Polymer foam articles and methods of making polymer foams

Abstract

Molded polymer foam articles are described as having a novel foam structure. The polymer foam articles include a continuous polymer matrix defining a plurality of pneumatoceles therein which is present throughout the entirety of the article. The surface region is further characterized as having compressed pneumatoceles. The novel foam structure is achieved even when molding polymer foam articles comprising a shape and volume wherein a sphere having a diameter between 2 cm and 1000 cm would fit within the article in at least one location without protruding from a surface of the article, and the article further has a total volume of more than 1000 cm3. Methods of making a stabilized molten polymer foam, and of making a molded polymer foam article using the stabilized molten polymer foam are also described.

What is claimed is: 
     
         1 . A polymer foam article having a continuous thermoplastic polymer matrix defining a plurality of pneumatoceles throughout the entirety of the article, further wherein a sphere having a diameter between 2 cm and 1000 cm would fit within the article in at least one location without protruding from a surface of the article. 
     
     
         2 . The polymer foam article of  claim 1  wherein a surface region extending 500 microns from the surface of the article comprises compressed pneumatoceles throughout the entirety thereof. 
     
     
         3 . The polymer foam article of  claim 2  wherein the article further comprises compressed pneumatoceles more than 500 microns from the surface thereof. 
     
     
         4 . The polymer foam article of  claim 1  further including one or more locations wherein a sphere having a diameter of 2 cm would not fit within the polymer foam article, and would protrude from the surface of the article. 
     
     
         5 . The polymer foam article of  claim 1  wherein the polymer foam article has a volume of 1000 cm 3  or greater. 
     
     
         6 . The polymer foam article of  claim 1  wherein the polymer foam article has a volume of 1000 cm 3  to 5000 cm 3 . 
     
     
         7 . The polymer foam article of  claim 1  wherein the polymer foam article has a volume of 2000 cm 3  to 5000 cm 3 . 
     
     
         8 . The polymer foam article of  claim 1  wherein the polymer foam article has a volume of greater than 5000 cm 3 . 
     
     
         9 . The polymer foam article of  claim 1  wherein a plurality of spheres having diameter of 2 cm would fit within the article without protruding from a surface thereof. 
     
     
         10 . The polymer foam article of  claim 8  wherein the plurality is 2, 3, 4, 5, 7, 8, 9, 10, 15, 20, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 100, 200, 300, 400, 500, 1000, 1500, or 2000. 
     
     
         11 . The polymer foam article of  claim 1  wherein a sphere having a diameter of 20 cm would fit within the article in at least one location, without protruding from a surface thereof. 
     
     
         12 . The polymer foam article of  claim 1  wherein two spheres, each having a diameter of 20 cm, would fit within the article without protruding from the surface. 
     
     
         13 . The polymer foam article of  claim 1  wherein the thermoplastic polymer is selected from polyolefins, polyamides, polyimides, polyesters, polycarbonates, poly (lactic acid)s, acrylonitrile-butadiene-styrene copolymers, polystyrenes, polyurethanes, polyvinyl chlorides, copolymers of tetrafluoroethylene, polyethersulfones, polyacetals, polyaramids, polyphenylene oxides, polybutylenes, polybutadienes, polyacrylates and methacryates, ionomeric polymers, poly ether-amide block copolymers, polyaryletherkeytones, polysulfones, polyphenylene sulfides, polyamide-imide copolymers, poly(butylene succinate)s, cellulosics, or polysaccharides, or any copolymer, alloy, admixture, or blend thereof. 
     
     
         14 . The polymer foam article of  claim 1  wherein the continuous polymer matrix comprises a polyolefin, a polyamide, an ionically functionalized olefin copolymer, or a polyether-amide block copolymer. 
     
     
         15 . The polymer foam article of  claim 1  wherein the continuous polymer matrix further comprises one or more additional materials selected from colorants, stabilizers, brighteners, nucleating agents, fibers, particulates, and fillers. 
     
     
         16 . The polymer foam article of  claim 1  wherein the continuous polymer matrix further comprises a talc or a colorant or both talc and a colorant. 
     
     
         17 . The polymer foam article of  claim 1  comprising a density reduction of 30% to 85%. 
     
     
         18 . The polymer foam article of  claim 1  comprising a void fraction of 70% to 85%. 
     
     
         19 . A method of forming a molten polymer foam, the method comprising:
 heating and mixing a thermoplastic polymer with a pneumatogen source to form a molten pneumatic mixture, wherein the temperature of the molten pneumatic mixture exceeds the temperature at which the pneumatogen source produces a pneumatogen at atmospheric pressure, and wherein a pressure applied to the molten pneumatic mixture is sufficient to substantially prevent formation of pneumatoceles;   collecting a selected amount of the molten pneumatic mixture in a collection region;   defining an expansion volume in the collection region proximal to the molten pneumatic mixture that results in a pressure drop at a rate of 0.01 GPa/s to 5 GPa/s; and   dispensing a molten polymer foam from the collection region.   
     
     
         20 . The method of  claim 19  wherein the method is carried out using an injection molding machine, further wherein a backpressure is set to be 500 kPa to 25 MPa. 
     
     
         21 . The method of  claim 19  wherein the method further comprises allowing 0 seconds to 5 seconds to pass after the defining and before the dispensing, wherein the molten pneumatic mixture is allowed to stand substantially undisturbed in the collection area. 
     
     
         22 . The method of  claim 19  wherein the method further comprises allowing 600 seconds to 2000 seconds to pass after the defining and before the dispensing, wherein the molten pneumatic mixture is allowed to stand substantially undisturbed in the collection area. 
     
     
         23 . A method of making a polymer foam article, comprising dispensing the molten polymer foam of  claim 19  into a mold.