High molecular weight polyamides and CoPolyamides with uniform RV and low gel content
A process of producing a polyamide polymer using in-line vacuum finishing technology in the absence of steam or other gases. The polyamide polymer, in particular Nylon 66, Nylon 6, and copolyamides, have a high molecular weight, excellent color, and low gel content. The polyamide polymer also has a relative viscosity greater than 50 as measured in a 90% strength formic acid solution; consistent viscosity with a standard deviation of less than 1; a gel content no greater than 50 ppm as measured by insolubles larger than 10 micron; and an optical defect content of less than 2,000 parts per million (ppm) as measured by optical control system (OCS). The polymer can be made into monofilaments or a multifilament yarn.
1 . A method of making a high molecular weight Nylon 6,6 polyamide polymer, the method comprising:
(a) feeding a concentrated nylon salt solution into a polycondensation reactor that heats the concentrated nylon salt solution over three stages to a temperature of about 230° C. and a pressure of about 18.5 bar, thereby to yield a first Nylon 6,6 polyamide polymer melt comprising a first Nylon 6,6 polyamide polymer with a first Relative Viscosity;
(b) feeding the first Nylon 6,6 polyamide polymer melt into a flasher that heats and decompresses the first Nylon 6,6 polyamide polymer melt to a final pressure of about 1 bar, thereby to yield a decompressed first Nylon 6,6 polyamide polymer melt;
(c) feeding the decompressed first Nylon 6,6 polyamide polymer melt to a finishing vessel that heats the decompressed first Nylon 6,6 polyamide polymer melt under a blanket of inert gas to further polymerize and remove moisture from the decompressed first Nylon 6,6 polyamide polymer melt, thereby to yield a decompressed second Nylon 6,6 polyamide polymer melt comprising a second Nylon 6,6 polyamide polymer with a second Relative Viscosity;
(d) feeding the decompressed second Nylon 6,6 polyamide polymer melt to a twin screw extruder that melt-processes the decompressed second Nylon 6,6 polyamide polymer melt under vacuum in the twin screw extruder in the absence of added steam or gas to remove moisture and other volatiles therefrom and to increase a molecular weight of the decompressed second Nylon 6,6 polyamide polymer melt, for a residence time in the twin screw extruder of less than 60-seconds, thereby to yield a third Nylon 6,6 polyamide polymer melt comprising a third Nylon 6,6 polyamide polymer with a third Relative Viscosity; and
(e) recovering a product Nylon 6,6 polyamide polymer, wherein the product Nylon 6,6 polyamide polymer is characterized by a precision Relative Viscosity greater than 60 as measured in a 90% strength formic acid solution, and wherein the precision Relative Viscosity has an RV Standard Deviation of less than or equal to 1.0 and a Gel content Parameter of less than 10 ppm as determined by parts per million insolubles larger than 10 microns in 90% formic acid at 25° C.
2 . The method of making a high molecular weight Nylon 6,6 polyamide polymer according to claim 1 , wherein the decompressed second Nylon 6,6 polyamide polymer melt is melt processed in the twin screw extruder at a temperature ranging from 280° C. to 350° C. under vacuum ranging from 600 mm Hg vacuum to 725 mm Hg vacuum, and wherein the residence time in the twin screw extruder ranges from 10 seconds to less than 30 seconds.
3 . The method of making a high molecular weight Nylon 6,6 polyamide polymer according to claim 1 , wherein, after step (d) and prior to step (e), the method comprises feeding the third Nylon 6,6 polymer melt to a residence time dwell vessel and melt-processing the third Nylon 6,6 polymer melt with mixing in the residence time dwell vessel at a temperature ranging from 280° C. to 350° C. for a residence time in the residence time dwell vessel of at least 1 minute, thereby to yield a fourth Nylon 6,6 polyamide polymer melt comprising a fourth Nylon 6,6 polyamide polymer with a fourth Relative Viscosity higher than the third Relative Viscosity of the third Nylon 6,6 polyamide polymer.
4 . The method of making a high molecular weight Nylon 6,6 polyamide polymer according to claim 1 , wherein the precision Relative Viscosity of the product Nylon 6,6 polyamide polymer is 85, as measured in a 90% strength formic acid solution, and wherein the product Nylon 6,6 polyamide polymer contains balanced amine and carboxyl groups.
5 . The method of making a high molecular weight Nylon 6,6 polyamide polymer according to claim 1 , wherein, prior to step (a), the method comprises:
concentrating a nylon salt solution at a pressure of about 2 bar, thereby to yield the concentrated nylon salt solution containing approximately 85% solids.
6 . The method of making a high molecular weight Nylon 6,6 polyamide polymer according to claim 1 , wherein the polycondensation reactor comprises a plug flow reactor.
7 . The method of making a high molecular weight Nylon 6,6 polyamide polymer according to claim 1 , wherein the first Relative Viscosity is from 3 to 20, the second Relative Viscosity is from 30 to 45, and the third Relative Viscosity is greater than or equal to 75, as measured in a 90% strength formic acid solution.
8 . The method of making a high molecular weight Nylon 6,6 polyamide polymer according to claim 1 , comprising:
(f) melt-spinning the product Nylon 6,6 polyamide polymer, thereby to yield a multifilament Nylon 6,6 polyamide yarn.
9 . The method of making a high molecular weight Nylon 6,6 polyamide polymer according to claim 1 , wherein, prior to step (c), the method comprises feeding the decompressed first Nylon 6,6 polyamide polymer melt to a phase separator that removes volatiles from the decompressed first Nylon 6,6 polyamide polymer melt.
10 . A method of making a high molecular weight polyamide polymer with a precision Relative Viscosity and low gel content, the method comprising:
(a) forming and concentrating a nylon salt solution;
(b) heating the concentrated nylon salt solution in a polycondensation reactor provided with a flasher, thereby to yield a decompressed first polyamide polymer melt maintained at a pressure of about 1 bar, the decompressed first polyamide polymer comprising a first polyamide polymer with a first Relative Viscosity;
(c) feeding the decompressed first polyamide polymer melt to a finishing vessel that heats the decompressed first polyamide polymer melt under a blanket of inert gas to further polymerize and remove moisture from the decompressed first polyamide polymer melt, thereby to yield a decompressed second polyamide polymer melt comprising a second polyamide polymer with a second Relative Viscosity;
(d) feeding the decompressed second polyamide polymer melt to a twin screw extruder to melt process the decompressed second polyamide polymer melt under vacuum in the twin screw extruder in the absence of added steam or gas to remove moisture and other volatiles therefrom and to increase a molecular weight of the decompressed second polyamide polymer melt, for a residence time in the twin screw extruder of less than 60 seconds, thereby to yield a third polyamide polymer melt comprising a third polyamide polymer with a third Relative Viscosity, the third polyamide polymer being characterized by either:
(i) a precision Relative Viscosity greater than 50 as measured in a 90% strength formic acid solution with an RV Standard Deviation of less than or equal to 1.25; or
(ii) a Gel Content Parameter of less than 50 ppm as determined by parts per million insoluble larger than 10 microns in a 90% formic acid solution at 25° C.; and
(e) recovering a product polyamide polymer characterized by either: (i) a precision Relative Viscosity greater than 50 as measured in a 90% strength formic acid solution with an RV Standard Deviation of less than or equal to 1.25; or (ii) a Gel Content Parameter of less than 50 ppm as determined by parts per million insoluble larger than 10 microns in a 90% formic acid solution at 25° C. and an Average Optical Defect level of less than 2000 ppm as measured by optical scanning at 50 micron resolution.
11 . The method of making a high molecular weight polyamide polymer with a precision Relative Viscosity and a low gel content according to claim 10 , wherein the decompressed second polyamide polymer melt is melt-processed in the twin screw extruder at a temperature ranging from 280° C. to 350° C.
12 . The method of making a high molecular weight polyamide polymer with a precision Relative Viscosity and a low gel content according to claim 10 , wherein the decompressed second polyamide polymer melt is melt-processed in the twin screw extruder under vacuum ranging from 600 mm Hg vacuum to 725 mm Hg vacuum.
13 . The method of making a high molecular weight polyamide polymer with a precision Relative Viscosity and a low gel content according to claim 10 , wherein the residence time of the decompressed second polyamide polymer melt in the twin screw extruder is less than 20 seconds.
14 . The method of making a high molecular weight polyamide polymer with a precision Relative Viscosity and a low gel content according to claim 10 , wherein the residence time of the decompressed second polyamide polymer melt in the twin screw extruder ranges from 10 seconds to 60 seconds.
15 . The method of making a high molecular weight polyamide polymer with a precision Relative Viscosity and a low gel content according to claim 10 , wherein, after step (c) and prior to step (d), the method comprises feeding the third polyamide polymer melt to a residence time dwell vessel having low pressure drop (LPD) static mixers included therein and melt-processing the third polyamide polymer melt with mixing in the residence time dwell vessel to provide a fourth polyamide polymer melt comprising a fourth polyamide polymer with a fourth Relative Viscosity higher than the third Relative Viscosity of the second polyamide polymer, the fourth polyamide polymer being characterized by either:
(i) a precision Relative Viscosity greater than 50 as measured in a 90% strength formic acid solution with an RV Standard Deviation of less than or equal to 1.25; or
(ii) a Gel Content Parameter of less than 50 ppm as determined by parts per million insoluble larger than 10 microns in a 90% formic acid solution at 25° C. and an Average Optical Defect level of less than 2000 ppm as measured by optical scanning at 50 micron resolution.
16 . The method of making a high molecular weight polyamide polymer with a precision Relative Viscosity and a low gel content according to claim 15 , wherein the third polyamide polymer melt is melt-processed in the residence time dwell vessel at a temperature ranging from 280° C. to 350° C.
17 . The method of making a high molecular weight polyamide polymer with a precision Relative Viscosity and a low gel content according to claim 15 , wherein the third polyamide polymer melt is melt-processed in the residence time dwell vessel for a residence time in the residence time dwell vessel of at least 1 minute.
18 . The method of making a high molecular weight polyamide polymer with a precision Relative Viscosity and a low gel content according to claim 10 , comprising:
(f) melt-spinning the product polyamide polymer, thereby to yield a multifilament polyamide yarn.