| 摘要 |
A process for preparing an extruded elongate foam body characterized as having minimal surface defects such as pearls, streaks, foamy appearance and corrugations and having a density of between about 14.4 and about 56.1 kg/m<3> which comprises the steps of (A) heat plastifying a mixture of at least one thermoplastic resin and at least one nucleating agent; (B) adding at least one blowing agent selected from the group consisting of chlorodifluoromethane; 1,1-dichloro-2,2,2-trifluoroethane; 1-chloro-1,1-difluoroethane; 1,1,1,2-tetrafluoroethane; 1,1-dichloro-1-fluoroethane; 1-chloro-1,2,2,2-tetrafluoroethane and mixtures of two or more thereof to the mixture; (C) forming a blowable resin mixture by uniformly mixing the blowing agent and the mixture of step (A) in the resin under a pressure sufficient to prevent blowing of the resin; (D) extruding the blowable resin mixture through a die (20), which has a die lip temperature maintained at about 10 DEG C to about 77 DEG C and into a region wherein the blowable resin mixture expands into a foam body; and (E) cooling the foam body. In one embodiment, the region of less than atmospheric pressure is formed by an elongated chamber (15) with the blowable resin mixture passing through a die at one end of such chamber and such foam body passing through a pool of water (17) at the opposite end of the chamber. The process results in the formation of extruded expanded thermoplastic resins such as polystyrene resins characterized as having relatively small average cell sizes such as from about 0.2 to about 0.5 mm., improved and higher compressive strengths, and higher cell volumes. |
