Other

Polymer Processing Institute

Joseph A Biesenberger

David B Todd

Subir K Dey

Thermoplastic foams are provided by a process in which a gaseous blowing agent of nitrogen, air, carbon dioxide, argon or mixtures thereof is injected into a melted thermoplastic polymer and the pressure is used to form a solution of the blowing agent and the melted polymer. The solution is cooled to a temperature which is within 10.degree. C. of the polymer freezing point while the pressure is held to a point within which both of the following conditions exist: A) the pressure must be high enough to keep the gas blowing agent in the solution with the melt, and B) the pressure must be low enough to avoid adding more heat to the solution. Just before the cooled solution is extruded, it is important to have the solution at a temperature which is sufficiently uniform to make: A) the thermoplastic foam at least about 65% by volume in closed cells, and B) a substantially uniform cell size in the product. The cooled solution is then extruded out of an extruder die to where the pressure drop across the die is in the range of from about 70 to about 90% of the pressure in the extruder so that a cellular product is formed.

Method of preparing thermoplastic foams using a gaseous blowing agent

A back mix, drag-flow apparatus that provides both radial and axial mixing of materials comprising at least two worms in screw form and parallel and tangential to one another that are of opposite hands and are rotatable only in the same direction or are of the same hand and are rotatable only in opposite directions; and a barrel casing completely enclosing said worms and containing a feed inlet and a product outlet.

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Wayne, NJ, United States of America

Joseph A Biesenberger