Method of producing thermoformed articles from gas impregnated polymer

Abstract

A solid state process utilizes gas impregnation to enhance thermoforming of thermoplastic material. If the gas is plasticizing, the article is thereby plasticized for thermoforming. In some embodiments, the invention provides foaming the polymer prior to or during thermoforming by creating high levels of dissolved gas during gas exposure. Foaming may proceed spontaneously upon decompression from gas pressure, or foaming may be enhanced by heating the polymer sheet near to or above the polymer's glass transition temperature, thereby producing plasticized foamed polymer for thermoforming. When objects of unfoamed polymer are desired, foaming may be suppressed by thermoforming gas saturated articles under gas pressure. This process may be used to enhance the thermoforming performance of articles that have been previously foamed, including articles foamed by prior art processes. In some embodiments, polymer is sufficiently plasticized so that it may be thermoformed without heating. Plasticization of the polymer is reversible.

1 . A method of forming a foamed polymeric object, comprising 
 (a) solvating a plasticizing gas under pressure in an article of solid raw polymeric material in which the gas is soluble, thereby forming a polymeric article which is at least partially gas-saturated;    (b) decompressing the polymeric article;    (c) heating the article, thereby simultaneously at least partially foaming the article and further softening the article for forming; and    (d) forming the foamed polymeric object from the at least partially foamed article.    
     
     
         2 . A method according to  claim 1 , wherein the temperature to which the article is heated after decompressing it is below the glass transition temperature of the raw polymeric material when it is not at least partially gas-saturated.  
     
     
         3 . A method according to  claim 1 , wherein the material comprises previously foamed polymer.  
     
     
         4 . A method according to  claim 1 , wherein the heating step is longer than four seconds in duration.  
     
     
         5 . A method of forming a polymeric object, comprising 
 (a) solvating a plasticizing gas under pressure in an article of solid polymeric material in which the gas is soluble;    (b) forming an object from the polymeric article while under pressure of the plasticizing gas; and    (c) decompressing the formed object and letting it desorb the plasticizing gas.    
     
     
         6 . A method of forming unfoamed polymeric objects enabling high definition and deep draw, comprising: 
 (a) solvating a plasticizing gas under pressure in an article of raw polymeric material in which the gas is soluble, thereby forming a polymeric article which is at least partially gas-saturated;    (b) forming an object from the at least partially gas-saturated polymeric article while under pressure of the plasticizing gas; and    (c) decompressing the formed object and letting it desorb the plasticizing gas.    
     
     
         7 . A method of forming unfoamed polymeric objects according to  claim 6 , wherein the article has two sides and the object is formed by using pressure differences between the two sides of the article.  
     
     
         8 . A method of forming unfoamed polymeric objects according to  claim 6 , wherein the object is formed using mechanical means.  
     
     
         9 . A method of forming unfoamed polymeric objects according to  claim 6 , wherein the object is formed using pressure.  
     
     
         10 . A method of forming unfoamed polymeric objects according to  claim 6 , wherein the object is formed using mechanical means to force the article into the desired shape of the object.  
     
     
         11 . A method of forming unfoamed polymeric objects according to  claim 6 , wherein the step of forming the object comprises thermoforming at temperature below foaming temperature.  
     
     
         12 . A method of forming a foamed polymeric object with an integral skin, comprising 
 (a) solvating a plasticizing gas under pressure in an article of raw polymeric material in which the gas is soluble, thereby forming a polymeric article containing solvated gas at a concentration sufficient to cause foaming of the article when it is heated;    (b) decompressing the polymeric article;    (c) holding the decompressed polymeric article for a period of time to permit at least partial desorption of solvated gas near the surface of the article, the holding period being sufficiently long that the concentration of solvated gas near the surface of the article drops below that for which foaming occurs upon heating and sufficiently short that the concentration of solvated gas within the interior of the article remains equal to or above that for which foaming occurs upon heating;    (d) heating the article, thereby simultaneously at least partially foaming the article's interior and further softening the article for forming; and    (e) forming a foamed polymeric object from the at least partially foamed article.    
     
     
         13 . A method of forming foamed polymeric objects according to  claim 12 , wherein the heating step is longer than four seconds in duration.  
     
     
         14 . A method of forming foamed polymeric objects according to  claim 12 , wherein more than 30% of the density reduction in the final formed object takes place prior to the step of forming the foamed object.  
     
     
         15 . (canceled)  
     
     
         16 . (canceled)  
     
     
         17 . A method of forming a previously foamed polymeric object, comprising 
 (a) solvating a plasticizing gas under pressure in an article of previously foamed polymeric material;    (b) decompressing the polymeric article; and    (c) thermoforming the foamed polymeric object from the polymeric article.    
     
     
         18 . A method of forming a previously foamed polymeric object according to  claim 17 , wherein the gas is solvated in the article until the gas pressure within cells of the previously foamed material is above atmospheric pressure and the object is thermoformed before the gas pressure within the cells falls to atmospheric pressure.  
     
     
         19 . A method of preparing foamed polymer for thermoforming, comprising solvating a plasticizing gas under pressure in the foamed polymer and decompressing the foamed polymer.  
     
     
         20 . A method of forming an unfoamed polymeric object, comprising 
 (a) solvating a plasticizing gas under pressure in an article of solid, unfoamed polymeric material;    (b) decompressing the polymeric article; and    (c) forming the foamed polymeric object from the polymeric article while holding the article below the temperature at which foaming occurs.    
     
     
         21 . A method of forming unfoamed polymeric objects according to  claim 20 , wherein the article has two sides and the object is formed by using pressure differences between the two sides of the article.  
     
     
         22 . A method of forming unfoamed polymeric objects according to  claim 20 , wherein the object is formed using mechanical means.  
     
     
         23 . A method of forming unfoamed polymeric objects according to  claim 20 , wherein the object is formed using pressure.  
     
     
         24 . A method of forming unfoamed polymeric objects according to  claim 20 , wherein the object is formed using mechanical means to force the article into the desired shape of the object.  
     
     
         25 . A method of forming unfoamed polymeric objects according to  claim 20 , wherein the step of forming the object comprises thermoforming at temperature below foaming temperature.  
     
     
         26 . A method of forming a polymeric object, comprising 
 (a) solvating a plasticizing gas under pressure in an article of solid raw polymeric material in which the gas is soluble, thereby forming a polymeric article which is at least partially gas-saturated;    (b) decompressing the polymeric article; and    (c) forming a polymeric object from the article before more than 95% of the gas has desorbed from the article    
     
     
         27 . A method of forming a foamed polymeric object, comprising 
 (a) solvating a plasticizing gas under pressure in an article of solid raw polymeric material in which the gas is soluble, thereby forming a polymeric article which is at least partially gas-saturated;    (b) decompressing the polymeric article;    (c) heating the article, thereby at least partially foaming the article; and    (d) forming the foamed polymeric object from the at least partially foamed article before more than 95% of the gas has desorbed from the article.    
     
     
         28 . A method of using a one-sided mold to form foamed polymeric objects having a depth to width ratio exceeding 1:1 from foamed polymeric sheet material substantially lacking a rubber component.  
     
     
         29 . A method of using a one-sided mold to form foamed polymeric objects having wall angles of less than 35 degrees from vertical from foamed sheet polymeric material substantially lacking a rubber component.  
     
     
         30 . A method of forming foamed polymeric objects of a density of less than 32 pounds per cubic foot and having a depth to width ratio exceeding 1:1 from foamed polymeric sheet material substantially lacking a rubber component.  
     
     
         31 . A method of forming foamed polymeric objects of a density of less than 32 pounds per cubic foot and having wall angles of less than 35 degrees from vertical from foamed sheet polymeric material substantially lacking a rubber component.