Rapid solid-state foaming

Abstract

Disclosed, among other things, are ways to manufacture reduced density thermoplastics using rapid solid-state foaming and machines useful for the saturation of plastic. In one embodiment, a foaming process may involve saturating a semi-crystalline polymer such as Polylactic Acid (PLA) with high levels of gas, and then heating, which may produce a reduced density plastic having high levels of crystallinity. In another embodiment, a foaming process may produce layered structures in reduced density plastics with or without integral skins. In another embodiment, a foaming process may produce deep draw structures in reduced density plastics with or without integral skins. In yet another embodiment, a foaming process may utilize additives, blends, or fillers, for example. In yet another embodiment, a foaming process may involve saturating a semi-crystalline polymer such as Polylactic Acid (PLA) with high levels of gas, and then heating, which may produce a reduced density plastic having high levels of crystallinity.

1 - 17 . (canceled) 
     
     
         18 . A method, comprising:
 inserting a polylactic acid polymer material into a pressurized chamber, the polylactic acid polymer material having a thickness of about 0.012 inches to about 0.040 inches;   exposing the polylactic acid polymer material in the pressurized chamber to a foaming agent at a pressure of at least about 500 psi for less than about ten minutes;   removing the polylactic acid polymer material from the pressurized chamber; and   heating the polylactic acid polymer material, thereby reducing the density of the polylactic acid polymer material.   
     
     
         19 . The method of  claim 18 , wherein the thickness of the polylactic acid polymer material is about 0.020 inches to about 0.024 inches. 
     
     
         20 . The method of  claim 18 , wherein the pressure is less than about 3,000 psi. 
     
     
         21 . The method of  claim 18 , wherein the polylactic acid polymer material is exposed to the foaming agent for at least 30 about seconds 
     
     
         22 . The method of  claim 18 , wherein inserting the polylactic acid polymer material into the pressurized chamber is via a first seal, and removing the polylactic acid polymer material from the pressurized chamber is via a second seal. 
     
     
         23 . The method of  claim 22 , wherein at least one of the first seal and the second seal includes a sealing surface configured to maintain a gap of less than about 0.1 inches between the sealing surface and the polylactic acid polymer material. 
     
     
         24 . The method of  claim 18 , wherein the foaming agent is an inert gas. 
     
     
         25 . The method of  claim 24 , wherein the inert gas is carbon dioxide. 
     
     
         26 . A method, comprising:
 inserting a polylactic acid polymer material into a pressurized chamber via a first seal, the polylactic acid polymer material having a thickness of about 0.012 inches to about 0.040 inches;   exposing the polylactic acid polymer material in the pressurized chamber to a foaming agent at a first pressure and a first temperature for a first time period to at least partially saturate the polylactic acid polymer material with the foaming agent, the first time period less than about ten minutes;   removing the polylactic acid polymer material from the pressurized chamber via a second seal; and   heating the polylactic acid polymer material at a second pressure and a second temperature for a second time period, the second pressure less than the first pressure, and the second temperature greater than the first temperature.   
     
     
         27 . The method of  claim 26 , wherein the thickness of the polylactic acid polymer material is about 0.020 inches to about 0.024 inches. 
     
     
         28 . The method of  claim 26 , wherein the first pressure is greater than about 500 psi. 
     
     
         29 . The method of  claim 28 , wherein the first pressure is less than about 3,000 psi. 
     
     
         30 . The method of  claim 26 , wherein at least one of the first seal and the second seal includes a sealing surface configured to maintain a gap of less than about 0.1 inches between the sealing surface and the polylactic acid polymer material. 
     
     
         31 . The method of  claim 26 , wherein the foaming agent is an inert gas. 
     
     
         32 . The method of  claim 31 , wherein the inert gas is carbon dioxide. 
     
     
         33 . A method, comprising:
 inserting a polylactic acid polymer material into a pressurized chamber via a first dynamic seal;   exposing the polylactic acid polymer material in the pressurized chamber a foaming agent at a first pressure and a first temperature for a first time period to at least partially saturate the polylactic acid polymer material with the foaming agent;   removing the polylactic acid polymer material from the pressurized chamber via a second dynamic seal; and   heating the polylactic acid polymer material at a second pressure and a second temperature for a second time period, the second pressure less than the first pressure, and the second temperature greater than the first temperature,   wherein at least one of the first dynamic seal and the second dynamic seal includes a sealing surface configured to maintain a gap of less than about 0.1 inches between the sealing surface and the polylactic acid polymer material.   
     
     
         34 . The method of  claim 33 , wherein the thickness of the polylactic acid polymer material is about 0.012 inches to about 0.040 inches. 
     
     
         35 . The method of  claim 34 , wherein the thickness of the polylactic acid polymer material is about 0.020 inches to about 0.024 inches. 
     
     
         36 . The method of  claim 33 , wherein the first time period is about 30 seconds and about 10 minutes. 
     
     
         37 . The method of  claim 36 , wherein the first pressure is about 500 psi to about 3,000 psi. 
     
     
         38 . A method, comprising:
 passing a polylactic acid polymer material through a pressurized chamber from an inlet to an outlet, the inlet including a first seal and the outlet including a second seal, the polylactic acid polymer material remaining in the pressurized chamber for less than about 10 minutes;   continuously exposing the polylactic acid polymer material to a foaming agent at a first pressure as the polylactic acid polymer material passes through the pressurized chamber to at least partially saturate the polylactic acid polymer material with the foaming agent; and   heating the polylactic acid polymer material at a second pressure less than the first pressure to reduce the density of the polylactic acid polymer material.   
     
     
         39 . The method of  claim 38 , wherein the polylactic acid polymer material is exposed to the foaming agent at the first pressure for about 30 seconds and about 10 minutes. 
     
     
         40 . The method of  claim 39 , wherein the first pressure is about 500 psi to about 3,000 psi.