| 摘要 |
A process is disclosed of obtaining a thermoplastic composition formed fr om a polyolefin matrix comprising a polypropylene with a fluidity index of f rom 2 to 100 g/10 minutes when measured at 230°C under 2.16 kg, and a minera l lamellar filler which is talc with a median diameter D50 of at least 1 .mu .m, as measured by Sedigraph, and a lamellarity index of at least 4 before i ntroduction into the matrix and at least 3 when measured in the thermoplasti c composition, by dispersing the lamellar talc in the polyolefin matrix in a viscoelastic state by means of at least on compounding extruder, which proc ess comprises (a) the formation of a viscoelastic mixture of the polypropyle ne matrix and the lamellar mineral talc particles by heating and kneading th e said composition at a temperature at least equal to the working temperatur e of the polypropylene, (b) the submission of the viscoelastic mixture to th ermo-mechanical work, (c) the elimination of volatile components from the vi scoelastic mixture, (d) the transformation of the viscoelastic mixture resul ting from step (c) into an industrially usable granulated material, characte rised in that, to obtain a controlled and homogenous dispersion and distribu tion of the lamellar mineral talc in the polypropylene matrix, while substan tially retaining initial morphological characteristics of the lamellar miner al talc particles, the viscoelastic mixture is subjected during steps (a) an d (b) to a weak and controlled rate of shearing of no more than 200s-1 and t he viscoelastic mixture is subjected in step (b) to at least one cycle of ex tension and relaxation in a dedicated zone which is at least 25% of the tota l length of the at least one screw of the compounding extruder. Also disclos ed is the use of thermoplastic compositions obtained by such process in the manufacture of products for the automotive industry, domestic appliance indu stry, electronic industry, building industry, construction industry, interna l design industry, sport and leisure industry, in packaging or in toys. |
