| 摘要 |
PURPOSE:To continuously manufacture a uniform expanded layer with high expansion ratio in a short period of time by a method wherein a stock pipe as core material, the expanded layer and a skin layer are extruded simultaneously by employing a long land die as the extruder die of an extruder. CONSTITUTION:Composition for forming expanded layer 2, composition for forming core material pipe 3 and composition for forming skin layer are simultaneously supplied to an extruder 1 so as to be extruded in the predetermined order at a long land die 5. The expanded layer formed onto the surface of a core material pipe is typically polyethylene expanded layer and formed at the expansion ratio of 20-60%. Because the forming is fully developed in the long die, the length in extrusion direction of which is at least 5 times and preferably 10 times as long as the diameter of a stock pipe, the extent of foaming of the expanded layer becomes nearly uniform and, in addition, the expansion ratio of the expanded layer is also improved remarkably. |
