Pellet-type foams of non-crosslinked polypropylene resin having lower melting point and process and device for producing the same and molded foams therefrom

A device for producing a pellet-type non-crosslinked polypropylene foam having a melting point of 125 to 140° C., comprising a first extruder, a second extruder connected to the first extruder, a pumping part connected to the second extruder, a homogenizing part connected to the pumping part and a dies part connected to the homogenizing part, wherein

• the first extruder comprises a cylindrical cylinder in which a screw shaft is mounted rotatably, a driving controller installed at an end of the cylinder for rotating the screw shaft and a plurality of cooling water passages and heaters that are alternately mounted on an outer circumference of the cylinder, wherein each set of alternating cooling water passages and heaters form a specific temperature zone, the cylinder has entrances formed at an end portion thereof corresponding to the driving controller for supplying a raw polypropylene and a nucleating agent thereto, an exit formed at another end portion thereof, entrances formed at a midportion thereof for supplying an additive and a foaming agent, respectively, whereby the raw material supplied to the cylinder via the entrances is flow compulsorily toward the exit by the screw shaft rotated according to the driving controller;
• the second extruder comprises a cylinder into which the polypropylene melt discharged from the cylinder of the first extruder is supplied through the guide, and a plurality of cooling heating units mounted to an outer circumference surface of the cylinder for adjusting a temperature of the polypropylene melt in the cylinder;
• the pumping part comprises a casing having an inner space into which the polypropylene melt discharged from the cylinder of the second extruder is supplied, a pair of gears installed rotatably and meshed with each other in the inner space of the casing and a driving unit for rotating the gears, whereby the polypropylene melt supplied therein is flow compulsorily;
• the homogenizing part comprises a first cylindrical housing into which the polypropylene melt discharged from the cylinder of the pumping part is supplied, the first housing being installed rotatably, a driving element for rotating the first housing, a screw connected to an exit end of the first housing, a second housing located on an outer circumference of the screw, a frame mounted to an outer circumference of the second housing for forming an airtight space between the second housing and the frame, and a homogenizer installed at a rear end of the second housing;
• wherein a spiral space is formed between the screw and the second housing along the entire length of the screw so that the polypropylene melt discharged from the first housing is flow in the space formed between the screw and the second housing and discharged to an outside, a heat transfer fluid oil flows in a space formed between the second housing and the frame to adjust a temperature of the polypropylene melt which flows in the second housing, and the homogenizer crushes the polypropylene melt;
• the dies part into which the polypropylene melt discharged from the homogenizing part is supplied includes a discharging part, a cutting part, and a driving member so that expanded foams are cut at a certain size.