CA1300865C - Lightly bonded polyamide yarns and process therefor - Google Patents

Abstract

TITLE
Lightly Bonded Polyamide Yarns and Process Therefor ABSTRACT OF THE DISCLOSURE
A substantially twist-free multifilament polyamide yarn particularly suited for use in cut pile carpet and the process for making the yarn including impinging the yarn with saturated steam is disclosed.
The filaments of the yarn are lightly bonded and the skin of the filaments is deoriented.

Description

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TITLE
Liqhtly Bo~ded Polyamide Yarn~ and Proce~s Therefor DESCRIPTION
Technical Eield Thi6 inYen~ion relate~ generally to improved polyamide mul~i-filamentary yarn6. ~ore particularly ~t relate~ to a polyamide yarn for u6e in ~ut pile carpets withou~ r~quiri~g ply-~wi~ti~g and the proces6 for ~aki~g ~uoh yarns.
Ba~kQround Two or ~ore bulked continuou6 filament nylon yarnfi to be u6ed a~ pile i~ cut pile ~axony carpets are usually ply-twisted together then heat 6et while ~raYeling o~ ~ moving ~elt in a relaxed condition ~hrough an enclo~ure in which 6aturated stea~ under pre~sure permeate~ the yarn. This treatmene 8et6 the yarn~ in t~e twi~ted configuration 60 that they retain a substantial degree of twi~t after tufting, ~utting.
dyeing and wear and give an appearance of compact, columnar tuft ~hafts. The appear~nce of compact, columnac tut 6hafts with well-defined tuft tip6 is de6ired or ~ut pile saxony carpet6~ as opposed to out pile velour carpet6 where the appearance of tuft ill~egrity ~8 not de6ired.
Yarn~ which are ~ot Euf~iciently twisted or heat-~et lo~e their twist ~4 that f ilaments of one tuft inter~ingle with tho~e of a~other, g~vl~g a ~a~ted appearance.
~owever, ply-twisting a~d heat ~e~ting are botb Elow and expen~ive operatio~. A yar~ meeting the ~àme performance ~tandard6 a6 ply-twist~d heat-~et ya~n without requiring twisting would be highly de6irable.

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, SummarY of the Invention A multifilament polyamide yarn product that doe~ not require ply-twi6ting and i8 particularly suited for use a~ pile in cut pile ~abri~, including both ~arpet6 and uphol6tery becau6e ~t does not spread out and mat, ha~ now been discovered. The yarn comprise~ fil~ment~ in S~e range of aboue 5-40 denier Rer filament having an orieated core portion and a deoriented ~kin portion characterized by a 5kin Deorientat~on Index of ~bout 0.1 or greater and prefer~bly le5~ than about Q.5 and a thickness o~ the deoriented skin port~on of absut 0.4-3.0 ~icrometer~.
~he fila~ent~ may be ~ei~ped ~y any of the known method~ but cr.imp~ are preferably random in frequency, direction and amplitude. The multif~lament yarn i~
char~c~erized by a bending rigidity ratio (a/RC~/) in the ra2ge of about 20-200 in the ab~ence of adhe~ive or ~ize, prefera~ly in ~he ranse of about 20-75, a lateral pull ~part di~tance of about g ~m., and the 2Q number of filaments are le~ than about 500, with a portio~ o the6e being lightly bonded together. Yarn hav~ng a bending rigidity ratio of 20-75 i6 generally ~uitable for re6~dential carpet~ while yarn at 75-200 ~an be used for heavy wear installations.
The yarn bundle ~ay be ~ubstantially free of true yarn twis~. Th~ 8 does not exclude a emall amount of twist whic~ ~ay occur ineidentally in the handling of the yarn bundle, such as by overend take off of the yarn bundle iR a conventional manner from a ~ationary packaqe, a6 ~rom a creel. A yarn bundle having no ~ore than a~out o~e turn o~ true tw~st per 3 cm i~
con6idered to be ~ubstantially twis~ free.
~ he i~proved properties are belleved to arise in part from a deorientation of the poly~er molecule6 , .

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in the outer region or ~kin portion of the filaments and in part from light bonding among the filaments.
Evidence for deorientation can be obtained rom observation of t~e birefringence difference between skin and core or by ob6e~ving the general lack of ani~otropy presen~ in a ~echanically delaminated ~ection of "6kln". Evldence o~ light bonding among the filament6 can be ob~erved by physically pulling the yarn apart by hand and al~o ean be ~een by following the procedures set out in Example 5. Yarns of this ~nvention are found to be ~ignificantly stiffer than yarn~ ~hat have not been sub3ected to the proce~ of thi~ inven~ion as determined by a ratio of the bending riqidity of the yarn bundle mea6ured as de~cribe~ herein to the ~omputed riqidity of ~he 6ame yarn bundle wherein the fila~ents are completely free to move relative to each other. Yaens of the invention derive ~uch ~tiffnes6 feom the heat and moi6ture treatment accompanied by the compacting e~fects of the clo~e-fiteing inlet and outlet passages of the 6team treating chamber witho~t the pre6ence of adhe6ive or 6ize. The inlet pa66age ha~ a diameter roughly the ~ame ~ize or ~maller than the diameter of the yarn bundle re6ulting ~n the crimped ~urface . filament~ of the yarn bundle being slightly eompre~6ed i~ the inlet pa6sage. It i8 indeed ~urprising that yarn~ ha~ing 6tiffne6se~ chara~teristic of the pre6ent product6 can develop 8UC~ a ~igh degree of bulk during carpet fini6~ing. The bending ~igidity ratio i6 a measure of the de~ree of light bo~din~ a~ong ~he filaments. At too low a bendi~g sigidi~y ~a~io. there i~ too lietle bonding amo~g the ~ilameAts in ~he yarn bundle and the carpet ~ade fro~ ~uch yarn bundle 6pread6 out to give a ~atted appea a~ce. ~t too high a bending rigidity ratio too ma~y ~tlong bond~ are , ,, .

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formed and the carp~t ~ade from the yarn bundle i~
har~h to the touch and the filament6 are exces6ively fused.
The yarn bundle of ~hi6 in~ention i8 radially compressed while pas~ing through the inlet and outlet pa~6age6 of the 6tea~ ~reatment cha~ber forcing the filaments into a more intimate arran~ement tha~ i~
characteri~;c of such filaments without such compre~sio~ and ~he filament6 are lightly bonded where the fila~ent~ touc~. Since the filaments re$ain a sub6tantial a~ount of their original crimp, the~e contact poi~ts are of a li~ited area a~d the llght bondlng at the contact point~ ~ub~tantially disappear later whe~ the yarn i~ fle~ed duri~g tufting and carpet fin~6hing. Neverthele~, the ccmbi~atio~ of light bonding and the more int~mate arra~gement give6 th~ product of the present invention a de6irable degree of 6tiffnes~ and coherency which allow it to ~e used in cut pile carpet6 withou~ the c06t of the usual ply-twi6ting and heat-setting. The temporary nature of the light bonding and the retQntion of crimp recovery ability permit6 the pre~ent yarn~ to recover bulk i~ final carpet form.
The proce6s of forming light bonds between fila~ents and compactnes~ o~ ~he present pLoduct i~
particulasly beneicial when unusually bulky ~eed yarn6 ara u~ed. Such yarns ~ay hav~ such large filament loops extend~g fro~ the yar~ surface that they cannot be ~ed ~atisfactorily ~hrough conventional 3Q yarn guide6 and needle6 of standard carpe~ tufting machine6. When 6uch yarn~ are proce~ed in accordance with ~he ære~ent inve~tion with adju~t~e~t6 o~
apparatus dimen6ion~ :~o suit the product i~ accorda~ce with the di6clo~ure~ her~in, the 6urface loop~ are found to be co~pressed o~to the yarn bundle ~ , . .

6uffi~iently for the yarn to feed ~atisfactorily through tufting, yet they unfold and expand during c~rpet fini~hing to recover their desired bulk and texture.
The product is ~ade by a pro~e6s of passlnq one or more cri~ped multi-filamentary polyamide yarns u~der t~nsion t~rough a clo~e-fitting inlet wherein the le~gth i8 5.1 cm cr more, ~ub3ecting them to ~aturated steam 6ub6tantially free of entrained water and impinged on the axi~ of the yarn bundle and ~po~ing it ~o the ~team for a time of 150 ~illisecond~ or le68. preferably about 30 to 70 milli~econd6 in a chamber of ~ufficient size to allow the fila~ent~ to ~pread and be treated indi~idually by the steam which i~ maintained at elevated pres~ure equivalent to ~aturation at the specific te~perature o the steam, and pas6ing the ~ila~ent~ through a close-fitting outlet si~ilar to the inlet pre~erably of the same di~meter to about 0.7 of ~he inlet Z dia~eter, at a ratio of outlet to inlet tension of l.l to l or grea~er, and windi~g on a package.
B~IEF D~SCRIPTION OF T~H~ DRAWINGS
~ig. l i~ a sch~matic representation of an apparatu~ for practicing the proce66 of the inYention.
Fig. 2 i6 a long~tudinal section taken along line~ 2-2 of Fig. l.
~ig. 3 i8 a ~chematic representation showing th~ fringe ~hift which characteElze~ skin-core orientation di~ference~ and skin thickness.
Fig. 4a and 5a are intetference micLograph~
o~ a cro~ ection of a fila~ent ~howing the fringe ~hift whi~h characterize6 ~kin-core orientation difference~ and skin ~hickn26s.

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~oo~s Fig. 4b and 5b are schema~ic cross-6ection repr~entation~ of the filament position from which the micrograph~ of Fig. 4a and 5a were taken.
F~g. 6 is a 6chematic repre~entation of a cros~-~ection of a trilobal filament.
Fig. 7 is a schematic diagram of an in~trumen~ for mea~uring bending rigidity o~ yarn ~ample~ .
Fig. 8 i~ a photograph of a cro6s-section of ~he yarn of ~his in~ention.
TAIL~D DE~ RIPTION OF THE DRAWINGS
~eferring to Fiq. 1. oue or ~ore crimped continuou~ filament yarn6 10 are taken from supply packagefi 12. combined into a yarn bundle 14 at guide 16 and led through steam treatment device la where the yarn ~ treated by i~pinginq saturated ~team at elevated pre66ure o~ the yarn bundle. Saturated steam i~ 6upplied from a ~ource (not 6hown) and enter6 the steam treatment device 18 throug~ pipe 20. Treated yarn 22 then pa6~es through forwarding roll6 24 to windup packa~e 26.
Fig. 2 ~hows a lo~gitudinal cro~ 6ection of the steam treatment deYice 18 in Fig. 1, ~herein yarn bundle 14 e~ter~ inlet 2~, a~ elo~gated tube haYing a close-fitti~g passage 30 through whic~ the yarn bundle pas6Q6 to chamber 32 where a portlon of the ~at~rated ~tea~ ~rom chamber 32 travels eou~tercurse~t to ~he direct~on of yar~ ~ovement and beyin6 to beat yarn bundle 14. A8 the yarn bundle enters cha~ber 32, ~aturated ~tea~ fro~ orifice 34 i~pinge6 on the long~tudinal axi~ of the chamber and the yar~ bundle, ~eparatins the fila~e~t6. and heating them individually on all ~ide~, after whic~ t~e yar~ pa~ses out of chamber 32 through close-fiteing pa&sage 36 of outIet 38.

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The pa~sage 30 6hould prefeEably have a Gylindrical bore of small enough in6ide diam~ter that ~o substantial a~ount of stea~ escapes from the upstream inlet 28 under the particular operat~nq ~ondition~ ~elected. On the other hand. it 6hould not be ~o s~all thae fric~on betwee~ the yarn bundle and ~let i~pose~ exce~sive ten6io~ on the yarn. The degree of crimp i~ th~ fila~e~ts. the denier and ~umber of the ilament~ and other factor~ ~ay influence the d~ameter ~elected. Steam condensing on the i~coming filaments assists in minimizing leakage a~ do higher yar~ spee~s.
Chamber 32 in which stea~ imp~ge6 on the yarn 6hould be of large e~ough in~ide diameter 60 that t~e filame~t~ can ~pread apart to be treated on all ~ide6 by the ~team. Surpfi~ingly, thi~ diame~er may a~tually be les~ than that of pas6age 30 under some mode~ of operation. The ten6ion on the filament6 is higher in the chamber than in pa~sage 30 due to the ~ncreasing drag between yarn and inlet wall as the yarn progresses, and this ten~io~, coupled with the increa6ing filament temperature, straightens the ~ilament6 temporarily. Thus, they occupy considerably les~ 6pace than previoualy and have much greater freedom to mo~e about while b~ing steam treated.
~he diameter of cha~ber 32 should not be ~o large that the yarn bundle ca~ avoid the direce impi~qement of steam from orifice 34. A maximum chamber diameter of about 1.5 ~ the dia~eter of paBsag~ 30 is preferred.
In ehamber 32, th~ la~ent sur~ace6 reaGh their ~aximum temperature appr~aching that of the ~ ea~. The water vapor lower6 the ~el~i~g point of polyamide yarn6 dra6tically, cau6i~g the ~urfaces or skin of tbe ~ilaments eo ~ole~ularly deorient and .

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reach a "tack point" at which they may form light bonds. The limited penetration of the water vapor prevent6 deorientation of the core of the filament~, thus pre6erving ~heir desired propertie6 such as S tenacity and their ability to recover ~ri~p and bulk during carpet fi~i~hing. The deoriented skin i8 a minor percentage of the ~otal filament.
The ~t~am treated yarn then pa~se~ into pa~age 36. which ~ay be of about the 6ame inside diameeer a~ pas6age 30 or 6maller. In this portion of the apparatu6, 60~e leakage of steam down6tream may be de~irable, since a sub~tantial steam throughput i8 nece66ary to give a high enoug~ velo~ity of 6team flowing through orifice 34 to ~eparate and treat the fila~ents adequately. A~ide fro~ leakage, a ~ub~tantial quantity of steam ~s carried down6tream with the yar~. ~herefore, the in6ide diameter of pa~sage ~6 may be the ~ame 6ize a6 pa~saqe 30 even though the yarn ten6ion and temperature ~traighten~
the cri~p and make~ the y~rn 60mewhat le66 bulky than when it passe~ through inlet 28. ~lternatively. the in6ide dîameter o pas6age 36 may be about 0.7 o~ the diameter of passage 30.
The 6ealing effect of the inlet a~d ouelet pa66ages depends on a co~bination of th~ir diameter6 as compared to the d~am~ter of the yarn and le~gths.
A very ~hort pas6age would ~eed to be very sDall to give adequate seali~g, but t~i8 ~ay impose ex~es6ive tens~on on ~he yarn. ~or practical ~urposee, lengths of 2 ~nche6 or more a6 ~ea~ur~ed fro~ steam impingement orifice 34 are preferred. The outlet pa~sage ~ay pte~erably be lo~ger than the inle~.
The ra~io of yarn een~on downstream of the outlet to yarn ten6io~ up6tream o~ the inlet ~6 a u~eful proce6~ control parameter. It is a ~ea~ure of the ~rictional drag i~posed on the yarn during its pa~age through 6team treatment device 18. ~hi6 ratio should be at least l.l:l, since any lower reading indicate~ inadequate ~ealing against steam leakage.
~hile there i8 no definite upper limitO each product will have preferred operating li~its to avold pulling out ex~e~ive a~ount6 o crimp. bulk or entanglement.
5team flashes off the yarn as it emerge6 from outlet 38 into atmospheric pres6ure. ~he yarn may be cooled and dried adequately by the rotation of the wlndup package or by ex~ending the di~tance between ~team treat~nt device 18 and w~ndup packaq~ 26. If ~orced ~ooling i~ ~ece~ary, ~e ~hould be performed in a ~anner which doe~ not separate the filam~nts, such as treating with cold alr under confinement similar to that i~ outle~ 38 or by ~onta~t with a heat 6ink.
It i6 impor~ant that the saturated 6team supplied through pipe 20 be sub6taneially free of entr~ined water, since the presence of liquid conden~ate cduse~ variation6 in the dye receptiveness of polyamide yarn6. To thi~ end. one or ~ore conden~at~ 6eparator6 40 may be iQstalled in the 6upply line leading to pipe 20, and the line and pipe ~hould be maintained at tbe de~ired temperature by known ~ean6 ~uch as wrapping electric heating cable~
42 around the line or ~t~am tracing.
When yarn~ of di~f~rent dyeabili~ie6 or other different ~ropereies ar~ e~ployed, the different component~ ~ay not be affscted equally by the proces~ing ~ond~t~o~s~
For exa~ple, lower-~elti~g filamen~ may be~ome exce~sively deoriented ~d fused, creatinq an unde6irably har6h and ~tiff product. Qpti~um proce~ing conditio~ or ~uch product~ ~ay be deter~i~ed by esperioentat~on.

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, A preferred product of thi6 invention i8 made from two or more crimped yarns 10 of at least two different colors or dyeabilities, at lea6t one but not all of whi~h i~ interlaced and then all yarns are entangled together as described in Nelson U.S. Patent6 No6 . 4,222,223 and ~,343,1~6. ~hen the above-pr~ferred product of the invention i8 made into cut pile carpet, dyed and ~inish2d, the added cohe~ion qive~ the yar~ by radial compre~sion i~ outlet 38 per~i6t~ during wear, effectively locking the fibers into their po6ition~ relative to one anothes which ~xi~ted at the time of proces6ing. Therefore, filaments of a given color remain substantially together, giving def~ni~e 6pot~ of color and t~e appearance of tuft definition. Y~rns described in Nel~on U.S. Patent 4,343,1~6 are parti~ularly bene~îtted by proce~ing in a~cordance with the present invention. In a yarn where too few or no light bonds are ~ormed, the ~ilament6 of a given ~olor ~epara~e and mingle with tho~e of a different color yiving a blur~ed and indi6tinct appearance.
TEST MæTHODS
LAT~BAL_ PULL~APART TEST
The Lateral Pull-Apart Test directly measure6 the lateral bundle ~ohe~i~eness of a yarn. Two hooks aee placed at a randomly selected point in aboue the ce~t~r of ~he yarn bun~le to separate i~ into two groups of filament~. The hooks are pulled apart at a rate of 5 inches/min. (12.7 cm~min.) at a 90 angle to the yarn axis by a ~ensile te~ti~g ma~hine which ~easure6 ~he re6i6tance to separatio~, such a~ an "Instro~ ac~ine~ The yarn i~ pulled apart by the : ~ook~ until a o~e-pound (~54 ym.) ~orce is exerted, at whach pQin~ the machina i~ 6topped and the di~tance 35~ between ~he two hooks i~ ~ea6u~ed and re~orded. Ten ~.

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, determination6 are made and the average taken as the pull-apart value. The test yarn length6 should be at least 4-6 inches (10-15 cm.) long and selected ra~domly throughout a yarn package.
Normally, in yarn~ co~po~ed o~ two or more f eed yarn~, the component yarns are not di6ti~guishable and ~o a random place~ent of the hook~
~ the yarn give~ a ~aei~actory m2asurement o~ bundle cohe6iYe~es~. I component yarn~ can be di6tinguished, the hooks 6hould be in6erted through at lea~t two of the ~omponents.
~EA uR~MæNT OF NSKI~N~DEORIENTATION INDEX~ (SbI3 ~hen the fiber~ pas~ through the steam chamber their outer region~ partially melt and deorient producing a s~in/core 6tructure. Evidence for thi~ deorientation can be 6een by ob~e~ations of the fiber~ in core-~atching ref~active index fluid6 ~elected a~ determined below for both refractive indice~, n " n,,. With the microscope 8et to ob6erve n, the fringe~ pas6ing through the ~ki~ are displaced in a direc~ion co~re6ponding to a higher re~ra~tive index ~elative to t~e ~ore. Conver~ely, when n,, i6 exam~ned, th~ ~ringe di~placement in the ~ki~
corre6pond6 to a lower refracti~e inde~ relative to the eore. The difference in refractive i~dices, i.e., the b~ refringence, of the ~kin i~ le8~ than ~he birefrl~gence of the core. Si~ce birefringe~ce r~1QCt~ molecular orientation, the ~kin i8 deoriented.
Other evide~ce fsr a deoriented skin ~an be ob~erved with a polarizing microscope. By carefully pull~g apare two bonded ~iber6, portion6 o~ the 6kin can be examined. ~en viewed i~ the 45 po~it~on, batwee~ cro~sed polar~ ~oEt o~ the ~kin appear6 isotropi~.

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SDI is an empirical mea~ure of the deorientation in the gkin. It i6 a value associated with the difference in refractive indices between skin and core ~or light polari~ed parallel to the fiber axis modulated by the skin thickne6s. I~ i~ deduced from ~he ob6ervation of ~he fibers with a two beam Leitz tran6mitted liqht interference microscope (Secial No. 592469) ~et ~or the f ri~ge ~ield mode.
~llumination i~ provided by a mercury arc la~p filtered to provide a wavele~gth of 546 nm. The iber6 are observed in a core-matching refractive index fluid tnominal value 1.572 at a wa~eleng~h of 589 nm and ae 25C), ~anufactured by ~. P. Cargille Laboratories, Inc.~ at a nominal ~agnifica~ion of ~500. The procedure ~or calculating the SDI entail~
~easuring tbe fringe displacement in the ~kin, d, relative to the inter~fringe 6pacing, D, a~ depicted in Pigure 3. Thifi is determined with the aid of the drum compensator on the interferometer and an eyepiece cro~s-ha~r reticle. D i~ an in~trumental ~onstant and for thi6 instru~ent correspond6 to 210.5 division~ of the drumscale for a wavelenqth of 546 ~.
The sa~ple i8 pr~pared a~ follows: A plain micro~cope slide i~ halved and some fibers are placed on both halve6, i~mer~ed ~n a ~elected fluid. A cover lip is pla~ed over both ~lide6. One slide preparation i6 placed on the sample stage of the micro6cope a~d positio~ed ~o there i~ a fiber in the ield o~ view. The other preparation i~ placed on t~e ~icro6cope~ reference stage with no fiber in the field of ~i~w. This is a standard pro~edure to en~ure that ~oth beams of ~he inter~erometer ha~e identical pat~ lengths. ~he interfero~eter i~ adjusted 50 that ~ertieal fringes appear in the ield o~ view and one fiber is oriented perpendicularly to the fringe6. Th2 .. ..
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micro6cope~c a~alyzer is ~et to transmit light vibrati~g parallel ~o ~he fiber axis. The in~erferometer ifi adju~ted for maximum ~harpnes~ of the fringes, Preli~inary ob~ervations are necessary to ~elect the core-matching refractiYe index fluid.
The selection of thi6 fluid i6 determined by ~ucces6ively i~mersing the fiber~ in a serie~ of ~fractive indeY ~luid~. The ~ore matching fluid i8 that 1uid producing the 6mallest fr~nge displacQment inside the fiber. ~hen hollo~ fibers are measured, region~ ~orresponding to the hollow part o~ the fibe~
are disr~garded.
A region of the ~iber i6 first 6elected wher~
the fringe shift i~ the skin i~ ~learly delineated For exa~ple, in t~e case of a hollow, qua~ quare cross-section, a proper at~itude relative to the li~ht beam i6 required. A proper attitude i6 one for which the fiber lays on one of its edge~ ~o that three void~
are seen. This i6 i~lu~trated in ~ig. 4a and 4b. If only two ~oid6 are observed. t~e fiber i~ laying on a face a~ 6hown in Fig. 5a and 5b. In such a ca6e the fri~ge pattern i~ the skin i6 obscured by ~efraction effect6 and d cannot be mea~ured. For fiber~ havinq a 6tar cro6~-section, e.q. trilobal, the measurement i6 obtained fro~ a lobe who~e ~ki~ is~'t eclip6ed by another lobe. For an attitude a~ depi~ed in Fig. 6, the mea6ur~ment would be take~ from lobe A: lobe~ B
and C cannot be ~easured becau6e the~r i~ages a~e superimposed.
To ~ea~ure d, the drum compensator is turned until the fringe pattern is posit~oned 60 that a baGkground ~ri~ge i8 ~upe~i~po6ed on the ~ertical line of the reticle; the corresponding compen~ator reading i~ noted. The patter~ ~ then translated to bring that region of tbe fringe where the di6placement i8 ~axi~um ti.e~. in the skin) in coincidence with the vertical line: the new compen~ator reading i 8 no~ed.
The a~olute value of ~he difference between the two readings is d. ~he SDI i6 calculated a~ follow6:
SDI ~ d D

Fihers o~ thifi invention have an SDI of at least 0.05.
SKIN ~HIC~NESS
The approximate skin thickness can be obtained by photographî~g the fiber i~ She fri~ge field ~ode at a ~o~inal magnificat~on of x500. The skin t~i~knes~ ea~ured from the ~crograph with a x4 magnifier containing a reticle~ 6sale of 50mm i~cremented in uni~ of ~ . The magnifier wa~
calibrated from another x500 micEograph of a micrometer slide (Carl Zei~ ruled eo .Olmm. ~he ~kin thickne~s is always les~ t~an 4~m.
B~NDING RIGIDITY RATI0 The bendi~g rigidity ratio (R/RCf.m) is determined ~y measuring the be~ding eiqidity (R) of the yarn6 and dividing by the computed rigidity of the ~ame basic yarn wherein the fibers are completely free to ~ove ~elative to each other, (R~fma, the sub~cript meaning ~Co~plete Freedom of ~otion".
The yarn b~nding rigidi~y can be ~easured by a nu~ber o~ ~echniqu~s such a~ by using a ~itex Hk II
Beudlng Te~ter manufactured by IDR, Needham, Ma~achus~tes, U.S.A. In thi6 ee6t. referring ~o Fi~. 7, the yarn sample 60, ~hich i~ about 2 inche~
~5.1 c~0) long! i6 i~erted a~ Ehow~ between pin6 61 and 62 ~ounted on block:63 and between pi~ 64 and arm : : ~ 66. Theu pin 64;:mounted on micro~eter 65 i~ adju~ted to br~i~g yar~ s~mpl~ 60 into l~gh~ contact with ar~ 66 of :foroe transducer ~. The distance ~ro~ pin 62 to arm 66 i~ 1 inch. Block 63 ~ove6 to bend t~e sample , . :

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ineo circular arc~ of progre ~ively increasing yarn ~urvature ~curvature - l/radiu~ of ~urvature). ~his deformation is accomplished by movement of block 63.
The maximum ~urvature i8 1. 5 ~n. 1, The output~ of the force transducer6 and a tran6ducer which mea~ure~
block rotation are fed to an X-Y recorder. Since the bending moment o~ the sample equal6 the force on ths force tran~ducer times the di~tance between pin~ ~4 and 66 and the curvature iE proportional to the blo~k rotation, the output plot give~ the yarn mo~ent-curvature re6pon~e.
The 610pe of the ~oment-curvature plot equals the sample rigidity and ha6 unit~ of force-length2.
~he in~trument i~ calibrated be~ore ~easure~ents are ~ade by measuring the ~lope of a stainle6s ~teel 6trip of calculted rigidity. O.G01 inch (0.0025 cm.) thick and 0.5 in~h (1.27 cm.) wide in~erted in place of the yarn. The rigidity of the ~tainless ~teel ~trip i6 ~alculated by the following aquation: Rc.wct3Ec/12 where 2c ~ Riqidity of calibration 6trip Wc ~ width of calibration ~trip ~ 0.5 in.
tc ~ thicknes6 of calibration 6trip . 0.001 in.
Ec ~ Young'6 modulus of calibrat~on strip ~ 30,000,000 p6i .
~5 t~ere~ore: 2 ac ~ 1250 in lb.
The 610pe of tbe calibratio~ ~tr~p plot is divided into the calibra~ion ~trip~ 8 calculated rigidity to give the calibration ~actor. The rigid~y of a~y unknown yarn ~amples equals it6 slope time~ the calibration ta~tor.
Five yarn ~amples from each item are mea~ured as above and the resul~ are averaged to give the value~ for ~. The value of acfm i8 co~puted by .,~.

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~U1t~P1Ying the riqidit~ Of a CY1inder haV~ng the mOdU1U~ Of a ~1ber bY the nUmber Of fibQr~.
In ter~8 Of the ~O~bined ~teXti1e" and en~ineer~g Unit8, the re1atiOn Can be Written a8:
NfEfwfZ
Wh~r~ C~m ' K d ~ ~ 3~02 X 10 11 1b. in.2/(den~(C~) N~ ~ NO. Of filaments in a Yarn (Ca1CU1ated frOm ratiO Of Yarn tO fi1ament den~er) ~ . Fiber ~OdU1U8 (g/denier) Wf ~ Fi1amen~ Linear DQn8ieY (denier3 df ~ Fi1ament Den~itY (g/~C) R i8 eh~n diVided bY R~m t giVe the bending rigiditY
rat~0 fO~ ~aCh item.
E~A~LES
ExamPl e 1 VariOU8 CrimPed ~U1tifi1ament Yarn8 are entang1ed tOgether bY ~eVera1 PrOCe~e8 and are Pa5~ed thEOUgh a ~atUrated ~t~am treat~ent deV1Ce U~der COnditiOn8 ~hOWn 1~ Tab1e 1. Feed Yarn A ~8 1~25 de~ier 19 denier Per f~1ament ~atiOniC dYeab1e ~et-~U1ked COntinUOU~ i1a~ent nY10n 66 Yarn, ~aC~
~i1a~ent haV~Ag a CrO~ ~QCtiOn aPPrOXi~a~ng a ~gUare With rOUnded COrner8 and a COn~nUOU~ YOid near aaCh COrn~. Y~r~ B 1~ the ~ame a~ Yar~ ~ e~CePt ~3r b~ing 1~ghe:aCid ~Y~ab1e. Y2rn C IB the ~ame ~B yarn A
except for being~deep a~id :dy~able and w~th She ~ addieion of 20 ~de~i~r; 3 filament ya~ ha~i~g :: ~o~duct~e carbon ~ t~e ~ore: for a~cis~cati~ purpo~e~
a~.d~s~los~d i~ U.S. Pat~t 3,803,453. Yar~ D ~ 1750 de~iQr ~ylo~ 6,31~de~ier per filament bulk~d contiauou~ f~ lame~t yar~, ~ach: filame~t having a 6 :: : ~
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void pentagon ~ross section. The jet entangling proces~ i8 in accordance with disclosure6 of the patents c~ted in Table 1.
Steam treatment device G consists of inlet 28 having a pa~sage 30 eight inches (20.3 c~.) long and 0.070 in~h (0.17B cm.) in6ide diameter. ~hamber 32 1,00 inch (2.54 cm.) long of 0.062 inch (0.157 cm.) inside diameter and or~fice 34 of 0.046 inch (0.117 cm.~ diameter, and outlet 38 having a pas6age 36 twelve inc~e~ (30.5 cm.) lonq and 0.070 inch (0.178 çm.) ln6ide diameter.
~tea~ treat~e~t device H is ~imilar to G
except that the infiide diameters of pa~age 30 and ~as~age 36 are 0.052 inch (0.132 cm.~. Steam temperature in pipe 20 i~ ~easured by a thermo~ouple ~nserted into pipe 20 approximately 3 inche~ ~7.6 cm.) up~tream of orifice 34. Steam temperature in chamber 32 is mea~ured by a thermocouple inserted in the wall of chamber 32 of device G flush with the in6ide bore of the cha~ber and opposite to orifice 34.
propereie6 of the yarn6 are 6hown in Table 1. Item 2 w~ich i6 not 6team ~reated, shows low bendi~ riyidity ratio ~haracteristic of untre~ted yar~6 and no filament skin ~odifi~ation. Item~ 5, 6, ~0 and 11 althouqh ~eeam treaSed, are below a~ceptable levels o~ properties.
Ite~ 12 has fila~ent fu~ing within the limit6 of acc¢ptability while Ite~ 13 i8 more heavily used and ~a~y o~ the filaments cannot be separated. Items 10 ehrough 13 are nylo~ 6 which ha~ a lower melting poi~t than nylon 66.
The ti~e during whi~h the yarn i8 exposed to the steam i~ con~idered to be ~he total time which ~he yarn spends within ~tea~ treatme~t devi~e 18 of Fig.
1. This i~ determi~ed by dividing the overall length , . ..

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of the device from inlet 28 to outlet 38 by the yarn velocity.
During the test no substantial amount of 6team wa~ observed e~caping from the inlet.
ExamPle 2 The yarn6 of Item~ 6 through 9 of Example 1 are tu~ted into carpet at lJ8 inch (3.18 mm) gauge and are tu~ted at a 5/16 (8 ~m~ inch cut-pile height, 3Z
oz./yd.2 (1.08~ kg/~2) and are dyed under the same conditions. Item 6 show~ ~ome tuf~ di6tinction. Item 9 ~a~ tuft~ where the ~ila~en~s appear ~ohesive with little inter~ingling of filament~ wlt~ ad3acent tufts, yet the ~arpet i~ ~oft and ~pringy withou~ harshness.
Item~ 7 and 8 are intermediate in tuft distinct~on.
Exa~ple 3 Three ends of cationic dyeable feed Yarn A
are entangled and 6tea~ treated at the conditions li~ted in Table 2. Feed yarn A i~ a copolymer of nylon 66 and the ~odium ~alt of 6ulfoisophthalic acid at about 2.2~ by weight having a lower melting point than yarn6 B and C, and the~efore the filament~ ~an be expected to bond to a greater degree at 6i~ilar condition6 than I~ems 1, 2, 4 or 5-9 of Table 1. The yar~s were treated at a ~eries of ~empera~ure6 to ~emonstrate product6 ranging fro~ ~nsuffi~iently to exces6ively bonded. This ~E a more extensiYe te6ting tha~ Item 3.
It can be 6een from the data in Table 2 that items 14-16 have bending rigidity ratios below about 20 and have ~kin thickne~s and Skin Deorientation Index too low to ~ea~ure accurately.

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A '.

' , ~13~ i5 ExamDle 4 The yarn~ of Items 14 through 24 are tufted into carpet at 1/8 (3.lB mm) in~h gauge and 5/16 ~B ~m) inch cut pile height, 32 oz/yd2 (1.086 kg/m2) and are dyed under the ~ame condition~. Item~ 14-16 have little cohesion within the tufes~ the filame~t~
of each tuft ~preading and intermingling with neiqhborin~ tuft~ to give a uniform matted appearance. Ite~ 17-22 have tuf~ wher~ the yarns lo appear cohes~ve with little inteEmingling of filament6 with ~djacent tu~, yet the ~arpet i6 50~ and springy without har~hne~s. Items 23 and 24 are har6h and exce~sively fused.
~xamPle 5 ~hi~ exa~ple demon~trate6 that the filaments are ligbtly bonded together. The yarn wa6 clo6ely examined as de~cribed below.
To avoid di6turbing the yarn6~ ~tructures, yarn~ are embedded in an epoxy matrix before ~ cross-6ectioning. To do thi~, the 6pecimen yarn is placed in a ~old. Eeoxy i6 poured around it and cured. The cured ~pecimen block i~ removed from the mold. ~haped a~d ~ectioned in a ~icrotome.
Cros6-~ec~ions, ~ounted on a ~icroscope slide. a~e photograph~d at euitable magnificatio~.
The ~oated mold i8 ~prayed llghtly with release ~gent, and eac~ cavity ~B lined with cellophane tape. Small ~pillows~ cf double-faced masking tape (approxi~ately 6 folds) are placed at the end6 of eacb cavity.
Before placinq the yarn i~ the mvlds, the : yar~ i6 prepared a~ follows. ~pproximately 200 ~m of yarn are taped a~ both end6 usi~g small pieces of ~ ~a~king kape, ~lamp~ are a~tached to both end6., and the yarn i6 hung o~ a raok hook. Sufficie~t weight i~

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added to the lower clamp So pull out any crimp. being ~areful not to ~tretch the yarn. U6ing an eyedropper.
clear acrylic lacquer i6 applied a few drops at a time dow~ the yarn. Approximately 10 application~ about 3 minutes apart are made, then the sample i8 allowed to dry about 2 houzs.
The ~oated ~pecimen i8 placed in the ~old cavity on the "pillows" of tape ~u~h ~hat ~t l~es below ghe mold surface but does not touch the bot~om.
Ths exce~6 yarn i8 then cut oPf.
~poxy re~n to ~ill ~8 mold cavities i8 prepared by ~i~ing the ~ollow~ng:
~arglas Resi~ 658 crystal-clear epoxy easting resin (m~nufactured by Ac~e Chemicals & In~ulation Co.l 21.7 g Mar~las Re6in 659 crystal-clear epoxy c~ting resin (~anufa~tued by Ac~e Chemicals ~ In~ulat~on Co.~ 4.4 g ~araset ~odi~ied diamine auring agent Hardener 558 manufactured by Acme Chemical~ ~ Insualtion Co.) 25.0 g The re~in mixture i~ stirred ~lowly for about 5 ~inut~ to prevent bubble formatio~. St~rring ~hould ~5 ~ont~nue until the ~olution i~ clear.
The ~poxy solution 1~ tbo~ poured over ea~h ~pecimen. Bubbles can be el~inated by man$pulation of the specimen ~ith a p~ir o ~or~eps. If the ~ample s~nk~ to the botto~ or rloa~s to t~e top o the ~old.
ebe yarn ~ust be ~e~o~itioned. ~he re~n ~an be cured at room temperature for 15 hour6 (or as 6SC ~or 3 hour6).
A~ter cur~ng, the roo~ temperature cured mold : i8 placed on a war~in~ table ~or abou~ inutes. By gra~ping the end~ o~ ~he ~ellophane ~ape~ the warm .

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~Q(~65 specimen block can be removed from the mold.
(Oven-cured ~pecimen~ are removed from the mold i~mediately after removal from the oven.3 The speci~en block i~ cooled on a flat surface and then the cellophane tape ~ cemoved.
Each ~pecimen block is ~haped and then placed on a warmi~g eable for about 2 minutes to relax filament~O The ~pe~imen block i~ then ~ounted in a ~icrotome tRotary Model 820 - American Optical) and 7-~icro~ thick cuts are made. The ~irst few cuts are di6carded. A good cut (one with no obvious air bubblefi or k~ife blade ~a~ks or ~ilt to the filaments) i8 laid o~ a microscope slide thinly coated with Primol 335 qn ~ 1.5) or ~neral oil (~ ~ 1.47). once the cut has been inspected under the micro~cope and determined to be ~ati6factory, a co~er glass is placed over the specimen. Photograph~ are taken at ~ppropriate magnification.
After carpet proce~sing (but before latexing) yarn rom carpet ~ufts is cros6-sectioned a6 described by the aboYe procedure with one exception. ~ecause ~he yarn length is ~o ~hort (approximately 15 mm). it 18 not ~uspe~ded and dropped with clear a~rylic lacquer. ~t i~ ~imply positioned in the ~enter of the mold using the "pillows" of tape to keep it rom tou~hing the ~op or the botto~ of the mold.
~rose-~ectional photograph~ of ~he yarns before and after carpet ~rocessi~g indicate increasi~g fu6ion points wi~h increas~ng steam temperature and the 108s of fusion point6 after carpet processing.
Fu~ion i6 determined by ~xamini~g the çros~-sectional photograph ~or lo~ o~ boundary definltion between two touc~i~g filaments D ~his ~8 showh i~ Fig. ~ which is : a c~o~s-sectional photograph of Item 21 before pro~essi~g. Ite~ 21 retains ~ome fusion poi~ts a~ter ,, ~30~6S

2~
carpe~ proce~ing and an increasing amount of fusion point6 are retained as ~team tempe~ature i6 increa~ed betwee~ Items 22 and 24.
ExamPle 6 Thi~ example show~ that above the temperature a~ which t~e l~ght bonds are ~irst formed the amount and the ~treng~ of the bonds i~crease~ a6 the steam temperatnre inc~eases.
A length of yarn i8 held down on a ~lock made from Teflon~ tetra~luoroethylene re~i~. A razor blade ~ held on the blo~k at a 30 angle and dra~n across the yarn ~wice to cut a yarn 6egment approximately 5mm long. Care i6 taken not to disturb in~erfilament bond~ which ~ay be presen~ in the segment of yarn which is ~ut. The ~a~ple ~egment 6hould be cut from an area of the yarn which i~ of ave~age ~i~ually apparent bundle co~e6ion. It ~hould not be cut from a section o~ yarn which i6 splayed or tightly knotted, as in an "interlace node~. A ~egment thu~ cut from a yarn having interfilament bond~ will remain 6ub~taneially intact.
The S ~m yarn seg~ent prepared as de6czibed above is placed in a 250 ml glass beaker eontaining 150 ~1 of water. A BRAUN-SONIC 7510 ~onic probe manufactured by ~. Braun Mel~unge~ AG i~ emerged in the water a~d ~h~ sa~ple ia agi~ated at about ~00 watts for 3 ~n. The degree o~ yarn segment bundle 6epara~ion ~nto indi~dual fila~ent~ i~ then obserYed.
Item Ob6ervation ~0 ~ollowing agitation yarn bundle ~ completely broke up into ;~ individual fila~entE.
C Follow~ agitation yar~ bundle completel~ bro~e up ~nto ~ndi~idual filament~.

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. ~ . , 7 Pollowing agitation yarn bundle broke i~to two large p~ eces, approxi~ately 6 clumps of f il2~1ent6, and approximately 12-24 indi~lridual filament~.
8 Bu~dle remained lntact, except for app~ox~ mately 15 f ilament~ that ~eparatad .
9 Bu~dle ~ained intact, except for approxilaately 5 f ilame~t~ that separatea .

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Claims (15)

1. A substantially twist-free multifilament polyamide yarn, comprising a plurality of crimped filaments having an oriented core portion and a deoriented skin portion, said yarn being characterized by a bending rigidity ratio (R/Rcfm) of greater than about 20 and less than about 200, said filaments being characterized by a Skin Deorientation Index of greater than about 0.05.

2. The yarn of Claim 1 characterized further by a thickness of the deoriented skin portion of the filaments of greater than about 0.4 micrometer and less than about 4.0 micrometers.

3. The yarn of Claim 2 where the number of filaments is less than about 500 and the denier per filament is greater than about 5 and less than about 40.

4. The yarn of Claim 1 where the Skin Deorientation Index is less than about 0.5.

5. The yarn of Claim 2 where R/Rcfm is greater than 20 and less than 75.

6. The yarn of Claim 5 characterized further by a lateral pull-apart distance greater than about 0.25 cm. and less than about 10 cm.

7. The yarn of Claim 6 wherein the thickness of the deoriented skin portion of the filaments is greater than 0.8 micrometers and less than 1.5 micrometers.

8. The yarn of Claim 1 where a portion of the filaments are lightly bonded together.

9. The yarn of Claim 1 where the multifilament polyamide yarn has a twist of from about 0.33 to 2.0 twists per cm.

10. A process for combining and treating a plurality of crimped multi-filament polyamide yarns, each filament having an outer surface and an interior core, to produce a substantially twist-free combined yarn suitably for use in cut pile carpets or other cut pile applications comprising the steps of:
a) combining the crimped multi-filament yarns to form a yarn bundle;
b) passing the yarn bundle under tension through a close-fitting inlet passage of known inside diameter to radially compress the filaments;
c) steam-treating the compressed filaments by directly impinging the axis of the yarn bundle with saturated steam in a chamber having an inside diameter less than 1.5 times the inside diameter of the inlet passage for a time greater than about 15 milliseconds and less than about 150 milliseconds, the steam being at elevated pressure, substantially free of entrained water, and at a velocity high enough to separate and treat the filaments individually so that the outer surfaces of the filaments are deoriented and the interior cores are not; and d) passing the steam-treated filaments through a close-fitting outlet passage of known inside diameter under tension so that the treated filaments are again radially compressed and bond together lightly where the filaments touch.

11. The process of Claim 10 wherein the ratio of the inside diameter of the outlet passage to the inside diameter of the inlet passage is from about 0.7 to 1Ø

12. The process of Claim 11 wherein the inside diameter of the inlet passage is small enough so that no substantial amount of steam escapes upstream therefrom.

13. The process of Claim 10 where the combining step is performed by jet-entangling the crimped, multi-filament yarns.

14. The process of Claim 13 wherein the ratio of the inside diameter of the outlet passage to the inside diameter of the inlet passage is from about 0.7 to 1Ø

15. The process of Claims 14 wherin the inside diameter of the inlet passage is small enough so that no substantial amount of steam escapes upstream therefrom.