US3256258A - Fibers - Google Patents

Description

June 14, 1966 A. J. HERRMAN 3,256,258

FIBERS 4 Sheets-Sheet 1 Filed May 5. 1961 FIG. FIG.2

INVENTOR ARTHUR JOHN HERRMAN Y *MLQQLVL.

ATTORNEY June 14, 1966 A. J. HERRMAN FIBERS 4 Sheets-Sheet 2 9 zizaziu 8 mdzl ICSINVENTOR ARTHUR JOHN HERRMAN HJINQG ISHVHS BY ),.W-

ATTORNEY June 14, 1966 J, HERRMAN 3,2565258 FIBERS 4 Sheets-Sheet 5 Filed May 5. 1961 FIG. 4

so so ELONGATION,

o' Hum ARTHUR JOHN HERRMAN BY w- ATTORNEY June 14, 1966 A. J. HERRMAN FIBERS 4 Sheets-Sheet 4 Filed May 5, 1961 EOUATOR FIG.6

INVENTOR ARTHUR JOHN HERRMAN ATTORNEY United States Patent O 3,256,258 FIBERS Arthur John Herrman, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Filed May 5, 1961, Ser. No. 108,001 4 Claims. ((31. 260-937) This invention relates to fibers and, more particularly, to elastomeric fibers of polypropylene.

Much effort has been expended heretofore in attempting to make fibers from synthetic polymers having many of the desirable attributes of fibers made from natural rubber without the disadvantages of natural rubber fibers. Results have been varied but, on the whole, these attempts have not been too successful. Usually, fibers have had extremely low moduli of elasticity in the regions of the elongation used in most applications of fibers. That is, the fibers were characterized by a very low stress at useful elongations and, hence, required heavy denier fibers to provide suitable resistance to elongation. The problem of getting a fiber with, in laymans language, some elasticity but not a ruinous amount, persisted.

Not only have the heretofore proposed polymers been lacking in desired degree of elasticity when formed into fibers but the solutions proposed have involved polymers whose production was quite expensive and difficult to control.

Fibers from highly crystalline, high molecular weight polypropylene are well known. Although some of these fibers have ben described as highly elastic, useful elastic fibers of propylene have nevertheless not been forthcoming and, in general, the problem of producing useful elastic polypropylene fibers and the like has been just as difficult as when using other synthetic polymers.

An object of this invention is to provide new fibers of polypropylene. A further object is to provide such fibers having a suitable balance between elasticity, i.e., recovery [from elongation, and a useful degree of resistance to elongation. A more particular object is to provide fibers of polypropylene adapted for a wide variety of uses in which some degree of elasticity is highly desirable, such as auto seat covers, covers for lawn chairs, carpets, and hose. Other objects will be apparent from the description of this invention given hereafter.

The above objects are accomplished according to the present invention by forming fibers of polypropylene whose physical structure is characterized by gamma orientation and a heat-stable orientation angle of 10 to 30. In a preferred form, the invention comprises a fiber of polypropylene having a gamma intensity ratio of at least 1.0 and a heat-stable orientation angle of 10 to 21".

It has been found that fibers of polypropylene whose physical structure is characterized by gamma orientation and a heat-stable orientation angle of 10 to 30 possess a highly favorable combination of properties, including good recovery from elongation. Such fibers have the following properties: a tenacity of at least 0.8 grams per denier, an elongation at break of from 100% to 700%, a tensile recovery on the second and the succeeding cycles from a 25% elongation of at least 82%, a compliance ratio (5% to 30% elongation) of from 2 to 15, a stress at 5% elongation of between 0.1 and 0.8 grams per denier, and an initial modulus of 5 to about 25 grams per denier.

In the preferred form of this invention wherein the fiber of polypropylene has gamma orientation, a gamma intensity ratio of at least 1.0, and-a heat-stable orientation angle of to 21, the fiber has a tensile recovery on the second and succeeding cycles from a 25% elongation of at least 85% and, as shown in the examples, may be above 90%.

"ice

For purposes of clarity and definiteness, certain terms used in describing the invention are defined below. They are used throughout the specification and claims as defined.

Orientation angle is a parameter which represents the alignment of molecular axes of the material forming a fiber with respect to the fiber axis. The orientation angle is indicated by the azimuthal extent of the intensity of the (040) X-ray diffraction are at 20=16.7. These indices are used according to G. Natta et al., Atti accad. nazl. Lincei, Rend. Classe si. fis. mat. e nat. [8] 21, 365 (1956). The orientation angles are measured according to the technique by H. G. Ingersol, Journal of Applied Physics, 17, 924 (1946), on the instrument described by J. E. Owens and W. O. Statton, Acta Crystallographica, 10, 560 (1957). This angle using the (040) are is a measure of crystallite orientation with respect to the fiber axis (C axis).

Gamma orientation is the unusual orientation or condition of material in an object which is detected by X-ray diffraction techniques by a diffraction pattern in which the diffraction are at 26=14.0 exhibits intensity maxima at an azimuthal angle greater than 50 from the equator. The intensity maxima has a ratio greater than 0.6 when compared to the intensity maxima of the (022, 122) X-ray ditfraction are at 20:28.6. This ratio (I'y/Iot), is determined from a radial photometer trace obtained 10 from the meridian on the Leeds and Northrup Knorr-Alber model 6700-P-l microphotometer with 0.01 mm. slit width and 1.5 mm. slit length. The peak intensities of the maxima are determined above the background scattering in the following manner: For the peak at 20:14.0" a straight line is drawn on the photometer trace connecting the intensity values at 26:93 and 20=ll.3; this sloping straight line is extended. under the peak and the intensity value of this line at the peak 20 position is used as the background value and subtracted from the peak value to give a quantity, 1 For the peak at 20=28.6 a sloping straight line is drawn connecting the intensity values at 26:26.0 and 312; the value on this line at the peak position is subtracted from the peak value to give a quantity, Ia.

Oriented fibers having a gamma intensity ratio (I'y/Ia) of less than 0.6 are designated as having normal orientation hereinafter. Oriented fibers having a gamma intensity ratio greater than 1.0 are preferred.

By the term potential gamma orientation is meant a structure that will show gamma orientation upon drawing to 1 to 2.5x and heating 10 minutes at C.

By the term heat-stable, used in connection with polypropylene in the gamma condition, is meant that the orientation angle does not change more than 8% upon heating at a temperature of 135 C. for 10 minutes.

By the term tensile recovery which is hereafter designated TR, is meant the percent of the elongation a fiber recovers after an elongation (stated as a subscript to the TR designation) at a rate of 100% per minute, being held at the maximum elongation for 1 minute and then being permitted to recover at the rate of 100% elongation per minute. Unless otherwise designated, the 'TRs used herein to describe the invention are obtained from the second cycle on a tester 1 minute following the recovery from the first test after reclamping the fibers.

By compliance ratio, hereafter designated CR, is meant(compliance at 30% elongation-compliance at 5% elongation)/ 5 which may be expressed as C ao 5) 5 Where L and L ar the stress in grams per denier at the respective elongations. It will be noted that a high com- =2 pliance ratio tends to indicate a fiber relatively easy to elongate 30% but requiring almost as much effort to elongate %a rubber band would be an extreme illus tration. On the other hand, a low compliance ratio tends to indicate a fiber relatively difiicult to elongate 30% but substantially easier to elongate 5%.

Initial modulus, hereafter designated Mi, is obtained by a straight line extrapolation of the initial portion of the stress strain curve from 0 elongation to 100% elongation. It is expressed in grams per denier, hereafter designated g.p.d. Tenacities and elongations at the break are expressed in the usual units of g.p.d. and percent, respectively, and are measured on dry samples of yarns.

Polypropylene adapted for use in making the fibers of this invention, is highly crystalline as shown by sharp and distinct X-ray diffraction patterns and should preferably show a stiffness of greater than 120,000 pounds per square inch when prepared in test bars according to ASTM test D-747. The polypropylene can be of any high molecular weight polymer characterized by a melt index (ASTM standards, 1958 D1238-57T, part 9, page 38) of 0.1 to 200, preferably 0.5 to 30. The preferred range affords products with significantly superior elastic properties.

The term inherent viscosity as used in the examples is defined as: ln(n),/c wherein c is the concentration in grams (0.10) ofthe polymer in 100 ml. of the solvent (decahydronaphthalene), (n) is .the relative viscosity which is the ratio of the flow times in a visoosimeter of polymer solution and of the solvent, both at 130 C. An antioxidant (0.2%) is normally added to both the polymer solution and the solvent.

The present invention resides in fibers of polypropylene as herein characterized and not in any particular method of preparing such fibers. However, preparation of the fibers does, in general, involve consideration of three critical areas which are discussed below specifically in terms of fibers for purposes of simplicity and clarity.

1. Spinning c0nditi0ns.The extrusion of the fibers should be'under such conditions so as to afford gamma orientation or potential gamma orientation. The spinning variables are adjusted to regulate the viscosity of the polymer melt as extruded through the spinneret hole, and the viscosity of the fiber as it changes from the molten to the solid state in the threadline. Under any one set of conditions of polymer type, spinneret orifice dimensions, the number of orifices and polymer throughput, gamma or potential gamma orientation is achieved through temperature regulation and windup speed. The temperature will be a function of the temperature of the molten polymer before being extruded, the rate of extrusion, the geometry of the spinneret, the extent of cooling or heating on the spinneret by outside heat or quenching air. A cooling air quench may be used as the fibers form to assist with the proper temperature control.

2. Orientati0n.The fiber should be oriented to an extent giving an orientation angle of to'55 by suitable selection of spin stretching under suitable quenching conditions (i.e., windup speed/calculated speed of polymer leaving the orifice) and/ or suitable drawing of the solidified fiber. The drawing can be done under any suitable conditions but the draw ratio must not exceed 2.5 X. Preferred products are made without drawing.

3. Heat treatment.This step is essential to the development of useful recoveries from tensional deformations in polypropylene. With fibers prepared under optimum spinning conditions (so that no separate drawing step is needed) a temperature of 105 to 160 C. can be used for useful products. For the best products, a temperature of from 130 to 140 C. should be used.

This treatment on fibers having gamma orientation produces a heat-stable orientation angle of 10 to 30, providing the fiber has an orientation angle between 10 and 55 before the heat treatment.

The fiber preferably is in a free-to-shrink condition dur ing the treatment, the amount of relaxation (shrinkage) by the treatment usually varying from 1 to 50%.

The time of treatment is not critical and can range from 0.6 second to 24 hours. The heating can be done as a distinct separate process as in an oven or an autoclave or it can be conducted continuously.

The following examples illustrate specific embodiments of the invention. Reference is made to the accompanying drawings wherein:

FIG. 1 is a schematic showing of a fiber spinning and treating apparatus suitable for producing the fibers of this invention;

FIG. 2 is an enlarged side elevation of a spinneret and quenching apparatus suitable for producing the fibers of this invention, shown partly in vertical section for purposes of illustration;

FIG. 2a is a section on the line 2a2a of FIG. 2;

FIG. 3 illustrates stress-strain curves for various fibers of Examples I, II and III;

FIG. 4 illustrates two stress-strain curves showing the difierence in behavior of a fiber in the first and second cycles on a tensile recovery tester;

FIG. 5 is a graphic representation of an X-ray diffraction photograph illustrating gamma-type orientation which characterizes the polypropylene of which the shaped articles of this invention are composed;

FIG. 6 is a graphic representation of an X-ray diffraction photograph illustrating the normal orientation characteristic of the polypropylene in heretofore known shaped articles.

EXAMPLE I Crystalline polypropylene of melt index 0.7 (inherent viscosity of 2.75) (Profax made by the Hercules Powder Co., Wilmington, Delaware) is extruded as a melt at 289 C. through a spinneret 9 at 238 C. (spinneret temperature measured at the surface) using the apparatus of FIG. 1 wherein the solidified yarn is advanced over the feed rolls 3 and 4 rotating at 45 yards per minute (y.p.m.) then over the draw rolls 5 and 6 rotating at the same speed, and is finally wound up on a package 7. The spinneret 9 contains 34 orifices of 0.015 inch in diameter arranged in a rectangle one inch by 7 inch in a staggered disposition. As indicated generally by A in FIG. 1 and shown in detail in FIGS. 2 and 2a, a quenching apparatus is disposed perpendicularly to the face of the spinneret 9. The quenching apparatus comprises a inch outside diameter tube 10 containing a plurality of inch diameter holes adapted to direct air against the walls of cylindrical chamber 11 in which it is mounted, except the wall facing the threadline. On the wall facing the threadline, the chamber 11 is provided with a ZOO-mesh screen 12. Air forced through the tube 10 strikes the solid walls of chamber 11 and is deflected therefrom through the screen wall 12 facing the threadline against the threadline. Air is supplied to the tube 10 at 1.8 cubic feet per minute. The as-spun yarn wound up on the package '7 has a total denier of 1409, an orientation angle of 22, gamma orientation, and a gamma intensity ratio of 1.5.

Physical properties of a sample of this as-spun yarn without further treatment are measured and set forth as item IA, Table I. The yarn has not been given a heat treatment and, as a consequence, the angle of orientation is not heat-stable. A second sample of this yarn is skeined and treated in an air oven for 10 minutes at C. After this hot relaxation step the fibers have a heat-stable orientation angle of 20, gamma orientation and a gamma intensity ratio of 3.1. This is an example of the preferred form of this invention and its physical properties are reported as item IB, Table I. The initial modulus (Mi), tenacity, and elongation are all given for one stress-strain test from zero elongation to the break for each sample. FIG. 3 of the drawings shows the stressstrain curves for samples IA and IB. Sample IA had a CR of 7.2 while IB had a CR of 9.1.

Items IA and IB are identical except that IE was heat relaxed. Table I shows that both samples have quite similar properties except for tensile recovery. IB has an excellent TR of 92% while IA has a very poor T12 6 EXAMPLE 11 This example illustrates the effect of drawing the fiber.

So far as favorable elastic behavior in the preferred f It is Surprising that the heat relaxation p range of 85% tensile recovery and up is concerned, it applied to this yarn could so drastically alter the tensile i r f r d not t dr th fiber at all. However, some recovery property. drawing is permissible but with too high a draw ratio,

The same P y as above is extruded through a p fibers having gamma orientation and the exceptional neret having 3 orifices 0f O-OZQiIICh diameter, quenched tensile recovery of the fibers of this invention are not as above With 1 cubic feet P minute of .Weuhd P obtained. A draw ratio up to 2.5 X can be tolerated but at 525 Y-P- and then hot felaXed as above- The Y is not preferred. The procedure of Example I is rehad gamma orientation, a heat-stable orientation angle t d ith th yarn b i f d d b the feed roll of and p y properties as wn in i IQ of at 45 y.p.m. and the draw rolls run at higher speeds to Table I. ThiS iS a preferred specific embodiment of the give the various draw ratios mentioned below. invention and possess excellent (94%) tensile recovery R f i t T bl 1, it HA i a fiber drawn 2 X after elongation, seeehd Cycle in room temperature air; item IIB is a fiber drawn 4 X In this Example none of the fibers has been drawn, over a metal pin (not shown in FIG. 1) 1 inch in diamthe spinning conditions efiecting the orientation. Item IA eter t 100 C, 360 wrap) placed between the vividly illustrates that merely having an orientation angle f d 11 3 d 4 d h d 11 5 d 6; d it the defined not give the fiber of is a fiber drawn 5 X ver a metal at 60 c invention; it must be heat-stable to get the high tensile Each fib is relaxed?) by heating at 135 f 10 recovery Combined With the other high level Physical minutes in a tensionless condition and the physical propproperties which characterize these fibers. erties are then determined A peculiar characteristic of the behavior of the elastic Item HA is a fiber within the present invention but it polypropylenes of this invention is illustrated in FIG. 4 25 represents a nompreferred embodiment and as Shown shovmg two Stress-Sham h Sample used to in Table I, has a TR of 82%, the lower limit on tensile Obtain these.curv.es i i i as IB above and recovery for fibers of this invention. But as the draw was supstantlauy ldentlcal Wlth The iample Was elonratio is increased, without change in other essential congated 1n the first cycle to 50% elongatlon and then 211- lowed to recover under standard conditions It was then moms the fiber does not have.g.amma oneniatlon. and

the TR drops well below the minimum 82%- note items reclamped 1n the testlng apparatus for the second cycle HB 3 T b1 I Th h I and elongated out to the break. As FIG. 4 shows, on the an a e t e mfwentwna Practlce first Cycle the fiber Showed a CR of 5.6 as against the of drawlng to increase tenaclty and MI, must be carefully appreciably higher CR of 13.3 for the second cycle. On restricted to g the fibers thls lnventlon the third and subsequent cycles the fiber behaved as in F 3 13 shown a portlon of the stress'stram CHI-Yes the second cycle. On boiling in a relaxed condition in for ltems HE and has a CR of Whlle Water the fiber reverts to a form which gives the first the curves for the other two lndlcate very low CRs for cycle behavior for the first time and thereafter goes to both- The contrast 9 the curves for Items HB and no the second cycle type of behavior. This behavior is as Compared to HA Is y markedcharacteristic to a greater or lesser degree of the polypro- 40 6 is a graphic representation of an Y pylenes of this invention and is the reason for giving TR tiOIl photograph Of a substantial duplicate Of fiber IIB. values based on thesecond cycle. Other polypropylenes It shows no apparent gamma orientation and has 9. outside of this invention may behave similarly. gamma intensity ratio of only 0.02. On the other hand,

' Table I Orientation Physical Properties Item Total Draw Hot Ratio Relaxation Tenacity Elongation Angle Type TR25, Percent g.p.d. 22% 9122231? Ml, g.p d D.p.f.

For example, Table I gives TR values of 57% and 92% for items IA and IB, respectively; these are based on second cycle measurements. However, based on first cycle measurements, items IA and 13 show TR values of and 90% respectively. Third and following cycle measurements conform with the second cycle measurements.

FIG. 5 is a graphic representation of an X-ray diffraction photograph of the fiber whose stress-strain curves are shown in FIG. 4. This clearly shows gamma orientation and is typical of the polypropylenes of which the fibers of the present invention are composed.

fiber IIA shows gamma orientation and a gamma intensity ratio of 1.6.

EXAMPLE III The procedure of Example I is followed with the substitution of a spinneret containing one 0.030 inch diameter orifice, a quench intensity of 1.9 cubic feet per minute, and the use of the same speeds on all'four rolls to give a windup speed of the as-spun yarn of 216 y.p.m. The as-spun monofilament (item IIIA, Table I) has a denier per filament of 108 and an as-spun orientation angle of about (indicating an almost completely unoriented structure). However, it has potential gamma orientation.

A portion of the stress-strain curve of the above yarn is shown in FIG. 3 as item IIIA. It has a compliance 8 EXAMPLE v This example illustrates the preparation of five fibers, items V-A to V- E, Table III, all exemplifying preferred embodiments of this invention. These fibers have exratio of Outside the range for fibers i this invention 5 cellent tensile recoveries of at least 85 gamma orienta- After above asfspun yam 1S i l the draw tion, and heat stable orientation angles from 10 to 21. rolls are ad usted to give a 2 draw in an and the yarn The fibers of this example are not drawn deislgnated Item Table is q i g 0 Various polypropylenes are spun using the apparatus thls yam are then drawn m i gg y g fis of Example I with the feed and draw rolls adjusted so draws of 3 4 5 X l X to yle t 10 that no drawing is performed and an undrawn yarn is respectlvely' X'ray dlflramop p O obtained. All preparations are made with a spinneret grap of Items Inc to IHF h no gamma Orientation having 34 holes of 0.012 inch in diameter similar to the A microphotometer trace of ltems IIIC and IIID gives spinneret of Example I except item V c for which is gamma mtenslty ratios of ol-lly and respectively used a spinneret containing holes of 0.014 inch in di- None of these samples, items IIIB to IIIF, as drawn, 15 ameter plawd on a 1 inch diamater circle shows a TR as much as A portion of each sample The p y Of Example I is used for items and is skeined and heat relaxed at 135 C. for 10 minutes V B For item a p yp py of melt index 15 to give reported m Table} HIE is made by heating the polymer of Example I in a screw a fiber within this invention and shows a fairly good TR extruder at 230 C in the presence of tdbutyl y p of 86%. None of the items 1110 to IIIF are within the '20 Oxide and then adding 1% f 4 4'- b'utylidene biS(6-t invention although heat relaxation does effect noticeable butyl m cresol) as a Stabilizer. improvement tenslle recovery as Table I w? The polymer of Example I is repeatedly extracted with Howevfirieven Hem Inc has a T Well below the boiling commercial grade n-heptane until approximately mum hmlt of Actually Item Inc takes Penna 8% of its weight had been extracted. The residue is nent set on 25 elongation of over 72% greater than the 25 used to prepare item IIIB fiber, a striking illustration of the loss of elastic A crystalline polyppopylene of melt index Q18 behavior by drawing the filament 3 X as against 2 X. con, mad6 by Enjay Co" of 15 51st St, New

Item IIIB tfiber has a compliance ratio between the York, NY, i d to prepare i E limits 2 and 15 and a stress at 5% elongation between the 30 Ph i l properties of h as spun fib aft r m limit 0.1 and 0. 8 g.p.d. laxin'g at 135 C. for 10 minutes are given in Table III.

Table III Spinning Conditions Physical Properties Item Orientation Elongation Spinneret Quench, Windup, TRQE, Tenacity, at break, Mi, g.p.d. D.p.f. Temp., C. c.f.m. y.p.m. percent gpd. percent Angle Type 290 3. 6 100 1 Gamma-" 93 1. 6 430 10 12 a; 2-1 W a 3% 3 290 3: 6 93 1: 7 342 12. 3 12'. 5 290 2. 6 1. 9 190 11.3 8.2 295 1. 6 74 1. 2 497 10. 0 16. 6 295 3. 6 s9 1. 6 520 9. 7 18.5 295 6. 0 93 1. 6 414 10.3 18.0 290 2. 0 77 1. 2 477 9. 3 13. 3 290 6. 0 s4 1. 6 469 9. 3 13. 0 260 6. 0 92 1. 6 417 11.3 10.7 250 3. 6 1. 8 312 12. 7 4.1 230 3. 6 85 2. 0 243 13. 0 3. 3 280 4.4 245 1021 do 90 300 3.2 123 Nor1nal 55 1.0 509 4.7 7 4 *These fibers all have compliance ratios between 2 and 15 and show stresses at 5% elongation of between 0.1 and 0.8 gpd.

EXAMPLE IV This example illustrates not only that heat relaxation is required to obtain the fibers of this invention but it must be appreciable to get a heat-stable orientation angle and a TR within the range of this invention. Further, too drastic .a heat relaxation (150 C. in Table II) can also be harmful.

Skeins of item IIIB of Example III (the drawn fiber before any heat treatment) are heated for ten minutes in an air oven in a tensionless state at various temperatures. The tensile recoveries from 25% elongation (TR on the second cycle are given below in Table II.

Table 11 Temperature of treatment C.: TR 42 58.2

EXAMPLE VI This example illustrates the preparation of ten fibers, items VI-F to VI-O, Table III, using different spinning variables to show the effect on the properties of the fibers produced. In all instances, the polypropylene .of Example I is extruded as a melt at 289 C. using the apparatus of FIG. 1 with the feed and draw rolls adjusted so that no drawing is performed and an undrawn yarn is obtained. The resulting fibers are allsubjected to identical heat relaxation, i.e., 10 minutes in a 135 C.

oven in a 'tensionless condition.

Fibers VII, VI-] and VIK are all prepared as above except the spinneret has 40 holes of 0.009 inch diameter in a pattern similar to that of the spinneret used in Example I and the top of the quenching chamber 111 (FIG. 2) is located one inch below the level of the face of the spinneret 9. However, the air supply and spinneret temperatures are varied as shown in Table III. The location of the quenching chamber delays the cooling of the fiber to a certain extent and fiber VII falls well outside this invention. Even using the same rate of air supply (6.0 cubic feet per minute) that gave the optimum VIH fiber, only a fiber (VI-J) in the non-preferred area of this invention is obtained. It was necessary to lower the spinneret temperature to 260 C. in order to get a fiber (VIK) approaching fiber VIH in desirable elasticity.

The effect of windup speed alone is illustrated by fibers VIL and VI-M spun from a spinneret having 34 holes (0.012 inch in diameter) arranged in in-line rows with the quenching chamber used as shown in FIG. 1. The faster windup speed used in spinning [fiber VI-M cools the threadline too rapidly and, as a result, the TR drops to 85% from the 90% of fiber VIL. Both fibers, however, are well within this invention.

Fibers VIN and VIO illustrate the effect of a combination of spinning variables. They are spun in the same manner as fiber VIL except for the spinning conditions set forth in Table III. Whereas fiber VIN is a preferred specific embodiment of the invention, fiber VI-O which uses a higher spinneret temperature, a lower quench intensity, and a lower spinning speed, all conditions tending to increase the cooling time, is far outside the invention with a TR of only 55%. It does not have gamma orientation.

EXAMPLE VII Using a spinneret having 3 holes (0.030 inch in diameter), yarn is spun according to the procedure of Example I but using an air feed rate of 0.9 cubic feet per minute in the quench and with the feedrolls 3 and 4 running at a speed of 189 y.p.m. and the draw rolls 5 and 6 at a speed of 264 y.p.m. The three drawn filaments thus produced are separated and wound on to separate packages. One of these packages of yarn is used in this example. It is heated for 30 minutes at 130 C., the yarn being under tension since it was in package form. This effects the so-called heat relaxation although it is usually preferred to heat the yarn in a tensionless condition and let it shrink as much as it will. However, in the present example, it was desirable to leave some shrinkage in the yarn.

The yarn is then coned by conventional means and knitted into hose on a 400-needle single feed seamless knitting maching using 44 courses per inch. Commercial 66 nylon yarn is used for welt, heel and toe sections. Normal 66 nylon knitting conditions are used except for a lower feed tension of 0.5 gram. The knit hose is boarded on a conventional metal form for 15 minutes in 150 C. air with a resulting 14% shrinkage. After boarding, the hose are scoured at 90 C., rinsed and dried. The hose thus formed have a good appearance and are notably superior in stretchability, indicated by high tongue stretch values, -to both hose knitted from normal polypropylene yarnor 66 nylon yarn. They resist bagging as well as 66 nylon hose and are much more resistant than normal polypropylene hose.

In the following Table IV, yarn samples are removed from the hose to determine tenacity and elongation while the tongue stretch is determined on the hose as explained below.

The polypropylene yarn removed from the finished hose made as above has gamma orientation, a heat-stable orientation angle of 1030, and a TR of 82%. Thus it is a fiber within the present invention.

The tongue stretch values given in Table IV are determined by measuring the inside diameter of the hose at the knee shape section under no stress (D under a stress of 7 grams (D and under a stress of 101 grams (D The stress is applied on the inside of the hose by 1 inch square plates pivotally mounted on the ends of 2 rods which rods are pivotally connected near their mid points.

Tongue stretch:- X

It will be understood that the above examples are merely illustrative and the present invention broadly comprises a fiber of polypropylene having gamma orientation and a heat-stable orientation angle of 10 to 30.

The preparation and description of numerous fibers not falling within the invention have been given in the examples, the purpose being to ilustrate the effect of changing various process conditions. These fibers not falling within the invention are not necessarily prior art fibers. So far as known, the single closest prior art is believed to be Australian application 36,834, Example 2. This Example 2 draws the polypropylene yarn 3.5 X too great to obtain the fiber of this invention even if other conditions were set in the light of the teaching herein. Actually, this Example 2 is so lacking in specificity of conditions that fibers of all sorts of properties could be obtained by varying con-ditions not specified. The example states the yarn produced is very bulky which is certainly not true of the yarns whose production is described in the examples herein. It would require further process changes to make the fibers of the instant examples bulky.

As previously noted, FIG. 5 is a graphic representation of an X-ray diflraction photograph of polypropylene fiber having gamma orientation and being within the present invention; FIG. 6 is a similar representation of a polypropylene fiber which is outside of the invention and has normal rather than gamma orientation.

The diffractions 21 located on the circle 22 (20: l4.0) at an azimuthal angle greater than 50 from the equator 23 in FIG. 5 are characteristic of gamma orientation. No such diffraction is observed on the circle 22 of FIG. 6. The portion of the diffraction 24 that is centered on circle 25 (26=16.7) determines the orientation angle of the fiber. The higher crystallite orientation angle of FIG. 5 (16) as compared to FIG. 6 (13) is apparent. The diifractions 26 are typical of all oriented polypropylene fiber but are not pertinent here. The diffractions 27 are located on a cycle 28 (20:28.6") and are used in the determination of gamma intensity ratio. It should be noted that the pattern is symmetrically divided by the equator. The meridian is located at right angles to the equator through the center of the pattern.

To those skilled in the art, the difference in the diffraction patterns of FIGS. 5 and 6 is striking and significant. The diifractions 21 of FIG. 5 are unusual and immediately reflect the unique crystalline structure of the polypropylene fibers of the present invention.

The elastomeric fibers of the present invention have an extremely favorable combination of properties, featured by an elasticity heretofore unknown in polypropylene fibers. Example VII shows the use of fibers of the invention in hosiery. These fibers are quite advantageous for use in such applications as automobile upholstery, seatcovers, and the like because such fabrics and material possess unusually good form recovery. The use of fibers of this invention in non-Woven fabric is likewise advantageous because they impart such good form recovery.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

The invention claimed is:

1. An elastomeric fiber of highly crystalline polypropylene characterized by melt index of from 0.1 to 200, said fiber having an elongation at break of from 100% to 700%, gamma orientation, a heat stable orientation angle of 10 to 30, and a tensile recovery on the second and succeeding stretch cycles from a 25% elongation of at least 82%, said tensile recovery having been achieved by a separate heat treatment of the fiber, after it has 12 been spun, at an elevated temperature of from 105 C. to 160 C.

2. The fiber of claim 1 having a gamma intensity of 'at least 1.0 and a heat-stable orientation angle of 10 to 3. The fiber of claim 1 having a tensile recovery on the second and succeeding stretch cycles from a 25% elongation of at least 90%.

4. The fibers of claim 1 in the form of a non-woven fabric.

References Cited by the Examiner UNITED STATES PATENTS 3,019,507 2/1962 Maraglia-no et al. 2872 FOREIGN PATENTS 223,630 1/ 1958 Australia.

JOSEPH L. SCHOFER, Primary Examiner.

ROSCOE V. PARKER, ]R., A. J. SMEDEROVAC,

E. M. OLSTEIN, M. B. KURTZMAN, Examiners.

Claims (1)

1. AN ELASTOMERIC FIBER OF HIGHLY CRYSTALLINE POLYPROPYLENE CHARACTERIZED BY MELT INDEX OF FROM 0.1 TO 200, SAID FIBER HAVING AN ELONGATION AT BREAK OF FROM 100% TO 700%, GAMMA ORIENTATION, A HEAT STABLE ORIENTATION ANGLE OF 10* TO 30*, AND A TENSILE RECOVERY ON THE SECOND AND SUCCEEDING STRETCH CYCLES FROM A 25% ELONGATION OF AT LEAST 82%, SAID TENSILE RECOVERY HAVING BEEN ACHIEVED BY A SEPARATE HEAT TREATMENT OF THE FIBER, AFTER IT HAS BEEN SPUN, AT AN ELEVATED TEMPERATURE OF FROM 105*C. TO 160*C.

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