Masterbatch (MB) is a solid or liquid additive for plastic used for coloring plastics (color masterbatch) or imparting other properties to plastics (additive masterbatch). Masterbatch is a concentrated mixture of pigments and/or additives encapsulated during a heat process into a carrier resin which is then cooled and cut into a granular shape. Masterbatch allows the processor to colour raw polymer economically during the plastics manufacturing process.
The alternatives to using masterbatches are buying a fully compounded material, or compounding from raw materials on site (which is prone to issues with achieving full dispersion of the colorants and additives, and prone to preparing more material than what is used for the production run). In comparison with pure pigments, masterbatches require more storage space and their lead times are longer. Another disadvantage is additional exposure of heat to both the carrier and the additive; this may be important e.g. for marginally thermally stable pigments.
As masterbatches are already premixed compositions, their use alleviates the issues with the additive or colorant clumping or insufficient dispersion. The concentration of the additive in the masterbatch is much higher than in the end-use polymer, but the additive is already properly dispersed in the host resin. In a way their use is similar to uses of ferroalloys for adding alloying elements to steels.