BASF produces decorative marbling effect for injection-moulded parts

With a patent pending BASF technology, it is now possible to produce marbled serial components made of Ultrason® using a standard injection moulding process. The colouring technique opens up virtually unlimited possibilities for designers to use BASF’s polyarylethersulphone to colour household appliances, catering bowls and containers, as well as visible components.

For the first time, surface effects such as colour shades, colour streaks and patterns can be reproduced: Injection-moulded parts of one series look alike but are not completely identical. The technique has proven to be successful with the two injection-moulding grades Ultrason® E (PESU: polyethersulphone) and Ultrason® P (PPSU: polyphenylsulphone) for the production of one-of-a-kind parts, which at the same time benefit from the outstanding properties of Ultrason® in terms of mechanical, thermal and chemical resistance, as well as approval for food contact.

The new process, which was developed at BASF’s pilot plant for injection moulding and extrusion in Ludwigshafen, makes it possible to produce marbled moulded parts on conventional injection moulding machines more easily and with a greater degree of process reliability than before, using new types of nozzle inserts and a special dosing technique. With its lightly honey-coloured tint, Ultrason® granules are suitable for light shades and tints, as well as abstract patterns by solid colouring that look like natural materials such as wood or marble.

"Marble effects have always been an eye-catcher in the plastics world," says Georg Graessel from global Ultrason® business development at BASF. "Until now, these effects were only possible with complex two-component injection moulding and did not guarantee reproducibility. With marbling, we are adding another way of colouring to the already versatile design possibilities of Ultrason®. With appropriate temperature control of the injection moulding machine, attractive, high-contrast patterns are possible for our P and E injection moulding grades. So far, our customers have been able to mould transparent, translucent and, of course, solid-coloured components from Ultrason®."

Marbled components made of Ultrason® can be used in a variety of ways: in household articles such as bowls, cups, plates and catering utensils, also for microwave usage. Additionally, marbling effects can be applied to eyeglass frames and handles, as well as visible components of electrical and electronic appliances, decorative panels and covers. These applications benefit from the excellent properties of BASF’s polyarylethersulphone: steam resistance up to 180°C, excellent strength and toughness over a wide temperature range, very good resistance to industrial cleaning agents and repeated sterilisation. Ultrason® also has the relevant food approvals for the EU and the USA.

Marbling according to the BASF process is possible on conventional injection moulding machines equipped with only one plasticising unit and an open nozzle. The pre-coloured base material and the high-contrast colour masterbatch must be fed synchronously to the injection-moulding cycle. The patterns in the moulded part are then achieved by separating and merging the melt streams. This is done with nozzle inserts, which are manufactured by 3D printing. These inserts offer great design freedom: not only mirror-image patterns can be created but also rotationally symmetrical patterns. This has not been possible with conventional processes to date. Other factors influencing the pattern design are the nozzle design itself, the mould’s gating system, the location of the gate, and the flow behaviour of the melt during mould filling. In addition to PESU and PPSU, the new BASF technique is also suitable for Ultrason® S and other thermoplastics.

Ultrason® is the trade name for BASF’s product range of polyethersulphone (Ultrason® E), polysulphone (Ultrason® S) and polyphenylsulphone (Ultrason® P). The high-performance material is used to manufacture lightweight components in the electronics, automotive and aerospace industries, as well as in water filtration membranes and in parts that come into contact with hot water and food. Because of their extraordinary property profile, the Ultrason® grades can substitute thermosets, metals and ceramics in many applications.