Milliken’s Hyperform® HPN nucleating agents provide major improvements in performance and processability of polypropylene (PP) grades intended for thermoforming as well as injection moulding. They provide the action to match the words of the company’s theme for K 2010 – “Increasing sustainability through additive innovation.”

Hyperform HPN additives provide isotropic shrinkage in formed parts. As a result, they can fix critical problems faced by processors involved in housewares, materials handling, high-speed moulding of thin-walled packaging and also technical components. “If you have a problem with shrinkage and warpage, productivity, aesthetics, or stiffness/impact balance, there is a good chance that we can go a long way to solving it with Hyperform HPN,” says Sami T.K. Palanisami, Market Manager Plastic Additives EMEA.

Typical applications range from increasing processability and optics in packaging grades, through cycle time reduction and warpage elimination in production of pallets and crates, to fine-tuning CLTE (coefficient of linear thermal expansion) and shrinkage in grades for automobile bumpers and instrument panels.

Palanisami cites Hyperform HPN-600ei, intended for incorporation into clear thermoformable sheet extrusion grades of polypropylene that can be deep-drawn into cups typically used in bars for serving cold drinks. HPN-600ei nucleated polypropylene presents a cost effective alternative to PET and polystyrene (PS). Cups are highly transparent and have an excellent visual appearance, rather than the yellowish appearance that results from the use of some other conventional nucleating agents. Meat trays and yoghurt cups are other important applications, especially in Europe.

The nucleating agent increases the achievable output rates on thermoforming equipment to levels normally only achievable with other plastics, says Palanisami. The PP parts can be made with the same wall thickness as other materials. So because the material is less dense, processors use less material, gaining further cost savings.

A second Hyperform HPN grade, HPN-20E, is intended for a wide range of injection moulding applications, from thin walled packaging containers to large automotive parts. Unlike other nucleating agents that improve the stiffness of PP at the cost of reduced impact properties, HPN-20E has no negative effect on toughness.

This additive is effective at much lower loadings than alternatives such as sodium benzoate and talc to provide very good dimensional stability and hence low or zero warpage in mouldings. HPN-20E also disperses very well in the high melt flow grades of PP favored for many thin wall injection moulding applications. The reduction in thermal expansion (CLTE) that it induces allows the production of “zero gap” automotive bumper fascias.

Hyperform HPN-20E complements another Milliken nucleating agent, HPN-68L, which can provide even higher polymer crystallization temperature and therefore lead to improved productivity. In addition, HPN-68L enables pigment ‘levelling’, which means that parts such as packaging caps can have the same shrinkage behaviour, whatever colour they are produced in, because the nucleating agent overrides any nucleating effect of the pigment. This is useful for processors making one part in several different colours, since they do not have to adjust their machine processing settings each time they change colour.