US 3641760 A
Foam fibrillated yarn having the appearance, hand and texture of conventional spun staple yarn may be prepared by initially forming a foam fibrillated film having narrow areas of preferential film weakness and pulling apart the film along said areas to form zones of free fibrillar ends. The film can either be completely severed into two or more bands or only internally split depending upon the character of the areas of weakness. Interentanglement of the separate bands or intratwining of the integral film containing a plurality of slits results in a yarn of spun staple quality coupled with high strength.
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Description (OCR text may contain errors)
United States Patent Keuchel  FOAM FIBRILLATED YARN AND PROCESS  Inventor: Herbert W. Keuchel, Charlotte, N.C.
 Assignee: Celanese Corporation, New York, NY.
 Filed: Mar. 7, 1969  Appl. No; 805,302
 US. Cl. ..57/157 R, 28/DIG. 1, 28/72 CS, 57/167, 264/51, 264/103, 264/147  Int. Cl ..D02g 3/02  Field of Search ..28/l F, DIG. l, 72 CS; 264/147, 51, 103; 57/34, 34 B, 140,165, 167,157, 31
 References Cited UNITED STATES PATENTS 2,954,587 10/1960 Rasmussen ..28/DIG. 1 3,402,548 9/1968 Wininger,Jr. et al.. 28/DIG. 1
2,728,950 1/1956 Annesser ..28/l F 2,853,741 9/1958 Costa et al.. ...28/l F 3,003,304 10/1961 Rasmussen ..57/157 3,081,519 3/1963 Blades et a1. ...28/1 F 3,214,899 11/1965 Wininger, Jr. et al. ..57/140 3,253,072 5/1966 Scragg et a1. ...28/1 F 3,335,560 8/1967 Ichikawa ..57/165 3,378,997 4/1968 Matsui et a1. ..57/34 1 Feb. 15, 1972 OTHER PUBLICATIONS Schulker, Jr. and Boy, Jr.; Cause of Melt Fracture; SPE Journal; April, 1960; pages 423-428 Primary ExaminerJohn Petrakes Attorney-Thomas J. Morgan, S. D. Murphy and Louis Gubinsky  ABSTRACT Foam fibrillated yarn having the appearance, hand and texture of conventional spun staple yarn may be prepared by initially forming a foam fibrillated film having narrow areas of preferential film weakness and pulling apart the film along said areas to form zones of free fibrillar ends. The film can either be completely severed into two or more bands or only internally split depending upon the character of the areas of weakness. Interentanglement of the separate bands or intratwining of the integral film containing a plurality of slits results in a yarn of spun staple quality coupled with high strength.
6 Claims, 7 Drawing Figures PATENTEUFEMS m2 3.641.760
sum 1 OF 2 INVENTOR HERBERT W. KEIJCIIEI.
\BY AM A Law/A ATTORNEY PATENTEBFEB 15 I972 3.641.760
SHEET 2 OF 2 FIG. 6
INVENTOR HERBERT W. KEUCIIEI.
v I BY ATTORNEY FOAM FIBRILLATED YARN AND PROCESS BACKGROUND OF THE INVENTION This invention relates to a process for preparing bulky yarns from synthetic polymers. Mores specifically, it relates to the preparation of bulky yarns from foam-fibrillated film.
Synthetic fibers are generally extruded in the form of continuous filaments. Although strong and durable, textile structures manufactured from continuous filaments lack certain of the highly desired aesthetic qualities of comparable articles constructed of spun yarn, such as hand, texture and loft. Fabrics constructed of continuous filaments are generally denser with less warmth per unit weight because of the closeness of alignment of adjacent filaments in such manufactured textile structures. On the other hand, fabric materials manufactured from spun yarn are noted for their fine texture, excellent hand, bulk, good covering power per unit weight, and warmth. However, the production of spun yarn is very costly and time consuming, usually entailing an initial cutting operation to form short, staple-length fibers from extruded continuous filaments and spinning the same by means of a series of complicated procedures to form a uniform, tenacious spun yarn. The spinning operation must include combining the staple fibers into an elongated funicular structure and drawing the structure to decrease its diameter while simultaneously twisting to prevent adjacent fiber slippage.
The prior art has also recognized that certain economic and process advantages would be present in a multifilament-forming method involving the extrusion of a film of fiber-formable material, cutting continuous, longitudinally aligned grooves along at least one lateral surface of the film and simultane' ously or subsequently drawing the film while severing it along the predetermined lines of weakness into a plurality of continuous multifilaments. However, the continuous multifilaments produced by the split film technique still lack the highly desired tactile properties of spun yarn. If desired, the film can be subjected to vigorous mechanical action for lateral fibrillation following an initial orientation and/or during a further drawing and longitudinal rupturing operation to form short, staplelength fibers characterized by a cross section substantially identical to that of the comparable continuous multifilament. Of course, the production of spun yarn therefrom must still involve the complications of the spun yarn spinning method.
Therefore, it is an object of the invention to provide a process for preparing continuous yarns having the highly desired properties of spun yarn. Another object of the invention is to provide an inexpensive, continuous process utilizing a minimum of operating steps for producing a yarn comprising a plurality of continuous networks of randomly interconnected fibrils having the appearance, hand, texture, and bulk of a spun yarn. Still another object of the invention is to provide a bulky yarn characterized by high strength but having the aesthetics and appearance of spun yarn. A further object of the invention is to provide a bulky yarn which has not been twisted to obtain high tenacity nor formed of staple fibers.
Another specific object of the invention is to provide a process to prepare a yarn having the highly desired aesthetic and tactile properties of spun staple yarn utilizing a scored film technique in conjunction with a foam-fibrillation process and the product of said process. Other objects of the invention will appear obvious to those of skill in the art from the detailed description of the invention hereinafter.
In accordance with the invention, a bulky yarn having the desired qualities of spun yarn in combination with the tenacity and easy processability of continuous filaments is produced by extruding a mixture of a thermoplastic, film-forming resin and an agent which is or evolves gas at extrusion temperature, longitudinally scoring said extrudate to form a plurality of narrow coextensive foam-fibrillated bands interconnected across scored areas of indentation, preferentially severing the film along the longitudinal grooves of decreased film strength into a plurality of separate foam-fibrillated yarns having coextensive narrow peripheral zones of high bulk due to the presence along said zones of a high density of cut, free fibrillar ends and recombining at least two of said yarns into an open, interlaced yarn characterized by high tenacity, bulk, loft, and resiliency resulting from increased interentanglement of free fibrillar ends and high number of free ends disposed along the surface of the yarn.
In particular embodiments of the process, the hot melt is scored as it emerges from the die lips, the die slot being of a serrated nature with the serrations sufficiently spaced to assure extrusion of interconnected areas of suitable initial width for allowing subsequent reduction of each band to yamlike material. The extrudate can be melt-phase attenuated into connected bands, each of which comprises an interconnected network of randomly positioned fibrils, and subsequently simultaneously oriented in the longitudinal direction and split into discreet, tenacious yarns of relatively low diameter to be recombined into a coherent, bulky, and tactile spun staplelike yarn of high covering power. The component yarns, which may be drawn or undrawn, but preferably are highly oriented with the polymeric units in longitudinal alignment along the fiber axis to assure a strong structure may be conveniently recombined by passage through one or more areas of high turbulence formed by an impinging jet of air or other fluid. The fluid stream opens the individual, relatively compact fibrillated and attenuated extrudates and forms a coherent, bulky yarn bundle therefrom.
In another embodiment of the invention, in which the foamed extrudate is not melt-phase attenuated directly into a fibrillated product but is instead directly quenched below its melting or softening point following extrusion to be subsequently longitudinally oriented and converted into a fibrillated structure through mechanical action, the film can be scored following solidification such as by passage in engaging contact over a suitably profiled roller prior, during, or subsequent to orientation. Of course, process advantages are gained by scoring prior to actual drawing, i.e., the film is oriented by passage between two sets of opposed rollers, the second set rotating at a higher peripheral speed than the first to effectively draw the film, with one of the first set of rollers having a resilient contact surface and the other carrying a plurality of parallel, appropriately spaced, continuous cutting ridges around its lateral surface positioned to engrave longitudinally aligned grooves into the moving film substrate as it passes between the nip of the rollers, and with opposed sets of diverging film edge engaging members positioned immediately prior to the second set of rollers to grasp the edges of the film and impart a sufficient stress in the transverse film direction to simultaneously preferentially disassociate the film into individual bands along the predetermined longitudinal grooves during the drawing operation. The separated bands are then mechanically worked such as by passage through a tortuous path for enhanced fibrillation and formed into a composite yarn. The bulked product obtained from either of the above variations may be used in textile fabrication procedures, i.e., knitting and weaving operations, without the necessity of further treatment or added twist. The product is a coherent, opened, bulky yarn comprised of a plurality of interconnected networks of randomly positioned fibrils, said product being characterized by a higher bulk factor and density of free, fine denier surface fibrils than comparable material which has not been subdivided prior to the same bulking treatment.
DETAILED DESCRIPTION OF THE INVENTION A better understanding of the invention may be had from the drawing wherein:
FIG. I is a graphical representation of one embodiment of the process;
FIG. 2 is a graphical representation of another embodiment of the process;
FIG. 3 is a front elevation of the serrated die employed in the process depicted in FIG. 1',
101023 ()OIO FIG. 4 is a perspective view of the scoring device employed in the process depicted in FIG. 2;
FIG. is a graphical representation of a cross section of the product resulting from the process of FIG. 1 immediately after emergence from the die;
FIG. 6 is the product resulting from the process of FIG. 1 prior to orientation and severance; and
FIG. 7 is perspective view of a scoring device to engrave discontinuous grooves into a suitable substrate.
Referring to the drawing in greater detail, and particularly FIG. 1 thereof, a molten blend of polymer and foaming agent contained in extruder l is passed through a serrated die 2 so as to form a satisfactory extrudate 3 containing approximately parallel, longitudinal, coextensive grooves of preferential product weakness. The temperature of extrudate 3 is maintained at a satisfactory temperature range which is above the melting temperature of the polymeric component composing extrudate 3 by means of fork member 4. Fork member 4 subjects extrudate 3 to a flow of gas or liquid and preferably air maintained within the desired temperature range, that is to say, the flow of air may be either a heating or cooling flow of air. The attenuation of the hot-melt extrudate 3 and the resultant fibrillation takes place immediately after the extrudate leaves die member 2. It should be understood that after hot-melt attenuation, a satisfactory fibrillated end product is produced.
The product is then oriented by passage between draw rolls 5 and 6, draw roll 6 operating at a greater peripheral speed than draw roll 5 and thereby simultaneously oriented the scored film while splitting it into a plurality detached fully fibrillated yarns 7 which are then fed through interlacing jet 8 having tangential air inlet 9. The single thread line 10, resembling spun staple yarn, issuing from the jet is taken up on a suitable yarn collection device 11.
Alternatively, the molten blend of polymer and foaming agent may be extruded as shown in FIG. 2, the polymeric material being passed through extruder 21 and nonserrated die member 22 into a quenching bath 23 which contains a suitable cooling liquid. Extrudate 25 which has been substantially cooled below the melting temperature of the polymer is then first passed over scoring member 30 followed by godet wheels 26 and 27, roll 27 operating at a higher peripheral speed than roll 26 in order to draw and thereby orient extrude 25 while simultaneously rupturing the extrudate along said score lines into a plurality of separated threads 31. The oriented threads 31 are then passed through a suitable mechanical working member 28 which may be a device, such as for instance, a false twist spindle, a knife edge or a series of pin guides which lead the ruptured extrudate 31 through a tortuous path. Upon emerging from mechanical working member 28 the threads 31 are in fully fibrillated form to be formed into a coherent yarn 33 by passage through interlacing jet 32 and may be taken up upon a suitable takeup package 29.
The process of the present invention is applicable to all thermoplastic resins which can be fabricated by melt extrusion. Suitable resins include one or more polymers and/or copolymers of materials such as polyoxymethylenes, polyethylene, polyropylene, polybutene, polymethyl-Ii-butene, polystyrene, polyamides such as polyhexamethylene adipamide and polycaprolactam, acrylic resins such as polymethylmethylacrylate, polyacetals such as halogenated polymers such as polyvinyl chloride, polyvinylidene chloride, tetrafluoro ethylene, hexafluoropropylene, polyurethanes, cellulose esters of acetic acid, propionic acid, butyric acid and the like, polycarbonate resins, polyether resins and compatible and incompatible blends thereof. Resins which have been found to be especially suitable for use in conjunction with the present invention are polyethylene, polyropylene, polystyrene, and polymethyl-3-butene.
When the hot-melt extrudate is extruded into a cooling medium to lower the temperature of the polymer to below the melting or softening temperature and the extrudate subsequently oriented, it is preferred that the polymeric material and polyolefins. The polyolefin polymers include polypropylene, polyethylene, polymethyl-B-butene, and copolymers thereof.
The term orientation as employed herein may be defined in terms of birefringence or X-ray diffraction. The index of birefringence is calculated by the following formula:
Index of birefringence /d =n n,wherein d is the diameter of a single extrudate, n is the refraction index parallel to the extrudate axis, n, is the refraction index vertical with respect to the extrudate axis, and is the value of retardation as measured by polarizing microscope with a Berek compensator. Where the diameter of the extrudate is difficult to measure, or is nonuniform, the index of birefringence may be obtained by measuring the refraction index parallel to the longitudinal axis of the extrudate and perpendicular to the iongitudinal axis of the extrudate while the extrudate is disposed in an immersion fluid.
Where fibrillated products are being produced from polypropylene, it has been found that satisfactory fibrillation can be obtained by the hot-melt attenuation process of this invention employing polypropylene having at the time of fibrillation a birefringence of less than about 0.020 and preferably from 0 to 0.015. Where, however, a fibrillated product is being prepared from a foamed polypropylene which has been extruded directly into a quenching bath and thereby cooled to a temperature below the melting or softening temperature and subsequently oriented, the birefringence must at the time of fibrillation be greater than 0.020 and preferably from 0.023 to 0.035.
The degree of orientation which is required in polymeric materials other than polypropylene is best described in terms of X-ray diffraction and more specifically in terms of orientation angle. Orientation angle" is a parameter which represents the alignment of molecular axes of the material forming the extrudate with respect to the longitudinal axis of the extrudate. The orientation angles are measured according to the technique of H. G. Ingersol, Journal of Applied Physics, 17, 924 (1946) on the instrument described by .l. E. Owens and W. O. Statton, Acta Crystallographic, I0, 560 U957). In general, where fibrillated products are obtained by the hotmelt attenuation process of this invention, the polymeric material may exhibit an orientation angle of up to Where, however, a fibrillated product is prepared by extruding directly into a quenching bath and thereby cooling to a temperature below the softening temperature, the polymeric material must exhibit an orientation angle which is an acute angle and preferably an angle of not greater than 55 and still more preferably not greater than 20.
The foaming agents which are useful in the extrusion of foam are known. As previously indicated, solids or liquids which vaporize or decompose into gaseous products at the extrusion temperatures, as well as volatile liquids, may be employed. Solids which are suitably employed in the process of the present invention include oxalic acid, azoisobutyric dinitrile, diazoamino benzene, 1,3 bis(p-xenyl) triazine azodicarbonamide, and similar azo compounds which decompose at temperatures below the extrusion temperature of the forming composition. Commonly used, solid foaming agents producing either nitrogen-containing gases or carbon dioxide include sodium bicarbonate and oleic acid, ammonium carbonate and mixtures of ammonium carbonate and sodium nitrite. Liquids which are suitable foaming agents include water, acetone, methyl ethyl ketone, ethyl acetate, methyl chloride, ethyl chloride, chloroform, methylene chloride, methylene bromide and, in general, fluorine containing normally liquid volatile hydrocarbons. Foaming agents which are the normally gaseous compounds such as nitrogen, carbon dioxide, ammonia, methane, ethane, propane, ethylene, propylene, and gaseous halogenated hydrocarbons are also desirable. A particularly preferred class of foaming agents are fluorinated hydrocarbon compounds having from one to four carbon atoms, which in addition to hydrogen and fluorine, may also contain chlorine and bromine. Examples of such blowing agents are dichlorodifluoromethane, dichlorofluoromethane, chlorofluoromethane, difiuoromethane, chloropentafluoroethane, 1,2-
dichlorotetrafluoroethane, 1 ,1-dichlorotetrafluoroethane, l ,l ,Z-trichlorotrifiuoroethane, 1 ,1 ,1 -trichlorotrifluoroethane, 2-chloro-1,1,1trifluoroethane, 2-chlorol ,1 ,1 ,2- tetrafluoroethane, 1 -chloro-1 ,1 ,2,2-tetrafluoroethane, 1 ,2- dichloro-l,1,2-trifluoroethane, 1-chloro-1,1,2- trifluoroethane, 1 -chloro-1 l -difluroethane, perfluropropane trifluoropropane, l-fluoropropane, 2-fiuoropropane, fluoropropane, 2 -fluoropropane, 1,1 ,1,2,2-pentafluoropropane, 1,1,l,3,3-pentafluoropropane, 1,1,l,2,3,3- hexafluorop ropane, 1, l 1 trifluoro-3chloropropane, trifluoromethylethylene, perfluoropropene, and perfluorocyclobutene.
The quantity of foaming agent employed will vary with the density of foam desired-a lower density requiring a greater amount of foaming agentthe nature of the thermoplastic resin foamed and the foaming agent employed. In general, the concentration of the foaming agent will be from 0.001-5 lb. moles/100 lbs. of the thermoplastic resin.
FIG. 3 in cross-sectional view shows the serrated die orifice 40 of die 2 having a plurality of uniformly aligned teeth 41 jutting downwardly into the orifice and spaced equidistantly along the upper die lip. These scoring members longitudinally groove the melt-attenuatable extrudate as it emerges from the die to be subsequently melt-phase fibrillated followed by splitting into distinct fibrillar yarns, if desired during orientation, and reformed into a coherent article. FIG. 5 illustrates the cross section of extrudate 3 as it issues from the die containing parallel, longitudinally aligned indentations 47 resulting from the application of scoring members 41. FIG. 6 represents, also in cross-sectional view, extrudate 3 as a fully fibrillated product having been melt-phase attenuated, but prior to the drawing operation. The extrudate is comprised of an interconnected network of fibroid segments 49 characterized by the substantial absence of flat or planar surfaces on cross section; that is, the individual fibrils do not exhibit the typical trapezoidal configuration on cross section of fibrils resulting from a fibrillated process in which a film is highly oriented in the longitudinal direction prior to mechanically induced fibrillation. Due to the compaction occurring during the scoring operation, areas of high density fibrillation are present beneath and adjacent the areas of indentation. During the longitudinal rupturing into discrete threads, the area of severance is concentrated below the deepest point of penetration into the extrudate occurring during scoring. Thus, the high density fibrillar area containing closely compacted, intertwined fibrillar segments is broken apart forming a large number of free ends. Each individual thread is then characterized by at least one coextensive area of high frequency of free fibrillar ends which aid interlacing during subsequent recombination as well as increasing crush resistance, loft, and tensile properties of the final product.
FIG. 4 is a detailed view of the scoring device 30 employed in the embodiment of the invention depicted in FIG. 2. Parallel cutting ridges 45 score the quenched film before passage to the drawing zone consisting of draw rolls 26 and 27.
A better understanding of the invention may be had from the following specific examples. It should be understood, however, that the examples are given for purposes of illustration and are not considered as limiting the spirit or scope of the invention.
EXAMPLE 1 Polypropylene polymer pellets (marketed by Hercules Company under the trademark Profax) 1.7 intrinsic viscosity are dry-blended with 1 percent of azodicarbonamide blowing agent. Blending is carried out in a tumbling vessel for minutes. The blended polymer is then loaded into an extruder having a chrome-plated single fluted uniform pitch screw, the extruder being fitted with a die of the horizontal ribboned type having a 2 inches 0.020 inch serrated slit. The serrations are seven parallel, triangular planar teeth which depend 0.010 inch from the top of the slit at equidistant spacing to sever the extrudate into A inch ribbons. The die is equipped with a 500- watt electric band heater. The polymer is extruded at a throughput rate of 2.5 grams per minute. The extruded sheet is maintained at temperatures above the melting temperature by means of a quench fork, the quench fork having tubes disposed on either side of the extruded film. The tubes have air orifices disposed therein, said orifices having a diameter of 0.04 inch, the orifices being spaced 0.125 inch apart, each tube containing two rows of orifices 60 apart. The extruded film is passed over a first roll at a speed of 25 to 35 meters per minute. At this point, a fibrillated product is obtained which is in a substantially undrawn, unoriented condition. The undrawn, unoriented, fibrillated polypropylene material is subjected to a simultaneous drawing and severing operation, the drawing operation being carried out by passage over a shoe heated to 130 centigrade and then taking the resultant eight fibrillated threads as distinct units over a roll having a winding speed of about 70 to 100 meters per minute.
EXAMPLE 2 Profax polypropylene (marketed by Hercules Company) having an intrinsic viscosity equal to 1.7 is blended with l percent azodicarbonamide blowing agent. The blended mix is then placed in a National Rubber Machinery extruder employing a screw 12 inches long and 1 inch in diameter. The extruder is equipped with a die for vertical extrusion, the die having a circular opening which is nine-sixteenths inch in length, one-half inch in diameter and approximately 1.6 inches in circumference. The rear temperature area or zone 2 is also maintained at 210 while the diehead is maintained at a temperature of 240 centigrade. The hot-melt is extruded into a water quenching bath, the die-head being disposed 10 inches above the surface of the water. The extrudate upon contacting water is cooled to a temperature below the melting temperature of polypropylene and is then passed under a snubbing pin disposed beneath the surface of the water in order to attenuate air voids in the extrudate. The extrudate is then withdrawn from the water quenching bath, slit into a flat film 1.6 inches in width which is scored into 0.4 inch interconnected ribbons by passage over an appropriate longitudinally ribbed shoe. The scored extrudate is then passed over a series of godet wheels at a takeup speed of 200 meters per minute whereby the polypropylene is oriented while the film is severed into four individual threads. The oriented material is then led around a series of pins which are disposed so as to force the slit and ruptured extrudate to travel through a tortuous path and thereby induce fibrillation. The fibrillated product is then taken up on a suitable takeup package as distinct 0.4 inch units.
EXAMPLE 3 Celcon M-25 (polyacetal resin marketed by Celanese Corporation) is blended with 0.7 percent of azodicarbonamide blowing agent. The blended material is then placed in a National Rubber Machinery extruder, the extruder being equipped with a screw 12 inches long and 1 inch in diameter. The rear portion, or zone 1 of the extruder is maintained at 200 centigrade as is the front portion or zone 2 of the extruder. The die-head is maintained at a temperature of 200 centigrade and the hot melt vertically extruded through a die having a serrated circular opening, the opening being nine-sixteenths inch in length and 1 inch in diameter and having V4- inch teeth spaced equidistantly around its perimeter. The
polyacetal extrudate is quenched by passage beneath an immersion roll disposed beneath the surface of the aqueous quench bath and then slit into a flat film and taken over a plurality of godet wheels at a speed of about 200 per minute. The material is thereby drawn and oriented while being severed, each continuous thread which is then sequentially passed through a tortuous path by going over a plurality of sharp edge snubbing pins in order to produce fibrillation with the separate fibrillated products wound on a suitable takeup mechanism.
The fully fibrillated products having longitudinal bands of unusually high, free-end fibrillar density produced in accordance with the above examples, and if desired along with other similar yarnlike, foam-fibrillated films, whether fully drawn or not, can be immediately subjected to the fluid jet reformation process. The degree of coherency will be determined to a great extent by the type, speed, and pressure of turbulence provided during the jet treatment step. The type of jet employed is not critical and may be selected from numerous tow opening or banding jets disclosed in the prior art. The nozzle configuration, orifice dimensions, yarn passageway-fluid inlet angle of juncture, and the like jet characteristics will be those of jets obvious to those of skill in the art. A typical configuration will be found in a rectangular jet device having a longitudinally bored cylindrical yarn passageway with a tangential fluid inlet disposed at an acute angle to the yarn passageway to affect a forward carrying motion to the individual threads in addition to the combining effect. As examples of suitable jets there may be mentioned those shown in the Hall US. Pat. No. 2,958,112.
The yarn passageways in the jet need not be of a uniform or circular cross section and may turn at a sharp angle within the jet to produce novel textured products. For instance, it may be desired to form a venturi in the yarn passageway at the point of juncture with the fluid medium inlet. in other variations, the fluid may be accurately metered in an intermittent manner or applied with an increasing or decreasing pressure to form yarns having varying cross-sectional effective areas and a degree of bulk differential along the length of the strand according to a regularly or irregularly spaced pattern.
The bulking medium is preferably air because of its low cost and availability. Other fluids in the gaseous state, such as inert gases, i.e., nitrogen, etc., and other readily available gases, for example, oxygen and carbon dioxide, are equally applicable. The fluid will generally be at ambient temperature but may be heated, i.e., steam may be employed up to the softening temperature of the yarn to give unique foam-fibrillated heat, i.e., steam, set and bulked yarns.
Air pressure will vary but will depend upon thread line speed, number of precursor threads to be combined or recombined, operating temperature, yarn tension, jet configuration, and the like process parameters. Of course, higher pressures produce a greater turbulence in the contact zone resulting in a greater opening and consequently a'higher bulked product with a high coherency factor. The essential criterion to be borne in mind is that the combining operation should not result in any substantial fibril breakage; that is, the coherent unitary network or randomly interconnected fibrils as formed remains essentially unchanged except for a recombining, and where desired, opening operation which increases void space but not specific surface area. The opening aspect of the invention is distinguished from prior art one-step, air jet fibrillation processes wherein an air jet simultaneously fibrillates and bulks an extruded and oriented ribbon. The product of the present invention where opened contains microfissures prior to bulking as a result of the foam fibrillation which are accentuated during the operation, individual fibrils becoming further apart from one another across these minute crevices but still joined as before similar to the opening of a flat rubber band up to the point prior to stretching. With such a process, the fibrils remain substantially aligned along the longitudinal fiber axis but with a high amount of fibril interlacing, particularly of the loose fibrils such as those fine denier hairs disposed on higher denier fibril surfaces and the numerous free ends developed during the severing operation. These latter fibrils may wrap completely around the bundle at random points along the strand. Various convolutions may also result throughout the yarn bundle and along individual fibrils.
The process may be employed with many modifications such as plying by passage through a high-velocity twisting jet following the combining process. For novel effects, one of the component threads may be preferentially heat shrunk or spontaneously elongated by exposure to fluids at elevated temperatures during the operation to give novel hand and bulk effects.
Considering specific operating conditions in greater detail, certain operable air pressure, air and yarn speed and yarn ten sion ranges may be stated for use with jet devices as described hereinbefore, that is, an axial bore having a slightly greater diameter than required for the total number of thread ends with a tangential air inlet entering therein at an acute angle. Extreme pressures are generally not required since the object is only to recombine with possible opening of the yarn and not to physically cut fibrils or sever the interconnected network at any point. Higher pressures will be required as yarn speed is increased because of decreased yam-fluid contact residence time.
Likewise, air speed would also have to be higher under such circumstances. Under thread line speeds of between about 10 to 1,000 meters per minute, air velocity is desirably of the order of 250 to 2,000 feet per second under a pressure of about 25 to pounds per square inch. With such conditions, yarn tension will vary between about 20 to 40 grams.
Preferred process conditions will entail the employment of air at relatively low pressures because of the increased cost and bulkiness of pressurized containers. Therefore, with an air pressure of about 35 to 40 pounds per square inch and a yarn running speed of about 220 to 275 meters per minute under a tension of about 30 grams using conventional jet devices, preferred bulky coherent foam-fibrillated yarns are produced.
As noted hereinbefore, jet design will vary, it being necessary only to determine the other optimum processing parameters, which themselves are limited to an extent by available takeup equipment, for a desired degree of coherency. Other nozzle configurations fully operable within the scope of the invention, without limiting the process thereto, are the Hardy Airguide US. Pat. No. 2,l9l,79l, the jets of Breen US. Pat. No. 2,783,609 and multiple jets operating in tandem on sequence on the same segments of the fibrillate, such as pneumatic false twist devices or alternating 8" and Z" twist jet systems.
EXAMPLE 4 The jet device used in this example is a 2 k-inch-long rectangular block with a Vs-inch-diameter bore centrally positioned along its longitudinal axis which is countersunk 45 degrees at both ends. At the midpoint along this lr-inch-yam passageway, and at one third inch to either side are sets of three air inlets of 0.0625 inch diameter spaced equidistantly with spacing around the periphery of the yarn passage way which enter the same at 90 angles. The jet is positioned vertically with the 8 untwisted drawn threads of Example I being fed simultaneously upwardly through the jet ofi a single spindle rotating at a constant value to give a thread line speed varying between 231 meters per minute initially to 363 meters per minute at the conclusion of the run. Individual thread line tension both below and above the jet is set at 30 grams with a winding tension of grams. Air pressure is at l00 pounds per square inch with velocity adjusted accordingly. The coherent, opened yarn should have a higher coherency factor as determined by a coherency entanglement test as well as a higher number of free fibrillar ends disposed along the yams length for a soft hand and increased loft unobtainable in the absence of additional processing if comparable as formed foam-fibrillated yarns are combined instead of threads disconnected from a unitary structure as disclosed herein. Coherency may be determined by tensioning a selected length of yarn under a weight equivalent to a predetermined fraction, i.e., two-tenths of the average filament denier in grams, inserting a selected needle through the yarn with at least one-third of the fibrils on each side of the needle, increasing the yarn tension until it equals the average fibril denier in grams and altarmeasuring the distance the yarn has travelled over the needle, a shorter distance indicating a higher coherency factor with comparative testing.
EXAMPLE Example 4 is repeated with the component threads of Examples 2 and 3 with equally good results.
The above examples are representative and it should be realized that other longitudinally ruptured, foam-fibrillated products may be air jet combined in a similar fashion.
As stated hereinbefore, various modifications, many of which will appear obvious to those of skill in the art, may be made within the scope of the invention. For example, the threads prior to air opening may be loosely plied with a fibrillatable, oriented film highly drawn in the longitudinal direction which has been pretreated for preferential fracture during passage through the fluid jet, e.g., being partially pierced at a plurality of closely spaced points by passage between two opposing rotatable wire brushes. During combining and opening of the foam-fibrillated yarn, the film is simultaneously fibrillated with many of the fibrils thereof being interentangled, interlaced, and otherwise intermingled with those of the foam-fabrillated components to form a tenacious coherent yarn exhibiting increased strength due to the presence of relatively long, continuous, axially aligned fibrils of the mechanically fibrillated film in conjunction with the loft and tactile properties of spun staple yarns. Where desired, the degree of mechanically induced fibrillation may be regulated to cause splitting of the oriented film with minimal entanglement between dangling fibrils of the foam-fibrillated and mechanically fibrillated substrates, i.e., employ sufficientair pressure, adjusting other operating parameters accordingly, to fibrillate the film and cause interlocking of discontinuous fibroid segments thereof into the foam-fibrillated materials without appreciable disturbance of the internal core areas of the substrates. The resulting composite resembles a multicomponent conjugate yarn with the interfaces being the areas of interlocking of the dangling mechanically fibrillated fibrils into the foam-fibrillated substrates with the components being in generally coextensive, eccentric association.
Similarly, in another modification of the invention which may be considered as one of the preferred embodiments thereof, two or more previously ruptured foam-fibrillated yarns are simultaneously fed to the inlet of a single fluid jet with at least one of the yarns being unopened. During passage through the air jet, fibrils of each yam become interentangled with fibrils of other yarns forming a composite yarn bundle characterized by a unitary, coherent fibrillar structure. With proper regulation of opening process parameters, particularly yarn residence time, fluid pressure, yarn tension, and number and spacing of fluid inlets, novelty yarns heretofore requiring ply twisting are obtainable. For instance, a composite yarn as prepared herein can display distinct surface zones along its length of each component yarn such as in the case of plytwisted structures as opposed to a homogeneous composite wherein there is a uniform blending of all component yarns throughout the composites length and cross section. This results, in part, from the higher number of individual fibrils in random association present in foam-fibrillated materials, in addition to the numerous free ends from the severing operation, than in mechanically fibrillated film allowing less fluid penetration into the internal core areas of the foam-fibrillated yarn than with the loosely or less tightly structured, multifilamentlike, mechanically fibrillated materials under the same operating conditions. The interentanglement with foam-fibrillated yarns occurs, firstly, preferentially along peripheral yarn regions without appreciable intermingling of one yarn into the core areas of adjacent yarns and secondly, with intermingling of entire segments of yarn with each other in the form of convolutions and the like looped about one another. in areas of extreme turbulence, yarn breakage occurs with the twisting of broken fibrils as a unit around adjacent yarn segments. The
net result is a composite yarn displaying repeated discrete segments of individual component yarns in random arrangement intermittently along its length. This construction enables the economical and high-speed production of unusual novelty yarns depending upon the type of effect desired and/or component threads selected. For example, threads chemically pretreated between severance and recombination to absorb varying levels and/or different dyes can be united into a coherent, opened yarn bundle and subsequently passed through a succession of individual dye baths to give a novelty yarn displaying bands of color corresponding to the individual dye baths throughout its length. in other comparable applications, threads characterized by different thermal shrinkage and/or thermal elongations, i.e., spontaneously elongatable or differentially shrinkable yarns, may be prepared by coextruding in the foam-fibrillation process coextensive film-forming materials displaying such thermal differential properties at preselected, longitudinally coextensive areas across the width of the extrudate. The extrudate is then scored approximately along the line of connection between different fiber-forming substances, ruptured, then recombined and exposed to chemi cal and/or physical activating treatments to produce yarns having a high crimp level. Numerous combination treatments may be employed to produce composite yarns displaying intermittent or regularly spaced-apart areas of different color, bulk, texture, loft and the like, all in accordance with the teachings herein.
Likewise, other methods to produce the longitudinal areas of preselected extrudate weakness may be employed. For example, instead of scoring and/or indenting devices, various types and degrees of chemical energy may be directed along the films surface to produce such areas, i.e., the extrudate may be passed under narrow intense beams of radiant energy. Further, the zones of severance need not be of a continuous nature but can be discontinuous as long as splitting along the preselected path is maintained.
In one particular aspect of the invention in which discontinuous zones of severance are formed in the substrate, i.e., the discontinuous ridged roller of FIG. 7 is employed to engrave the substrate, sufiicient stress is exerted during the splitting operation so that the fibrillar substrate is severed only along the discontinuous score lines. In this case, the substrate retains its overall structural integrity but is characterized by a plurality of internal longitudinal slits, the inner periphery of each slit being essentially composed of free fibrillar ends. Following free-end formation, the fibrillated substrate need only be intratwined or bunched such as by passage through an air jet operating under relatively low pressures and velocities, to form a coherent yarn of spun staple quality. During yarn formation, intralacing involving coiling and intraentanglcment of fibroid segments as well as free ends occurs resulting in a yarn containing areas of free fibrillar ends along its surface as well as partially or entirely within the core area of the yarn,
the latter functioning as yarn strengthening components. In practice, the areas of free fibrillar ends are so numerous that discrete areas of higher surface texture are not discernible to the eye along the surface of the yarn but the yarn has an overall uniformity of surface character similar to spun staple.
With the employment of the composite yarn process techniques disclosed herein, it is possible to produce coherent, highly fibrillated yarns of relatively fine fibril denier because of the inclusion within the product of the foam-fibrillated substrates. When oriented films are fibrillated according to conventional teachings, initial mechanical action transversely ruptures the film in a random fashion producing relatively high denier fibrils associated in a random but coherent structure. Additional mechanical working does produce fibrils of finer denier but destroys the unitary, coherent nature of the yarn. In fact, once the mechanically induced fibrils have been reduced to the degree of fineness found in foam-fibrillated yarns, structural coherency is destroyed and the yarn resembles a conventional multifilament structure. The composite yarns as described herein exhibit the ideal combination of desired physical properties of both components, namely, the tactile properties of finer denier foam-fibrillated yarn with the tenacity of multifilamentlike, mechanically fibrillated materials.
The product of the invention may be directly employed in the fabrication of high quality textile structures without added twist being given to the tenacious strand. At times, if subjected to vigorous manufacturing, i.e., knitting and weaving operations, 3 low twist in either 2" or S direction may be given to the strand for increased strength. In any event, a much lower twist of the order of 0.5 to 6 turns per inch is required to provide a strand having a strength comparable to that of high twist spun staple yarns.
When the yarn passageway includes an abrupt angle or if the yarn is subjected to a sharp turn upon exiting from the jet, it may be desirable to overfeed the yarns to avoid tight yarn contact with the jet face. in such instance an overfeed of about 1 to 10 percent as calculated by feed roll-take-up roll take-up roll is sufficient. In some instances it may be desirable to allow such contact, particularly if a sharp edge is involved to impart a helical crimp configuration in the yarn.
The bulked strands, as exemplified by the examples hereinbefore, will possess a tenacity of about 0.5 to grams per denier at about 16 to 100 percent elongation at the break, Modulus will be in the range of about 12 to 45 grams per denier. Preferred foam fibrillated yarns as prepared herein possess a tenacity of about 1.5 grams per denier at 75 percent elongation with an l8 grams per denier modulus and, as all others, are characterized by the substantial absence of nonplanar sur faces. Such products possess a total denier in the range of 100 to 100,000 and, preferably depending upon use, i.e., continuous or staple tow, about 200 to 6,000, with the denier of individual fibrils being about 5 to 20 d.p.f., and usually about 6 to 15.
The lack of planarsurfaces, and particularly the trapezoidal cross section of prior art mechanically fibrillated products enables the preparation of fabrics having a softer hand, added warmth, increased crush resistance and higher loft because of the rounded profile of the strand as opposed to the flatlike surfaces of other comparable products of similar number of filaments or fibrils and total and individual fiber denier. Strand diameter is also higher, particularly with respect to spun staple yarns because of the bulked rounded profile.
The enhanced interentanglement and softer hand as compared to the composite products as disclosed in copending, commonly assigned application, Ser. No. 779,644, filed Nov. 27, 1968 of the same inventor are distinct advantages flowing from the present process. Comparable coherency factors and tactile properties would be obtainable only through additional processing involving extreme mechanical working prior to jet treatment and/or application of violent force along the composites surface regions to preferentially open the yarn along its surface and further fibrillate these regions.
Thus, the novel yarn produced by the process of the invention is inexpensive, of high quality, and readily processable on automated knitting and weaving equipment into quality fabrics competitive with higher cost textile materials.
The process is a method for advantageously converting foam-fibrillated products of enhanced physical properties into high quality yarns having the appearance of spun staple without diminution of strength.
Numerous modifications within the scope of the invention will appear obvious to those of ordinary skill in the art.
What is claimed is:
l. A process for producing a coherent, composite, fibrillated yarn comprising a plurality of foam-fibrillated materials which comprises extruding and scoring a mixture of a thermoplastic resin and an agent that foams at about extrusion temperature, wherein the extrudate is scored as it emerges from the extrusion die, said extrudate is subsequently meltphase attenuated into a substantially fully fibnllated material having at least one narrow area of predetermined preferential film rupture along at least one film surface, severing said film along said area to form at least two distinct foam-fibrillated materials having a plurality of free ends along said region of severance and recombining said materials into a coherent yarn.
2. The process of claim I wherein there are a plurality of said score lines in approximate parallel relationship arranged longitudinally along one of said film surfaces.
3. The process of claim 2 wherein said scored fibrillated film is produced by extruding and scoring said mixture of a thermoplastic resin and an agent that foams at about extrusion temperature through a serrated die, said extrudate is then drawn at a draw ratio sufficient to simultaneously split said film along said longitudinal score lines and said resulting distinct foam fibrillated materials are formed into a composite, coherent yarn by passage through a zone of fluid turbulence.
4. The process of claim 3 wherein said thermoplastic resin is polypropylene.
5. The process of claim 3 wherein said yarn is opened during passage through said zone of fluid turbulence.
6. A process for producing a hot melt fibrillated yarn of spun staple yarn appearance comprising extruding and scoring a mixture of a thermoplastic resin and an agent that foams at about extrusion temperature, wherein the extrudate is scored as it emerges from the extrusion die, said extrudate is subsequently melt-phase attenuated into a substantially fully fibrillated material having a plurality of narrow areas of predetermined preferential film rupture along at least one film surface, each of said areas having at least one end which terminates internally of said film, splitting said film along said areas to form a foam-fibrillated film having a plurality of slits, the internal peripheral areas of which are characterized by free fibrillar ends and intratwining said film to form a yarn.