GB1122226A - Production of expanded thermoplastic synthetic resins - Google Patents

Abstract

An expanded thermoplastics material is made by heating an expandable thermoplastic crystalline material to a temperature above its softening point and cooling with shaping, the plastics material used containing (a) an emulsion consisting of a liquid in emulsified form which is dispersed under pressure in the molten plastics material, said liquid having at least one constituent which boils below the m.p. of the plastics material and having a viscosity 0.01-10 times that of the plastics material at the temperature at which the emulsion is prepared, and said pressure being higher than the v.p. of the liquid at said temperature, and (b) at least one constituent which boils below the m.p. of the plastics material. Exemplified thermoplastics are polyethylene, polypropylene, P.V.C. or ethylene/vinyl acetate copolymer, all suitably having a crystallinity of at least 20%. The emulsified liquid may be water, ethanol, methanol or acetone, containing P.V.A., polyalkylene oxides, polyvinylidene chloride, ammonium polyacrylates, or polymethyl methacrylate. Blowing agents may also be present; e.g. ammonium salts or ammonia or CO2 dissolved in water. The ingredients may be compounded under, e.g. a nitrogen pressure of 5 at., and subsequently have (a) the pressure released to cause foaming or (b) the pressure maintained during cooling to give a potentially foamable product, which may be heated, e.g. in the form of granules in a mould to expand it.