Method of manufacturing a tough thermoplastic resin foam

Claim 1

A method according to claim 1 wherein said cooling is carried out at such a rate that the growth of cells is completed in 2 to 25 minutes after the extrusion of said mixture.

Claim 12

A method of manufacturing a tough thermoplastic resin foam having a low density and large cell size which comprises a. introducing into an extruder a thermoplastic resin, 2 to 20 parts by weight of a volatile foaming agent based on 100 parts by weight of said resin and soluble in said resin at extruding temperature and less than 3 parts by weight of a nucleating agent based on 100 parts by weight of said resin, b. extruding into the atmosphere the mixture in the form of a board through a die orifice at a temperature between the softening or melting point of said mixture and a temperature 20*C higher than the softening or melting point of the thermoplastic resin itself, c. cooling the surfaces of the board rapidly by blowing cooled gas, spraying liquid, placing the board in contact with a cooled metal material or fixing a cooling sheet-like material to form skin layers on both sides thereof, and d. cooling the board with skin layers slowly to cause the formation of foam nuclei therein and to make cells grow more than 5 mm in average cell diameter by permitting the extruded mixture to stand in the open air or placing it in a heat transfer medium, while taking up the board at a speed less than the extrusion speed at the die orifice.

Claim 14

A method of manufacturing a board formed of tough thermoplastic resin foam surfaced on both sides thereof with hard skin layers about 1 mm thick, more than 50 percent of cells of the resin foam having a diameter of more than 5 mm, the thickness of the board being between about 10 to 200 mm and the density of the board being between about 0.05 to 0.3 g./cc., which comprises: a. Introducing into an extruder a thermoplastic resin, 2 to 20 parts of a volatile foaming agent based on 100 parts of said resin and soluble in said resin at extruding temperature and less than 3 parts by weight of a nucleating agent based on 100 parts by weight of said resin, b. extruding into the atmosphere the mixture in the form of a board through a die orifice at a temperature between the softening or melting point of said mixture and a temperature 20*C higher than the softening or melting point of said thermoplastic resin, c. cooling the surfaces of the board rapidly by blowing cooled gas, spraying liquid, placing the board in contact with a cooled metal material or fixing a cooling sheet-like material to form skin layers on both sides therof, and d. cooling the board with skin layers slowly to cause the formation of foam nuclei therein and to make cells grow more than 5 mm in average cell diameter by permitting the extruded mixture to stand in the open air or placing it in a heat transfer medium, while taking up the board at a speed less than the extrusion speed at the die orifice.