US 3017684 A
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Jan. 23, 1962 E. H. PlTTMAN 3,017,684
TEXTILE MATERIALS AND METHOD OF MAKING THE SAME Filed Jan. 24, 1956 2 Sheets-Sheet 1 INVENTOR.
EDGAR HENRY PITT MAN ATTORNEY Jan. 23, 1962 E. H. PlTTMAN 3,017,584
TEXTILE MATERIALS AND METHOD OF MAKING THE SAME Filed Jan. 24, 1956 2 Sheets-Sheet 2 INVENTOR.
EDGAR HENRY PITTMA N mw w ATTORNEY 3,017,684 TEXTILE MATERHALS AND METi-ltill) F MAKING THE SAME Edgar Henry Pittman, Clemson, SAG, assignor to Deering Millilren Research Corporation, Spartanhnrg, SA), a corporation of Delaware Filed Start. 24, 1956, Ser. No. Sfitififi 4 Claims. (Cl. 28-72) This invention relates to staple fibers having an elastic, curly nature, to yarns andv fabrics formed thereof, and to methods for producing such staple fibers from tow or smaller groupings of individual filaments, or individual filaments, as may he desired, and for the forming of yarn therefrom.
A number of processes have been proposed for the production of elasticized, wavy or kinky staple fibers which may be suitable for use in yarns. All of the prior art methods have one or more serious disadvantages. A serious disadvantage of all known prior art methods resides in the fact that the crinkle or kink is fully developed before the filaments can be cut into staple fibers, and thus before it can be formed into a staple fiber yarn or otherwise formed into suitable end products. This obviously makes for difiiculty in the handling of such fibers in the various processes involved subsequent to formation of the staple. Also, in some instances, the crimp or kink produced is of a temporary nature, so that it is largely lost as time progresses, and this is particularly true of the crimping action obtained by passing yarns through a crimping Wheel or the like, and of the crimping action obtained by passing the yarn over a dull blade or the like at room temperature.
In still other instances, the elasticity of the staple is not as great as desired, and in other instances, the prior processes are inherently expensive due to the relatively complicated equipment needed to practice the process, or due to the large number of operations that must be performed.
A further serious disadvantage in the prior art processes, and particularly in the processes relating to passing the yarns through a crimping wheel or the like, resides in the fact that such processes do not lend themselves to controllable variation of the degree of crimping action, and consequently it is very difficult, if not impossible, in many cases to obtain crimped staple utilizing such processes which staple is suitable and lends itself readily to spinning into staple yarn.
It is accordingly an object of this invention to provide a novel process for the production of crimped or curly staple fibers from tow or the like, or from individual filaments of thermoplastic material in which the staple fibers produced thereby readily lend themselves to the spinning of highly suitable yarn therefrom.
It is a further object of this invention to provide a method for the production of crimped or curly staple filaments in which the degree of crimp may be readily controlled.
It is astill further object to provide a method of producing crimped or curly staple fibers in which the full crimping of the fibers may be delayed until any suitable time after their formation.
Still a further object is to provide textile yarns and fabrics composed of a plurality of staple fibers which are linearly convoluted in shape and in a state of unrelieved internal linear convoluting stress.
Still a further object of the invention is to provide a method of producing crimped staple fibers, which method is well adapted to producing such fibers from heavy denier tow as well as from intermediate multifilament yarns and monofilaments.
A still further object is to provide novel staple fibers 3,017,684 Patented Jan. 23, 1962 which lend themselves to considerable versatility, as in the bulkiness and the controllable variation thereof in yarns spun therefrom and inother end products made therefrom.
The above, as well as other objects of the invention, are accomplished by a process which, in its broadest form, comprises passing a thermoplastic yarn or tow under tension from a source of supply along a linear path having a curved portion providing. an abrupt change of direction, followed immediately by a portion having a relatively great radius of curvature, and subsequently chopping the yarn or tow into staple fiber lengths. The yarn or tow is heated so that at least during its passage through the first curved portion of the path it is at an elevated temperature, and is preferably also cooled or allowed to cool as it passes through and emerges from the first mentioned curved portion and during its passage through the portion of the path having a relatively great radius of curvature. After being allowed to cool under tension, and either subsequent to or preceding the chopping operation, the fibers are then reheated under such conditions as to permit them to assume a distorted linear configuration, and this second heating operation fully develops the elastic nature of the fibers. The second heating operation is most conveniently performed after the staple filaments are chopped and formed into a yarn and/ or fabric, as it is normally found that the staple will be sufficiently developed to permit spinning and other process operations without fully developing the fibers, and such is one great advantage of this process and the product produced thereby, particularly in that latent crimp may be retained in the fibers, as desired, while still having some desired degree of actual positional crimp or curl. However, it will readily be understood that there will be instances in which it is desirable to fully or more fully develop the latent crimp or curl in the staple fibers prior to any one or more of the various process operations.
The staple fibers produced by the instant process may be utilized to form an ultimate end product such as a spun yarn, woven fabric, felted or other non-woven fabric either in pure or mixed state with other staple fibers or continuous filaments.
The yarnor tow, as well as the staple fibers formed therefrom, subsequent to passage through the angular course but before the second heating operation, is herein referred to as latently elasticized yarn since, as explained above, it is not until after the second heating operationthat the yarn or tow either in continuous filament or staple fiber lengths, develops its full elasticization. The fibers in the latently elasticized yarn, tow and staple fi-ber form are characterized by a moderate wavy or coiled appearance when in an untensioned condition, and in many instances have 'a slightly flattened cross-section.
It is a feature of the invention that if the starting yarn or tow is free of torsional stresses, and if no torsional stresses are deliberately introduced during processing, the latently elasticized staple fibers will be fully free of torsional stresses.
The mechanism by which the process of the instant invention operates to produce elasticityin the thermoplastic yarn is not entirely understood, but according to present understanding of the invention, at least three different actions are obtained by passing the yarn or tow through the angular course while in aheated condition. The first action is broadly analogous to a phenomenon well known to everyone and- Which may be observed by progressively bending a length of ribbon over the blade of a knife or the like to produce a pronounced curl. It is this phenomenon which is believed to be, at least to some extent, responsible for the linear distortions in the yarn or tow which are observed prior to the second heating operation. This action is apparently not dependent upon the yarn or tow being heated as it is passed through the angular course, and, in fact, the action may be noticeably lessened by heating of the yarn as it passes through the angular course.
A second phenomenon which can be observed in many instances is a definite flattening of one side of the fibers, and in some instances this flattening occurs to the extent that the individual fibers become crescent shaped in the cross section. It is not definitely known whether this flattening of the fibers has any bearing on the degree of elasticization, but it is not generally considered to be otherwise advantageous since this flattened shape many times interferes with the subsequent operations involved in the utilization of the staple fibers.
Still a third phenomenon which is observed is the imparting to the yarn or tow of latent stresses or, in other words, stresses which do not make themselves immediately apparent by changing the linear configuration of the staple fibers when the tension on the fibers is relaxed. This phenomenon is, of course, quite desirable, since it is the release of these stresses during the second heating operation, referred to above, that causes the fibers to develop their full elastic nature, and While the exact mechanism involved in the creation of these stresses has not been fully determined, it is known that the stresses are not torsional in nature. For lack of a better phrase, the stresses are referred to as differential longitudinal stresses since their potential action is to cause a differential lengthening or shortening of one longitudinal cross sectional area of the fiber. While their exact nature is not fully understood, the factors which contribute to the creation of these stresses have been determined and will be discussed in subsequent paragraphs.
The yarn or tow to be elasticized according to the new process of this invention can satisfactorily comprise any continuous filamentary strand composed of an organic, hydrophobic, thermoplastic fiber material; however, nylon yarns such as those formed from the reaction product of hexamethylene diamine and adipic acid or from polymers of caprolactam, are preferred since they can be processed with fewer precautions, are operative through a wider range of conditions and give a higher degree of elastic ization than other types of yarn or tow. The invention can, however, also be employed with polyester yarns, such as those prepared from a reaction product of ethylene glycol and terephthalic acid and sold under the name of Dacron, and under certain conditions, the invention can be employed for the elasticization of polyacrylic fibers formed by the polymerization of acrylonitrile or by the co-polymerization of acrylonitrile with a minor amount of another polymeric monomer. Esters of cellulose, such as cellulose triacetate or cellulose diacetate, are also satisfactory in some instances and a suitable material of this type is available under the trade name of Arnel. Some yarns or tow give difficulty not so much because of their chemical composition or inherent physical properties but because of their cross sectional configuration. For example, an acrylic fiber sold under the name of Orlon has a cross sectional shape resembling the silhouette of a dumbbell and is very difficult to elasticize by the process of this invention. Yarns or tow wherein the filaments have a generally circular cross section and a smooth surface are most readily employed and give the most satisfactory results.
The denier and filament size of the yarn or tow to be processed may vary within wide limits, and substantially all of the commercially available yarns or tow within the previously specified class can be satisfactorily employed. As an illustration of the wide range of denier and filament sizes that can be employed, one may readily use nylon yarns or tow of the following descriptions; 15 denier monofilament; l2 denier, four filament; 200 denier, 34 filament; 800 denier, 51 filament; 3,360 denier, 192 filament; 200,000 and 300,000 denier tow of various deniers per filament, including the deniers per filament as illus- 4 trated in the preceding examples, and otherwise as may be desired. In other words, under suitable conditions, the deniers per filament can range from one to twenty or more, and the total denier can readily be as high as 200,000 to 300,000 or more.
Reference will now be made to the accompanying drawings in which:
FIGURE 1 is a schematic view in perspective of apparatus suitable for performing the first series of steps of the process of this invention.
FIGURE 2 is a schematic view of a modified form of apparatus according to the invention.
FIGURE 3 is a schematic view of a further modified form of the invention.
FIGURE 4 is an enlarged view in perspective of a staple yarn according to the invention.
As shown in FIGURE 1, a yarn or, preferably, a tow of filaments 10 of suitable material is led in laterally ribbon form between a pair of idler rolls 12, 14 and under suitable tension through a heater and blade assembly 20 and a feedback tensioning apparatus 30, thence through feed rolls 40, 42 and into a chopper 50 from which it emerges as latently elasticized moderately wavy or coiled staple fibers 60 in any suitable or desired length or lengths, at which point the fibers may be collected in any suitable or desired container such as an open box 62.
At the entry point into the rolls 12, 14 the yarn or tow 10 may be either in a state of lateral compression as will normally occur when a tow or multifilament yarn is passed between rollers in a state of longitudinal tension, or in a substantially non-compressed or partially compressed laterally spread out ribbon form, such as normally exists in tow as it emerges from the conventional drawing apparatus, not illustrated. Preferably for the fullest control and elasticizing of the filaments of the tow or yarn in the edge crimping operation, the yarn or tow should be in the ribbon form with substantially all or most of the filaments suitably laterally positioned for engagement with the heater and blade, next to be described in detail. In such case the yarn or tow 10 may pass directly from the conventional drawing apparatus to the rolls 12, 14, or from any other suitable source as may be desired. However, it will be apparent that such condition of a laterally uncompressed ribbon is not always practic'all-y attainable, and in most cases a partial laterally compressive force with overlapping of the filaments will occur during the passage of the yarn through the idler rolls and over the heater and the blade. As a matter of fact, it is most desirable in some instances to have the yarn in this latter state in order to achieve a ribbon, or in-phase, wave or curl in the filaments of the yarn or tow as it passes into and from the chopper 50. This is found in some instances to constitute a suitable manner of reducing the positional curl or wave in the staple fibers as they emerge from the chopper 50, to provide for easier opening and handling of the staple, until such time as the full development of the latent crimp is desired and obtained by further processing.
The yarn or tow 10 is gripped between idler rolls 12 and 14, the peripheral speed of which is controlled by a friction brake 32 on a circumferential end portion of the roll 14 in order to regulate, and maintain a substantially constant, tension in the yarn or tow as it passes in engagement with the heater and blade assembly 20.
In passing through the area of the heater and blade assembly 20 the yarn or tow 10 passes first into engagement with heater 2.2, where it is suitably heated, and thence to and over the edge of a preferably sharp edged blade 24 at a sharp angle. The heater as here illustrated comprises an arcuate heater strip 22, preferably formed of stainless steel or the like, but may be straight or otherwise formed, as desired. Likewise other heaters such as high frequency, space heaters, and the like might suitably b employed, if desired. The resistance heater strip 22 is adapted to be heated by means of an electric current passed therethrough and is connected by a pair of electrical conductors 25, 26 to a variable transformer 27 which is supplied from any suitable source of power, not illustrated, through leads 28, 29.
Mounted on a suitable support, not illustrated, adjacent the heater strip, preferably in slightly spaced apart of otherwise partially or wholly insulated relation thereto, is blade member 24. The acuate edge 24a of the blade extends beyond the rear (lower, as shown) edge of the heater strip 22 a short distance so that the yarn or tow passes in contact with the outer arcuate side of the heater strip 22 and over the edge 24a of blade 24 positioned at the apex of the angular path.
The yarn or tow Ill passes from the blade 24 to and over a tension-sensing roller 34 rotatably mounted on arm 35, which is pivotally mounted in any suitable manner. As illustrated, arm 35 is secured to a collar 36 and shaft 37 which are pivotally supported as by journal bearing supports 38. Coupled to arm 35 for movement therewith is a brake arm 39 having brake shoe 32 secured to the end thereof for frictional engagement with roll 14, as heretofore described. Brake arm 39 and sensing arm 35 are as a unit suitably biased against the tension action of the yarn or tow as exerted on roller 34, as for example by a tension spring 31, preferably having a tension adjustment, such for example as a turnbuckle arrangement 33 as shown.
Thus it will be apparent that tension assembly 30, through action of sensing arm 35 and roller 34, together with brake arm 39 and brake shoe 32, responds to longitudinal tension in the yarn or tow as it leaves blade 24 and operates to regulate this tension by selective braking action on the roll 14, and thus on the yarn or tow It as it leaves the heater and blade assembly 20.
As heretofore described, the yarn or tow 10 next proceeds through feed rolls 4t), 42 which serve in the instant example to pull the yarn or tow through the preceding illustrated apparatus including heater and blade assembly 26) and tensioning assembly 30. Rolls 44 and 4.2 may be driven in any suitable manner, as by a motor 44 and gearing arrangement 46, in order to achieve the desired yarn or tow velocity.
As illustrated in the instant example, the yarn or tow 10 passes from feed rolls 40, 42 to and through a chopper 50 which may be of any conventional or desired construction. It is preferable, however, in most instances, in order to avoid the introduction of torque stresses into the tow or yarn, which stresses may be partially retained, that a non-torque-introducing type of chopper be utilized, such as that schematically illustrated. It will be apparent, however, that while such is usually desirable, it may not always be a critical element, and in such case torque introducing choppers, such as the centrifugal type, may be suitably utilized, if desired.
The staple filaments may upon collection, as in a container 62, or at any suitable later time, be processed in the usual manner of cotton, wool or synthetic fibers, and formed in either pure or mixed state with other staple fibers or continuous filaments, into a spun yarn. In many cases where the fibers are to be spun into yarn, it is highly desirable to carry out all of the various steps of the foregoing described process, as well as the subsequent steps including the spinning of the yarn, in an atmosphere of relatively low humidity and a temperature below the full or fast crimp development temperature for the filaments, in order to prevent the staple fibers from substantially fully developing their latent crimp and becoming matted to such an extent as to unduly interfere with the fiber separation and subsequent processing steps. In such cases the yarn may readily be developed at any subsequent time after it is spun, by exposing it in a warm, or warm moist, atmosphere, or by passage through a warm bath of water, at a suitable development temperature, as described hereinafter.
However, there may be instances where a developing atmosphere is permissible during one or more of the steps, and this is particularly true as for instance in the formation of non-woven materials such as felt, as well as prior to processing the staple fibers in some cases for spinning into yarn.
FIGURE 2 discloses schematically a modified arrangement wherein the yarn or tow is developed prior to chopping. In this arrangement the yarn or tow is fed from feed rolls 40a, 42a through a hot air or heater box '70, the air temperature therein being within the range of temperatures at which the particular yarn or tow will fully develop in a short period, as discussed more fully hereinafter. It is desirable that the air be blown across the tow transversely to the lateral face formed by the spread out tow or yarn, in order to achieve most advantageous results in fast and even development. Preferably, the air is both hot and moist, particularly in the case of nylon, but, if desired, the air may be merely hot and of low or normal room humidity, as in the cases where Dacron or acetate is employed.
In the illustrative hot air blower arrangement, the box 70 has a pair of laterally extending openings 72, serving as inlet and outlet ports for the ribbon of yarn or tow as it passes through the box 70. A blower 74, heater 76, and conduit system 78, 79 are provided for circulating suitably warm developing air through the ribbon of yarn or tow as it passes through the heater box 70. Preferably, the conduit system is arranged so as to blow transversely to the lateral surface of the ribbon of yarn or tow, as illustrated, and is also arranged either in a substantially closed loop air path or so as to discharge the warm air at a point where it will not afiect the yarn at preceding points in the process, particularly, the point where the yarn or tow 10 passes over the blade 24. This will, however, not always be a point of prime importance, and it may be desirable from a practical standpoint to permit the discharge merely adjacent to or not far removed from the heater box 7 0.
Subsequent to the reheating operation, the yarn or tow passes through a further pair of feed rolls 30, 82 and thence to the chopper 50a as in the apparatus of FIGURE 1. The feed rolls 443a, 42a and 82 are driven by a suitable drive source, such as motor 44a, and are geared such that rolls 40a, 42a, are driven at a faster overfeeding rate than rolls 80, 82, by a differential peripheral speed factor sufiicient to permit the yarn to physically shrink and crimp to the desired degree of development between the two sets of rolls.
A further modified form of the invention is shown in FIGURE 3, in which the staple fibers are developed subsequent to passing through the chopping device. This modification may thus be suitably employed by adding the additional apparatus shown in FIGURE 3 to the apparatus of FIGURE 1, if desired. A conveyor belt 99 is arranged with its upper reach 92 being disposed beneath the discharge orifice of chopper 50b, and thus serves to receive and convey away the moderately wavy or curly undeveloped staple fibers as they issue forth from the chopper. Conveyor belt may be driven in any suitable manner, such as, for example, by a drive motor 94- and drive roll 95.
The staple fibers are thus conveyed by the upper reach 92 of the belt 90 to an area suitable for development thereof. In this area there is provided a steam box 96, or hot air box as may be desired or necessary, supplied with hot air or steam by any suitable source or means, not shown, through which the belt 90 and the staple fibers are passed. By employing suitable temperature in steam box 96, the staple fibers will emerge therefrom in a fully or substantially fully developed wavy and curly state.
As may be desired the fibers may then be conveyed to any desired point for immediate processing toward ultimate use in any suitable end product, or may be collected, as shown, in a container 98 beneath the discharge end 97 of the upper reach of belt 90, to await further use thereof.
Asmall segment of yarn which is formed of crimped staple fibers according to this invention is illustrated in side view in FIGURE 4. The general appearance and structure of this sample of yarn is similar in many respects to that of wool. Yarns having various characteristics may be spun or otherwise formed by use of the staple fibers formed according to this invention, as for example by mixture with various other staple fibers such as Wool, cotton, synthetics, and by combination in various continuous filament yarns. In the preferred form, however, the yarn Will as a result of the action of the instant process in the production of the staple fibers, contain staple fibers according to the invention which are in a more or less randomly convoluted shape and which are internally stressed, even after development, to a more or less degree, the combined shape and stress being characteristic of the novel staple fiber according to this invention, in that it is both convoluted in shape and is in a state of partially unrelieved internal convoluting stress of a nature which if positionally relieved would tend to convolute the fibers even further in the same direction.
In the type of apparatus described, the yarn or tow is forced through an abrupt change of direction by passing the same over an acuate edge, and while this is presently the most convenient method of accomplishing the desired results, it will be apparent that the yarn or tow can be caused to undergo the required abrupt change of direction in other ways.
Although the apparatus for producing the novel staple fiber of this invention is relatively simple, there are several variables which affect the nature of the staple produced, and thus the nature of the novel yarn spun therefrom and/or the novel fabric formed therefrom. For example, the radius of curvature of the blade edge, the tension in the filaments as they are passed over the blade, the temperature of the heater element, the rate of cooling of the yarn or tow after it passes the acuate edge, and the linear velocity of the yarn or tow can all have their effect on the nature of the staple fiber, staple yarn, and fabrics produced therefrom. In subsequent paragraphs, these variables will be further discussed in detail.
The radius of curvature of the acuate edge can vary within reasonably wide limits but is preferably as small as possible without severing the yarn. The smallest possible radius of curvature of the blade in turn depends upon the nature of the yarn or tow being passed over the edge, the size of the filaments in the yarn or tow and upon the texture of the material from which the blade is formed. With a blade formed from a finely grained material, it is possible for the radius of curvature of the edge to be as small as one or two microns when running nylon yarn or tow composed of filaments of about 2 denier or less, but with larger filaments or with other types of yarn or tow the radius of curvature of the edge should generally be at least about 3 to 6 microns. Even with nylon yarns or tow composed of very small filaments, it is frequently necessary that the radius of curvature be as much as 4 or 5 microns in order for satisfactory results to be obtained if the blade is formed from a coarse textured material. In processing monofilament or yarns having a small number of filaments razor blades may be suitably utilized to form the acuate edge over which the yarn is to be run. However in the case of large quantities of filaments, such as in tow, it is desirable, and in most cases necessary, that the width of the blade edge be much wider, in order to accommodate the full ribbon width of the yarn or tow, although the radius of curvature may be substantially similar to that of a razor blade for a given case.
The maximum radius of curvature of the acuate edge depends primarily upon the size of the yarn or tow filaments being passed thereover, but will also vary to some extent with the chemical nature of the yarn or tow being employed. However, with any type of yarn or tow it is a general rule that the radius of curvature should be no more than about one to four times the diameter of the yarn or tow. For example, when using 70 denier 34 filament nylon a good degree of elasticization is generally obtained, only if the radius of curvature of the angular portion of the yarn or tow path is less than about 30 microns, but with a yarn or tow having large filaments, such as 15 denier monofilament nylon, a blade having an edge with a radius of curvature as great as about 70 to 150 microns can sometimes be employed with good results. Even in the latter instance, however, an edge with a radius of curvature less than about 30 microns generally gives the greatest degree of elasticization.
Nylon yarn or tow can be passed over the acuate edge in a dry unlubricated condition, but all other yarns or tow generally require the use of a lubricating oil for completely satisfactory results, and, even with nylon, better results can be achieved by lubricating the yarn or tow prior to its passage over the acuate edge. In the case of multi-filament nylon yarns or tow, it has been found advantageous to employ a lubricating agent which at least partially vaporizes at the temperature of the heater element and while the exact reason for this is not known, it is believed that the vaporization of the lubricant results in better heat transfer among the various filaments. In the case of other types of yarn or tow, it is generally preferable to employ a lubricating agent which vaporizes only to an inappreciable extent at the temperature of the heater strip since the yarn or tow needs to be fully lubricated at the time it is passed over the acuate edge or else breakage might occur. In the case of nylon yarns or tow, the preferred lubricating agent has been found to be a low viscosity mineral oil such as that sold under the trademark of Esso Mentor 28. In the case of other yarns or tow, the preferred lubricant has been found to be one with a low viscosity and a high flash point and one which can be readily removed from the treated yarn or tow. Sorbitan trioleate is an example of a material which is generally satisfactory. The lubricant can be applied by means of a felt wick, by means of capillary action or by any other means generally used in the textile industry for the application of lubricants to yarns or tow.
The angle of approach and the angle of departure of the yarn or tow to the blade may also vary within wide limits, although the total of these two angles should be less than about 120 and preferably less than about It is generally advantageous to make the angle of approach relatively large, for example from 30 to 100, so that the blade is displaced from the heater element and is, therefore, at a lower temperature. On the other hand, it is generally advantageous that the angle of departure be less than about 50 and preferably as small as the grind of the acuate edge will permit. When the angle of approach is relatively large, better than average results can be achieved by allowing the yarn or tow to follow the surface of the blade across its entire width after the yarn or tow passes over the acuate edge. The exact reason or reasons for this are not known with certainty, but it is known that the yarn or tow should preferably be cooled as soon and as rapidly as possible after its contact with the acuate edge, and it is believed that contact across the width of the blade or blowing air across the yarn or tow results in a more rapid dissipation of heat from the yarn or tow than is achieved by simply air cooling the yarn or tow as it travels from the acuate edge.
If desired, various expedients can be employed to retain the blade at a temperature appreciably below that of the heater element. For example, the blade can be isolated from the heater element by means of heat resistant insulation or a cooling medium can be circulated in contact with the blade to retain it at any desired temperature. While satisfactory results have been achieved with the blade at a temperature equal to that of the heater element, a very marked improvement can be achieved by retaining the blade at a temperature of at least about 20 to 50 F. lower than that of the heater element and preferably at a temperature at least about 150 to 250 below the temperature of the heater element.
The tension in the yarn or tow passing over the blade is another important factor and this variable must be maintained within specified limits to obtain maximum elasticity. Operative limits for the tension in the yarn or tow following its contact with the acuate edge vary depending upon a number of factors including the temperature of the yarn or tow and the type of yarn or tow being employed, but as a general rule the operative range extends from about .05 gram per denier to approximately 1 gram per denier with the preferred range for nylon, for example being from about .1 to .4 gram per denier. The optimum tension will not only vary with the temperature of the yarn or tow and the composition thereof, but also appears to vary slightly with yarns or tow of substantially the same composition made by different manufacturers or even for difierent lots of yarn or tow made by the same manufacturer. It has been determined that the optimum tension for Du Pont type 200 at a temperature of from about 220 to 360 F. at the acuate edge is generally from about 0.15 to 0.28 gram per denier.
The linear velocity of the yarn or tow over the blade may also vary within wide limits depending upon'the temperature of the heater element, the distance through which the yarn or tow is in contact with the heater element, the distance of the heater element from the edge of the blade and the type of yarn or tow being passed over the blade. It is important that the velocity of the yarn or tow be such that it accumulates suflicient heat to be at the proper temperature at the moment it contacts the acuate edge, and it will be apparent that the yarn or tow velocity required to accomplish this result will vary with the above factors. In other words, with the yarn in contact with the heater element for a given distan e and with the heater element at a given temperature, it will take an appreciably longer period of contact for a 70 or 100 denier yarn to be heated than will be required for a 15 or 7 denier yarn an likewise for a 200,000 denier tow compared to a smaller denier tow or yarn, so that a lower yarn or tow velocity must as a usual rule be employed with the larger yarn or tow. Likewise, if the acuate edge is too far from the heater element, there is a tendency for the yarn or tow to cool between the heater element and the acuate edge, and it will be apparent that a smaller yarn or tow will cool more rapidly than a larger yarn or tow so that a higher linear yarn or tow velocity must be employed in the first instance.
Although the distance of the acuate edge from the heater element may vary within reasonably wide limits and may be as much as two inches or more, as a general rule it is preferred that the acuate edge be placed as close to the heater element as is possible without actual contact therewith. By placing the acuate edge as close to the heater element as possible, it is only necessary to heat the yarn or tow to substantially that temperature at which it is desired that the yarn contact the acuate edge, whereas if the heater element is removed from the acuate edge, it is necessary that the yarn or tow be heated sufficiently above the temperature at which it is desired that it contact the acuate edge to compensate for the cooling of the yarn or tow that occurs during its passage from the heater element to the edge. Heating the yarn above the optimum temperature for cont-act with the acuate edge is generally undesirable, since nearly all yarns or tow are weakened to some extent by heat and since temperature control is thereby made more difiicult.
The distance over which the yarn or tow is in contact with the heater element should, for optimum results, be as great as is possible without resulting in an undesirably high tension in the yarn or tow. It will be apparent that the greater the distance that the yarn or tow is in contact with the heater element, the greater will be the area of contact and the higher will be the tension required to transport the yarn or tow, but under some conditions it has been found that the yarn or tow may be maintained in contact with a heater element for a much as 10 feet or more, for example, without introducing excess tension.
A further factor which need be considered in the production of the latently elasticized yarn or tow is the temperature of the heater element, and it will be appreciated that the operative range for this variable depends upon the type of yarn or tow being employed, the linear velocity of the yarn or tow, and the distance for which the yarn or tow is in contact with the heater element. If a moderately high yarn velocity is employed, for example to 1000 feet per minute, and the contact of the yarn with the heater strip is limited to a short distance, for example 1 inch or less, it is possible to obtain satisfactory results with the heater element at an average temperature appreciably higher than the melting point of the yarn or tow. For example, under such conditions operative results can be achieved with nylon yarns with the heater element at a temperature of 500 F. or even higher. On the other hand, if the yarn or tow is maintained in contact with the heater element for a relatively long distance,
'it is possible to obtain operative results with the heater element at a temperature of the order of the second order transition point for the material of the yarn or tow, which for type 66 nylon as now marketed is 180 F. The optimum temperature for the heater element will, of course, depend upon the type of yarn or tow being employed as well as the other factors considered above, but even with yarn or tow of the same composition, the optimum temperature of the heater element appears to depend upon the yarn or tow being employed, and in nylon is known to be closely connected with the drawratio used by the manufacturer in drawing the yarn. For example, with the yarn or tow in contact with the heater element for a distance of approximately 3 inches and with a yarn velocity of feet per minute, an operating temperature of from about 290 to 330 F. has been found to be optimum for processing 15 denier monofilament nylon (type 66, semi-dull) while a temperature of from about 330 to 380 F. for the heating element appears to be optimum when processing 30 denier l0 filament nylon. In other words, since the optimum temperature of the heater element will vary slightly depending upon many factors, it is generally advantageous to conduct a series of tests to determine the optimum temperature for the heater element for each particular set of conditions encountered.
The temperature of the heater element has been emphasized since under normal operating conditions the exact temperature of the yarn or tow passing over the acuate edge is difficult to measure, but it will be apparent that the really important consideration is the temperature of the yarn or tow as it begins its passage over the blade edge. With all yarns or tow of a given construction and chemical composition there is a well defined operative temperature range for the yarn or tow at this point and some of the values for the heater element temperature set forth above are only made necessary or possible because of other variables. Although the exact lower operative limit for any given type of yarn or tow will vary slightly, it can be stated as a general rule that the lower limit is that temperature which is suificient to at least largely relax the stresses normally present in the yarn or tow or, in other words, suflicient to relieve the yarn or tow of a large part of the residual shrinkage present therein. For nylon yarns or tow, the lower operative limit will vary from about 180 F. for Du Pont type 200, 15 denier monofilament, up to and above approximately 240 F. for nylon yarns or tow which are very difficult to elasticize. For other types of yarns or tow the operative lower limit will vary from about to 300 F. The upper operative temperature for the yarn or tow as it contacts the acuate edge is generally that temperature at which the yarn or tow begins to display a tendency to stick to surfaces with which it is in contact, or as it is called in trade and scientific publications, the sticking temperature of the yarn or tow. The optimum temperature for the thermoplastic strand as it contacts the acuate edge will vary with a number of factors including filament size and chemical composition and generally must be empirically determined for each specific yarn or tow. For example, by actual operation it has been found that the optimum temperature for Du Pont type 200 nylon, 15 denier monofilament yarn is about 290330 F., while the optimum temperature for type 200 nylon, 70 denier, 34 filament yarn or tow is about 340 to 370 F. A simple test, which has been found to be of some value in estimating an optimum temperature for most types of yarn or tow, comprises measuring the tension developed in a given length of the yarn or tow as the temperature is raised. As the temperature of the yarn or tow is increased, a point is reached where the tension developed in the yarn or tow falls off rapidly and this point is generally a near optimum for passing this particular type of yarn or tow to the acuate edge.
While it is not absolutely necessary that the thermoplastic end of yarn or tow be cooled after its contact with the acuate edge, cooling the yarn or tow is generally more convenient than retaining it at an elevated temperature and, in most instances, rapidly lowering the temperature of the yarn or tow 200 to 300 F., or more, results in a better product. For example, with nylon Du Pont type 200 the temperature of the yarn or tow should be lowered at least to about 160 F. One convenient method of cooling the yarn or tow comprises subjecting the yarn or tow immediately subsequent to its contact with the acuate edge to the atmosphere so that the yarn or tow end is cooled by air currents. Still another and generally more satisfactory method comprises passing the yarn or tow into contact with a cold metallic surface such as the side of the blade when the blade is so positioned that it is not heated to a high temperature by the heating means. the yarn or tow end after its contact with the acuate edge will readily suggest themselves to those skilled in the art.
The radius of curvature of the portion of the yarn or tow path immediately following the point where the yarn or tow passes about the acuate edge and wherein the yarn or tow is subjected to cooling conditions, should be relatively large as compared to the radius of curvature of the acuate curved portion of the yarn or tow path. It is believed that the low to moderate degree of the crimp in the latently elasticized yarn or tow is at least partially a result of passing the yarn or tow from the highly curved portion of the path into a portion of the path having a relatively large radius of curvature. As a general rule, the radius of curvature of the portion of the path immediately following the acutely curved portion should be no less than about 600 microns and should preferably be at least one inch. The length of this por tion of the path need not be great, and adequate cooling of the yarn or tow can generally be accomplished in inch or less, particularly with low denier yarns, although a length of one inch or more is generally preferred, particularly in the case of high denier yarns and tow.
To transform the latently elasticized yarn or tow to a fully elasticized condition, it is necessary to positionally relax the stresses created in the yarn or tow as a result of its being passed through the angular path in a heated condition, and as previously mentioned, it is an advantage that the relaxation of these stresses can be postponed until after the staple fibers have been spun into yarn, or after the staple fibers or yarn has been woven, knitted or otherwise formed into a fabric. Relaxing the stresses in the yarn or tow after it has been formed into a fabric, however, requires special precautions since it is quite difficult to make certain that the yarns or tow are under a sufficiently low tension that the Other means of cooling stresses are, at least to an appreciable degree, positionally relaxed rather than internally relaxed or heat-set. In such cases, it is usually desirable to agitate and gradually raise the reheating or developing temperature of the yarn or fabric during development of the crimp therein in order to assure maximum possible positional relaxation of the stresses in the fibers, although there are times when maximum positional relaxation is not necessary or desirable.
If the full elastic nature of the latently elasticized fibers is to be developed before the fibers are formed into yarn or fabrics, agitation and a gradual temperature rise are not required. Hence, the fibers can be readily placed in a substantially tensionless condition, and when in this condition the positional relaxation of the stresses in the fiber prevails over the internal relaxation of the stresses to the extent that excellently elasticized fibers are obtained even if the temperature rise is very rapid. In this instance, the heating can be conducted by overfeeding the tow or yarn after cooling and prior to passing through the chopping apparatus into a heated fluid, such as water, air or steam or into contact with a heated surface, so that the yarn or tow is allowed to coil freely, or as desired, at the time its temperature is elevated. In the full development of the staple fibers subsequent to chopping and prior to any further operations, such may be readily developed in the open state and in the yarn or fabric state by immersing in a tank of suitably warm water or by subjecting the fibers to a warm, or warm moist, atmosphere. A high temperature is not required, and satisfactory results can generally be obtained if the fibers are heated to a temperature of only about F., although a temperature of from about to 400 F. is generally preferred. Care should be exercised to insure that the fibers at the time they are heated are under as little tension as possible, for if the tension in the fibers is allowed to rise above about .004 to .01 grams per denier, good elasticizing may not be obtained. Additionally, by exposure for relatively long periods of time, on the order of several days or weeks, it is possible and sometimes desirable to develop the staple fibers through exposure to normal room atmosphere, for instance of the order of 70-90 and 30-40 .or more relative humidity. If the tension is at a proper level, the fibers when exposed to the 140400 F. conditions assume a highly convoluted linear configuration almost immediately, so that the heating need not be continued for more than one or two seconds.
Having thus described my invention, what I desire to claim and secure by Letters Patent is:
1. The method which comprises placing, while at an elevated temperature, a plurality of continuous thermoplastic textile filaments in a tensioned and substantially straightened condition but not under a tension of more than about 1 gram per denier, said filaments in each instance having a pronounced tendency to assume a crimped configuration, cooling said filaments while in said straightened and tensioned condition to thereby result in said filaments being partially heat-set in said condition, chopping said filamens into staple fibers, and thereafter heating said staple fibers while in a positionally relaxed condition to at least partially eliminate the effect of said heat-setting and to cause said fibers to develop a more pronounced crimp.
2. A method according to claim 1 wherein the temperature of said thermoplastic filaments while in said straightened and tensioned condition is at least 180 F., but below the sticking temperature of the filaments, and wherein the temperature of said staple fibers in said second heating operation is at least 140 F. but below the sticking temperature of the staple fibers.
3. A method according to claim 2 wherein said staple fibers are spun into yarn before said second heating operation.
4. A method according to claim 2 wherein said staple 13 fibers are formed into a fabric before said second heating operation.
References Cited in the file of this patent UNITED STATES PATENTS 2,369,395 Heymann Feb. 13, 1945 2,394,165 Getaz Feb. 5, 1946 2,575,839 Rainard Nov. 20, 1951 14 Hemmi Dec. 30, 1952 Keen Feb. 16, 1954 Hay Feb. 14, 1956 FOREIGN PATENTS Australia July 15, 1955 Great Britain Dec. 30, 1943 Great Britain Ian. 25, 1956