Expanded polymer pellets
The invention refers to a method for producing expanded polymer pellets, which comprises the following steps: melting a polymer comprising a polyamide; adding at least one blowing agent; expanding the melt through at least one die for producing an expanded polymer; and pelletizing the expanded polymer. The invention further concerns polymer pellets produced with the method as well as their use, e.g. for the production of cushioning elements for sports apparel, such as for producing soles or parts of soles of sports shoes. A further aspect of the invention concerns a method for the manufacture of molded components, comprising loading pellets of an expanded polymer material into a mold, and connecting the pellets by providing heat energy, wherein the expanded polymer material of the pellets or beads comprises a chain extender. The molded components may be used in broad ranges of application.
1 . A method for producing expanded polymer pellets, the method comprising:
melting a polymer comprising a polyamide to form a polymer melt, wherein the polyamide comprises a polyamide 12;
adding at least one blowing agent to the polymer melt via an injection device;
expanding the polymer melt through an extruder and a die faceplate to produce an expanded polymer, wherein the die faceplate comprises a hole, wherein a diameter of the hole ranges from 2.3 mm to 2.6 mm; and
pelletizing the expanded polymer to form the expanded polymer pellets;
wherein the expanded polymer pellets have a density from 20 to 400 kg/m 3 and a variation of less than 50% in their storage modulus in the temperature range of −40° C. to 40° C.
2 . The method of claim 1 , wherein the polymer melt further comprises at least one of flame inhibitors, plasticizers, reinforcing agents, pigments, dyes, heat- or light-stabilizers, antistatic agents, fillers, and mixtures thereof.
3 . The method of claim 1 , wherein the blowing agent comprises nitrogen, carbon dioxide, ethanol, isopropanol, or mixtures thereof.
4 . The method of claim 1 , wherein the blowing agent is added to the polymer melt, the polymer melt is cooled, and then the polymer melt is extruded.
5 . The method of claim 1 , wherein the blowing agent is added to the polymer melt in the extruder.
6 . The method of claim 1 , wherein the extruder has a die through which the polymer melt is expanded.
7 . The method of claim 1 , wherein the expanded polymer pellets have a variation of less than 40% in their storage modulus in the temperature range of −40° C. to 40° C.
8 . The method of claim 1 , wherein the expanded polymer pellets have a variation from 30 to 40% in their storage modulus in the temperature range of −40° C. to 40° C.
9 . The method of claim 1 , wherein a density of the expanded polymer pellets is from 50 to 300 kg/m 3 .
10 . The method of claim 1 , wherein a density of the expanded polymer pellets is from 70 to 100 kg/m 3 .
11 . The method of claim 1 , wherein two extruders are used in series.
12 . The method of claim 11 , wherein a first extruder is a twin screw extruder and a second extruder is a single screw extruder.
13 . The method of claim 1 , wherein the extruder is operated at a temperature at which the polymer material is completely melted.
14 . A method for producing expanded polymer pellets, the method comprising:
melting a polymer comprising a polyamide to form a polymer melt, wherein the polyamide comprises a polyamide 12;
adding at least one blowing agent to the polymer melt via an injection device;
expanding the polymer melt through two extruders in series to produce an expanded polymer; and
pelletizing the expanded polymer to form the expanded polymer pellets;
wherein the expanded polymer pellets have a density from 20 to 400 kg/m 3 and a variation of less than 50% in their storage modulus in the temperature range of −40° C. to 40° C.
15 . The method of claim 14 , wherein the polymer melt further comprises at least one of flame inhibitors, plasticizers, reinforcing agents, pigments, dyes, heat- or light-stabilizers, antistatic agents, fillers, and mixtures thereof.
16 . The method of claim 14 , wherein a density of the expanded polymer pellets is from 50 to 300 kg/m 3 .
17 . The method of claim 14 , wherein a density of the expanded polymer pellets is from 70 to 100 kg/m 3 .
18 . The method of claim 14 , wherein a first extruder is a twin screw extruder and a second extruder is a single screw extruder.
19 . The method of claim 14 , wherein a first extruder is operated at a temperature at which the polymer material is completely melted.