US2988802A

US2988802A - Apparatus for spinning polyvinyl alcohol fibers and product

Info

Publication number: US2988802A
Application number: US336166A
Authority: US
Inventors: Akaboshi Michijiro; Tomonari Tatsuko; Tomonari Natsuko
Original assignee: Kurashiki Rayon Co Ltd; Air Reduction Co Inc
Current assignee: Kurashiki Rayon Co Ltd; Airco Inc
Priority date: 1949-07-26
Filing date: 1953-02-10
Publication date: 1961-06-20
Anticipated expiration: 1978-06-20
Also published as: US2642333A; GB697097A; FR1017625A

Description

June 20, 1961 TSUKUMC TOMONARI ETAL APPARATUS FOR SPINNING POLYVINYL ALCOHOL FIBERS AND PRODUCT Filed Feb. 10. 1953.

2 Sheets-Sheet 1 TJIZZ..

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June 20, 1961 'rsuKUMo ToMoNARl ET AL 2,988,802

` APPARATUS POR SPINNING POLYVINYL ALCOHOL PIBERS AND PRODUCT Filed Feb. 1o, '195s 2 sheets-sheet 2 Tlc'. E.

INVENTORS Y 7%, @ww/MAA( AGENT UnitedA States Passat 2,988,802 APPARATUS FOR SPINNING POLYVINYL ALCOHOI: FIBERS AND PRODUCT Tsukumo Tomonari, Osaka, 'and Michijiro Akaboshi, Kurasluki, Japan; Tatsuko Tomonari and Natsuko Tonionari, heirs 'of said Tsukumo Tomonari, deceased, assignors, b y direct and mesne assignments, of onefourth to Air Reduction fCompany, Incorporated, New York, N. a corporation of New York, and threefourths to 'Kurashiki Rayon Co., Ltd., Okayama, Japan, a corporation of Japan n Filed Feb. 10, 1953, Ser. No. 336,166 Claims priority, application Japan July 26, 1949 2 Claims. (Cl. 28-82) The invention relates to the wet spinning of polyvinyl 1 alcohol bers.

A principal object of the invention is to provide a process for producing polyvinyl alcohol laments having high tensile strength in the dry as well as in the wet state and high resistance to hot water.

Another object of the invention is to provide a polyvinyl alcohol ber having the recited characteristics and being suitable as a synthetic ber for the manufacture of textiles.

Other objects and advantages will be apparent from a consideration of the specification and claims.

The wet spinning process for producing bers has been particularly developed for the manufacture of cellulose and other bers from the corresponding solutions of cellulose and cellulose derivatives. The spinning of such solutions is usually based on the coagulation and simultaneous chemical change of the celluose derivatives dissolved in the solution and stretching of the obtained regenerated bers to increase their tensile properties. In case of viscose ber manufacture, for example, the coagulation takes place very rapidly with simultaneous decomposition of the cellulose xanthate to regenerate cellulose in the form of laments. The solidiedlament can be handled safely without damaging the ber. When lusing a relatively short dipping length in the coagulating bath and a relatively high spinning speed, good bers are obtained. The stretching is being applied to the lament during spinning and after spinning to increase the tensile properties.

The process and equipment successfully used for spinning viscose or other cellulose bers cannot be used for the spinning of polyvinyl alcohol because of its fundamentally diiferent chemical physical, and ber forming properties; therefore, the conventional spinning methods and devices must be adapted to the specic properties of polyvinyl alcohol in order to spin polyvinyl alcohol bers which meet the requirements of commercial textiles.

In our copending application, Serial No. 154,872, led April 8, 1950, now Patent No. 2,642,333, of which this application is a continuation-impart, we have disclosed and claimed a method of spinning polyvinyl alcohol bers comprising the steps of extruding a polyvinyl alcohol solution into an lip-flowing column of a coagulating liquid having a higher specic gravity than said polyvinyl alcohol solution, imparting to said coagulating column and said polyvinyl alcohol solution a parallel upward direction of ow without turbulence, maintaining said unturbulent parallel llow until ythe polyvinyl alcohol coagulates to laments, subsequently reducing the diameter of said column, thereby increasing the rate of flow thereof, and stretching said coagulated laments by said increased rate of flow and the uplift of the filaments in the Y specically heavier column of the coagulating liquid.

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tion and distinguish it from other spinning solutions. (l) During the spinning of an aqueous solution of polyvinyl alcohol, the chemical composition of the polymer is not changed. The physical changes which occur during spinning are coagulation and dehydration which take place very slowly even in a strong coagulating medium. lf an aqueous solution of polyvinyl alcohol is extruded into a solution which is capable of coagulating the polyvinyl alcohol, a very thin membrane of coagulated lm is formed on the surface of the extruded stream. The coagulating bath diffuses through the membrane in the interior of the stream and slowly coagulates the in terior which is still liquid at a time when the membrane is already formed. Simultaneously the water .diffuses from the interior of the partly coagulated ber in the coagulating bath. This partly coagulated ber consists of a liquid or semi-coagulated core and a very thin outer skin and must be handled very carefully; any disturbance of the ber as well as any pulling or stretching force should be avoided, as such inliuences will damage the lament in statu nascendi. Stretch can be applied only after the .filament has become strong enough to withstand such forces without damage; for this purpose, the thickness of 'the surface membrane or skin must be increased until the laments assume the required strength. Before the lament reaches this state a long contact with the coagulating bath is needed. Although there are means to accelerate thedifusion of the coagulating agent through the surface membrane and such means may somewhat shorten the time interval necessary between the moment when the extruded liquid enters the coagulating bath and the point 'where stretch can be applied to the lament, they cannot substantially change the characteristic feature of slow coagulation of polyvinyl 'alcohol solutions.

(2) A second distinctive feature of polyvinyl alcohol bers is due-to the strong cohesive power of the polyvinyl alcohol molecules. The polyvinyl alcohol molecules in the coagulated surface membrane tend to aggregate very rapidly and if a slight pull is applied at the proper time the yaggregate is oriented in the direction of the pull; whereas if an aggregate is fully formed in a non-oriented state it becomes diicult to orient the molecules. Therefore, it is necessary to apply a pull at a moment when the molecules are aggregating for the purpose to orient the polyvinyl alcohol molecules. The molecule aggregates are very dense and therefore, those oriented onthe surface membrane have the effect of impeding the diffusion of the coagulating agent into the interior of the stream as well as the outward dilfusion of the water; consequently, they retard the coagulating progress in the interior part, which results in a filament having a thin oriented surface membrane and a non-oriented core. In order to increase the thickness of the oriented surface skin, a very slight pull is to be applied from the beginning of the coagulation, which pull is to be gradually increased asy the coagulation progresses from the outside inwardly. The molecule aggregate forming the skin part-of the lament is responsible for the mechanical properties of the-la- Vment, and as the oriented skin is developed, the mechanical strength of the lament is increased.- 'I'he lament with a thin skin obtained at an early stage of the Vspinning process is not strong enough to withstand a strong external force, for example as applied by solid guide rods; therefore, care has to be taken that the lament is pulled only ment, the speed difference exerts a pulling action onthe lament. While the lament travels inthe bath, coagulation of the solution progresses. Conforming to the progress of coagulation, the flow speed of the eoagulating bath is gradually increased to exert an increasing pull on the filament. By the pulling action the molecules in the :surface membrane of lthe filament are `aligned along the direction ofthe upward ow of the bath and the thickness .of thc .membrane is gradually increased. If the skin part becomes sufficiently thick, then the filament can be stretched without being damaged or broken by an external force such as friction caused by the bath iiow or a guide By an adequate strong stretch, the orientation of fthe molecules is increased and the tensile properties of the filament are improved. During the travel of the filament stream in the bath, the stream or filament is being drawn and the coagulation and dehydration of the polyvinyl alcohol vmolecules proceed; hereby the diameter of the stream is gradually decreased and the stretching force per unit of cross section must be therefore gradually .-increascd.

ln accordance with the properties of polyvinyl alcohol filaments Vset forth hereinbefore, our process consists in .drawing the extruded lamentary polyvinyl alcohol stream and the coagulated filaments in such a way that the drawing (elongation) is larger at the beginning and smaller at the end, whereas the applied stretching force is very slight at the beginning, increases gradually and becomes fairly strong after the coagulation has sutciently progressed. 1(3) The third characteristic feature of polyvinyl alco- ,hol is the limited plasticity of the polyvinyl alcohol aggregates. As the coagulation of polyvinyl alcohol solutions is very slow and the spinning time is very short, a too strong stretching during spinning is apt to destroy the structure of the aggregating filament. In order to improve the tensile strength, it may be necessary to apply 'an additional stretch to the already sufficiently solidified V.Sllln filament, Vwhen it can withstand such stronger stretching. But as the polyvinyl alcohol aggregate structure has .only limited plastic deformability, it cannot be subjected to such -a strong drawing as applied to typical plastic compounds, which would cause unevenness and breakages of the polyvinyl alcohol filaments.

Further characteristic properties of the newly spun polyvinyl alcohol filament are its water sensitivity and solubility, which have `to be reduced or eliminated Vby an after-treatment of the filament. As the invention is concerned substantially with the spinning process proper, the after-treatment of the spun filaments need not be considered here.

For carrying out the spinning process of our invention aV suitable polyvinyl alcohol solution and eoagulating bath should be used. Among the factors which determine the spining properties of polyvinyl alcohol solutions, the degree of polymerization (DP) of the polyvinyl alcohol and the concentnation of the solution are important. The DP may vary from 1200 to 2500 and the concentration of the aqueous spinning solution from 8% to 20%, increasing with decreasing DP. In special. cases as for example for the spinning of very fine denier filaments, the concentration can be reduced below 8% and the DP increased to above 2500. As eoagulating bath, an aqueous solution containing one or more inorganic salts such as sodium sulfate, ammonium sulfate, zine sulfate, is used; the concentration of the salts is preferably close to the saturation point.

The invention will now be described more in detail in connection with the accompanying drawing, in which FIG. l illustrates a suitable apparatus employed for practicing the method of the invention, and

FIG. 2 is a diagram illustrating the flow conditions in the apparatus of FIG. 1.

FIGS. 3 to 6 show modifications of the spinning tube.

FIG. 7 isa photograph of a cross section of staple liber spun according to the invention (magnification: 390).

The apparatus shown in FIG. l, comprises a casing 4 and seated therein a smaller tube 1, which ends in the 4 receptacle 3. A tube 2 is slidably arranged inside tube 1 and extends into the receptacle 3 and with a trumpetshaped extension into casingll. Supports 11 allow of displacing the tube 2 upwardly or downwardly; a shoulder may be provided on the inner wall of the casing 4 to limit the downward movement of the funnel 16.

The wall of the casing 4 can be provided with window .openings which are normally closed by the cover 17 and allow of inspecting and adjusting the coagulated filaments.

The casing 4 and tube 2 provide a vertical spinning zone A-D, where the lower part A-B has substantially constant diameter, the middle part B-C has decreasing diameter and the upper part has reduced substantially constant or a very slightly decreasing diameter.

An aqueous solution of polyvinyl alcohol is extruded through small holes of a spinneret 5 into a eoagulating bath column. The eoagulating bath is fed into the spinning Zone through holes 10 of an annular pipe 9 arranged around the spinneret and ows upwardly substantially without turbulence from A to B. The polyvinyl alcohol filaments take form in said unturbulent column and are subsequently drawn by the increasing rate of bath flow in the funnel part 16 and tube 2 until they are taken up by the Godet roller 15. The bath finally ows out from the .column top and is withdrawn through the discharge 12. Guide rods 14 may be provided to guide the filament and to adjust the stretch on the filament.

Several factors determine the exact spinning conditions.

(l) The denier of the filament to be spung determines the .extrusion amount of the polyvinyl alcohol solution in relation to the spinning speed. The denier of the polyvinyl alcohol filament can be varied in a wide range of about 0.5 denier to about 20 denier.

(2) The extrusion speed (VA) of the polyvinyl alcohol solution from the spinneret must be higher than the rate of flow of the eoagulating bath at A and is determined from the extrusion amount of polyvinyl alcohol solution of a definite concentration and the diameter of the spinneret holes. The speed varies usually from 5 m./min. to 50 m./mn. The preferable speed may be in a range of from l0 m./min. to 30./min.

The extruded stream of the spinning solution enters the eoagulating bath, loses gradually its speed and finally floats up only due to the gravity difference between the filament stream and the eoagulating bath. The specific gravity of the polyvinyl alcohol solution is about 1.1, that of the eoagulating bath about 1.3. The floating up speed is usually 1.5 m./min. to 3 m./min.

(3) The spinning speedl (VE) is determined by the peripheral speed of the Godet roller and can be changed from about l0 rn./min. to about 150 m./min. When the spun filament is taken up by the Godet roller, any resistance applied to the filament results in a drawing of the filament and consequently the speed of the filament is reduced, depending on the extensibility of the filament formed. As such a resistance, the iiow resistance of the eoagulating bath and the frictional resistance exerted by the guide rods or rollers may be of importance.

(4) The dipping length is the total length of contact of the extruded stream with the eoagulating bath. Because of the very slow coagulation of the polyvinyl alcohol solution, the `dipping length must be at least 500 mm. and will necessarily be longer for spinning coarse deniers and for spinning at higher spinning speeds. The long dipping length causes a strong iiow resistance of the bath to the travelling stream of polyvinyl alcohol and said ow resistance draws the filament and decreases the travelling speed toward the upper part of the lower section of the eoagulating column until the traveling speed is reduced almost to the floating up speed of the polyvinyl alcohol stream.

If the eoagulating bath does not liow upwardly, the traveling speed of the stream extruded from the spinneret to be taken up by the Godet roller may be schematically illustrated by the dotted line in FIG. 2. The line shows spese-a! that the extruded stream loses its speed tn the Bathsuddenly and after traveling in thebath for 100 to 200 mm, comes to the floating up speed and afterwards increases its speed due to the pull by the Godet roller. At the lowerI part of the column the pull of the Godet roller may have no influence on the traveling speed of the stream. That means that the stream is floating up freely. The speed change at the upper part of the column, however, is very considerable; that is, the flow resistance of the bath causes a heavy stretching of the iilament. AtV high spinning speeds, the filament Iwould be liable to` ,break during its travel between thetop of the column and the Godet roller, and a filament having superior properties could not be obtained. Therefore, it is necessary to reduce the tlow resistance due to the long dipping length by causing the-coJ agulating bath to flow up in the direction of the travel of the filament stream or by reducing Ythe traveling speed by guide rods placed beneath the Godet roller.

.The ow resistance is proportional to the difference between the flow speed of the coagulating bath and the traveling speed of the lament; it must not be too high in l order to avoid injury to the filament. We adjust the ow speed of the bath and the traveling speed of the lament in the upper part of the column so that the speed diierence at the end of the coagulation when the filament yleaves the bath at D, is not larger than 50%.

The flow of the coagulation bath has Va great influence on the spinning of the tilaments. The flowing speed in the column changes accord-ing to the shape of the column, its position and the amount of liquid, as illustrated in FIG. 2. The fiow speed is constant from point A to B, increases gradually and attains again a constant speed at C. The bath flows out from the column at D. The flow of the bath exerts an influence on the traveling polyvinyl Ialcohol stream, accelerates its traveling rate and changes it to the speed curve shown by the dash-dottedl line in FIG. 2. Along this curve the traveling stream is subjected to Idrawing and stretching and the diameter of; the stream decreases. yThe diameter is also `decreased as the' coagulation and dehydration progresses.`

(6) The distance d of the funnel edge from the spinneret surface is important so `far as it determines the moment when the influence of the increasing ow speed of the .bath starts. From A to B the extruded stream gradually loses its speed and reaches the lowest speed (Vp). As ,this flow speed is lower than the traveling rate of the polyvinyl alcohol stream, the bat-h flow can here not exert a pulling action on the stream. The extruded stream contractslacconding to the speed decrease and the coagulating bath diffuses into the stream; a very thin coagulated membrane is Iformed on the surface of the stream, while the linterior of the stream 4remains a semi-coagulated or noncoagulated solution. As the dehydration is very small, the diameter of the stream m-ay increase inversely proportional to the decrease of the speedrof the stream.

At the point B where the stream enters the funnel, the stream is pulled by the increasing flow speedof the coagulating bath and the speed ofthe stream is lgradually increaesd from Vp to Vd. The point (P) where the stream speed is lowest may be located 4a little higher than the point B, but the 'difference is small so that the lowest speed VP may be yassumed to be the same as the speed VB at point B.

At the point P or B the drawing of the stream starts and is caused by the speed difference between the bath and .the stream. As previously mentioned, the stretching of the stream at the early stage of coagulation is important and necessary to improve the tensile properties of the produced filament. But a too early start of the stretching iwould be harmful because such a stretching destroys the coagulation structure whereas a too late start of the stretching would be less eliicient because such a stretch- Iing contributes little to the orientation of the polyvinyl alcohol molecules which have already aggregated at random. The proper distance d is determined essentially by the increasing flow speed. During this travel from B to C, the speed difference between bath and stream gradually increases and consequently the stream is gradually drawn and its diameter gradually decreases. The diameter decreases also due to the dehydration of the polyvinyl alcohol molecules. By the increased drawing, the stretching of the filament stream is increased and the coagulated polyvinyl alcohol molecules are aligned along the fiber axis to improve the tensile properties of the produced filament. At the point C the bath and the filament stream enter intothe narrow section of the coagulating column and the speed difference between the bath and the stream attains a maximum.

The flow speed of the coagulating bath at C determines the magnitude of the drawing or stretching applied to the solidifying filament and the shape of the funnel determines the increasing rate of drawing or stretching. The increasing rate and the maximum value of drawing or stretching may be adjusted to the coagulation characteristics of the polyvinyl alcohol solution and they should be neither too big nor too small; the rate of drawing from B to C may be, for instance, about 50 to 150% per second. The appropriate shape of the funnel and the liow speed are easily determined in each practical case, according to the denier of the filament to be 'spun and to the spinning speed imparted by the Godet roller.

(8) The length of the narrow section of the spinning column determines the contined coagulation and drawing of the filament stream in the coagulating bath column. During the travel from C to D, the flow speed of the bath is constant, e.g. about 5 to 50 m./min.,and the traveling speed of the stream increases due to the take up by the Godet roller; therefore, the pulling force exerted by the iiow speed of the bath decreases. However, the pulling action by the Godet roller becomes now effective. The stream increases its speed gradually and is taken out of the bath at D with the speed (VD) and reaches finally at the Godet roller the speed VE.

Because the spinning speed VE is usually higher than the flo'W speed of the bath, the traveling speed of the stream must exceed the flow speed of the bath at a certain point Q; below this point the coagulating bath exerts a pulling action on the stream and abofve this point the bath exerts a braking action due to the ow resistance against the pull of the stream by the Godet roller. The point Q changes its position according to the relation between spinning speed, flow speed of the bath and dipping length. If the point Q falls below C, the pulling effect of the Godet roller will act on the filament stream at an early stage of the coagulation and may destroy the structure of the solidifying filament stream if the eiect is too strong. To avoid this undesirable effect, the length of the section C-D must be extended. However, if the section is too long, the liow resistance of the bath is increased, which may destroy the solidifying stream. The How resistance should not be too strong, that is, the speed difference between the filament and the bath should be relatively small.

If a mechanical resistance such as guide rods are put between the top of the column andthe Godet roller, the travelling speed of the stream in the bath is reduced and the point Q moves toward the point D and may pass this point, in which case the traveling speed at point D becomes lower than the ow speed as illustrated by the solid line in FIG. 2. In such a case, the flow resistance of the bath is decreased but the guide resistance is increased.

During.; thetravel. from. C to. D, thee filament isfurther drawnzaceordingftothe'speed relationand the extensibility. of the filament, itsy diameter is further' decreased andthe stretching is increasedto improve, its tensile strength. The, rateV of: drawing in this section is aboutV 10 to 5.0% per second. By adjusting the dipping length, ow speed of the bath. and the'position of the guide rods the most suitable conditions may be determined. As stated, above, theatraveling speed VDO. thelilament at D should. preferably beabout the sameV at theA iiow-out speed of the bath and should. diifer from saidiiow-out rate by not more than 5.0%, i.e. VD=(1i0.5.) Xllow-out speed of the bath.

(9) Thelament drawn out from the coagulating bath column atiD is` taken up by the Godet roller at E. At D` and E. the iilament is. already sufficiently coagulated and does not undergo; any substantial further coagulation.` Thedistance from, D'. to E is of little importance and may be adjusted to the available space.

To sum up: According to the invention the spinning process is divided in. three diterent stages-free coagulation, drawing and stretchingl in the bath, and outside of the-l bath. In the coagulation stage, the speed of the extruded stream is reduced to, or almost to the floating up speed of 1.5 to 3 m./lmin., at most 5 m./min., andfree coagulation without turbulence and without pulling' action-with stream is obtained. In the drawing stage in the coagulating bath, the stream is drawn by increasing its rate of ow from the lowest speed indicated hereinbefore to a speed corresponding to the flow speed of the bath, exceeding said speed by not more than about 50%. The .drawing and consequently the stretching is to be performed over theA whole range; it is very slight in the early stages and obtained mainly by increasing the ilow speedl ofrv the bath, and it is gradually increased in the later stages, Where the coagulation has progressed, by the pulling action of the bath ow and sometimes by the flow resistance of the bath. The increase of drawing or stretching' should be gradual and a sudden change must be` avoided. A spinning column of trumpet shape with gradually decreasing diameter would give the most satisfactoryperformance; for practical purposes, columns where the upper part is of aconstant small diameter as shown in the drawings, are sufficient. The edge of the trumpet can be located closer to A if the' diameter of the trumpet edge is big enough and the shape of the trumpet wallsgentle enough and if the ilow speed of the bath is kept much smaller than the floating` up speed of the stream in this zone so as to prevent any turbulent action of the spinning bath in the polyvinyl alcohol streamin the zone of` beginning coagulation (see FIGS. 5 and 6).

The drawingof the iilament after leaving the coagulating bath can -be asserted by means of one or more guide rods or revolving rolls placed before the Godet roller.

YIn this stage, the filament is drawn from the speed near to flow-out speed of the bath to the revolving speed of the Godet roller. The drawing rate may be increased from nearly zero up to tive times. When the coagulation is nearly completed, strong stretching and a sudden change areallowable, but also here too strong stretching is to be avoided..

Thelfollowingexamples are given to illustrate the spinning conditions and their relation to the properties of the Tobtained filament. The dimensions of the funnel used (FIG. l) were: a=100 mm.; b=25 mm.; c=200 mm.

Example .I

`containing 39,0` g,'/l. NaaSO,` thetemperature ot which was, maintained at 45"v C.. The extrusion speed4 VA` was 30mm/min. and the takey upfspeedby the Godet rollenVEc was 50m/min. 'Ihe;dipping ;length.in the bath was 1200 mm. The flow speedofrr the coagulating bath` was.Y 15, m./ min. Two guide rode were placed before the Godet roller andthe speed of the-.filament at the outlet from the bath was adjusted to about the same speed as theiiow speed o f-the bath.

The spun filament tow was dried at 100 C. and then heated in air at 220 C. for a period of 3 minutes. During drying and heating, the length` of the tow was keptv constant. After washing and drying a finished tow of 4000 denier composed of 1000 lilaments of 4 denier was obtained;

The location ofthe funnel d was varied, and the results of. the iniluence of the funnel location were as follows:

The results indicate that if the pulling action by the, flow of the coagulating bath was too early applied to a not suiiiciently coagulated stream of the extruded spinning solution, the tenacity, especially the wet tenacity of the finished lament was lower, and the elongation higher. This shows an insufficient orientation of the molecules. On the other hand,l if the pulling action was applied too late,the tenacity and elongation decreased somewhat at the same time probablydue to the injuring influence of the, pull` by the bath flow or to the stretching applied to the coagulated stream of the spinning solution.

I n this example,kthe highest tensile properties were obtained when the funnel was 300 mm. above the spinneret. lf the distance is decreased, then the flowing speed of the bath must be changed. This means that if the pulling action is very slight, it canbe appliedat an early stageof the coagulation.

Example 2 The spinning conditions employed were the same as in Example 1, with the difference that the location of the funnel was maintained at d=300 mm., but its length was varied. Again 4000 denier tow, composed of 1000 filaments, of 4 denier was spun.

'Iihe results of the iniiuence of the length c of the funnel were as follows:

Length of the funnel c (mm.) 50 100 150 200 300 400 Dry tenacity, g./d 2.15 2. 56 2. 68 2. 89 2. 94 2. 54 Dry elongation, percent 39. 1 29. 3 27. 5 22.8 20. 5 1l?. 8 Wet/Dry tenacity ratio, percent. 57 65 74 84 85 75 Wet/Dry elongation ratio, percent 98 105 110 108 109 Example 3 The spinning conditions employed were the same as in Example 1, with the difference that the location of the funnel was secured at d=400 mm. and the flow speed of the coagulating bath was varied. A 4000 denier tow composed' of- 1000 filaments of`4 denier was spun.

'aosaeo'a 'The results of the influence of the slow 'speed were as follows:

10 V1000 filaments of 2.0 denier was spun. Some suitable conditions are shown as follows:

From these figures, it is evident that an increase of the iiow speed increases the stretching at the earlier stage which results in `an increase of the tenacity and a decrease of the elongation of the iilament produced. However, if the iiow speed is too high, the polyvinyl alcohol stream or thread is too strongly stretched and the orientation of the molecules is disturbed, resulting in low tenacity and high elongation of the spun filament. At a high iiow speed, the speed difference between the spinning speed and the speed of the thread at the outlet of the coagulating column is also reduced, which acts in the direction of low tenacity and high elongation under the conditions employed. Optimum properties were obtained at a flow speed of between 8 to 16 meters per minute.

Example 4 The spinning conditions employed were the same as described in Example 1 with the diierence that the extrusion speed of the polyvinyl alcohol solution was maintained at l m./min., and the location of the funnel was kept at d=400 mm., whereas the dipping length was varied. A 2000 denier tow composed of v100 filaments of V2 denier was spun.

ADipping length, mln. 700 900 1, 200 1, 500 2, 000 VDry tenacity, g./d 3.12 3. 36 3. 31 2. 96 2. 40 Dry elongation, percent..` 18.4 16.5 16.1 17. 9 20.0 Wet/Dry tenacity ratio, percent 83 84 75 76 75 Wet/Dry elongation ratio, percent 105 121 117 136 115 Example 5 The conditions employed were the same as in Example l with the diierence that the spinning speed was varied. The location of the vfunnel was maintained at Y400 mm. A 1500 denier tow composed of` 1000 iilaments-of L5 denier was spun.

Spinning speed, m./min 30 50 55 60 70 Dry tenacity, g./d 3.39 3.64 3. 26 2.61 2. 38 Dry elongation, percent 16.7 16. 6 15. 6 14. 5 15.3 Wet/Dry tenacity ratio, persen `81 84 91 91 83 Wet/Dry elongation ratio, percent. 106 98 109 115 129 The higher the spinning speed, the larger is the stretching at the later stage of the spinning, which increases the tenacity. But too high speed spinning is apt to destroy the structure of the solidifying thread stream and to de- ,crease the tenacity and elongation. It is to be noted that `for higher spinning speeds, larger amounts of the spin- Aning Vsolution must be extruded and a larger degree of ldrawing betweenB'and E is to be applied, and that such conditions are undesirable for obtaining the stretching effect. However, higher spinning speeds can be employed rby properly adjusting the dipping length, the flow speed of the coagulating bath and the Vfunneldistance and dimensions.

` Exampla The conditions employed were the same as in -Example 1 with the difference that .the dipping length and the ilowof the coagulating bath were varied corresponding to the spinning speed. The location of the funnel was kept at d=400 mm. and a 2000 denier tow composed of Wet/Dry tenacity ratio, percent Wet/Dry elongation ratio, percent The example shows that the ratio of spinning speed to iiow speed should be at least 3 and preferably greater. By strictly adjusting the spinning conditions, the properties of the iinished filament may be further improved and it can be'spun at higher spinning speeds.

Example 7 The conditions employed were the same as in Example 1 with the difference that the extruded amount of the spinning solution, the dipping length, the location and length of the funnel and the flow speed were changed. Tows of diierent size were spun at a spinning speed of 50 m./min.

Denier oi' single filament 1.0 2.0 4.0 7. 0 Dipping length A-D in mm 800 1, 000 1, 400 1, 800 Extrusion spee IIL/min 7. 5 15 30 52 Flow speed oi spinning bath, n n/min. 10 12 16 18 YLocation of funnel d=mm 200 250 300 400 Time to travel A-B in sec. 4 4. 5 5 6 Length of funnel 200 250 300 400 Time to travel B-G in sec 8. 4 4 4.5 5. 5 Time to travel G-D in sec 3. 6 4 5. 5 6. 2 Rate of drawing B-C in percent sec. 88 80 74 68 Rate of drawing near D in ercent sec. 20 20 20 20 Dry tenaci g./d 3.64 3. 55 3.00 2. 63 Dry elongation, percent.. 16. 6 17. 8 19.8 24. 3 Wet/Dry tenacity ratio, percent 86 84 83 80 Wet/Dry elongation ratio, percent 98 96 100 110 vThe results show that with increasing denier theA tenacity vorientated by a slight pulling and the oriented structure retards the progress of coagulation, so that the proportion of the oriented skin layer to the total area of the cross section of the lilament will be smaller for higher denier laments which causes the decrease of tenacity.

The examples show the general inuence of funnel location, ilow speed, and dipping length on the tensile properties of the iilament obtained in the spinning of filaments of different deniers at diierent spinning speeds. By properly adjusting the conditions, polyvinyl alcohol iilaments of very iinedenier (0.5) or very coarse denier (20) having excellent superior properties, can be produced at a high spinning speed.

Additional stretch can be applied by providing one or more stretch rollers behind the Godet roller, whereby the speed diierence between the Godet roller and the stretch rollers determines the rate of drawing. The additional Vstretch (second stretch) may be applied to the filaments too high temperatures, the laments may be softened to such an extent as to be broken by strong stretching. On

the other hand, at high concentrations and low temperatures, the iilaments are di'icult to draw. By strong stretching a stress is induced in the orientated structure which results in crimping when the dried fibers are cut to staples and heated for a short time to temperatures of to 225 C.

Spinning speed of the Godet roller,

ru min Yif lthe filaments have .been .already drawn in the preceding stage, they cannot withstand too strong a drawing or stretching in the second stage, which may destroy their structure. The rate of the second drawing should be limited to less than five times, preferably to less than two times their length. This second drawing may be applied in one or more steps which can be carried on in air and/or in a bath.

The following examples illustrate the influence of the second stretching on the properties of the finished filaments.

Example 8 A 14.0% `aqueous solution of polyvinyl alcohol having a polymerization degree of 1600 was prepared and after filtration and deaeration extruded through a spinneret having 1000 holes of 0.08 mm. diameter into a column of a coagulating bath containing 400 g./l. of sodium sulfate and having a temperature of 45 to 47 C. The dipping length was 1250 mm. and the flow conditions of the coagulating bath were appropriately adjusted in accord- .ance with the above examples. The extruded solution stream traveled upwardly in the bath, passed over guide rods, was taken up by the Godet roller at different spinning speeds `and led over a second stretch roller, the speed of which was 50 m./min. From the speed of the second stretch roller and the speed of the Godet roller, the drawing rate in the second stretching step is calculated.

The filament tow was then dried at a temperature below 160 C. and then heated in air at 220 C. for 3 minutes. During drying and heating, the length of the tow was kept constant. After washing and drying, a finished filament tow of 3000 denier composed of 1000 filaments of 3 denier was produced.

The tensile properties of the filament produced are illustrated in the following table:

. 50 42 33 28 21 Speed of the second stretch roller,

m. mln .50 50 50 50 50 Rate of drawing or stretch, percent... 20 50 80 140 Dry tenacity, g./d 3.05 3. 60 3. 50 3. 20 2.60 Dry elongation, pcrccnt 18. 6 19. 8 18. 2 18. 8 19. 0 Wet/Dry tenacity ratio, percent 86 88 88 86 86 Wet/Dry elongation ratio, percent. 109 106 105 109 112 The results show that a second stretching of between to 50% gives the most desirable effect and that a higher second stretching is less effective.

Example 9 The conditions employed were the same as in Example 8 and the spun tow was stretched to 46% by the `second stretch rollers and then further stretched to different rates by the third stretch roller. Between the second stretch roller and the third stretch roller, the tow passed for a length of 200 mm. through -a bath containing 280 g./l. of sodium sulfate and maintained at a temperature of 90 C. The speed of the third stretch roller was 50 m./min. From the speed of the third roller, the second roller and Godet roller, the drawing rates could be calculated.

The tensile properties of the 3 denier filament obtained are shown as follows:

Spinning speed of the Godet roller,

rn ln Speed ci the second stretch roller, m./

min 42 38 34 28 Speed of the third stretch roller, 1n./

min 50 50 50 50 l Rate of the second drawing, percent... 46 40 46 46 46 Rate of tho third drawing, percent. 0 20 30 45 80 Dry tenacity, g./d 3.56 3.90 4.15 3.82 3.71

Dry elongation, percent 1.0.0 17.0 17.6 1G. 5 16.5

Wet/Dry vtenacity ratio, percent 88 89 89 89 88 A Wet/Dry elongation ratio, percent.. 105 100 98 102 100 In this case, too intensive stretching in the third stretching stage was less effective and 'this stretching should be kept within certain limits. According to this example, the best conditions to achieve highest tensile strength and to maintain still an adequate elongation were to stretch to an extent of 46% by the second stretch roller and then to an extent of 30% by the third stretch roller. The total stretch of the second and third stretching stage was therefore 46-l-30X1.46=89.9%. From these experiments, it is evident that the additional drawing applied to the filament after passing the Godet roller should not be too strong, even though it be applied in several stages, whereas the first drawing applied inthe spinning column .before the take up by the Godet roller should be very extensive, for example, 10 times or 50 times for drawing the slowly floating thread stream at the funnel edge with a speed of about 2 m./min. to the spinning speed of 20 m./min. or 100 m./min. Therefore, it is important to adjust properly lthe stretch in the first drawing range.

Example 10 Under the seine conditions as in Example 9, a lament tow was spun' at a spinning speed of the Godet roller of 30 m./min.; the speed of the second stretch roller was 42 .m./min. and the speed of the third stretch roller 50 m./ min. Between the second stretch roller and the third stretch roller the tow passed through a second bath containing 250 g./l. sodium sulfate and having a temperature of C.

Percent Degree of drawing in the spinning column 510 Degree of drawing between guide rod and Godet roller (14 and E in Fig. 1) 170 Degree of drawing in the 2nd drawing 40 Degree of drawing in the 3rd drawing 19 Total degree of 2nd and 3rd drawing 67 The flowing-up speed of the polyvinyl alcohol stream at the funnel edge 13 was about 1.8 m./min. The spinning speed at the exit of Ithe spinning column D was about 1l m./min. The degree of drawing immediately after leaving the spinning column is determined by the equation (see FIG. 2):

x E25-@doux =173% The tensile properties of the 2 denier filament were as follows:

Dry tenacity, g./d. 4.25

Dry elongation, percent 15.4

Wet/dry tenacity ratio, percent 87 Wet/dry elongation ratio, percent 103 Example 1I An 11.5% aqueous solution of polyvinyl alcohol having a polymerization degree of 1800 was spun as in Example 10, and a tow of V500 denier composed of 1000 filaments of 0.5 `denier was produced. The tensile properties of the filament were as follows:

Dry tenacity, g./d. 4.62 Dry elongation, percent 15.4 Wet/dry .tenacity ratio, percent 88 Wet/ dry elongation ratio, percent 98 skin Vlayer and a core. The skin layer is highly oriented and very dense whereas lthe core is unoriented. The difference between the two parts can'readily Ibe distinguished under a microscope. The ratio of the skin and the core part can be measured with good accuracy. Generally we have found that the bers spun iby our method consist of about toy60% skin part and 75% to 40% bore part. The ratio depends on a number of factors, such as the denier spun, the rate of drawing, spinning speed, the polymerization degree of the polyvinyl alcohol. This characteristic structure is a result of our spinning, process where the orientation of the skin part is achieved slowly and advantage is taken of the specific coagulating characteristics of the polyvinyl alcohol. AS pointed out hereinabove, the polyvinyl alfcohol solution contacting the coagulating bath forms a thin skin of coagulated membrane on the surface of the extruded fiberstream. -This skin is oriented first slowly in the funnel part of the column; in the upper part of the column the size of the skin part is increased and the degree of orientation is also increased.

The gentle and progressively increasing stretching force resulting from the increased speed of flow in the coagulating column orients primarily the surface membrane and cannot orient the liquid or partly coagulated inner core. The stretching Iforce in this stage is produced by the surface friction resulting from the flow differences of the coagulating bath and the travel-ing filament. This can act only on layers in contact with the bath whereby the coagulated and aggregate forming polyvinyl alcohol micelles on the surface `are oriented along the direction of ow. The core can be dehydrated and coagulated in this stage, but cannot be oriented. At the moment when the skin part is strong enough to allow the application of stronger stretching for the filamentby the guide rods, Godet roller and stretch rollers-#both the skin and Score part are further oriented. However, at this point already a substantial .difference exists in the degree of orientation of these two parts. The degree of stretching in the second and third stage of the spinning process must be a limited one. The degree of plastic deformability of the surface skin sets an upper limit to the degree of stretch. If the limit is exceeded it results in injury to the skin layer. The core is, of course, also oriented to a certain degree during the second and third stretching stage but the degree of orientation cann'ot be equal to that of the skin layer. The afterstretch, however, partly destroys the skin layer, inasmuch as the outer layer of the skin is cracked and dow not form a coherent tight skin over the core. This cracking of the skin is of importance as the cracks in the skin allow the penetration o-f dyestuffs, water vapor, and other processing agents, in the interior of the fiber. The degree of orientation of the skin layer can be estimated from the X-ray diagrams of the fiber.

If a polyvinyl alcohol ber is spun by coagulation and afterstretched in one operation after the ber is completely coagulated, such a distinct structure can-not be achieved, and a polyvinyl alcohol fiber spun by a dryspinning method has an entirely different internal structure. It has been known that viscose bers `also exhibit a certain degree of core and skin structure. However, due to the extremely fast coagulation of the viscose in the spinning hath an orientation must be achieved by stretching and the degree of orientation of the very faint skin portion is only very slightly higher than the orientation of the core part. The dierence in the case of viscose can be seen also by the fact that the transition from core to skin is not sharply distinguishable and that special dyestuffs must be used to recognize the two distinct parts in viscose laments.

Not only is the skin and core structure characteristic for our bers but the skin part is largely responsible for the superior physical properties of the fibers. The highly oriented and dense skin imparts the 'high abrasion resistance of the ber and the ratio of skin to core determines to a large degree the high wet and dry tenacity and wet anddry elongation ratio. A ber 'composed only of skin would have a very high strength but low elongation and high brittleness, whereas a ber composed entirely of the core part would have poor strength and excessive elongation particularly in the wet state. The proper ratio of skin can be varied in our process and the bers produced have a wide range of properties suited for a large number of practical applications.

For drying the spun laments special cautions are to be taken. If the filaments are relaxed in an unstretched stage, they tend to shrink and said shrinkage occurs unevenly. Therefore, the drying of the filaments should follow directly the spinning or the additional drawing in the stretched state. Drawing of the filaments during drying is to be avoided because it may cause uneven stretching. If a drawing is applied, the rate of drawing should be limited to less than about 10% Y Higher temperatures may shorten the time of drying but may cause sticking of the filaments. The temperature of drying should be maintained lower than 160 C. Low temperature and long time drying are preferred for obtaining even drying, especially for making ne crimped bers.

The degree of drying is an important factor. If the dried filaments contain much moisture, they tend to shrink in the following heating stage and said shrinkage occurs unevenly and is undesirable, especially for the manufacture of crimped bers. Therefore, the filament should be dried completely or at least to a content of less than 10, preferably less than 4 percent.

The dried filaments as such are not sufficiently waresistant. They swell in water to some extent at ordinary temperature and dissolve in water at higher temperature, for example above 70 C. To impove the Water resistance, the dried filaments are subjected to an aftertreaitment, for instance to a heat treatment in a gaseons medium at a temperature of from 140 C. to 225 C. for a certain period. A suitable heat treatment is disclosed lin the co-pending patent applications, Serial No. 154,873, filed April '8, 19510, by Tsukumo Tomonari and Shigeki Nomura, and Serial No. 154,874, filed April 8, 1950 by Tsukumo Tomonari, now Patent 2,639,970, ssued May 26, 1953.

Example 12 Denier 2.03 Dry tenacity, g./d 3.96 Dry elongation, percent 14.4

Wet/ dry tenacity, percent Wet/ dry elongation, percent 104 Number of crimps per inch 32.0

Example 13 Under the same condition as in Example 8, a lament tow was spun and passed from the Godet roller to a second roller and drawn in air by 67%. After having been dried to a moisture content of 3%, the tow was cut into staple ber and treated as in the above example. The nished ber had ne crimps and the following properties:

Denier 5.06 Dry tenacity, g/d 2.86 Dry elongation, percent 18.5 Wet/dry tenacity, percent 85 Wet/dry elongation, percent 108 Number of crimps per inch 26.4

As shown in the examples the tensile properties are 15 not remarkably injured by heat treatment ,in the relaxed state. While the heat treatment inthe 'stretched state is appliedv for making high tenacity laments, the heattreab ment in the relaxed state is usefulfor making crimped laments.

The laments thus spun, stretched, dried, and heattreated are water resistant and shrink in hot water of a temperature of 80 to 95 C. less than J5%. The water resistance and other properties can be further improved by a chemical treatment with aldehydes, organic acids, and the like.

The term polyvinyl alcohol ber as used in the specification and claims is understood to mean not only a ber Spun from pure polyvinyl alcohol but also bers spun from copolymers of p olyvinvyl alcohol with other polymerizable compounds such as ethylene, maleic anhydride, acrylonitrile, and the like, provided such copolymers contain at least 80 percent of polyvinyl alcohol. Such copolymers are known in the art and have been proposed for the preparation of textile Vbers in the same way as polyvinyl alcohol.

What we claim is:

1. An apparatus for up-spinning polyvinyl alcohol bers or filaments comprising a chamber for a coagulating liquid, feeding means at the bottom of said chamber provided with a plurality of apertures for injecting coagulating liquid upwardly in the form of a spray of ne parallel streams into said chamber, a spinneret arranged to delivery a polyvinyl alcohol solution into said chamber into the center of said-injected coagulating liquid, a slidable cylindrical tube extending upwardly from said chamber and opening into said chamber by a funnel of grad ually increasing diameter, Ymeans to hold said cylindrical tube slidably at a predetermined distance from said spinneret, and a Godet roller above said tube to withdraw the laments formed in said tube.

V2. A textile ber consisting essentially of polyvinyl alcohol and presenting a distinct core and vskin part, vthe core part making up about to 75 percent by weight of the ber and consisting of a substantially unoriented polyvinyl alcohol structure, the skin part making up the remainder of the ber and showing in an X-ray diagram a crystalline structure.

References Cited in the le of this patent UNITED STATES PATENTS 827,434 Friedrich Iuly 31, 1906 838,758 Thiele Dec. 18, '1906 2,169,250 Izard Aug. 315, 1939 2,190,265 Hubert et al. Feb. 13, 1940 2,255,594 Berndt Sept. 9, 1941 2,610,360 Cline et al. Sept. 1,6, V1952 2,642,333 Tomonari June 16, 1953 2,711,559 Lynch et al. 'June 28, l1955 UNITED STATES EETENT eEEICE CERTIFICATE Patent Neo 2,988,802 June 20, l96l Tsukumo Tomonari vet el*a It is hereby certified that error appears the above numbered patent requiring correction and that the said Letters Patent. should read as "corrected below.

Column l, line l32, for "celluose" read cellulose column 3, line 52, for "'spiningn read spinning column 4, line 29, for ,'spung" read spun line 4l, for "30o/mine vreed 30 rar/min., column 6, line 36, for contined read continued column 7, line lO, for "at" read as n-; column 9, irst table, column 5, line 2 thereof,7 for "2.65" read 2.64 column 9, line 30, for "lOOn read lOOO column ll, line 29, for "160 C read l6O6 C., column 16, line l, for "delivery" read deliver Signed and sealed this 14th day of November 1961.

(SEAL)v Attest:

ERNEST W. 'SWIDER Attesting Officer DAVID L. LADD Commissioner ofl Patents USC0MMD C

Claims

1. AN APPARATUS FOR UP-SPINNING POLYVINYL ALCOHOL FIBERS OF FILAMENTS COMPRISING A CHAMBER FOR A COAGULATING LIQUID, FEEDING MEANS AT THE BOTTOM OF SAID CHAMBER PROVIDED WITH A PLURALITY OF APERTURES FOR INJECTING COAGULATING LIQUID UPWARDLY IN THE FORM OF A SPRAY OF FINE PARALLEL STREAMS INTO SAID CHAMBER, A SPINNERET ARRANGED TO DELIVERY A POLYVINYL ALCOHOL SOLUTION INTO SAID CHAMBER INTO THE CENTER OF SAID INJECTED COAGULATING LIQUID, A SLIDABLE CYLINDRICAL TUBE EXTENDING UPWARDLY FROM SAID CHAMBER AND OPENING INTO SAID CHAMBER BY A FUNNEL OF GRADUALLY INCREASING DIAMETER, MEANS TO HOLD SAID CYLINDRICAL TUBE SLIDABLY AT A PREDETERMINED DISTANCE FROM SAID SPINNERET, AND A GODET ROLLER ABOVE SAID TUBE TO WITHDRAW THE FILAMENTS FORMED IN SAID TUBE.

2. A TEXTILE FIBER CONSISTING ESSENTIALLY OF POLYVINYL ALCOHOL AND PRESENTING A DISTINCT CORE AND SKIN PART, THE CORE PART MAKING UP ABOUT 40 TO 75 PERCENT BY WEIGHT OF THE FIBER AND CONSISTING OF A SUBSTANTIALLY UNORIENTED POLYVINYL ALCOHOL STRUCTURE, THE SKIN PART MAKING UP THE REMAINDER OF THE FIBER AND SHOWING IN AN X-RAY DIAGRAM A CRYSTALLINE STRUCTURE.