Jan. 1964 BLACKBIIXN AND WARD- DYEING MAN-MADE-FIBRE TOWS 9

Proceedings of the Society Dyeing and Wet Processing of Man-rnade-fibre Tows

I). BLACKBURN and J. S. WARD

Meeting of the Bradford Junior Branch, held at the Institute of Technology, Bradford, on 12th December 1962, Mr . C . T . Hardisty in the chair

A brief review is made of the uses of man-made-fibre tows. The development of batchwim dyeing methods for such tows is described and an account is given of current commercial procedures, with particular reference to the handling tcchniques needed to preserve the physical form of tho tow. Possible methods for the continuous dyeing of tow are discussed, including the use of continuous high-pressurc steaming. Experimental results are given for various dye-fibre systems.

Introduction Tow can be defined as an assembly of parallel

untwisted filaments, arranged in either rope-like or ribbon-like form. It is a primary product of the man-made-fibre industry and, as such, has been made in this country since the early 1920s, when Courtaulds Ltd first started to produce Fibro (Courtaulds) viscose rayon staple. In those days, however, it existed only within the production factory as the form in which the filaments were convoyed from the spinnerets to the cutting machine, and it was not until the late 1930s that tow became an article of commerce.

TOW-TO-SLIVER CONVERSION

It was at this time that the Greenfield top was developed by Courtaulds’ technologists and intro- duced to the worsted trade. This was a viscose rayon top produced, not by carding and combing staple fibre, but by cutting the tow on a Greenfield converter and redistributing the fibre ends, whilst maintaining parallelism, in a gill-box. This product gained widespread acceptance in the worsted industry and the tow-to-sliver principle has subsequently been adopted for all the man- made fibres, t,o such an extent that there exist today top-making firms who do not use carding engines a t all. Many types of tow-to-slivcr converter are now available and their principles and uses have been fully described in the literaturez~a. For the present purpose, it is convenient to distinguish between two types of tow-to-sliver converter.

The first of these prodnccs a sliver by cutting the tow and then redistributing the fibre ends. This type of machine is exemplified by the Greenfield and Pacific Converters, in each of which tow is fed between two rollers, the upper one carrying a helical blade. This cuts the tow at a very shallow angle to a relatively constant staple length.

The machines differ in the method of re- distributing the fibre ends. In the Greenfield Converter redistribution is achieved by carrying the cut tow on a belt into an intersecting gill-box, whereas the Pacific Converter incorporates a “shuffling section” in which fibres on top of the cut tow are made to move faster than fibres on the bottom. Both machines are intended to process tows of total denier about 2 million and are generally used in the production of normal

worsted-type yarns, though heat-stretching facilities are available on the Pacific Converter. Other machines which use the cutting method have been introduced into this country more recently; examples are the Rieter D.6/2 and the Roberts- Tematex.

The second type of machine employs stretch breaking rather than cutting as the means of conversion, and is exemplified by the HallB-Seydell and Turbo-Stapler machines. The former is often used in the production of so-called Schappe-spun yarns4, but does not appear to have been widely used for processing dyed tow. The Turbo-Stapler is designed to produce high-bulk yarns on the worsted system, and its use is mainly confined to acrylic tows. This machine consists of a heat- stretching zone, in which the tow is stretched by 40-80% whilst passing between hot plates a t a temperature of 240-34OoF, followed by a stretch- breaking zone, in which i t is converted into sliver. A proportion (usually about 60%) of the sliver so produced is relaxed in steam, and is then blended a t the gill-box with the remaining unrelaxed sliver to give a Turbo top. When yarn spun from this top is subsequently steamed, the unrelaxed fibres shrink and cause the yarn to bulk. It is fundamental to the type of yarns produced via the Turbo-Stapler that the stretch-breaking gives a spectrum of staple lengths, since the short fibres contribute to the apparent bulk of the yarn.

It is of interest to note that the forerunner of the Turbo-Stapler, the Perlock machine, which was in operation in the U.S.A. in the early 1930s, was to some extent rejected because of the inherent yarn shrinkage introduced by stretch-breaking 5 .

However, i t was redesigned to take advantage of the stretch potential of acrylic tows, and it is largely because the capacity of this machine is 400,000-500,000 den that acrylic tows are produced a t this size.

The operation of these machines imposes considerable demands on the physical condition of tows. Ideally they should be twistless, knotless, free from broken ends, crossed filaments, entangle- ments, folded edges and fused filaments, and uniform in width, thickness, crimp, and finish. It is a tribute to the manufacturers of tows that, despite such exacting requirements, many firms in the worsted industry have found i t worth while to install converters of one form or another.

-4 3

OTHER APPLICATIONY

Practically all the man-made fibres are now available in tow form in a range of filament deniers. The majority of these tows have a total denier between 100,000 and 500,000 and are supplied in package weights of 75-250 lb, usually giving 1500-3000m of knotless tow. Their use is no longer confined to the worsted industry, other applications being-

(a) Processing on the flax system. The uncrimped tow is cut and fed direct,ly on to the flax card, thus avoiding entanglement of the long staples used. Additional impetus has recently been given to the use of tows for flax spinning with the introduction of the A - t o 3 processR, which is a technique for imparting bulk to flax- spun yarns through the use of heat-stretched tows.

( b ) Processing on the cotton system. Staple cut from dyed tow is usually easier to process than stock-dyed material, particularly in the case of thermoplastic fibres of fine denier.

(c) Conversion into flock. Tow is cut into 4-1 mm lengths for flock coating, printing, and similar techniques involving electrostatic deposition.

(d ) Production of dolls’ hair and wigs, etc.

Batchwise Dyeing VISCOSE RAYON TOW

Although the use of viscose rayon tow for dolls’ hair and flock cutting developed later than its use for worsted conversion, i t was for these two outlets that tow was first dyed as such in our dyeliouse a t Droylsden in the immediate post-war years. By means of the procedure then in use for Fibro warps, the tow was dyed in the cage of an Obermaier or similar type of dyeing machine. These cages hold thc material to be dyed in an annular compartment (race) whose width varies from 6 in. to 16 in. and the overall diameter of the cage varies from 24 in. to 60 in. The viscose rayon tow was fed into t h e cage by hand through an eye mounted above the stationary cage. As the operative pulled the tow through tile eye he guided i t circumferentially round the annulus and allowed it to fall loosely into the cage (see Fig. 1). When the tow was subsequently withdrawn from the cage after dyeing, there was, therefore, no overall insertion of twist into the tow, Hand loading has now been ’ replaced by mechanical methods, to be described later.

In this manner, viscose rayon tow can be packed to densities of 15-20 lb/ft3, according to denier. An Obermaier cage of overall diameter 60 in. wi th a 16 in. race will thus hold about 700 lb of tow and this can be dyed by the usual techniques to give level and well-penetrated dyeings. Although somc tinlevelness is tolerable, the standard required is far above that in loose-wool dyeing, and with the increasing tendency towards shortened processing, and hence fewer doublings, the levelness require- ments may be raised even higher. For normal uses, direct dyes generally give adequate fastness, though czreful selection is needed to achieve the required light fastness for the worsted trade. It

has also been demonstrated 7 that R satisfactory level of fastness to milling can often he obtained by using aftertreated direct dyes or copper-complcx dyes. When a higher standard of wet fastness is required, e.g. fastness to cross dyeing, vat dyes must sometimes be used, despite thcir relatively high cost. IH this case, satisfactory results can often be obtained by the usual leuco-dyeing procedures, but with somc dyes on fine-denier filaments i t may be necessary to use pigmentation- reduction methods. More recently, reactive dyes, of both hot- and cold-dyeing types, have also been successfully applied by standard techniques to viscose rayon tow in Obermaicr-type cages.

After dyeing, i t is uxually necessary to apply finish to the tow and this varics according to the proposed use. Tow for flock cutting requires a very soft finish, very evenly applied, otherwise “balling” of thc flock (i.e., acciimulation into small aggregates) may occur, and tow for flax processing requires a finish giving low cohesion. For worsted spinning, a certain amount of static friction is desirable, in order to obtain adequate sliver cohesion; soap has heen widely used as a finish in this case. .It is usual to apply the finish by circulating a solution of siiit.able concentration through the dyed tow in the dyeing machine.

The proposed use also affects the drying method used for the tow. Where a smooth, polishcd fibrc is required, drying is carried out under slight tension on steam-heated cylinders (Fig. 2). This type of drying, however, remows even t.he small amount of crimp present' in viscose rayon tow and t.hus introduces difficulties into thc proccssing on flax or worsted equipment. Ifor thcse latter purposes i t is preferable to dry the tow by plaiting it across a bratticc or across a Flc After being dried, viscose rayon tow is usually packed into litied sacks for transportation, although cross-wound packages itre s0mtbt.i iiies preferred.

COLJRTELLE TOW When Courtelk (Courtaulds) acrylic fibre was

first marketed some six years ago, onc of its main outlets WRS the worsted tradc, and a large proportion of the production cont.iiiues to be consumed in this \vay. Tow is processed on the Turbo-Stapler to give high-bulk yarns or on Greenfield or Pacific converters to give regular yarns. In the latter case, dyeing can be carried out at the slubbing stage, but this is not possible for Turbo tops, since the potential shrinkage would be loat in dyeing. At the time of its int.roduction? therefore, Courtelle for high-bulk yarns had to bo dyed either as yarn or in garment form. I t there- fore seemed appropriate to investigate the possi- bility of dyeing Court,elle tow, RS :tn alternative method of providing colouretl yarn in bot ti high-bulk and regular form, and as it means of obtaining mixture effwts in high-biillc yarns.

Since Courtelle was at first protluccd i n ;t tow-denier of 30,000 or 60,000, one of our first approaches to d,yeing the materia,l was by winding the tow into a pseudo-ball-top. This was achieved by using the balling head on the back of an ordinary gill-box, a “top” of diamcter 14 in, arid

PIG. 1- Feeding viscose rayon tow into csgc of dyeing iiischino

FIG. 2- Drying tow on stestu-hcatod cyliudcrs

J.G.D.C. 80 (Jan 1964) Facing p . 10

Ym. 3- hfcctiaiiical loading of tow into cage of dyeing iiiaaliine

VIG. 4- Kollrad Peter padding iiiangle

Jan,. 1964 BLACKBL~~N AND WARD- DYEING MAN-MADE-FIBRE TOWS 11

height 8 in., with a weight of 14 lb, being produced (1900 m of 30,000-den tow). This could be dyed on a spindle in a manner analagous to top dyeing, where good results are obtained with disperse, basic, and 1 :2 metal-complex acid dyes. For processing on the Turbo-Stapler, an appropriate number of these small tows were assembled in a creel, wound off, and brought together to give a composite tow. Processing reports were encourag- ing, but this method was discarded when the total denier of the undyed tow was increased to 480,000 at the production factories.

At the suggestion of various manufacturers of dyeing machinery, we also considered the possibility of dyeing Courtelle tow wound on beams. Two winding methods were advocated. In the first, the 480,000-den tow was split into several component tows of denier 50,000-60,000, and these were then section-wound on the beam a t a low traverse angle. Alternatively, the whole tow was parallel-wound (i.e., minimum traverse angle) across the full width of the beam. In either case winding was carried out with the tow under considerable tension and in a plastic condition (hot and wet). There was a tendency for the beams so produced to be either so tightly wound that rupture occurred on dyeing or to be unstable when the winding tension was reduced and to sag during dyeing. Channelling occurred in both methods, producing unlevel dyeings. When a relatively stable beam was obtained, there was considerable difficulty in avoiding inside-to-outside unlevelness, even with disperse dyes, and this was presumably due to the high resistance to liquor flow. In addition, the dyed tow was entirely devoid of crimp and was difficult to handle and pack.

From our experience, therefore, we have concluded that Courtelle can best be dyed in Obermaier or similar types of cages. The method used is basically the same as that described for viscose rayon tow, but numerous refinements have been introduced, including completely mechanical loading (Fig. 3). The tow is withdrawn from its carton at full width and fed, via a plaiting mechanism, into the cage, which is mounted on a slowly rotating turntable. The traverse of the plaiting arm is adjusted to suit the width of the annulus and the tow falls loosely, thus retaining its crimp. As the cage slowly rotates, the loosely packed tow passes under a spray of hot water and then under a mechanically operated tamping device. This brings about the consolidation of the pack necessary for the successful dyeing of Courtelle, and package densities of about 30 lb/ft3 are obtained. An Obermaier cage with a 16in. race thus accommodates about 1200 Ib of tow. Despite this high package density, i t has been found possible to obtain high standards of levelness in dyeing Courtelle tow.

Disperse dyes, with their reasonably good level- dyeing properties, present few difficulties, so long as adequate temperature control is maintained. Since disperse dyes are seldom used on Courtelle tow except in pale depths, filtration problems are not usually encountered, although it is advisable to use brands of good dispersibility. When basic

dyes are being used, pH control, as well as temperature control, is essential. It is usual to set the bath with acetic acid, to raise the tem- perature gradually to the boil, and to add sodium acetate only when it bccomes clear that this is necessary to obtain the required exhaustion. Dyeing is carried out for a t least two hours a t the boil in order to obtain full penetration of the filaments, after which the material is cooled and rinsed.

A substantive cationic softening agent is then applied in order to obtain the required frictional characteristics. Alcamine (Allied Colloids) has proved particularly suitable for this purpose and, because of its large molecular weight, it can be incorporated in the dyebath without affecting dye uptake when dyeing with basic dyes. This is not possible with disperse dyes because of inter- action between Alcamine and the anionic dispersing agent. Occasionally spinners desire a rather more cohesive finish and this can usually be obtained by adding an appropriate amount of polyoxy- ethylene condensation product, e.g. Dispersol VLX (ICI), to the finishing bath.

After hydroextraction in the dyeing cage, Courtelle tow contains approximately 20% moisture, and i t is therefore possible to dry it a t temperatures of 80°C or lower, in relatively short times, the actual drying times depending on the t,ype of dryer used. In any case, it is desirable that the tow be dried straight from the dyeing cage without intermediate handling. To achieve this the cage is mounted on a turntable immediately in front of the dryer and the turntable is rotated, in the opposite direction to that used in dressing the tow, a t such a speed that the tow is always withdrawn from the cage a t a point directly underneath fixed guide bars. These guide bars are mounted as high above the turntable as headroom permits in order to allow any loose folds or false twist to fall out. By this technique it is possible to present the tow to the dryer in an untwisted, well-spread, parallel condition.

The method of drying has a great bearing on the physical quality of the dyed tow, and several methods have been examined. When drying is carried out on steam-heated cylinders, the tow is kept straight and parallel and generally free from false twist. Because of the unavoidable tensions, however, much of the crimp is removed from the fibre and this can give rise to low cohesion in subsequent processing or, in the extreme, to great difficulties in packaging. Another drawback to cylinder drying is its low productivity and poor thermal efficiency.

A much more efficient and productive method of drying is to plait the tow across a brattice or Fleissner-type drum dryer, drying being effected by drawing warm air through the bed of tow. This also serves to hold the fibre to the brattice or drum. One disadvantage of this type of drying is that, in plaiting the tow on the dryer, and more particularly in lifting up the plaits after drying, folds ant1 half twists (false twists) tend to be formed. However, by appropriate use of spreading and

12 BLACKBURN AND WARD- DYEING MAN-MADE-FIBRE TOWS J.S.D.C. 80

tension bars these defects can be largely eliminated to give a tow in satisfactory physical condition.

Probably the best method of drying Courtelle tow is to feed the well-spread tow onto the drum of a Fleissner-type dryer in a similar manner to that used for drying wool dubbing after back- washing. This has the advantage of avoiding any folds or false twists that arise from plaiting and, provided that a certain amount of overfeed is used, no tension is applied in drying and the crimp is thus retained. The principal disadvantage is that, to achieve an economic loading, i t is necessary to feed several ends of tow simul- taneously. This clearly involves the use of a multiplicity of turntables, creels, and packaging equipment.

After drying it is usual to pass the tow through a spray box where an antistatic agent is applied, and then to the packaging equipment. This consists of a plaiting mechanism which lays the tow a t a width of about 6in. into a polythene-lined carton. The movement of the plaiter is such that the tow is evenly distributed within the box in uniform layers, so that i t can later be withdrawn without one layer snagging on the next.

These dyeing and handling methods were developed largely with the worsted trade in mind, but dyed Courtelle tow has also been used in other fields. One of these is coloured cotton spinning. When fine-denier staple (3 den or less) is dyed as loose stock in cage-type dyeing machines, the consolidation which occurs on loading and dyeing necessitates a rather severe opening treatment to the dyed fibre before it can be spun on the cotton system. If filament of this denier is dyed as tow, however, and subsequently cut to staple, a well- opened product is obtained which gives improved processing with reduced fibre breakage and wastage.

TRICEL TOW

Tricel (British Celanese) triacetate-fibre tow can be successfully dyed in Obermaier-type dyeing machines in a manner essentially similar to that used for Courtelle tow. As the second-order transition temperature of Tricel is considerably higher than that of Courtelle, i t does not exhibit the samc plasticity under hot, wet conditions. In consequence it packs less tightly than Courtelle, and package densities around 20 lb/ft3 are usual, giving a 700-lb load in a 16-in. race.

By using selected disperse dyes it is possible to dye Tricel to a wide range of hues with reasonably good light fastness and adequate wet fastness. Provided that the temperature is controlled, level and well- penetrated dyeings are obtained. Difficulties are occasionally experienced when dyeing very full depths because of the filtering out of the concen- trated dye dispersions. When this occurs, the loose dye can usually be removed by scouring with a suitable dispersing agent, e.g. Dyapol PT (YDC) or Lissapol D (ICI), but sometimes i t is necessary to use a reduction clear u.

After dyeing and, where necessary, clearing, a suitable finish is applied in the dyeing machine. Cationic agents, q.g. Arquad 2HT (Associated Chemical Companies), appear to be preferable

for worsted and flax spinning, but they give insufficient cohesion for cotton spinning. The frictional requirements for successful spinning of Tricel on the cotton system would seem to be low dynamic friction, to give low drafting forces, combined with relatively high static friction, to give good cohesion to the fibre web in carding. This combination is usually associated M ith a “scroopy” handle 9, lo. In addition, full antistatic protection is essential. We have not found any one agent which combines all these properties, but satisfactory frictional propcrtics can be imparted by poly- ethylene glycol csters, e.g. Noncx 29 (Union Carbide) and Etliylan S4 (Lankro). Antistatic protection is obtained by spraying the dried tow with an antistatic agent chosen to give minimum interference with the frictional properties.

Where it is necessary to preserve the crimp, drying is carried out under relaxed conditions, i.e. on ti brattice or Fleissner-tyIw dryer. For flax processing, however, there appear to be advantages in drying under some tension on steam-heated cylinders, in order to remove the crimp partially. One of the main outlets for tow-dyed Tricel has been coloured cotton spinning, i n which staple cut from dyed tow processes much better than does stock-dyed fibre. This is due, a t least in part, to the fact that Tricel has a rclativcly low tenacity, and extensive fibre breakage can occur if severe opening treatments have to be applied. The staple produced by tow-dyeing and cutting has been used to produce blended mixture yarns for pleatable skirts and suitings, and also for candlewick yarns. For the latter i t is advantageous to dye undcr pressure (120-130°C) to produce a heat-sot staple, which gives a better burst of the pile yarns in the candle wick fabrics.

Continuous Dyeing Since tow is itself a continuous material, it is

natural to consider dyeing it, by continuous methods. The most obvious rnctliod is the pacl- steam onc bccausc it is applicable to many dye-fibre systems, but other methods have also bcen examined.

PADDING

In most of thcsc methods a patltling operation is necessary. Uniform imprrgnat ion by padding is more difficult to achievr on tow than on most fabrics, although this is largcly compensated by the less stringent levelness requirements. Ikspitc the fact that acrylic, triacctate, arid polyester tows are supplied in ribbon-like form, it is not easy to introduce a completely even sheet of filaments to the. nip of the mangle. It is thus desirable to use soft bowls which can deal with the irregularities of presentation. In our work we have used thc Konrad Peter mangle, which has two pneumatically loaded. horizontally opposed bowls of about 60-70” Shore hardncAsn. This machine (Fig. 4), coupled with adequate creeling arrangements, has given paddings of satisfactory levelnesx on acrylic tows ~ i t h expressions ranging from 7 0 to 100yo a t padding speeds of 5-20 m/min.

Viscose rayon tows are usually supplied in a rather more rope-like form than other types and

.Inn. ID61 Br,AcKnrn<N hNn WAw- 1)YElNC MAN-MADE-FIRRE TOWS 13

because of this i t is not always possible to avoid thin edges to the fibre sheet. These show u p after padding as dark edges because they are more lightly squeezed than the main body of the tow'. To avoid such faults we have found it advantageous to use a flanged pad-mangle". In one form i t consists of two nips in series, each of which comprises a flanged metal bottom roller and a rubber-covered upper roller fitting closely inside the flanges. Thus the tow is compressed a t the first nip so that i t has a rectangular cross-section, about 1 in. x 4 in. for a 400,000-den viscose rayon tow. The second nip has its flanges spaced closer together than those of the first, nip, so that the tow undergoes a further lateral constriction in passing from the first pair of rollers to the second. The purpose of this is to prclvent the squeezed tow from wiping off expressed liquor from the flanges of the first roller and thus exhibiting dark edges. To avoid the possibility of this happening a t the second nip, the pressures on the top rollers are adjusted so that all the expression of liquor occurs at the first nip and the second nip serves merely as a traction unit, and constricting device. We have used this mangle to apply both dyes and non- substantive finishing agents to viscose rayon tows, and it has proved very reliable over long runs.

STEAMING

Employing the padding techniques described above, we have investigated the possibility of using steam as a fixation medium for various dye-fibre systems and in this work we have used thrce types of steamer. The first is a small laboratory-scale steamer in which short lengths (< l2 in.) of padded tow are steamed batchwise. It can be operated a t or above atmospheric pressure and was used for preliminary invcstigations, assessing optimum fixation conditions, and the like. Secondly, we have used a festoon steamer which is wide enough to take one acrylic-fibre tow or two viscose rayon tows. This machine holds a maximum of 50 m of tow and the speed is variable over the range 5-25 m/min, giving steaming times varying from 1 to 10min a t a temperature of 103°C (dry bulb), 100°C (wet bulb). Thirdly, we have had access, to carry out trials, to two types of con- tinuous pressure steamers, the Konrad Peter l2 and the Ilma13 machines, which are worthy of further description.

In a continuous pressure steamer, the vital parts are the pressure seals a t the exit and entry points of the machine. In both the Konrad Peter and the Ilma model, the seals are formed by the nip of a pair of rubber rollers and by sealing strips pressing against these rollers. The difficulties to be over- come in perfecting such a seal appear to be associated with obtaining rubber-like materials with the required physical and chemical resistance a t the working temperature, and with the mechanical arrangement of the sealing strips. The main body of the steamer is simply an autoclave with some mechanism for conveying the tow from the entry rollers to the exit rollers. In the Konrad Peter machine, the autoclave is rectangular and thc tow is carried through the machine by mcans of

rollers, the upper ones being driven and the lower ones idling. The capacity of the autoclave is approximately 20m of tow and the speed is variable over the range 1040 m/min, giving steaming times from 2 min to 30 s. Temperatures of up to 120°C can be attained. The Ilma machine, on the other hand, has a cylindrical autoclave and the tow falls from the entry rollers on to a moving belt. This carries i t to a position directly under the exit rollers, which then lift i t up and out. The tow capacity of the machine is thus variable, but a typical figure, for the smaller of the two models available, is 32 m, corresponding to 4 min steaming a t 8 m/min linear tow speed. A maximum temperature of 125°C is claimed for the machine.

COURTELLE TOW

The application of both disperse and basic dyes has been investigated.

Disperse Dyes With disperse dyes the rate of fixation in steam

a t atmospheric pressure was found to vary con- siderably from dye to dye and with depth of colour. For example, Serisol Fast Yellow GGL (C.I. Disperse Yellow 33) padded a t a concentration of 3 g/l. gave a fixation of 85% after 5 min steaming, but when the concentration was increased to 10 g/l. only 32% of the dye was fixed. Extending the steaming time to 20 min increased this to 87% (see Pig. 5 ) . With Artisil Scarlet GFL ((3.1. Disperse Red 63), however, 5 min steaming gave fixations of only 31% and 20%, respectively, for pad-bath concentrations of 3 g/l. and 10 g/l. By steaming for 20 min the amounts of dye fixed were increased to 61% and 44%, respectively (Fig. 6).

When the temperature was increased to 120°C by the use of a pressure steamer, it was found that a reasonably high extent of fixation (ca. 80%) could be obtained in as little as 2 min steaming

FIQ.

0 5 10 15 20 T i m e of steaming, rnin

Dye concn. a 3 g/l. b lOg/l.

5-Rate of RxIttion in Hteani ot' Serisol 4b-drn Conrtelle tow

l'ast. Yellow OGT, on

14 BLACKBURN ANI) WARD- DYE] [NG MAN-MADE-FIBRE TOWS J.K.D.C. 80

loo 1 90

70 aQ d $ 60 - I=

I

0 5 10 15 20 Time of steaming, min

Dye concn. a 3 g/l. b 10 g/l.

FIG. 6- Rate of Rxation of Artisii Scarlet GFI, 011 4i.den Courtclle tow

when pale depths were being dyed. Fixation again fell off, however, with increasing depth of colour.

In all cases the unfixed dye was easily removed from the fibre by a mild washing treatment and the dyeings then exhibited fastness properties similar to those obtained when the same dyes were applied conventionally.

One of the principal reasons for using disperse dyes to produce pale depths on acrylic fibrcs by conventional methods is their good levelling power as compared with basic dyes. In a pad-steam operation, however, this factor is of negligible importance and, coupled with the fact that most disperse dyes inevitably give fixations considerably

0 I 2 3 4 5

Time of steaming, min

Dye concn. a 5 g I L b 20gjl.

FIG. 7- Rate of Axatlon in steam of Mhxilon Red BL on 1 I-den Courtelle tow

below lOOyo in full depths, i t would appear that these dyes will be of minor interest for the process.

Basic Dyes Because of the high affinity of basic dyes for

Courtelle, it might be expected that rrasoriably efficient fixation could be obtained, cvcn in full dcpths, and this has proved to be generally true. For instance, when Maxilon Red BL (C.I. Basic Red 22) was applied at a pad-bath concentration of 20 gfl., which is a heavy depth for this dye, a fixation of approximately 90% was obtained after 8 min steaming at atmospheric pressure. As with disperse dycs, paler depths were more rapidly fixed, and at 5g/l. Maxilon Red BL gave a fixation of about 76% after only 2 min steaming (Fig. 7) .

loo I 80 90 t

d a 60 c- 0

,” 50 r

40

4 30 E

20

10

0 I 2 3 4 5

Time of steaming, min

a 5 g/l. acetic acid b 2g/l sodium acetate

BIa. 8- Effct t of 1iH on rata of Hutlon of AYtrnzone IHue FGL on 41-dm Courtcllc tow

Reference has bcen made to the use of pH control when dyeing Courtelle with basic dyes by conven- tional means, and pH also has its effect in pad- steam application. This is illustrated (Fig. 8) by studying the fixation of Astrazone Blue FGL (C.I. Basic Blue 44), padded at a concentration of 30 g/l. with the addition of

( a ) 5 gfl. acetic acid pH 3.5 ( I r ) 2 g/l. sodium acetate pH 6.3

It can be scen that considerably higher fixation (64% after 5 min, compared with 43%) was obtained a t the higher pH.

Thomas has described a process14,15 for the continuous dyeing of Orlon tow in which ethylene carbonate is used as a swelling agent 16, This is incorporated in the dyebath at il concentration of 50 g/l. (100 g/l. for certain dyes) and steaming is carried out for 5 rnin at atmospheric pressure. The effect of this agent on the application of Astrazone Blue FGI, (30 gil.) to Courtclle was examined and i t was indeed found to increase the fixation (Fig. 9). Similar increases in fixation were obtained with 20 g/l. Astrazone Red GTL (FBy)

Jan. 1964 BI,AC+KBIJRN ANn WARD- DYEING MAN-MADE-FIBRE TOWS 15

and 40g/l. Astrazone Blue 5GL ((2.1. Basic Blue 45).

From the point of view of fixation efficiency, i t would therefore appear that a wide range of depths could be obtained by stearning for 5-10 min at atmospheric pressure, particularly if ethylene carbonate wcre used in the pad-bath. However, microscopic examination of cross-sections of the dged Courtelle rrvealed that penetration of the dye was nogligible in the absence of ethylene carbonate, and incomplete even in its presence.

Experience with conventionally dyed Courtellc has indicated that incomplete penetration of basic dyes into the fibre can result in reduced fastness properties, particularly fastness to heat-finishing treatments, e.g. pleating and decntising. In order

I00

90

80

70 aQ i 60

50

X b=

- 40

a E 4 30

20

10

0

/ I I I I 1 I 2 3 4 5

Steaming time, rnin

o 2 g/l. sodium acetate, I 5 Ib/ins steam 2 g/l. sodium acetate

2gJl. sodium acetate SOg/I. ethylene carbonate

FIU. !+-MFect of ethglcne mirl,onate and of steaming at above atmospheric presslire 011 rate of Rsation of Astraxone Hlue BOI, on

.i+-den Courtelle tow

to avoid such faults and yet keep steaming times short, i t has been found neccssary to use temperatures higher than 100°C. For example, a cross-section of Courtelle tow padded with 30 g/l. Astrazone Blue FGL and steamed for 2 min at 120°C (15 lb/iii2) showed that penetration was complete. Comparable results were obtained with Astrazone Blue 5GL and Maxilon Red BL.

The grcatly increased rate of diffusion of basic dyes at steam pressures greater than atmospheric is also illustrated by the following results (Fig. 9). Astrazone Blue FGL a t a concentration of 30 g/l. gave about 64% fixation after 5 min in stearn at 100°C, increased to 97% by the addition of 50 g/l. etliylcnc carbonate; raising the temperature to 120°C and omitting thc cthylenc carbonate gave a fixation of 97% in 2 min. A similar increase in rate of fixation occurred when applying 20 g/l. Maxilon Red BL.

The optimum procedure for applying basic dyes to Courtelle tow by a paci-steam technique

therefore appears to consist in padding the tow through a bath adjusted to pH 5-6 and steaming the tow for 1-2 min a t 120°C. High fixations are obtained and washing off is therefore relatively simple. Reproducibility is good and an output of about lOOlb/h can be obtained when dyeing a single tow. Because of the slight tension applied to the tow in the roller steamer, the dyed tow is largely devoid of crimp. I n a vertical concern, where dyeing and processing can take place within the same factory, this loss of crimp is not important. but for the commission dyer i t would give rise to considerable dificulties in packaging. In order to overcome this defect i t would be desirable to be able to steam the tow in a relaxed condition, and the Ilma machine would, in principle, appear to be capable of achieving this.

VISCOSE RAYON TOW

Direct Dyes The application of direct dyes to cotton or

viscose rayon fabrics by pad-steam techniques has received some attention in recent years. The general conclusions seem to be that, as the steaming time is reduced, the number of dyes capable of being adequately fixed decreases, and for a steaming time of 5 min the choice of dyes is rather limited.

We have not, therefore, done much experimental work in this field except to demonstrate that, by using temperatures above lOO"C, i t is possible to obtain a high fixation on viscose rayon tow with a much wider range of dyes. Trials have been carried out in which slowly diffusing direct dyes have becri satisfactorily applied in full depths to viscose rayon tow in 2 min steaming a t 120°C in the Konrad Pcter machine. Similar results have been reported by Kern17, who showed that improved penetration is obtained a t 120°C and also established which direct dyes are best suited to this process.

Vut Dyes The pad-steam application of vat dyes to

cellulosic fabrics is another subject that has been well explored. Various methods are used or have been advocated, but all have their drawbacks when considered from the point of view of application to viscose rayon tow. The most generally successfiil method is the pigment-pad-dry-chemical-pad- steam sequence, but intermediate drying is considered inappropriate and rather uneconomic in tow dyeing. Two methods that have been suggested to avoid this intermediate drying are wet-on-wet padding and leuco padding. In the former the material is pigment-padded a t minimum liquor pick-up and then chemical-padded at a higher pick-up. In the latter, only a single padding stagc is used, with the dye in its alkaline leuco (substantive) state. Both these schemes appear to be subject to difficulties in respect of maintenance of hue.

Van Lamoen and Borsten, however, have claimed lX that it is possible to use an "all-in'' pad-bath (i.e. one containing dye, reducing agent, and alkali) and yet retain the non-substantive

unreduced pigment form of the dye. This is achieved by using a reducing agent which is effective only a t high temperature. Sodium formaldehyde sulphoxylate [Formosul (Associated Chemical Companies), Rongalite C (BASF)] is stated to meet this requirement to a certain extent, but it is claimed that, by adding more formaldehyde, the reduction potential a t room temperature can be made considerably less negative without sub- stantially affecting fixation during steaming.

Although we have been able to dcmonstrate that excess of formaldehyde does tend to have this effect, we have not been able to establish any one dyebath composition or reducing agent which meets the requirements-

(a ) no reduction of dye in the pad-bath at room temperature and

(a) good fixation in steaming times of 2-3 min a t 100°C for a wide range of vat dyes a t various concentrations. This is probably because the leuco potentials of individual vat dyes vary with dye concentration and temperature. For a given concentration of a suitably chosen vat dye, however, it is often possible to choose a dyebath composition which does meet the above stipulations. For example, a bath containing

SQ Caledon Gold Orange 3G 35 g/l.

Formosul 100 g/l. Sodium hydroxido (100"Tw) 65 ml/1.

showed negligible reduction a t 25"C, and when a viscose rayon tow was padded through i t and steamed for 2+min a t 100°C good fixation was obtained. It is relevant to point out that the requirements for the reducing agent can be made rather less stringent by lowering the pad-bath temperature to (say) 5°C.

The problem of continuously aftertreating dyed tow will be discussed later, but tow dyed under the conditions described was successfully oxidised, soaped, and rinsed continuously. After finishing and drying i t was processed on a Greenfield converter without difficulty.

Reactive Dyes Because of their rapid rate of fixation, reactive

dyes are particularly suitable for continuous dyeing techniques, and pad-steam methods have been suggested for each of the various types of reactive dye. Many of these, however, require a two-stage padding with intermediate drying. We were more interested to evaluate single padding processes without drying, and the use of the cold-dyeing Procion M (ICI) dyes and sodium bicarbonate appeared particularly attractive because of the high stability of the pad-bath, coupled with rapid fixation as the bicarbonate is converted to carbonate during steaming. A somewhat similar process has been suggested for the Remazol dyes (FH).

In applying Procion dyes by this method, it has been found that good fixation can be obtained in steaming times of about 1 min at 100°C a t pad-bath concentrations giving up to 3% dye on weight of fibre. It has been suggestedlg that this method is limited to pale depths unless the material is dried

(C.I. Vat Orange 16)

before steaming, but we have not found this limitation to apply. For example, the amounts of dye fixed on 4i-den viscose rayon tow when applying 2% of Procion Brilliant Orange M-2RS (C.I. Reactive Orange 4) and Procion Blue M-3GS ((3.1. Reactive Blue 1) were G9O/, and 59%, respectively. The corresponding figures 20 for cotton piece by the pad(bicarb0nate)-dry-steam sequence are 71y0 and 590/. It may be that the pick-up obtained on viscose rayon tow (about 70% on dry weight of fibre) has helped to increase the fixation by keeping the efkctive liquor ratio low.

For dyeings that are fast to milling, the difference in the cost of dyes and chemicals between Procion dyes applied by pad-steam methods and direct dyes (aftertreated when necessary) applied by con- ventional techniques varies Considerably with the type and depth of the dyeing. It is generally true, however, that the cost is unlikely to be less with Procion dyes than with direct dyes, and in many cases is considerably greater. Nevertheless, there are numerous occasions when the use of Procion dyes is justified, either by the increased brightness of colour obtainable or by the superior fastness properties.

STANDFAYT MOLTEN-METAL MACHINE

For fabric, an alternative method of continuously dyeing with vat or reactive dyes is provided by the Standfast Molten Metal machine 21. Standfast have also designed a machine for the dyeing of tow and slubbing and we have had the opportunity to evaluate its use in our laboratory. The machinc is similar in principle to the machine for dyeing fabric, but differs from it mechanically in that a rotating drum carries the tow or slubbing through the metal and thus reduces the tcnsions applied to the material. The fact that Fibro slubbing can be passed through the machine without being broken indicates that the tensions are in fact quite small. The tow machine is also much narrower, being approximately 9 in. wide.

The techniques used are essentially similar to those employed on the fabric-dyeing machine. When a leuco-pad bath a t 80°C was used, satisfactory results were obtained with a number of dyes. The machine can also be used for a wet-on-wet padding process in which the tow is pigment-padded through a separatc mangle and then chemical-padded in the Standfast machine. It is not possible to measure the expression of the Molten Metal machine directly, but for viscose rayon tow we estimate it to be about ZOO%, thus allowing for a large differential pick-up. This process can also be used for applying cold-dyeing reactive dyes, as in the fabric-dyeing machine.

The tow or slubbing was in a satisfactory physical condition as it left the machine and very little metal was picked up by it. Although our experiments were carried out a t somewhat lower speeds, comparison with the fabric-dyeing machine indicates that speeds of about 60 m/min would be possible, which would give a production rate of about 5 Ib/min for a single viscose rayon tow.

Jan . 1964 BLACKBURN AND WARD- DYEING MAN-MADE-FIBRE TOWS 17

CONTINUOUS WASHING OR AFTERTREATMENT OF DYED TOW

One of the major difficulties we have experienced in the continuous dyeing of tows is that of continuously washing or aftertreating the dyed fibre. In the case of Courtelle dyed with basic dyes, or viscose rayon dyed with direct dyes on the Konrad Peter machine, washing-off is a compara- tively easy process and simple apparatus can be used successfully. When extensive washing treat- ments are required, however, the need for more complicated equipment arises and the capital cost of such equipment is high. For example, a seven- box open soaper capable of dealing with a single viscose rayon tow would cost about S3,000-24,000, and other units of rather different design cost

In our view the problem is greater with reactive dyes than with vat dyes. As regards the latter, information is available 22 to show which dyes can bc most effectively “soaped” in 30 s a t the boil, as compared with 30 min a t the boil in batchwise dyeing. The criterion used, in classifying the dyes in this manner, is that of difference in hue between the rapidly “soaped” dyeing and the fully (‘soaped’’ dyeing. In our work with vat dyes we have assumed, therefore, that “soaping” for 30-60 s will be acceptable and have achieved this by using what can best be described as a “liquid J-box”. This consists of a narrow tank containing the “soaping” solution at the boil, into which the tow is allowed to fall. After the desired residence time, the tow is lifted out by squeeze rollers. The tow is contained in the bath in a series of loose folds, and sheet-metal forms are used to guide the tow and prevent it from snagging or entangling.

This technique is, however, less effective with reactive dyeings, particularly those in which dyes of high substantivity have been used. This is presumably because one is concerned hcrc to remove dye from the fibre rather than change its state within the fibre, and more vigorous mechan- ical action may be required. In any case, when one considers the uses of viscose rayon tow, the presence of a little unfixed reactive dye on the fibre is likely to be more troublesome than the presence of slightly underdeveloped vat dye.

26,000-28.000.

PAD-BATCH PROCESS

One of the most successful methods of applying reactive dyes to fabrics ir;l the pad-cold batch process“, and this seems to provide a way of avoiding the washing-off difficulties for reactivc- dyed viscose rayon tow described above. Again the most suitable dyes would appear to be the Procion (cold-dyeing) dyes, because of their short fixation time, although the recently introduced Levafix E dyes (FBy) and the Cibacron Catalyst CCB

(CIBA) process also hold promise. The suggested process is as follows- the tow is padded through a conventional mangle or, preferably, a flanged mangle, using Procion dyes and sodium carbonate. This necessitates the use of a dye-alkali mixer to reduce hydrolysis of dye in the pad-bath. As the tow leaves the pad mangle it is plaited down into the cage of an Obermaier or similar dyeing machine. After completion of the padding, the cage is left to stand for 2-3 h and then the tow is transferred into the dyeing machine, where it is washed off in the normal batchwise manner. This process offers the following advantages-

( a ) fixation is high and suitable dyes are not limited to those of good substantivity,

( b ) the likelihood of producing unlevel dyeings is small,

(c) reproducibility should be good, and (d ) specialised and expensive washing-off

machines are not required. * * *

We wish to thank our colleagues, particularly the staff a t Droylsden dyehouse, and Mr. G. W. Lewis, for assistance in the work described. COURTAULUS LTD RESEARCH LABORATORY

DROYLSDEN MANCIIESTDR ( M S . received 8th July 1963)

CAMPBELL STREET

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Wray, G. S., (Ed.), “Modern Yarn Production”

Rrf. 3, Chap. 2. Ashton, H., privato rommuniration. Man-made Tezt., 39, 58 (June 1962). ’ Boulton, J., J .S .D .C. , 67, 401 (1951). ‘‘Trice1 Manual”, Sect. VIII(e) (British Celanese Ltcl). Olofsson, R., and GralBn, N., Text. Research J . , 20, 467

lo Guthrie, J. C . , and Oliver, P. H., J . Textile Inst., 43,

1949), p. 40. a Linen Researrh, 67 (Sept 1962).

(Colunibinr Press, 19GO).

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T579 (1952). Courtaulds Ltd, B P Application No. 15812/61. Dyer, 126, 784 (1961).

l3 Dyer, 126, 675 (1961). l4 Thomas, R. J., Amer. Dyestuff Rep., 50, 708 (1961). l 5 Du Pont Dyes & Ghem. Tech. Bull., 16, 115 (1960). lR 13.1. du Pont de Nemours 8.. Co. Inc., USP 2,654,652

1’ Kern, R., Amer. Dyestuff Rep., 50, 366 (1961). l8 Lainoen, F. L. J . van, and Borsten, H., J.s.D.c., 76, 349

(1955).

(1960). lD “Pimion Dyes in Textile Dyeing” ( ICI Ltd, 1962),

Sect. 8.2.2.1. 2u Ref. 19, Sect. 8.2.2.2.

Morton Sundour Fabrics Ltd.. B P 620.584 (1949). 22 “Continuous Dyeing by Pad-Steam Techniques”

( I C I Ltd. 1955). n. 25. 23 F&vler, J. ’A., Mi&hall, W. J., and Seltzcr, I., Dyer,

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