US 3925525 A
Liquid polymeric materials, in a fiber spinning operation, are extruded through extrusion passageways of a spinneret plate. The passageways are designed to establish an essentially constant extensional strain rate condition for flow of liquid.
Description (OCR text may contain errors)
United States Patent 1111 LaNieve Dec. 9, 1975 SPINNING METHOD 3,006,026 10/1961 Martin 6t 21]. 425/464 3,210.45l [Cl/I965 Manning et al 425/464  memo" Henna Lameve1 summti 3.382535 5/[968 Ferrari 264/177 F Assignee: celanese C rp rati N w Y k, Santeangelo r r i r i i I I Y v v v v FOREIGN PATENTS OR APPLICATIONS  Filed: Aug. 10, 1973 246,828 11/1960 Australia .5 425/464 [2 AWL 3 7 7 OTHER PUBLICATIONS Polymer Processing by J. M. McKelvey, pp. 8797, [52 us. (:1 ,1 264/40; 264/176 F; 264/177 F; John wley Sons New York 1962' 264 204' 264 7 511 1111. 0. F02M 1 1 /30 pr'mary Emmmekjay W00  Field of Search 425/464; 264/177 F, 176 F,
264/40, 204, 207 ABSTRACT L1qu1d polymeric materials, in a fiber spinning opera  References Ci tion, are extruded through extrusion passageways of :1 UNITED STATES PATENTS spinneret plate. The passageways are designed to es 2 21 l 946 8/940 G 425/464 tablish an essentially constant extensional strain rate raves 4. 1 2,341,555 2/1944 16m I I I I I I 425/464 Condmon for flow of hquld 2,742 667 4/1956 Clauzeau et al 425/464 13 Claims, 5 Drawing Figures U.S. Patent Dec. 9, 1975 FIG.1
M. w ilililii i- SPINNING METHOD BACKGROUND AND OBJECTS OF THE INVENTION This invention relates to the spinning of synthetic filaments. More particularly, this invention relates to a novel method and apparatus for the spinning of synthetic filaments utilizing a spinneret nozzle designed to establish an essentially constant extensional strain rate.
In connection with the production of filaments from man-made fiber forming materials, it has been common to utilize spinnerets including a plurality of exit passageways in the form of nozzles or orifices machined in a spinneret plate. A liquid comprising a polymer melt or a solution of a polymer in an appropriate solvent is extruded through these nozzles in the filament forming process.
As will be appreciated, the profile of such spinneret nozzles has been the subject of considerable research efforts. In this connection, reference may be had to U.S. Pat. No. 3,537,135 (issued Nov. 3, I970), U.S. Pat. No. 3,303,530 (issued Feb. 14, I967), U.S. Pat. No. 3,210,451 (issued Oct. 5, 1965), U.S. Pat. No. 3,227,009 (issued Jan. 4, l966), and U.S. Pat. No. 3,174,183 (issued Mar. 3, 1965) for disclosures of spinnerets with exit passageways having a variety of profiles.
An important consideration in fluid flow through a spinneret passageway of any given profile is that of fluid pressure drop. The pressure drop across a spinneret can be expressed as the sum of the viscous dissipation in the passageway and the entrance and exit flows, the pressure due to kinetic energy effects, and that due to storage of elastic energy.
Another important consideration in spinneret fluid flow is that of extrudate swell or die swell, i.e. the ratio of the fiber cross-sectional area after it passes the exit orifice of the spinneret exit passageway to the crosssectional area of that exit orifice. Die swell has a direct effect on draw ratios and fiber elongation.
For example, in the case of spinning polyethylene terephthalate (PET), increased extrudate swell resulting from increased spinning productivity would produce decreases in after-draw ratio. Similarly, in con nection with production of dry spun fibers from cellulose triacetate (CTA), increased extradate swell would reduce fiber elongation.
It has been found that extrudate swell in connection with flow through a capillary is inversely related to the ratio of the capillary length to its diameter. However, under high spinning productivities, attempts to reduce extrudate swell by increasing that ratio may produce an excessive presure drop due to viscous dissipation.
Since costs associated with the operation of spinning equipment are considerable, adequately high spinning productivity must be maintained.
It would, therefore, be highly desirable to provide a novel spinning method and apparatus based upon a passageway profile designed to advantageously accomodate desirable spinning productivity consistent with acceptable pressure drop and extrudate swell. Accordingly, it is a general object of the present invention to provide such a novel spinning method and apparatus.
In spinning operations, one important viscosity consideration is that of fluid pressure drop in spinneret flow due to viscous dissipation. Under high productivity spinning conditions, viscous pressure drop often becomes excessive. As such, viscous pressure drop to some extent constitutes a limiting factor on spinning productivity. Since the costs associated with the operation of spinning equipment are considerable, it would be highly desirable to provide for increased spinning productivity by minimizing viscous pressure drop or to provide for a viscous pressure drop consistent with a given spinning productivity.
In realizing this object, the present invention departs from those prior art approaches to design of spinneret nozzle profiles which have been governed primarily by direct viscosity considerations, and perhaps, to some extent, inertial and turbulence considerations.
In this connection, the present invention embodies a recognition that spinneret flow for fluids generally classified as viscous, such as PET melts or CTA solutions, is dominated by elastic" forces. More particularly, according to the present invention a nozzle profile is provided so as to establish an essentially constant extensional strain rate, viz. a constant change in veloc ity with respect to the incremental distance of fluid travel (an elastic force consideration). In this fashion the flow condition for the liquid is such as to provide for a low total pressure drop. At the same time adequate spinning speeds may be employed with acceptable die swell.
The essentially constant extensional strain rate leads to a low total pressure drop through several mechanisms. First, since the elastic pressure drop contribution to the total pressure drop is governed by the maxi mum extensional strain rate, a low constant extensional strain rate may be chosen to reduce that contribution as compared with prior art nozzle profiles. Secondly, as hereinafter more fully described, at a chosen constant extensional strain rate, the viscous pressure drop is minimized. In addition, the gentle streamline entry flow provided by the nozzle profile of the present invention is believed to reduce dissipation due to vena contracta type eddies.
It may be here noted that an apparently similar profile has been proposed for an entirely different purpose, namely, the design of a minimum length die to be used for extruding on a wire, plastics which are subject to melt fracture. (See U.S. Ferrari Pat. No. 3,832,535, issued May I4, 1968.) Considerations directed toward elimination of melt fracture and minimizing die length in the environment of extruding plastics on a wire are unrelated to the present invention, in that polymers involved in the contemplated spinning operations do not exhibit any significant melt fracture in the range of op erating conditions selected in contemplation for practice of the present invention.
Consistent with the foregoing, it is, therefore, a further object of the present invention to provide a novel spinning method and apparatus wherein an essentially constant extensional strain rate is established for flow through a spinneret nozzle.
It is a further object to the present invention to provide such a novel spinning method and apparatus wherein adequate spinning speeds may be employed with acceptable die swell.
It is yet another object of the present invention to provide such a novel spinning method and apparatus wherein a low total pressure drop is produced.
It is still another object of the present invention to provide such a novel spinning method and apparatus which minimizes breaking of filaments in a spin line,
and thus minimizes the occurence of incomplete packages. In this connection, it is believed that breaking of filaments in a spin line might, in some respects, be attributable to faults or impurities, in the spinning material. The particular improved spinneret flow produced according to the present invention is thought to minimize the adverse consequences attributable to such faults or impurities.
SUMMARY OF PREFERRED EMBODIMENTS OF THE INVENTION A preferred form of the invention intended to accomplish at least some of the foregoing objects entails the spinning of fibers through the provision of a spinneret plate for extruding polymeric materials and including at least one converging extrusion passageway having an entry opening and an exit orifice, with the passage profile being designed to establish an essentially constant extensional strain rate.
Spinning speeds in the range of about 500 to I500 meters per minute in the case of solution spinning and 500 to 6000 meters per minute in the case of melt spinning are usually appropriate, with about 1000 meters per minute and about 1200 to 3000 meters per minute being preferred respectively for dry and wet solution and for melt spinning. Solution spinning temperatures of about 50 to l lC, preferably about 90C are usually contemplated. For melt spinning, temperatures in the range of about 275 to 330C, preferably 285 to 300C, are involved.
Preferably the approach angle, defined as the angle of intersection between the axis of the converging extrusion passageway and the tangent to the wall of that passageway at the entrance opening, is between about to 45.
The passageway (i.e. the spinneret plate thickness) and exit orifice area may vary, with lengths in the range of about 0.020 to 0.060 inches for solution spinning and 0.1 to 0.6 inches for melt spinning, and areas in the range of about 3 X 10 to 50 X 10 square centimeters (solution spinning) and about l X l0 to 50 X 10 square centimeters (melt spinning) being desirable.
In accordance with the present invention, it will be appreciated that spinning of fiber-formin g materials by solution spinning (wet or dry) or melt spinning (without significant melt fracture in the range of operating conditions selected for the materials in contemplation for practice of the present invention) of any suitable polymeric materials, such as polyamides, polyesters, acrylics, polyimides, cellulosics, vinyl chloride and vinylidene cyanide polymerics and the like, may be practiced. Particular applicability of the present invention may be found in high speed spinning of cellulose esters or polyesters, especially polyethelene terephthalate.
For example, the process is of particular value in the dry solution spinning of cellulose triacetate from solution in a solvent comprising a major amount of a halo genated hydrocarbon such as methylene chloride.
In this connection, as employed herein, cellulose triacetate has reference to cellulose acetate having fewer than about 0.29 and preferably fewer than about 0.12 free hydroxyl group per anhydroglucose unit of the cellulose molecule, i.e., an ac etyl value calculated as combined acetic acid by weight of at least about 59 percent and preferably at least about 61 percent.
Advantageously, its intrinsic viscosity ranges from about 1.5 to 2.5 and is preferably about 2, and it is pres ent in the dope to a concentration ranging from about 20 to 25 percent. In place of methylene chloride, the dope solvent may comprise other halogenated lower alkanes such as ethylene dichloride or propylene chloride. Preferably, up to about 15 percent by weight of the dope solvent comprises a lower alkanol such as methanol, ethanol, isopropanol, etc. The preferred dope solvent is methylene chloride-methanol in the proportions of about -10 by weight.
The cross-sectional configuration of the nozzle employed in accordance with the present invention is preferably symmetrical about the nozzle axis, with a circular cross-section being the preferred form. However, non-circular configurations conventional in the spinning art, such as for example those depicted in US. Pat. No. 3,303,530, issued Feb. 14, 1967, are also contemplated.
Other objects and advantages of the present invention will become apparent from the following detailed description thereof with reference to the accompanying drawings in which like numerals indicate like elements, and in which:
THE DRAWINGS FIG. is a plan view of a spinneret in accordance with the present invention;
FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;
FIG. 3 is an enlarged sectional view showing the profile of the exit passageway of the spinneret of FIGS. 1 and 2;
FIG. 4 is an enlarged sectional view showing the passageway of FIG. 3 contiguous, adjacent its entry end, with a frusto-conical passageway;
FIG. 5 is a schematic illustration of a dry spinning op eration in accordance with the present invention.
DETAILED DESCRIPTION With reference now to FIG. 1, a spinneret or jet 10 in accordance with the present invention may be seen. This spinneret is made of any suitable material such as stainless steel.
As may be seen FIG. 2, the spinneret is generally cupshaped. The cup bottom indicated at 12 is provided with a plurality of circumferentially disposed, spaced apertures or exit passageways l4 therethrough.
During spinning operations, a liquid comprising a polymer melt or a solution of a polymer in an appropriate solvent is supplied to the spinneret 10 and is extruded through the exit passageways I4 in the filament forming process. An enlarged view of a preferred forms of the exit passageway 14 may be seen in FIGS. 3 and 4.
Each passageway 14 is in the form of a converging nozzle, the profile of which is hereinafter more fully described, that terminates in an exit orifice 16. After flow into the entry orifice 17, through the nozzle passageway and out the exit orifice l6, elastic energy stored in the liquid is recovered so as to result in extrudate swell or die swell. This storage of elastic energy occurs by reason of the extensional flow of the fluid.
In FIG. 5 there is shown a dry spinning cabinet 20 to which dope is supplied through a pipe 22. The liquid dope is extruded through the spinneret 10 of FIGS. l-3 with no intervening plating of the spinneret. I-Iot air may be admitted to the cabinet 20 through a suitable conduit 23 and may be exhausted through a suitable conduit 24 along with vapors of the dope solvent. The filaments 26 leaving the spinneret 10 through the extrusion passageways 14 are directed about a guide 28 and out of the cabinet at a location indicated at 30. The filaments are pulled as a yarn 32 by suitable draw rolls 34. The yarn 32 by suitable draw rolls 34. The yarn 32 passes through a guide 36 and is twisted and taken up on a bobbin 38 by a conventional collector such as a ring spinner 40.
With renewed reference to FIG. 3, the nozzle profile in accordance with the present invention may be more fully appreciated. In FIG. 3, the radius of the exit ori- 1 fice 16 is indicated by R. The nozzle preferably is circular in transverse cross-section, and has smooth, gradually curving walls 18 in the form of a surface of revolution defined by a generatrix moving about the central axis 19 of the passageway 14. The wall profile, conforming to the shape of this generatrix, provides an essentially constant extensional strain rate during flow of the polymeric material through the passageway 14 by being designed to essentially respond to the following cubic equation:
f= z+ll 2 where:
R is the radius of the exit orifice l6;
r u is the wall radius measured perpendicular to the axis 22;
Z is the distance along the axis 19 of the nozzle measured from the exit orifice 16; and
A is a constant hereinafter more fully described.
One the criterian of constant extensional strain rate is selected, the foregoing Equation (1) may be derived by integrating the following equation:
61 152 x where:
6v/6Z is the extensional strain rate represented by the partial derivative of velocity (V) with respect to distance measured from the exit orifice 16 along the nozzle axis 19; and
K is a constant, while recalling that:
V is the fluid velocity;
no is the wall radius as defined for equation (1); and
Q is the volumetric flow rate. and while also recalling the limit condition that )1!) is equal to R [as defined for equation (l)]at the exit orifree 16.
Preferably the constant A of Equation (l) is determined by equating the constant extensional strain rate K of Equation (2) with the maximum extensional strain rate for a conical spinneret wherein the die swell is acceptable (hereinafter referred to as equivalent conical spinneret"). Then,
K Ev/EZ maxi cone where:
Sv/SZ max. cone is the maximum extensional strain 55 rate for the equivalent conical spinneret. The well known equation for the wall profile of a conical spinneret is:
rm Z tan 0 4K A P v Q where:
rm and Z are as defined in Equation l); and 6 is the half angle of the equivalent conical spinneret,
preferably in the range of 2 to 7%" 6 By combining equations (3) and (5), and recognizing that for a cone 5r/8Z is a maximum at the exit orifice 16 where Z is zero and rm is R, it will be determined that:
52 maxvcone= 2 (6] where:
7,; is 4Q/1rR the wall shear rate.
Equations (2) through (6) may then be combined and integrated to produce equation (1) where A of equation (l) will be defined as:
V 2 tan where:
no is the wall sheer stress; and K, and n are fluid constants, Describing the viscous pressure drop A P v as:
Z indicates the axial position where no becomes infinite and combining Equations (8) and (9) yields:
APv=2K,( (10) When equation (3) is partially differentiated with respect to Z to produce:
and Equation (ll) is rearranged and substituted in Equation (10), it will be seen that Since 5v/8Z appears in the denominator of Equation (l2), the largest possible value of 8v/5Z provides the smallest viscous pressure drop (APv) However, the provision for a constant extensional strain rate inherently imposes the constraint that:
fir/BZ 6 6v/8Z maximum. (l3) leading to the conclusion that the viscous pressure drop of Equation (I2) is minimized by the extensional strain rate being at a constant that is also the maximum.
With reference now to FIG. 4, a further nozzle passageway that may be employed according to the present invention may be seen. The passageway of FIG. 4 is comprised of the nozzle passage 14 of FIG. 3 contiguous with a passageway extension 42 in the form of a frusto-conical countersink. It has been found that manufacturing of the spinneret with a passageway 14 profile establishing an essentially constant extensional strain rate as discussed above is more convenient when such a countersink is provided.
To aid in insuring a smooth flow transition, it is, however, desirable that the intersection of the conical section 42 with the passageway 14 be such that the walls of the cone are tangent to the walls 18 of the passageway 14 at its entry orifice 17. If such tangency is not provided, and the cone makes a steeper angle than the tangent then the extensional strain rate in the conical section 42 will be greater. As such, the chosen die-swell characteristics will not be met, and viscous pressure drop will be greater than the minimum which the constant extensional strain rate otherwise would provide.
Although the invention has been described with reference to preferred forms thereof, it will be appreciated that additions, substitutions, modifications and deletions may be made without departing from the spirit and scope of the invention as defined in the appended claims:
What is claimed is:
I. In a method of spinning fibers from fiber-forming, liquid polymeric material utilizing a spinneret for extruding said material through at least one converging nozzle passageway having an entry opening and an exit orifice. the improvement comprising establishing an essentially constant extensional strain rate condition for flow of said liquid through said passageway by providing a nozzle passageway bounded by gradually curving walls having a profile described essentially by the equation R is the perpendicular distance between an axis of the passageway and the nozzle wall at the exit orifree;
r w is the perpendicular distance between nozzle wall and points along that axis;
Z is the distance along that axis measured from said exit orifice; and
A is a constant.
2. The method according to claim 1 wherein said protile is defined by a surface of revolution defined by a generatrix described by said equation and moving about said axis in a generally circular path.
3. The method according to claim 2 wherein the constant A in said equation is defined by -2 tan B/R where 0 is the conical half angle of an equivalent frustoconical passageway for establishing a maximum extensional strain rate essentially equal to said essentially constant extensional strain rate.
4. A solution spinning method according to claim 3 wherein said liquid material consists essentially of cellulose acetate and wherein said material is extruded at spinning speeds in the range of about 500 to 1500 meters per minute at spinning temperatures of about 50 to ll0C.
5. A melt spinning method according to claim 3 wherein said liquid material consists essentially of polyethylene terephthalate and wherein said material is extruded at spinning speeds in the range 500 to 6000 meters per minute at spinning temperatures of about 275 to 330C.
6. The method according to claim 1 wherein said passageway is contiguous with and tangent to the walls of a frusto-conical passageway.
7. The method according to claim 1 wherein said liquid material comprises polyethylene terephthalate.
8. The method according to claim 1 wherein said liquid material comprises cellulose acetate.
9. The method according to claim 1 wherein said liquid material comprises cellulose triacetate.
10. A solution spinning method according to claim I wherein said material is extruded at spinning speeds in the range of about 500 to 1500 meters per minute.
11. A melt spinning method according to claim 1 wherein said material is extruded at spinning speeds in the range of about 500 to 3000 meters per minute.
12. A solution spinning method according to claim 1 wherein the spinning temperature is in the range of about 50 to ll0C.
13. A melt spinning method according to claim 1 wherein the spinning temperature is in the range of about 275 to 330C.
UNITED STATES PATFNT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,925,525 Page I of 5 DATED December 9 1975 |NVENTOR(S) Herman L. LaNieve It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 5, line 21, equation (1) should read:
line 24, "rm" should read r line 29 "One" should read Once line 32, equation (2) should read:
3V az K;
line 34, "(W/ 52" should read BV/BZ line 39, equation (3) should read:
lines 42, 44 and 65, "rm" should read r line 52,
equation (4) should read:
U NITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,925,525 Page 2 f 5 DATED December 9, 1975 INVENTOR(S) Herman L. LaNieve It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
line 55, "(iv/62" should read BV/GZ and, line 59, equation (5) should read:
I Z tan 8 Column 6, line 2, "Sr/62" should read ar/az lines 3 and 44, "rw" should read r -lines 4-9, equation (6) should read:
i; tan 6 az 2 R max cone lines 14-18, equation (7) should read:
A 2 tan 6 lines 30-34, equation (8) should read:
UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION Page 3 of 5 PATENT N0. 3,925, 525
DATED December 9 |NVENTOR(S) Herman L. LaNieve It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
line 35, "Tm" should read 1 lines 37 and 68 "A should read AP read shear line 35, "sheer" should lines 38-42, equation (9) should read:
r; NTTED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,925,525 Page 4 of 5 DATED December 9 1975 INVENTOR(S) Herman L. LaNieve It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
lines 60-65, equation (12) should read:
rm an AP) -4K Q n+1 2 dr n r and aZ w r =R lines 66 and 67, "6V/6Z" should read 8V/8Z 82 Z maximum Claim 1, line 11, the equation should read:
1 and UNITED sTATEs PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,925,525 Page 5 of 5 DATED December 9, 1975 mvgmoms) Herman L. LaNieve It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
line 16, "rm" should read r Signed and Scaled this Twenty-second Day of May 1979 [SEAL] DONALD W. BANNER RUTH C. MASON Arresting Oflicer Commissioner of Patents and Trademarks