Wool Dyeing—A Path to Progress

WOOL DYEING-A PATH TO PROGRESS

Chairman-Mr W. A. EDWARDS

101

Wool Dyeing-A Path to Progress

International Wool Secretariat, H.Q. Product Development Laboratories, Church Bank House, Church Bank, Bradjord I

Recent advances in the dyeing technology of man-made and cellulosic fibres have far outstripped those for wool. The reasons for this are discussed, and possible developments are described on the basis of achievements in other fields of textile dyeing. The present position is analysed from the viewpoint of dyeing techniques and in terms of the dyes and auxiliary products available. Current difficulties in producing dress fabrics to meet fashion demands for bright fast colours are used to illustrate the points raised, and possible methods of surmounting this immediate problem are examined. Special attention is given to the possibilities offered by continuous dyeing procedures for wool, and existing methods are critically surveyed. An attempt is made to define the operating limits of common wool-dyeing machinery, and thereby to underline the areas where re-equipment is needed if instrument-control and

automation techniques are to be utilised fully.

Introduction Over the past 10 years there has been a tremendous increase

in the production of man-made fibres, paralleled by advances in their dyeing technology. Alongside this development, the advent of reactive dyes led to a renaissance of cellulose-dyeing technology. Before this development occurred, cotton dyeing had already reached an advanced level with the widespread use of highly mechanised processing equipment. The most recent developments in colorimetry have opened the way to a major break- through towards achieving automation in textile processing within these advanced sectors of the industry ( I , 2).

Wool producers have reacted to the challenge of textiles made from man-made fibres by improving existing processes mainly by chemical means rather than by improved process control. This does not mean, however, that automatic procedures have been completely ignored by dyers of wool. In the U.S.A. and Japan, for instance, there has always been a keen interest in highly automated processing. Unfortunately, there is much largely unwarranted prejudice against automation in many wool- producing centres.

At present automation in the wool-dyeing industry simply means pre-controlled temperature, rate of rise of temperature, addition and draining cycles and flow reversal. One of the most important variables-pH-is not controlled. This is exemplified by the latest types of automatic control units that are to be installed at our new Ilkley plant. These units can be programmed by a punched card to give any combination of temperature-rise and temperature-hold cycles, together with additions from up to four storage tanks, drainage and flow-reversal cycles. We hope that, in collaboration with manufacturers of control equipment, control of pH may be developed, initially by taking the spare outputs from the controller, converting the signal from digital to analogue and coupling to a pH meter. The controller would then give instructions as demanded by the pH setting for the addition of standard acid or alkali from storage tanks. Precise pH control is very desirable in dyeing wool and a vast improvement in quality, levelness and reproducibility of the dyeing results, especially with the fast wool dyes that are very sensitive to pH changes in the near-neutral region at which they are applied.

One of the main reasons why wool dyers have not accepted automated control is that traditional wool-dyeing techniques have not been easy to control automatically. The complex sequences involved, for example, when dyeing wool hanks in a Hussong machine with milling acid dyes greatly increases the cost of the controller required and therefore, although these controllers are now available, there has been no demand for them from the wool trade, at least in the U.K. Continuous dyeing techniques and, ideally, the development of cold-dyeing reactive

dyes for wool are needed before automatic process control can be applied sufficiently simply, cheaply and efficiently to be accepted by the dyers of wool. Before this situation can be realised, more work into the chemical processes is needed to improve existing methods and develop new ones.

Dyeing Hanks of Knitting Yarn in Bright Colours Dyers of all classes of knitting yarns are expected to achieve

and maintain a very high standard of levelness and reproducibility. This sector is one of the most critical in the dyeing industry, where there is little or no room for manoeuvre in absorbing relatively slight colour differences between batches. The single-stick hank-dyeing machine was standard equipment in this sector for many years. To minimise risks in processing, dyers preferred to use levelling acid dyes for bright colours, so

I00

80

60 x f

B 0”

a c

a3

40

20

0 30 60 90 Time, min

Levelling acid dye _ _ _ - _ _ Milling acid dye

Figure I-Curves contrasting the migration properties of milling acid and levelling acid dyes. (The upper curve represents the amount of dye retained by the dyed material and the lower one the amount of dye

transferred to the undyed material)

102 JSDC FEBRUARY 1968; LEWIS AND SELTZER

that the effects of uneven strike could be overcome by migration of dye during subsequent heat treatment. Unfortunately, good migration properties are generally associated with inadequate wet fastness. ‘Easy-care’ shrink-resist pretreatments tend to reduce the wet-fastness properties of migrating acid dyes even further. Dyers are thus forced to consider the use of milling acid and reactive dyes to produce fast bright dyeings on yarns (Figure I).

The last decade has also seen the rapid development of reactive dyes. Originally effort was concentrated on cellulose dyeing, and great advances in application techniques were achieved (3). Reactive dyes for cellulose are now successfully used to produce fast dyeings on wool (4). Recently, several ranges of reactive dyes specific for wool have been marketed. These include the Procilan (ICI), Remazolan (FH) and Lanasol (CIBA) dyes, all of which can be applied in the presence of milling acid dyes.

The wide exploitation of fast dyes demands (a) better control in dyeing operations at all stages and (b) the use of auxiliary products (levelling agents) developed and produced by dye manufacturers to improve the performance of their fast-dye ranges.

Control of Dyeing Operations With non-migrating milling acid or reactive dyes, level dyeings

can be obtained only if a uniform strike is achieved. This demands careful control of the pH and temperature of the dyebath throughout dyeing. Level dyeings should be achieved as quickly as possible to achieve economies and to limit yellowing and fibre damage, which may be more marked with milling acid dyes than with levelling acid dyes because they are usually applied at a higher pH (about 5-6).

Traditional single-stick hank-dyeing machines, in which redistribution plays an important part in producing level dyeings, cannot be subjected to much process control. Uneven flow of dye liquor and relatively crude methods of steam injection tend to produce wide differences in temperature and dye concentra- tion, leading to uneven strike of highly substantive milling acid dyes.

Machine manufacturers have now developed equipment that gives much greater process control. Developments include mounting the hanks between two sticks, improving the methods of liquor circulation and employing enclosed steam-coil heaters throughout the machine.

lmprovements in the mechanical performance of dyeing machinery facilitated the development of control equipment. Initially the developments were concerned with the control of the rate of temperature rise during dyeing. Steam-inlet valves were designed to operate mechanically against electrical input information from thermocouples in the dyebath. The information received was used to regulate the flow of steam by means of diaphragm valves, using either pneumatic or magnetic impulse systems. The Vaco-pilot system (5 ) is based on the use of air pressure to operate diaphragm valves. Valve designs were modified as experience was gained to ensure maximum efficiency of operation. One of the earlier difficulties was the oscillation effect that could be produced when controls were ‘hunting’.

Closed-coil steam heaters can also be adapted to effect cooling by using cold water in place of steam. The next stage in process control, therefore, was to enable the operator to select both heating and cooling programmes through simple control devices. From this stage, the development of more complex programmes of process control, paralleling developments in other industries. followed. The Vaco-pilot system was one of the earliest developments in Europe. A ‘musical box’ type of control unit based on a feeler mechanism was used to control not only temperature changes but also additions of solutions of reagents from stock tanks into the dyebath; it could also be used to fill and enipty the dyebath.

The application of electrical control of pneumatic diaphragm valves has resulted in the development of units such as the Celcon (Courtaulds Engineering Ltd), by which relatively complex operations may be controlled by punch-card programming of a simple computer. It is claimed that the new Celcon automated dye-cycle controller enables operations to be precisely controlled within the following limits- Temperature control 1 deg C, at all temperatures during all

temperature changes Temperature-control range 0.25 deg C in I deg C divisions Stability better than 0.5 deg C for ambient temp-

erature change of 25 deg C Calibration accuracy better than 0.2 deg C

Experience has shown that the greater the automatic control that can be exercised the higher is the chance of success in producing, with ‘difficult’ dyes, fast dyeings of the type required to meet Woolmark Standards.

Although dyers are often prepared to re-equip when processing man-made fibres, they have been content to rely on obsolescent equipment for dyeing wool. One of the reasons advanced for this is that dyers can often charge more for processing man-made- fibre yarn than for processing wool yarn. They naturally prefer to use new equipment for the former purpose. We hope that the present intensive campaign of wool promotion will correct this position.

Levelling Agents in Dyeing In the following procedures for the application of fast dyes to

wool yarn, it has been assumed that efficient machine performance and careful yarn preparation have already been attained.

To illustrate procedure and the use of levelling agents, consider an operation that is agreed by most yarn dyers to be one of the most difficult, namely the production of bright greens based on combinations of ‘phthalocyanine blue’ milling dyes and yellow halogeno-reactive dyes. Both products show negligible migration and levelling agents normally have to be used.

Auxiliary products for use as dyebath assistants (6) have been known for a long time. Originally, these were introduced to overcome ‘skittery’ effects. In current practice, wide ranges have been developed for various purposes. The Avolan (FBy) range (7) may be considered as typical (Table 1).

TABLE 1 Typical Examples of Auxiliary Agents

Type Character Commercial name

RIR2R&fCH2CH20),,H bifunctional Avolan SC non-jonjc/cationic Avolan ON

RO(CHzCHzO),H non-ionic Avolan IW Avolan 1L

RS03-Na+ anionic Avolan IS Avolan P

Most manufacturers recommend cationic agents, in the presence or absence of non-ionic agents, when dyeing the bright greens mentioned above, e.g. Avolan SC and Avolan AV (FBy) mixtures, Albegal B (CIBA; bifunctional; specially developed for dyeing wool with reactive dyes) (8) and Lissolamine A and Lubrol W (ICI) mixtures.

Cationic agents form ionic bonds with sulphonated acid dyes and the complex thus produced is absorbed at the wool surface. Dye then diffuses into the fibre mass. This process depends on the achievement of uniform strike for level dyeing. Conventional non-ionic or anionic dye-restraining agents increase the danger of producing skittery dyeings when reactive dyes of low sub- stantivity or dyes of high molecular weight of the phthalocyanine turquoise blue type are used. In any case, the dyebath exhaustion may be uneconomic unless the cationic agents are used as carriers.

WOOL DYEING-A PATH TO PROGRESS 103

In addition to the normal problems associated with the application of milling acid dyes, the presence of the yellow reactive dye demands careful pH control in the region of pH 5 . 5 , to prevent too rapid dye-fibre reaction and hydrolysis. At higher pH the dyebath exhaustion is markedly reduced, despite the presence of auxiliary products.

A typical procedure is illustrated in Figure 2. The agents used were Lubrol W and Lissolamine A 50%. The rate of exhaustion depends on the temperature and hence it is important to have careful control and equalisation of temperature throughout the fibre mass. If there is a sudden rise in temperature, rapid and uneven deposition of the dye-auxiliary agent complex occurs.

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*O t B’ueA

Figure 2-Rate of exhaustion of a blue phthalocyanine milling dye and a yellow monochforotriazine reactive dye applied by the standard

procedure

A further improvement in this technique has been suggested by CSRIO (9). Since milling acid dyes show little migration during boiling, there is no need to use a prolonged heat treatment once a level strike has been achieved. Fastness tests show that, by raising the dyebath temperature to 85°C under controlled conditions to effect an even strike and then heating further for about 30 min at 9 0 T , dyeings similar in fastness properties to those obtained by boiling for long periods are produced. This technique has proved successful in mill practice in Australia. Considerable economies in heat and power consumption ensue, and the productivity of a given machine may be significantly increased. It must be noted, however, that some reactive dyes developed specifically for wool, such as Procilans and Remazo- lans, are not applicable by this method, since boiling is necessary for efficient fixation (10).

The capital cost of new machinery and control equipment may be thus offset by the advantages gained. In addition, the damage to the substrate, particularly yellowing, is markedly reduced compared with that caused in dyeing at the boil.

Despite the extensive development work carried out on this problem, manufacturers are not prepared to give general recom- mendations for dyeing procedures without a careful study of the conditions existing in any specific dyehouse. It is still the general recommendation that these dyeings should be produced by dyeing the slubbing or loose stock before spinning the yarn.

The development of exhaustion procedures for reactive dyes solved a similar problem for the dyer of cotton hanks by providing a simple reliable dyeing process (11). Here dyeing proceeds in two stages. In the first, ‘inert’ stage, excellent levelling is achieved ; when even distribution of dye has been attained, alkali is added and the dye reacts with the fibre in situ. We can at present only look forward hopefully to a similar solution of the wool-yarn dyer’s problems.

Fabric Dyeing The machine traditionally used for dyeing wool fabric is the

winch. This machine poses similar problems in operation to the single-stick hank-dyeing machine ; level dyeings and good penetration are ensured by using dyes with good migration properties. Damage to the wool is minimised by dyeing at a pH of about 4-5. Very few dyers are prepared to risk dyeing non- migrating dyes on the winch, even on open-weave fabrics. The dyeing of tightly woven fabrics under these conditions is almost impossible.

The real answer to the problem may ultimately be provided by the development of a pad mangle that enables levelness of strike to be achieved mechanically. Everyone is familiar with the pad- develop technique (12) widely used for dyeing cotton fabric, of which the pad-steam range is an outstanding example. The system can be subjected to careful process control and many suitable dyes are available. The quality of the result is largely determined by the mechanical efficiency of the equipment.

CONTINUOUS DYEING OF WOOL FABRIC

Machinery designed for dyeing cotton fabric is not considered suitable for wool fabric because of the mechanical strain occurring when the fabric is transported through the steamers and dryers. Continuous open-width processing of fabric, however, is widely practised in wool scouring and finishing and there is probably no reason why wool fabric of suitable construction should not be dyed on similar equipment. During the Second World War, considerable quantities of wool uniform fabrics were dyed with vat dyes on the duPont pad-steam range. Indigo dyers still dye wool continuously.

Continuous dyeing operations entail three stages, viz. impregnation, development, and washing off and drying.

The dyes are usually applied from aqueous solution; conse- quently, the more hydrophilic the substrate the more easily is uniform impregnation of dye achieved. The success of the pad- steam process, widely used for dyeing cotton fabric, is due to the ease of impregnation of well-prepared fabric with dye liquor and to the wide range of dyes that may be rapidly fixed by steaming. Highly mechanised complex equipment has been developed for this process.

Wool is relatively hydrophobic compared with cotton and needs greater care in mechanical handling to prevent damage of the fibres, The lower volume of wool production, coupled with the fact that long runs of one colour are less frequently required, has reduced the use of continuous dyeing techniques.

In general, development work has been concentrated on the dyeing of loose wool and slubbing (13, 14), where relatively long runs of one colour are more common than in fabric dyeinq.

The problems include ( I ) selection of assistants to achieve satisfactory impregnation (2) mechanical handling during impregnation and develop-

(3) colour selection (organisation of production to exploit ment, and

economic advantage).

Wetting Agents and Auxiliary Products Padding assistants for wool generally must (a ) rapidly wet the unmodified fibre, (h) increase dye solubility, (c) assist uniform penetration and efficient fixation of dye,

( d ) be readily removed during subsequent washing. Work carried out over ten years ago (15) established that a

pad liquor for loose-wool dyeing should be based on a mixture of a wetting agent, a thickener, e.g. sodium alginate, and electro- lytes.

eliminating skitteriness and frostiness, and

1 04 JSDC FEBRUARY 1968; LEWIS AND SELTZER

It was observed that wetting agents based on ethylene oxide condensates formed complexes with certain acid dyes in solution and that the complex tended to adhere to the surface of the wool after padding. A reservoir is probably formed at the surface, from which dye diffuses into the fibre during heat development, giving level, well-penetrated dyeings, free from skitteriness and frostiness. The fact that the dye-wetting agent complex is insoluble in mildly acid solutions at temperatures above the ‘cloud point’ of the auxiliary product gave rise to an alternative continuous development technique, viz. the ‘acid flash’ treatment. In this process, the padded fabrics are developed by immersion for short periods in boiling acid solutions. The technique has not been applied widely because of the difficulties of colour control.

A wide range of new wetting agents, specific for wool, has now been developed that exploit dye-film formation in pad-steam dyeing. These include-

Cibuphasol C and A S (CZBA)-The active agent in these products (24) is probably a condensate of an organic base and a fatty alcohol. These products promote the formation of two aqueous phases in the pad-liquor, viz.

(a) the coacervate, which contains the bulk of the dye and the active agent, and

(6) the equilibrium liquid. During padding, the coacervate forms a homogeneous film of dye on the fibre surface.

Zrgapadol P (Gy)-This product (23) is similar in film-forming action to Cibaphasol C and AS, but is said to be less selective with regard to dyes and pad-liquor compositions.

Levalin VK and VKC (FBy)-These are anionic products (7) that again fulfil the requirements for film formation and fibre wetting during padding.

Urea-A new pad-steam technique has recently been announced by CSIRO (16), which entails the use of high concentrations of urea (300-350 g/l.) in the pad-liquor. High concentrations of urea have long been used in the continuous dyeing and printing of viscose rayon, where urea acts both as an efficient humectant in steaming and as a solubilising agent for the dyes, assisting rapid diffusion into the fibre. Presumably, a similar mechanism applies in wool dyeing. Conventional wetting agents are used in conjunction with urea.

Urea is probably the least selective agent with regard to the dye and further development of this process is to be expected, particularly in the application of reactive dyes to wool.

The relatively low cost of urea makes it possible to consider the use of the high concentrations required, if the outlay is justified by the result.

Pad Mangles A wide variety of mangles is available for processing. Mangles

with relatively soft bowls with delivering and batching devices that act under minimum tension are preferred for wool. Low- capacity pad troughs or Febe-type mangles are needed to minimise wastage of pad-liquor in short runs.

Pad-Steam Procedures Whether or not a particular steamer is used for processing

wool fabric depends on the fabric construction, the mechanical cloth-transport system, the capacity of the steamer and the steam temperature. The last factor is related to the nature of the dyes.

Steamer Construction Most standard steamers used by dyers transport the cloth up

and down over a series of rollers arranged in parallel horizontal lines. Cloth tension is determined by the distance between the lines, the number of idle rollers between driver rollers or driving

mangles, the friction in the bearings and the roller diameter, which determines the angles of bend of the cloth. Strong fabrics can be moved over a whole series of idle rollers in a steamer by a single mangle.

In steam processing of all classes of wool, particularly light- weight fabrics, it is considered advisable to drive at least half the rollers, e.g. the top set in a steamer. Experience gained in con- structing open-width scouring machines suggests that the minimum roller diameter should be 4 in. Rollers should be made from stainless steel with sandblasted surfaces or rubber skins, to minimise fabric slippage. The drop between rollers should ideally be about 3-4 ft, but a compromise must be reached to limit the over-all length of the machine. For longer drops, jockey rollers can be used between the parallels to steady the fabric. Bearings should be of the minimum-friction type and independent spring loading should be incorporated. Many modern steamers meet these requirements.

Steamer Capacity If the minimum padding speed is 10 yd/min, to prevent

excessive tailing and ending the capacity and length of the steamer should be as indicated in Table 2.

TABLE 2 Capacity and Length of Steamer for different Steaming Times Steaming time Capacity of Approximate*

1 10 5 5 50 25

10 100 50 30 300 150

(min) steamer (yd) length (ft)

‘Distance between roller centres is If1 and the drop betneen rollers is 3 ft

Obviously, from these figures, to provide compact equipment suitable for the short runs to a colour common in dyeing wool fabric, short steaming times are essential. For loose-wool dyeing, manufacturers of continuous dyeing equipment have built large machines capable of providing steaming times of up to 30 min. The notable exception is the Northco machine (17), which uses steam under pressure at 120°C to accelerate dye fixation.

Comparison of Auxiliary Agents Four methods for continuously dyeing wool fabric have been

examined on the laboratory scale to determine the effect of the agents used on the time required for fixation. Steaming was carried out at 100°C in each case. Current work includes studies of the effect of increasing the steam temperature on the rate of fixation.

To compare the efficiency of the agents available, two dyes, Coomassie Ultra Sky SES (C.I. Acid Blue 112) (I) and Carbolan Brilliant Blue 2 RS (C.I. Acid Blue 140) (lI), were selected on the basis of an investigation into the rates of fixation of milling acid dyes applied to wool by a pad-steam technique carried out by Lemin (15). Dye I became fixed at a very much lower rate than dye 11. Such a difference was of obvious interest in establishing a quick comparison between the various commercial methods.

The methods investigated were- (1) Pad-dye, with detergent as assistant: steam then acid boil

(Lemin’s method) (15) (2) Irgapad (GY) (23) (3) Cibaphasol (CIBA) (14) (4) Urea process (CSJRO) (16). The effect of steaming time on fixation in medium-depth

dyeings of dyes I and I1 was investigated and the results (Figure 3) clearly indicate that the CSIRO urea method gives the highest rate of fixation. It is, therefore, the most suitable for use in the compact equipment required for short runs to a given colour.


I I I I

2 4 6 0 V I I I I 0 2 4 6 0 10

Time of steaming, min I CSIRO I I I Cibapharol

II lrgapad I V Method described by Lemin

Figure 3-Rates of fixation of (a) Carbolan Brilliant Blue 2RS and (b) Coornassie Ultra Sky SES on wool using various pad-steam processes

Pad-Batch Techniques RYDBOHOLM PAD-ROLL SYSTEM

This system has been used for all types of fabric. Its main feature is that long development times are used without serious interference with production flow. Fabric transport is kept to a minimum during processing.

The machine consists of a vertical pad mangle and a series of large batching chambers in which very large batches of fabrics can be maintained under controlled conditions of temperature and humidity for any desired period. The impregnated fabric is fed into the chamber through an infrared heater. As each chamber is filled, another is rolled into place to accept the impregnated fabric. Fabrics of different colours, and even different fabrics, may be batched on the same roll, using suitable end- cloth as a separator. After being batched, the goods are removed from the chamber and washed-off before being finished. Thus a continuous production flow is achieved despite the time lag in batching.

Good results have been reported on wool fabric by using acid, reactive and metal-complex dyes with batching for up to 24 h at 80-95°C.

PAD-BATCH (COLD) SYSTEMS

These systems are likely to prove more attractive if, and when, satisfactory techniques are established. Possible lines of approach may be to use solvents such as benzyl alcohol (18), which are known to promote rapid dyeing of wool. The main problem is the recovery of the solvent.

Concentrated formic acid (19) has also been shown to promote rapid dye fixation at room temperature, but an efficient method of acid recovery is needed if the process is to be economic.

CIRA have developed a cold pad-batch process using Ciba- phasol and formic acid that appears to be very promising for knitted fabrics and carpets.

The urea process (16) (300-350 g/l. urea in the pad liquor) has been shown to produce efficient fixation of acid dyes in pale depths on wool after the impregnated fabric has been left at room temperature for short periods. The process is probably limited to low-molecular-weight acid dyes and lacks the versatility of hue and depth range offered by heat-development techniques.

Speculative Systems Techniques based on established continuous dyeing procedures

have so far been discussed. The following techniques may be worthy of consideration in planning future work.

A recent article (20) has suggested the possibility of using solvent systems for dyeing textiles. Solvent processes have already been established for scouring (Triklone X process; 1CI) and finishing (Zeset process; DuP) wool fabrics and it has been demonstrated that wool may be dyed very rapidly at room temperature in the presence of organic solvents.

The problems include the selection of suitable dyes and the achievement of efficient solvent recovery. The high capital cost of the solvent-recovery system is one of ihe main reasons why the ICI Solvent Scouring process has failed to achieve wide popularity despite the over-all economy afforded in terms of processing costs once the capital outlay has been made.

An alternative technique (21), using hydrophobic solvents, would simulate the soap-charging methods used in dry-cleaning and solvent-milling procedures. Small amounts of water introduced into chlorinated hydrocarbon solvents are rapidly absorbed by wool on immersion. I f this system could be successfully adapted, fibre, yarn or loose stock could be impregnated, without squeezing between rollers, with an aqueous dye solution dispersed in solvent. Wastage of dye liquor would be minimal and many of the handling problems associated with padding of yarn, for example, would be eased.

In both cases, development of the dyeing, either by steam or by hot air, could be combined with solvent recovery.

Conclusions We have attempted to stress the importance of improving

process control in dyeing in existing machinery as the first step in advancing the technology of wool dyeing.

I n the dyeing of wool yarn, there is a basis for increased mechanisation in the rapid advances made in hank- and package- machine construction and in control equipment over the past few years. Progress made in modernising fabric-dyeing procedures has been negligible, and a new look at the possibilities offered by continuous and semi-continuous processing is essential, paralleling the established techniques used by cellulosic-fibre dyers. ( M S . received 31 May 1967)

106 JSDC FEBRUARY 1968; LEWIS AND SELTZER

References 1 Greenaway, R., Dyer, 137 (2 Dec 1966) 839. 12 Mawson, J. F., and Rattee, I. D., J.S.D.C., 78 (1962) 161. 2 Seltzer, I., J.S.D.C., 81 (1965) 251. 13 Beal, W., ibid., 83 (Jan 1967) 3. 3 Rattee, I. D., Endeavour, 20 (1961) 154. 14 Casty, R., Melliand Textilber., 41 (1960) 1365. 4 Derbyshire, A. N., and Tristram, G. R., J.S.D.C., 81 (1965) 584. 15 Lemin, D. R., J.S.D.C., 74 (1958) 746. 5 Text. Rec., 81 (May 1964) 82. 16 Angliss, I. B., and Delmenico, J., ibid., 80 (1964) 543. 6 Craven, B. R., and Datyner, A., J.S.D.C., 83 (Feb 1967) 41. 17 Khachoyan, J., Proc. Znternat. Wool Text. Res. ConJ Paris 7 FBy, ‘Wool’ Farben Revue, Special Edition No. 8. (CZRTEL), 3 (1965) 333. 8 CIBA, ‘Lanasol Dyes on Wool’ (3300). 18 Peters, L., Stevens, C. B., Budding, J., Burdett, B. C., and Sykes, 9 Swanepoel, 0. A., and Mellet, P., S. Afr. Wool Text. Res. Inst., J. A. W., J.S.D.C., 76 (1960) 543.

19 Milligan, B., ibid., 77 (1961) 106. 20 Text. Indust., 130 (Oct 1966) 295. 21 Peters, L., and Stevens, C. B., 73 (1957) 23.

Tech. Rept No. 92. I0 Hine, R. J., and McPhee, J. R., Dyer, 132 (1964) 523. I 1 Rattee, I. D., Amer. Dyestuff Rep., 52 (1963) 320.

Discussion Mr A. W. LANDMANN: What is the mechanism by which better

fastness is obtained by steaming and for what period does the material have to be steamed for the best fastness?

*Why is better fastness obtained at the boil or by steaming than with the same dyes at lower temperatures?

Dr LEWIS: If conventional dyebaths are used, better wash fastness is obtained by steaming or boiling, since the wool fibre swells significantly during these processes, giving excellent diffusion of the dye into the fibre. Furthermore, the higher the temperature the lower is the state of aggregation of the dye and thus the greater is the degree of penetration. Low-temperature dyeing is capable of giving fast results if a dye-disaggregating auxiliary and a swelling agent are used.

Mr G. E. CHARLES: This year tremendous advances have been made in the production on coarse-gauge machinery of warp- knitted fabrics made from high-quality worsted yarns and continuous-filament synthetic-polymer fibres. In the warp- knitting section of the textile industry rapid expansion is under way, particularly in the automation of dyeing and finishing machinery, and clearly it is desirable to achieve this progress on worsted warp-knitted fabrics. Have the lecturers any information on any investigation they have made in processing wrap-knitted worsted-synthetic-polymer fibre mixture fabrics, bearing in mind the existing machinery used in warp-knitting dyehouses ?

Mr SELTZER: We have had no specific experience of dyeing this material, but equipment is available for continuous processing at other stages and no doubt it could be adapted to continuous dyeing.

Dr G. H. CRAWSHAW: With reference to Mr Seltzer’s answer to the previous question, considerable progress has already been made in continuous finishing techniques. Continuous methods of scouring and setting have been in use, particularly in Sweden, for several years. The need for batchwise milling has prevented totally continuous finishing, but prospects for success with a continuous light-milling process now exist.

Mr W. A. EDWARDS: When I was in the U S A . a few years ago, they were trying to develop a continuous method of milling based on that used by the hat trade; I do not know whether this proved successful. The lecturer described the pad-steam method of dyeing tubular knitted fabric. Was there any difficulty with the edging?

Mr SELTZER : Several machine manufacturers, notably Konrad Peters and Farmer Norton, have been concerned with the development of padding machinery for knitwear over the past few years. Interest has centred mainly on cotton knitwear, but although some progress has been made the methods have not been widely adopted by the industry. Only one firm, in Australia, is currently using a padding technique for dyeing wool knitwear, and no detailed information is available.

Further progress will depend on creating a demand for high productivity in knitwear dyeing so that a wider trade experience may be gained.

Mr H. R. HADFIELD: Dr Lewis mentioned the dyeing of wool by pad-batch methods. Any padding operation needs very uniform and consistent preparation of fabric. This is well established and successful for cellulosic fabrics. Preparation of wool is a very much more complex operation, because the number of qualities available is much greater. I take issue with the lecturer on this question of pad-batching and the difficulties of getting the colour easily. An accurate padding formulation is still needed to obtain the colour at the subsequent batching. Have the lecturers any experience of the reproducibility from fabric to fabric over a long period and of the consistency of the dyeing?

Dr LEWIS: I agree with Mr Hadfield that uniform preparation of fabric is essential for successful padding. We have observed that oxidation of spinning oil owing to the fabric being left too long in the loom state can cause marked unlevelness. We have carried out several trials and have so far been satisfied with the reproducibility of the method.

Mr F. ILLINGWORTH: Have the lecturers considered the impact of the pad-steam-roll method on the very important carbonised-fabric trade? Merchants often require delivery of this type of fabric within 24 h and dyers can process it in this period with the machinery at present installed.

Mr SELTZER: As technologists, we can but develop new and better procedures for increasing productivity in wool dyeing. The question has raised what is essentially an issue of the over-all reorganisation of the industry, which is as much economic as technical in aspect. We believe that economic and technical revolutions must progress simultaneously if the best use is to be made of advanced techniques. We cannot, therefore, base our advances on providing services for the man whose finances only permit him to live from piece to piece, where a 24-h delay would apparently mean the difference between solvency and bankruptcy.

Mr S. M. JAECKEL: The chairman mentioned knitted wool garments. What do the lecturers think of the relative merits of present and possible future methods of dyeing garments? The laundry-sheet method was considered unsuitable for leather, as at present handled, because of the shape of the hide, and may be difficult, if quality is to be maintained in levelness and even penetration, unless impressionistic effects become fashionable. This type of approach, pressure dyeing on forms and conventional methods require comparison.

Mr SELTZER: This question again raises an economic issue rather than a technical one and demands a re-appraisal of the organisation of this section of the industry.

Mr JAECKEL*: What action do you suggest, if bottle-green yarn has been knitted into fabric from which, somehow, fully- fashioned outerwear has to be cut and, say, Mary Quant intro- duces a lilac colour so that, overnight, all orders for green are cancelled and replaced by orders for lilac?

Dr LEWIS: No comment.


Mr W. J. MARSHALL: I think the Keymatic principle is the solution to two previous questions, but more particularly as far as pad-batch dyeing is concerned. Pad-batch dyeing of cotton knitwear is carried out in Sweden; this is done by slitting the material and batching in open width, thereby overcoming the difficulty associated with the wet edge. There are, however, two questions that I would like to ask. The first refers to the dyeing of wool using urea, making it parallel to the dyeing of cellulose using urea with reactive dyes. It was at one time thought that cellulose could not be dyed in the absence of water. With the advent of reactive dyes and the pad-dry-bake process, this has been proved incorrect. With wool, by using high temperatures, can a rate of reaction necessary to give complete fibre penetration and reaction in times similar to those used in cotton dyeing be obtained? Alternatively, can one use continuous pressure-dyeing equipment such as that developed for the preparation of fabrics? I appreciate that the difficulty with continuous pressurised equipment is in passing the wool un- damaged through the seal, but this can be overcome by passing it through in mechanical carriers.

Mr SELTZER: We thank Mr Marshall for his informative comments; the issues raised are largely a matter for future

experimental work. In operating a pad-dry-bake process for wool using reactive dyes and urea, the rates of penetration and reaction would be as high as those for cotton. However, the amount of yellowing likely to occur at these high temperatures would have to be considered, especially if the time of treatment were prolonged. The suggestion that continuous pressure-dyeing equipment may be of use is very interesting.

Mr J. W. BUNTING: Is programmed control of pH required, i.e. rate of rise and steady-state control?

Dr LEWIS: Yes. Mr BUNTING: There would seem to be a case here for sampled

data control, i.e. take a sample and make a correction propor- tional to the error. Wait for the effect of this and then take a further sample and make a further correction. The electrodes may have to be chemically cleaned automatically at frequent intervals. There is no difficulty in programming the desired value. This can be done in exactly the same way as the temperature programme on the Celcon.

Mr SELTZER: We are very pleased to hear that pH control may be possible and assure Mr Bunting that we will offer him every facility to develop it at our Ilkley Celcon unit.

Documents

Wool Dyeing—A Path to Progress