Process for preparing a polymer concentrate

A process for preparing a polymer concentrate which comprises:

• (A) mixing together (i) at least one additive selected from the group consisting of a liquid, a paste and a waxy low melting solid, and (ii) a particulate inorganic solid which remains solid at temperatures in excess of those used to process the polymer component of the polymer concentrate in said process using a solids mixing device, said additive being added to said inorganic particulate solid at a rate such that a free-flowing powder is obtained and being selected from an anti-fog agent, a clarifying agent, an antioxidant, a U.V. stabilizer, an infra-red absorber, a biocide, an antistatic agent, a plasticizer or a flame retardant;
• (B) adding to the resulting free-flowing powder mixture a powdered thermoplastic polymer and continuing to mix to obtain a homogeneous mixture, said polymer being selected from polystyrene, high impact polystyrene, a styrene-acrylonitrile copolymer, an acrylonitrile-butadiene-styrene copolymer, an ethylene polymer or copolymer, a vinyl chloride polymer or copolymer or a propylene polymer or copolymer;
• (C) subjecting the mixture to intensive mixing for a time sufficient to melt the polymer;
• and
• (D) cooling and granulating the resulting mixture so as to obtain a polymer concentrate which contains, on the basis of the weight of concentrate, from 40-80% of said additive, from 5-20% by weight of the particulate solid and at least 5% by weight of the thermoplastic polymer.