|Publication number||US2988777 A|
|Publication date||Jun 20, 1961|
|Filing date||May 12, 1955|
|Priority date||May 12, 1955|
|Publication number||US 2988777 A, US 2988777A, US-A-2988777, US2988777 A, US2988777A|
|Inventors||Carl Bieber Roman, Miller Jr Frederick John|
|Original Assignee||Du Pont|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Referenced by (18), Classifications (7)|
|External Links: USPTO, USPTO Assignment, Espacenet|
June 20, 1961 R. c. BIEBER ET AL 2,988,777
SPINNING APPARATUS Filed May 12, 1955 INVENTORS ROMAN C.- BIEBER FREDERICK J. MILLER, JR.
gm) 7 Y W e, QL/
ATTORNEY United States Patent 2,988,777 SPINNING APPARATUS Roman Carl Bieber and Frederick John Miller, Jr., Richmond, Va., assignors to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Filed May 12, 19-55, Ser. No. 507,826 1 1 Claims. (Cl. 18-8) This invention relates to the production of artificial filaments by a wet-spinning process. More particularly, it relates to an improved spinning assembly and spinning arrangement for producing the artificial filaments.
Several processes have been developed recently for improving the properties of regenerated cellulose yarns, cords and fabrics. In these processes, a viscose filament-forming solution is extruded through the orifices of a spinneret into acid coagulating baths containing a zinc salt in the presence of certain compounds, coagulation modifiers. These modifiers, under the conditions specified for the processes, retard coagulation of the viscose filaments and thus tend to promote cross-sectional homogeneity in the individual filaments. Cross-sectional homogeneity is apparent from microscopic examination of the filaments. The filaments display surfaces that are smooth (noncrenulated) and their cross-sections show substantially all skin. It is this result, homogeneous filament crosssections, that is believed to contribute to the high tenacity, high fatigue resistance, improved launderability, etc., of the regenerated cellulose yarns, cords and fabrics. The modifier processes are discussed in US. Patents: 2,535,044, 2,535,045 and 2,536,014 all issued December 26, 1950, to N. L. Cox and 2,696,423 issued December 7, 1954, to M. A. Dietrich; U.S. applications: 228,979 filed May 29, 1951, to N. L. Cox and now abandoned 414,029 filed February 17, 1954, to N. L. Cox and W. D. Nicoll and now Patent No. 2,910,341; 450,255 filed August 16, 1954, to E. C. Pontius and now Patent No. 2,810,- 658 and 498,090 filed March 30, 1955, to D. D. Bachlott and now Patent No. 2,855,321.
These processes, though tending to improve the properties of the regenerated cellulose products, are difiicult to control. The filaments remain in the viscous, nonsolid state for longer periods. Slight tension on the weak filaments damages them and often results in filament breaks. When spinning continuity is impaired or when filaments are damaged, many of the advantages gained by the coagulation modifier processes may be substantially lost. Furthermore, high spinning speeds of 100 yards per minute or more, desirable for commercial operation, intensify the problem. At high spinning speeds the filaments must travel greater distances in the bath and the coagulating bath must be circulated at a higher rate. More opportunity is thereby provided for damaging the weak filaments.
Conventional apparatus for spinning artificial filaments,
as illustrated in FIGURE 1, consists of a cylindrical spinneret containing a plurality of orifices mounted within a cylindrical holder or housing. It will be noted that the spinneret face projects beyond the face of the surrounding housing; the outer edge of the housing is a relatively small distance beyond the periphery of the spinneret; and the face of the housing is not usually flat. To protect the weak filaments emerging from the spinneret, several additions to or modifications of the apparatus have been proposed. These include tubes through which the filaments are drawn along with spinning bath after emergency of the filaments from the spinneret (also illustrated in FIGURE 1); cylindrical sleeves extending from the the spinneret or the spinneret housing to surround the emerging filaments until they are suificiently coagulated;
and streamlining the housing or the spinneret itself in an See eifort to prevent bath currents transverse to the path of the filaments. However, none of these methods has proved completely satisfactory. Filament breaks have continued to be a bothersome problem, especially in the modifier processes and particularly when spinning at high speeds.
The object of the present invention is to improve the quality of filaments spun by a wet-spinning process by reducing the number of filament breaks during spinning. Another object is to provide an improvement in yarn and cord properties. Other objects will appear hereinafter.
The objects are accomplished by a spinning assembly comprising a housing, a supply conduit connection for a filament-forming solution in the housing, a spinneret having a plurality of orifices, said spinneret mounted in the housing so that the face of the spinneret forms a continuous, substantially flat surface with the face of the housing, the face of the housing extending an appreciable distance radially from the periphery of the spinneret, preferably a distance at least equal to the diameter of the spinneret.
By flushing mounting the spinneret within a housing so that the face of the spinneret and the face of the housing form a continuous, substantially flat surface in accordance with this invention or by placing a cap over the conventional housing to provide the same result, the quality of filaments as measured by the reduction in the number of filament breaks during spinning may be improved as much as ten-fold over those produced with conventional spinning assemblies.
In the preferred spinning arrangement, the above spinning assembly is used in conjunction with a spinning tube, Whose entrance is spaced a short distance from the spinneret face (a distance less than the tube diameter) and whose radius of curvature at the entrance must be exceedingly low (of the order of 0.4 to 1.6 times the tube diameter). With the preferred spinning arrangement, not only is the quality of the filaments improved but the yarn and cord properties are improved as well.
For the purpose of defining the invention, it has been assumed that the outermost orifices of the spinneret are located very close to the periphery of the spinneret. In practice, the distance may vary from 5 inch to inch depending on the size of the spinneret, the orifice size, etc.
The details of the invention will be more clearly apparent from the following description in conjunction with the accompanying illustrations in which:
FIGURE 1 is a plan view of a prior art spinning assembly and tube entrance.
FIGURE 2 is a plan view of the spinning assembly constructed in accordance with the present invention and the preferred tube entrance.
FIGURE 3 is a 'view in perspective of the preferred apparatus for spinning viscose rayon.
As shown in FIGURES l and 2, the housing for the spinning nozzle may be composed of two or three parts fitted together. In FIGURE 1 only two parts form the housing, namely: a cylinder 11, having threads along part of its internal surface and a cylinder 12, having threads along its external surface. The goosenec-k or supply conduit 13 is flared at one end 14 and fitted within the cylinder 12 to supply filament-forming solution. The spinneret or spinning nozzle 15, in the shape of a cup having a lip 16 and a plurality of orifices 10, is mounted within cylinder 11. The spinneret projects from inch to inch beyond the surrounding cylinder 11. Cylinder 11 is adapted at the end opposite the threaded end to receive the lip 16 of the spinneret 15. A tube of rubber or similar material 17 conducts filament-forming solution from the supply conduit 13 to the spinneret 15. By screwing the cylinder 12 within cylinder 11, the flared end 14 of the supply conduit is pressed against the rubber tube 17; the
- mately inch tube, the radius of curvature, r,
tube in turn is pressed against the lip 16 of the spinneret; and the lip in turn is pressed against the inner wall of cylinder 11 to make a snug fit.
In FIGURE 2 an adapter cap 18 of polyethylene or similar plastic material is fitted over the end of cylinder 11 to complete the housing for the spinning nozzle of the present invention. The face of the housing thereby forms a continuous, substantially flat surface with the face of the spinneret and extends radially from the periphery of the spinneret, preferably a distance at least equal to the diameter of the spinneret. The spinning assembly illustrated in FIGURE 2 provides a simple method for converting the conventional spinning assembly of FIGURE 1 into the spinning assembly of this invention. However, the possibility of redesigning the spinneret housing to achieve the same result is offered as an alternative.
FIGURES 1 and 2 also provide a comparison to bring out the critical elements in the design of the improved tube entrance preferred for use with the spinning assembly of the invention. In FIGURE 1 the spinning tube 19 is merely a tube of glass or similar material flared at one end to receive the filaments and the coagulating bath. The radius of curvature at the entrance is usually 2 inches or more. In FIGURE 2 a specially designed tube entrance is provided. Over the constant diameter glass tube 20 is superimposed a moulded Lucite or similar plastic entrance 21, adapted to fit snugly over the end of the glass tube 20. A plastic set screw 22 holds the tube entrance 21 in place. The entrance 21 has a flat face and the opening within the entrance is flared according to critical specifications. The flare is such that the radius of curvature, r, of the tube at its entrance is from 0.4 to 1.6 times the tube diameter. Thus, for a 15 millimeter or approximay It is believed that when is less than inch, high turbulence results at the tube entrance as bath seeks to enter the tube; while an r greater than 1 inch reduces the bath velocity in this neighborhood so that the flowing bath acts as a drag on the moving filaments. In either case, damage to the nascent filaments tends to result.
The distance between the spinneret face and the tube entrance, shown as d in FIGURE 2, is another critical factor in the preferred embodiment of the present invention. It has been found that the distance d should be less than 1.0 times the tube diameter. Thus for a 15 millimeter or approximately /a inch diameter tube, d should be less than inch.
In the apparatus shown in FIGURE 3, filament-forming solution is pumped by metering pump 23 through a candle filter 24 to the supply conduit or gooseneck 13. The solution is extruded through the orifices of spinneret and the emerging filaments 25 are introduced into the tube through the tube entrance 21. The tube usually has an inside diameter of about 7 to 15 millimeters, though it may be higher or lower, and a length of about 8 to 50 inches. The tube is disposed within the coagulating bath 26 contained in the trough 27. The entrance of the tube is near the face of the spinneret, as discussed in the preceding paragraph. The filaments are carried through the tube by the flowing bath liquid. The liquid is forced to flow through the tube by enclosing part of the bath encompassing the spinneret and the tube entrance by enclosure 28 and providing a bath head of about 1.5 to 2 inches.
After emerging from the tube, the filaments are converged into a yarn by guide 29 and passed over rollers 30, 31, 32, 33 and 34 which serve to stretch the yarn about 80% in gradual increments. The yarn is withdrawn from the bath by draw-off roller or feed wheel 35. The yarn is stretched an additional 20% between feed wheels 35 and 36. During this latter stretching, the yarn may be treated with hot dilute acid or bath solution by spray 37 or by passing through a container of the treating solution or by other suitable means. The yarn is then led into range from inch to 1 inch.
a rotating bucket 38 at a speed of 20 to 100 yards per minute or higher where the yarn is collected as a cake. The yarn is then purified, slashed and processed in the conventional manner.
In the following examples, the spinning assembly of the present invention is compared to prior art spinning assemblies under commercial operating conditions.
EXAMPLE 1 A viscose spinning solution containing a coagulation modifier was prepared from wood pulp sheets using about 39% carbon disulfide based on the weight of airdried pulp. The viscose solution containing 6.25% cellulose by weight, 5.75% total alkali calculated as sodium hydroxide and .04% cyclohexylamine by weight as a modifier, was spun into an acid-sulfate bath containing about 9.3% sulfuric acid, about 17.5% sodium sulfate and 9.5% zinc sulfate. The viscose solution had been filtered, deaerated and permitted to ripen. It was spun at a salt index of 16.6, a viscosity of about 30 stokes and a temperature of 42 C.
In case A, the spinning assembly of the invention was used. The spinneret was flush mounted, its periphery being /2 inch from the outer edge of the surrounding cap. The spinneret face was set A. inch from the entrance of the spinning tube and the radius of curvature of the tube entrance was inch.
In case B, the conventional spinning assembly shown in Figure 1 was used. The spinneret face projected about inch beyond the surface of the surrounding housing. The spinneret face was set inch from the tube entrance and the radius of curvature of the tube entrance was 2.7 inches.
In case C, the conventional spinning assembly as described for case B but with the spinneret face set inch from the tube entrance was used.
In all cases the spinneret measured /2 inch in diameter, contained 60 orifices of .0025 inch diameter each, and the outermost orifices were & inch from the periphery of the spinneret; the spinning tube had an inside diameter of 7 millimeters and was 18 inches long. The following results were obtained:
weight of cellulose, 5.75% by weight total alkali calculated as sodium hydroxide and 069% sodium N-methylcyclohexyldithiocarbamate was prepared from wood pulp sheets using about 38% carbon disulfide based on the air-dried sheets. The viscose solution was filtered, deaerated and permitted to ripen to a salt index of about 17 and a viscosity of about 32 stokes. The solution was heated prior to spinning and spun at a temperature of about 44 C. into baths maintained above 50 C. and containing various amounts of sulfuric acid, 17.5% sodium sulfate, 9.5% zinc sulfate and 30 parts per million of nitrogen.
The filaments were led through a spinning tube having a diameter of 15 millimeters. After emerging from the tube, the filaments were converged and led over a series of rollers in the bath which served to stretch the filaments about in gradual increments. After leaving the bath, the filaments passed over two feed wheels in succession, the feed wheels being sufficiently dilferent in diameter to stretch the filaments an additional 20%. During this latter stretching the filaments were treated with dilute bath solution at about C. The filaments were then led into a rotating bucket at a speed of yards per minute to form cakes. The cakes were purified, slashed and processed into cord in the conventional manner.
Three levels of sulfuric acid were used in the spinning bath and two spinning arrangements were compared. In case A,- the arrangement of the present invention was used. A spinneret, having a inch diameter was flush mounted within the housing. The periphery of the housing was about 1 inch beyond the periphery of the spinneret. The outermost orifices were inch from the periphery of the spinneret. The spinneret face was inch from the entrance of the tube and the radius of curvature of the tube entrance was inch.
In case B, the inch spinneret was mounted in the conventional housing so that the face of the spinneret projected A; inch. The outer edge of the housing was only about 4 inch beyond the periphery of the spinneret. The sipnneret face was about inch from the tube entrance and the radius of curvature of the tube entrance was over 2 inches.
The following properties were obtained:
9.1% sulfuric acid in bath Case A B 00rd Properties:
Tu- 3. 64 3. 57 o-d- 3.79? 3. 88 16"-- 7.0 D.B. Fatigue. 344 332 Yarn Properties:
d- 4. 76 4. 67 Tw--- 3. 40 3.39 TI 3. 34 3.33 Quality 14 196 8.5% sulfuric acid in bath Case. A B
3.64 3. 53 3. 95 3. 82 a 7. s 7.1 D.B. Fatigue 369 282 Yarn Properties:
Ta- 4. 66 4. 52 T- 3. 37 3. 21 TI s. 37 3.3a ualit 78 800+ 8.0% sulfuric acid in bath Case- A B 00rd Properties:
T 3.67 3. 43 T 3.92 3.69 Em 6.8 6. 7 DB. Fatigue 310 231 Yarn Properties:
7, 4. 70 4. 52 T, 3. 29 3. 24 T1 3. 39 3. 23 Quality 420 800+ In the foregoing tables:
T represents conditioned tenacity in grams/denier.
T represents oven-dry tenacity in grams/denier.
E represents percent elongation when a load of 15 lbs.
T represents wet tenacity in grams/denier.
T represents loop tenacity in grams/denier.
D. B. fatigue represents the number of minutes required to break the cord with the dynamically balanced fatigue tester.
Quality represents the number of broken filaments in 400 yards of unslashed yarn.
6 EXAMPLE 3 A viscose spinning solution containing 6;25% by weight of cellulose, 5.75% by weight of alkali, calculated as sodium hydroxide, and 103% cyclohexylamine as a coagulation modifier was prepared from cotton linters sheets using about 39% 08 The viscose solution was filtered, deaerated and permitted to ripen to a salt index of about 14 and a viscosity of about 39 stokes. The viscose solution was extruded through a spinneret having a diameter of 1% inches containing 7732 holes with the outermost holes %2 inch from the periphery of the spinneret. The spinneret was flush mounted in a cylindrical housing having a diameter of 6 inches. The filaments were extruded into a bath containing 6.5% sulfuric acid, 9.5% zinc sulfate, 17.5% sodium sulfate and .03.05% cyclohexylamine. The bath was maintained at a temperature of about 60 C. The filaments were passed through 44 inches of bath at a speed of 30 yards per minute, after which they were processed into staple fiber using a staple cutter in the conventional manner. Staple fiber, produced in this manner, was compared to staple fiber produced using the conventional spinneret assembly. In the conventional assembly, the 1% inch diameter spinneret was mounted in a 2 /2 inch diameter housing and the spinneret face projected A inch beyond the face of the housing. No spinning tube was used in either case.
Examination of the staple fiber revealed that the fibers produced using the spinneret assembly of this invention were much more uniform in length than those produced using the conventional assembly. When the spinneret assembly of this invention was used, the percentage of long fibers (fibers which are 0.25 inch or more longer than the standard length) was reduced by 50% as compared to the conventional spinneret assembly. The percentage of long fibers correlates with the number of broken or otherwise defective filaments. Defective filaments tend to slip from the staple cutter and are not cut. Longer, non-uniform fibers result.
As shown in the foregoing examples, the spinneret assembly of the present invention serves to improve the quality of yarns produced by the modifier processes, especially at high spinning speeds. It had been believed that some improvement in quality might be achieved by using a tube and reducing the space between the spinneret face and the tube entrance in the conventional spinning arrangement. As shown in Example 1, cases B and C, just the opposite occurred. With the spinneret assembly of the present invention in conjunction with a critically smaller space between spinneret face and tube entrance and a specially-designed tube entrance, not only was quality improved but as shown in Example 2, the physical properties of the yarns and cords were also improved.
The following theory is suggested to explain the improvements obtained with the present invention. The theory should not be considered as limitative of this invention. It is believed that the adverse effects on the rapidly moving, slowly coagulating filaments are caused by turbulence and bath drag in the region of the spinneret. The filament bundle, as it moves through the bath, carries with it a column of liquid. In this manner bath is removed from the face of the spinneret and is replaced by liquid pulled in from the sides. If, as in the conventional spinneret assembly, the bath which is induced to flow transversely toward the spinneret face strikes the protruding edge of the spinneret, turbulence is caused at the face of the spinneret where it does the most damage to the emerging filaments. Flush-mounting the spinneret in a streamlined cap is of little value since the change in the direction of the bath flow as it moves around the edge of the cap still causes turbulence at the spinnerets face. The turbulence created when using prior art spinning assemblies appears to strain the freshly formed filaments non-uniformly resulting in filament breaks, uneven denier yarns and poor dyeing uniformity in the resulting yarns. In contrast to the conventional assembly or the streamlined assembly, the assembly of the present invention causes the bath to flow smoothly into the area adjacent to the face of the spinneret, the turbulent area being removed well away from the spinneret. By extending the face of the housing radially from the outer periphery of the spinneret to form a continuous flat surface with the face of the spinneret, rather than streamlining the housing or the spinneret, the area of turbulence caused by the converging bath streams from around the periphery of the spinneret is displaced away from the spinneret face.
In the preferred embodiment of this invention which involves the use of a specially-designed spinning tube, the following additional explanation is offered as theory. By moving the tube entrance close to the spinneret face, the linear velocity of the bath in this area is increased. The increased velocity tends to reduce the drag of the bath with accompanying strain on the freshly formed filaments. The low radius of curvature of the tube entrance, as specified, promotes filament homogeneity by preventing bath turbulence and bath drag at the face of the spinneret as discussed earlier.
An attempt was made to substantiate the above theory by observing the flow pattern around the spinneret when using various spinning assemblies. The Milling Yellow dye technique was used. This technique is described by Peebles, Garber and Jury in Proceedings of the Third Midwestern Conference on Fluid Mechanics, pages 441 454, published by University of Tennessee in 1953. The method takes advantage of the doubly refractive nature of a water solution of Milling Yellow. A 1% solution of Milling Yellow, made doubly refractive by adding a saturated salt solution, was pumped into the bath trough in such a manner that it flowed around the spinneret assembly and into the spinning tube. The bath trough was transparent and polarized light from a source behind the trough illuminated the space adjacent to the face of the spinneret. The transmitted light was observed through crossed Polaroid film. Regions of constant shear appeared as alternating areas of light and dark patches. Since flow gradients are essentially shear forces, this behavior made flow patterns visible. Although no actual spinning was involved, it was observed that only with the spinning assembly and tube entrance of the present invention was there a smooth flow pattern of Milling Yellow solution.
The present invention is useful in all wet-spinning systems, particularly where the liquid spinning bath must be replenished and circulated. Although it has been described for the production of regenerated cellulose filaments by the viscose modifier process, it is also applicable to the production of regenerated cellulose filaments by the viscose process in general and to the production of filaments of cellulose acetate, cuprammonium, cellulose nitrate and the like by wet-spinning processes.
Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited except to the extent defined in the following claims.
The invention claimed is:
1. In the process of producing an artificial filament by extruding a filament-forming solution through the orifice of a spinneret into a coagulating liquid, the improvement which comprises flowing the coagulating liquid smoothly into the area adjacent to the face of the spinneret.
2. The process of claim 1 wherein the filament-forming solution is viscose.
3. In the process of producing an artificial filament by extruding a filament-forming solution through the orifice of a spinneret into a coagulating liquid and thereafter passing the filaments through a spinning tube to gether with a co-current stream of coagulating bath, the improvement which comprises flowing the bath smoothly from the regions surrounding the spinneret into the spinning tube, the smooth flow beginning at a distance from the outer periphery of the spinneret at least equal to the diameter of the spinneret, the direction of bath flow being initially parallel to the spinneret and then curving to flow co-currently with the filaments, the radius of curvature of the path followed by the bath in entering the spinning tube being 0.4 to 1.6 times the diameter of the tube.
4. The process of claim 3 wherein the filament-forming solution is viscose.
5. An apparatus for wet-spinning which comprises in combination: a spinneret assembly comprising a housing, a supply conduit adapted to supply a filament-forming solution to the housing and a spinneret containing a plurality of orifices mounted in one end' of the housing so that the spinneret face and housing form a continuous fiat surface which extends radially from the periphery of the spinneret a distance at least equal to the diameter of the spinneret, the outermost orifices of the spinneret being located within Vs in. of the said periphery of the spinneret; and a tube disposed in the coagulating liquid through which the filaments flow upon extrusion from the spinneret, said tube placed a distance less than the inside tube diameter from the face of the spinneret, the inside diameter of said tube at the entrance being flared so that the radius of curvature of the flare is 0.4 to 1.6 times the inside diameter of the tube.
6. The spinning assembly of claim 5 wherein the outside diameter of the entrance of the said tube is at least equal to the outside diameter of the spinneret housing.
7. A spinning apparatus comprising a spinneret having a flat outer face extending normal to an extrusion axis, first means defining a surface flush with the face of said spinneret and extending radially from the periphery thereof, a conduit having a mouth coaxial with but spaced slightly from the face of said spinneret, second means defining a surface flush with and extending radially away from the mouth of said conduit, said first and second means defining therebetween an annular zone surrounding the extrusion axis, and means to circulate coagulating liquid radially inwardly through said zone and coaxially into said conduit.
8. A spinning apparatus as set forth in claim 7 wherein the mouth of said conduit is flared outwardly and faces said spinneret.
9. An apparatus for the Wet spinning of synthetic yarn comprising a spinneret having a flat outer face extending normal to an extrusion axis, first means defining a surface fiush with the face of said spinneret and extending radially from the periphery thereof, a conduit having a flared mouth coaxial with but spaced slightly from the face of said spinneret, second means defining a surface flush with and extending radially away from the flared mouth of said conduit, one of said means being adjustable toward and away from the other, said first and second means defining therebetween an adjustable annular zone surrounding the extrusion axis, and means to circulate coagulating liquid radially inwardly through said zone and coaxially into said conduit.
10. Apparatus for the wet spinning of synthetic yarn that comprises a spinneret, a cap for supporting said spinneret, the end of said cap being flush with the face of said spinneret, means defining a conduit having a flared mouth coaxial with but spaced from the face of said spinneret, said means and the end of said cap defining therebetween an annular zone surrounding the extrusion axis and immediately adjacent to but extending in a direction parallel with and outwardly from the face of the spinneret, and means to deliver coagulating liquid uniformly about the margin of said zone for radial inward movement thereacross.
11. In the method of wet spinning including the steps of flowing a spinning solution to a region of extrusion, extruding said solution through a spinneret into a coagulating liquid in the form of a plurality of filaments arranged in a bundle around an axis, and thereafter withdrawing the bundle of filaments and coagulating liquid 5 together along said axis from the region of extrusion through a confined zone, the improvement comprising the step of flowing said coagulating liquid radially toward the extrusion axis while confining the flow thereof to a zone normal to said extrusion axis and contiguous to but 10 extending outwardly from the face of said spinneret.
References Cited in the file of this patent UNITED STATES PATENTS Welch Dec. 4, 1934 Dove June 13, 1939 Taylor Oct. 9, 1945 Hays May 1, 1951 Lynch June 28, 1955 Bradshaw Jan. 24, 1956 Wicker Jan. 31, 1956 Hesselink May 13, 1958
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|U.S. Classification||264/180, 425/66, 425/68, 264/188|