CA2028061A1 - Low shrinkage, high tenacity poly(hexamethylene-adipamide) yarn and process for making same - Google Patents

Abstract

TITLE
Low Shrinkage, High Tenacity Poly(Hexamethylene Adipamide) Yarn and Process for Making Same ABSTRACT OF THE DISCLOSURE
A polyamide yarn is disclosed which is at least 85% by weight poly(hexamethylene adipamide) and which has a relative viscosity of greater than 50, a tenacity of at least about 9.5 g/d, a modulus of at least about 30 g/d, a shrinkage at 160°C of less than about 2 percent, a crystal perfection index of greater than about 83, and a long period spacing of greater than about 105 .ANG.. The process for making the yarn includes drawing of a feed yarn while heating to at least about 190°C in at least a final draw stage to a draw tension of at least 3.8 g/d, subsequently decreasing the tension while heating to at least about 190°C to produce a length decrease of between about 13.5 and about 30%, and cooling and packaging the yarn.

Description

-1- 2~2~().~il TITLE
Low Shri~kage, High Tenacity Poly(Hexamethylene Adipamide) Yarn and Process for Making Same BACKGROUND OF THE INVEN~ION
The pre~ent invention relates to indus~rial polyamide yarns and more particularly relates to high tenacity poly(hexamethylene adipamide) yarn having low shrinkage and a proces6 for making such yarns.
A wlde variety of high tenacity polyamide yarn~
are known and are used commercially for a variety of purpos~s. Many o~ 6uch polyamide yarns are use~ul in cords for tlre~ due to high tenacity, i.e., up to but generally not exceeding 10.5 g/d. 9uch yarns also have tolerable level~ of dry hsat shrinkage for ~onver~ion to tire cords, typically 5-10% at 160C.
For certain applicationfi 6uch a~ ropes, indu~trial fabrics, airbags, and reinforced rubber good~
such as hoses and conveyer belts, yarns with shrlnkage less than that found in tire yarns are desirable. While 60~e low shrinkage yarn~ are known, the tenacity o~ such yarns generally decrea~e6 with decreasing 6hrinkage. The lower tenacity thus require~ the usually undesirable use of heavier denlers or th~ increa6ed number of yarns in the end-u~;e application. Other low 6hrink~ge yarns with high tenacity level~ have been made u~ing proces6es employing tre~tment steps ~uch a6 steaming for relatively long periods after drawing but ~uch processes are u~ually not well-suited for commercial production. In addition, the yarns made by ~uch proce~es typically have ~reatly reducsd modulus levels and undesirable growth properties.
A heat-~table polyamide yarn with very low shrinkage while at the same time providing high tenacity RD-4637 would be highly desirable for such applications, particularly with a balance of propertie including a low shrin~age tension and high modulus. Such yarns would be

-2 2~2~

even more desirable if the yarns were readily manufactured in a commercially-fea~ible process.
SUMMARY_OF THE INVENTION
In accordance with the invention, a polyamide yarn which i~ at least about 85% poly(hexamethylene ~dipamide) i8 provided which ha~ a relative visco~ity of greater than 50, a tenacity of at least about 9.5 g/d, ~
modulu6 of at le~st about 30 g/d, a dry heat ~hrinkage at 160C of les6 than about 2 percelnt, a cry6tal perfection index of greater than about 83, and ~ long period spacing o gr~ater than about 105 A.
In accordance with A preferred ~orm o~ the pre~ent invention, the yarn has a modulus of greater than about 35 g/d and a density of at le~st about 1.15 g/cc.
Preferred yarn6 ln accordance with the invention have a tenacity greater than about 10 g/d and maxlmum 6hrinkage teneions o~ le66 than about 0.37 g/d. Yarns in accordance with the invention preferably have values for elongation to break of greater than about 18~ and toughne~ values o~
greater than 200 g/d-%.
~he novel high tenacity yarn~ in accordance with the invention provide dry heat shrinkagee of le66 than 2 percent while al~o maintaining an ~xcellent combination of other end-use.characteristic~ including a high modulus.
In addition, the dry heat ~hrinkage tension of preferred yarns doec not exceed about 0.37 g/d. Thus, in uses ~uch a6 in a woven fabric in which the yarns are constrained, the actual ~hrinkage ~ay be considerably less than the value for th~ yarn~ at 160C.
In accordance with the invention, a proces~ is provided for making an at least about 85%
polythexamethylene adipamide) yarn having a tenacity of at least about 9~0 g/d, ~ dry heat shrinkage of lss~ than about 2%, and modulus of at least 30 g/d from a drawn, partially-drawn, or undrawn fe~d yarn. The process include~ drawing the yarn in ~t least a final draw staye 2~28~

while heating the feed yarn. The drawing and heating is continued until the draw tension reaches at least about

3.8 g/d when the yarn is heated to a yarn draw temperature of at least about 190C. The tension on the yarn is decreased after drawing sufficiently to allow the yarn to decrease in length to a maximum length decrease between about 13.5 and about 30%, preferably between about 15 and about 25%. During the relaxation, the yarn is heated to a yarn relaxation temperature of at least about 190C when the maximum length decrease ls reached.
In a preferred process, the heating during the relaxation i5 continued for a duration sufficient to cause the yarn ~o have a crystal perfection index of greater than about 83. Preferably, the decreasing of the tension is performed by decreasing the tension partially in at least an initial relaxation increment to cause an initial decrease in length and then further decreasing the tension to cause the yarn to decrease further in length to its maximum length decrease in a final relaxation increment.
In a preferred process, the yarn relaxation temperature is attained by heating in an oven at between about 220 and 320C for between about 0.5 and about 1.0 seconds as the maximum length decrease is reached.
The process of the invention provides a commercially-feasible process in which a warp of multiple feed yarn ends can be convertèd to yarns with both high tenacity and low shrinkage. ~eed yarns ranging from undrawn to "fully drawn" yarns can be used successfully in the process. When fully drawn yarns are used as feed yarns in the process, the shrinkage of those yarns can be reduced to levels below 2% while other functional properties such as high tenacity, high elongation and high modulus are maintained. When undrawn or partially. drawn feed yarns are used, they can be converted to high tenacity, low shrinkage and high modulus yarns.

2 ~ 2 ~

BRIEF DESCRIP'rION OF THE DRAWING
The Figure i6 a diagrammatical view of a process useful in making preferred yarns in ~ccordance with the pre~ent invention.
DETAILED DESt:RIPTION
Fiber-for~ing polyamidles u6eful for yarn~ in accordance with the invention are at lea6t about 85%
poly(h~xamethylene adipamide) h~ving ~ rel~tive vl~c06ity of above about 50 on ~ formic ~cid basi~ and which are typically melt-~pinnable to yield high tenacity ~lber~
upon drawing. Pr~ferred polyamides have a relative viscosity of above about 60. Pre~erably, the polyamide is homopolymer poly~hexamethylene adipamide) which i6 o~ten referred to as 66 nylon.
~he tenacity of the yarn~ in accordance with the invention l~ at least about 9.5 g/d ~nabling the yarns to be useful for application6 requiring high ten~citie~.
Prefer~bly, the yarn ten~city i~ ~t lea6t about 10.0 g/d.
In yarns of the invention, yarn tenacitie~ can be as high as about 1~.0 g/d or ~ore. The modulu6 o~ preferred yarns is at least about 30 g/d and preferably is at lea6t about 35 g/d. Modulu~ values of up to about 60 g/d or more are po6sible. The preferred elongation to break i6 at lea6t about 18~ ~nd can be a~ high a~ about 30% re~ultlng in preferred toughne6~ value~ (tenacity x break olongation) of greater than about 200 g/d %, mo~t pre~erably above about 225 g/d-%. Toughne66 c~n be a~ high as about 300 g/d % or more.
The denier of the yarn~ will vary widely depending on the intended end u6e and the capacity o~ the equipment used to m~ke the yarn~. Typical denier~ are, for example, on the order of 100-4000 denier. The denier per fila~ent (dpf) can al~o r~nge widely but i~ generally between about 1 and about 30 denier for ~o~t industrial application~, prefer~bly between about 3 and about 7 dpf.

2~2~
The dry heat 6hrinkage of the yarns of the invention i~ less than 2.0% at 160C making the yarn~
particularly well-suited for applications where low shrinkage is desirable. In general, it is very difficult to decrease the shrinkage below about 0.3% and still maintain high tenacity and high modulu~ and thus a preferred ~hrinkage range i~ bet.ween about 0.3% and about 2.0~. For yarns of the invention, ~hrinkage ten~ion~ ~re exceedingly low ~t typlcal tempe!rature~ of u~e since maxlmum shrinkage tensions do not occur until clo8e to the meltlng polnt of the polymer, l.e., greater than about 250C. Maximum ~hrlnkage ten6ion is preferably less than about 0.37 g/d and most preferably les6 than about 0.30 g/d. Shrinkage tension levels in yarns of the invention can be a~ low as about 0.15 g/d or less. Growth o preferred yarn~ is less than about 9% and can be as low as 5% or le6s.
The combination of high tenacity, low 6hrinkage and high modulus in yarns in accordance with the invention, a6 well as other useful properties, are due to the novel fine structure of the fiber. The novel fine structure is characterized by a combination of properties including a cry~tal perfection index (CPI~ greater than about 83 which ha6 not previously been ob6erved in polyamide fibers. A long period spacing greater than about 105 ~ i6 al~o characteri6tic of the fiber6 of the invention. A normalized long period intensity (LPI) of greater than about 2.7 i~ observed in preferred yarns in accordance with the invention. The apparent crystallite ~ize (ACS) 16 v~ry large, preferably greater than about 62 in the 100 plane. Preferred yarn~ of the invention have a high density of gre~ter than about 1.15 g/cc and values of birefringence which are greater than about 0.056.
Preferred yarns have ~onic modulus values which are greater than about 80 g/d.

2 ~ 2~

It is believed that the fiber fine structure function6 as follows to provide the combination o~ high tenacity, low ~hrinkage, high modulus and other excellent properties. In polyamide fibers, there are at least two pha~e~ which are functionally connected in 6erie~ and which are respon~ible for fiber properties. One of these pha~es i6 crystalline and is made made up of cry6tals which are effectively nodes in a highly on~-dimen~ional molecular network. Connecting the crystals are noncrystallin~ poly~er chain seyment~. The concentrAtion (l.e. number per unit cros6-~ectional area) and uniformity of these connector molecules determines the ultimate fiber ~trength.
In a fiber ln accordance with the invention, the crystallinlty, n~ revealed by the exceptlonally high den~ity, htgh crystal perfection index, and high apparent cry~tal size, .i6 extremely high which reduces the fraction of the fiber ~usceptible to ~hrinkage due to thermal retraction of the connector molecules. The fibers have a highly extended structure but with low internal 6tress 6tructure a6 revealed by the high birefringence and low shrinkage and shrinkage tension. Furthermore, ln the yarn6 of the invention, it i8 believed that the cnnnector molecule~ are organized 60 that their concentration across plane6 perpendicular to the fiber axis is at an extremely high level. It i~ believed that the connector molecules are thereby clo~e enough together laterally that they interfere with each other in a way which reduces 6hrinkage, while 6till incre~sing ~trength and maintainin~
modulu~.
Yarns in accordance with the invention c~n be produced from known polya~ide yarns in a process in accordance with the invention which include~ carefully controlled drawing and relaxation ~teps. The process is advantageou~ly practiced u6ing a warp of a multiplicity of feed yarn ends ~o improve economics relating to the production of the yarn of the invention.

-7- 2~2~

A~ will become more apparent hereinafter, feed yarns for producing yarns of the invention mu~t be of good quality and can be "fully" drawn, partially drawn, or undrawn polyamide yarns. Good quality feed yarns, that i8, yarns with few broken filament~, wlth low along end denier variability, and compri6ed of polymer containing little or no none66ential material~ fiuch a~ delusterant~
or large ~pherulites ~re e66ent1al for acceptable proce~6 continulty. "Fully" drawn i6 intended to refer to yarn~
having properties corre~ponding to yarn~ which are drawn to a high tenacity level for an intended end u~e in a currently-used, commercially~practical manu~acturing procesa. Typic~l commercially-avallable "fully" drawn yarns suitable for u~e as foed yarns hav~ a tenacity o~
about 8-10.5 g/d and have a birefringence o~ about 0.050-0.060. Partially drawn and undrawn feed yarns ar~
typically not widely available commercially but are well-known in the art. Partially drawn yarns have been drawn to some extent but generally are not u~eful without further drawing. Such partlally drawn yarn6 typlcally have a birefringence of about 0.015-0.030. Undr~wn iB
int~nded to refer to yarn which ha6 been ~pun and quenched but has not been drawn 6ub6equently to quenching.
Typically, the birefringence of undr~wn yarns is on the order of about 0.008.
Referring now to the Figure, apparatus 10 ls illu6trated which can be employed in a proce~ o~ the invention to make yarns in accordance with the invention from "fully" drawn, partially drawn or undrawn feed yarns.
While a single end proce~ i6 shown and descrlbed hereinafter, the proc2~s i~ directly applicable to a multiple end proc0~s in which a warp of a multiplicity of feed yarn end~ is employed to improve economy. With reference to the Figure, feed yarn Y i8 led from a supply package 12, passed through a ~uitable yarn ten6ion control element 14, and enters a draw zone identified ~enerally by the numeral 16.

-B- 2~2~30~:~

In the draw zone 16, feed yarn~ are drawn while being slmultaneou61y heated in at lea6t a final draw 6tage a~ will become more apparent hereinafter. The drawing and heating is performed until a draw tension of at least about 3.8 g/d i8 applied to the yarn when the yarn ha6 been heated to the yarn draw te~perature of at least about 190C. To achieve thi~, different drawing ~teps, differing total draw ratios and different heating pattern6 are used fsr differing feed yarn~. For example, a total draw of 5.5X or more with an initial unheated draw ~tage may be nece~sary Eor undrawn yarn6 while a draw of 1.1-1.3X may be ~uitable for "fully" drdwn yarn~.
Partially drawn yarn~ may be drawn to some intermediate ratio. In the drawing of all the feed yarn type~, the tenacity during the final draw etage, if mea~ured, generally will increa6e to greater than the initial tenacity of a typical "fully" drawn yarn by about 10% to 30%, i.e., to about 10.5-12.5 g/d.
In the final draw stage, the drawing is preferably performed in increment6 a6 the yarn is heated.
Drawing can be begun on heated roll6 with a 6erie6 of succe66ive drawing step6. Due to the high temperature~ to be reached when the draw ten~ion i~ at least about 3.8 g/d, non-contact heating of the yarn i~ preferred. Such heating can be accompli6hed in a forced-air oven, with an infrared or microwave haater, etc., with heating in an oven being preferred.
Referxing again to the Figure, the drawing of the yarn Y in draw zone 16 of the process illustrated begin~ a6 the yarn pa~ses in a ~erpentine fa6hion through a Pir~t ~et of ~ven draw rolls identified collectively as 18 and individually ~s 18a-18g. ~he~e roll6 are suitably provided by godet rolls which have the capability of being heated ~uch a~ by being internally-heated by the circulation of heated oil. In addition, the rotational velocity o~ khe rOllB i6 controlled to impart a draw of ~9~ 2~2~06:?~

typically .5% to 1~ to the yarn between ~ach ~uccessive roll in the set of rolls to draw the yarn slightly and to maintain tight contact of the yarn with the rolls. The yarn Y is pressed against the first roll 18a by a nip roll 20 to prevent slippage.
Yarn Y i6 then forwarded to a second set 22 of 6even draw rolls 22a-22g which are internally heated and the rotation~l velocity of which ifi co~trolled ~lmilarly to the first roll set 18. Typically, the rot~tional velocity of the rolls iæ controlled to i.mpart a draw of typically .5~ to 1~ to the yarn between each ~uccessive roll in the ~et of rolls afi ~n the flr~t roll æet. The veloclty difference between the first roll set 18 and the æecond roll set 22 ~between roll 18a and roll 22a) can be varled to draw the yarn as it advance6 between the ~ets of rolls. ~or undrawn ~eed yarn6, ~ m~ority of the draw, e.g., ~.5-4.5X i~ u~ually per~ormed in an lnitial "space"
draw area between the first and second roll 6ets with only moderate or no heating of the fir6t roll set 18. For "fully" drawn eed yarns, substantially no draw is typically imparted to the yarn between the first and second roll set6 18 and 22 and the first roll set 18 can be bypa~æed if desired although it i6 u~eful to run the yarn through the nip of rolls 18a and 20 to e~tabli~h positive engagement of the y~rn and avcid slippage during later drawing. Partially drawn yarns generally should be drawn as needed in the æpace draw zone so that the overall draw experienced by the yarns after sp~ee drawing i~
~imilar to or somewhat le6s than "fully" drawn feed yarns.
Usually, for all feed yarnæ types, the second roll eet 22 is used to heat the yarn by conduction ~n preparation for the final drawing at elevated temperature, e.g., roll temperature~ of typically about 150-215C.
After advancing pa~t the 6ec~nd roll çet 22, the yarn Y enter6 a heated draw area provided by two ovens, Z4 and 26, reæpestively, which can be the forced hot air type -lo- 2~

with the capability to provide oven temperatures of at least about 300C. The final draw ~tage which achieve6 the maximum draw of the process i6 performed in the heated draw area. The residence time and the temperature of the ovens i~ such that the yarn Y i5 heated to at lea~t about 190C but the yarn temperature cannot exceed or approach the polyamide melting point too clo~ely. To accompli6h the heating ef~ectlvely, the oven temperaturea may exceed the yarn temperature~ by a6 much A6 130C or more at typical proce~s ~peeds. For the poly(hexa~ethylene adipamide) yarns of the invention, preferred y~rn temperatures are between about 190 and about 240C and the oven temperatures are pre~erably between about 220 and about 320C with a residence time of between about 0.5 and about 1.0 ~econd6. The draw ln the heated draw area l~
determined by the speed of th~ fir~t roll 22~ of the socond roll 6et 22 and the fir6t roll 28a of the third roll set 28 ~seven rolls 28a-2Bg) through which the yarn Y
advance~ in a ~erpentine fa~hion after leaving the ovens 24 and 26. The total draw for the proce~ is determined by the velocity of the first roll 18a in the fir~t roll set and the speed of the first roll 2Ba in the third roll 6et. This first roll 28a in the third roll ~et marks the end of the draw zone 16 since, unlike the ~ir~t And 6econd roll sets, the v~locity of succes6ive roll6 of roll 6et 28 decreases by between 0.5-1.0% a~ the yarn advances. Thus, a relaxation zone of the proce6s, which ic identi~ied generally by the numeral 30, begins at roll 28a.
In the relaxation zone 30, the yarn i6 relaxed in a controlled fashion (the tension i~ decre~sed and the yarn is allowed to decrease in l~ngth) by between about 13.5 and about 30%, pref~rably between about 15 and about 25%. The yarn is heated during the relaxation ~o that a yarn relaxation temperature of above about 190C is reached. To assist in maintaining proce6~ continuity during r~laxation and ~aintain high modulus and low growth in the product, a 6mall tension ~hould be maintained on the yarn, typically above about 0.1 g/d.
The relaxation is preferably performed in increments as the yarn is heated. The lnitial relaxation can be perf~rmed on heated rollE; and advantageously i6 a series of ~ucce6sive relax~tion 6teps within the initial relaxation increment. Due to the high temperature6 neces~ary during the final relaxation incre~ent, non-contact heating of the yarn i6 pre~erred, preferably in an oven. In the preferred proce~s, the heating during relaxation i6 continued for a duration ~u~ficient to cause the yarn to have a cry~tal per~ection index of graater than about 83.
A6 illu6trated in the Figure, the relaxation in the preferred procegs illu6trated i~ performed initially by the incremental ~elaxation on the third roll ~et 28 the roll5 of which are heated to about 150-215C. The yarn then pa~ses through relaxation ovens 32 and 34 capable o providing maximum oven temperatures of at least about 300C during which the maximum relaxation occur~.
Achieving the nece6~ary yarn relax~tion temperature depends on the oven temperature and re~idence time of the yarn in the ovens. Preferably, the ovens contain air at temperatures in exce~s of the yarn te~perature by a~ much as about 130C for e~fective heating at rea~onable process 6peeds. For the poly(hexamethylene adipamide) yarns of the invention, preferred yarn temperatures are between about 190 and abou~ 240C and the oven temperatures are preferably betw~en about 220 and nbout 320C with a residence time of between about 0.5 and about 1.0 ~econds.
A~ter the yarn pas6e~ through the oven~ 32 and 34, yarn Y then pa~es through a fourth roll 6et 36 of 3 roll~ (36a-36c) in a 6erpentine fa~hion with the yarn Y
being pres6ed against the la~t roll 36c by nip roll 38 to prevent slippage. The ~urfaces of the fourth roll set 36 can be internally cooled with chilled water to assist in ` -12- %~280~

reducing the yarn temperature to a level suitable for wind-up. The yarn is re~ensioned ~lightly on roll 36c in order to produce a stable running yarn and avoid wraps on roll 36b. The total relaxation is thus determined by the velocity difference between the first roll 28a of the third roll ~et 28 and the fir~t roll 36a of thP fourth roll 6et 36.
After leaving the relaxation zone 30 of the proce~s, the yarn Y i6 fed through a yarn ~urface treatment zone 40 which can include an interlace jet (not ~hown) to commingle the yarn filaments, a Pini6h applicator 42 to apply a yarn fini6h or other treatments to the yarn. At a wind-up station (not ~hown), the multiple ends of yarn Y are wound up onto suitable packages for shipping and end use.
In a proce~ in accordance with the invention using apparatu~ as illustrated for a warp of multiple end~, preferred wind-up speeds are from 150 mpm to 750 mpm.
The following examples illustrate the invention and are not intended to be limiting. Yarn propertie~ are mea6ured in accordance with the following test methods.
Percentages are by weight unle6s otherwise indicated.
TEST METHODS
Conditioning: Packaged yarns were conditioned before te6tlng for at least 2 hour~ in a 55% +2% relative humidity, 74F ~2F (23C *1C) atmo6phere and measured under ~imilar condition~ unles~ otherwise indicated.
Relative Vi~cosity: Relative viscosity refers to the ratio of solution and solvent viscosities measured in a capillary viscometer at 25C. The ~olvent is formic acid containing 10% by weight of water. The ~olution is .4% by weight polyamide polymer di6solved in the solvent.
Denier: Denier or linear density is the weight in grams of 9000 meters of yarn. Denier i6 measured by forwarding a known length of yarn, usually 45 meters, from 2~?,80~ ~

a multifilament yarn packa~e to a denier reel and weighing on a balance to an accuracy of 0.001 g. The denier is then calculated from the measured weight of the 45 meter length.
Tensile Properties: Tensile properties (Tenacity, Elongation at break and Modulus) are measured as described by Li ln U.S. Pat~nt No. 4,521,484 at col. 2, line 61 to col. 3, line 6, the disclosure of which is hereby incorporated by re~erence.
Init~al modulu~ i6 determined from the ~lope of a line drawn tangentiAl to the l'lnltl~l" stralghtllne portion o~ the stres~ strain curve. The "initial"
~traightline portion is defined a~ the stralghtline portion ~tarting at 0.5% o~ full 6cale load. For example, Eull scale load i8 50.0 pounds for 600-1400 deni0r yarns~ therefore the "initial" ~traightline portion of the stress-6train curve would start at 0.25 lb~. Full 6cale load is 100 pounds for 1800-2000 denier yarns and the initial stralghtline portion o~ the curve would start at 0.50 lbs.
Toughness: Toughness is calculated as the product of the measured tenacity g/d and measured elongation at break (%).
_ry Heat Shrinkage: Dry Heat Shrinkage i6 measured on a Testrite ~hrinkage instrument manufactured by Testrite Ltd. H~lifax, England~ A ~24" (61 cm) length o~ multifilament yarn 1B inserted ~nto the T~strite and the shrinkage recorded after 2 minutes at 160C under a 0.05 g/d load. Initial and final lengths are determined under the 0.05 g/d load. Final length is measured while the yarn is at 160C.
Shrinkage Tension: The maximum shrinkage tension and the temperature at ~aximum shrinkage tension are measured as de~cribed in U.S. Patent 4,343,B60, col.
11, lines 15 to 33, the disclosure of which is incorporated by reference. In this method a 10 cm loop is ~2~0~ 3 -1~- . ...

heated in an oven at 30C per minute and the tension is measured and plotted against temperature to obtain a tension/temperature spectrum. The yarn samples were heated up to the melting point of the yarn (260-265C.).
The temperature at maximum shrin~age tension and the maximum shrinkaye tension or force are read directly off of the tension/temperature spectrum.
Growth: The fiber growth is measured by suspending a 50 to 60 cm length of yarn from a frame, measuring its initial length under a 0.01 y/d load, an~
then measuring its length after 30 minutes under a 1.0 g/d load. The growth is calculated as a % from the followiny formula:
L(~:)-L(i) ~ Growth = ----~~ X 100 L(i) Where L(f) is the final length after 30 minutes and L(i) is the initial length.
~irefringence: The optical parameters of the fibers of this invention are measured according to the method described in Frankfort and Knox U.S. 4,134,882 beginning at column 9, line 59 and ending at column 10, line 65, the disclosure of which is incorporated by reference, with the following exceptions and additions.
First, instead of Polaroid T-410 film and lOOOX i~age magnification, high speed 35mm film intended for recording oscilloscope traces and 300X magnification are used to record the interference patterns. Also suitable electronic image analysis methods which give the same result can also be used. Second, the word "than" in column 10, line 26 is replaced by the word "and" to correct a typographical error.
X Ray Parameters Cr~stal_ erfe_ti n Index and Apparent Cryst_llite Size: Crystal perfection index and apparent crystallite size are derived from X-ray diffraction scans.

2~0~

The diffraction pattern of fiberfi of the6e compositions is characterized by two prominent equatorial X-ray reflections with peak6 occurring at 6cattering angle approximately 20-21 and 232~.
X-ray diffractlon pattern6 of the6e fiber6 are obtalned with an X-ray di4fractometer (Phllip6 Electronic Instrument6, Mahwah, N.~., c~t. no. PW1075/00) ln reflection mode, using a diffracted-beam ~ono-chromator and a scintillation det~ctor. Intensity data a~e mea~ured with a rate mete~ and recorded by a computerized data collection/reduction system. Diffraction pattern~ are obtained u6ing the in6trumental ~ettings:
Scanning Speed 1 2~ per minute;
Stepping Increment 0.025~ 20;
Sc~n R~nge 6 to 30, 2~; and Pulse ~eight Analyzer, "Diferential".
For both Cry6tal Perfection Index and Apparent Crystallite Size ~ea6urements, the difPraction data ara proce~sed by a computer program that smoothe~ the data, determines the baseline, and mea~ures peak locations and heights.
I~he X-ray diffraction mea6urement of cry~tallinity ln 66 nylon, 6 nylon, and copolymers of 66 and 6 nylon i~ the Cry~tal Perfection Index (CPI) (~6 taught by P. F. Dismore and W. 0. Statton, J. Polym. Sci Part C, No. 13, pp. 133-148, 1966). The po6ition6 of the two peak6 ~t 21 and 23 29 are ob~erved to ~hift, and a~
the crystallinity incre~es, the peak6 shift farther apart and approach the positions corresponding to the "ideal"
po6ition6 based on the Bunn-Garner 66 nylon ~tructure.
This ~hift in peak location provides the basis of the mea~urement of Cry6t~1 Perfection Index in 66 nylon:
[d(outer)/d(inner)] - 1 CPI ~ --------~ X 100 0.189 where d(outer) and d(inner) are the Bragg ~d~ ~pacings for ~16~

the peak6 at 23 and 21 re6pectively, ~nd the denominator 0.1~9 ls the value for d~100)/d(010) for well-cry6tallized 66 nylon as reported by Bunn and Garner (Proc. Royal Soc.(London), A189, 39, 1947). An equivalent and more useful equation, based on 2~ values, is:

CP~ ~ [2e(outer)/2~(inne!r) - 1] X 546.7 Apparent Cryetallite Size: Apparent cry6talllte size i6 calculated from mea~ure~ents o~ the half~height peak width o the equatorial dii-fraction peAks. Because the two equatorial peak6 ov~rlap, the measurement o~ the half-height peak width is based on the half-width at half-height. ~or the 20-21 peak, the position of the half-maximum peak height i6 calculated and the 2a value ~or thi6 intensity i6 measured on the low angle 6ide. The diference between thi6 2~ value and the 20 value at maximum peak height i8 multiplled by two to give the half-height peak (or "line") width. For the 23 peak, the po~ition of the half-maximum peak height is calculated and the 2~ value for thi6 intensity i~ measured on the high angle ~ide; the difference between thi6 2~ value and the 2~ value at maxi~um peak height i6 multiplied by two to give the half-height peak width.
In this mea~urement, eorrection is made only for instrumental broadening; ~ll other broadening effects are a6sumed to be a result of cry6tallite 6ize. If 'B' is the measured line width of the sample, the corrected line width 'beta' i r--/\/ B2 _ b2 where 'b' i the instrumental broadening con~tant. 'b' is determined by measuring the line width of the peak located at approximately 28 2~ in the diffraction pattern of a silicon crystal powder sample.

-17- 2~

~he Apparent Crystallite Size tACS) i6 given by ACS - (KA)/(~ cos ~), wherein X is taken as one (unit:y);
i6 the X-ray wavelength (here 1.541a A9;
i6 the corrected lin~ breadth in radians; and i6 half the Bragg anqle (half of the 23 value of the ~elected peakl as obtained ~rom the dl~fraction pattern),, _r~y Orlentation Angle: A bundle o~ ~ilament~
about 0.5 mm ln diameter i~ wrapped on a s~mple holder with care to keep the filament6 e6sentially parallel. The ~ilaments in the filled sample holder are expo6~d to an X-ray beam produced by a Philips X-ray generator (Model 12045B) available from Philip~ ~lectronic Instruments.
The diffraction patt~rn from the 6ample filaments is recorded on Kodak DEF Diagnostic Direct Expo~ure X-ray ~ilm (Catalogue Number 154-2463), in a Warhu~ pinhole camera. Collimator~ in the camera are 0.64 mm in diameter. The exposure i~ continued ~or about fi~teen to thirty ~inute~ (or generally long enough so that the diffraction feature to be mea~ured is recorded at an Optical Density of ~1.0). A digiti~ed image of the diffraction pattern i~ recorded with a video camera.
Tran~mitted lntensitie~ are calibrated using black and white referencefi, and gray level (0-255) i~ converted into optical den6ity. The dif~raction p~ttern of 66 nylont 6 nylon, and copolymers of 66 and 6 nylon has two prominent ~quatorial reflection~ at 2~ approximately 20~-21 and 23; the outer (~23~ reflection i~ u6ed for the measur~ment of Ori~ntation Angle. A data array equivalent to an azimuthal trace through the two 6elected equatorial peak~ (i.e. the outer reflection on each side of the pattern) i~ cre~ted by interpolation from the digital O t~ ' image data file; the array is constructed so that one data point equals one-third of one degree in arc.
The Orientation Angle (OA) is taken to be the arc length in degrees at the half-maximum optical density (angle subtending points of 50 percent of maximum density) of the equatorial peaks, corrected for back-ground. Thi6 i~ computed from the number of rlata point6 between the half-height point6 on each side of the peak (with interpolation being u6ed, this :l~ not an integral number).
Both peak~ are measured and the Orientation Angle i5 taken a6 the average o~ the two mea6urements.
Long Period Spaci~Land Normallz~d Long Period Intensity: ~he long period ~paclng ~LPS), ~nd long period lntensity (~PI), are meAsured with a Nratky small Angle diffractometer manufactured by Anton Pa~r K.G., Graz, Au~tria. Ths di~fractometer is installed at a line-focu~
port of a Phllips XRG3100 x-ray generator equipped with a long fine focu~ x-ray tube operated at 45KV and 40ma. The X-ray focal 6pot i8 viewed at a 6 degree take-off angle and the beam width is defined with a 120 micrometer entrance 61it. The copper ~-alpha radiation from the X-ray tube is filtered with a 0.7 mil nickel filter and i6 detected with a NaI(TI) Scintillation counter equipped with a pulse height analyzer 6et to pass 90~ of the CuR-alpha radiation symmetrically.
The nylon samples are prepared by winding the flbers parallel to each other about ~ holder containing a 2 cm diameter hole. The area eovered by the fiber~ is ~bout 2 cm by 2.5 cm and a typical 6ample contains about gram of nylon. The actual amount of ~ample i8 determined by measuring the attenuation by the ~ample of a strong CuX-alpha X-ray ~ignal and adjusting the thickness of the ~ample until the tran6mi~sion of the X-ray beam is near 1/e or .367~. To ~eafiure the transmi~sion, a ~trong 6catterer i~ put in the diffracting position and the nylon 6ample i~ in~erted in front of it, immediately beyond the -19- 2~813r~

baam defining slits. If the measured intensity without att~nuation ~6 Io and the attenuated intensity is I, then the transmis~ion T i8 I/(Io). A sample with a transmission of 1/e has an optimum thickness since the diffracted intensity from a sample of greater or le~s thickness than optimum will be less than that ~rom a sample of optimum thickne66.
The nylon sample is ~ounted such that the fiber axis is perpendicular to the beam length ~or parallel to the direction of travel of the detector). For a Kratky dif~ractometer viewing ~ horlzontal line focus, the fiber axis is perpendicular to the table top. A scan of 180 point6 i~ collected betwe~n 0.1 and 4.0 degrees 20, ~6 follows: 81 points wlth 6tep size 0.0125 degrees between 0.1 and 1.1 degrees; ~0 pointG with step size 0.025 degrees between 1.1 and 3.1 degrees; 19 points with step size 0.05 degrees between 3.1 and 4.0 degree6. The time for each scan is 1 hour and the counting time for each point is 20 seconds. The resulting data are smoothed with a moving parabolic window and the instrumental background is subtracted. The in~trumental background, i.e. the scan obtained in the absence of a sample, i8 multiplled by the tran~mission, T, and subtracted, point by point, from the scan obtained from the sample. The data points of the scan are then corrected for sample thickness by multiplyinq by a corr~ction factor, CF - -1.0/(eT ln(T)).
Here e i~ the base of the natural logarithm and ln(Tt is the natural logarithm of T. Since T is le6s than 1, ln(T) is always negative ~nd CF i8 positive. Also, if T~1/e, then CF-1 for the sample o~ optimum thickness. There~ore, CF i~ always greater than 1 and corrects the intensity from a sample of other than optimum thickness to the intensity tha~ would have been observed had the thickness been optimum. For sample thicknesses reasonably close to 3S optimum, CF can generally be maintained to less than 1.01 so that the correction for sample thickness can be 2~0~:~

maintained to less than a percent which is within the uncertainty imposed by the counting statistics.
The measured intensities arise from reflections whose diffraction vectors are parallel to the fiber axis.
For most nylon fibers, a reflection is observed in the vicinity of 1 degree 2~. To determine the precise position and intensity of this re~flection, a background line is first drawn underneath the peak, tangent to the diffraction curve at angles both higher and lower than the peak itself. A line parallel to the tangent background line is then drawn tangent to th~? peak near its apparent maximum but generally at a slight:ly higher 20 value. The 2~ value at this point of tangency i~ taken to be the position ~inc~ it is position oE the maximum if the sample back-ground were subtracted. The long period spacing, LPS, is calculated from the sragg Law using the peak position thus derived. For small angles this reduces to:

LPS = A/sin(2~) The intensity of the peak, LPI, is defined as the vertical distance, in counts per second, between the point of tangency of the curve and the background line beneath it.
The Kratky diffractometer is a single beam instrument and measured intensities are arbitrary until standardized. The measured intensities may vary from instrument to instrument and with time for a given instrument because of x-ray tube aging, variation in alignment, drift, and deterioration of the scintillation crystal. For quantitative comparison among samples, measured intensities were normalized by ratioing with a stable, standard reference sample. This reference was chosen to be a nylon 66 sample (T-717 yarn from E. I.
du Pont Co., Wilmington, De.) which was used as feed yarn in the first example of this patent (Feed yarn 1).

2 1 2 ~ 2 ~ O 6 1!.

Sonic Modulus: Sonic Modulus i.~ measured as reported ln Pacof~ky U.S. Patent No. 3,74B,844 at col. 5, lines 17 to 38, the disclo~ure of which is incorporated by reference except that the fibers are conditioned for 24 hours at 70F (21 C) and 65% relative humidity prior to the te~t and the nylon fiber~ arle run at a ten6$0n of 0.1 grams per denier rather than the 0.5-0.7 reported for the polye6ter fiber6 of the r~ferenced patent.
Density: D~nsity of the pol~amide fiber is mea~ured by u6e of the density gradient column technique de~cribed in ASTM D150556-68 using carbon tetrachlorlde and h~ptane liquids at 25C.
Ten~lon: While the procefis i~ runnlng, ten~ion measurement6 are made in the draw and rel~x zones ~in the ~lgure, after oven ~6 in the draw zone ~nd a~ter aven 34 in the relaxatlon zon~ about 12 inches (30 cm) ~rom the exits of the ovens) u~lng model Checkline DXX-40, DXX-500, DXX-lK and DXX-2K hand-held ten610meters manufactured by Electromatic E~uipment Company, Inc., Cedarhurst, N.Y.
11516.
Yarn ~emperature: Yarn Temperature6 are mea6ured after the yarn leaves draw oven 26 and relaxation oven 34 with the measurements m~de about 4 inches ~10 cm) away from the oven exit. The meagurements ~re made with a non-contact infrared temperature mea6urement ~ystem compri6ed of an infrared optical scanning ~ystem with a 7.9 micron filter ~band pass of about 0.5 micron~) and broad band detector to sense the running yarn and a temperature re~erenee blackbody placed behind the yarn which can be precisel~ heated to temperatures up to 300C.
A type J thermocouple, buried in the reference, i6 used with a Fluke Model 2170A digital indicator traceable to National Bureau Standards to measure the reference temperature. Highly accurate mea~urement of the temperature of polyamide yarn i6 obtained ~ince the 7.9 micron filter corresponds to an absorption band where the 2~?,~0~ 1 emissivity i6 known to be close to unity. In practice, the temperature of the reference i~ adju6ted 60 that the yarn line fican image di6appear6 afi viewed on an 06cillo6cope and, at this null point, the yarn will be at the 6ame temperature as t~he reference.
Example :L
A fully drawn B48 denier, 140 filament yarn with a formic acid relative visco6ity of about 67 (Feed Yarn 1) was prepared by continuous polymeri%ation and extru~ion o~
homopolymer poly(hexamethylene adipamlde) and drawn concomitantly u6ing the process o~ Good, U.S. Patent 3,311,691. Thi~ "ully drawn" yarn with 9.6 gpd tenacity, 8.8% 6hrinkage, 163 g/d-% toughrles6, and other propertie~
as more fully ~et ~orth in Table 2 wa6 used as a feed yarn in a proces~ as illu~trated in the Figure.
Using apparatu~ as illu~trated in the Figure operated using the proces6 conditions listed in Table 1, 4 ends of the yarn were t~ken o~ a feed pack~ge 12 over end, forwarded to the tension control element 14 for tension control, and then nipped by nip roll 20 and godet roll 18a of roll ~et 18. The godet rO118 18b through 18g of roll 6et 18 were bypa~ed and the yarn wa6 forwarded directly to godet rolls 22a-22g of roll 6et 22, through oven6 24 ~nd 26 to roll set 28. The draw tension wa6 4.02 g/d at a yarn temperature of 240C. The yarn then passes through all ~even roll~ of roll set 28, through oven~ 32 and 34, and through the rolls o roll set 36 before wind-up. The yarn temperature of the yarn emerging from relaxation oven 34 wa~ 240C and the relaxation percentage wa6 13.5~. Incremental draws of 0.5~ were u~ed between each pair of roll6 in roll ~et 22 and incre~ental relaxations ~f 0.5% were u~ed between each pair of rolls in the third roll set 28.
A detailed li~t of proce~s parameters including roll speeds and oven and roll temperatures i~ provided in Table 1.

-23- ~2~

The 796 denier yarn obtained at wind-up had the same formic acid relative viscosity as the feed yarn but with a tenacity and 6hrinkage balance of 10.4 g/d and 1.9%, respectively. The modulu6 was 45.0 g/d ~nd the toughnes6 wa~ 210 g/d %. The cryst~l perfection index wa6 86.1, long period ~pacing wa6 114 A, and density was 1.1526. A more detailed list o~ propertie6 i6 provided in Table 3.
Example ?
The feed yarn for Example 2 was the 6ame as that de6cribed in Example 1 (Feed yarn 1) and the proce~s wa6 similar to Example 1 but with only one end and the proces6 condition6 a~ de~oribed in T~ble 1. The draw tenslon wa6

4.35 g/d at a yarn temperature of 232C a~ter oven 26.
'~he yarn temperature of the yarn emerging ~rom oven 34 was 240~C and the relaxation percentage was 18.2%.
The 804 denier yarn obtained at wind-up had the 6ame formic acid relative vi6cosity of 67 but with a tenacity and 6hrinkage balance of 10.1 g/d and 1.4%, respectively. The modulu6 was 42.8 g/d and the toughness wa6 227 g/d-%. The cryEtal per~ection index was sa ~ 1 ~
long period rpacing wa6 120 ~, and density was 1.1540. A
more detailed list of properties i~ provided in Table 3.
Example 3 A "fully drawn" 1260 denier, 210 filament yarn with a formic acid relative visc06ity of 89 was prepared by continuous polymerization and extrusion of poly(hexamethylene adipamide) and drawn concomitantly u6ing tha process of Good, US Patent 3,311,691. This 3~ "fully" drawn feed yarn with 10.0 gpd tenacity, 7.6%
shrinkage, and 27B g/d % toughne6s (~eed Yarn 2) wa~
proces~ed 6imilarly to Example 1 but with the process conditions a~ de~cribed in Table 1. The draw ten~ion was 4.78 g/d at a yarn temperature of 212C after ov~n 26.
The yarn ~emperature of the yarn emerging from oven 34 was 218~C and the relaxation percentage was 21.4%.

-24- ~2.~

The 1340 denier yarn obtained at wind-up had the ~ame formic dcid relative vi6co~ity of 89 but with a tenacity and shrinkage balance of 10.2 g/d and 0 9%, respectively. The modulu6 wa~ 31.9 g/d and the toughne~
~as 294 g/d ~. The crystal perfection index was B5.9, long period 6pacing wa6 113 A, ~nd den6ity was 1.1527. A
more detailed list of propertiel; i6 provided in Table 3.
Ex~mple 4 The feed yarn for Example 4 was the same a6 that de~cribed in Ex~ple 3 ~Feed Yarn 2) ~nd the proce6~ wa~
the ~ame as Example 3 but the proces~ conditlons were a8 in Table 1. The draw ten6ion w~ 4.79 g/d at a y~rn temperature of 212C. Th~ yarn temperature of the yarn emerging from oven 34 wa~ 218C and the relaxation percentage was 21.2~.
The 1336 denier yarn obtained at wind-up had the 6ame formic acid relative visco~ity of B9 but with a tenacity and 6hrinkage balance of 10.5 g/d and 1.5%, re~pectively. The modulu~ wa6 37.2 g/d and th~ toughness was 271 g/d ~. The cry~tal perfection index wa~ B5.0, long period spacing wa~ 112 A, and density was 1.1572. A
more detailed li6t of properties i6 provided in Table 3.
Example 5 A ~pun, but undrawn, 3714 denier, 140 filament yarn with a formic acid relative vi~cosity of 60 (Feed Yarn 3) was prepared by continuou6 polymerization and extru6ion, of poly~hexamethylene adlpamide) polymer.
After extrusion the yarn was quenched, treated with an oiling agent and wound up directly at 440 ypm. The 33 bire~ringence of the spun yarn was about .G08 ~nd the elongation to break was 575~. The yarn wa6 ~ubsequently stored at 65% RH for 48 hour6 to achieve near equilibrium moi6ture content of about 4.5~.
Using apparatu6 a~ illu~trated in the Figure operated using the proce~s conditions li~ted in Table 1, one end of feed yarn 3 was taken off a feed package 12 -25~

over end, forwarded to the tension control element 14 for tension control at 70 g, and then nipped by nip roll 20 and godet roll 18a of roll set 18. All of the godet rolls 18b through 18g of roll set 18 uere u~ed and the yarn was drawn at low temperature between roll 6et lB and godet roll~ 22a-22g of roll set 22 to the draw rat1o indicated in Table 1. As in the previou~ Example~, the yarn was forwarded through oven~ 24 and :26. The draw ten~ion wa~
4.04 g/d at a yarn temperature o~ 226C ~fter oven 26.
The yarn then pa~e~ through ~l:L 6even roll6 of roll fiet 28, through ovens 32 and 34, And through the roll~ of roll set 36 before wind-up. The yarn temperature of the yarn emerging rom oven 34 wa~ 226C and the relaxation percentage wa~ 14.4%. Incremental draw6 o~ 0.5% ware u~ed between sach pair of rolls in roll set 22 and incremental relaxation~ of 0.5% were used between each pair of rolls in the third roll 6et 2B.
The 792 denier yarn obtained at wind-up had the same formic acid relative viscosity of 60 but with a tenacity and ~hrinkage balance of 9.9 g/d and 1.7~, respectively. The modulus wa6 46.4 g/d and the toughne6s wa~ 204 g/d-%. The cry~tal perfection index was 84.8, long period 6pacing was 108 A, and density was 1.1500.
more detailed li~t of properties is provided in Table 3.
Examples 6-11 Using appar~tu~ as illustrated ln the Figure with the proce6~ parameters li6ted in Table 4, one end of the indicated feed yarn was u~ed to make yarns in accordance with the invention. A partial listing of properties for feed yarn~ 4, 5 and 6 i6 provided in Table 2; the~e feed yarn~ were poly(hexamethylene adipamide), 6pun from continuou~ly polymerized polymer and drawn by the method described in U.S. Patent 3,311,691. A listing of denier, tensile propertie~ and 6hrinkage of the yarns of Examples 6-11 is provided in Table 5.

~25-,.

- 0 - ~ ~ 2 ~

~ s ~ ~ o~
, ~ ~L o 00 ~ ~ .~
~ l ~ ~9 , ~ ~ o ~
.~ 5Z
~1 . ~ I~
_ ~ ~ @~ oz @~

5 1 ~1 ~ o o ~D
~ ~ 01 j~ ~

~ ~ 5 2 ~

Sf ,~ 0 ~i .~
~ ~ o o d o ,~
~ ~ SZ
.~ ~

OZ
8 ~
_~ ~! ~ 3 Sl ~ 01 ~ ; 5 ~1 2 ~ 2 ~

-z~: -3 3 ~ I ~ 3 ~ ,~
o ~ ~ . o o CO ~ ~

~ ¦ ,~&1 ~ 3 ' ~ ~
~ ~ ~ o ~ ~ o~ ~ ~ I I I I
~ o a~ ~ ~ ~ ~
$ ~ I ~ Y ~ '~ u~
.
~3 ~ ~ ~, . . .

, ~
B2 1 ~ G G ~
,~ O ~ ~ ~ ~ ~ `D

_z~ _ - - 2 ~J ~

, ~
o o C~ o o ~, ~x ~1 ~
~ o ~ ~ ~ 5Z
8~ ~
~ ~ o~ ~t ~ ~
~ ~ ~ O ~ ~
a ~ ~
Y~ ~ .~ -~ . O O O O O
; ~ ~ ~ ~ oz E~ 3 ~ ~ ~ ST

~ ~1~ ~
~ ~ o o~
~ 3 ~ ~
~ ~ ~:r ~1 ~ 01 ~ ~ c~ O o~
~ ~
~ ~o o. o, ~ ~ s ?~1 5; G 1~ ~ 53 ~! ~
~1 ~1 -~~

~- 2~2$~

~1 ~! ~ r,~
~i 1~ 1 1 1 1 1 ~ cq r; ri ri r~i ~i ~ ~ o~
. ~ ~ O ~0 r~ l O
~! ~ ~ ~'bl ill ~-1 o r-i r1 r~
, ~ ~ rl ~ ~ ~ ~;t S Z

~ ~ o u~ ~ 1 co ~

~ ~ ~ oz r~
~3 1 ~ r ~ ~ ~1 ~ ~ ~
Sl ~1~ ' ' ' ' ' ~ ¦ ~ ~ r~ ~
~ M 01 ~ ~ ~ r~ ~ t~
;~!lt~l ;~1! ;~! 1! ;~! ~! ~1 ~ i s ~1 r ~ ~ 3 ~ ~o r~ ,o~

_5~_ 2~2~

OE

()Z
o ~ o S

2 Z,~ 2 ~ ~ ~3 ~

O

Y ~ ~ o OZ

~ ~1 ~ S T

~ O T

i~ G

~ ~ S

Claims (25)

CLAIMS:

1. A polyamide yarn comprised of at least about 85% poly(hexamethylene adipamide) having a relative viscosity of greater than about 50, a tenacity of at least about 9.5 g/d, a modulus of at least about 30 g/d, a shrinkage at 160°C of less than about 2%, a crystal perfection index of greater than about 83, and a long period spacing of greater than about 105 .ANG..

2. The yarn of Claim 1 having a modulus of at least about 35 g/d.

3. The yarn of Claim 1 having a density of at least about 1.15 g/cc.

4. The yarn of claim 1 having a birefringence of greater than about 0.056.

5. The yarn of Claim 1 having a long period intensity of greater than about 2.7.

6. The yarn of Claim 1 wherein said tenacity is at least about 10 g/d.

7. The yarn of Claim 1 having an elongation to break of at least about 18%.

8. The yarn of Claim 1 having a toughness of greater than about 200 g/d?%.

9. The yarn of Claim 1 having a toughness of greater than about 225 g/d?%.

10. The yarn of Claim 1 wherein said relative viscosity is greater than about 60.

11. The yarn of Claim 1 having a sonic modulus of greater than about 80 g/d.

12. The yarn of Claim 1 having a maximum shrinkage tension of less than about 0.37 g/d.

13. The yarn of Claim 1 having a maximum shrinkage tension of less than about 0.30 g/d.

14. The yarn of Claim 1 wherein said polyamide is comprised of homopolymer poly(hexamethylene adipamide).

RD-4637 15. The yarn of Claim 1 having an apparent crystallite size of greater than about 62 .ANG. as measured in the 100 plane.

16. The yarn of Claim 1 wherein said yarn has a growth less than about 9%.

17. A process for making a polyamide yarn comprised of at least about 85% by weight poly(hexamethylene adipamide) and having a tenacity of at least about 9.0 q/d, a shrinkage of less than about 2.0%
and a modulus of at least about 30 q/d from a feed yarn selected from the class consisting of drawn, partially-drawn and undrawn yarns, said process comprising:
drawing said feed yarn in at least a final draw stage;
heating said feed yarn during at least said final draw stage;
said drawing and heating of said feed yarn being continued until the draw tension reaches at }east about 3.8 g/d when said yarn is heated to a yarn draw temperature of at least about 190°C;
decreasing the tension on said yarn after said drawing sufficiently to allow said yarn to decrease in length to a maximum length decrease between about 13.5 and about 30%;
heating said yarn during said decreasing of said tension to a yarn relaxation temperature of at least about 190°C when said maximum length decrease is reached; and cooling and packaging said yarn after said decreasing of said tension.

18. The process of claim 17 wherein said tension is decreased sufficiently that the maximum length decrease of the yarn is between about 15 and about 25%.

19. The process of claim 17 wherein said heating during said decreasing of the tension is continued for a duration sufficient to cause said yarn to have a crystal perfection index of greater than about 83.

20. The process of claim 17 wherein said decreasing of the tension is performed by decreasing the tension partially in at least an initial relaxation increment to cause an initial decrease in length and then further decreasing the tension to cause said yarn to decrease further in length to its maximum length decrease in a final relaxation increment.

21. The process of claim 17 performed on a multiplicity of yarn ends simultaneously at a packaging process speed between 150 and 750 mpm.

22. The process of claim 17 wherein said feed yarn is a partially-drawn or undrawn feed yarn and said drawing further comprises at least one initial draw stage before said final draw stage.

23. The process of claim 17 wherein said yarn draw temperature is between about 190 and about 240°C and said yarn relaxation temperature is between about 190 and about 240°C.

24. The process of claim 23 wherein said heating during said drawing is performed in an oven having a temperature of between about 220 and about 320°C, the residence time in said oven being between about 0.5 and about 1.0 seconds.

25. The process of claim 23 wherein said heating during said decreasing of the tension is performed in an oven having a temperature of between about 220 and about 320°C, the residence time of said yarn in said oven being between about 0.5 and about 1.0 seconds.