CA1181555A - Pan based carbon fiber and process for producing the same - Google Patents

Abstract

IMPROVED PAN-BASED CARBON FIBER AND PROCESS FOR
PRODUCING THE SAME

ABSTRACT

A PAN-based carbon fiber having both high Young's modulus and high tensile strength is disclosed along with a method for producing the same.

Description

IP~PB.OVED 13AN BAS~D ÇAR30N E: IBE~ AND PB~OC~5 5 YO~ PROD'JCIN(; T~ SAM~

~ he invention .elate~ to an i~proved PAN-b~sed carbon fib r and a me~hod for producing the same.
The co~mercial Yalue o polyacrylonitrile (PAN~-ba~ed carbo~ fiber~ is ~S~ll kno~n in the prior art .
Gen2rally, a PAN~bas~d carbon f iber iB
produced by Rpinning p~lyacsylonitrile into ~ fiber, infu~ibili~ing the fiber by raising it to an elevated ee~perature in air, and the~eafter ~rbonizing the infu~ibili~d fiber st an eleY2.ed tempe~sture in an iner~ atmo~pher~ under ten~ion in a thre~dline to produce ~ ~sbosl fiber.
Co~me~cially, thou~nds o contir.uouR
f ilalhent~ or f ib~r3 ~re ~pun ~ ule~neou~ly and eollec~ed together to fDr~ ~ ~reen yar~ and the y~sn i~ proces3ed ~uboequen~ly to p~oduce an infu~ibili~ed y~rn and th~n ~ car~on yarr..
The c~rboni~ing oper~e ion or the infu~ibili~ed yarn i8 carried ou~ thre~dline operation in orte~ to ~ubject ~he yarn to ten~ion D- 1 ~4 14 du}ir~ ~he carbonizing ~tep~ The c~rbo~:izirlg ~t p c~r~ b~ c~rried out ~ a ~equence of operaCions usi;~
~paraCe h2ating unit~. Fs3r ~x~pl~, one heating unie c~qn be u~ed ~t a t~r~peratur2 of abs~u~ 13QO~C tc carboni2e the infusie~ilized yarn initially arld another he~tirlg unit ~n be u~ed to carboniz~ the yarn to ~ higher ~emper~ure and thereby irnprove the D~2chanical p~operties oi the c~rbon yarn.
One of the drawb~ck~ of eh~ prior a-re processe~ for commercaally proclucin~S PA~-ba3ed carbon ysrn3 i8 that the ~ensile strength of the ibers degr~des as the carboT3izing proce~3irlg ~esult~ in a higher Young's modulus. T~ble I ~hows typical propertie3 of cor~DDercially available PAN based carbon f ib~rs.

TABLE I
Cs~r~ercisl Young' 3 Mod T~ncil2 Str~ Density Fiber 106 p8i103 pr~ 5g/p53 A 33 450 l. 74 B 34 450 l. 81 C 34 470 1. 77 39 420 1.67 E 52 360 l. 82 F 53 320 1. 83 G S7 350 lo 81 ~1 75 270 1 . 96 In csntra~t, ehe in3eant invention produc~
~ PAN~ba~ed carbon y~ra h3vin~ as avera~ fibar properties ~ Young'a ~Dodulu~ of greater chan ~bc,uc 50 ~illi~n p~i ~nd a een~ile ~trength at lea~e on~
third sr~at~ th2n the commer~ially available PA~d-ba~eB ~aabon fibar having a similar avera~e v~lu~ o~ Young' il mo~!ulu ~ 3 --ddition, the proce~ a-cording to the invent ion i~ ~imple to i~pl~mene and carl b~ carried QUt ~conomically with i~proved productivity, yieldin~ high quality ~AN-ba3ed carbon fiber~.
The inYention in one e~bodi~ent is a PAN~baaed carbon fiber having ~ Young~9 modulu~ o about 56 ~;illion p~i and a tensile strength of about ~7~,000 p~i.
The proce~3 invention in its b~o2dest embodi~ent relate~ to the production of a PQN-ba~ed c~rbon fiber ~ompri~ing the 3tep~ of 3pinning a polyacrylonitrile fiber, infusibilizing the fiber, and ~hereafter ~arboni~ing th~ infu~ibiliæed fiber to produce a carbon iber; and feature3 the improvement of carrying out the ca~bonizing by winding ehe infu3ibilized fiber3 on to ~ bobbin whi~h i~ eher~lly and ~echanically sCable at temperatur2s used to pyroly~e and carbonize the infu~ibili~ed fib2r and ~hich i~ chemic211y co~patible with the infu~ibili2~d riber, subjecting ~he infusibiliz2d fiber on the bobbin to a predecer~ined irst heat ereaemenc in an inert ~t~osphere to pyrolyze and carboni2e the inf~ibilized fiber, ~nd thereafter subjecting the carbonized fiber3 to a 3econd heat treaCment in an inert at~osphere in a threadline operationO
For co~mercial operation3, thc process Yould be carried ou~ u~ing yar~, 3 plurality of fibers.

~ ~ 3;~

Fhe bobbin for car~ying out the proce~0 co~pri~e~ a cylindrical b~dy m~de of ~areri~l ~uch A9 ~t~inl~9 ~teel, or r~er~ctory o~ide~, or boroa nitride, or graphiee ~nd preferably ha3 ~ layer o co~pres3ible re3ilie~t carboa ~ateri~l ~uch ~
ca~bon felt po~ition~d on thz o~tside 3urface o the cylindricisl body eO receiv2 the infu~ibilized fiber and thereby mini~i~e the 3tre~8 bet~e~n the cylindric~l body and Che inf~ibilized fiber during ~he ~re~t~nC~ ~he bobbin c~n be with or without cnd flan8es~ For relatively high ~inding a~le~
end flan3e~ are not ae~ded.
Typically, the cylindrical body of the bobbin can h~ve an in3ide di~eter of ehree inch~
and sn out~ide dia~eter of about three ~nd ~ half inches ~ith an over~ll lea~th of ~bout ele~zn in~he~.
Preferably, carbon felt h~s a ehickne3s of froM about 1/4 inch to about 1/2 inch ~hick.
The ~indin8 of the infusibilieed yarn onto bobbin can be oarri~d out u3in~ ~ r~ngP of vindi~
~nele3. Preferably ~ wind angle of at lea~t ewO
degrPe~ ~hould be used and as high a3 about twen~y~thre~ degree~ i~ ad~antageou3. During the heat treatment on the bobin~ ehe fibers t~nd eo ~hrink con~iderably ~nd the u3e of ~ hi8h vind an~le per~its ~hrinkage ~ithout ~dver~e effeet~ on ~he fibers. ~oreoYer, the u~e of ~ high wind an81e le2d~ co unifor~ fibe~ properCi~ ~hroughou~ the length o~ the fiber fro~ Che core to the outer ~inding layer.

~-13414 Th~ heat t~e~t~ent of the ~iber~ o~ the bobbin~ conveniently allo~ th2 bulk he~c treat~ent of ~ lar~2 a~ount of fiber3, st a relaciYely 319~
rate of inere~se in temperature ~o an elevated final te~perature. The surpri~ing adYanra~e of thi~ heat treatme~e i~ that both the rate o reduction in nitrogen content o~ the fiber~ and ~he iinal nitrog2n content are much lo~er ~ to compared ~o a heat trea~ent to ehe ~ame iinal te~perature u3ing a convention~l threadline ærran~ement. A~ a r~sult, the ~ub~equent threadline heat tre~tment can be carried out ~t a high rate of mo~e~ent of the yarn through the heating unit even if a con3iderably elev~ted temperature i~ u~ed. Thi~ threadline ereatment seraighten3 out the fibera and e~tabli~he3 the final fiber ~echanical propert ie3~
Generally~ Che threadline temperature should be at least about 600~C high~r than ehe te~per~ture u~ed for che f ir~t heat treatmen~ oi Che yarn on the bobbin.
Table II ~ho~ a typical 3chedule o te~peracures for the first and ~econd~heat treaments ~ccording to the invention in ordPr to obtain PAN-based carbon fiber~ having predetermined valu~s for the Young'~ modulus. The esci~ated nitrogen coneent aftYr the first h~a~ treatment i~ an i~portant criteria for deter~ining the hP~t of the threadLine for any given eer~perature for the second heat treat~ent~ A hi~h ni~rogen coneent ~ill result in se~ere fiber da~a8e due to the sudden evolu~io~
of the nitrogen fro~ the fibar during a sudden te~p rature increas~ ior a ~econd he~e treat~en~.

TABL II
- E~tim~ted Se ond D ~ired First Hea~ ~icro3en ~eat Young's ~od Treatmen~ Conc~ Treacmen~
106p~ i C ~ o~
__ _ ~0 1300 l 19~
l50G 0.7 2300 1703 0.4 ~50Q

Cenerally, ~he fir~t heae treaCmene ~ccordiny, to the invention can be c~rriad out at race of fr~ abouc 50 C to about 500 C per hour co ~ ¢~xi~u~ c~mperatur~ o~ irom about 1300 C to about 1700 C.

Preferably, Che fir t heac treat~ent i~
carried out by increa~in~ the temperaeure ~t the r~te of about 50~C for an hour fro~ room te~peYature eO about 800C and thereafter increasing the te~perature at ~ sate of 250C per hour until th~
predetermined ~xi~u~ ee~perature i~ reached and ehe ~axi~um temperature is ~aint~ined for zn ~ddicional t~J~ hour~ The ~axi~u~ te~prature i9 maineained in order to give all oi ~he iibera on Che bobbin the opporeunicy to re~ch a te~peratur equilibriu~.
A typical prior art threadline he~
treat~ent at ~ ta~pera~ure of 1300C re~ult~ in a P~n-based c~rbon f iber having a nitrogen contene of about 4~ or ~ore by ~deight vhere~ ehe a~q~e hest ereatD~ent c~srried out ~sing the firit he~t tre~tmen~:
~ccordin8 to the inYention result~ in a PAN-based c~rbon f iber h~ving ~ nitrogen content o sbout 1~
by ~ei~ht. ~he lo~er nitrogen eontent i~ impor~ant ior c~r~ying out ~1 3 cond heat treat~laent u~ a threadline ~t ~ rel~tively hi~h speed.

D- 13~14 For a fuller under~e~ndin~ of the nature ~nd objeces of ~he invention, refe~nce ~hould be had to the fQllo~in~ detailed d~cription, ~aken in connection ~ith the aec~p~nyi~ dr~in~, in ~hich:
Fig. 1 i~ a graph ~ho~ing the effec~ of ~
fir3t heat tre~tmPnt according to the inYention or.
the chemical co~po3ition of PAN~based fiber3~
~ ig. 2 i3 ~ ~raph ahowing che efect of thre2dline te~perature and line ~peed on the density of recarbonized conveneional PAN-ba3ed carbon fiberR;
Fig. 3 i3 a graph ~ho~ing the effect of line ~peed on ehr2adline te~peratur~ on ~he dPnsiey of recarbonized eonvention~l PAN-ba~ed carbon fib2rs;
Fig. 4 i~ ~ graph comparin~ the effect of threadline te~perature on ~he density of recarbonized conve~ntion~l PAN-ba~?d carbon fibers and recarboni~ed PRN~based carbon fibers produced accorting Co ~he in tant inven~ion;
Fig. 5 is ~ graph ~ho~ing ehe effect of t`nreadline te~perature and line ~peed on the tensile 3tren~th of recarbonized conventional PAN-based carbon fib2rs;
Fig. 6 i3 a graph 3ho~ing a compari~on of the eifect of threadline te~perature on the ten3ile strerlgth oi boeh recarbonizecl conventional PAN-based carbGn f iber3 and recarbonized PAN-ba~ed carbon ibers produced accordin~ to the in3Cant invention;
Fig~ 7 i~ a graph co~paring the offecLR of threadline temperaeure and line ~p~et on the Young'a ~odulu~ of both recarbonized conventional PA~-ba~ed carbon fiber~ and recarbonized PA~-based carbo~
fiber3 p~oduced ~ccording ~ the in3tant i~Yention;

D~13414 Fig. 8 i~ a graph ~howing a compara~on of ehe t2naile s~rength versu~ Youn~' 8 ~odulu~ for both recarboniz~d conventional PAN-ba~ed carbon fi.bers and r~cflrbonized PAN-ba~ed c~rbon fiber~ produced ~ccording tc Ch~ inventio~; .
~ i~. 9 i3 a gr3ph 3howin~ a co~parison between the tenqil~ stren~th ~er3u~ Young's modulus fo~ bsch recarbonized PAN-b~ied cgrbon fiber~ and recarbonized PAN-baDed carbon iiber~ produced according to the invent-vn.
In carrying out the invenCion, certain embodiments have been sel2cted for description in the spe~ification and reference i~ h~d to the Fig. 1 t~ 9.
It is econo~ical in the com~Prcial production of PAN-based c~rbon yarns eo carry out the c3rbonizing ope~ation in Cwo separate ~tep~
The first step ia ~ c~rbonizing in ~ threadline ~o a te~per3ture oi about 1300~C vhile the second step is threadline oper~tion at a higher te~peratur~ to improve the ~echanical properties of the re3ulting c~rbon y~rn.
Subjec~in~ an infusibilized fiber to a heat treaeme~t resules in the relea~e of nitrogen, oxygen, ~nd hydrogen fro~n the f iber. Fig. 1 sho~s the weight pereent of the afore~entioned E ases ~nd c~rbon 118 ~ re~ult of ~ f irst heat treatrQent in ~ccord~nee ~ith the iaYencionO The rçd~;ction in nitro~en contenC i~ partieularly important bec~u5P
the 1059 of nitrogen dursng a ~IJbaequent threadlin~
heat ereatment at ~ higher te~per~ture can re~ult in seriou~ de$r~dation of the fibers.

_ 9 ~

The cests for Fig~ 1 ~2re carried ouc u~ing a 8r2phite bobbin ~r~pped with a sin~le layer of graphite fel~ and the teDperature ~a~ increa~ed frolQ
roo~ ~emperature to the inal temperature ~t the r~te of abou~ lOQDC per hour ~iCh the fin~1 eemp~rflture a~ ~ho~n b i~g held f or t~o hours.
In addition to th~ ~ubstantial reduction in nitrogen content, it i~ ~ignifi~an~ that eh~
evolution of nitrogen ~as ~t ~ relativ~ly ~low rate, particularly i~ compari~on to ~ threadline operation at 1300C. lt i~ i~por~ane th~t the evolucion of nitroge~ be 2t a 810w rat2 ~0 thst the e3c~ping g~es will not prDduce flaws and degradation in the quality of the f iber~.
Fi8. 2 show3 the result3 of a ~econd heat treat~ent u~ing ~ threadli~e operation for fibers vhich ha~e been iubjected to a fir~t heat tre2t~ent u8ing a cDnventional threadline operation ac a te~perature of about 135QC. The los~ in the den8ity of ehe c~rbon fibers for high speed~ through the f~rnace i du2 to the ~lmo~t explosive evolution of nitrogen.
Fig. 3 presents the daCs of l~i~. 2 in a dif ferent arrangelnent . Fro~ Fi8~. 2 and 3 it i3 eYidellt chat a threadline heat treatulent o' a PAN-ba~ed f iber ~hieh h~ be~n 3ubjeceed to a previ~us threadline heat trealt~nerlt ha3 li~itation as to the Lhread~ e ~peçâ and ~ximum treatment temper~ture.

Fi8. 4 i~ ~ compari~on ia the fiber den~ity after a thre~dline he~t trentment of a fiber which ha~ been ~ubjecred to a prior art threadline heat treatment ond a iber which ha~ be~n ~ubiec~ed tc th2 fir~ he~t tre~t~æn~ in accordance with the invention. In both case~, th2 fir~t heat treatmenr had a maxi~um tempefacur2 of 1300~G. The line ~peed the ~econd hea~ treatmenc in both cas2~ w~
maint~ined ~t 60 feet per ~inute. ~he eviden~
de~radntion in fiber den~i~y ia ~ re~ult of the rapid evolueion of nierogen. The fiber given iir~t heat trestment in accordance wich the invencion ha3 a very low nitrogen cont~nt.
Fig. S ~ho~s the effect of second convention~l threadliae te~perature and line ~peed on the ten~ile 3tren~th of recarboni~ed PAN-based carbon fib~r~ which h~ve been subjected eo a fir~
conveneional threatliae treaemenC~ The ten~ile ~rength dec1ines r~pidly in each ca3e even or relatively ~low line 3peed~ ~ the ~aximum hea~
treatment temperature increa~es.
Fig. 6 3ho~s the t~n~ile 3tren~th of fibers afcer bein& ~ubjected to 3 ~econd heat trea~ment u~ing a conventional threadline. The fib~r ~hich has been giYen a ir~e heae trea~mPn~ in ~ccordance ~ieh the invention i~ si~nific~ntly better than the iib2r which h~ been subject~d for ~ iir3t he~t Cre~tme~t in accordance with eh~ prior are. The line speed in all case~ was 40 feet per minute.

~-13~14 Fig. 7 ~ho~s the YQUn~ odulus ver~us um temper~ture for ~ ~econd heat treat~n.
uaing a conventional thre~dline for fibers havi~g a fir~t he~t treae~ent according eo ehe invention and for iibers haYi~g a heat treat~en~ ;~ccordin~ to ~he prior ~rt. The fir~t heat treaem~n~ in all ca~e~
had a ma~imum temperaeure of 1300~C. The carbon fiber~ accordin~ to the in~tant invention con~istently sho~ed higher value for the Young's modulus even when the line 3pe~d for the ~econd heat treat~ent wa~ ten eimes greater than th~ line speed used for the fiber~ accordin~ to the prior art.
Fig. 8 sho~ the relacio~3hip for tenRLle stren~th ~nd Youn~'s ~odulus for fiber~ according to the in~e~t inveDtion and prior art. In each ca~e, the fir~t heat treatment wa~ carried out u~ing a maximu~ tempera~ure of 1300C ~hile ehe ~econd heat trestm2nts were both convention threadline oper~tion~. For both operaeion~, ~he ~a~e threadline ~peed ~s u~ed and differene te~peratures were u~ed to obeain vsrious fiber properties. The data show thae for 3ch Young's ~odulu~ ehe tensile strength of the fibers produced by the in~tanc inveneion i3 3ubstantially higher thAn the tensile strength of the fiber~ produced according to the prior arC.
Fig~ 9 ~how3 a compari30n bet~een thP
ten~ile ~trengeh ~nd the You~g'~ ~odulus for fiber3 prep~red accordin8 ~o the inst~nt invention and the prior ~re. In each C~82, the maxi~um t~mper~ture u3ed ior the first heae treaem~nt ~a3 1300DC and the m~iMu~ te~perature u3~d in the 3econd he~e ~ 3~

.reae~ent ~aa lgO0C. ~he v~ri~tiona in ~,echanical proper~ies wer~ produced by changea in ~hr~adline ape~d. Ihc carbon fibess accordin~ to th~ invention were o~erwhelmingly auperior t3 the fibers produced ~cco~ding Co ~he prior art.
Illu~trati~e, Don-limitin8 example~ of the practic2 oE the in~ention ar~ 9ec out below.
Nu~erous other e~a~plea can be re~dily evolved in the lighC ~f the guiding principle~ and teachings contai~ed herein. Ex~ple~ given herein are intended ~erely eo illu3~r~t9 the invention and not in any 3ense to li~it the ~anner in vhich the inYention ~an be practiced. rh2 parta and percen~ages ~ cited herein and all through th ~pecification, unle~a specifically ~tated other~i3e, refer to parta by ~eight and percentages by ~ei~hc.

A PAN-based infusibilized y~rn wa3 used.
The fiber~ in the yarn had a composition of 64.0 carbon, 3.9~ hydrogen, 6.2~ o~y~en, and 25~1~
nitrogen. The ysrn was ~ound on 3 bobbin used in com~ercial production. The y~rn was unwound from the bobbin and rotated eS,t 500 r~volutions per minuce ~dhile being un~do~,nd esC ~he r~,te of 63 feet per minuCe !!o thD~ ~ CwiRC of 0. 7 turn~ per inch W~3 e~;tr,bliah~d. The Cwisted yarn ~e,~ rewound wiCh c, ten~ion of 259 gr m~ onto a gr~phir~ bobbin h~ ~ring dimension~ of 3.5 inches in dia~e~er and 11 inches long. Th~ sraphite bobbin h~d a layer of one qu~,rcer inch of ~raphite felc on rhz cylind~ical D- 1 34 1 ~

portion to recei~e ~he ya~n. A wind a~gle of 23 degrees w~ u~ed and the p~o~age pressure wa3 3 lb~
~ith a tr~n~r3e length of te~ inche~ The rewound yarn ~ounC~d to 23,500 f~e~ of yarn and ~a~ in the fOr2 Gf a squ~re-sided packa~
~ e p~ck~ge ~g placed hori~ontally in a gr2phit~ tube induction furnace ~hi~h w~ pun ed with nitrog~n ~d fired ~t the r~te of S0C per hour to 800C ~nd thereafter temper~ture W~3 raised at 250C p~r hour eo 1300C~ Th~ fin~l temperatur2 ~a~
~aintained for two h~ur~ ~nd the pack3ge was ~llowed to cool b~ck to room tempPra~ure. A3 a re~ult of the heAt treat~ent, the packa~e h~d ~hru~k longitudinally about 1.5 to 2 in-he~ from it3 original ~n inch l~ngth.
The paokage was then moun~ed horizontally on a ten6ion-lo~ded payoff rreel, ~nd the yarn ~a~
unwound under ~ ten~ion of approximately 50 grams, pas~ed through a grooved-reel, ten3ion-controled drive ~y3tem m2intain~d ~t ~ tension of about 1,825 grams and there~fter through graphite tube electric reai~Cance furnace having a hot zone maintained at temperatuse of about 1~30C and five feet long. Th~
yarn e~iting the f~rnace ~s then ~ubjeceed to ~
fini~h treaC~snt in ac~ordance ~i~h the prior ~rc ~nd wound onto bobbin~ made of cardboard in one thouaand ioot length~ nty-t~o 3amples of che yar~ v~re tDke~ at ab~ut 1~000 foo~ i~terval~.
The ~vera~e t~nsile ~ren8th of Ch~
re3ulting fiber ~a 500,000 pai ~ith a coefficienc oi variaCio~ of 1.3~. The averagP Youn~' 3 modulus for the re~ulein8 fiber ~g about 41.2 ~illion p8i with a coeficient of v~ri~tion oi 2.9~. The a~erage den~ity of the fiber~ wa~ a~ 766 M~ per cubic ~eter with ~ coefficlent of ~ariation o 0~6XA The ~er~8e yield VB3 3571 f~et per pound with coefficient of v~riation o 2.1~.
The c~rbon yarn ~btained had an excell2nt 2ppearance ~nd w~ equi~alent in quality to a carbon yarn produced by carboni2ing ~ith two ,~eparate thre~dline~ in accordance with the priOf art.

Inusibilized yarn a3 in Exampl_ 1 wa~ used in this example. For thi~ exampl~, ho~e~er, 47Q0 feet on i~fu~ibilized yarn was u3ed. As in ~xample 1, the yarn was wound onto the ~r~phite bot~bir.
having a gr~phite felt layer.
The ~a~e te~p~rst~lre ~cheaule ~aa u~ed for the iirst he~t CreaC~nt. The ~econd heat treatment va5 differen~ in this exa~ple fro~ Example 1 in th~t ~he furnace temperature was held ~t 2460C, the take off tension W88 100 gr~2~s, the line tension ~as 1950 ~ralD~, the line speed ~a~ 70 f~e~ per ;ninute, ~nd only w~ter ~ applied t:o the carbon y~rn inseead of f ini~h.
samples t~ken ac abou~ equal sepa~ation~ wer~ te3ted. The faber.~ hsd an average ten~ile str~n~h of 477,000 p3i~ ~n averag2 Young's tDodulus of 56, 7 million psi, ~ den~ity of 1. 313 Mg p~r cubic ~eter, ~nd ~ yield of 3796 eet per poundO ~he yarn w~s e~cell~n~ in ~ppearanceO

~ ~3414 EXA~PLE 3 4700 feet of carbon yar~ produced fro~ Che at~p3 ~f E~ple 1 ~ere ~Gund OD a ~raphite bobbiu h~vi~g a dia~æeor o~ 4.5 inches ~nd ~ length of seven inches. No carbon fplE ~a~ u~ed and eh2 wind ~n~le ~a~ abo~t 0.4. Thi~ p~ckage v~ then loaded horizont~lly i~ a graphi~e rube induction furn~ce, purged with arBon, and fired ~C the rnte of 100C
per ho~r ~o a te~prature of 2950C. The final temperature ~a~ m~intained for tYo hou~ and the package was allo~ed to cool back to roo~ temperature.
The average properti2~ of the fibers so obt~ined wa9 ~ ten3ile strength oE 360,05Q p~i, Young'~ ~odulus of 96.9 million p8i, den~ity of

2.080 M8 per cubic meter, and a yi~ld of 4218 feet per pound. The reduction in ~trenBth over the valuex obeained from xa~ple 1 indicates th~C ne~
f la~s were introduced during the ~ub~equ2nc then~al processing and h~ndling.
ID any e~ent, the carbon fiber3 of thi~
e~a~ple constitut2 a 3ignificant improvement over comm~ ~ ially av~ilable PAN-ba~ed carbon fib r~.
I wi~h it to be under~tood that I do not de3ire t~ be li~it d to th~ exact dPtail~ ~how~ and de3cribed, or ob~iou~ modific~tions ~ill oc~ur to 3 person ~killed in th~ art.
~ a~ing thus d~3cribed the invention, ~hat I
~laim a3 ne~ and desired CQ be 32cured by L2tter~
P~te~c~ i3 a3 follo~:

Claims (8)

1. In a method of producing a PAN-based carbon fiber comprising the steps at of spinning a polyacrylonitrile fiber, infusibilizing the fiber, and thereafter carbonizing the infusibilized fiber to produce the carbon fiber, the improvement comprises carrying out the carbonizing by winding the infusibilized fiber onto a bobbin which is thermally and mechanically stable at temperatures used to pyrolyze and carbonize the infusibilized fiber and which is chemically compatable with the infusibilized fiber, subjecting the infusibilized fiber on the bobbin to a predetermined first heat treatment in an atmosphere to pyrolyze and carbonize the infusibilized fiber, and thereafter, subjecting the carbonized fiber to a second heat treatment in an inert atmosphere in a threadline operation.

2. The method of Claim 1, wherein the threadline temperature is at least about 600°C
higher than the maximum temperature used for the first heat treatment.

3. The method of Claim 1, wherein the first heat treatment is carried out at a rate of from about 50°C to about 500°C per hour to a maximum temperature of from about 1300°C to about 1700°C.

4. The method of Claim 1, wherein the infusible fiber is wound onto the bobbin with a wind angle of at least about two degrees.

5. The method of Claim 3, wherein the wind angle is about 23 degrees.

6. The method of Claim 1, further comprising a third heat treatment subsequent to the second heat treatment and having a maximum temperature greater than the maximum temperature of the second heat treatment.

7. A PAN-based carbon fiber having a Young's modulus of about 97 million psi and a tensile strength of about 360,000 psi.

8. A PAN-based carbon fiber having a Young's modulus of about 56 million psi and a tensile strength of about 477,000 psi.