US3156752A - Method and apparatus for heat treating filaments - Google Patents

Description

Nov. 10, 1964 A. P. COPE 3,156,752

METHOD AND APPARATUS FOR HEAT TREATING FILAMENTS Filed Sept. 11. 1961 INVENTOR /l/l DF[ 11/ 7/455mkf COPE BY 7 M ATTORNEY ,transfer and in reducing heat losses.

turbulence is known to be of use.

United States Patent 3,156,752 METHOD AND APPARATUS FOR HEAT TREATING FILAMENTS Andrew Passmore Cope, Wilmington, Del., assignor to E. I. du Pont tie Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Sept. 11, 1961, Ser. No. 137,162 Claims. (Cl. 264-345) This invention relates to novel improved means for heat-treating thermoplastic materials or filaments of synthetic organic fibers and the like in a continous manner and more particularly heat-treating such filaments by .means of a flowing gas stream of elevated temperature contacting the filaments as they are forwarded substantially without tension.

It is known to cause filaments, yarns, and the like to traverse a heated zone at a predetermined rate, the temperature of the zone being maintained substantially constant so that the filaments reach a required temperature by the time they emerge from the heated zone, and this required temperature is such as to affect the molecular structure of the filaments in a required manner to achieve some desired physical property. US. 2,445,042 to Silverman is an example of such a technique. The heat-treatment may relieve internal stress, it may cause shrinkage, it may induce stretching when combined with tension or other circumstances, or it may set twist and the like in the filaments, and so on. It is also known to accelerate the heat-treating process by taking advantage of nonequilibrium conditions by contacting a rapidly moving material with an extremely hot surface or fluid for a time brief enough to prevent heating above a temperature at which undesired deterioration occurs.

Ordinarily, tubes for the heat-treatment of traveling filamentary materials have a small uniform circular cross section and this is particularly the case Where the heat transfer is by radiation or conduction from the heated surface of the tube. In such cases, the small uniform circular section is beneficial in increasing the rate of heat Where the manner of heat transfer is from a fluid at elevated temperature traveling in counter-current or co-current manner, a uniform circular cross section of minimum dimension contributes to efiiciency of heat transfer by reduction of cooling losses and through the beneficial elfect of high velocity for a given volume of fluid, the over-all efficiency of the system being related in an inverse manner to the volume of heat transfer fluid handled, and directly to the velocity, as is well known in fluid systems, especially those in which the heat transfer fluid is a gas. Small area and high velocity bring problems of turbulence which under some circumstances are not beneficial, resulting in tangled neps and the like which are not desired, although under other circumstances where there is a controlled system of turbulence, as in the bulking of yarn, such However, where it is not desired to bulk or the like and it is desired to heattreat continuously traveling filaments when they are under little or no tension, the teachings of the prior art have hitherto been found wanting. For example, it is desirable to produce nonwoven structures from a multiplicity of continuous filaments of synthetic organic polymeric materials, thereby taking advantage of the reduced manufacturing cost inherent in such a procedure in addition to producing structures of greatly increased strength having other useful and distinctive properties. The application of Kinney, S.N. 859,614, filed Dec. 15, 1959, now abandoned, sets forth a process distributing continuous filaments to form a web composed of fibrous elements disposed in random nonparallel arrangement. This ap- 3,156,752 Patented Nov. 10, 1964 plication further teaches such a process in which continuous filaments are processed in a manner whereby electrostatic charges are placed upon the multiplicity of filaments to provide a separating force therebetween, as well as a means by which such filaments, having been drawn to enhance physical properties in an air jet, are forwarded therefrom to a collecting surface in conjunction with an attractive electrostatic force. It further teaches that if such filaments have the potential of spontaneous elongatability, an appropriate heat-treatment may be applied in a dynamic manner by relaxing these filaments by means of a heat-treatment applied immediately downstream of the aspirating jet. The treatment may be accomplished by using a gas of elevated temperature in the drawing jet, and is particularly adaptable to filaments of polyethylene terephthalate, cellulose acetate, certain polyamides, and the like which have the property of spon taneous elongation when, after an initial relaxing or shrinking heat-treatment at some predetermined temperature, the filaments will exhibit a lengthening upon an appropriate heat-treatment at a second predetermined temperature, as it is now well known to those experienced in the art. Such procedures have been delineated in US. 2,900,669 of M. H. Booth and in the Kitson and Reese patents, US. 2,952,879 and US. 2,931,068, for example.

Experience with the dynamic heat-relaxing system of Kinney in which air at elevated temperature is introduced into the draw jet to produce a web of spontaneously elongatable fibers which on later heat-treatment, as for example, pressing such a web between screens at a temperature sufiicient to bond the fabric and to simultaneously extend eiongatable fibers, has shown it to be an advantageous method of producing a soft, drapable nonwoven fabric. It has the advantage that, where the fabric is restrained to its original dimensions while the fibers are made to elongate, the fibers will crimp between bond points and provide the mobility required to impart superior drape to the resultant product. However, disadvantages in this process have been noticed and, prior to the instant invention, appeared insurmountable. In particular, attempts to use both steam and hot air in the draw 'et or in a general zone between the draw jet and the collecting surface produced webs having less than an optimum uniformity. Such webs were characterized by an excessive number of tangled or ropey fiber bundles. Furthermore, it has been found that where the hot fluid is improved means for a dynamic heat-relaxation of continuous filaments downstream of a drawing and forwarding jet. It is an object of this invention to provide heattransfer means and apparatus for uniformly heat-treating thermoplastic yarns in a continuous manner. It is a further object to provide a unique and improved form of heater for traveling filamentary materials. And it is still a further object to provide heat-treating means for such filaments when under little or no tension. And it is yet a further object to heat-treat such filaments in an economical and expeditious manner without entangling. And it is still yet another object to perform such heat-treatment continuously and without interruption over long periods of time.

The objects of this invention are met by a relaxing chamber employed immediately downstream of a drawing jet through which a hot fluid, preferably air, is circulated uniformly co-current with the traveling filaments and at an elevated temperature and at a fluid velocity not greatly in excess of the velocity of the traveling filaments, in which swirl-reducing and uniform fiow producing means are employed, and in which the bore is of uniform small circular cross section not greatly in excess of the size necessary to encompass the bundle of filaments without substantial contact with the sides of the bore, and in which cooling means are provided for the walls of the bore in the chamber.

The process of this invention is one of heat-treating a continuously forwarded fluid-borne filamentary material under little or no tension and comprises contacting the material with an additional co-current stream of fluid elevated in temperature above the stick temperautre of the material in a temperature zone annularly surrounded by a second temperature zone having a thermal gradient rapidly declining to a temperature below the stick temperature, the velocity of the additional fluid being not greatly in excess of the velocity of the material.

The above and further objects of the present invention will become apparent from a reading of the following description wherein the present invention is described in further detail in connection with the accompanying drawings in which:

FIGURE 1 is a schematic of a spinning system employing the relaxation chamber unit of the present invention,

FIGURE 2 is an elevational view in longitudinal cross section of the relaxation chamber unit of the present invention.

In FIGURE 1, one or more spinnerets 1, 1 are disposed in a spinning head generally indicated by 2. From spinneret 1 issue a multiplicity of continuous filaments 3 which are converged on rotatable guide 4. Optionally, from some other spinneret such as 1', there may issue a multiplicity of filaments 3' which may be composed of a binder fiber. If such a stream of filaments 3 is employed it, too, is converged on rotatable guide 4. On guide 4, by means of electrostatic charging means 5, there is placed upon the filaments an electrostatic charge. Electrostatic charging means 5 may be a corona discharge head as schematically indicated in FIGURE 1 or may be any of the equivalent electrostatic charging systems such as a triboelectric surface-contact device. Having been charged, the filaments are forwarded to draw jet 6 wherein by action of air or other fluid entering draw jet 6 through inlet 7, the filaments are forwarded and drawn emerging through tail pipe 8 into relaxation unit 9. Air or some other fluid is passed through pipe 10 to heat exchanger 11 where it is elevated in temperature by means of some heating means such as resistance coil 12, thence passing through pie 13 into heat transfer and filament forwarding device, or relaxation unit, 9 wherein its action will be described in greater detail further on in this specification. Similarly, a coolant which may be water is passed through pipe 14 to relaxation unit 9 emerging through pipe 15. Ernitted from relaxation unit 9, the filaments are forwarded and deposited upon moving belt 16 which travels in the direction of the arrow, forming web 17. As a result of the charge previously placed upon the filaments, they repel one another, thus forming a substantially cone-like laydown pattern indicated by 18. Laydown pattern 18 comprises filaments forwarded under the action of gravity and of the emitted fluids from draw jet 6 and relaxation unit 9 and, in addition, electrostatic forces between the filaments and belt 16, which forces may be enhanced by electrostatic target 19 which is either grounded or given an opposite charge to aid in controlling the laydown. It will be apparent that by a suitable combination of temperature in relaxation unit 9 and time at temperature, appropriate heat treatments may be accomplished. It will also be apparent that a multiplicity of patterns may be combined to form a broad web.

Referring to FIGURE 2, the relaxation unit 9 comprises a housing composed of two main parts, body 22 and cap 23, which are fastened in sealed faying relationship by means not shown in a manner assuring appropriate concentricity of parts constituting fluid flow passages. Cap 23 is generally circular in cross section and is distinguished by upstanding neck 33 having bore 34 therethrough. The upper portion of bore 34 is counter-bored at its upper end to permit attachment to draw jet tail pipe 8 by means not shown. The lower periphery of cap 23 is machined to the form of a downwardly extending body 41 which is tapered inwardly to provide an annular sharp-edged orifice 2% at the base or juncture with bore 34. Plenum chamber 25 is annularly disposed about upstanding neck 33 within cap 23 and is closed at the upper end by seal disc 26 which is fastened to cap 23 in sealed relation by means not shown. Plenum 25 is provided with two ports, 35 and 36, to which are attached pipes 14 and 26, respectively.

Body 22 is circular in cross section, comprising an upper disc-like portion 42 joined to a downwardly extending lower portion or tube 28 of smaller diameter, and is bored through vertically on the axis to provide relaxation chamber 31, opening to the outside at the lower end through port 32 and widening at the upper end to provide inwardly tapering annular space 40 when body 22 is assembled to cap 23 and forming annular nozzle 24 at the juncture with orifice 20. Relaxation chamber 31 is enclosed by the inner wall of tube 28 which in turn is enclosed in spaced radial relationship by tube 29 which is fastened to body 22 and spaced from wall 28 by means of spacer 30 to thus enclose annular cooling space 27. Tube 29 has pipe 15 fastened thereto to provide an external opening to cooling space 27 near the lower end and is similarly connected to pipe 26 at the upper end. Fittings, not shown, are provided in pipe 26 to permit separation during disassembly. Plenum chamber 21 is machined annularly within the upper portion 42 of body 22, there being a cooperating and shallower annular groove 37 in cap 23. Two or more thin radial fins 38 are fastened by appropriate means or otherwise located within annular groove 37. Pipe 13 is fastened to port 39 providing external communication to annular plenum chamber 21. Directly below fins 38 is installed porous disc 44 mounted in step 43 cut in the upper portion 42 of body 22 at the top of the inner wall of plenum chamber 21. The heat losses can be minimized by lining the annular plenum chamber 21 and the annular groove 37 with an insulating material.

Again referring to FIGURE 2, the emitted air and drawn filaments from draw jet tail pipe 8 enter chamber unit 9 through bore 34 to orifice 20. Orifice 20 is sized so that the air velocity therein is approximately the same as the velocity of the filaments. The heat transfer fluid, which ordinarily is hot air, emerges from pipe 13 and port 39 to plenum chamber 21 and passes through porous disc 44 which acts as a uniform flow-producing means and is constrained to radial flow by fins 38, there being more than one fin and preferably at least three, smoothly flowing without swirling and uniformly distributed into annular inwardly inclined space 40.

The heat transfer air passes through space 40 to throat 24 which, as described before, is annular about orifice 20. Throat 24 is sized so that the annular smoothly flowing stream of the hot air engages the filaments at a velocity not greatly in excess of filament velocity, a ratio of 2 to 4 times having been found to yield adequate heat transfer with acceptable filament separation. The proportioning of orifice 2t and throat 24 and the regulation of the velocities of the hot air, the jet air, and the filaments so that relative velocities are as described, is important as is an angle of about 8 between the inclined space 40 and the axis, a ratio of at least 10 to 1 between the space 40 and the throat gap 24 and the use of vane elements or fins 38 or other swirl-reducing means so that flow in relaxation space 31 is axial without swirling and turbulence is minimized or eliminated and thus filaments do not interlace or tangle. Furthermore, the flow must be uniformly distributed. This may be .accompanied by sizing port 39 so that it is appreciably larger in area than the area of throat 24; at least twice as large having been found a minimum relationship when no distribution or uniform flow producing means such as porous disc 44 is used. Preferably disc 44 is used, the heating fluid flowing through the disc as described, reducing need for the carefully controlled portthroat area relationship.

Cooling water or other fluid enters relaxation unit 9 through pipe 14 and port 35 into annular space 25 in cap 23 closed by disc 26 which is appropriately fastened by means not shown to cap 23. The cooling water then passes through port 36 to tube 26 into annular cooling space 27 between relaxation chamber tube 28 and tube 29. The cooling water emerges through pipe 15, the bottom of space 27 between relaxation chamber tube 28 and tube 29 being closed by spacer 30. The relaxed filaments and emitted drawing fluid and heat transfer fluid emerge from relaxation space 31 by way of port 32. It is preferable if emergence conditions are achieved such that the exit velocity of the filaments and fluid are substantially the same.

It will be recognized that in the employment of relaxation unit, or device for continuously heating and forwarding filaments, 9, its most appropriate use is Where rapid heat transfer is desired and hence the temperature of the heat transfer fluid is elevated well above the stick temperature, and usually well above the melting point, of the filaments being heated. Such a practice is known to be expedient for physical processes requiring a rapid rate of heating and because of the economies obtained in reduction of the size of apparatus employed. Thus, the degree of cooling required must be adjusted so that heat transfer does not occur in .a manner elevating any of the parts of the equipment above that temperature at which a contacting filament will stick and deposit polymeric ma terial thereon and so that by this means periodic hang-ups of filaments are avoided. 'This is accomplished by the cooled walls themselves and because there is created a temperature zone having a rapidly declining thermal gradient surrounding the zone of heating temperature and in a portion of which the temperature is below the stick temperature. Thus, annular space 25 acts to thermally isolated the relaxation unit 9 from the draw jet tail pipe 8 and to maintain the bore 34 ahead of orifice 20 at or below the moderate temperature required to prevent the deleterious action described. Similarly, annular cooling space 27 maintains the inner wall of tube 28 and the contiguous region which encloses relaxation space 31 similarly below the critical temperature at which improper action occurs.

Apparatus to aid in layd-own may be applied following or attached to relaxation unit 9.

As an illustration of the employment of the relaxation unit of this invention in the formation of a nonwoven web of continuous filaments of polyethylene terephthalate, a spinning system is employed according to the schematic of FIGURE 1 in which fibers emerging from the relaxation unit are obtained having no residual shrin age and having spontaneous elongations of up to 25% when heated to 210 C. In this system, binder filaments are co spun with the primary filaments of polyethylene terephthalate, the binder filaments being an 80/20 blend of polyethylene terephthalate and polyethylene isophthalate, the proportion of binder filament being optionally between 3 and 30% of the total weight.

Example In a specific instance, 91% of polyethylene terephthalate was co-spun with 9% of an 80/20 copolymer of polyethylene terephthala-te and polyethylene isophthalate, the polyethylene terephthalate being spun through a 23-hole spinneret at a rate of 15.5 grams per minute total, each spinneret hole being 0.007 inch in diameter with the temperature of the spinneret at 292 C. The binder fiber,

the /20 copolymer of polyethylene terephthalate/isophthalate, was spun through a l0-hole spinneret at a rate of 15.5 grams per minute total, each spinneret hole being 0.007 inch in diameter and the temperature of the spinneret at 269 C. One only of the binder filaments was combined with the 23 filaments of polyethylene terephthalate on the rotatable guide opposite the corona charging head. The charged filament-s were then passed into a draw jet supplied with about 3 s.c.f.m. air at about 45 p.s.i. and 20 C. To the exit of the draw jet a relaxation unit 8" long with diameter bore was attached. The velocity of the filaments was in excess of 3,000 y.p.m. and all conditions were adjusted accordingly. The temperature of the 5 s.c.f.m. air entering the relaxation unit was adjusted to 550 C. to remove all shrinkage from the fibers and the fibers emerging from the relaxation unit were deposited as a web on a moving belt. This web then exhibited spontaneously elongatable fibers of about 25%' when processed by pressing and restraining between a 40 and a 30 mesh screen in apress at 220 C. and 50 p.s.i. for 1 minute. This web was further finished by washing in an automatic washing machine and tumble drying to produce a fabric having excellent drape and good strength as shown by an initial modulus measurement of 500 p.s.i. and a tensile strength'measurement of 6.9 lb./in./ oz./yd. A photograph of the web was enlarged 20 and examined to confirm the initial subjective rating of excellent uniformity of filament separation.

In the drawings and the specification, there has been set forth a preferred embodiment of the invention and although specific terms are employed, they are used in a illustrative and descriptive sense only and are not intended as limiting the invention spirit or scope. The scope of the invention iswas defined in the claims.

I claim:

1. An improved heatrelax-ation unit of the type especially adapted for use in a system for continuously extruding, drawing, heat-relaxing, and manipulating a plu rality of separate continuous self-elongatable filaments of synthetic organic material to form non-woven web structures, said improved unit comprising a structure defining a first fluid flow conveyor means to continuously heat and forward a plurality of separate untwisted unentangled continuous filaments simultaneously in a fluid conveying medium through an enclosed heat-relaxing zone in the structure in a substantially untensioned condition, a second means in said Zone cooperating with said first means to maintain the moving filament-s; in a substantially straight unentangled untwisted relationship with respect to each other and the enclosed zone, and a third means in the zone, cooperating with said first and second means to prevent clogging and accumulation of the filaments in the zone clue to adherence of the heated filaments to structure of the heat-relaxation unit.

2. The improved heat-relaxation unit of claim 1 in which said first means defined by said structure comprises an inlet passageway adapted to receive a moving fluid stream conveying a plurality of continuous filaments, said first means further comprising a substantially straight outlet passageway in communication with said inlet passageway to provide for exit movement of the fluid and filaments conveyed thereby, said first means further comprising an inlet conduit means adapted to introduce into said unit a heat exchange medium, said inlet conduit means intersecting said connected passageways in such a way as to directthe heat exchange medium into contact with the filaments during their movement through said passageways in said zone to uniformly heat the filaments and assist in maintaining their movement through the unit.

3. The improved unit of claim 2 in which said second means comprises, in cooperation with said inlet conduit means, a flow controlling means to smoothly and uniformly direct the flow of heat exchange medium to produce substantially straight line low turbulence flow of heat exchange medium and fluid stream through the passageways to prevent entangling and twisting of the moving filaments in the unit.

4. The improved unit of claim 3 in which said third means comprises a heat exchange device in cooperative association with said passageways and operative to maintain the structure of the first means defining said passageways at a temperature which prevents adherence of the heated filaments to said structure and clogging of the passageways.

5. The improved unit of claim 4 having the inlet passageway so dimensioned with respect to the fiow of the moving fluid stream that said moving stream and filaments carried therein move at substantially the same velocity through said inlet passageway and having the dimensions of said inlet conduit with respect to the moving heat exchange medium and in conjunction with the construction of the intersection of the conduit with said passageways selected so that the entrance velocity of the heat exchange medium into the passageways is from about two to about four times the velocity of the incoming fluid and filaments.

6. The improved unit of claim 5 in which said inlet conduit intersects said passageways in a restricted annular orifice of uniform width.

7. The improved unit of claim 6 in which said flow controlling means comprises a flow equalizing element interposed in said inlet conduit a limited distance upstream of and adjacent the intersection of said conduit with said passageways and a plurality of flow directing vane elements in said conduit positioned between said flow equalizing element and said annular orifice.

8. The improved unit of claim 7 in which the dimensions of the passageways, the conduit, the annular orifice, the velocities of the fluid and the medium and the temperature of the medium are controlled so that the velocities of the filaments and the combined fluid-medium stream are substantially the same as they emerge from the unit.

9. In a continuous process for extruding, drawing, heat-relaxing, and forming continuous self-elongatable filaments of synthetic organic composition into nonwoven web structures, the improvement comprising, during the heat-relaxation step, forwarding a plurality of the filaments simultaneously in separate untwisted and unentangled condition through an enclosed heat-relaxing zone in substantially a straight line, directing an annular stream of moving heated fluid into contact with the filaments to heat and assist in forwarding them through the zone, while simultaneously controlling the annular stream so that it moves parallel to the line of filament movement after contact without swirling or significant turbulence to prevent twisting or entangling of the filaments and simultaneously maintaining peripheral portions of the zone at temperatures below the sticking temperatures of the filaments in order to prevent clogging or filament accumulations in the enclosed zone.

10. An improved process for heat-treating continuously forwarded fluid-borne plurality of untwisted unentangled continuous filaments comprising contacting the moving filaments with a co-current stream of heated fluid elevated above the sticking temperature of the filaments while maintaining a boundary surrounding the contacting filaments and co-current streams at a temperature below the sticking temperature of the filaments to avoid interference with filament movement by adherence of the filaments to the boundary.

References Cited in the file of this patent UNITED STATES PATENTS 2,425,037 Jackson et al. Aug. 5, 1947 2,468,081 Koster Apr. 26, 1949 2,509,279 Sisson May 30, 1950 2,584,043 Oberly Jan. 29, 1952 2,952,879 Kitson et al Sept. 20, 1960 FOREIGN PATENTS 531,732 Canada Oct. 16, 1956

Claims (1)

10. AN IMPROVED PROCESS FOR HEAT-TREATING CONTINUOUSLY FORWARDED FLUID-BORNE PLURALITY OF UNTWISTED UNENTANGLED CONTINUOUS FILAMENTS COMPRISING CONTACTING THE MOVING FILAMENTS WITH A CO-CURRENT STREAM OF HEATED FLUID ELEVATED ABOVE THE STICKING TEMPERATURE OF THE FILAMENTS WHILE MAINTAINING A BOUNDARY SURROUNDING THE CONTACTING FILAMENTS AND CO-CURRENT STREAMS AT A TEMPERATURE BELOW THE STICKING TEMPERATURES OF THE FILAMENTS TO AVOID INTERFERENCE WITH FILAMENT MOVEMENT BY ADHERENCE OF THE FILAMENTS TO THE BOUNDARY.

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