scratch and mar | Additives
Above left: Wacker’s highly concentrated Genioplast ultra high molecular weight silicone is compatible with most thermoplastics. Above right: Aside from its SMR benefits, Wacker’s Genioplast silicone-based SMR additive also improves flow during processing
tively as slip and mould releases as well as anti-scratch additives, but these can result in a white, waxy layer that is undesirable in some visible applications. In addition, the additives can display poor oxidative stability, which can cause surface stickiness and organoleptic (odour) issues. Now Croda says its Incroslip SL low visible-bloom
additive, which was introduced in 2013 as a slip additive with friction-reducing properties similar to erucamide but with greater oxidative stability, has been finding new applications as an anti-scratch additive, particu- larly in PP. The Incroslip SL additive’s long-term stability
results in good organoleptic performance, while its low visible bloom can help maintain good gloss properties. “Demand for improved anti-scratch additives is strong, particularly in the automotive area, where the use of plastics is increasing quickly due to light-weighting requirements,” says Jill Ullathorne, Global Marketing Manager of Polymer Additives at Croda. In addition to Incroslip SL, Croda’s Incroslip G and its new IncroMold K are designed for improved scratch resistance. Incroslip G is optimised for homopolymer PP with good mould release. IncroMold K is optimised for PP impact copolymers, and shows dramatic improvements in scratch width and scratch whiteness, which is meas- ured using delta L (Figure 2). Croda has also tested scratch performance of its
various additive chemistries in other polymers, including PC, PET, PS and PMMA. “We have undertaken a significant project in the area of anti-scratch so that we are able to advise our customers which product and addition level will give optimum performance in their formulation. We are continuing with this work and would like to engage further with our customers to continue this process and meet future needs in the area of anti-scratch for a wide range of plastics,” says Martin Read, Applications Team Leader at Croda.
36 COMPOUNDING WORLD | February 2016
Silicone solutions Silicone additives have been used for over a decade to improve scratch and mar resistance. In automotive interiors, for example, lower-cost compact cars often use talc-filled PP parts for the car interior trim, including glove compartment covers, the panels below the door handles, and the lower part of the dashboard. These parts often have a matte-finish, which gives them a velvety feel, looks good and avoids the light reflections that could irritate or dazzle the driver, notes Klaus Pohmer, Director of Global Business Development at Wacker’s Performance Silicones business unit. However, matte surfaces are more prone to scratch and mar, PP scratches more easily than many other polymers, and talc fillers can make scratches more obvi- ous. In this application, high molecular weight silicone additives can be an effective solution for improving scratch and mar resistance. High molecular weight silicone additives do not migrate out of the polymer but reduce surface friction so objects slide over the surface more easily and leave fewer visible marks, says Pohmer. Wacker’s Genioplast Pellet S is a highly concentrated
additive in pellet form with 70% (by weight) of a non-crosslinked, ultra-high-molecular, linear silicone polymer active ingredient in a pyrogenic silica carrier material that has been tailored for this purpose. Because the silica is compatible with all thermoplas- tics, the additive can be used to compound every type of thermoplastic, says Pohmer. He notes that the silica also anchors the additive in the polymer matrix. In-house tests in talc-filled PP show that Genioplast
reduces surface friction and makes scratches less deep and rough so that they are less visible. Basic polymer properties, such as tensile strength, hardness and heat distortion, as well as printability and weldability, are not impaired. Adding Genioplast Pellet S to mineral filled thermoplastics additionally boosts the notched impact strength and elongation at break, says Pohmer. The
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