US3184369A - Polyester filaments having improved frictional characteristics - Google Patents

Description

y 1965 E. A. HASELEY 3,184,369

POLYESTER FILAMENTS HAVING IMPROVED FRICTIONAL CHARACTERISTICS Filed July 10, 1963 FIG. Ia

INVENTOR EDWARD ALBERT HASELEY ATTORNEY United States Patent POLYESTER FILAMENTS HAVING IMPROVED FRICTIONAL CHARACTERISTICS Edward Albert Haseley, Grifton, N.C., assignor to E. I.

du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Filed July 10, 1963, Ser. No. 293,996

5 Claims. (Cl. 161-179) This invention relates to novel filaments and fibers suitable for use in the textile industry. More specifically, the invention relates to new melt-spun synthetic organic polymer filaments having improved frictional characteristics.

Mob-spun synthetic organic polymer fibers, e.g., the poly(ethylene terephthalate) fibers disclosed in Whinfield et al. US. Patent No. 2,465,319, dated March 22, 1949, have become well-known articles of commerce and are preferred for many uses because of their outstanding physical and chemical properties. However, it is recognized that some features of melt-spun fibers are undesirable for some purposes. In particular, the remarkable level of surface smoothness of melt-spun fibers has resulted in an undesirably high level of dynamic friction between these fibers and surfaces rubbing against them, which, among other things, gives rise to high drafting tensions, high tension in running threadlines, poor staple processability, and an excessive degree of wear on machine surfaces in contact with moving yarns.

Among the various methods which have been tried for roughening the surface of melt-spun synthetic polymer fibers may be mentioned the treatment of fibers with a chemical etching agent, e.g., a solvent, the incorporation of dispersed insoluble particles in the polymer before spinning, and the incorporation of soluble materials in the polymer before spinning followed by a leaching treatment after spinning which removes the soluble material and leaves holes in the fiber surface. Mechanical treatments for embossing a pattern upon fiber surfaces have also been tried. However, few previously known methods have been found to give a significant reduction in friction without also adversely affecting some other fiber property, e.g., tensile strength.

It is an object of this invention to provide new and improved filaments and fibers from melt-spun synthetic organic polymers. Another object is the provision of melt-spun filaments and fibers with improved frictional properties. A further object is the provision of oriented polyester filaments and fibers having a rough surface, but with other properties equivalent to smooth surfaced filaments and fibers. Other objectives will become apparent from the description and examples which follow.

The objects of this invention are achieved by the provision of a substantially oriented synthetic linear condensation polyester fiber (continuous filament or staple) having a surface characterized by a series of randomly spaced, discontinuous circumferential ridges of submicroscopic size occurring with a frequency between and 130 ridges per millimeter along the length of the fiber. The fiber is further characterized by the absence of diameter variations in excess of 5% of the base fiber diameter, i.e., there is no significant number of sizable bumps or nodules along the length of the fiber.

An important characteristic of the fiber of this invention is the absence of internal voids, or bubbles, associated with the surface ridges. The presence of such internal voids in some bumpy or nodular filaments of the prior art is thought to be a cause of the decreased tensile 3,184,369 Patented May 18, 1965 ice strength observed in those filaments. Preferably, the fibers are free from voids, either internal or etched holes, or dispersed insoluble particles other than conventional delustrants.

The term discontinuous, as used above, is intended to indicate that a majority of the ridges do not make a complete, closed circle around the circumference of the filament. In general, the ridges are found to be of such a length that the arc is a minimum of of the circumference and usually there is at least 180 of are. Some of the ridges appear to extend through 270 of arc, but the sub-microscopic nature of the phenomenon makes it difficult to identify and follow any given ridge completely around the circumference of the filament.

The use of the term circumferential is intended to indicate that the long dimension of a ridge travels along the circumference, or perimeter, of the cross-sectional figure made by a plane passing through the filament at right angles, or nearly so, to the fiber axis. In general, the angle between the fiber axis and a plane containing a given ridge will fall between 70 and The use of the word circumferential is not intended to restrict the invention to filaments of round cross-section.

The term sub-microscopic is intended to indicate that the height of the ridges above the surface of the fiber is less than the theoretical limit of resolving power of the usual light microscope, which is generally stated to be about 0.25 micron. The ridges on the surface of the filaments and fibers of this invention have a height no greater than about 0.2 micron above the fiber surface, and for the most part have a height falling within the range 0.07 to 0.12 micron.

The characteristic ridges of the fibers of this invention are best identified and examined by means of the electron microscope. Standard replica techniques and shadowing procedures may be used. Such examination usually reveals that the ridges are smoothly rounded, wavelike bulges in the fiber surface which are characterized by the substantial absence of sharp corners and edges or abrupt changes of direction. Because there is no abrupt dividing line between the ridge and the adjacent fiber surface, the width of a ridge is diificult to measure precisely. It has been estimated, however that a majority of the ridges have a width in the range of 3 to l0 the ridge height.

Surprisingly, it has been found that the fibers of this invention exhibit a substantial reduction in rubbing friction in comparison with older smooth-surfaced meltspun fibers. For example, a drop of 40% or more in the coefficient of hydrodynamic friction is commonly observed in comparison with similar yarns which do not possess high frequency, submicroscopic transverse ridges as described above. Furthermore, the reduction in friction is obtained without any significant loss in tensile strength.

In the drawings, FIGURES 1a, 1b and 1c are diagrammatic illustrations of three stages in the formation of the fibres of this invention. FIG. 1a represents a side view of a portion of an undrawn filament as it would appear when greatly magnified. FIG. 1b is a corresponding view of the filament after initial treatment to produce a multiplicity of circumferential surface cracks. Most of these, e.g., cracks 10, 12 and 13, are clearly discontinuous in that they do not encircle the filament, but others may appear to follow completely around the circumference, e.g., crack 11. FIGURE 1c is a corresponding view after part of the filament has been drawn to much smaller diameter. Crack It) is still visible on the incompletely drawn part. However, on the completely drawn part, small ridges 21, 22

A area-,aeo

and 23 occur at positions corresponding to cracks 11, 12 and 13, respectively.

FIGURE 2 is a drawing prepared from a photograph at 1600 magnification of a typical filament of this invention. An electron microscope andstandard replica tech.- nique were used, so that a negative surface replica was photographed rather than the filament surface shown in the drawing.

The fibers of this invention may be prepared by a process which comprises melt spinning a synthetic linear condensation polyester to produce unoriented filaments, aging the filaments in contact with certain crack promoting agents until a fracturable skin'is produced as described more fully below, predrawing the filaments in contact with the crack-promoting agent by subjecting them about 1.011.'1 times their original length, disassociating the filaments from the influence of the crack-promotlng agent, and final-1y drawing the filaments according to wellknown drawing procedures to give substantially oriented fibers having good tensile properties.

Aging the as-spun fiber in contact with certain crackpro rnoting agents before subjecting it tothe initial stretch-' ing operation is important in obtaining the productof this invention. Aging, in some manner not completely understood, changes the character of the fiber surface so that in the low draw ratio ipredrawing flstep a multiplicity of fine, transverse cracks is formed in the fiber surface. some fashion the presence of these cracks leads to the formation of sub-microscopic ridges inthe subsequent ally not preferred because offstorage problems in a yarn 'to sutficient tension at low temperature to stretch them to The liquid chosen for test should not, in general, be

' a solvent or strong swelling agent for the polymer. Appreciable solvent action by a liquid necessarily eliminates the formation of surface cracks. Certain liquid cracking agents whichare otherwise suitable but which exert a certain amount of solvent or swelling action on the polymer may be employed provided that the contact time between the liquid and the polymer is kept short enough for cracking to occur before the swelling or plasticizing action proceeds to an appreciable extent. 7

The following criteria maybe used for selection of outstanding cracking agents suitable for use in aqueous solutions on polyester fibers:

' (1) The agent should be unsaturated or contain other sources of unpaired electrons.

(2) The. agent should be sufiiciently soluble or dispersible inwater for aqueous application.

(3) The agent should be liquidat the cracking temperaturc employed in the process. I

' (4) The agent should not be strongly self-associating (e.g., as difunctional alcohols or amines) since this re,- duces possibilities for association with polymer, which is postulated to be necessary.

5 The agent should be r fairly high molecular 'weight, i.e., above about 200.

Observance of the. above criteria has led to the use of high-boiling esters such as butyl stearate and isopropyl myristate, polyet-hers such as the poly(ethyleneoxide) glycols of molecular weight 400 and 600, poly(ethyleneoxide.) glycol 400 monolaureate, and random copolymers of ethyleneoxideand propyleneoxide, as well as high molecular weight hydrocarbons such aseicosane.

In the predrawing step, the filaments are preferably stretched until the drawn length is about 1.01 to 1.1 times the undrawn length. "Less drawing does not produce a I sufficient number of ridges in the final product to yield a manufacturing plant. Aging times shorter than 2 days may significant reduction in friction. On the other hand, too

great a draw leads to significant numbers of denier nonuniformities, nodules, and large size bumps which change the character of thefilaments to the extent that they no longer can be considered the equivalent of smooth-surfaced spinning finish, will'reduce the minimum aging time to 7 about 2 hours.

The use of high molecular weight cracking agents is absolutely essential if the novel filarnents described herein are to be obtained. Low molecular weight cracking agents such as acetone, ethanol, dimethyl formarnide, or pyridine cause undesired large diameter variations or nodules or else introduce voids into the filaments in present invention it is believed that the restriction of the melt-spun fibers. The predrawing step may be carried out at room temperature or at temperatures up to about 80 C. Above this temperature the nature of the drawing phenomenon changes so that the necessary incipient surface crack ing is not. achieved. Temperatures below room temperature are satisfactory. Although the use of a snubbing '50 such a manner that tensile properties are impaired. In the cracking agents to those of high molecular weight is necessaryin order that the cracking effect beconfined strictly to the surface of the filaments, penetration to any extent into the interior of the fiber being prevented by the large size of the cracking agent molecule.

Liquid cracking agents are preferred. These agents may be pure compounds or their solutions. S No complete list of cracking agents can be given which is operable for all polymers, but the following simple test enables one to determine whether a liquid is a cracking agent or not. In the test a freshly spun, undrawn fiber is drawn a small amount '(about 1.5 under'the surface of the liquid to be tested. By freshly spun is meant a fiber that is less than one week old. This restriction is for the purposes of this test only, since the process of this invention is applicable to a wider range of aged fibers; Microscopic examination-of the filaments will show transverse cracks and/ or multiple neck drawing if the liquid is a suitable cracking agent. It is characteristic of multiple neck drawing that a lower drawing force (as much as 90% less force) is required in comparison with conventional (single neck) cold drawing under the same temperature and speed conditions,

drawing procedures.

pin is not required in the predrawing step, it may be used if desired, and in "some instances gives more satisfactory results.

Following the predrawing step, the filament is further thicker sections have a diameterat least 30% greater ditions which disassociate the filament from the influence of the cracking agent, so that an oriented filament having good tensile properties is produced as in normal In this second drawing step the influence of the cracking agent can be disassociated by drawing at a temperature at which the cracking agent is no longer active, e.g., above 80 C., or by removing the cracking agent from the filament by evaporation, washing, or wipi ng the filament. In order to draw at least 1.5 times in thls second step, the filament orientation must be sufliciently low prior to the predrawing step. Preferably, the initial .undrawn filament is substantially unoriented, i.e., has a birefringence that is less than 10% of the maximum possible, since this provides for more effective surface modification.

H; J. Woods, in the Journal of the Textile Institute Transactions, Vol. 46, pages 629-631 published September 1955, has described a phenomenon of surface cracking in unoriented synthetic polymers and has shown that drawing nylon filaments in the presence of certain cracking agents such as ethanol or acetone, leads to an oriented fiber with a certain degree of surface roughness. Woods. procedure applied to polyethylene terephthalate is found to produce filaments having a configuration similar to a turned bedpost, i.e., the filaments have asuccession of abrupt changes in diameter in which the thicker sections have a diameter at least 30% greater than the thinner sections. The phenomenon described by Woods differs from the invention described herein not only in the size of the non-uniformities imparted to the individual filaments, but also differs in the fact that the process described by Woods always results in a fiber having a reduced tensile strength, which is thought to be a result of the presence of numerous voids observed at the junctions between fiber segments. In contrast, the fibers of this invention are substantially equivalent in tensile strength to conventionally drawn smooth-surfaced fibers.

The coefiicient of hydrodynamic friction used herein is measured by hanging a test filament over a /z-inch diameter polished chrome-plated mandrel so that the filament contacts the mandrel over an arc of approximately 180. A 0.3-gram weight is attached to one end of the filament (input tension) and a strain gauge is attached to the other end (output tension). The mandrel is rotated at a speed of 1800 y.p.m. and the area of contact flooded with a drop of No. 50 mineral oil immediately before strain gauge readings are made. The coefficient is calculated from the belt friction equation:

where j is the coeificient of hydrodynamic friction, T is the input tension, T is the output tension, and on is the angle of wrap. In this test, a commercially available terephthalate polyester yarn is found to give values in the range 0.6 to 0.7 on the particular mandrel employed.

The following examples are presented to illustrate the invention, and are not intended to be limitative.

Example I Polyethylene terephthalate is melt spun to produce an undrawn, 34-filament yarn having a total denier of 210. A 15% aqueous emulsion of butyl stearate is applied to the undrawn yarn which is then wound on a package and stored for 3 Weeks. The aged yarn is then drawn in two stages by passing the yam over a feed wheel having a peripheral speed of 100 feet per minute, then around a -inch diameter unheated stationary ceramic snubbing pin, then around a draw roll rotating at 110 ft./min., around a l fit-inch diameter ceramic stationary snubbing pin heated to a temperature of 90 C., then around a second draw roll rotating at a surface speed of 330 ft./min., and finally to a windup.

The yarn produced is examined under a light microscope at 200x magnification and the filaments found to have a smooth surface with no significant number of bumps or nodules. No voids or bubbles are apparent. Birefringence measurements indicate uniform molecular orientation along the length of the filaments.

The yarn is examined by means of an electron microscope using standard replica techniques and the filaments found to have a surface characterized by randomly spaced, circumferential ridges occurring at an average frequency of about 60 ridges per millimeter along the length of the filament. The average height of the ridges above the surface of the filament appears to be about 0.09 micron. The filament diameter is about 14 microns. Measurement of the hydrodynamic friction coefficient of the yarn gives a value of about 0.43 (as measured on a /z-inch diameter polished stainless steel mandrel rotating at a speed of 1800 y.p.m.). This value is in sharp contrast to a value of 0.74 exhibited by a similar yarn drawn in the same way with the exception that the first draw stage (predraw) is eliminated.

The general procedure described above is repeated, using 15% aqueous solutions or emulsions of the following cracking agents, instead of butylstearate, and the coefficient of hydrodynamic friction measured to give the results shown in the following table:

Cracking agent: 1'- Polyethylene oxide (400 mol. Wt.) 0.48 Polyethylene oxide (600 mol. wt.) 0.47 Poly(ethylene glycol) monolaurate 0.46 Oleylalcohol/9 mols ethylene oxide 0.50

Copolymerized ethylene glycol/propylene glycol (random) 0.49 Eicosane 0.54 Isopropyl myristate 0.55

The low coefficient-of-friction values shown in the table correlate well with the reduced running tensions and improved processability shown by these yarns.

Example 11 Polyethylene terephthalate is melt spun to give an undrawn yarn of 4.5 denier per filament. During spinning a polyethylene oxide of molecular weight 400 is applied to the filaments as a spinning finish from an aqueous solution. The undrawn yarn is aged for 2 days. Yarn ends from 25 bobbins are then combined to form a tow of 50,000 total denier and drawn as follows: The tow is passed around a set of feed rolls rotating at peripheral speed of 60 ft./min., then passed in an S-shaped wrap around a pair of /z-inch polished stainless steel stationary snubbing pins, and then around a second set of rolls rotating at a peripheral speed of 63.5 ft./min., then passed through an aqueous bath maintained at C., then around a third set of draw rolls rotating at a peripheral speed of 203 ft./min. The drawn tow is crimped to give a nominal 8 crimps per inch, relaxed for 5 minutes at 105 C. in an oven, and then cut to give a staple in which the filament length is 1 /2-inCh. The staple is then carded and spun into a yarn on the cotton system.

A control sample is prepared from the same supply yarn in a similar fashion with the exception that the firststage snubbing pin is eliminated and the speeds of the first and second set of rolls are the same, i.e., there is no predrawing step.

Tests carried out on the two above items to show tensile and frictional properties gave the results shown in the following table:

The test staple is examined under an optical microscope and found to have the smooth surface normally associated with melt-spun fibers. Under the electron microscope, however, the surface of the filaments is found to possess randomly distributed, transverse ridges occurring along the length of the filament at a frequency of about ridges per millimeter. The average height of the ridges appears to be about 0.10 micron. Most of the ridges appear to travel more than halfway around the circumference of the filaments, but do not appear to make a complete circle. No significant number of bumps or nodules are found on the filaments.

Example Ill Polyethylene terephthalate containing 0.3% TiO delusterant is melt spun to give a 34-filament yarn having a total denier of 210. During spinning, an aqueous finish containing polyethylene oxide of molecular weight 400 is applied to the filaments. The filaments are aged 30 days and then drawn in a two-stage process as follows. In the first stage the filaments are drawn to 1.05 times the 7 a original length at roomtemperature with a snubbing pin in the draw zone.

ln the'second stage the filaments are ."ments) is melt s puri and a 15% emulsion of butylstearate passed around a draw pin heated to 95 C. and drawn to 3.0 times greater length. "(The filaments have a tenacity of 3.6,g.p.d. at. a break elongation of 20%.

The filaments producedabove are examined by optical microscopy and found to have the smooth surface characteristic of melt spun fibers. or sections of enlarged diameter. are apparent. V

The filaments are examined in profile by electron microscopy and found topossess surface bumps which occur with a frequency of about 50 ridges per millimeter along the filament. The average height of thebumps above the surface of the filament is found to be about.0.07 micron. When surface replicas are prepared and examined by electron microscopy, the above-observed bumps are found to be transverse ridges extending for the most part .more than half-way around the'filament. 5

A control yarn prepared in a similar fashion, with the exception that no. predrawnstep is used, is found to have No bumps, protuberances,

" 2.8times its length ona third set of rolls operating at :1

erties of these three yarns are tabulated below:

a smooth surface by optical microscopy and also by elecf tron miscroscopy. 7

Measurement of the hydrodynamic friction coefiicientof the test and control yarns gives a valueof about 0.55

for ridged test yarn anda value of about 0.67 for the smooth control yarn.

' Example IV A copolyrner of polyethylene terephthalate containing" 2 mol percent S-sodiumsulfoisophthalic acid, and with no TiO present, is melt spun to give a 34-filament yarn having a total undrawn denier of- 230. Y-shaped spinneret;

holes are used and the quenching condition adjusted so that the yarn produced has a trilobal cross-section of the type disclosed in FIG. Zof Holland US. Patent No. 2,939,201, dated June 7, 1960. Duringspinning, poly ethylene oxide of molecular weight 400 is applied to theperipheral speed of250 ft./ min. The yarn is then relaxed for 6 minutes at 140 C. under no load. Item B is prepared similarly, except that the yarn is not snubbed in the first drawzone Item C is prepared similarly to items A and B except that no snub is used inthe first stage and the speed of the second set'of rolls is set at 90 ft./min. so that no drawing takes place in the first stage. The prop- Tenacity, Elonga: Initial 100 0. Item g.p.d. V tion, modulus, shrinkage f 1 percent g.p.d.

Examination of the three yarns by means of an electron microscope shows that control item C is made up of smooth-surfaced filaments in contrast to items A and B which show numerous circumferential ridges, in accord with the present invention.

..Exa mple VI A series of textile yarns are melt spun from several different polyesters and the undrawn yarn aged in contact yarn as an aqueous finish. After aging for '3 days, the p yarnis drawn at room temperature'to 1.06 times its length with the draw taking place on an unheated ceramic snub bing pin. Subsequently, the yarn is drawn to 2.7 times itslength over a snubbing pin immersed in bath maintained at a temperature of 90 C. 7

Measurement of the tensile properties of the yarn gives values of 2.75 g.p.d. for tenacity and 25% for break elongation.

an aqueous is used.

Examination of the test yarn by optical microscopy revealed filaments of smooth profile having no visible bumps or significant changes in yarn diameter. However, the filaments do exhibit a number of randomly'dispersed transverse flines which are vunresolvable under the light, microscope, and which occur with a frequency of about;

80 ridges per millimeter. v

Surface replicas of the test filaments are observed under an electron microscope; The surface is characterized by a series of randomly spaced,'discontinu'- These values are substantially the same as, those obtainedfor a control yarn prepared in exactly'the' same manner with the exception-that no predrawing step.

prepared and with butylstearate'for three days. The aged, undrawn yarns are the'predrawn at a .draw ratio of 1.1, using a 3/ 16-inch diameter snubbing pin in the draw zone. ,These predrawn yarns are then further drawnover a hot pin to give a total draw of about 3.0 times. Examination of the .drawnfilamentsby electron microscope shows the presence of circumferential ridges occurring at a frequency lowing table.

Copolyester of ethylene ephthalate/isophthalate) (90/10 mol ratio), poly(ethylene terephtha1ate[hexahydroterephthalate) (90/ '10 and /20), poly[ethylene terephthalate/S-(sodium sulfo)isophthalate] [965/35], poly(ethylene 2,6-naphthalene dicarboxylate), poly[ethylene 2, 6-naphthalenedicarboxylate/S-(scdium sulfo)isophthalate] (97/3).

0 Example V k A polyethylene terephthalate'yarn (4.5 d.p.f., 140 fila- Thepolyester of 2,6-bisinthe range of 35 to 55 ridges per millimeter.

Control samples are prepared in a similar manner, but with thepredrawing step eliminated. Examined by electron microscope, thefilaments are found to have a smooth surface. 1 a

I The test andcontrol yarns are tested for coeificient of hydrodynamic friction, with the results shown in the fol- In the table, 1 values in the column labeled flooded are from a test carried out. as described. in ExampleI. Coeificient values in the. column marked film are from a test similar to that in Example I, with the exception that the drop of oil is wiped off the mandrel- Film Flooded Polymer Test C ontrol Test Control glycol, terephthalic acid and hexahydroterephthalic acid (acid mol ratio 83/17) The copolyester of ethylene glycol, terephthalicacid, and sebaeic acid (acid mol, ratio /10)"; The polyester of ethylene glycol and bibenzoic acid;

0. 83 0. 78 hydroxymethyldecalin and bibenzoie acid The copolyester of hexahydrop=xylylene glycol, bibeuzoio'acid and i50 propylidene dibenzoic acid (acid mol ratio 90/10) The data in the table clearly show the improved frictional properties of the fibers of this invention.

Although the examples above show the application of the principles of the present invention in connection with certain specific polyester filaments, it is obvious that any fiber which cold draws, and which possesses a surface which can be caused to crack by extending the length of the filament up to about after proper aging treatments, can be employed to give ripple-surfaced filament products of the type described. Thus, many other melt-spun polyester filaments are also useful for providing the products of this invention.

Because of their commercial availability, ease of processing and excellent properties, the condensation polyesters and copolyesters, particularly those that can be readily melt spun, are preferred for application in this method. Suitable polyesters are described, for example, in US. Patents Nos. 2,465,319, 3,018,272, 3,057,826, 3,057,827, and 2,901,466.

In a preferred embodiment of the invention, the fiberforming polymer is a synthetic linear condensation polyester of bifiunctional ester fonming compounds wherein at least about 75% of the repeating structural units of the polymer chain include at least one divalent carbocyclic ring containing at least six carbon atoms present as an integral part of the polymer chain and having a minimum of four carbon atoms between the points of attachment of the ring in the polymer chain (para-relationship in the case of a single 6-membered ring) The polyesters may be derived from any suitable combination of bifunctional ester-forming compounds. Such compounds include hydroxy acids such as 4-(2-hydroxyethyl)benzoic acid and 4fl(2-hydroxyethoxy)benzoic acid, or mixtures of the various suitable bifunctional acids or derivatives thereof and the various suitable dihydroxy compounds and derivatives thereof. The repeating structural units of the polymer chain comprise recurring divalent ester radicals separated by predominantly carbon atom chains comp-rising hydrocarbon radicals, halogen-substituted hydrocarbon radicals, and chalcogen-containing hydrocarbon radicals wherein each chalcogen atoms is bonded to carbon or a different chalcogen atom, and no carbon is bonded to more than one chalcogen atom. Thus, the repeating units may contain ether, sulfonyl, sulfide, or carbonyl radicals. Sulfonate salt substituents may also be present in minor amount, up to about 5 mol percent total sulfonate salt substituents in the polyester based on the number of ester linkages present in the polyester. Other suitable substituents may also be present.

Among the various suitable dicarboxylic acids are terephthalic acid, bromoterephthalic acid, 4,4'-sulfinyldibenzoic acid 4,4-dip*henic acid, 4,4-benzophenonedicarboxylic acid, 1,2-bis(4-carboxyphenyl)cthane, 1,2-bis(pcarboxyphenoxy)ethane b-is-4-carboxyphenol ether and various of the naphthalenedicarboxylic acids, especially the l,-4-, 1,5-, and 2,7-isomers. Isophthalic acid is also suitable, especially when used in combination with a 1,4- dihydroxyaromatic compound. Carbonic acid is similarly suitable.

Among the various suitable di hydroxy compounds are the glycols, such as ethylene glycol and other glycols taken from the series HO(CH OH, where n is 2 to 10; cisor trans-p-hexahydroxylylene glycol; diethylene glycol; quinitol; neopentylene glycol; 1,4-bis(hydroxyethyl)- benzene; and 1,4-bis(hydroxyethoxy)benzene. Other suitable compounds include dihydroxyaro-matic compounds such as 2,2-bis(4-hydroxy-3,S-dichlorophenyl)- propane, hydroquinone, and 2,5- or 2,6-dihydroxynaphthalene.

Since many diiferent embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.

I claim:

1. A substantially oriented synthetic linear condensation polyester fiber having a surface characterized by a series of randomly spaced, discontinuous circumferential ridges of sub-microscopic size occurring with a frequency between 10 and 130 ridges per millimeter along the length of the fiber, the fiber being free of diameter variations in excess of 5% of the base fiber diameter.

2. A fiber as defined in claim 1 wherein the ridges are of such length that the arc is at least of the circumference.

3. A fiber as defined in claim 1 wherein most of the ridges are at angles between 70 and to the direction of the fiber axis and have a height within the range 0.07 to 0.12 micron.

4. A fiber as defined in claim 1 which is free from voids or dispersed insoluble particles other than conventional delusterants.

5. A fiber as defined in claim 1 wherein the fiber is composed of ethylene terephthalate linear condensation polyester.

References Cited by the Examiner Kunze: Reyon Zellwolle and andere Chemiefasern, Jahrq. 32, Heft 11, November, 1954, pp. 703-708. (PP. 703 and 704 of interest only) EARL M. BERGERT, Primary Examiner.

Claims (1)

1. A SUBSTANTIALLY ORIENTED SYNTHETIC LINEAR CONDENSATION POLYESTER FIBER HAVING A SURFACE CHARACTERIZED BY A SERIES OF RANDOMLY SPACED, DISCONTINUOUS CIRCUMFERENTIAL RIDGES OF SUB-MICROSCOPIC SIZE OCCURRING WITH A FREQUENCY BETWEEN 10 AND 130 RIDGES PER MILLIMETER ALONG THE LENGTH

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