Anti-Scratch Additives for PP and Automotive Interior Plastics
Direct answer
Scratch visibility in a filled polypropylene interior part is not one failure — it is two. There is the mechanical groove the stylus or fingernail cuts, and there is the whitening around it caused by stress and by talc particles debonding from the matrix. An anti-scratch additive addresses the first by lowering surface friction so the indenter slides instead of ploughing; it does not fix the second. Reducing whitening is a formulation job: finer talc, better coupling, a tougher matrix and a grain that scatters light.
Why siloxane displaced amide
Amide slip additives — erucamide in particular — lower surface COF cheaply and were the first generation of scratch aids. They migrate, so the effect appears over days and then decays; they contribute to fogging on the windscreen in a hot cabin; and they can carry an odour. Ultra-high molecular weight polysiloxane systems, usually supplied as a masterbatch on a polyolefin carrier, stay largely at the surface without the classic bloom behaviour, hold their effect over the life of the part, and are the reason modern interior specifications can require both low fogging and low odour.
Test methods are the specification
There is no generic "scratch resistant" claim worth buying. Automotive OEMs specify a defined method — a cross-hatch scratch under a stated load with a stated stylus radius, followed by a ΔL measurement of the whitened area, or a Erichsen or five-finger test to a stated grade. The additive that wins one method does not automatically win another, because the methods weight ploughing and whitening differently. Ask for the OEM standard and the pass threshold before comparing suppliers.
Interactions that catch people out
Siloxane at the surface is a release agent. It will reduce paint adhesion, adhesive bond strength and weldability, so a part that is later painted, foamed or ultrasonically welded needs the loading validated on the assembly, not just on the moulding. High siloxane also affects gloss and can alter grain appearance. Talc content and grade change the baseline: a high-talc PP scratches whiter than an unfilled one, and moving from a coarse to a fine surface-treated talc often does more for perceived scratch resistance than raising the additive.
Specify it properly
State the base compound including filler type and level, the OEM test method and pass grade, the grain and gloss target, whether the part is painted, welded or foamed, and the fogging and odour limits that apply. Those constraints determine the additive far more than the scratch requirement alone.
What we supply
Allzone supplies an anti-scratch masterbatch for polypropylene based on a siloxane system, presented with the delivery form and compatibility taken from the verified product record. Loading is confirmed against the supplier document at quotation and should be validated on the target compound.