US 6,103,153 A · Production of foamed low-density polypropylene by rotational molding

Abstract

Compositions and processing conditions are disclosed for the production by rotomolding of polypropylene foams, hither to satisfactorily produced only by injection molding and extrusion molding. Rheological properties of the polypropylene resin, processing conditions and choice of composition of the chemical blowing agent were found to play important roles in obtaining high quality polypropylene foam structures. High strength fine-cell polypropylene foams could in particular be formed by first melt compounding a suitable chemical blowing agent with the resin under conditions which allow for homogeneous mixing without appreciable decomposition of the blowing agent.

Claims8

Dependent claims

A process for the production of foamed polypropylene resins by rotational molding, consisting essentially of the steps of:

(i) charging a mold with a physically dry-blended mixture of (a) a powdered polypropylene resin characterized by a melt flow rate sufficiently high to conduce to thorough sintering of the powdered resin under rotomolding conditions, and (b) a selected amount of chemical blowing agent capable of releasing gas to foam said powdered resin, at a temperature above the sintering temperature of the resin, in an amount to produce a selected volume expansion ratio;
and
(ii) rotationally molding said dry-blended mixture until it has expanded to said selected volume expansion ratio.

Dependencies are inferred from the claim text.

Production of foamed low-density polypropylene by rotational molding

Life of this patent

Production of foamed low-density polypropylene by rotational molding

Life of this patent

Abstract

Claims8