Mixtures must insure uniform distribution of colorant and material and identical
procedures must be used from batch to batch. Good housekeeping is mandatory
to eliminate discoloration due to contamination and static electrical charges.
Resin and additives (colorants) must be weighed as accurately as
possible. Once this ratio is established, it must be reproduced exactly, as many
times as necessary.
Ribbon blenders, cement mixers, double cone blenders, drum tumblers, and high-intensity mixers are utilized. A timer is mandatory on any of these devices. Varying mixing times may change the color. Short durations (thirty
seconds to five minutes) are recommended for high intensity mixing where frictional heat will develop on the mixing blades and actually melt the material.
Dry Color Mixing
Fifteen to thirty minutes is required for tumbling or low intensity mixing. Chains
or similar mechanical devices can be used in cement mixers, tumblers, and
double cone mixers to add “shear” to the blend of pigment and powdered resin.
A minimum of 25% of the vessel or drum must remain empty to provide adequate
The use of 1 to 2 ounces of mineral oil, surfactant, or liquid anti-stat per
100 lbs. of resin pellets can help dispersion and reduce airborne contamination.
Mineral oil can be added and pre-dispersed or added and tumbled with the dry
color into any resin except polycarbonate.
The key to uniform color from batch to batch is consistency.