|The luxury impression of an automobile's interior largely depends on the surface quality of the plastic interior trim parts. In higher level vehicles, this is achieved by covering the plastic surfaces with PVC or Thermoplastic Olefin (TPO) skins, fabrics or paint. However, cost constraints influence the use of unpainted, molded color plastic parts in most vehicles. The typical materials currently in use for these parts are PP, talc-filled PP, talc-filled TPO, ABS, Polyamide/ABS (PA/ABS) and PC/ABS. The essential factors of these plastic part surfaces are low gloss appearance along with good scratch and abrasion resistance, which has improved through extensive development efforts over the past several years. However, there exists a considerable gap in surface quality and robustness vs the painted solution. This has led to the development of innovative materials that provide breakthrough improvements in low gloss appearance with excellent scratch and mar resistance. Scratch and mar resistance (SMR) is important and critical for interior auto parts such as instrument panels and other trim because the scratch is associated with poor quality. So far, OEMs demanded short-term scratch-resistance, which has changed to longer-term scratch resistance, on increasing demand by consumers for their vehicle to look good over time. The importance of overall interior quality is increasing. Besides scratch and mar resistance, other key properties include gloss, soft-touch feel, and low fogging or emissions due to volatile organic compounds (VOCs), as per Plastics Additives & Compounding.
The Scratch Consortium, part of the Polymer Technology Center at Texas A&M University (TAMU), developed a test that was established in 2005 as ASTM standard D7027-05 and in November, 2008 as ISO standard 19252. TAMU Scratch-4 Surface Testing System thus developed is gaining wider acceptance. A key benefit of the new testing is in direct comparisons of scratch resistance between radically different materials or additive formulations, and can evaluate textured surfaces, which cannot be reliably achieved using earlier test methodology. This system, currently the only commercial device for the ASTM and ISO scratch methods, is manufactured through an exclusive license by Surface Machine Systems, LLC.
Erucamide have traditionally been used to improve scratch and mar performance. Its migration to the surface over time and fogginess due to its volatile content has compelled processors to other additives. Amides provide only short term scratch resistance. Ciba� Irgasurf� SR100, an anti-scratch additive, is used globally for both interior and exterior automotive parts as well as non-automotive PP/TPO applications like snowmobiles. It shows improved SMR in filled TPO, high-gloss TPO and soft TPE. Multibase�s Dow Corning� MB50-001/ MB50-321siloxane masterbatch contains a non-migrating, anti-scratch additive that improves scratch and mar resistance in rigid, mineral-filled TPOs. The ultrahigh molecular weight siloxane offers long-term scratch and mar resistance with no fogging or emissions and very little effect on gloss. MB50 masterbatches can be used in TPOs, TPVs, TPEs, and other engineered plastics and elastomers. For soft-touch over moulding, Multibase offers siloxane-enhanced TPE (SiE-TPE) and cross-linked silicone thermoplastics (TPSiV) that give long term scratch and mar protection with very low emissions. Evonik introduced the organic modified siloxane (OMS) Tegomer� AntiScratch 100 (TAS100) additive, targeting improved scratch and mar resistance in talc-filled PP and PP/TPO parts. TAS100 does not migrate, yielding permanent scratch resistance and no fogging or gloss change. AXEL Plastics Research Laboratory�s non-migratory additives are a complex mix of polymeric materials and amides that have no fogging, odour, or interaction with UV stabilizers.
Automotive TPO parts are typically filled with minerals like calcium carbonate, talc, kaolin or wollastonite that have a significant effect on scratch performance. When a part is scratched, exposed mineral particles reflect light and make the scratch more visible. As the mineral loading increases, scratches become more easily visible. Morphology and particle size play a role, with better scratch resistance from finer particle sizes. Minerals with a surface treatment like silane show improved scratch and mar resistance over formulations with untreated grades. Mineral coatings reduce absorption of slip or other anti-scratch additives onto the mineral, leaving more to function at the part surface. Surface treatments may improve dispersion, which improves scratch resistance, and create a better bond between polymer and mineral so that less of the bright mineral surface is revealed by scratching.
IMI Fabi recently introduced its NS100 micronized, coated talc for improved dispersion and scratch and mar resistance in TPO. Joint research with Evonik has optimized combinations of NS100 with Evonik�s TAS100 siloxane additive for scratch-resistant compounds. Multibase�s new micro talc masterbatch improves SMR in filled, rigid TPOs. The product combines very fine particle size talc with proprietary processing technology to create excellent dispersion in the PP matrix, allowing lower filler levels. This micro talc masterbatch can achieve comparable physical properties with only 3-5% micro talc. Lower talc levels help reduce weight as well as improve scratch and mar resistance. Rio Tinto Minerals� Luzenac R-7 surface treated talc 1 micron particle size is used globally as a scratch and mar resistant, UV-stable, and high-impact talc.
Wollastonite, because of its hardness has better scratch resistance, and is used in both interior and exterior automotive engineering thermoplastics, although not as widely as talc in PP/TPO.
Polymer makers are also working on newer grades for use in automotive interiors, as per ICIS. SABIC Innovative Plastics' STAMAX long fiberglass polypropylene (PP) resin, used in floor consoles and instrument panels, delivers 10-15% cost savings and 20% lower weight, and enables parts integration. It has a better surface finish than short fiberglass products, allowing molding in color and processability. Its Lexan EXL PC, which has good impact resistance and improved chemical resistance to automotive fluids, is now being validated for steering wheels. Innovative and colored solutions are being developed for interiors. Dow Automotive Systems has introduced advanced polyurethane (PU) foam technology for instrument panels and interior trim, giving significant weight reduction, improved airbag deployment properties and fast cycle times. The company is also collaborating with polyvinyl chloride (PVC) suppliers to develop PU foam solutions for instrument panels that will not discolor or develop skin cracks. Germany's Bayer MaterialScience can create light-colored, ultraviolet and scratch-resistant surfaces for interior parts via its DirectSkinning technology, necessitating very little secondary finishing.