Elastic particle foam based on polyolefin/styrene polymer mixtures

Abstract

Thermoplastic particle foams which have cells having a mean cell size in the range from 20 to 500 μm and in which the cell membranes have a nanocellular or fibrous structure having pore or fiber diameters below 1500 nm, and also processes for producing them.

1 . A thermoplastic particle foam which has cells having a mean cell size in the range from 20 to 500 μm, wherein the cell membranes have a nanocellular or fibrous structure having pore or fiber diameters below 1500 nm. 
     
     
         2 . The thermoplastic particle foam according to  claim 1 , wherein the mean pore or fiber diameter of the nanocellular or fibrous structure is in the range from 10 to 1000 nm. 
     
     
         3 . The thermoplastic particle foam according to  claim 1 , wherein the polymer matrix comprises a continuous phase which is rich in styrene polymer and a disperse polyolefin-rich phase. 
     
     
         4 . The thermoplastic particle foam according to  claim 1 , wherein the polymer matrix comprises
 A) from 45 to 98.9 percent by weight of styrene polymer,   B) from 1 to 45 percent by weight of polyolefin and   C) from 0.1 to 10 percent by weight of a hydrogenated or unhydrogenated styrene-butadiene block copolymer.   
     
     
         5 . An expandable, thermoplastic polymer particle comprising a polymer matrix comprising
 A) from 45 to 98.9 percent by weight of styrene polymer,   B) from 1 to 45 percent by weight of polyolefin and   C) from 0.1 to 10 percent by weight of a hydrogenated or unhydrogenated styrene-butadiene block copolymer, with the sum of A) to C) being 100% by weight, and, in add it ion,   D) from 1 to 15 percent by weight, based on the polymer matrix, of a blowing agent,   E) from 0.3 to 5 percent by weight, based on the polymer matrix, of a nucleating agent.   
     
     
         6 . The expandable, thermoplastic polymer particle according to  claim 5  which has a coating comprising a glyceryl stearate. 
     
     
         7 . A process for producing thermoplastic particle foams according to  claim 1 , which comprises
 a) producing a polymer mixture having a continuous phase and a disperse phase by mixing two incompatible thermoplastic polymers,   b) impregnating this mixture with a blowing agent and pelletizing it to produce expandable thermoplastic polymer particles,   c) prefoaming the expandable, thermoplastic polymer particles to produce foam particles and   d) fusing the prefoamed foam particles in a mold by means of hot air or steam at a processing pressure which is kept sufficiently low for the nanocellular or fibrous structure in the cell membranes to be retained to produce particle foam moldings.   
     
     
         8 . A process for producing thermoplastic particle foams according to  claim 1 , which comprises
 a) producing a polymer mixture having a continuous phase and a disperse phase by mixing two incompatible thermoplastic polymers,   b) pelletizing this mixture and after-impregnating it with a blowing agent in an aqueous phase under superatmospheric pressure at elevated temperature to produce expandable thermoplastic polymer particles,   c) prefoaming the expandable, thermoplastic polymer particles to produce foam particles and   d) fusing the prefoamed foam particles in a mold by means of hot air or steam at a processing pressure which is kept sufficiently low for the nanocellular or fibrous structure in the cell membranes to be retained to produce particle foam moldings.   
     
     
         9 . The process according to  claim 7 , wherein the mean diameter of the disperse phase of the polymer mixture is in the range from 1 to 1500 nm. 
     
     
         10 . The process according to  claim 7 , wherein the polymer mixture is produced in step a) by mixing
 A) from 45 to 98.9 percent by weight of styrene polymer,   B) from 1 to 45 percent by weight of polyolefin and   C) from 0.1 to 10 percent by weight of a hydrogenated or unhydrogenated styrene-butadiene block copolymer.   
     
     
         11 . The process according to  claim 7 , wherein from 1 to 10 percent by weight, based on the polymer mixture, of a C 3 -C 8 -hydrocarbon is used as blowing agent in step b). 
     
     
         12 . The thermoplastic particle foam according to  claim 2 , wherein the polymer matrix comprises a continuous phase which is rich in styrene polymer and a disperse polyolefin-rich phase. 
     
     
         13 . The thermoplastic particle foam according to  claim 2 , wherein the polymer matrix comprises
 A) from 45 to 98.9 percent by weight of styrene polymer,   B) from 1 to 45 percent by weight of polyolefin and   C) from 0.1 to 10 percent by weight of a hydrogenated or unhydrogenated styrene-butadiene block copolymer.   
     
     
         14 . The thermoplastic particle foam according to  claim 3 , wherein the polymer matrix comprises
 A) from 45 to 98.9 percent by weight of styrene polymer,   B) from 1 to 45 percent by weight of polyolefin and   C) from 0.1 to 10 percent by weight of a hydrogenated or unhydrogenated styrene-butadiene block copolymer.   
     
     
         15 . A process for producing thermoplastic particle foams according to  claim 2 , which comprises
 a) producing a polymer mixture having a continuous phase and a disperse phase by mixing two incompatible thermoplastic polymers,   b) impregnating this mixture with a blowing agent and pelletizing it to produce expandable thermoplastic polymer particles,   c) prefoaming the expandable, thermoplastic polymer particles to produce foam particles and   d) fusing the prefoamed foam particles in a mold by means of hot air or steam at a processing pressure which is kept sufficiently low for the nanocellular or fibrous structure in the cell membranes to be retained to produce particle foam moldings.   
     
     
         16 . A process for producing thermoplastic particle foams according to  claim 3 , which comprises
 a) producing a polymer mixture having a continuous phase and a disperse phase by mixing two incompatible thermoplastic polymers,   b) impregnating this mixture with a blowing agent and pelletizing it to produce expandable thermoplastic polymer particles,   c) prefoaming the expandable, thermoplastic polymer particles to produce foam particles and   d) fusing the prefoamed foam particles in a mold by means of hot air or steam at a processing pressure which is kept sufficiently low for the nanocellular or fibrous structure in the cell membranes to be retained to produce particle foam moldings.   
     
     
         17 . A process for producing thermoplastic particle foams according to  claim 4 , which comprises
 a) producing a polymer mixture having a continuous phase and a disperse phase by mixing two incompatible thermoplastic polymers,   b) impregnating this mixture with a blowing agent and pelletizing it to produce expandable thermoplastic polymer particles,   c) prefoaming the expandable, thermoplastic polymer particles to produce foam particles and   d) fusing the prefoamed foam particles in a mold by means of hot air or steam at a processing pressure which is kept sufficiently low for the nanocellular or fibrous structure in the cell membranes to be retained to produce particle foam moldings.   
     
     
         18 . A process for producing thermoplastic particle foams according to  claim 2 , which comprises
 a) producing a polymer mixture having a continuous phase and a disperse phase by mixing two incompatible thermoplastic polymers,   b) pelletizing this mixture and after-impregnating it with a blowing agent in an aqueous phase under superatmospheric pressure at elevated temperature to produce expandable thermoplastic polymer particles,   c) prefoaming the expandable, thermoplastic polymer particles to produce foam particles and   d) fusing the prefoamed foam particles in a mold by means of hot air or steam at a processing pressure which is kept sufficiently low for the nanocellular or fibrous structure in the cell membranes to be retained to produce particle foam moldings.   
     
     
         19 . A process for producing thermoplastic particle foams according to  claim 3 , which comprises
 a) producing a polymer mixture having a continuous phase and a disperse phase by mixing two incompatible thermoplastic polymers,   b) pelletizing this mixture and after-impregnating it with a blowing agent in an aqueous phase under superatmospheric pressure at elevated temperature to produce expandable thermoplastic polymer particles,   c) prefoaming the expandable, thermoplastic polymer particles to produce foam particles and   d) fusing the prefoamed foam particles in a mold by means of hot air or steam at a processing pressure which is kept sufficiently low for the nanocellular or fibrous structure in the cell membranes to be retained to produce particle foam moldings.   
     
     
         20 . A process for producing thermoplastic particle foams according to  claim 4 , which comprises
 a) producing a polymer mixture having a continuous phase and a disperse phase by mixing two incompatible thermoplastic polymers,   b) pelletizing this mixture and after-impregnating it with a blowing agent in an aqueous phase under superatmospheric pressure at elevated temperature to produce expandable thermoplastic polymer particles,   c) prefoaming the expandable, thermoplastic polymer particles to produce foam particles and   d) fusing the prefoamed foam particles in a mold by means of hot air or steam at a processing pressure which is kept sufficiently low for the nanocellular or fibrous structure in the cell membranes to be retained to produce particle foam moldings.