Abstract: A method of producing a breathable film which comprises the steps of: (a) producing an inorganic filler by treating particles of an inorganic particulate material comprising an alkaline earth metal carbonate compound by reaction with a hydrophobising surface treatment agent comprising one or more aliphatic carboxylic acids having at least 10 chain carbon atoms to produce a hydrophobic coating on the particles under conditions such that the inorganic filler produced has a total surface moisture level comprising moisture adsorbed on the particles and trapped within the hydrophobic coating thereon of not greater than 0.1% by weight based on the dry weight of the inorganic particulate material; (b) producing a filled thermoplastic composition by mixing the inorganic filler produced in step (a) with a heated thermoplastic polymer; and (c) shaping the composition produced in step (b) by heat processing to form a film product.

Abstract: A method of preparing an inorganic particulate material suitable for incorporation in a composition comprising a hydrophobic polymeric material includes the steps of (a) processing an aqueous suspension of an inorganic particulate material in the presence of a water soluble dispersing agent; (b) adding a surfactant to the particulate material; and (c) drying the particulate material. The inorganic particulate material to which the surfactant has been added may be further treated by addition thereto of a further surface treatment agent which is a hydrophobising surface treatment agent, eg. a carboxylic acid or salt thereof. The surfactant may be a non-ionic surfactant and may be added to the particulate material whilst in the form of a dispersed aqueous suspension. The further surface treatment agent may be added to the particulate material during or after the drying step (c).