Polyamide beads and method for the production thereof
Certain polyamide beads or granules are useful as a sustaining material for underground natural or artificial cracks of the earth's crust essentially employed for the extraction of hydrocarbons such as crude oil or natural gas; such polyamide beads have a spherical or ellipsoidal shape and have a surface free of concave portions, advantageously having a uniform shape, and having a mean diameter lower than or equal to 1.7 mm and a porosity lower than 0.1 ml/g, and are produced using a particular cutting device/extruder.
1. A method for the production of polyamide beads or granules, said method comprising:
introducing a polyamide or polyamide-based composition into a granulating device having an underwater pelletizer, wherein the underwater pelletizer comprises a die having die holes with an average diameter ranging from 0.3 mm to 1.7 mm, and a cooling liquid at a temperature ranging from 70° C. to 100° C.; and
feeding the polyamide or polyamide-based composition into the die holes at a pressure ranging from 70 bar to 250 bar, wherein the polyamide or the polyamide-based composition is fed into the die holes with establishment of at least 80% of the nominal feed pressure no later than 5 seconds after the start of feeding the die holes with thus molten polyamide or polyamide-based composition.
2. The method of claim 1 , wherein the polyamide or polyamide-based composition is fed into the granulating device through a feed device comprising a single-screw or twinscrew extruder combined with a gear pump.
3. The method of claim 1 , wherein a throughput of the polyamide or polyamide-based composition in the die is from 3 and 15 kg/h per hole.
4. The method of claim 1 , wherein a rotational speed of the cutting means ranges from 3,000 to 6,000 rpm.
5. The method of claim 1 , wherein the polyamide beads or granules have a spherical or ellipsoidal shape.
6. The method of claim 1 , wherein the polyamide beads or granules have a surface which does not comprise concave portions.
7. The method of claim 1 , wherein the polyamide beads or granules have an average diameter less than or equal to 1.7 mm.
8. The method of claim 7 , wherein the polyamide beads or granules have an average diameter ranging from 0.8 mm to 1.5 mm.
9. The method of claim 1 , wherein the polyamide beads or granules have a porosity, measured according to the mercury porosity measurement method, of less than 0.1 ml/g.
10. The method of claim 1 , wherein the polyamide or polyamide-based composition comprises a reinforcing filler and/or a bulking filler.
11. The method of claim 10 , wherein the weight concentration of the reinforcing and/or bulking fillers in the polyimide or polyamide-based composition ranges from 5 percent to 90 percent, with respect to the total weight of the composition.
12. The method of claim 10 , wherein the reinforcing and/or bulking fillers are selected from the group consisting of glass fibers, aramid fibers, ceramic fibers, mineral fibers, clays, kaolin, silica, alumina, molecular sieves, glass beads, ceramic beads, fillers and plant fibers.
13. The method of claim 1 , wherein the polyamide is selected from the group consisting of polyamide 6, polyamide 6,6, polyamide T6, polyamide 4,6, copolyamides of these polyamides and semi-crystalline semi-aromatic polyamides.
14. The method of claim 13 , wherein the polyamide is polyamide 66 or copolyamide 6,6/6.
15. The method of claim 1 , wherein the polyamide or polyamide-based composition contains additives selected from the group consisting of additives for stabilization to oxidation and to light, pigments, dyes, mattifying agents, flame retardants, plasticizers and crosslinking agents.
16. The method of claim 1 , wherein the granulating device further comprises: one means of cutting; means for feeding, under pressure, the polyamide or polyamide-based composition to the cutting means through the die holes, wherein the feeding means includes a pressure control means; and a fluid circuit comprising means for controlling the temperature of the cooling liquid to be ranging from 70° C. to 100° C.
17. The method of claim 16 , wherein the feeding means comprises a single-screw or twin-screw extruder combined with a gear pump.
18. The method of claim 16 , wherein the feeding means comprises a means for controlling the throughput of the polyamide or polyamide-based composition in the die to be from 3 to 15 kg/h per hole.
19. The method of claim 16 , wherein the cutting means comprises a rotating knife driven by a rotary drive at a rotational speed of from 3,000 to 6,000 rpm.