Patent Application
20070110998
The invention relates to an improvement in synthetic polyamide polymer yarn production via melt extrusion and to a modified yarn provided by this process. More particularly, the improved process includes the steps of modifying a polymer in a melt extruder, passing the modified polymer melt to a filament formation stage, and onto a coupled process step prior to being would up as a package of yarn. Yarns produced according to the invention are optionally drawn, in a process coupled drawing stage to form either partially oriented yarns (POY) or drawn oriented yarns.
U.S. Pat. No. 4,721,650 (Nunning et al. and assigned to SOLUTIA INC.) discloses the trifunctional amine triaminononane (TAN) or 4-aminomethyl-1,8 octanediamine as a polymer chain branching agent to alter yarn properties in high speed spinning. In general, about 0.01 to 1 weight percent of TAN is employed with the N66 (polyhexamethylene adipamide) polymer having a relative viscosity (as measured in formic acid) of 50 to 80 to obtain the benefits described in the '650 patent. The benefits of TAN modified N66 polymer based yarns are most readily obtained for partially oriented yarns (POY). Accordingly, the '650 patent teaches TAN modified polymers for use in making POY and most advantageously applied in POY for draw texturing. In draw texturing, also called friction false twist texturing (FFT), the TAN modified polymer yarns could be drawn and textured at higher speeds according to the teachings of the '650 patent. POY is often called a feed yarn for FFT. It was hypothesized that the addition of small amounts of TAN effectively reduced the yarn's spin orientation making it a more suitable feed yarn. Spin orientation refers to the apparent yarn elongation via an aerodynamic drag force on the yarn as spin speeds increase. Consequently, the effect of TAN was to permit increases in spinning speeds and still retain sufficient yarn elongation to perform FFT of a feed yarn.
In previous work, the TAN was added to the polymer during polymerization in an autoclave. In subsequent processing steps the autoclave produced polymer with TAN modification was made into polymer flake. The flake polymer, also known as chips or granulated polymer, was then used in a polymer remelt operation and fed via a melt extruder to the filament yarn spinning process. At the spinning speeds of more commonly practiced spinning processes (>4800 meters per minute) significant spin orientation of the yarn takes place. However, TAN modified N66 polymer yarns also exhibited a strength loss as measured by tenacity. This strength loss could be overcome by the use of higher draw ratios in fully drawn yarns but was difficult to overcome in partially oriented yarns used in texturing due to the tension demands of the texturing process.
It is hypothesized that yarn strength loss, especially in POY, was due to the undesirable cross linking of some portion of the polymer and that this cross linked polymer is related to the autoclave addition process. With this prior art process, the TAN was injected over a short period of time into the autoclave creating a localized high concentration of branch polymer where the reaction continued to form cross links—the precursor to high molecular weight polymer or soft gel. Some evidence of this effect is the short autoclave life between cleaning (⅓to ½of normal polymer), the gel particles observed in the polymer, and the poorer spinning performance observed with polymer produced at the end of the autoclave life.
The invention provides an improved process for spinning a synthetic polyamide multifilament yarn from a polyamide polymer, modified prior to a spinning step, which includes the steps of providing a melt extruder with polyamide polymer chips, melting the chips and forwarding the melted polymer to an extrusion die during a period of time, forming at least a single filament, quenching the filament in a draft of air, forwarding the quenched filament using a feed roll assembly into a drawing zone, wherein the filament is optionally drawn and thereby increasing its length by an amount determined by a draw ratio; the draw ratio is independently chosen and equal to a quotient formed by the surface speed of the draw roll assembly to the surface speed of the feed roll assembly, and forwarding the optionally drawn filament to a winding assembly and winding up the filament on tube core. Herein, the improvement to this process may include contacting at the entrance to the extruder and prior to melting the polymer a triamino compound, capable of reacting with the polymer, e.g. branching the polymer, such that the time period during which the triamino compound and polymer are in a molten state is less than or about 12 minutes.
According to an embodiment of the invention a process for spinning a polyamide multifilament yarn comprising the steps of: providing to a melt extruder polyamide polymer chips, melting the polymer chips and forwarding the melted polymer to an extrusion die during a time period, forming filaments, quenching the filaments, optionally drawing the filament according to a draw ratio and winding up the filament; the improvement comprising: providing at the entrance to the extruder and prior to melting the polymer a triamino compound, capable of branching the polymer, such that the time period where the triamino compound and polymer are melted is less than about 12 minutes.
According to an embodiment of the process of the invention the triamino compound is selected from the group consisting of TAN (triaminononane and also known as 4-aminomethyl-1,8-octanediamine) and TREN (tris-(2-aminoethyl) amine).
According to an embodiment of the process of the invention the draw ratio is about 1 to about 2.
According to an embodiment of the invention provided is a synthetic polyamide yarn comprising nylon 66 polymer having a formic acid relative viscosity (RV) of about 40 to about 55 and having an elongation at break of about 60% to about 100%, having a TAN content by weight of about 0.01 to 0.10 per cent, wherein the yarn is provided according to a process including the steps of: providing to a melt extruder polyamide polymer chips, providing TAN at the entrance to the extruder and prior to melting the polymer, such that the time period during which TAN and polymer are melted is less than about 12 minutes, forwarding the melted polymer to an extrusion die during a time period, forming filaments, quenching the filaments, converging the filaments into a yarn and passing the yarn to a process step having a draw ratio of about 1.0 and winding up the yarn.
According to an embodiment of the invention provided is a synthetic polyamide yarn comprising nylon 66 polymer having a formic acid relative viscosity (RV) of about 40 to about 55 and having an elongation at break of less than about 60%, having a TAN content by weight of about 0.01 to 0.10 per cent, wherein the yarn is provided according to a process including the steps of: providing to a melt extruder polyamide polymer chips, providing TAN (a triamino compound) at the entrance to the extruder and prior to melting the polymer, such that the time period during which TAN and polymer are melted is less than about 12 minutes, forwarding the melted polymer to an extrusion die during a time period, forming filaments, quenching the filaments, converging the filaments into a yarn and passing the yarn to a process step having a draw ratio of about 1.1 to about 2.0.
The invention provides a synthetic polyamide polymer yarn produced via an improved melt extrusion process. The improved process can include the steps of: providing a polyamide polymer for melting in a screw-type extruder, modifying the polymer in the extruder with a triamino compound while melting the polymer, passing the modified polymer melt to a filament formation stage, forming filaments from the polymer melt by passage through a spinneret plate having a capillary orifice for each filament, cooling and solidifying the filaments in conditioned air, converging the filaments into a yarn, applying a primary yarn finish oil to the yarn, forwarding the yarn to a coupled draw stage, optionally drawing the yarn according to a draw ratio which is equal to a quotient formed by the surface speed of the draw roll assembly to the surface speed of the feed roll assembly, and winding up the yarn as a package of multifilament yarn on a tube core. Such multifilament yarns produced according to the invention are either partially oriented yarns (POY) or fully drawn yarns (FDY) characterized by their respective elongations at break and determined according to a process draw ratio.
The partially oriented yarns (POY) according to the invention can include those characterized by an elongation to break of about 70 percent to about 95 percent. The POY elongation to break is determined by the feed roll speed of the process. At feed roll speed of 4400 meters per minute a POY elongation of 93% is obtained, while at a feed roll speed of 5900 meters per minute a POY elongation of 70% is obtained. This relationship is substantially linear and allows a range of elongations.
It is observed that POY productivity is positively impacted with the use of TAN. For example, the POY elongation at a given feed roll speed without TAN can be related to the process feed roll speed with an effective amount of TAN. In the case of 0.09 weight per cent TAN, a POY elongation of 85% is achieved at a feed roll speed of 5000 meters per minute. Without TAN the equivalent POY elongation of 85% is achieved at a feed roll speed of 3500 meters per minute. The process feed roll speed without TAN cannot be increased to provide a productivity increase without decreasing the POY elongation and making the yarn less suited for draw texturing.
The yarns of the invention show an improvement in “quality index” defined as the square root of the product of elongation to break and tenacity (grams per denier). Quality approximates the area under the stress strain curve. This dependence upon TAN concentration is plotted for the two methods in
Methods to prepare drawn yarns, also called fully drawn yarns or FDY are disclosed in U.S. Pat. No. 5,750,215 (Steele et al.), the disclosure of which is incorporated herein by reference. The Steele et al. '215 patent teaches a high spinning speed process for making highly oriented N66 yarns of long elongation to break, e.g. 22 to 60 per cent. However, increasing the elongation to break of the yarns prepared according to the methods of Steele et al. can be accomplished by changing the “slip ratio”; equal to the yarn speed to feed roll speed ratio in
As known in the art, nylon 66 based polyamides have polymer chain terminal amino groups and terminal carboxyl groups. Triamino compounds, e.g. TAN and TREN, can chemically react with one or, at most, three of the terminal carboxyl groups of the polyamide polymer chains. As a result of such reactions, the polymer becomes branched. Herein the meaning of branching is the capacity of a triamino compound to produce branched polyamide polymer. However, this definition of branching is meant in no way to be a limiting definition. Furthermore, this definition of branching is in no way a limiting or detailed description of any underlying chemical mechanism by which branched polymer is formed.
Relative Viscosity (RV) of the polyamide refers to the ratio of solution and solvent viscosities measured at 25° C. in a solution of 8.4% by weight polyamide polymer in a solvent of formic acid containing 10% by weight of water.
Tenacity and Break Elongation are measured for yarns according to ASTM D2256 using a 10 in (25.4 cm) gauge length sample, at 65% RH and 70 degrees F., at an elongation rate of 60% per min. Elongation to break is measured according to ASTM D955.
A “quality index” is defined to be the square root of the quantity percent elongation to break multiplied by tenacity.
“quality index”=[% elongation X tenacity (grams/denier)]1/2
Boil-Off Shrinkage (BOS) is measured according to the method in U.S. Pat. No. 3,772,872 column 3, line 49 to column 3 line 66.
X-ray scattering measurements were performed on data acquired through the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory in New York.
The NSLS is a national user research facility funded by the U.S. Department of Energy's Office of Basic Energy Science. Two electron storage rings at NSLS provide an intense source of x-rays for chemistry/materials research with emphasis on polymers.
Herein a combined small angle x-ray scattering (SAXS) and wide angle x-ray scattering (WAXS) technique was used to collect x-ray patterns of the yarns. A two dimensional analysis technique provided the spacing of amorphous regions, long period spacing, orientation angle, and the crystalline perfection index (CPI).
Equivalent methods to obtain the SAXS and WAXS data are the following. A diffraction pattern of fiber of these compositions is characterized by two prominent equatorial X-ray reflections with peaks occurring at scattering angles approximately 20° to 21° and 23° 2θ. X-ray patterns were recorded on a Xentronics area detector (Model X200B, 10 cm diameter with a 512 by 512 resolution). The X-ray source was a Siemens/Nicolet (3.0 kW) generator operated at 40 kV and 35 mA with a copper radiation source (CU K-alpha, 1.5418 angstroms wavelength). A 0.5 mm collimator was used with sample to camera distance of 10 cm. The detector was centered at an angle of 20 degrees (2θ) to maximize resolution. Exposure time for data collection varied from 10 to 20 minutes to obtain optimum signal level.
Data collection, on the area detector, is started with initial calibration using an Fe55 radiation source which corrects for relative efficiency of detection from individual locations on the detector. Then a background scan is obtained with a blank sample holder to define and remove air scattering of the X-ray beam from the final X-ray pattern. Data is also corrected for the curvature of the detector by using a fiducial plate that contains equally spaced holes on a square grid that is attached to the face of the detector. Sample fiber mounting is vertical at 0.5 to 1.0 mm thick and approximately 10 mm long, with scattering data collected in the equatorial direction or normal to the fiber axis. A computer program analyses the X-ray diffraction data by enabling one dimensional section construction in the appropriate directions, smoothes the data and measures the peak position and full width at half maximum.
The X-ray diffraction measurement of crystallinity in 66 nylon, and copolymers of 66 and 6 nylon is the Crystal Perfection Index (CPI) (as taught by P. F. Dismore and W. O. Statton, J. Polym. Sci. Part C, No. 13, pp. 133-148, 1966). The positions of the two peaks at 21° and 23° 2θ are observed to shift, and as the crystallinity increases, the peaks shift farther apart and approach the positions corresponding to the “ideal” positions based on the Bunn-Garner 66 nylon structure. This shift in peak location provides the basis of the measurement of Crystal Perfection Index in 66 nylon:
CPI=[d(outer)/d(inner)]−1×1/(0.189)×(100)
where d(outer) and d(inner) are the Bragg ‘d’ spacings for the peaks at 23° and 21° respectively, and the denominator 0.189 is the value for d(100)/d(010) for well-crystallized 66 nylon as reported by Bunn and Garner (Proc. Royal Soc. (London), A189, 39, 1947). An equivalent and more useful equation, based on 2θ values, is:
CPI=[2θ(outer)/2θ(inner)−1]×546.7
The same procedures (as discussed in the previous CPI section) are used to obtain and analyze the X-ray diffraction patterns. The diffraction pattern of 66 nylon and copolymers of 66 and 6 nylon has two prominent equatorial reflections at 2θ approximately 20° to 21° and 23°. For 6 nylon one prominent equatorial reflection occurs at 2θ approximately 20° to 21°. The approximately 21° equatorial reflection is used for the measurement of Orientation Angle. A data array equivalent to an azimuthal trace through the equatorial peaks is created from the image data file.
The Orientation Angle (Orient. Angle) is taken to be the arc length in degrees at the half-maximum optical density (angle subtending points of 50 percent of maximum density) of the equatorial peak, corrected for background.
The LP Space and LP Intensity are obtained from small angle X- ray scattering (SAXS) patterns recorded on a Xentronics area detector (Model X200B, 10 cm diameter with a 512 by 512 resolution). The X-ray source was a Siemens/Nicolet (3.0 kW) generator operated at 40 kV and 35 mA with a copper radiation source (CU K-alpha, 1.5418 angstroms wavelength). A 0.3 mm collimator was used with sample to camera distance of 40 cm. For most nylon fibers, a reflection is observed in the vicinity of 1° 2θ. The detector was centered at an angle of 0° (2. theta.) to maximize resolution. Exposure time for data collection varied from ½to 4 hours to obtain optimum signal level.
Data collection, on the area detector, is started with initial calibration using an Fe55 radiation source which corrects for relative efficiency of detection from individual locations on the detector. Then a background scan is obtained with a blank sample holder to define and remove air scattering of the X-ray beam from the final X-ray pattern. Data is also corrected for the curvature of the detector by using a fiducial plate that contains equally spaced holes on a square grid that is attached to the face of the detector. Sample fiber mounting is vertical at 0.5 to 1.0 mm thick and approximately 10 mm long, with scattering data collected in the meridional and equatorial direction. Scanning patterns were analyzed in the meridional direction and parallel to the equatorial direction, through the intensity maxima of the two scattering peaks. Two symmetrical SAXS spots, due to long period spacing distribution, were fitted with a Pearson VII function [see: Heuval et al., J. Appl. Poly. Sci., 22, 2229-2243 (1978)] to obtain maximum intensity, position and full-width at half-maximum.
The Long Period Spacing (LP Space) is calculated from the Bragg Law using the peak position thus derived. For small angles this reduces to 1.5418/(sin (2θ)). The SAXS Long Period Intensity (LP Intensity), normalized for one hour collection time; the average intensity of the four scattering peaks corrected for sample thickness (Mult.Factor) and exposure time, were calculated. The Long Period Intensity (LP Intensity) is a measure of he difference in electron density between amorphous and crystalline regions of the polymer comprising the filament; i.e.,
LP Intensity=[Average Intensity×Mult.Factor×60]/[Collect time(minutes)]
This example illustrates the process of the invention to make a 100 denier 68 filament nylon 66 yarn which is partially oriented (POY). A process employing the spinning machine as represented by
In another trial with a 100 denier 68 filament count yarn the feed roll speed was increased to 5900 meters per minute. The yarn produced had an elongation of 70%.
This comparative example illustrates a prior process to make a 100 denier 68 filament nylon 66 yarn which is partially oriented (POY). A process employing the spinning machine as represented by
In another trial with a 100 denier 68 filament count yarn the feed roll speed was increased to 5000 meters per minute. The yarn produced had an elongation of 70%.
The above results are illustrated with reference to
Table 1 shows the x-ray wide angle scattering data compared for two nylon 66 yarns. The first yarn (40 denier 13 filaments) was produced by the autoclave addition method using the copolyamide polymer. The second yarn (95 denier 68 filaments) was produced by the invention extruder addition method of TAN to the copolyamide polymer. A 40 denier 13 filaments control yarn having no TAN was also prepared for the autoclave addition method. A control yarn of 95 denier 68 filaments yarn having no TAN was also prepared for the extruder addition method.
Table 2 shows the x-ray small angle scattering data compared for two identical yarns. The first yarn is produced by the extruder addition method and the second produced by autoclave addition method of TAN to the polymer.
These data in tables 1 and 2 show there exists a crystalline fine structure difference in the yarns produced by the two different methods of adding TAN. In summary, the autoclave addition process for TAN provides a yarn having a large change in crystal parameters, both size and perfection. There is an increase in amorphous phase fraction and larger space between crystals with an increase in the amorphous volume fraction. A small change in crystal volume fraction is observed, mostly due to a decrease in mesophase volume fraction.
By contrast the invention method of direct extruder addition provides a yarn a small or no change in crystal parameters. An increased amorphous level volume fraction with larger space between crystals is observed. A large rearrangement of crystalline character is observed where the percentage increase in crystalline volume fraction is compensated by a decrease in mesophase volume fraction.
The data presented as
Those skilled in the art, having the benefit of the teachings of the present invention as herein and above set forth, may effect modifications thereto. Such modifications are to be construed as lying within the scope of the present invention, as defined by the appended claims.
