Formed articles comprising expanded thermoplastic resinous materials and method for their formation

Abstract

Abstract An expandable mass for the formation of foam structures comprises a thermoplastic resinous material in particle form containing a blowing agent, the particles being coated with a non-volatile polymeric bonding agent which flows at a temperature lower than the foaming temperature of the mass. The foam is prepared by preforming the mass to a coherent, further expandable form by heating at a temperature in the range from the flow temperature of the bonding agent to the foaming temperature of the mass, and finally heating to a foaming temperature. The preforming may be effected at the foaming temperature to give a limited pre-expansion, and it may be performed by moulding, calendering, extruding, &c. The bonding agent may be applied to the particles in the form of a solution, dispersion or suspension, in which case the coated particles are dried before preforming, or conventional dry blending methods may be employed. Specified solvents are acetone, carbon tetrachloride, monomeric styrene and vinyl toluene. Suitable thermoplastic materials are polymers of vinyl aromatic compounds, particularly styrene, but including also a -methyl styrene, vinyl toluene, ar-dimethyl styrene, and mono- and di-chlorostyrenes, copolymers thereof with, for example, vinylidene chloride, and cross-linked copolymers containing small amounts of divinylbenzene; polymers of acrylic compounds, e.g. methyl methacrylate and ethyl acrylate, and their copolymers with, for example, vinylidene chloride; polymers of vinyl acetate or vinyl butyral; and cellulose derivatives such as the nitrate and acetate. The coated particles generally comprise from 0.5 to 20 per cent by weight of bonding agent. Suitable bonding agents are the relatively lower molecular weight polymers, e.g. polystyrene having a molecular weight of from 10,000 to 40,000, latexes of styrenebutadiene copolymers, copolymers of butadiene and acrylonitrile containing at least 55 per cent of butadiene, vinyl acetate-methyl methacrylate copolymers, polyvinyl chloride, which may contain a plasticizer, and polymers of dichlorostyrene, vinyl toluene, isobutylene, methyl acrylate and methacrylate and acrylonitrile. Specified blowing agents are dichlorodifluoromethane, carbon dioxide and low-boiling hydrocarbons such as pentane. The Specification refers to many applications of the foamed materials.

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