Color, Combi or Additive Masterbatches (including antioxidant masterbatches) with solid or liquid carriers aim to color (colored masterbatches) or to confer other properties (additive masterbatches) to plastics.
Masterbatch is a concentrated mixture of pigments and / or additives encapsulated during a heating process in a carrier resin that is cooled and cut into a granular form. The Masterbatch allows the transformer to color natural polymer economically during the plastics transformation process.
The alternatives to the use of masterbatches are the purchase of a composite raw material (which may imply an increase in cost and less flexibility, for example, product color variability), or the mixing of raw materials on site (process potentially problematic with regard to the total dispersion of dyes and additives and prone to mandatory acquisition of materials in excess of the necessary ones). Compared to pure pigments, masterbatches require more storage space with longer delivery times.
As masterbatches are already pre-mixed compositions, their use avoids problems of agglomeration of additives or dyes as well as problems of dispersion. The use of masterbatches allows the transformer to acquire a smaller number of degrees of polymer, thus providing conditions for the purchase of raw material in scale.
Masterbatches can be highly concentrated (compared to the final blend), with high “reduction rates”. A 25 kg bag can process a ton of raw material. The relatively diluted nature of materbatches, when compared to raw additives, allows greater precision in the dosing of small quantities of high cost components. The compact nature of the solid masterbatch grains eliminates dust problems, which are inherent in refined solid additives.
Solid masterbatches do not contain solvents and subsequently tend to have a longer service life if they are not evaporated. The masterbatch usually contains 40-65% of additive, but the range can reach values between 15-80% in extreme cases.
The carrier of the masterbatch can be based on a wax (universal vehicle) or on a specific polymer, identical or compatible with the polymer to be transformed to transform. For example, EVA or LDPE can be used as a carrier for polyolefins and nylon, polystyrene can be used as a carrier for ABS, SAN and sometimes polycarbonates.
When a carrier of the masterbatch is incompatible with the raw material, the masterbatch can modify the properties of the transformed material, so whenever necessary, the transformer must specify the characteristics of the raw material.
The percentage of use of masterbatches in relation to the raw material is between 1 and 5%. Several masterbatches (color and additive (s)) can be combined. The transformation equipment is usually fed with raw material and masterbatch. The homogenization of both materials is verified at the end of the machine’s spindle stroke.
Sometimes the system is prone to adverse effects such as the separation of the masterbatch from the raw material in the machine hopper. The masterbatch can also be added directly to the machine’s spindle, as a free-flowing solid or, in the case of a liquid masterbatch via a peristaltic pump. The use of liquid masterbtches allows obtaining highly accurate dosages in addition to rapid color changes between productions.
Masterbatches can be used in most processes, except rotational molding, Plastisol and other liquid resin systems.
Antioxidants are used to protect polymers from degradation, both during processing (=short term stabilization) and during use (=long term stabilization). Polymer degradation generally results in gel formation and changing melt flow index, loss of mechanical and esthetical properties (crazing, gloss reduction, chalking), and discoloration.
Generally during polymer degradation free radicals are formed, resulting in uncontrolled chain reactions. Anti-oxidants are used to decrease the amount of free radicals by different mechanisms e.g. by avoiding the formation of free radicals using complexing agents or hydroperoxide decomposers, or by decreasing the amount of radicals using radical scavengers or hydrogen donors.
A complete range of anti-oxidants exist, starting from cheaper, general purpose anti-oxidants, up to anti-oxidants specially designed for high end applications like hot water pipes. High end anti-oxidants typically have better properties towards discoloration (yellowing/pinking), migration/chalking or hydrolisation.