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Pigments**/Fillers
The choice of dispersant is also related
to the surface nature of the pigment. The polarity of the surface of the
pigment differs from organic (non-polar) to inorganic (more polar), and
this means that the nature of the dispersant anchor group is critical
for optimum adsorbtion. The choice of anionic anchor group should allow
for better performance with inorganic pigments and a cationic anchor group
should be more appropriate for organic pigments.
The surface area of the pigment also affects the level of dispersant used,
and in general, if too little is used then the full benefits will not
be realised. If too much is used, it can be shown that the thickness of
the protective barrier is actually reduced as a result of overcrowding
on the pigment surface. Therefore the use of an excess level of dispersant
actually leads to final coating properties which are inferior to those
obtained with an optimised dosage. Furthermore, film properties such as
adhesion or hardness can be adversely affected by the use of an excess
of dispersant because of the free molecules in the drying film.
The Table below show a
typical white solvent-based coil coating formulation (Polyester/Melmine Formaldehyde System) using polymeric
dispersant (Solsperse).
Millbase |
% |
| Titanium Dioxide (TiPure™ R60) |
1.48 |
| SOLSPERSE 36600 |
1.48 |
| Cymel™ 303 (98%) |
10.32 |
| Di Basic Esters |
2.98 |
| MPA |
8.92 |
| Xylene |
2.24 |
| Butanol |
0.06 |
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100 |
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For technical advices on how to disperse your
pigments / fillers in your resin solution, contact our experts via TechDirect |
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