US2604689A - Melt spinning process and fiber - Google Patents

Description

Patented July 29, 1952 MELT SPINNING PROCESS AND FIBER Harold Henry Heheler, Eggertsville, N. Y., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application August 23, 1950, Serial No. 181,091

9 Claims.

This invention relates to a process for spinning a synthetic polyester and is more particularly concerned with a process for melt-spinning polyethylene terephthalate material to produce tenacious, resilient fibers and yarns.

The preparation of useful textile fibers from synthetic linear polymers of the type first described ;in United States Patents 2,071,250 and 2,071,251 to Carothers by previous processes has requiredthe two separate operations of spinning and then drawing. Melt-spun fibers of synthetic linear polyesters and polyanides in the as-spun state have previously been weak and not suitable forv textile uses, except in special applications, until drawn. The as-spun tenacities have been in the range of 0.2 to 0.8 grams per denier, at elongations of several hundred per cent. By a drawing operation, in which both orientation and crystallization occur, useful fibers are obtained having tenacities as high as 4 to 10 grams per denier. This is generally true for synthetic yarns made from condensation or addition polymers.

It is apparent that considerable economic advantage would be achieved by providing a process which produces useful as-spun fibers. Elimination'of the necessity for a drawing operation subsequent to the normal spinning process would result in a considerable saving in both manpower and equipment and would speed up production considerably. Furthermore, for a given production capacity less space would be necessary, since the floor area currently needed for drawing yarn would be eliminated.

Considerable research eifort has been directed toward discovering or developing a satisfactory substitute for natural wool. A variety of synthetic fibers have been subjected to many different processes, both mechanical and chemical in an .efliortto so modify their properties that they could'take the place of wool. The prior art discusses at great length the use Of staple fibermaking equipment and crimpers, as well as various chemical and heat-treating methods, for treating synthetic fibers in efforts to secure characteristics normally associated with natural Wool. However, in no instance have such synthetic materials been properly classifiable as wool-like in other than superficial appearance. A great new field of use would be open to a synthetic fiber which could be woven into fabrics having the hand, resilience, wrinkle resistance, fullness, warmth and other such properties normally associated with fine woolen fabrics.

It is an object of the present invention to provide a process for spinning fibers and yarns of polyethylene terephthalate material which are tenacious in the as-spun condition and do not require a subsequent drawing operation. A further object of the invention is to providea high-.- speed process for spinning polyethylene terephthalate fibers of textile denier and yarns which have the property of spontaneously crimping to a tenacious structure having the hand, resilience and wrinkle-resistant characteristics of fine wo'ol when heated in the as-spun condition and.al-, lowed to assume a relaxed condition. Other objects of the invention will become apparent from the following description and claims.

The objects of this invention are accomplished by a process which comprises extruding a molten fiber-forming material containing at least 90 mol percent of polyethylene terephthalate through a spinneret and cooling the extruded material until solidified into fibers while attenuating the extruded fibers by winding up or forwarding the solidified fibers to the next operation at .a spinning speed, measured after the fibers have completely solidified, or from 3000 to 5200 yards per minute. The tenacious as-spunfibers or yarns produced spontaneously crimp when relaxed and allowed to shrink at a temperature of from about 90 to 200 C., to a material having the resilience characteristics of fine wool. Preferably the spinning speed is further controlled within the above degree of polymerization of the polyester and may be defined as Limit as C approaches 0,

wherein r is the viscosity of a dilute solution of the polyester in a mixture of parts phenol and 40 parts tetrachloroethane, divided by; the,

viscosity of the phenol-tetrachloroethane .mix

ture, per se, measured in the same units at the 3 same temperature, and C is the concentration in grams of polyester per 100 cc. of solution.

The fiber-forming material is principally polyethylene terephthalate, but the inclusion therein of up to mol percent of modifying materials is intended whenever the expression polyethylene terephthalatematerial is used. Polyethylene terephthalate itself is a polycondensation product of ethylene glycol and terephthalic acid or an ester-forming derivative thereof.

During the preparation of this polyester, minor amounts of a modifying material may be added, e. g another glycol and/or another dicarboxylic acid. Thus, a suitable funicular structure comprised essentially of polyethylene terephthalate may have included in the polymer molecule up to 10 mol percent of another glycol, such as diethylene glycol, tetramethylene glycol, or hexamethylene glycol. Or again, the molecule may contain up to 10 mol percent of another acid. As suitable examples of modifying acids, there may be mentioned hexahydroterephthalic acid, bibenzoic acid, adipic acid, sebacic acid, azelaic acid, the naphthalic acids, 2,5-dimethy1 terephthalic acid and bis-p-carboxy phenoxyethane.

These modifiers may be added as one of the initial reactants during the polymerization process, but the modifying materials may also be polymerized separately and then melt-blended with the polyethylene terephthalate. case the total amount of modifier in the-final polymeric material should not exceed 10 mol percent. While the polymerization process is preferfably carried out in the melt, it may also be performed in the solid phase, or in solution or emulsion by conventional procedures. An explanation of suitable polymerization processes for the type of polyesters comprehended herein is contained in United States Patent No. 2, l55,319 to Whinfield and Dickson.

In preparing useful resilient yarns by this invention, the following general procedure is used: The polymer, prepared by a conventional polymerization process, is cooled, broken into chips and dried. The chips are then melted on a heated grid and pumped, by means of a metering pump of the type commonly used in the synthetic textile industry, through a filter pack and spinneret orifices into room temperature air. The extruded filaments cool and solidify by passage through the air and are subjected after solidification to a means for forwarding them at spinning speeds in the range of 3000 to 5200 yards per minute.

By spinning speed is meant the speed of the yarn at a point after complete solidification has occurred, when no more reduction in denier is observed. A convenient point for determining this speed is at the wind-up or forwarding regions. It will be obvious that the speed of an extruded polymer stream will not be the same while in the fiuid or semi-fluid state as it is at the wind-up or forwarding place.

The means for forwarding the filaments. may comprise a high speed wheel, roll or pinchrolls, an air jet or other suitable means. Under the impetus imposed by the forwarding means, the filaments elongate in the distance between the spinneret face and the point of complete solidification. The inertia of the material and the drag of the surrounding air apparently provide sufiicient drag on the filaments to induce orientation of the polymer molecules in the solidification range. Actually, no useful orientation takes In either 3 .ments, beginning at the solidification range.

4 place until the filamentary streams begin to solidify. For several inches from the spinneret, the filaments appear to be just dangling from the spinneret. In the solidification range, the filaments can be seen to accelerate and become taut. fibers, moving along'their length at high bined filaments from a spinneret are generally forwarded bymeans of an air jet to a high speed cutter, after which the staple fibers are heated to a temperature of -200 C. in the relaxed state.

All of the fibers and yarns prepared in accordance with the present invention are capable of spontaneous crimping. This term is applied herein to the type of crimp that appears in fibers produced by the process of this invention when the fibers are relaxed by heating them to an elevated temperature under little or no tension, and is to be distinguished from crimp produced bymechanical means. Generally speaking, spontaneous crimping is observed when the yarns or fibers are heated to the vicinity of C. within the broader range of 90 to 200 C. previously mentioned.

Suitable heating media include hot air, hot or boiling Water, saturated or superheated steam, and various hot solutions that exert a mild plasticizing action on the polyester material, e. g., dilute nitric acid. This heat treatment also stabilizes the yarns and increases the degree of crystallization, while at the same time'reducing residual shrinkage. If desired, the fibers may be forwarded directly from the spinning operation through a suitable bath or a heated chamber and allowed to crimp spontaneously before being wound up or cut into staple. On the other hand, the'fibers can be woven into fabric'and then crimped spontaneously by heating to 90 to 200 C. as described above. I

r In addition to being wool-like' by virtue of the crimp, yarns and fibers prepared in accordance with the process of this invention possess a property of wool which is most difficult to duplicate, namely, resilience. 'Thisjproperty is not easy to measure quantitatively, but may be defined to a considerable extent by three important parameters Initia1 tensile modulus, tensile recovery, and compliance ratio. I

p The initial tensile modulus (represented by the symbol Mi) is defined as the slope of the first reasonably straight portion of a stress-strain curve of the funicular structure obtained by plotting tension on a vertical axis vs. elongation on a horizontal axis as the structure is being elongated at the rate of 10% per minute under a standard condition of temperature (21 C.) and. humidity (60% RH). In almost every instance, this first reasonably straight portion is also the steepest slope to be found on the curve. The values as used herein are in units of kilograms per square millimeter per'100% elongation.

The initial tensile modulus, Mi, is a measure of resistance to stretching and bending. The effects of the filament modulus are felt in a fabric chiefly when the fabric is folded or crushed in the hand or otherwise handled. If the modulus is too low, the fabric is "rubbery or limp; with too high a modulus in the fibers, the fabric is wiry or boardy. When the modulus is in the proper range, a soft fabric results. Attempts have been made to counteract .the efiectsof a modulus lying outside the wool range by a suitable adjustment of filament diameter. In each instance, this straying away from the usual diameters of wool filaments has resulted in deleterious effects on properties such as liveliness and recovery from wrinkling. Since the filament properties which are almost entirely responsible for fabric resistance to bending are (1) the initial modulus and (2) the diameter, and since the range of suitable diameters seems to be confined to those typical of Wool, it follows that a woollike handle will be obtained in the fabric when fibers having an initial modulus in the wool range are used.

The tensile recovery (TR) defined as the extent to which a yarn recovers its original length after being stretched, a stress-strain curve being used to determine tensile recovery under the testing conditions. The test consists in ex-- tending the funicular structure at a constant rate of elongation of per minute. A specimen is held at the maximum elongation desired for 30 seconds, e. g., by the use of a time switch, and is then allowed to retract at the same rate at which it was extended. The same specimen is extended approximately 1.0, 3.0 and 5.0% extent for each determination. The extension during elongation and the recovery during retraction are measured along the elongation axis. The-tensile recovery is then the ratio of the extent to which the yarn retracts to the extent to which it was elongated. This test is run under standard conditions at 60% R. H. and 21 C.

It is well known that resistance to wrinkling and mussing and rapid recovery from unavoidable wrinkles are highly desirable traits in apparel fabrics. The tensile recovery correlates in a high degree with these properties. The tensile recovery from a 1% elongation correlates with fabric recovery from mild wrinkling, and, as might be expected, the tensile recovery from higher elongations correlates with recovery from more severe wrinkling and sharp creasing. In this instance, the words resistance to may be used alternatively to recovery from since resistance to a crease or wrinkle really involves a very rapid and complete recovery from a crease or wrinkle when the deforming force is removed.

The compliance ratio (CR) is associated with the shape of a stress-strain curve and is a measure of the rate of change of compliance with elongation. Compliance is defined as elongation divided by tension in kg./mm. Hookean systems, those for which. the stress-strain curve is a straight line, exhibit equal compliance at all elongations: for these the change of compliance with, elongation is 0, on the other hand one of the most important properties of wool is its change toward higher compliance as it is progressively deformed. It is this property which enables wool to feel simultaneously crisp and soft This property is measured by determining the average rate at which compliance changes in the range 5 to 10% elongation and is computed by the following formula:

C IO/tension at 10% elongation 5/tension at 5% elongation) The stress-strain curve of wool has two distinctly different regions, consisting of (1) an initial portion in which the resistance to deformation is relatively great, and (2) a later portion in which the resistance decreases regularly and to a high degree. It is for this reason that a wool fabric which is crisp and firm to the touch will feel soft and compliant when severely crushed in the hand. Among the natural fibers this dualistic behavior is found only in wool and other animal hairs (not in silk, cotton, etc.) and this is one of the most attractive and valuable characteristics of wool.

In applying the above methods for evaluating wool-like resilience, it has been found that the better grades of wool for outer garment uses have values for these three parameters in the following ranges Mi=110 to 550 kg./mm. CR=0.05 to 0.17 TR=55 or more from extensions of 3 In accordance with the process of the present invention synthetic yarns or fibers are produced which have wool-like resilience within the above limits. Furthermore the synthetic fibers have these desirable resilience characteristics throughout the fiber length. This is accomplished by means of this invention because the filaments receive uniform treatment throughout their lengths during formation and subsequent processing.

The spontaneous crimping operation also reduces the tenacity and initial tensile modulus (M1), and increases the compliance ratio (CR). The effect on the Mi value becomes important at the higher spinning speeds. Frequently yarns spun at speeds near 5000 yards/minute will initially have values of M1 which are above the desired range. After the spontaneous crimping operation, however, the M1 value will have been decreased sufiiciently to be within the desired range. This reduction in M1 value may be accentuated by using more severe relaxing conditionsthan would normally be employed, e. g., steam, glycol, glycerine or mineral oil at l60-200 C., or dilute nitric acid, and/or longer treating times.

The properties of polyethylene terephthalate yarns spun under various conditions in accordance with the present invention are given in the table. The general procedure described above was followed, with specific conditions as indicated in the table. In the table, spinning speed is in yards per minute, tenacity is in kilograms per square millimeter and in grams per denier, and intrinsic viscosity, initial tensile modulus (M1), compliance ratio (CR) and tensile recovery (TR) are as defined previously. The physical properties were measured on the crimped fiber after the fiber samples were boiled in water for an hour. The percent shrinkage was calculated from the difference in length between fibers as spun and after boiling for five minutes in water. This shrinkage relates the length of the shrunk crimped fiber bundle to the length of the initially straight unshrunk fiber bundle and, hence, is a summation of the effect produced by the contraction in the length of the fiber bundle and the effect produced by the crimping of the fiber bundle. Examples 1-15 inclusive, were carried out using polyethylene terephthalate. In Example 16, a copolymer prepared from ethylene glycol and a :5 mol ratio mixture of terephthalic and sebacic acids was used and, in Examples 17 and 18, a similar copolymer containing 10 mol percent of sebacic acid was used. In Examples 6 to 9, the fibers were crimped by blowing them through a pneumatic tube type relaxer fed with air at 150 C. In Examples 3, 4, and to 18, the fibers were crimpcd while supported on a moving belt in an infrared-heated, oven type relaxer.

ages- Staple with less than shrinkage does not crimp well spontaneously on relaxed boil-01f. On the other hand, shrinkages much greater than 30% result in very tight wads of staple on batch boil-off that are difiicult to open, although this difficulty can be essentially eliminated by spontaneously crimping the. staple in hot air as it emerges in a fluify state from the cutter. For

\ Pleiicent R'lensile l m r S Tensile onecovery Ex. I Ii tI iHSC Te m p. Speed Spun Tenacity Strength gation Mi CR from 3 figgfigz Crimping Conditions Viscosity C m f kgJmmJ at percent Break Fxfpnsirm .47 2 5 4 300 3.0 2.0 24.4 80 366 0.10 91 Boiling water-l5 min. 3. 58 225 4', 200 3. 1 1. 3 15.9 69 159 0.15 83 31 90 C watermin. 0.58 295 4, 300 3. 0 2. 0 24. 4 92 231. 0. 10 64 22 150 C air-30 min. 0. 58 295 4, 200 3. 1 2. 2 2'3. 8 70 366 0. 09 79 30 30 D. S. 1. Steam -5 mm. 0. 60 285 4, 200 2. 9 2.6 31. 4 105 377 0. 10 83 20 125 C a r-3 mm. 0. 60 280 4, 100 3. 5 2. 8 34. 2 90 195 0. 05 59 40 150 C a r-5 Sec. 0. 60 280 4, 620 3. 1 2. 9 35. 4 82 232 0. 07 67 7 150 C a r-5 sec. 0. 60 280 4, 840 3. 2 3. 0 36. 6 81 244 0. 06 02 5 150 C a r-5 sec. 0. 60 280 5, 220 3. l 3. 1 37. 8 76 242 0. 06 64 3 150 C a r-5 sec. 0. 60 280 3, 500 1. 6 2. 6 31. 4 102 387 0. 09 74 23 125 C air-3 m n. 0.60 280 3,000 l. 2 2.0 24. 4 75 367 0. 08 70 27 125 C a r-3 m n. 0. 62 285 4, 300 4. 0 2. 8 34. 2 101 378 0. 10 83 18 130 C a1r-4 m n. 0. 62 230 4, 100 5. 9 2. 9 35. 4 86 354 0. 10 81 59 150 C air-3 131111. 0. 00 280 3, 800 3. 9 2. l 25. 6 142 208 0. 10 85 150 C a1r-4 min. 0. 60 280 4, 100 4. 2 2. 9 35. 4 71 390 0.07 94 15 5 p. 5.1. steam-5 min. 0. 59 270 4, 30d 5. 4 2. 7 33. 0 89 378 0. 07 07 30 150 C air-4 m n. 0. 59 270 3 400 5. 5 l. 7 20. 8 111 244- 0. 14 65 35 150 C a r-4 m n. 0. 59 270 3; 400 4. 3 1. 9 23. 2 200 208 0.16 74 35 150 C air-4 min.

Depending upon the exact shrinkage properties of-yarn desired, the spinning speed may be varied within the range of from 3000 to 5200 yards per minute. The higher spinning speeds result in yarn with lower shrinkage and, conversely, lower spinning speeds result in higher shrinkages. Spinning speeds higher than 5200 yards per minute result in highly oriented, silk-like yarns which do not attain the appearance or resilience characteristics of wool upon hot water or hot air relaxation. Spinning speeds in the range of from 1500 to 3000 yards per minute result in lowly oriented yarns, having very high shrinkages and tenacities of around 1.0 to 1.5 grams per denier, which also do not attain wool-like. resilience when crimped. Speeds below 1500 yards per minute do not give yarns useful in the as-spun state, since they approach the roperties of conventional unoriented, as-spun polyesters or polyamides.

.In the range of spinning speeds between 3000 and 5200 yards per minute, the physical properties of the fibers produced are related to the denier of the filaments being spun as well as the spinning speed when the filament denier is less than three. Spinning speeds near the lower limit of 3000 yards per-minute are preferred for low denier filaments in order to obtain optimum wool-like resilience characteristics.

The spinning speeds essential in the process of this invention may be obtained by several methods. There may be used a driven bobbin, a high speed pirn take-up or an air jet may be used as a tensioning and forwarding device wherein the yarn, together with other yarns to form a tow, can-be forwarded directly to a staple cutter or to a crimper without an intermediate wind-up.

The fibers prepared by means of the process of this invention can be crimped spontaneously by treatment in the relaxed state in water at 90 C. to 100 C. Preferably the spinning speed is controlled to give fibers which shrink from 15% to 30% when crimped in water at 90 to 100 C., although, as can be seen from the results given in the table, desirable wool-like resilience characteristics are obtained with much higher shrinkany given set of conditions, the spinning speed which will give a specified shrinkage can readily be determined by adjusting the speed upward if the shrinkage is too great, or downward when the shrinkage is too little, until the desired shrinkage range is reached.

The fibers of this invention can be crimped spontaneously by treatment in relaxed condition in hot air at C. to 200 C. Fibers which shrink from 15%-30% crimp well when supported on a solid surface, e. g., a moving belt, in an oven. The preferred method of crimping is to support the fibers by a current of air heated to from 95 C. to 200 C. This method of crimping is highly effective and rapid. By this method fibers having shrinkages as low as 3% and as high as 30% or higher can be crimped satisfactorily in a few seconds. A convenient method is to blow staple fibers through a pneumatic tube fed with hot air at a temperature of about C.

The molten polymer can be extruded through the spinneret at temperatures in the range of from 260 to 310 C. For optimum results with polyethylene terephthalate this extrusion temper ature should be between 280 and 295 0., although properties of the final yarn vary but little over the entire range. The preferred temperature range is from 10 to 20 C. lower when copolymers of ethylene terephthalate are used, depending on the copolymer,and typically in the range of from 270 to 285 C.

When the molten polymer is extruded into room temperature air, the resulting filaments should be allowed to travel at least 45-50 inches before they reach the forwarding means. This distance is required for complete solidification. When the distance is in the range of 30-40 inches, fused filaments often result with an otherwise standard spinning procedure because of inadequate quenching time.

The particular fibers prepared by the process of this invention not only duplicate fine wool fibers in appearance, but also. in the important physical characteristics of initial tensile modulus. tensile recovery and compliance ratio. As a result, a wool-like fabric may be produced from them which is crisp and firm to the touch and. nevertheless, feels soft and compliant when severely crushed in the hand. These fibers and yarns .of polyethylene terephthalate materials possess,in addition, much greater strength and wear resistance than'wool fibers and are not attacked by moths. Fabrics made from these fibers are extremely lively and wrinkle resistant, with desirable drape and excellent crease retentivity. They arerem'arkably insensitive to water and changes in humidity. Also of importance is the versatility which these fibers possess overand above that of wool for processing into fabrics. They are useful, particularly in staple form'y'in felts of various kinds, including papermakers felts, carpets, mens and womens suits, bathing suits, sweaters, knitting yarns, as the warp in Turkish towels and the like.

Suiting fabrics prepared from the staple fibers produced in accordance with this invention are particularly outstanding. These are equal to or better than high grade woolen suiting fabrics in wrinkle resistance, recovery from wrinkling, and retention of ironed creases. Trousers may be cleaned by washing in an automatic washer and hanging them up to dry; they do not shrink appreciably, retain their original creases, and need no further pressing.

From the above disclosure it is seen that the present invention provides a high-speed direct method for spinning fibers and yarns of polyethylene terephthalate materials in a condition in which the fibers or yarns will crimp spontaneously to desirable resilient structures. The process accomplishes this result without the necessity of a subsequent drawing operation. The fibers or yarns may be passed directly from the spinning operation to the crimping operation to form highly useful fibers or yarns in a continuous operation.

As difierent 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 processes disclosed'except as defined in the appended claims.

What is claimed is:

1. A process for producing tenacious as-spun fibers which comprises extruding a molten fiberforming material containing at least 90 mol percent of polyethylene terephthalate through a spinneret, cooling the extruded material until solidified to a fiber, and attenuating the fiber in the solidification range by pulling the fiber away from the spinneret at a spinning speed, measured after the material has completely solidified to a fiber, within the range of from 3000 to 5200 yards per minute, said extruding being at a rate in denyards equal to the product of said spinning speed and the spun denier desired.

2. A process for producing tenacious as-spun fibers which comprises extruding a molten fiberforming material containing at least 90 mol percent of polyethylene terephthalate through a spinneret, cooling the extruded material until solidified to a fiber, and attenuating the fiber in the solidification range by pulling the fiber away from the spinneret at a spinning speed, measured after the material has completely solidified to a fiber, within the range of from 3000 to 5200 yards per minute, said spinning speed being further controlled to produce a fiber having a shrinkage of from 3% to 30% when immersed in water at a temperature of 90 to 100 C. in a relaxed condition and said extruding being at a rate in denyards equal to the product of said spinning speed and the spun denier desired.

3. A process for producing tenacious as-spun fibers which comprises extruding, at a temperature in the range of from 260 to 310 C., a molten fiber-forming material containing at least mol percent of polyethylene terephthalate through a spinneret, cooling the extruded material until solidified to a fiber, and attenuating the fiber in the solidification range by pulling the fiber away from the spinneret at a spinning speed, measured after the material has completely solidified to a fiber, within the range of from 3000 to 5200 yards per minute, said extruding being at a rate in denyards equal to the product of said spinning speed and the spun denier desired.

4. A process for producing tenacious fibers having wool-like resilience which comprises extruding a molten fiber-forming material containing at least 90 mol percent of polyethylene terephthalate through a spinneret, cooling the extruded material until solidified to a fiber, and attenuating the fiber in the solidification range by pulling the fiber away from the spinneret at a spinning speed, measured after the material has conpletely solidified to a fiber, within the range of from 3000 to 5200 yards per minute, and then heating the fiber to a temperature of from 90 to 200 C. in a relaxed condition until the fiber has spontaneously crimped, said extruding being at a rate in denyards equal to the product of said spinning speed and the spun denier desired.

5. A process for producing tenacious fibers having wool-like resilience which comprises extruding a molten fiber-forming material containing at least 90 mol percent of polyethylene terephthalate through a spinneret, cooling the extruded material until solidified to a fiber, and attenuating the fiber in the solidification range by pulling the fiber away from the spinneret at a spinning speed, measured after the material has completely solidi fied to a fiber, within the range of from 3000 to 5200 yards per minute, and then heating the fiber to a temperature of from 90 to 200 C. while supported by a current of air in a relaxed condition until the fiber has spontaneously crimped, said extruding being at a rate in denyards equal to the product of said spinning speed and the spun denier desired.

6. A process for producing tenacious fibers having wool-like resilience which comprises extruding a molten fiber-forming material containing at least 90 mol percent of polyethylene terephthalate through a spinneret, cooling the extruded material until solidified to a fiber, and attenuating the fiber in the solidification range by pulling the fiber away from the spinneret at a spinning speed, measured after the material has completely solidified to a fiber, within the range of from 3000 to 5200 yards per minute, and then immersing the fiber in 90 to C. water in a relaxed condition until the fiber has spontaneously crimped, said spinning speed being controlled to produce a fiber having a shrinkage of from 15% to 30% in the crimping operation and said extruding being at a rate in denyards equal to the product of said spinning speed and the spun denier desired.

7 A process for producing tenacious fibers having wool-like resilience which comprises heating to a temperature of from 90 to 200 C. in a relaxed condition until spontaneously crimped a fiber of polyethylene terephthalate material formed by extruding the material in a molten condition through a spinneret, cooling the extruded material until solidified to a fiber, and attenuating the fiber in the solidification range by pulling the fiber away from the spinneret at a 11 spinning speed, measured after the material has completely solidified to a fiber, within the range of from 3000 to 5200 yards per minute, said extruding being at a rate in denyards equal to the product of said spinning speed and the spun denier desired.

8. A process for producing tenacious fibers having wool-like resilience which comprises immersing in 90 to 100 C. water in a relaxed condition until spontaneously crimped a fiber of polyethylene terephthalate material formed by extruding the material in a molten condition through a spinneret, cooling the extruded material until solidified to a fiber, and attenuating the fiber in the solidification range by pulling the fiber away from the spinneret at a spinning speed, measured after the material has completely solidified to a fiber, within the range of from 3000 to 5200 yards per minute, said spinning speed being controlled to produce a fiber having a shrinkage of from 15% to 30% in the crimping operation and said extruding being at a rate in denyards equal to the product of said spining speed and the spun denier desired.

9. A tenacious as-spun fiber containing at least 90 mol percent of polyethylene terephthalate and having the property of spontaneously crimping. when heated to a temperature of from 90 to 200 C. in a relaxed condition, to a crimped fiber having an initial tensile modulus of from 110 to 550 kg./mm. a compliance ratio of from 0.05 to 0.17, and a tensile recovery of at least 55% from extensions of 3%.

HAROLD HENRY HEBELER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 20 2,249,756 Finzel July 22, 1941 2,465,319 Whinfield et a1 Mar. 22, 1949

Claims (1)

1. A PROCESS FOR PRODUCING TENACIOUS AS-SPUN FIBERS WHICH COMPRISES EXTRUDING A MOLTEN FIBERFORMING MATERIAL CONTAINING AT LEAST 90 MOL PERCENT OF POLYETHYLENE TEREPHTHALATE THROUGH A SPINNERET, COOLING THE EXTRUDED MATERIAL UNTIL SOLIDIFIED TO A FIBER, AND ATTENUATING THE FIBER IN THE SOLIDIFICATION RANGE BY PULLING THE FIBER AWAY FROM THE SPINNERET AT A SPINNING SPEED, MEASURED AFTER THE MATERIAL HAS COMPLETELY SOLIDIFIED TO A FIBER, WITHIN THE RANGE OF FROM 3000 TO 5200 YARDS PER MINUTE, SAID EXTRUDING BEING AT A RATE IN DENYARDS EQUAL TO THE PRODUCT OF SAID SPINNING SPEED AND THE SPUN DENIER DESIRED.