Method and apparatus for preparing thermoplastic resin foam

Claim 1

A method for preparing a thermoplastic foam board having a thickness greater than 10 mm by extruding molten thermoplastic resin having uniformly distributed therein a foaming agent for said resin, the method comprising the continuous steps of: (a) introducing an extruded mass of said molten thermoplastic resin from an extrusion zone into a cooling zone; (1) the cooling zone comprising an elongated barrel having a rotating member positioned axially therein in spaced relationship to the barrel so as to provide a passage for the extruded mass between an outer surface of the rotating member and an inner surface of the barrel, (2) the temperature of the cooling zone being controlled by fluid heat exchange, and (3) the extruded mass being under pressure in the extrusion zone and in the cooling zone; (b) passing the pressurized extruded mass through said passage while simultaneously: (1) intimately mixing the mass by means of projections extending radially from the outer surface of the rotating member into the passage and reaching a close proximity to the inner surface of the barrel and (2) substantially lowering the temperature of the mass, the cooled mass being maintained in its molten flowable state; (c) dividing the cooled mass into a plurality of separate, non-parallel streams in a zig-zag mixer under substantially adiabatic conditions; (d) separating and recombining at least a portion of said streams in said zig-zag mixer under substantially adiabatic conditions to form a combined homogeneous mass having a substantially uniform temperature; and (e) extruding the homogeneous mass into a lower pressure zone to form a substantially uniform thermoplastic foam.

Claim 2

A method for preparing a thermoplastic foam board having a thickness greater than 10 mm by extruding molten thermoplastic resin having uniformly distributed therein a foaming agent for said resin, the method comprising the continuous steps of: (a) introducing an extruded mass of said molten thermoplastic resin from an extrusion zone into a cooling zone; (1) the cooling zone comprising an elongated barrel having a rotating member positioned axially therein in spaced relationship to the barrel so as to provide a passage for the extruded mass between an outer surface of the rotating member and an inner surface of the barrel, (2) the temperature of the cooling zone being controlled by fluid heat exchange, and (3) the extruded mass being under pressure in the extrusion zone and in the cooling zone; (b) passing the pressurized extruded mass through said passage while simultaneously: (1) intimately mixing the mass by means of projections extending radially from the outer surface of the rotating member into the passage and reaching a close proximity to the inner surface of the barrel and (2) substantially lowering the temperature of the mass, the cooled mass being maintained in its molten flowable state; (c) dividing the cooled mass into a plurality of separate, non-parallel streams in a zig-zag mixer under substantially adiabatic conditions; (d) separating and recombining at least a portion of said streams in said zig-zag mixer under substantially adiabatic conditions to form a combined homogeneous mass having a substantially uniform temperature; and (e) extruding the homogeneous mass into a lower pressure zone to form a substantially uniform thermoplastic foam.

Claim 5

An apparatus for preparing a substantially uniform thermoplastic foam board having a thickness greater than 10 mm extruded from an extrusion means for continuously mixing and extruding a mass of molten thermoplastic resin having uniformly distributed therein a foaming agent for said resin, said apparatus comprising: cooling-mixing means connected to said extrusion means to continuously receive said extruded mass for intimately mixing and substantially lowering the temperature of the extruded mass, substantially adiabatic zigzag mixing means connected to said cooling-mixing means for dividing the cooled mass into a plurality of separate non-parallel streams and for separating and recombining at least a portion of said streams under substantially adiabatic conditions to form a combined homogeneous mass having a substantially uniform temperature, and die means connected to said zigzag mixing means for extruding said combined homogeneous mass into a lower pressure zone to form a substantially uniform thermoplastic foam.

Claim 6

An apparatus for preparing a substantially uniform thermoplastic foam board having a thickness greater than 10 mm extruded from an extrusion means for continuously mixing and extruding a mass of molten thermoplastic resin having uniformly distributed therein a foaming agent for said resin, said apparatus comprising: cooling-mixing means connected to said extrusion means to continuously receive said extruded mass for intimately mixing and substantially lowering the temperature of the extruded mass, substantially adiabatic zigzag mixing means connected to said cooling-mixing means for dividing the cooled mass into a plurality of separate non-parallel streams and for separating and recombining at least a portion of said streams under substantially adiabatic conditions to form a combined homogeneous mass having a substantially uniform temperature, and die means connected to said zigzag mixing means for extruding said combined homogeneous mass into a lower pressure zone to form a substantially uniform thermoplastic foam.

Claim 10

The apparatus of any one of claims 4, 5, 6, or 7, wherein said zigzag mixing means comprises a conduit having two ends, and an axis, said conduit being connected at one of ends to said cooling-mixing means and at the other end to said die means, and at least one separating element positioned in said conduit having therein a plurality of passages each passage having an inlet end and an outlet end defining an advancing direction for said streams, said advancing direction of each passage being at an angle greater than 0° with respect to said axis of said conduit, different passages being at different angles, said outlet ends opening towards said die means.