| 摘要 |
<PICT:1084746/C3/1> A process for producing foamed thermoplastics material comprises heating a thermoplastics material in the presence of 20-50% by weight of a liquid of boiling point less than 150 DEG C. to a temperature of from 150-300 DEG C. at a pressure greater than 15 atmospheres gauge a substantially closed chamber, said liquid having a solvent action on the thermoplastics material at least when in the vapour state, and forcing the thermoplastics material/liquid mixture so formed through a discharge outlet in the chamber, into a region of substantially lower pressure, thereby causing the liquid to vaporize from the thermoplastics material/liquid mixture and hence said thermoplastics material to foam. The liquid used may be a mixture of liquids, such as acetone, methylene chloride, benzene and benzine. Thermoplastics materials specified are polyvinyl chloride, polystyrene, polyacrylic ester, polyethylene, cellulose acetate and mixtures of these. The process may be carried out in an apparatus comprising an extrusion press having a screw 2 mounted in a heatable housing 1 and having at least one inlet opening 5 through which a thermoplastic plastics material is introduced, and a discharge outlet 15 through which the material is forced under pressure, the outlet communicating with a substantially closed container 16 positioned adjacent to the press and having a wall provided with an outlet through which passes a conveyer belt 17, the arrangement being such that in use the pressure in the container is less than the pressure in the housing whereby when the mixture enters the container the liquid in the mixture is caused to vaporize and expand the thermoplastic material, the foamed material being removed from the container by the conveyer belt. |
