Scratch-proof, Odourless And Cost-effective: Plastic Parts In Vehicle Interiors With Silicone Compounds

Nowadays people spend many hours in the car – the interior should therefore be as homely as possible and offer a high-quality impression when seen and touched. However, the further down the model hierarchy, the more price-sensitive the potential buyers become. In addition, the interior is one of the few areas of a car where manufacturers can save without sacrificing functionality or safety. For the claddings are therefore often used components made of materials that are much less expensive to produce – such as talc filled polypropylene. Disadvantage: They are scratch-sensitive and can quickly become unsightly in use

Often matte plastic surfaces are used – they feel velvety, look good and avoid light reflections that could irritate or dazzle the driver. But the softer such a surface is, the greater is its scratch and abrasion sensitivity. The plastics processor has many methods at his disposal with which he can permanently give the inexpensive plastic a lasting impression. The hard material can e.g. be coated with a thermoplastic elastomer, painted or refined with hot stamping foils. However, all these methods make the components significantly more expensive.

It is simpler and cheaper if the compound manufacturer modifies the surface properties of the plastic with the aid of an additive. However, conventional additives have significant weaknesses and side effects that are not tolerated easily, especially in the automotive industry. Organic lubricants, for example, smell unpleasant and migrate out of the plastic over time. The passing of the plastic surface lubricant also gives an unpleasant haptic impression, which must be avoided.

Silicone lubricants, however, which are also classics among lubricants, are odourless and easily handle high temperatures – but they too tend to migrate out of the plastic even more than organic lubricants. Manufacturers responded by bringing to market ultra-high molecular weight silicone polymers that are virtually non-emissive due to their high molecular weight. However, these are highly viscous, so they can hardly be incorporated into the thermoplastic mixtures.

Silicone Pellets As A Problem Solver

Compound producers solved this problem with silicone master batches, which have been available since the end of the 1990s, which can be mixed in as solid granules without difficulty. But for them, manufacturer must accept the disadvantage that they must provide an own additive master batch for each individual thermoplastic that they want to modify with the additive. Certainly not very economical. The aim was therefore to develop a highly effective and easy-to-use silicone additive that would be universally suitable for any thermoplastic.

Like the two authors Klaus Pohmer and Martin Schmid from Wacker Chemie (Munich) in the journal Plastverarbeiter write, the industry has meanwhile taken the right step:

After the preparation of the first samples of the new additive, the extensive performance tests began. Here the silicone pellets had to prove their effectiveness and practicability on the basis of talc-filled polypropylene blends and also face the comparison with competing commercially available products.

Test series have been carried out with regard to possible side effects, which lead to a clear result: The silicone pellets reduce the surface friction of the plastic and hereby improve the scratch and abrasion resistance. The tensile strength and rigidity are even better. In addition, the tests showed that the modified plastic does not become tacky when exposed to ultraviolet light. Therefore, the components made of modified polypropylene still feel good even after intensive sun exposure.

Unlike organic additives, the long-chain silicone does not migrate out of the plastic, even at higher temperatures. Unpleasant odours and efflorescence as well as annoying coverings on the windshield are a thing of the past. And because plastic surfaces are significantly scratch and abrasion resistant with the new additive, they look almost as good as new in the vehicle interior even after prolonged and intensive use.