The extruder: The core machine of the masterbatcher

A single or twin-screw extruder with electric motor that drives long worm shafts in a cylinder is the most common machine for producing masterbatches.

From kneader to extruder
Th is was the birth of the medium-sized composite and masterbatch industry. “Special wishes” were – and still are – its business model. The masterbatcher produces precisely the compounds that the plastic processor requires. Or alternatively, a ten to eighty-fold concentrated premix consisting of pre-dispersed pellets of basic plastic and additives that the plastic producer adds to the base plastic.

The kneading technology used in the rubber industry was just right for the budding industry. Th e Banbury mixer produced the “masterbatch,” a uniform, concentrated mixture of the additives in a base plastic. Th us, the term “masterbatch” migrated from rubber to plastic materials. With an increasingly better dispersion capacity, the extruder quickly became an alternative to the kneader. Today, twin-screw extruders are usually used to homogenise the thermoplastic materials, fillers and additives in the compounding process, which is followed by granulation to form the masterbatch, that is, the concentrated dye or functional polymer. Extruders are still the first choice for standard thermoplastics. Th e name “masterbatch” has prevailed in Europe as an umbrella term for the product family of colour and additive concentrates.

As far as we know, the company Americhem produced the fi rst colour concentrates in 1959. Italian manufacturers took the lead in Europe. Th e company Sarma was already producing concentrated colour pellets there in the early 1960s. By the end of the 60s, the industry was beginning to develop dynamically. In Germany, Siegle/BASF started masterbatch production in Stuttgart while Treff ert operated in Bingen (1969). Additional masterbatch manufacturers took up production in 1971: Schroeder & Stadelmann in Lahnstein, Albert Schleberger in Remscheid and Constab in Rüthen.

Colourful brilliance thanks to new pigments
As the carrier polymer, the masterbatch manufacturer generally uses the polymer to be coloured by the processor. Colourists compose the required colour from various pigments and use additives to achieve the other properties of the plastic product. The processor adds the granulated concentrate to the uncoloured plastic in quantities of between two and six percent. Production is largely clean. If there is an error in the calculation, the producer is left only with small residual quantities of the masterbatch and not as before with large amounts of coloured plastic. Polyolefi ns and polystyrenes were coloured with inorganic pigments at fi rst, which maintained the process temperatures. Th e development of heat-stable, organic pigments in the 1970s and 80s facilitated the production of a greater variety of brilliant colours. Plus, new colourants hit the market not too long aft er which enabled metallic and lustre eff ects and transparent shades. At the same time, an increasing number of additives expanded the range of thermoplastic applications: UV absorbers, for example, now provide resistance to sunlight in numerous plasticitems and other functional additives improve heat aging. The latest additives make plastics laser-inscribable or heat-absorbing and even provide forensic safety features that make product counterfeiting more diffi cult.

The success of the Masterbatch industry has contributed to various technical developments. Since the end of the 70s, colour measuring systems have been used in parallel with conventional visual matching to increase quality. Th e extruder, the core of masterbatch production, also steadily improved, as have mixers; new designs have allowed better homogenisation of the premix. Moreover, the development of gravimetric metering has made the premix partly unnecessary. Masterbatches in pellet form have become ever more prevalent and masterbatch manufacturers typically use strand or underwater pelletising for this purpose. Water-sensitive products are air-cooled.

Uniqueness as a success model
Today, masterbatch manufacturers use a wide variety of techniques and materials. Only by combining them correctly can the diff erent requirements and objectives of the manufacturers of plastic items be met. Th e application of colour eff ects is only one – obvious – feature of the masterbatch that makes unique product ideas economically successful. Th e masterbatch manufacturer can use their expertise to show the user where the industry is heading in the 21st century. Together, they create new applications for thermoplastics – possibilities that manufacturers and users of the new masterbatches in the 70s could have hardly imagined.

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