| 摘要 |
A process for the production of expanded PVC of the type which comprises the heating of a mass of polymeric mixture (13) inside a closed mould, said process including: (a) control of the expansion of said mass (13) due to the hot moulding process in the environment having a constant volume defined by the mentioned closed mould (10), said control being effected by the presence, in the mentioned mass of polymeric mixture (13), of microparticles (16) of compressible material, suitable for being contracted, under the action of the pressure generated by the formation and expansion of microcells (20) of expanding gas in the same mass (13), from an initial form (A) having a larger volume, to a form (B) having a. smaller volume; and (b) the expansion of the mentioned microparticles (16) contained in the mass of the moulded expanded material, from their configuration (B) to the initial configuration (A) with a larger volume, the density of said expanded material thus obtained being determined by the contemporary presence, in the mass (13c) of the latter, of both microcells (20) of expanding gas and the mentioned microparticles (16) in their configuration A having a larger volume. With respect to the known technology for the production of expanded plastic materials, the process of the invention not only avoids the formation of melt losses during the moulding process, but also allows an expanded PVC having the desired density value to be obtained, even using much lower quantities of blowing agents with respect to those used in current processes of this type. |
