Masterbatch: Colors and Pigments for Plastic
Master batch is very familiar term in plastic industry but very little peoples know what actuality a master batch is. Its common understanding that a master batch is a color. Second name of master batch in many plastic industries is color. Master batch is alternative name of color but it’s not only the color. Masterbatch have minimum two components 1st is carrier resin/plastic and 2nd is color, additive or filler.
Carrier resin is a plastic/Polymer which is used for holding the high concentrations of pigment in color masterbatch. Carrier resin is selected on the basis of final products material/resin. The carrier material of the masterbatch can be based on a wax (universal carrier) or on a specific polymer, identical or compatible with the natural polymer used (polymer-specific). E.g. EVA or LDPE can be used as carriers for polyolefins and nylon, polystyrene can be used for ABS, SAN, and sometimes polycarbonates. When a carrier different than the base plastic is used, the carrier material may modify the resulting plastic’s properties; where this could be important, the carrier resin has to be specified. The usual ratio of masterbatch to the base resin is 1 to 5 percent. Several masterbatches (color and various additives) can be used together. The carrier can also double as a plasticizer (common for liquid masterbatches) or a processing aid.
Colors are added to enhance the quality aesthetic look of final product. Colors are further dived into two categories. Color that increase the opacity of the product and colors that colors the product but no effect on transparency of the products.
Processing of Masterbatch
There are several distinct stages in the manufacture of masterbatches, and these are mainly as follows:
Firstly, and most important is the color formulation – or additive ratio, for without this, one cannot proceed.
Secondly all the necessary ingredients are weighed and where necessary pre-mixed or fed to individual hoppers. In some instances these are high speed mixed to produce a more homogeneous product.
To regulate the rate at which this pre-mix is fed to the extruder, it is necessary to have a screw fed system, matched to the extruder’s output. As extruders are starve fed devices, the feeder is an important control variable.
The melt mixing stage needs to be carried out at exact pre-determined temperatures where the barrel is set to just liquefy the resin mixture. Too high or too low will give a poor shear with poor pigment dispersion.
Master batch can be divided into different categories
- Color Masterbatch
- Additives Masterbatch
- Fillers Masterbatch
Color masterbatches are the most used master batch. Why masterbatch is preferred over simply adding the color the answer is that when we add color directly to mixer there are many issues relating to this. Poor mixing is of color, color density difference, agglomerations etc.