolin 
feed and its particle size. The upper limit of temperature of calcination 
is dictated by the mullite index. The mullite index measures the amount of 
mullite (3Al.sub.2 O.sub.3.SiO.sub.2) formed from calcination. 
As taught in Fanselow et al and other patents in the art, kaolin clay is 
conventionally dispersed before spray drying to provide fluid slurries of 
commercially practical solid levels. In typical practice soda ash is added 
normally as a part of a dispersant package during dispersion of kaolin 
slurries. As in the illustrative examples herein, two dispersant 
combinations, SAP and SAC, are generally used. SAP is an 18 to 21% 
solution of soda ash, partially neutralized polyacrylic acid (C211) and 
SHMP (sodium hexametaphosphate) at an active ratio of 49/22/29 
respectively. SAC is an 18 to 20% solution of soda ash and C2111 at an 
active ratio of 50/50. Normally the highest level of these dispersants 
used is 6 #/T or 0.3% by weight (pH of slurry adjusted to 7.5). This 
translate to 0.15% soda ash added with SAP and 0.15% soda ash added in the 
case of SAC. The highest level encountered in a typical commercial plant 
is approximately 8 #/T SAP (pH of slurry adjusted to 8.0) which translates 
to 0.20% soda ash. It is believed that other kaolin manufacturers also use 
the same range of soda ash concentrations to disperse their slurries. In 
the practice of our invention, one of the preferred fluxes is soda ash. 
The lowest soda ash level (.gtoreq.0.30%) employed is at least 50% higher 
than the highest soda ash level used for dispersing kaolin slurries. 
Suitable, preferred and especially preferred feeds for the practice of this 
invention have PSD as follows: 
______________________________________ 
Cumulative Mass Finer (%) 
Diameter (um) 
Suitable Preferred 
Most Preferred 
______________________________________ 
10.0 100 100 100 
5.0 100 100 100 
2.0 87-100 95-100 96-100 
1.0 70-100 80-99 88-99 
0.5 37-95 60-93 70-93 
0.3 19-95 35-70 50-70 
______________________________________ 
At a given dosage of flux, the finer the feed, the greater is the degree of 
coarsening across the whole particle size rage. The degree of coarsening 
is defined as the change in % cumulative mass finer between the calcined 
product and the hydrous kaolin feed at a given diameter (equivalent 
spherical diameter esu). At the same dosage of flux as the hydrous kaolin 
feed becomes coarser, the degree of coarsening across the whole particle 
size range is less. A broad window for controlled coarsening is available 
with a fine feed, the fineness of the feed only being limited by 
processing capability and economics. If, however, the feed is too coarse, 
it becomes increasingly difficult to achieve controlled coarsening for low 
sheen, high hiding pigments. 
The fluxing agents employed are capable of wide variation that will produce 
controlled coarsening of hydrous kaolin on calcination. The fluxing agents 
include alkali and alkaline metal ion salts of metal oxides, carbonates or 
their combinations. Typical metal oxides are boron oxides, silicates, 
alkali and alkaline earth oxides, germanates, phosphates, alumina, 
antimony oxide, lead oxide, zinc oxide, arsenic oxide and zirconate. Also 
included is boric acid. Typical carbonates are alkali and alkaline earth 
carbonates such as sodium carbonates, sodium bicarbonates, calcium 
carbonate and magnesium carbonate. This list is by no means exhaustive. 
Also included are organic and inorganic non-oxide salts of alkali or 
alkaline earth metal capable of forming metal oxides on exposure to air at 
calcination temperatures including halides, nitrates, acetates, 
hydroxides, sulfates and organic polyelectrolytes such as a sodium salt of 
poly[acrylic acid]. The key criteria is that the fluxing agent produces 
controlled coarsening of hydrous kaolin on calcination. Preferred fluxing 
agents are alkali and alkaline earth of boron oxides, silicates, 
phosphates, alkali and alkaline earth metal salts of carbonates and 
bicarbonates, or their combinations. Especially preferred are borax 
[sodium borate, Na.sub.2 O.2B.sub.2 O.sub.3 either in hydrated or 
anhydrous form], soda ash [Na.sub.2 CO.sub.3 ], sodium silicates with 
weight ratio of SiO.sub.2 Na.sub.2 O of 2.00 to 3.25. They are especially 
preferred for their ready availability, ease of mixing with hydrous kaolin 
in slurry form and low dosage level to affect controlled coarsening and 
its low cost. 
The amount of flux added to the hydrous kaolin slurry may vary with the 
particle size distribution of the hydrous kaolin feed and the 
characteristics of the fluxing agent including its inherent coarsening 
ability and its alkali or alkaline earth metal oxide equivalent weight. It 
is recognized that in certain complex flux such as borax, the boron oxide 
component acts as a network former while the sodium oxide component acts 
as a network modifier to give a more random network structure. Therefore, 
both components of complex fluxes such as borax and sodium silicates 
contribute to coarsening of the particles. For ease of description, the 
amount of flux is given in terms of sodium oxide weight equivalent. The 
sodium oxide weight equivalent range is different for simple fluxes such 
as sodium carbonate to that for complex fluxes. The ranges are summarized 
as follows: 
______________________________________ 
% flux as Na.sub.2 O wt equivalent 
based on dry clay 
Simple Flux 
Complex Flux 
______________________________________ 
Range 0.02-1.50 0.02-0.75 
Preferred 0.20-1.00 0.08-0.55 
Most Preferred 0.40-0.75 0.16-0.40 
______________________________________ 
In the presence of flux, calcination temperatures range from above 500 to 
1200C and preferably between about 750 to 1100C, embracing both metakaolin 
and fully calcined conditions. The preferred temperature range is chosen 
to achieve a good balance between pigment PSD, brightness and opacity. 
Prior art publications disclose that the presence of certain flux reduces 
the calcination temperature to arrive at a given mullite content in 
calcined clay. We found that mullite content for fluxed calcined kaolin is 
not an issue in performance. 
The PSD of products preferred and most preferred are: 
______________________________________ 
% Cumulative Mass Finer Than 
Diameter (um) Preferred 
Most Preferred 
______________________________________ 
10.0 75-95 80-95 
5.0 55-85 75-88 
2.0 45-70 50-70 
1.0 30-50 35-45 
0.5 2-15 5-15 
0.3 0-5 0-5 
______________________________________ 
The most preferred PSD range gives the best balance of low sheen and high 
hiding for the calcined product. 
In the practical use of pigments of this invention for paints, it is 
undesirable to have residue levels [retained on a 325 U.S. mesh screen] to 
be higher than 0.15%(wt.). The residue may appear in the paint film as 
grit or give an unsmooth feel. In fact, it is preferred to have products 
with +325 mesh residue at or below 0.10%(wt.). This is controlled by 
preventing excessive coarsening. The most preferred range of PSD for the 
product normally provide +325 mesh residue at or below 0.10%. For calcined 
products without flux, the amount of mullite (3Al.sub.2 O.sub.3.SiO.sub.2) 
is controlled by avoiding excessive calcination times and temperature. Our 
experience with the fluxed product is that even with mullite index 
normally thought to be high enough to give unacceptable abrasion with 
paper coating grades of calcined kaolin, in fact gave low abrasion. 
Therefore, for fluxed calcined kaolins, the value of mullite index is not 
an issue for performance in paints. 
Intended use is in architectural paints in general and in flat interior 
trade paints in particular. Flat paints account for over 50% of the total 
volume of trade paint sales. These are high PVC (pigment volume 
concentration) ranging from 55 to 80% formulated above CPVC (critical 
PVC). Flat paints as the name suggest have very low gloss. A sheen 
(measured on 85 degree glossmeter) of 5 or less is highly desirable. The 
top of the line paints customarily have a high TiO2 loading and lower PVC. 
They therefore exhibit better hiding and film integrity. Flat paints also 
use maximum amount of extenders and calcined kaolin clay is invariably one 
of the extenders. The role of the calcined clay is to extend TiO2, improve 
opacity and tint strength and provide sheen control. Products of this 
invention give very low 85 degree sheen, excellent opacity and tint 
strength particularly in top of the line flat paints. 
A typical premium flat paint formulation is: 
For a 55 PVC flat paint using a vinyl acrylate latex resin as binder, the 
pigment composition is: 
______________________________________ 
Lb./100 gal 
______________________________________ 
TiO2 50-100 
Calcined kaolin 
180-210 
______________________________________ 
Other potential application area are in exterior flat & interior egg-shell 
(or satin) paint. 
In all examples, pre-dispersed slurries of hydrous kaolin containing 
dispersant mixtures were used prior to flux addition. In all cases, fluxes 
were added as solutions prior to incorporation into pre-dispersed 
slurries. 
The following test procedures were used in the illustrative examples: 
GEB--TAPPI Method T646 om-86 (brightness of clay and other mineral 
pigments) 
PSD (Particle Size Distribution)--Measured with Sedigraph using 
Micromeritics SEDIGRAPH 5100; reported on a weight bases. 
Contrast Ratios--measures hiding power of paints by reflectometry--ASTM 
D2805-88 
Reflectance--ASTM D2805-88 
Whiteness--ASTM E313-73 
Yellowness--ASTM E313-73 
Sheen--measures near-grazing shininess or specular gloss at 85.degree. 
geometry--ASTM D523-80 
Tint Strength Y--standard method for relative tint strength of white 
pigments by reflectance measurements--ASTM D2745-80 
Gardner Coleman Oil Absorption Test is based on ASTM D-1483-84 
Mullite Index is determined by an Engelhard Standard Lab Test Method MGA 
0990.1. The automated powder X-Ray diffractometer is used to determine the 
integrated peak intensities of 2 Mullite reflections (121 and 331) for the 
calcined kaolin sample, a 100% reference Mullite and one working standard. 
The method generates a number designated as the Mullite Index, which is 
the ratio of the average integrated intensity of the reflections for a 
sample, to the corresponding reflections for the set of working standards.

EXAMPLE 1 
Several hydrous kaolin feeds of different average particle size and without 
added flux were calcined at 1066.degree. C. The particle size of the feed 
and calcined product are given in Table 1. Data in Table 1 show that on 
calcination, the average particle size increased with feed particle size. 
The pigments were formulated into 55 PVC latex flat paints using a vinyl 
acrylic latex resin as binder. The pigment formula used in units of lb/100 
gal consisted of 100 lb. of TiO2 and 180 lb. of calcined kaolin clay. 
Total solids were 35.64% by weight and 22.81 by volume. 
When formulated in 55 PVC latex flat paints, A and B pigments have high 
hiding (high contrast ratio) and tint strength but very high sheen. Note 
that A and B are representative of pigments obtained by practicing the 
teachings of Fanselow et al. These attributes disqualify A and B pigments 
from being used in flat paints. The coarser C pigment at 1.4 micron 
average particle size gave 5.9 sheen and sufficient hiding and tint to 
qualify it for use in flat paints. For premium flat paints, however, sheen 
values of 4.0 or below is desired. 
TABLE 1 
______________________________________ 
Typical Paint of Conventional Calcined Kaolin Clays 
in 55 PVC Latex Flat Paint 
Pigment A B C 
______________________________________ 
Ave Particle Size of feed in um 
0.3 0.4 0.7 
Ave Particle Size of product in um 
0.8 0.9 1.4 
As 55 PVC latex Flat Paint* 
Properties 
Contrast Ratio 1.5 mils 
95.9 96.02 91.5 
Contrast Ratio 3.0 mils 
98.8 98.5 96.4 
Reflectance 94.8 95.0 92.2 
Whiteness 81.3 84.0 76.6 
Yellowness 3.57 2.88 4.24 
Sheen 85 degree 22.7 13.4 5.9 
Tint Strength Y 56.3 55.4 47.2 
______________________________________ 
*Pigment Formula in lb/100 gal: 100 TiO2, 180 calcined kaolin clay 
EXAMPLE 2 
In accordance with the present invention, a filter cake of hydrous kaolin 
with an average particle size of 0.2 micron was dispersed and sufficient 
aqueous solution of 2.0% sodium tetraborate decahydrate (borax) added to 
provide a 1.0% dosage on kaolin solids. The slurry was mixed thoroughly 
for an additional 15 minutes. The pH of the slurry was 8.8. The slurry was 
spray dried and pulverized in a Mikro Mill (from Pulverization Machinery 
Co., of Summit, N.J.). The pulverized material was calcined in a 
Thermolyne muffler furnace at 815.degree. C. The product was pulverized in 
conventional manner. The sample was identified as D. A separate sample, 
identified as E, was calcined at 1066.degree. C. and pulverized. The 
pigments were formulated into 55 PVC latex flat paints using a vinyl 
acrylic latex resin as binder. The pigment formula used in units of lb/100 
gal consisted of 50 lb. of TiO2 and 210 lb. of calcined kaolin clay. Total 
solids were 36.86% by weight and 22.78 by volume. 
The properties of pigments D and E are compared with C together with flat 
paint performance properties in Table 2. Also compared is a commercial 
double calcined pigment supplied under the registered trademark OPTIWHITE 
(flash calcination followed by conventional calcination) from Burgess 
Pigment. 
The borax containing pigments D and E are finer in average particle size 
than C, but produced dramatically lower sheen, higher hiding and tint 
strength than C. Pigments D and E are considered excellent pigments for 
premium flat paints. The commercial shock calcined kaolin showed slightly 
higher sheen, lower hiding and tint strength than either D and E. Pigment 
E gave higher whiteness and less yellowness than OPTIWHITE pigment. 
TABLE 2 
______________________________________ 
Comparative Properties and Flat Paint Performance 
of Borax Flux Calcined Kaolin 
OPTI- 
Pigment C D E WHITE 
______________________________________ 
% borax 0 1.0 1.0 0 
Calcination Temperature 
1066.degree. C. 
815.degree. C. 
1066.degree. C. 
GEB 90-92 91.0 92.9 91 
Ave Particle Size of Feed 
0.7 0.2 0.2 
in um 
Ave Particle Size of Product 
1.4 0.7 1.0 1.4 
in um 
% at 10 um 98.1 88.6 85.0 95.9 
% at 5 um 89.0 73.6 70.0 87.7 
% at 2 um 61.7 61.6 57.6 62.1 
% at 1 um 38.2 56.0 48.8 34.8 
% at 0.5 um 10.5 20.0 13.8 5.6 
As 55 PVC latex Flat Paint* 
Properties 
Contrast Ratio 1.5 mils 
89.5 92.7 91.2 90.1 
Contrast Ratio 3.0 mils 
96.3 97.4 97.1 96.1 
Reflectance 91.8 95.2 95.0 94.3 
Whiteness 79.0 73.4 76.3 72.7 
Yellowness 3.48 4.71 3.92 4.73 
Sheen 85 degree 
5.1 2.5 2.8 3.1 
Tint Strength Y 
47.9 56.9 55.8 53.1 
______________________________________ 
*Pigment in lb/100 gal: 50 TiO2, 210 calcined kaolin clay 
EXAMPLE 3 
A hydrous feed slurry used for making ANSILEX 93 hydrous kaolin was mixed 
thoroughly with 0.75% of sodium carbonate (soda ash). The slurry was spray 
dried and pulverized in a Mikro Mill. The pulverized material was calcined 
in a Thermolyne muffler furnace at 1066.degree. C. The product was 
pulverized and the sample identified as F. A separate sample identified as 
G was prepared in the exact manner as F except that the feed slurry was 
mixed with 1.0% soda ash before spray drying. The physical properties and 
flat paint performance of pigments F and G are compared with OPTIWHITE 
pigment in Table 3. 
The soda ash modified pigments F and G showed at least equivalent 
properties compared to that of OPTIWHITE. An advantage seen is 
significantly lower 85 degree sheen than OPTIWHITE to give greater 
flatness in paint. 
TABLE 3 
______________________________________ 
Properties and Flat Paint Performance of Soda-Ash Flux Calcined Kaolin 
Pigment F G OPTIWHITE 
______________________________________ 
% soda ash (NA2CO3) 
0.75 1.0 0 
Calcination Temperature in C. 
1066 1066 
GEB 91.7 91.4 91 
Ave Particle Size of Feed in um 
0.25 0.25 
Ave Particle Size of Product in um 
1.5 1.8 1.4 
% at 10 um 87.0 83.3 95.9 
% at 5 um 75.7 70.2 87.7 
% at 2 um 57.5 52.6 62.1 
% at 1 um 33.8 30.3 34.8 
% at 0.5 um 6.6 6.1 5.6 
As 55 PVC latex Flat Paint* 
Properties 
Contrast Ratio 1.5 mils 
90.4 90.2 89.8 
Contrast Ratio 3.0 mils 
96.6 96.3 96.2 
Reflectance 89.8 89.4 89.4 
Whiteness 73.3 72.4 73.1 
Yellowness 4.58 4.74 4.57 
Sheen 85 degree 1.5 1.1 3.0 
Tint Strength Y 51.7 50.47 51.5 
______________________________________ 
*Pigment in lb/100 gal: 50 TiO2, 210 calcined kaolin clay 
EXAMPLE 4 
In accordance with a presently preferred embodiment of our invention, an 
ANSILEX 93 hydrous feed slurry was mixed thoroughly with 1.0% by weight of 
sodium silicate (based on clay solids) with a modulus of 2.88. The slurry 
was spray dried and pulverized in a Mikro Mill. The pulverized material 
was calcined in a Thermolyne muffler furnace at 1066.degree. C. The 
product was pulverized and the sample identified as H. A separate sample 
identified as I was prepared in the exact manner as H except that the feed 
slurry was mixed with 1.25% sodium silicate before spray drying. The 
physical properties and flat paint performance of pigments H and I are 
compared with OPTIWHITE pigment in Table 4. The paint formulations were 
identical to that described in Example 2. 
The sodium silicate modified pigments H and I showed at least equivalent 
properties compared to that of OPTIWHITE pigment. An advantage seen in 
that H gave significantly lower 85 degree sheen than OPTIWHITE pigment. 
TABLE 4 
______________________________________ 
Properties and Flat Paint Performance of 
Sodium Silicate Flux Calcined Kaolin 
Pigment H I OPTIWHITE 
______________________________________ 
% Sodium Silicate (2.88 modulus) 
1.0 1.25 0 
Calcination Temperature in C. 
1066 1066 
GEB 90.9 91.0 91 
Ave Particle Size of Feed in um 
0.25 0.25 
Ave Particle Size of Product in um 
1.4 
% at 2 um 54.9 59.2 62.1 
% at 1 um 29.5 35.5 34.8 
% at 0.5 um 5.2 6.5 5.6 
As 55 PVC latex Flat Paint* 
Properties 
Contrast Ratio 1.5 mils 
91.3 91.2 90.8 
Contrast Ratio 3.0 mils 
96.7 96.5 96.7 
Reflectance 89.1 89.3 88.9 
Whiteness 72.5 72.4 73.0 
Yellowness 4.67 4.74 4.47 
Sheen 85 degree 2.3 3.1 3.1 
Tint Strength Y 44.4 44.2 44.2 
______________________________________ 
*Pigment in lb/100 gal: 50 TiO2, 210 calcined kaolin clay 
EXAMPLE 5 
This example shows that the controlled coarsening of feed useful to produce 
ANSILEX 93 with calcined kaolin pigment soda ash flux resulted in lower 
oil absorption that is similar to that produced by the flash calcined 
OPTIWHITE pigment. The lower oil absorption is a desired property with 
benefits in providing higher loading of extender and improved scrub 
resistance of the paint film. 
______________________________________ 
Oil Absorption Data Comparison: Gardner Coleman Method 
1.0% Soda Ash 
ANSILEX 93 
flux ANSILEX 93 
OPTIWHITE 
______________________________________ 
Oil Absorption 
105-120 87 85 
APS um 0.78 1.32 1.4 
______________________________________ 
EXAMPLE 6 
The results of the following tests indicate that wet processing (using soda 
ash and sodium chloride) followed by spray drying of ANSILEX 93 feed 
produces benefits not obtained by dry blending. The desired coarser but 
balanced PSD products are obtained using the wet processing method. The 
dry blend method gave significantly higher residue (retained on a 325 mesh 
screen) that was about 5 to 19 times higher than the wet processing 
method. 
For these samples calciner feed and spray dryer feed was recovered at a 
commercial plant. To simulate prior art, the dry soda ash was added (0.8%, 
1.2% and 1.6%) and mixed with hydrous kaolin in a roller mill for 1 hour. 
Then it was ball milled for 15 minutes. PSD analyses were performed, 
before and after ball milling. NaCl (dry) was added to one sample in 
amount of 3% by weight of the kaolin, following which it was pulverized, 
using the same procedures employed with soda ash. The particle size 
distribution (PSD) of the dry blended kiln feed samples are given in Table 
5. Within experimental error for measuring PSD using SEDIGRAPH analysis, 
no change was seen in the PSD resulting from dry blends of soda ash (SA) 
to ANSILEX 93 feed. This was true whether the blend was simply roller 
milled or subsequently ball milled. For purposes of comparison the same 
amounts of soda ash and NaCl were added to predispersed slurries and spray 
dried. These were then pulverized and all were calcined at 1950.degree. F. 
and post pulverized. 
TABLE 5 
______________________________________ 
Properties of Dry blended Kiln Feed Samples 
Sample Ball mill 2 um 1 um .5 um .3 um 
Med. um 
______________________________________ 
A93 NO 95.8 88.0 71.4 49.0 0.31 
A93 YES 96.8 88.6 71.9 49.7 0.30 
.8% SA NO 96.3 88.5 72.1 49.6 0.30 
.8% SA YES 95.9 88.0 71.7 49.0 0.31 
1.2% SA NO 96.4 89.1 71.6 48.9 0.31 
1.2% SA YES 96.1 88.1 70.8 48.5 0.31 
1.6% SA NO 96.4 88.5 70.9 48.3 0.31 
1.6% SA YES 96.3 88.7 70.4 48.1 0.31 
______________________________________ 
TABLE 6 
__________________________________________________________________________ 
Properties of Flux Calcined Kaolins Derived From Dry Blended and Slurried 
Feeds 
Dry/ 
Test 
slurry 
br L A B YI 2 um 
1 um 
.5 um 
.3 um 
Med. 
Res. 
__________________________________________________________________________ 
As is 
Slurry 
92.4 
97.66 
-0.65 
2.95 
4.44 
81.8 
58.3 
11.9 
2.8 
0.88 
0.015 
As is 
Dry 92.2 
97.66 
-0.60 
2.85 
4.31 
89.7 
69.7 
19.7 
4.1 
0.74 
0.032 
.8% SA 
Slurry 
91.8 
97.51 
-0.68 
2.90 
4.39 
74.5 
47.3 
9.4 
2.3 
1.05 
0.037 
.8% SA 
Dry 91.7 
97.39 
-0.54 
2.77 
4.19 
87.7 
68.4 
19.8 
4.1 
0.75 
0.170 
1.2 SA 
Slurry 
91.7 
97.54 
-0.70 
2.91 
4.39 
68.3 
39.8 
6.1 
1.3 
1.21 
0.037 
1.2 SA 
Dry 91.7 
97.37 
-0.62 
2.75 
4.16 
85.1 
66.3 
19.6 
4.4 
0.76 
0.307 
1.6 SA 
Slurry 
91.5 
97.44 
-0.69 
2.96 
4.47 
67.2 
38.7 
7.0 
2.6 
1.24 
0.018 
1.6 SA 
Dry 91.5 
97.33 
-0.62 
2.71 
4.10 
82.4 
64.7 
19.1 
3.7 
0.77 
0.340 
3NaCl 
Slurry 
92.6 
97.74 
-0.70 
2.74 
4.14 
72.4 
36.2 
5.3 
2.0 
1.24 
0.04 
3NaCl 
Dry 92.8 
97.73 
-0.58 
2.56 
3.86 
80.5 
44.9 
7.3 
2.1 
1.08 
0.256 
__________________________________________________________________________ 
Br = GEB, pigment brightness TAPPI T646om-86 
L = Hunter L* 
A = Hunter A* 
B = Hunter B* 
YI = pigment yellowness index* 
Res = +325 mesh residue in % 
*ASTM D224479, also, Color Science, G. Wyszecki/W. S. Stiles, Wiley 1967 
The properties of flux calcined kaolins derived from dry blended and 
slurried feeds are summarized in Table 6. In all cases, the wet processing 
or slurry route for incorporating the flux to the pigment gave more 
extensive coarsening but significantly less residue. This indicates that 
desired coarsening is achieved more advantageously by the wet processing 
or pre-slurrying the flux with the hydrous kaolin pigment than by dry 
blending.