A screw type, polymeric material extruder with an elongated body having a cylindrical bore with a hollow screw in the bore, the screw having external and internal threads. A cylindrical body is within the internal threads, and the screw with the wall of the bore and with the cylindrical body forms, respectively, an external material flow chamber and an internal material flow chamber. The cylindrical body can have channels for heating fluid and for additives or dyes. The screw can have openings for feeding one material to a single extrusion head with one mouth by way of both chambers, or the chambers can be supplied with the same or different materials which are fed by way of the chambers to an extrusion head with two mouths for applying the latter materials separately.

A single extruder provided with a hopper at one end and a restricted nozzle at the opposite end and two press-screws arranged coaxially in one another within an outer jacket, each of said screws being provided with a male thread for feeding in the direction of said nozzle, said male threads extending into an outer annular space between said jacket and the outer press-screw and extending into an inner annular space between said two press-screws, said threads being oppositely oriented, means to rotate the outer of said press-screws and means maintaining the inner of said two press-screws stationary, said outer press-screw being provided with window-like openings communicating with said inner press-screw in the area of said hopper and separate feed means in said hopper to separately feed to said outer annular space and to said inner annular space through said window-like openings, the improvement consisting in that a rotating mixing element is positioned between said nozzle and said press-screws and attached to said rotating outer press-screw and having outer bearing support means in sliding contact with said outer jacket and inner bearing support means in sliding contact with said inner stationary press-screw, said outer and said inner bearing means being supported from said attachment to said outer press-screw by radial walls, said mixing element being provided with a series of open conical chambers between said radial walls, the inlets of said open conical chambers alternately opened to said inner annular space and said outer annular space and the outlets of said open conical chambers opened to said restricted nozzle.

A method for the production of multi-color striped pieces of soap by continuously extruding two strands of colored soap, passing said two strands of colored soap through a die orifice whereby a single strand of parallel stripes is formed having a varied colored aspect in cross-section, passing said single strand through a static mixer having a different configuration from said die orifice, cutting said strand and recovering multi-color striped pieces of soap, as well as the apparatus.

In the production of foamed plastic articles using a screw extruder, it is known to introduce a gaseous foaming agent into the plastic while the latter is passing through the extruder. It has been found that a foamed thermoplastic with pores or cells of uniform size and distribution can be produced by passing a gaseous foaming agent, e.g. nitrogen gas through a central passage extending substantially the entire length of the extruder screw, discharging the agent into the thermoplastic proximate the discharge end of the extruder, and mixing the foaming agent with the plastic immediately prior to discharge of the mixture into a mold.

An improved stick preparation is provided which is made up of at least two separate phases and at least one phase contains spherical polymer particles which can contain a pigment. The particles provide smoothness to the preparation and can be used to provide an interesting visual appearance to the stick.