Volumen II - SAM

each particle diameter selected, the curves were adjusted to a polynomial equation (Y = A + Bx + Cx 2 + Dx 3 )
employing a regression method; then, the root of the second order derivative was calculated for estimating
the corresponding CPVC (inflexion point).
In short, according to factorial design 81 coatings (nine compositions of the flame retardant pigments x three
particle diameters of micaceous iron oxide x three PVC values) were formulated.
COATINGS MANUFACTURE. Coatings manufacture was carried out by employing a ball mill of 1.0 liter
jar capacity under optimized operative conditions. In a first stage, the flame retardant pigments, the inhibitor
and the opaque pigment together with the dispersant and the rheological agent were added to the chlorinated
alkyd resin solution (50% w/w in white spirit); then, micaceous iron oxide was incorporated up to reach the
dispersion times leading to the mean particle sizes prefixed, Table 3. In all the cases, the total dispersion time
elapsed 24 hours. Finally, internal and superficial dryers were added into the can.
The whole of the experimental samples included duplicates; so 162 coatings were prepared.
LABORATORY TESTS. SAE 1010 test panels (150 x 80 x 2 mm), sandblasted to attain the A Sa 2 ½ (SIS
05 59 00-67) grade and a 30 m maximum roughness Rm, were prepared; then, they were degreased in
vapor phase with toluene. Experimental coatings were brush-applied (2 coats) with a 24 hours lapse between
them, achieving 100-110 m dry film thickness. Coated panels remained at laboratory conditions during a
week and then they were placed in a Salt Spray (fog) Chamber (ASTM B 117); tests were done in duplicate
(162 coatings x 2 panels) and the observations took place after 1000 hours.
Other series of panels were placed in a 100% Relative Humidity Cabinet (ASTM D 2247); the tests were
also done in duplicate making the visual inspections after 1000 hours.
Table 1. Coatings compositions, solids % in volume
Sample
Component A B C
Titanium dioxide 11.5 12.8 14.0
Flame retardant pigment* 7.5 8.3 9.2
Micaceous iron oxide** 17.0 18.9 20.8
Zinc hydroxyphosphite 6.9 7.7 8.4
Chlorinated alkyd resin (solids) 52.4 47.6 42.9
Inorganic rheological additive 2.8 2.8 2.8
Additives 1.9 1.9 1.9
PVC, %
* Table 2
45.0 50.0 55.0
** Three dispersion times (mean particle diameter)
Component
Table 2. Flame retardant pigment composition
%, in volume
I II III IV V VI VII VIII IX
Antimony trioxide 100.0 0.0 0.0 50.0 50.0 30.0 25.0 20.0 15.0
Zinc borate 0.0 100.0 0.0 50.0 0.0 35.0 37.5 40.0 42.5
Trihydrated alumina 0.0 0.0 100.0 0.0 50.0 35.0 37.5 40.0 42.5
Table 3. Dry film permeability (100-110 m thickness) vs. micaceous iron oxide dispersion time
PVC, % Dispersion
time, min
Permeability*,
10 4 g.cm -2 .h -1
Dp, m CPVC, %
120 5.5 45 54/58
45.0 165 3.0 40 55/59
225 1.5 35 56/60
210 9.0 45 54/58
50.0 265 7.1 40 54/58
335 3.8 35 56/60
250 15.1 45 54/58
55.0 305 13.0 40 54/58
375 11.1 35 56/60
952