Method for treating a mineral filler with a polydialkylsiloxane and a fatty acid, resulting hydrophobic fillers and uses thereof in polymers for breathable films

1. A method for manufacturing a breathable film of polyolefin(s), comprising manufacturing said breathable film from a master-batch comprising said polyolefin(s) and a mineral filler, wherein the master-batch has a melt volume-flow rate greater than 9 cm 3 /10 min (temperature 190° C., load 5 kg, die diameter of 2.095 mm) measured in accordance with ISO 1133 and a thermal stability expressed, according to the strip method, by a length of non-discolored strip greater than or equal to 20 cm;

and wherein the filler has been treated by a process comprising a two-step surface treatment of the filler, wherein the first step (pretreatment) comprises treating the filler with at least one polydialkylsiloxane, and the second step comprises treating the polydialkylsiloxane treated filler with at least one fatty acid having more than 10 carbon atoms, and the two steps can be carried out simultaneously, the filler is selected from the group consisting of marble, calcite, precipitated calcium carbonate, talc, kaolin, magnesium hydroxide, clays, silica, alumina, barium sulphate, mica, calcium oxide or hydroxide, aluminium oxide and mixtures thereof, and the filler has a turbidity index of between 0.9 and 1 and a foam index of between 0.7 and 1, the two indices being determined by the whizzing method, and a moisture pickup less than or equal to 0.42 mg/m 2 measured by the moisture pickup method.