Injected foamed resin structure forming loudspeaker cone especially, comprises foam sandwiched by thin, non-foamed resin layers, with further single, unfoamed layer, produced in single machine and operation

摘要

Two zones are produced. The first is a tri-layer structure comprising an internal, foamed layer with an external, non-foamed (double or surrounding) layer. The second is a single, unfoamed layer. An Independent claim is included for the method of manufacture. Resin containing foaming agent is injected into a mold. The mold is opened on expiry of a set interval. A mold cavity includes a hollow space corresponding with the (future) foamed zone and a thin region corresponding with the non-foamed region. The interval is selected such that hardening of the resin in the thin region is complete, whereas hardening in the thick region is still incomplete. Preferred features: The unfoamed zone is up to 0.5 mm thick. A loud speaker membrane (or cone) based on this structure is claimed. The loudspeaker cone is circular. The foamed zone is located symmetrically about the center. Further variants of the method, based on the foregoing principles, are described. A significant feature is reduction of dwell pressure after expiry of the set interval.