Extrusion blowing of hollow thermoplastic prods. and process appts. - involves extruding parison, to suitable length, sealing lower end, partially inflating, cutting off at top to avoid damage to next parison and fully inflating

摘要

An extrusion blowing process for prodn. of hollow products involves (i) extruding a parison (116) from an annular die (112) of an extrusion head between the open halves of a tool (114); (ii) sealing off the lower end of the parison (116) when the length is sufficient to avoid altering the cross-section of the parison (116) in the region of the extruder head (110) which can lead to defects on contact between them; (iii) partially inflating the parison (116) with the tool halves (114) in an open position; (iv) closing the tool halves (114) and cutting (125) off the parison above the tool (114) such that again no changes are produced in the cross-section of the next parison length where it leaves the die; and (v) moving the closed tool (114) to a second station and inflating the parison (116) against the tool walls. Claimed process equipment includes a first station with extrusion head (110) and annular die, mould (114), lower parison sealing device (122a,122b) and upper parison cut off device below the extruder head (110). USE/ADVANTAGE - For prodn. of hollow thermoplastic products, esp. for packaging. Allows use of thermoplastics which are pressure sensitive or have low viscosity in the plastic state. Prevents surface defects using such materials.