Polyamide beads and method for the production thereof

Abstract

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.

Claims

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.

Description

EXPERIMENTAL SECTION

Example 1

(1) A polyamide of type 66 sold by RHODIA under the tradename STABAMID 27 AE1 has a viscosity index VI equal to 136 (measured at 25 C. in a Hubbelhode type viscosimeter from a solution containing 5 g/l of polymer dissolved in a mixture composed of 90% by weight of formic acid and 10% by weight of water) and a melting point of 263 C. (determined by the DSC method).

(2) This polymer is melted at a temperature of 308 C. using a twin-screw extruder having a diameter of 50 mm sold by Leistriz and is fed into a gear pump sold by Maag. This gear pump feeds an underwater pelletizing device sold by GALA under the tradename A5 PAC 6 at a material pressure of 169 bar. The die of this underwater pelletizing device has 32 holes that are 0.8 mm in diameter. The die is heated at a temperature of 345 C. The device comprises a knife holder equipped with 16 blades that turn in the cutting chamber at a speed of 5000 rpm. In this same cutting chamber, water at 76 C. circulates with a flow rate of 22 m.sup.3/h. Under these conditions, the method makes it possible to produce, for a polymer throughput in the holes of the die equal to 170 kg/h with a throughput per hole of 5 kg/h, substantially spherical particles having a diameter equivalent to 1.4 mm.

Example 2

(3) A copolyamide 66/6 comprising 40% by weight of kaolin as mineral fillers is melted at a temperature of 329 C. using a twin-screw extruder, having a diameter of 50 mm sold by Leistriz, which feeds a gear pump sold by Maag. This gear pump feeds an underwater pelletizing device identical to that from example 1 under a pressure of 91 bar, pressure observed 3 seconds after the feeding of the polymer into the die. The die of this underwater pelletizer has 72 holes of 1.2 mm and is heated at a temperature of 369 C. A knife holder equipped with 16 blades turns in the cutting chamber at a speed of 4500 rpm. In this same cutting chamber water at 89 C. circulates at a flow rate of 11 m.sup.3/h. Under these conditions, for an extrusion throughput of 420 kg/h, substantially spherical particles are obtained having a diameter equivalent to 1.5 mm.

Example 3

(4) A copolyamide 6/66 comprising 40% mineral filler constituted by kaolin is melted at a temperature of 333 C. using a twin-screw extruder identical to that from examples 1 and 2, which feeds a gear pump identical to that from examples 1 or 2. This gear pump feeds an underwater pelletizing device identical to that from example 1 or 2 under a feed pressure of 135 bar. The die of this underwater pelletizing device has holes of 1 mm in diameter and is heated at a temperature of 389 C. A knife holder equipped with 16 blades turns in the cutting chamber at a speed of 5000 rpm. In this same cutting chamber, water at 92 C. circulates at a flow rate of 20 m.sup.3/h. Under these conditions, for an extrusion throughput of 400 kg/h, particles are obtained having a diameter equivalent to 1.25 mm.