Method of manufacturing structural foam plastic products free from undesirable contaminant constituents

Claim 1

The method of making structural foam plastic products which comprises: (a) mixing a granular thermoplastic resin and a heat activated blowing agent to form a foamable granular mixture containing thermally activatable gas and vapor-forming constituents which include both undesirable contaminant constituents, such as water and low-boiling point impurities, as well as desired blowing and cell-forming gaseous constituents; (b) feeding said granular mixture from a hopper to a first compressive working and heating zone located at the inlet at one end of a barrel-enclosed, screw-advancing, two stage plasticating apparatus wherein the granular mixture is plasticated and heated to a temperature at which said blowing constituents at least being to vaporize and form gases to thereby produce a molten foamable thermoplastic resin mixture; (c) advancing said plasticated and heated mixture from said first zone by means of said screw to a selective venting and a decompression second zone of said apparatus wherein the compression on the mixture is relieved and said undesirable contaminent constituents are substantially vented from the mixture without substantial loss of the molten foamable thermoplastic resin mixture; (d) advancing said vented mixture by means of said screw to a third zone of said apparatus wherein the mixture is again subjected to compression, working and heating to further raise the temperature thereof and to plasticate the mixture to a more fluid foamable condition; and (e) thereafter discharging the foaming mixture from said third zone through suitable means for forming the foamed mixture into a structural foam plastic product.

Claim 2

The method of making structural foam plastic products which comprises: (a) mixing a granular thermoplastic resin and a heat activated blowing agent to form a foamable granular mixture containing thermally activatable gas and vapor-forming constituents which include both undesirable contaminant constituents, such as water and low-boiling point impurities, as well as desired blowing and cell-forming gaseous constituents; (b) feeding said granular mixture from a hopper to a first compressive working and heating zone located at the inlet at one end of a barrel-enclosed, screw-advancing, two stage plasticating apparatus wherein the granular mixture is plasticated and heated to a temperature at which said blowing constituents at least being to vaporize and form gases to thereby produce a molten foamable thermoplastic resin mixture; (c) advancing said plasticated and heated mixture from said first zone by means of said screw to a selective venting and a decompression second zone of said apparatus wherein the compression on the mixture is relieved and said undesirable contaminent constituents are substantially vented from the mixture without substantial loss of the molten foamable thermoplastic resin mixture; (d) advancing said vented mixture by means of said screw to a third zone of said apparatus wherein the mixture is again subjected to compression, working and heating to further raise the temperature thereof and to plasticate the mixture to a more fluid foamable condition; and (e) thereafter discharging the foaming mixture from said third zone through suitable means for forming the foamed mixture into a structural foam plastic product.