Masterbatches are colourant and/or additive concentrates in a solid plastic or plastic-like matrix with a higher colourant and/or additive content than in the final application. They are available in various forms (granulate, liquid, paste, powder).
Masterbatches sind Farbmittel- und/oder Additiv-Konzentrate in fester Kunststoff- oder kunststoffähnlicher Matrix mit Gehalten an Farbmitteln und/oder Additiven, die höher sind als in der Endanwendung. Dabei gibt es verschiedene Lieferformen (Granulat, flüssig - Paste, Pulver).
Masterbatches have become an indispensable part of the plastics processing industry. They are used in all major processing methods in the plastics industry, e.g. extrusion, injection moulding, hollow blow moulding, and are used in a wide variety of costumer industries such as packaging, medical products and the automotive industry.
The advantages for processors are obvious: the production is largely “clean” and, if there is an error in calculation, the producer is left only with small residual quantities of the masterbatch and not as before with large amounts of coloured plastic.
Masterbatches can be used to adjust the look, feel and other properties of plastics. The variety of colourants allowed for metallic and gloss effects or transparent shades. At the same time, more and more additives expanded the range of applications for thermoplastics: UV absorbers, for example, ensure resistance to sunlight in many plastic articles today; other functional additives improve heat ageing. The latest additives make plastics laser-markable, heat-absorbent or even provide forensic security features that make product counterfeiting more difficult.
The manufacturers tailor the colour or additive concentrate to the needs of each individual customer - from producers of cosmetic packaging to automobile manufacturers. The variety is almost infinite, as manufacturers can compose from a wide portfolio of raw materials.
As a carrier polymer, the masterbatch manufacturer usually uses the polymer that is to be coloured by the processor (thermoplastics). More and more recycled materials are now being used. The processor usually adds the granulated concentrate to the uncoloured plastic in quantities of between 2 and 6 percent.
Around 1900, it was important for tyre production to homogeneously distribute the additives and pigments in the rubber mixture, namely sulphur, zinc oxide, chalk and later also carbon black. This was the only way tyre manufacturers could obtain a good result. The components that were difficult to disperse were therefore first mixed well together before they were added to the rubber. Each batch of rubber plus pre-dispersed pigments - so it is said - first had to be checked by the experienced "master". After heating, nothing could have been saved if the mixture had been inadequate. Thus the name "master batch" was born. About half a century later, the term was adopted for customised colour and additive concentrates in the plastics industry.
Alongside colouring agents for polymers, additives have an important role: they improve certain properties of polymers and enable easier handling of plastic products. Similar to colouring agents, there are various different options for additives to polymers. In many fields, preference is given to additive masterbatches – beside the use of treated raw materials.
Where colouring agents are concerned, a differentiation is made between dyes and pigments, with the latter being of much greater importance in the plastics sector. Pigment particles (primary particles) – as they are usually generated in manufacture – have strong forces of attraction, due to their extremely small particle sizes. Consequently, primary particles gather to form so-called aggregates.
The extruder is the core machine of the masterbatch production. Single or twin screw extruders, in which long screw shafts are driven by an electric motor in a barrel, are usually used to produce masterbatches.
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