Method for producing foamed polymer molded bodies and said foamed polymer molded bodies

Abstract

Method for producing foamed microporous polymer molded bodies by melting a thermoplastic polymer in a first zone of an extrusion device, mixing in a highly volatile blowing agent, conveying the polymer melt containing the blowing agent into a second zone in which dissolution of the blowing agent occurs to saturation of the polymer melt at the foaming temperature, and molding and foaming of the loaded polymer melt to a foamed structure, whereby, in the second zone, a pressure above 90 bar, a blowing agent concentration above the critical minimum concentration for complete foaming, and the foaming temperature, lying above the solidification temperature of the polymer melt saturated with blowing agent, are set such that the polymer molded body obtained has a porosity in the range between 40 and 90 vol. % and an open-cell pore structure with uniform cross-sectional distribution. Foamed microporous polymer molded bodies in the form of particles comprising a thermoplastic polymer with uniform open-cell pore structure, a porosity of 40 to 90 vol. %, an accessible proportion of pore volume of at least 0.75 and an average cell size between 1 and 100 μm.

1 . A method for production of foamed microporous polymer molded bodies comprising at least one thermoplastic polymer, comprising
 a. melting of the at least one thermoplastic polymer at a first temperature in a first zone of an extrusion device, and introduction of a blowing agent, at a pressure higher than that of the polymer melt so produced, into the first zone of the extrusion device,   b. loading of the polymer melt in the first zone of the extrusion device with the blowing agent, and mixing of the blowing agent into the polymer melt under the action of a shearing and/or kneading device on the polymer melt, whereby at least partial dissolution of the blowing agent in the polymer melt occurs simultaneously,   c. conveying of the polymer melt loaded with blowing agent, by a conveyor system coupled to a pressure regulating device, through a second zone of the extrusion device connected to the first zone and into a die positioned at the end of the second zone, whereby the temperature in the second zone is set to a second temperature, defined as the foaming temperature, which is equal to or lower than the first temperature, whereby dissolution of the blowing agent to saturation of the polymer melt occurs in the second zone,   d. molding of the polymer melt in the die and subsequent foaming of the molded polymer melt loaded with blowing agent, on exit of the polymer melt from the die, to give a foamed structure on account of the blowing agent contained in the polymer melt,   e. cooling of the foamed structure until its solidification,
 whereby a pressure greater than the minimum pressure p min  of 90 bar is set in the second zone of the extrusion device and the polymer melt loaded with blowing agent produced in the second zone of the extrusion device has a solidification temperature, wherein, 
 a blowing agent concentration is set that is at least equal to a critical minimum concentration for complete foaming, and 
 the foaming temperature is set to a value above the solidification temperature such that the porous polymer molded body obtained has a porosity in the range between 40 and 90 vol. % and an open-cell pore structure with uniform cross-sectional distribution, wherein the open-cell pore structure is a three-dimensional network of cells separated from one another by thin walls. 
   
   
   
       2 . Method according to  claim 1 , wherein the foaming temperature is set to a value that is up to 30% higher than the solidification temperature. 
   
   
       3 . Method according to  claim 1 , wherein the foaming temperature is set to a value that is 10 to 30% higher than the solidification temperature. 
   
   
       4 . Method according to  claim 1 , wherein the foaming temperature is set to a value 10 to 20% higher than the solidification temperature, such that the porous polymer molded body obtained has an open-cell structure and a porosity in the range of 50 to 80 vol. %. 
   
   
       5 . Method for production of foamed microporous polymer molded bodies comprising at least one thermoplastic polymer, comprising
 a. melting of the at least one thermoplastic polymer at a first temperature in a first zone of an extrusion device, and introduction of a blowing agent, at a pressure higher than that of the polymer melt so produced, into the first zone of the extrusion device,   b. loading of the polymer melt in the first zone of the extrusion device with the blowing agent, and mixing of the blowing agent into the polymer melt under the action of a shearing and/or kneading device on the polymer melt, whereby the blowing agent simultaneously dissolves at least partially in the polymer melt,   c. conveying of the polymer melt loaded with blowing agent, by a conveyor system coupled to a pressure regulating device, through a second zone of the extrusion device, connected to the first zone, to a die positioned at the end of the second zone, whereby the temperature in the second zone is set to a second temperature, defined as the foaming temperature, which is equal to or lower than the first temperature, whereby dissolution of the blowing agent occurs to saturation of the polymer melt in the second zone,   d. molding of the polymer melt in the die and subsequent foaming of the molded polymer melt loaded with blowing agent, on exit of the polymer melt from the die, to give a foamed structure on account of the blowing agent contained in the polymer melt,   e. cooling of the foamed structure until its solidification,
 whereby a pressure greater than the minimum pressure p min  of 90 bar is set in the second zone of the extrusion device and the polymer melt loaded with blowing agent produced in the second zone of the extrusion device has a solidification temperature, wherein, 
 a blowing agent concentration is set that is at least equal to a critical minimum concentration for complete foaming, and 
 the foaming temperature is set to a value that is 10 to 30% higher than the solidification temperature. 
   
   
   
       6 . Method according to  claim 5 , wherein the foaming temperature is set to a value that is 10 to 20% higher than the solidification temperature. 
   
   
       7 . Method according to  claim 1 , wherein the blowing agent is introduced into the first zone of the extrusion device at a pressure that is higher than that in the first zone of the extrusion device. 
   
   
       8 . Method according to  claim 1 , wherein the polymer melt loaded with blowing agent is mixed in the second zone by means of mixing elements. 
   
   
       9 . Method according to  claim 1 , wherein the blowing agent is CO 2 . 
   
   
       10 . Method according to  claim 1 , wherein the die is conditioned to a die temperature that can be set independently of the foaming temperature and is higher than the foaming temperature. 
   
   
       11 . Method according to  claim 10 , wherein the die temperature is set to a value that is up to 20% higher than the foaming temperature. 
   
   
       12 . Method according to  claim 1 , wherein the pressure p min  in the second zone of the extrusion device is at least 120 bar. 
   
   
       13 . Method according to  claim 1 , wherein the at least one thermoplastic polymer is at least one polyolefin. 
   
   
       14 . Method according to  claim 13 , wherein the at least one polyolefin is polypropylene. 
   
   
       15 . Method according to  claim 1 , wherein the foamed polymer molded body is a solid fiber. 
   
   
       16 . Method according to  claim 1 , wherein the foamed polymer molded body is a hollow fiber. 
   
   
       17 . Method according to  claim 1 , wherein the foamed polymer molded body is a film. 
   
   
       18 . Method according to  claim 1 , wherein the foamed structure is broken up into foamed polymer particles. 
   
   
       19 . Method according to  claim 1 , wherein the foamed structure is granulated. 
   
   
       20 . Method according to  claim 5 , wherein the blowing agent is introduced into the first zone of the extrusion device at a pressure that is higher than that in the first zone of the extrusion device. 
   
   
       21 . Method according to  claim 5 , wherein the polymer melt loaded with blowing agent is mixed in the second zone by means of mixing elements. 
   
   
       22 . Method according to  claim 5 , wherein the blowing agent is CO 2 . 
   
   
       23 . Method according to  claim 5 , wherein the die is conditioned to a die temperature that can be set independently of the foaming temperature and is higher than the foaming temperature. 
   
   
       24 . Method according to  claim 23 , wherein the die temperature is set to a value that is up to 20% higher than the foaming temperature. 
   
   
       25 . Method according to  claim 5 , wherein the pressure p min  in the second zone of the extrusion device is at least 120 bar. 
   
   
       26 . Method according to  claim 5 , wherein the at least one thermoplastic polymer is at least one polyolefin. 
   
   
       27 . Method according to  claim 26 , wherein the at least one polyolefin is polypropylene. 
   
   
       28 . Method according to  claim 5 , wherein the foamed polymer molded body is a solid fiber. 
   
   
       29 . Method according to  claim 5 , wherein the foamed polymer molded body is a hollow fiber. 
   
   
       30 . Method according to  claim 5 , wherein the foamed polymer molded body is a film. 
   
   
       31 . Method according to  claim 5 , wherein the foamed structure is broken up into foamed polymer particles. 
   
   
       32 . Method according to  claim 5 , wherein the foamed structure is granulated.