US3470685A - Synthetic textile yarn - Google Patents

Description

i Oct. 7, 1969 HALL ETAL 3,470,685

SYNTHETIC TEXTILE YARN Original Filed March 50, 1967 EXTRUDER FIG?) 29 3O 29 G-' FlG.ll l9 no FIG.? 34 FIG'Q JOHN N,H CH ES wi VENTORS. y h/(MM ATTORNEY United States Patent ()fi :"ice

3,470,685 Patented Oct. 7, 1969 U.S. Cl. 57-140 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a bulky synthetic yarn having a spun-like appearance and comprised of filaments having, in cross-section, a maximum depth at the transverse midpoint of the filament and a decreasing depth in both directions laterally of the filament to a minimum depth at at the opposite edges thereof, and a plurality of fine denier fibrils protruding from the side edges.

This application is a division of application Ser. No. 627,104, filed Mar. 30, 1967.

The present invention relates to yarn of synthetic polymers and particularly to yarn adapted to be formed from a relatively narrow strip or ribbon of film, which yarn, while it consists of continuous filaments, has a so-called spun look, that is, a bulky appearance characterized by a plurality of fiber ends extending laterally from the yarn in the manner of the fiber ends in a yarn spun from short length fibers or staple.

In the most commonly used methods employed in the production of synthetic yarn, the yarn is formed from a plurality of continuous filaments that are simultaneously extruded in a molten condition and are melt drawn to a reduced diameter. The filaments are subsequently drawn at an orienting temperature, which drawing further reduces the diameter of the filaments and imparts strength thereto. The filaments are then twisted into yarn. The linearity and surface characteristics of the filaments so formed affect the yarn both in physical properties (e.g., strength, filament density, and frictional and thermal characteristics) and in appearance (e.g., bulk, softness or hand, and light reflectivity). To modify the appearance and physical properties of the yarn, the yarn is usually further processed through a bulking or crimping operation wherein a permanent crimp is imparted thereto.

Yarns have also been produced from synthetic fibers by cutting the continuous filaments, usually in the form of tow, into short lengths or staple and processing them, for example, in the same manner as cotton and wool fibers are normally processed. Yarns so produced have an apparent breaking strength that is reduced relative to continuous filament yarns of comparable denier and are more expensive to process, but they can be formed of different fibers blended to achieve various effects, and have improved appearance and hand relative to the continuous filament yarns.

Processes have also been developed heretofore for producing continuous filament synthetic yarns from uniaxially oriented plastic film in the form, for example, of narrow strips slit from a wide sheet of film. In such processes, the film is reduced to filaments to form a multifilament yarn by mechanical working such as by brushing, rolling or twisting, or by the action of an air jet. Because handling and working a film is generally easier than handling or working a plurality of individual filaments, it is usually less expensive to produce continuous filament yarn from film than from individually formed filaments. However, with filaments formed from film, there is no control of the width of the filaments other than the inherent weakness of the film in the direction transverse to the direction of orientation. Thus, there are appreciable variations in the width of the filaments along their lengths, with corresponding variations in the strength, hand and appearance of the yarn, and there are many broken or run-out filament ends.

In making continuous filament yarn from film, an advantage of using a jet of air to separate the film into individual filaments rather than mechanical working is that the jet not only splits the film but the turbulence thereof also acts to interm-ingle the filaments, which contributes to the cohesiveness of the yarn and reduces the twisting required to form the filaments into a yarn. There is also a certain number of filaments broken to produce ends that, in the yarn, project laterally in the manner of the fiber ends in a spun yarn so that the yarn formed from these filaments tends to simulate the appearance of a spun yarn. In such a yarn, however, since the ends are formed by broken filaments, the strength of the yarn is reduced relative to the strength of a corresponding yarn of continuous or unbroken filaments and the number of such filament ends that can be accommodated is therefore limited. At the same time, since the ends generally correspond in cross section to the cross section of the filaments, they tend to be relatively coarse and thus their effect upon the hand or softness of a fabric produced from such a yarn is limited. Examples of the use of an air jet for splitting an oriented film into filaments are found in Patents Nos. 3,214,899 and 3,242,035.

It has also heretofore been proposed to produce synthetic yarn from strips of striated film, that is, from film having a plurality of spaced parallel longitudinally extending filament-forming portions or striations that are generally circular in cross section and are connected together longitudinally by integral webs of reduced thickness. Such films may be used in ribbon form, as illustrated in Patent No. 3,164,948, or in a random or partial split form as disclosed, for example, in Patent No. 3,273,771 and in Japanese patent publication No. 16,450/ 65. Yarns formed in this manner have generally been formed for the purpose of obtaining more flexible yarns than were obtainable by conventional melt-spinning processes, that is, in comparing a striated ribbon with a monofilament of comparable denier, the individual striations of the ribbon are smaller as well as easier to form on a commercial basis and the yarn is also more flexible. Among the other advantages of striated film, the webs define lines of weakness whereby the film can be readily split along the webs as by tearing or brushing. A further advantage of striated film is that, with a limited amount of splitting at the web and the individual striations or filaments thus connected together by the unsplit portions of the web, a reduced amount of twisting is required to form the filaments into a yarn.

Notwithstanding the fact that the prior art includes various methods for splitting film into filaments, various attempts to produce a bulky appearance in a continuous filament yarn, and various examples of the use of striated film, for example in making cordage, there has not heretofore been produced a synthetic yarn having tensile strength substantially equal to a continuous filament yarn of comparable denier while having the appearance and hand of a spun yarn, and having improved bulk and the corresponding covering, thermal and frictional characteristics.

Accordingly, the objects of this invention are to provide a bulky synthetic yarn having the appearance and hand resembling that of a yarn spun from staple and having improved covering capacity, insulation and tensile strength. At the same time, it is an object of this invention to provide such a bulky synthetic yarn that is relatively inexpensive and is adapted to be manufactured in commercial quantities with a minimum of equipment, labor and other items of expense.

A further and specific object of this invention is to provide a continuous filament synthetic yarn consisting of individual filaments having a plurality of laterally projecting side hairs or fibrils of reduced cross section relative to the filament and wherein the number and length of such side hairs or fibrils are relatively large.

In accordance with this invention, the above objects have been achieved by providing a yarn adapted to be formed from a strip or ribbon of striated film that is highly oriented uniaxially in the longitudinal direction, which strip is split lengthwise into the plurality of individual continuous filaments. The filaments are formed from the striations and are very uniform in cross section lengthwise thereof. At the same time, there is formed from the webs of the strip of filament a plurality of fibrils or side hairs on each of the filaments, which fibrils have a reduced cross section relative to the cross section of the filaments. The number of fibrils and the length of them as well as the efficiency in the separation of the striations are primarily a function of the dimensions of the striated film and its cross sectional profile, the degree of orientation, the characteristics of the jet, the characteristics of the polymer such as its molecular weight, and the process conditions such as the temperature of the film.

For a more complete understanding or" this invention, a preferred embodiment thereof is hereinafter disclosed with reference to the accompanying drawings, in which:

FIG. 1 is a schematic illustration of equipment employed in making a striated film in accordance with this invention.

FIG. 2 is a schematic illustration of equipment employed in orienting and fibrillating striated film.

FIG. 3 is a fragmentary detail sectional view of the die lips of the extruder illustrated in FIG. 1.

FIG. 4 is a fragmentary detail cross sectional view of a striated film approximately as it may appear immediately upon extrusion from the die lips of FIG. 3.

FIG. 5 is a view similar to FIG. 4 of the striated film after it has been melt drawn.

FIG. 6 is a view similar to FIG. 5 of the striated film after it has been oriented.

FIG. 7 is a view of the striated film of FIG. 6 after fibrillation.

FIG. 8 is a fragmentary plan view of the yarn of FIG. 7.

FIG. 9 is a fragmentary view on an enlarged scale of one of the filaments of the yarn of FIG. 7.

FIG. 10 is a cross sectional view taken substantially on the line 1010 of FIG. 9.

FIG. 11 is a view similar to FIG. 3 but illustrating the die lips for making a single striated film strip.

In the drawings, there is illustrated schematically an apparatus for making a yarn in accordance with this invention. The illustrated apparatus comprises a conventional extruder 1 having a hopper 2 at the input thereof. At the discharge end of the extruder 1 there is a metering device 3 having a discharge die 4 from which issues the as-extruded film strip 5a illustrated generally in FIG. 4. Immediately upon issuing from the die 4, the film strip 5:: is melt drawn, the melt-drawn film strip being designated at 5. The melt-drawn film strip 5 is quenched, for example, in a quench tank 6 that is filled with a liquid, which may be water at tap temperature. The melt draw of the film strip may be in the range of 3:1 to 10:1 or higher.

Located within the quench tank 6 are idler rolls or bars 7 for directing the filament strip 5 to a pair of feed rollers 8 that effect the melt draw of the film strip. The rollers 8 operate at a peripheral speed sufiiciently high relative to the speed at which film strip 50 is extruded to produce the desired melt draw of the strip 5.

4 As illustrated, from the feed rollers 8, the film strip 5 is wound to form a film roll 9, although the film strip 5 could of course be led directly to a subsequent operation in a continuous process without intermediate winding and unwinding.

As illustrated in FIG. 2, the melt-drawn film Strip 5 is pulled from the film roll 9 by a set of low-speed feed rollers 10. Between the low-speed feed rollers It and a comparable set of high-speed draw rollers 11, the film strip 5 is directed over a heated drum 12, a pair of idler rollers 13 and 14- and a cold drum 15. The heated drum in maintained at a temperature sufficient for heating the film strip to the optimum orienting temperature for the particular material and which, for example, may be about C. for a film strip of polypropylene. The cold drum 15 is maintained at ambient temperature. The high-speed draw rollers 11 are operated at a peripheral speed relative to the low-speed feed rollers 10 to provide the desired draw ratio, which for example may be up to about 15:1, and with a melt draw ratio of about 4: 1, is preferably about 6:1 or 8:1. Drawing the film strip occurs between the hot drum 12 and the first idler roll 13. The oriented film strip is designated 16. After drawing, the strip 16 is cooled by the cold drum 15.

The oriented film strip 16 is pulled from the delivery end of the draw rollers 11 by a pair of feed rollers 17. Between the rollers 11 and 17, there is a fibrillation device 18 that separates the film strip 16 into a yarn 19 that consists of a. bundle of individual continuous filaments. From the rollers 17, the yarn 19 is taken up into a yarn package 20.

The illustrated fibrillation device 18, which is an integral part of the invention that forms the subject matter of said application Ser. No. 627,104, comprises a cylinder 21 having guides 22 in the opposite ends thereof and an air tube 23 in the side wall thereof. The guides 22, as illustrated, are in the form of plugs inserted into the ends of the cylinder and having central bores that serve as the guides for the incoming film strip 16 and the outgoing yarn 19. The air tube 23 comprises a tube arranged substantially radially of the cylinder 21 and located near the longitudinal center of the cylinder, the tube being connected at one end to a source of air under pressure (not shown) and at the other end to the interior of the cylinder 21 through an aperture in the side wall thereof.

In FIG. 3, there is illustrated in cross-section a portion of one set of die lips 24 for the die 4 for producing the film stri 5a. As shown, the die lips 24 have a matched series of opposed die grooves 25 equally spaced along the length thereof and separated by intermediate die faces 26. In their operative relation in the die 4, the die lips 24 are positioned with the opposed die faces 26 slightly spaced. Thus, as illustrated in FIG. 4, the film strip 5a comprises a plurality of substantially rounded filament-forming strips 27, which are herein referred to as the striations and which are arranged in spaced parallel relation and are interconnected by integral webs 28. In FIG. 5, the meltdrawn film strip 5 is illustrated in cross-section and as shown comprises a series of striations 29 and webs 30 corresponding respectively to the striations 27 and webs 28 of the film strips 5a. The relative dimensions of the film strips 5a and 5, as shown in FIGS. 4 and 5, roughly represent a melt draw ratio of about 4:1. The oriented film strip 16 is illustrated in cross section in FIG. 6 and comprises a series of striations 31 and webs 32 corresponding respectively to the striations 27 and webs 28 of the as-extruded film strip 5a. The relative dimensions of the film strips 5 and 16 represent a draw ratio of about 6:1. In FIG.7, there is illustrated in cross section a portion of the yarn 19.

As shown in FIG. 7, the film strip 16 has been split longitudinally of the webs 32 into a plurality of filaments 33 that embody the present invention. In FIGS. 9 and 10, there is illustrated somewhat schematically and on an enlarged scale a typical filament 33 of the yarn 19. This filament comprises an individual striation 31 together with a portion of the web 32 on each side thereof, which web portions terminate in side edges 34 and which constitute the edges along which the webs 32 have been slit to separate the respective filament 33 from its adjacent filaments on the film.

The filament 33 has a shape that is generally round or, more particularly, has a maximum thickness substantially at its transverse center between an upper edge 35 and a lower edge 36. Outwardly in both directions from the edges 35 and 36, the thickness of the filament decreases to the minimum thickness at the side edges 34 equal to the thickness of the web 32 in the oriented film strip 16. The configuration of the side walls of the filament 33 intermediate the edges 34, 35 and 36 is a function of the draw ratios in the melt draw and in the orientation and, with the film 5a as illustrated in FIG. 4, may be substantially circular as shown in FIG. 10. Lengthwise of the filament 33, the thickness between the edges 35 and 36 and the width between the opposite side edges 34 are substantially uniform.

In addition to the fact that the film strip 16 has split into a plurality of individual continuous filaments 33 substantially corresponding in number to the number of striations 31, the webs 32 have formed a plurality of fibrils or side hairs 37, FIG. 9, at the opposed side edges 34. Under the action of the air jet, the fibrils 37 are torn loose or run-out at one end from one of the two filaments between which it is formed and sodefine side hairs of varying lengths. Each of the side hairs 37 has a cross section that, except where broken, decreases from the base to a point at the free end. This apparently results from the lateral wandering or migration of the molecular orientation in the film between two adjacent filaments that is present even in highly oriented film. Since each fibril 37 has a thickness comparable to the original thickness of the web 32 from which it was formed and a width that at the base may be roughly equal to its thickness, the fibril 37 is substantially finer than a filament 33.

In the yarn 19, the number of filaments 33 corresponds to the number of striations 31 in the film strip 16 and this in turn is determined by the number of die grooves 25 in the die lips 24. Inasmuch as the filaments 33 are all continuous and are not broken, the tensile strength of the yarn is determined by the polymer characteristics and is not dependent upon the degree of twist in the yarn as are yarns of staple or of broken filaments. Accordingly, twisting of the yarn is not necessary for purposes of strength so the amount of twist imposed upon the yarn need be no more than that required to establish coherence of the yarn, which requires a low level of twist, and can otherwise be selected for other desired effects. From this standpoint, since a high twist is not required, the yarn can be made quite loose and bulky with the resulting advantages of improved covering capacity and increased insulation for a given weight of yarn.

The fibrils or side hairs 37 of the filaments 33 contribute to the above advantages. Inasmuch as the fibrils 37 extend laterally relative to the filaments 33, they tend to support the filaments in spaced relation to increase the bulk of the yarn relative to a comparable yarn of equal twist but without the fibrils. At the same time, the fibrils increase the covering capacity of the yarn and the insulation.

The free ends of the fibrils 37 extending from a fabric formed from the yarns 19 adds a softness to the surface of the fabric as well as creates the appearance of a fabric formed from spun yarn. The fineness of the fibrils 37 increases the softness of the fabric. With fiber ends formed by the fibrils or side hairs 37, the breaking strength of the yarn is greater than it would be if they were formed by broken filaments.

A more complete understanding of the present invention will be had from the following specific example of one process for forming yarn in accordance with this invention. A polypropylene film was extruded through a die having die lips as shown in FIG. 3, the die lips having semi-circular die grooves 25 with a radius of 6 mils and 30 mils from a point on one groove to the corresponding point on the adjacent groove. The die faces 26 were 18 mils wide and were spaced a distance of 2 mils from the corresponding die face 26 of the opposite die lip 24. The

total width of the die lips 24 was 2 inches and there were 67 of the die grooves 25.

The as-extruded film strip 5a was melt drawn at a ratio of 4:1 to provide a melt drawn film strip 5 having a total width of about 1.5 inches and striations 29 having a total thickness of about 5 mils. The strip 5 was oriented at a draw ratio of about 6:1 to provide the oriented film strip 16 having an overall width of about 0.7 inch, having striations 31 with an average total thickness of about 1.5 to 2.5 mils and a gauge or a distance from a point on one striation to the corresponding point on the adjacent striation of 10 mils, and having webs 32 with an average thickness of 0.5 to 1.0 mil.

The film strip 16 was fed through a fibrillation device 18 comprising a cylinder 21 that was 6 inches long and had an internal diameter of 0.75 inch, and had an aperture at the center thereof that was connected to an air tube 23 arranged radially of the cylinder 21 and having an internal diameter of 0.125 inch. Air at 40 p.s.i.g. was supplied to the tube 23. There was a slight over-feed, for example, five percent, of the draw rollers 11 relative to the feed rollers 17, so that there was limited play of the film strip 16 in the cylinder 21. The film strip 16 was substantially completely reduced to individual filaments corresponding to the striations 31 of the film strip and there was no discernible migration of the splitting across any of the filaments so that all of the filaments were in fact continuous. On each filament, there was an average of about six fibrils 37 per inch, equally divided between the opposite sides thereof, which fibrils had an average cross section of about 0.5 mil compared to a filament diameter of about 3 mils, and varied in length from about inch to about Mi inch, with an average length of about /a inch.

The yarn 19 can formed of any polymer that can be extruded and drawn into an oriented striated film, for example, polyethylene, polypropylene and copolymers of ethylene and propylene.

The yarns in accordance with the method described above are substantially linear, but, for the usual reasons, for example, resilience and covering capacity, may be bulked in any conventional bulking process such as stuffing box or knife edge crimping.

The number as well as the width and length of the fibrils 37 can be controlled by control of the width of the web 28 in the film 5a, the degree of orientation, the tension on the yarn at fibrillation, the direction and velocity of the jet, the polymer characteristics and the operating or process characteristics. Generally, a wider web in the film and more linear orientation lengthwise of the web will provide a greater number of and longer fibrils. As the tension on the yarn during fibrillation is increased, the number of hairs and lengths of them are reduced because the film is afforded less opportunity to wave or vibrate relative to the air jet and thus to be worked repeatedly by the jet. When the jet is directed lengthwise of the film rather than transverse to it, the degree of fibrillation or separation is reduced.

While the film strip is herein disclosed as extruded as a strip, it will be obvious that it could be formed either as a fiat sheet or tube and subsequently slit into strips of the desired width.

While air is preferably used for the jet for the fibrillation of the film, it will be obvious that the jet may be provided by a gas or fluid other than air. It is also possible to use means other than the fluid jet type fibrillation device 18 for fibrillation of the film.

The degree of fibrillation or separation of the film into filaments under given circumstances can be increased if necessary by providing a second fibrillation device 18 arranged in tandem relative to the first device.

It will of course be apparent that the specific configuration of the striations 27 is not critical. Rather than circular as herein disclosed, they could for example be substantially diamond-shaped or square. At the same time, the striations could be single rather than double, that is, they could extend in one direction only from the web rather than in both directions from the Web 28 as illustrated in FIG. 4. In FIG. 11, there is illustrated a die lip 40 for making a single striated film, which die lip comprises a plurality of die grooves 41 adapted to cooperate with a flat or straight die lip 42. The single striated film has the advantage that it can be cooled by running it over a chilled roll and can otherwise be handled by engaging the fiat face thereof without crushing or otherwise damaging the striations. Since the die grooves 41 areformed in only one of the die lips, the die lips are less expensive and the alignment of the die grooves 25 that is necessary in the opposed die lips 24 for making double striated film has been eliminated.

What we claim and desire to protect by Letters Patent 1. A bulky synthetic yarn having a spun-like appearance comprising a plurality of continuous longitudinallyoriented filaments of substantially uniform maximum thickness between bottom and top edges and a substantially uniform width between an opposed :pair of side edges, said yarn being characterized in that the maximum thickness of each of said filaments is substantially at the transverse midpoint thereof and the thickness decreases in both directions therefrom to a minimum thickness at the opposed side edges, each of said filaments having a plurality of fibrils integral at one end with said filaments along the opposed side edges thereof and extending to a free end, said fibrils having a thickness corresponding to the thickness of said filament at said opposed side edges.

2. A bulky synthetic yarn having a spun-like appearance and a relatively soft hand comprising a plurality of con tinuous longitudinally-oriented filaments of substantially uniform cross section along the length thereof, said yarn being characterized in that it comprises filaments having opposed side edges and a minimum thickness at said side edges and a maximum thickness intermediate said side edges, and a plurality of fibrils integral with said filament along said side edges and extending laterally therefrom to a free end, said fibrils having a thickness corresponding to the thickness of said filament at said opposed side edges.

References Cited UNITED STATES PATENTS 3,177,557 4/1965 White 2872 3,214,899 11/1965 Wininger et al. 57-140 3,273,771 9/1966 Beaumont 57140 XR 3,336,174 8/1967 Dyer et al. 28-72 XR JOHN PETRAKES, Primary Examiner US. Cl. X.R.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,470,685 Dated October 7, 1969 Inventor(s) John N. Hall and Charles W. Kim {Case 1) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 61 of the printed patent, "strips" should read -strip- Column 7, line 27, claim 1 of printed patent, after "uniform" insert -cross section along the length thereof and including a substantially uniform-- 6160.6 ,wu' SEALED (SEAL) Attest:

, M. F1 [6118]. Ire Edward WILLIAM E. SOHUYLER, JR- Attestmg officer Oomissioner of Patents

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