Color Masterbatch Production

At present, there are two processes for color masterbatch production: premix and split-feed.The flow could be summarized as: 

Material preparing(drying)→weighing→Premix/split-feed→ twin-screw compounding extruder →cooling →air drying →pelletizing →sieving→ homogenizing→ packing

For pre-mix process,the components of color masterbatch are blended by conventional means in mixers, such as the Banbury mixer, High speed mixer. This requires carrier resin intimate mixing with pigments,dispersing agents and additives in only one process step before introduced to the extruder by a volumetric feeder.This process step is very important because it determines the the quality of the masterbatch.If agglomeration has formed during this process, it cannot be remedied in the extrusion process.

For split-feed process, carrier resin, pigment and additives are fed by two or more seperate gravimetric feeder. It is suitable for heat shear sensitive pigment. Introduced by side feeder along the main extruder, the pigments experience less mechanical shear by the two co rotating screws in the compounding process.Wetting by molten polymer, the dispersion is subsequent.For color-pigment powder loadings higher than 20% and anywhere up to 80%, side -split will also be more efficient.

Comparison between premix and split-feed

Pre-mix need lower investment cost and easier to operate however volumetric feeding in pre-mix process is less automatic than split-feeding by gravimetric feeders. 

The most widely used processing technology is high speed mixing and co-rotating twin-screw extrusion technology. This involves the uniform mixing and dispersion of pigments and the control of the screw extrusion process.

The uniform mixing and dispersing of pigments is mainly accomplished by high-speed mixing machine.When the high-speed mixer operates, the rapidly rotating blades utilize friction with the material's surface and the thrust on the material's side to induce a tangential motion along the blades. When it reaches a certain height, influenced by gravity, it falls back to the center of the blades, then is thrown upward again. The combination of this upward and tangential motion places the material in a continuous spiral up-and-down movement.

Due to the high speed of the blades, the material moves rapidly, and the particles in fast motion collide and friction with each other, causing agglomerates to break, elevating the material's temperature accordingly. This facilitates rapid interactive mixing, promoting the uniform distribution of components and the absorption of liquid additives.

In extrusion process,materials are mixed and melted—generally in a twin screw extruder of some type—then pelletized.Under the motion of the rotating screw, the mixed materials are continuously conveyed forward, during which the materials are continuously compressed and pushed under pressure. Friction, shear, and heat generation occur between the materials and between the materials and the screw barrel. Simultaneously, with the application of external heating, the phase structure of the materials undergoes a transformation, gradually melting into a viscous molten state. Subsequently, under the action of the extrusion system, the homogenized plastic melt is quantitatively, temperature-controlled, and pressure-controlled extruded through the extruder's head and die.

In order to achieve good dispersion of pigments and maintain dispersion stability, in addition to controlling the composition of the formulation and extrusion temperature and speed, the length-to-diameter ratio of the screw and screw configuration are also crucial.