ADDITIVES | SURFACE MODIFICATION
Croda’s range also includes products for
transparent polymers including polycarbonate and PMMA, which in applications such as headlights and interior parts can be prone to scratching if not coated. IncroMax products are said to show excellent anti-scratch performance with no nega- tive impact on clarity.
Figure 3: Comparison of visible blooming of a standard grade of erucamide versus Incroslip SL in a PP automotive compound after exposure to UV light.
Source: Croda
odour and maintained gloss. “This combination of benefits makes them perfect for use in a variety of polymers and applications from high gloss surfaces to transparent parts,” says the company’s Global Marketing Manager Jill Ullathorne. Incroslip G, which is intended for PP homopoly- mer applications, is a type of erucamide with enhanced thermal and oxidative stability. It has been available for some time but its use as an anti-scratch additive is quite recent. Aside from its cosmetic improvement, it has the added benefit of reducing mould release force so eliminates the need for external mould release agents during injection moulding. Two proprietary formulations for impact copolymers, Incroslip SL and IncroMold K, have been on the market for three years, which is relatively new in automotive testing terms, says Ullathorne. All of the Croda additives are said to be able to withstand challenging processing conditions and offer long term in-use performance in the finished products. Additionally, their low usage levels do not cause any detrimental effect on mechanical properties.
Method of operation The method of operation of an anti-scratch additive is quite complex and is influenced by polymer type, structure and temperature. Croda Europe Research Fellow Adam Maltby explains that migrating anti-scratch additives are designed to be compat- ible with the polymer melt during processing but to become insoluble in the matrix and migrate to the surface as the polymer cools. Migration is faster through amorphous regions of the polymer and at higher temperatures (up to 50-60°C); it is retarded in highly crystalline polymers, at low temperature and by the presence of adsorbing or solubilising components in the formulation. Once the additive has migrated to the surface of
the part it forms lubricating solid layers. These cause scratching indenters to slide across the surface, thus reducing scratch visibility (Figure 4). Maltby says that among the more traditional additives available, erucamide has proved to be very good where high slip/scratch performance is required while oleamide is a good choice for applications requiring fast migration.
Polymer alternatives Polymer makers are also working hard at modifying and improving surface properties, reducing or possibly even eliminating the need for extra addi- tives or for surface coating of finished parts. At the Fakuma plastics processing show in Friedrichshafen, Germany, last month, BASF showed its new Ultramid Deep Gloss specialty polyamide. This combines the chemical resistance of semi-crystalline polyamides
Figure 4: Bruker profilometry images show how IncroMold K reduces scratch depth – and hence visibility – by 80% in a PP impact copolymer compound at an addition rate of 1% (8N load)
60 COMPOUNDING WORLD | November 2017
Source: Croda
www.compoundingworld.com
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