Brushstrokes - October 2011 - Surface Coatings Association of New ...

Table 1 – interior wall paint formulation
techniques to achieve the optimum particle size distribution without
affecting the unique morphology. The deposit is fine and white with
a high carbonate content and an iron content of only 0.03%.
Details of the morphology and physical properties can be seen in
figure 1 and table 1. It occurs naturally as an aggregate of platy
crystals with sides of ≈ 0.5 – 1.0µm and an aspect ratio of 10:1.
The defining properties are the high brightness, low particle size
and the high oil absorption/ surface area. The advantages of
these properties will be shown in the following work.
The properties of the other test fillers (as measured by SSME)
are summarised in table 3. Where quoted, the manufacturers
D50 particle size is also given. Measurements were made using
the Sedigraph technique which is useful for platy materials
such as hydrous kaolin, but can give discrepancies for round
or needle shaped particles such as PCC. A lower value would
be expected for the calcined kaolin suggesting this sample was
highly agglomerated.
Methods
7% TiO2
7% TiO2
+ 20%
Binder
3.5% TiO2
Dispersion - All coatings were produced using a high speed
disperser with a toothed blade. The water, dispersants, calcium
scavenger, biocide, antifoam and thickener were dispersed at
6 SURFACE COATINGS ASSOCIATION OF NEW ZEALAND
3.5% TiO2
+ 10%
Binder
Water 270 270 270 270
Dispersant A 4 4 4 4
Na HMP 1 1 1 1
Dispersant B 1 1 1 1
Biocide 3 3 3 3
Antifoam 2 2 2 2
Cellulose thickener 3 3 3 3
TiO2 80 80 40 40
5µm GCC 290 290 290 290
Test extender 100 100 140 140
Talc 80 80 80 80
Styrene Acrylic
binder
160 192 160 176
Thickener 3 3 3 3
TiO2 PVC 7 6.7 3.5 3.4
Total PVC 72.2 68.4 72.7 70.8
Figure 3 Ankerpoort mine in Greece
Figure 4 (left) - Morphology of complex carbonate extender
Table 2 - Physical properties of complex carbonate extender
Density 2.7g/cm3
Mohs Hardness 2 - 3
Refractive index 1.61 – 1.64
D50 (Sedigraph) 0.56µm
Oil Absn 55-60g/100g
BET 18m2/g
Brightness (Ry) 95
Brightness (ISO) 92.3
pH 10
Table 3 – physical properties of competitive test extenders
Fine GCC PCC
low speed until fully dissolved. The pigment, fillers and extender
were added and dispersed at high speed for 30 minutes until a
grind of 5 or better was achieved. Following this the binder and
thickener were added and dispersed at low speed for a further
30 minutes until a uniform dispersion was achieved.
Brightness and contrast ratio - The coatings were drawn
down onto a Leneta No. 2 opacity chart using a bird type
applicator to give a 150µm wet film thickness and allowed
to dry for 7 days. Brightness was measured as L* using a
spectrophotometer. Contrast ratio was measured as the ratio
of reflected light from the coating over the black and white
portions of the card (RB/RW) expressed as a percentage.
Viscosity measurement - Viscosity was measured using a
Brookfield viscometer fitted with spindle 5. High and low shear
measurements were made at 100rpm and 10rpm.
Results and discussion
Hydrous
Kaolin
Calcined
Kaolin
Density 2.7 2.6 2.6 2.6
D50 (Sedigraph) 1.1 1.38 0.62 6.6
D50 (TDS) 0.2 - 0.3 0.7
Oil Absn 30.5 37.5 42.0 74.5
Brightness (ISO) 91.0 95.5 85.5 90.9
The results for all test measurements are shown in table 4a and
4b. There was no significant difference in the brightness measured
for all formulations, being in the range 95.0 ± 0.6 although it
should be mentioned that the highest brightness for each series