US2588584A - Spinning artificial filamentary materials - Google Patents

Description

March 11, 1952 F. T. SMALL 2,588,584

SPINNING ARTIFICIAL FILAMENTARY MATERIALS Filed NOV. 12, 1949 2 SHEETS-SHEET 1 FIG I 2 l4 l7 EXHAUST T0 SOLVENT RECOVERY EXHAUST T0 SOLVENT RECOVERY JNVENTOR.

FREDERICK T. SMALL ATTORNEYS.

March 11, 1952 F. T. SMALL 2,588,584

SPINNING ARTIFICIAL FILAMEINTARY MATERIALS Filed Nov. 12, 1949 I 2 SHEETS-SHEET 2 EXHAUST 7'0 SOLVENT RECOVERY INVENTOR.

FREDERICK T. SMALL ATTORNEYS.

Patented Mar. 11, 1952 UNITED STATES PATENT OFFICE SPINNING ARTIFICIAL FILAMENTARY MATERIALS Application November 12, 1949, Serial No. 126,745

2 Claims.

This invention relates to the spinning of artificial filamentary material and relates more particularly to a process for the spinning of artificial filamentary material wherein a high-velocity stream of evaporative medium fiows through a portion of the spinning cabinet in the direction of travel of the filamentary material.

In the so-called dry-spinning process for the production of artificial filamentary material such as filaments, yarns, tow, ribbon and the like, a solution or dope of filament-forming material in a volatile solvent is pumped or otherwise forced through a spinning jet, containing at least one spinning orifice, into a spinning cabinet or metier. As the filamentary material passes through the spinning cabinet, the solvent is evaporated therefrom by means of a stream of any suitable evaporative medium such as air. The filamentarymaterial is then drawn from the spinning cabinet and may be lubricated and have a twist imparted thereto before it is taken up in package form.

To obtain satisfactory results in carrying out this process, it is important to maintain the tension on the filamentary material as it leaves the spinning cabinet at between about 0.02 and 0.2 gram per denier. Tensions lower than about 002- gram per denier are undesirable since, when filament yarns are being produced, they result in a loopy yarn, namely a yarn in which some of the filaments are longer than others and stand away form the body of the yarn in loops. On the other hand, tensions above about 0.2 gram per denier are equally undesirable since they affect the physical properties of the filamentary material in" an unfavorable manner. Tensions above about 0.2 gram per denier, acting on the filamentary material while it is still ina plastic state, tend to embrittle said material and reduce its percentage elongation under stress. Furthermore, if the tension rises much above about 0.2 gram per denier, it may even cause breaks in the filamentary material, thus interrupting the continuity of spinning.

As a result of these limitations upon the tension, it has hitherto been customary to maintain the speed of the filamentary material during the spinning operation below about 600 meters per minute. If an attempt is made to employ higher spinning speeds, the tension on the filamentary material rises rapidly about about 0.2 gram per denier producing defective products and causing breaks in the filamentary material. This limitation on the maximum permissible spinning speed seriously curtails the productive 5 filamentary material passes into a drying zone in capacity of. conventionalspinning, operations.

It is an important object of this invention to provide a process for spinning artificial filamentary material which will be free from the foregoing and other disadvantages of the processes and apparatus hitherto employed for this purpose and which will be especially efiicient in operation.

Another object of this invention is to provide a process for spinning artificial filamentary material at high spinning speeds.

A further object of, this invention is the provision of a process for spinning artificial filamentary material wherein a, high-velocity stream of evaporative medium flows through a portion of the spinning cabinet in the direction of travel of the filamentary material.

Other objects of this invention, together with certain details of construction and combinations of parts, will be apparent from the following detailed description and claims. V

I have now discovered that the excessive tension on the filamentary material at high spinning speeds is due, at least in part, to air drag and that the filamentary material may be spun at higher speeds than have hitherto been considered possible without developing excessive tension by employing a spinning cabinet which is divided into two zones. The two zones comprise a filament-forming zone'into which the filamentary material enters as it emerges from the spinning jet and through which a stream of evaporative medium flows in a direction opposite to the direction of travel of the filamentary ma terial, and a drying zone into which the filamentary material passes after leaving the filament-forming zone and through which a stream of evaporative medium flows at a high velocity in the direction of travel of the filamentary material.

As the filamentary material passes through the filament-forming zone, the major portion of the solvent is evaporated therefrom and the filamentary material is caused to set. In addition, the stream of evaporative medium flowing through the filament-forming zone in a direc-, tion opposite to the direction of travel of the filamentary material places a sufiicient tension on said material while it is still relatively plastic to raise the tenacity and elongation of the filamentary material to commercially acceptable levels. An excess increase in the tension on the filamentary material in the filament-forming zone is, however, avoided by limting the total length of said zone.

- After leaving the filament-forming zone, the

which more of the solvent is evaporated from said material. To reduce the solvent content of the filamentary material sufliciently to permit its removal from the spinning cabinet, it is necessary to make the length of the drying zone several times as great as the length of the filamentforming zone. At high-spinning speeds, the air drag on the filamentary material in the drying zone would be sufficient to raise the tension on the filamentary material as it leaves the spinning cabinet to above about 0.2 grams per denier producing defective products and causing breaks in the filamentary material. However, I have discovered that at high spinning speeds, it is possible to reduce the tension on the filamentary material, as it leaves the spinning cabinet, to between about 0.02 and 0.2 gram per denier, by

passing a stream of evaporative medium at a high velocity through the drying zone in the direction of travel .of the filamentary material.

The specific velocity at which the evaporative medium should flow through the drying zone will depend upon the spinning speed, the denier of the filamentary material, and the type of filamentary material being produced, which elements will determine the drag between the filamentary material and the evaporative medium. In all cases, however, the velocity of the evaporative medium flowing through the drying zone should be high enough to reduce the tension on the filamentary material as it leaves the spinning cabinet, at high spinning speeds, from whatever value above about 0.2 gram per denier it would have in the absence of said stream of evaporative medium to a value of between about 0.002 and 0.2 gram per denier. The drying zone may advantageously have a cross-sectional area less than that of the filament-forming zone to reduce the total volume of evaporative medium passing through the drying zone and thereby simplify the recovery of the solvent from said evaporative medium.

In order to restrict the circulation of the evaporative medium between the filament-forming zone and the drying zone, the spinning cabinet may be made with a restricted cross-sectional area between said zones, or the two zones may be separated to an even greater extent wherein the filamentary material passes through the atmosphere in traveling from one zone to the other.

While it has previously been proposed to have a stream of evaporative medium flow through the spinning cabinet in the direction of travel of the filamentary material, the velocities hither- .to employed have been so low as to have substantially no effect on the tension. In fact, the velocities of the evaporative medium have been sufliciently low as to permit comparable results to be obtained with the evaporative medium flowing either in the direction of travel of the filamentary material or in a direction opposite thereto.

Any one of a number of expedients may be employed to obtain the desired velocity of the evaporative medium in the spinning cabinet. For example, the evaporative medium may be admitted into the spinning cabinet under pressure, or the evaporative medium may be exhausted from the spinning cabinet. Although the desired velocities may be obtained by employing either of these alternatives, the use of pressure is somewhat less desirable since it requires that the static pressure Within the spinning cabinet be above atmospheric. When such an access of pressure exists within the spinning cabinet,

the evaporation of the solvent from the filamentary material is inhibited and there is a tendency for the evaporative medium to escape into the atmosphere carrying with it the solvent vapors. If, however, the desired velocity of the evaporative medium is developed by exhausting the evaporative medium from the spinning cabinet, the static pressure in said cabinet will be below atmospheric, so long as the total volume of evaporative medium entering the spinning cabinet is restricted, and there will be no tendency for the escape of the solvent vapors into the atmosphere. Upon leaving the spinning cabinet, the solvent vapor laden evaporative medium is passed to a solvent recovery system in which the solvent is recovered for further use.

Any means well known in the art may be provided to preheat the evaporative medium entering the spinning cabinet and/or to the control the temperature of the medium as it passes therethrough. For example, the heating means may take the form of a jacket through which a heating fluid is passed, heating coils positioned inside or outside the cabinet, electrical resistance elements and the like. The heating mean may extend over the whole or only a portion of the spinning cabinet, and may be divided into a number of sections under separate control to permit a differential in temperature to be maintained at various points within said spinning cabinet. The heating means or the spinning cabinet, or both, may be insulated to reduce the heat loss.

In carrying out this invention, I may employ any suitable filament-forming material such as,- for example, cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate-prop'ionate, cellulose acetate-butyrate, ethyl cellulose, polyvinyl acetate, polyvinyl chloride or vinyl acetate-vinyl chloride copolymer. To form the spinning dope, the filament-forming material is dissolved in a suitable solvent or solvent mixture such as, for example, acetone ethylene dichloride, methylene chloride and ethyl alcohol, chloroform and ethyl alcohol, or chloroform and methyl alcohol. As the evaporative medium, I prefer to employ air since it is the least expensive and the most readily available. However, other gases may also be employed such as for example, nitrogen and carbon dioxide. In my preferred embodiment, there is employed a solution of cellulose acetate in acetone as the spinning dope and air as the evaporative medium.

In the accompanying drawings,.

Fig. 1 is a view in cross-section of a spinning cabinet embodying one form of this invention, and

Fig. 2 is a view in cross-section of a spinning cabinet embodying another form of this invention.

Referring now to the drawings, the reference numeral H designates a spinning jet to which a heated and filtered spinning dope, comprising a solution of cellulose acetate in acetone, is fed under pressure through a conduit 12, connected to any suitable source of supply, and a candle filter 13. The spinning dope passes through orifices (not shown) in the spinning jet 1 I and emerges as a bundle of filaments I4 into the filament-forming zone 15 of a spinning cabinet indicated generally by reference numeral IS. The filament-forming zone l5 has conduits l1 and 18 opening into the upper and lower portions thereof, respectively. A stream of air is caused to flow through said filament-forming zone l5 ma direction opposite to the direction of travel of the filaments M by exhausting air from said zone through the conduit I1 to a solvent recovery system, the air being admitted into said zone through the conduit 18. The air in the filament-forming zone [5 is heated by means of a coil l9 positioned therein through which a heating fluid is circulated from conduits 2| and 22. As the bundle of filaments l4 passes through I the filament-forming zone [5, which may be forming zone I5 or the drying zone 23 so as to;

minimize the circulation of air from one to the other of said zones. At the lower end of .the

drying zone 23, there is a chamber 21 having a hinged door 28 provided with an aperture 29 through which the filaments 14 are drawn from the spinning cabinet 16 by means of a feed roller 3!. As the filaments l4 pass through the drying zone 23, more of the acetone is evaporated there from by means of a stream of air which enterssaid zone through a conduit 33 and is exhausted from said zone to a solvent recovery system (not shown) through a conduit 34 opening into the? chamber 21. The air flows through the drying,

zone 23 in the same direction as the filaments l4 at a velocity so adjusted as to reduce the tension on said filaments as they leave the spin-j ning cabinet [6 at high spinning speeds, say

above about 800 meters per minute, from above about 0.2 gram per denier to a value of between about 0.02 and 0.2 gram per denier. After leaving the spinning cabinet I 6, the filaments [4 may be lubricated, twisted and packaged, or otherwise treated to put them in condition for further use.

Referring now to Fig. 2 of the drawings wherein another embodiment of this invention is shown, the reference numeral 4| designates a spinning jet to which a heated and filtered spinning dope is fed under pressure through a conduit 42 and a candle filter 43. The spinning dope passes through orifices (not shown) in the spinning jet 4| and emerges as a bundle of filaments 44 into the filament-forming zone 45 of a spinning cabinet indicated generally by reference numeral 46. The filament-forming zone 45 has conduits 41 and 48 opening into the upper and lower portions thereof, respectively. A stream of air is caused to flow through said filamentforming zone 45 in a direction opposite to the direction of travel of the filaments 44 by exhausting air from said zone through the conduit 41, the air being admitted into said zone through the conduit 48. The air in the filament-forming zone is heated by means of a coil 49 positioned therein through which a heating fluid is circulated from conduits 5| and 52. As the filaments 44 pass through the'filament-forming zone 45, which may be from about 3 to 6 feet in length, from 60 to 80% of the volatile solvent is removed therefrom.

The filament-forming zone 45 is closed at its lower end by means of a plate 53 carried by legs 54 that rest on a support 55. The plate 531s provided with an aperture 56 extending therethrough for the passage of the filaments 44 from the filament-forming zone 45 into the atmos'-- phere. Positioned centrally below the aperture 56 is a drying zone 51 independent of the filament-forming zone 45 and having a funnel shaped entrance opening 58 to receive the filaments 44. At the lower end of the drying zone 51 there is a chamber 59 having a hinged door 6| provided with an aperture 52 through which the filaments 44 are drawn from the spinning cabinet 46 by means of a feed roller 63. As the filaments 44 pass through the drying zonew51, more of the volatile solvent is evaporated therefrom by means of a stream of air which enters said zone through a conduit 64 and through the funnel-shaped entrance opening 58 and is exhausted from said zone to a solvent recovery system (notshown) through a conduit 65 opening into the chamber 59. Once spinning is under way, a longitudinally split tube 66 may be positioned around the filaments 44 between the lower surface of the plate 53 and the funnel-shaped entrance opening 58 to restrict the quantity of air that is drawn into the drying zone 51 by the filaments 44 and thereby prevent an increase of pressure in said drying zone. Alternatively, the conduit 64 and the tube 66 may be omitted and all the air entered into the drying zone 51 through the funnelshaped entrance opening 58. The airfiows through the drying zone 51 in the same direction as the filaments 44 at a velocity so adjusted as to reduce the tension on said filaments as they leave the spinning cabinet 46 at high spinning speeds, say above about 800 meters per minute, from above about 0.2 gram per denier to a value of between about 0.02 and 0.2 gram per denier. Since the cross-sectional area of the drying zone 51 is materially less than the cross-sectional area of the filament-forming zone 45, the total volume of air pa sing through the drying zone 51 will be less than if both zones had the same cross-sectional area. As a result, there will be a greater concentration of solvent vapors in the air leaving the drying zone 51 and the recovery of said solvent will be simplified. After leaving the spinning cabinet 46, the filaments 44 may be lub'ricated, twisted and packaged, or otherwise treated to put them in condition for further use.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of my invention.

Having described my invention, What I desire to secure by Letters Patent is:

1. In a dry-spinning process for the preparation of artificial filamentary material from a spinning dope containing a filament-forming material and a volatile solvent, the steps which comprise forming filamentary material from said spinning dope, first passing the solvent-containing filamentary material through a filamentforming zone, passing a stream of evaporative medium through the filament-forming zone in a direction opposite to the direction of travel of the filamentary material to evaporate a portion of the solvent from the filamentary material, next passing the filamentary material through a dryin zone, and passing a stream of evaporative per denier in the absence of the stream of evaporative medium, and the velocity of the stream of evaporative medium through the drying zone being sufliciently high as to reduce the tension on the filamentary material leaving the drying zone to below about 0.2 gram per denier.

2. In a dry-spinning process for the preparation of artificial filamentary material from a spinning dope containing a filament-forming material and a volatile solvent. the steps which 10 medium through the filament-forming zone in a 5 direction opposite to the direction of travel of the filamentary material to evaporate a portion of the solvent from the filamentary material, next passing the filamentary material through a. drying zone, and passing a stream of evaporative medium at a high velocity through the drying zone in the direction of travel of the filamentary material to evaporate more of the solvent from the filamentary material, the spinning speed being above about 800 meters per minute so that the tension on the filamentary material leaving the drying zone would be above about 0.2 gram per denier in the absence of the stream of evaporative medium, and the velocity of the stream of evaporative medium through the drying zone being sufficiently high as to reduce the tension on the. filamentary material leaving the drying zone to between about 0.02 and 0.2 gram per denier.

FREDERICK T. SMALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,060,048 Dreyfus Nov. 10, 1936 2,142,121 Dreyfus Jan. 3, 1939

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