Patent ID: 8349938
Filing Date: 2013-01-08
Classification: B29C,C08K,C08L

Abstract:
1. A process of obtaining a thermoplastic composition formed from a polyolefin matrix comprising a polypropylene with a fluidity index of from 2 to 100 g/10 minutes when measured at 230° C. under 2.16 kg, and a mineral lamellar filler which comprises talc with a median diameter D50 of at least 1 μm as measured by Sedigraph, and with a lamellarity index of at least 4 before introduction into the matrix and at least 3 when measured in the thermoplastic composition, by dispersing the mineral lamellar talc in the matrix in a viscoelastic state by means of at least one compounding extruder, which process comprises (a) the formation of a viscoelastic mixture of the matrix and the mineral lamellar talc by heating and kneading the thermoplastic composition at a temperature at least equal to the working temperature of the polypropylene, (b) the submission of the viscoelastic mixture to thermo-mechanical work, (c) the elimination of volatile components from the viscoelastic mixture, (d) the transformation of the viscoelastic mixture resulting from step (c) into a granulated material, characterised in that, to obtain a controlled and homogenous dispersion and distribution of the mineral lamellar talc in the matrix, while substantially retaining initial morphological characteristics of the mineral lamellar talc, the viscoelastic mixture is subjected during steps (a) and (b) to a rate of shearing of no more than 200 s −1 and the viscoelastic mixture is subjected in step (b) to at least one cycle of extension and relaxation in a dedicated zone which is at least 25% of the total length of the at least one screw of the compounding extruder.