scratch and mar | Additives
Figure 1: Erichsen cross-cut test performance of polyolefi n reinforced with talc and Nyglos and Nylite wollastonite from Imerys group company Nyco
and harmony in gloss, color, and haptic properties. He also says that, although frequently grouped together, scratch, mar, and abrasion are actually quite different failure modes. “Scratch is damage to the surface, including
deformation, cracks, fractures, delamination, or some combination of those. With a scratch, there will be a macro-cut or ploughing on the surface that is associ- ated with a sharp/hard object and sudden force. Mar is a surface or near surface property change (optical, colour, gloss, haze, etc.) due to micro-crack or phase separation. It’s a chronic fatigue process involving internal stress or strain. Abrasion is a gradual surface degradation caused by ‘grinding or removing’ materials from the surface involving contact force and relative motion,” Dr He explains. Although researchers have achieved a level of
understanding of failure mechanisms and the relation of material properties, Dr He says there is an ongoing
Right: Pencil hardness test results of PMMA with
TenasiTech’s treated
nano-clay show scratch
resistance up to 6H
need to increase this fundamental understanding at the atomic and molecular level to match today’s needs and technologies.
Filler optimisation When a mineral (for example a talc or calcium carbon- ate) in a fi lled part is exposed at the surface by a scratch, the mineral particles refl ect light and make the scratch more visible. With a talc, particle size has a signifi cant effect on scratch visibility, says Jérôme Crépin-Leblond, plastics expert at Imerys Filtration and Performance Additives EMEA. He says using Imerys’s Jetfi ne 3C (an ultrafi ne talc) to replace coarser talc has been shown to optimise scratch resistance, impact strength, stiffness, and dimensional stability for automotive PP formulations. Formulations with Jetfi ne talc are said to show good
scratch performance even with reduced levels of anti-scratch additives such as siloxanes or amides. In North America, Imerys recently introduced Jetfi ne 3CW, which has the advantages of Jetfi ne 3C but is produced with local ore. Both Jetfi ne grades are made using a proprietary micronisation technology. Imerys has now optimised the process for making Jetfi ne at its Canadian facility and is in full production, says Crépin-Leblond. In early 2015, Imerys acquired Nyco Minerals and
added wollastonite to its portfolio. This mineral is also known to demonstrate a good balance of mechanical and scratch properties in automotive formulations. Crépin-Leblond says that combinations of talc and wollastonite together display a low odor profi le and the company now plans to develop data on scratch resist- ance of engineered mineral-blend solutions, which it anticipates will show good performance. Another scratch-resistant mineral modifi er introduced a few
32 COMPOUNDING WORLD | February 2016
www.compoundingworld.com
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