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Polyolefins, being nonpolar are difficult to colour.
Typically PE waxes are needed to enhance pigment dispersion. These
PE Waxes are so far being manufactured using Ziegler-Natta catalysts.
These catalysts generally produce waxes with broader molecular structure/variations.
These variations lead to wide variations in melting points and viscocities.
Pigment dispersions with the conventional waxes therefore could
show variations.
Recently PE as well as PP Waxes have been developed by companies
using metallocence single site catalysts. These waxes have a more
well defined molecular structure on account of excellent control
in polymerization. Some waxes developed with propylene and ethylene
to achieve better polarity have been evaluated as replacements for
the conventional waxes for manufacture of colour concentrates along
with the conventional PP carrier. These Metallocence PP/PE waxes
have been found to enhance the dispersion of some difficult colourants
like red and yellow. Infact these 'difficult to disperse' pigments
would be used at higher concentrations without affecting dispersion
adversely.
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