Polyolefin and other plastic films have a tendency to adhere together, often making it difficult to separate layers, This adhesion between film layers, called blocking.
Antiblocking additives can be added to the plastic to minimise this adhesion and so lower the blocking force between layers. Once compounded into a plastic these additives create a micro rough surface which reduces the adhesion between film layers and lowers the blocking tendency.
Two factors determine the antiblocking effect as number of particles of antiblock at the film surface. and size of the antiblock particles. Synthetic silica is used in high quality films and RI close to that of PE and PP with high transparency and clarity.
Limestone is a naturally occurring mineral calcium carbonate + Traces of magnesium carbonate & used in lower quality film applications.
Talc is a magnesium hydrosilicate. It has very low hardness & RI close to PP & PE.