continuoui dyeing of cottor fabrics using reactive dye:

I tconomy and ecology ir continuoui dyeing of cottor fabrics using reactive dye: - Dipl.-Ing Kurt van Wench, of Monfoi-ts Textilmaschinen GmbHC Co., describes the ECOATROL process Figure 1. The four main processes in use world-wide for continuous dyeing of cellulose fibres with reactive dyestuffs. T he textile finishing industry is faced with more or less the same problems world-wide. Environmental protection regulations (waste water and exhaust air) energy consumption, personnel problems, and cheap imports are just a few of the difficulties to be overcome. Only through close co-operation berween the textile finisher, machine maker and chemicals industries, can these problems be addressed. This article details a success in the field of continuous dyeing of cellulose fibres using reactive dyesruffs achieved as a result of this type of co-operation. Processes There are presently four main processes in use worldwide for continuous dyeing of woven cellulosic fabrics, e.g. 100% cotton, using reactive dyestuffs (Figure 1):- (i) Pad-batch or KKV Figure 2. Reactive substances for dyeing of cellulose fibres1,, (ii) Pad-dry thermofixing (iii)pad-steam (iv) Pad-dqipad-steam The first of these requires the smallest machine range, whilst the other three demand more or less complex ranges. Reactive dyestuffs Reactive dyestuffs used can be classified according to their reactivity. Figure 2 shows a selection of reactive dyestuffs with widely differing chemical composition, arranged from low to high reactivity,,,. The reactivity of the dyestuffs is reflected in: Duration of the dzell time in the pad-batch Temperature and time in the pad-dry thermo f~ing Temperature and time in the pad-d y/pad-steam The level of the colour yielc and the degree of futation ari also dependent on the ievel o dyestuff reactivity. Ancillary substances In order to bind the reacuvt dyestuff to the fibres, tht dyestuff makers recommend 2 wide variety of ancillary sub stances and substanct volumes, depending on the dyeing process employed. Two sliver samples (one for a red shade and one for : blue shade) were sent to five European dyestuff manufacturers for recipe formulation for three processes using reactive dyes. The resultant recipes represented the current state-of-the-art. Figure 3 shows a summary of the volumes of ancillary substances recommended for the individual processes. Sodium hydroxide solution. water glass, soda, urea and 28 INTERNATIONAL DYER JANUARY 1996

salt are the chemicals which are used in relatively large quantities. These chemicals are discharged partly with the exhaust air, but for the most part contaminate the waste water during washing-off. The ECONTROL process was developed jointly by Monforts and Zeneca. In contrast to the processes already described, ECONTROL is characterised by the fact that no ancillary substances such as urea, water glass, soda, sodium hydroxide solution or salt are required. In this process, the reactivity of the dyestuffs is exploited together with the drying behaviour of the fabric in such a way that optimum colour yields can be achieved without the use of large and aggressive volumes of alkalis. ECONTROL is a combination of a continuous batch process and a drying A common recipe for use with the ECONTROL process is s.hown in Figure 4. Apart from the dyestuffs, only log4 of sodium bicarbonate is used as an ancillary substance. The urea, water glass, soda, Figure 4. Typical ECONTROL process recipe. sodium hydroxide solution or salt used in other dyeing processes are replaced in the ECONTROL process by a controlled steam content during drying. Only reactive dyestuffs with high reactivity can be used for the ECONTROL Dichlorotriazine (Procion MX) dyestuffs were employed in the development of this process and are used in practice. These are commercially available and also used in other dyeing processes. The dye attaches itself to the fibre as illustrated in Figure 5, but under mild fixing conditions. Dyestuff fixation In the ECONTROL process, the dye liquor is padded onto the textile web. In addition to the dyestuffs, the liquor also Figure 3. Summary of ancillary substances used in the dyeing of cellulose fibres. contains 1-2gA of wetting agent and log/] of sodium bicarbonate. After a short air passage, the wetted and uniformly squeezed fabric web is. transported directly to the dryer (hot flue) where the fabric remains in the chamber continuously for 2 minutes at approx. 25 vol.% steam content. These conditions are quite sufficient to fix the - dyestuff. Figure 5. Dyestirff reaction with cellulose fibre. In general, reactive dyestuffs require alkali and long dwell times for fixation, e.g. in the cold pad-batch process; akali, urea and high temperature in the pad-dry thermofixing process; or, salt, steam and temperature in the pad-steam However, since highly reactive dyestuffs are used in the ECONTROL process, even a weak alkali (sodium bicarbonate), a short dwell time (2 minutes) and a low fabric temperature (6ST = cooling limit temperature) are sufficient for dyestuff fxation. The dwelling chamber is a hot flue in which the fabric dwells under controlled conditions. Range configuration With reference to the configuration shown in Figure 6 it is possible to consider the ECONTROL process in greater detail. As normal, the range has an infeed section (1) with cloth scray for continuous fabric changing.. The textile fabric web then enters the Matex-3 Color padder where it is wetted with dye liquor and uniformly squeezed. After a short passage in air, the fabric web is transported to the dryer.. The wetting unit (3) is used when starting the range in order to: (a) build-up the chamber climate in the dryer to 25 vol.% with a feeder and water; and, (b) to cool the guide and transport rollers of the hot flue down to production conditions before the dyeing process starts. From the start of dyeing, a chamber climate of 12OOC nozzle outlet temperature and 25 vol.% steam content exists in the hot flue (4). The steam content is monitored and regulated by a chamber climate measuring unit (5) in which the exhaust air fan. is control led. If, with very lightweight fabric, the water in the fabric is not sufficient to maintain the chamber climate of 25 vol.%, steam is added via the steam injection unit (6). The outlet section (71, makes it possible for the fabric web to be discharged directly to the washing machine (8). INTERNATIONAL DYER JANUARY 1996 29

Figure 6. Range layout for ECONTROL procgss. 1. lnfeed section, 2. Matex 3-color padder, 3. Wetting unit, 4. Thermex hot flue, 5. Measuring and control unit (chamber climate), 6. Steam injection unit, 7. Outlet section, g. Washing During the drying process proper, the fabric web has a cerrain temperature (cooling limit temperature) - as long as it is damp - which is dependent on the steam content in the hot flue (Figure 7). An increase in the steam content to 25 vol.% at a nozzle temperature of 12OOC produces a fabric temperature of 68OC. Although the increase in the steam content in the dryer causes a slight reduction in the drying capacity of the hot flue (Figure. 81, this has no effect on the ECONTROL process as only the 2 minute dwell time is important here. For example: With a hot flue length of 68m, the 2 minute dwell time is obtained at a fabric speed of 34dmin. Articles of 100g/m2 leave the hot flue dry. Articles of 5OOg/m2 leave the hot flue still damp. Whether the dyed fabric leaves the hot flue damp or dry is of no significance, as the dyestuff is fixed and the fabric now only needs to be washed-off. can thus be regarded as a dyeing process with a liquor ratio of 1:0.7 in which the dyeing time is 2 minutes. As this process is preferably performed on hot flues, these dryers can be considered more as dyeing machines. Process comparisons In order to evaluate the ECONTROL process more closely, a number of comparative trials were performed using the dyestuffs and recipes shown in Figure 9. The results of these trials are summarised in Figure 10 Figure 7. Fabric temperature during drying as a function of steam content. which shows the influence of of urea produces no improvc the chamber climate on the ment. final appearance of the fabric. With the ECONTRC The same shades were also process, the use of urea c2 Figure 8. Dwell temperature of the fabric during drying with different steam contents X in the dryer and change in performance over X at 120 C. dyed via different processes but using the same range of dyestuffs. The results of this comparison are summarised in Figure 11. Figure 10 clearly shows that without steam in the circulating air and without urea, only a low colour yield is achieved for both shades. The best colour yield is obtained with 25 vol.% stesm content (without urea). Urea alone (without steam) produces an increase, but still not a match for the best result. It is also interesting that 2 j vol.% steam content in the circulating air plus 1OOg4 be eliminated as a pola medium as long as th chamber climate is controlle at 25 vol.% steam content. Figure 11 shows that wit. ECONTROL the Red dye. colour yield was higher tha. with the other processes: fc the Navy Blue the colour )-le1 was better than with the pat batch process and equally a good as with the pad-dry the: mofixing process and pad dry/pad-steam The pure pad-steam proces without intermediate dryin was not evaluated as th colour yield is generally 30 40% lower with these dar: 30 INTERNATIONAL DYER JANUARY 199,

shades, due to the fact that with the high steam content, sudden condensation occurs on the cold fabric whereby the liquor ratio increases from 1:O.i to approx. 1:l.l and the substantivity is also reduced. Advantages of ECONTROLI,] Advantages for the fabric include: 8 Softerhand. 8 Less dyestuff migration. Pile articles are notpressed. 8 Better through dyeing with dense articles. 8 No bar marts on teny goods 8 Dead cotton is covered better. 8 No yrosting effect on viscose. Advantages in chemicals consumption: 8 No urea, no salt, no water glass, no sodium hydroxide solution and no anti-reduction chemicals. 8 Stability of the liquor (approx. 8 hours). Machine advantages: 8 No Infra-red (IR)predryer, no steamer, and no two-component metering Pump.?%e range can be used as a normal dryer. No dwell station (pad-batch) is necessary. 8 It k ideal for short batches and large batches. 8 Minimumenergy consumption through exhaust air monitoring. Advantages for the process: 8 Theprocess and the recipe are simple. No batching, no steaming One-bath process with PES/u&cose is possible. One-bath process with PWcotton with excellent sulface image. 8 No reduction in light fastness as with the hot air fixing Ideal for short batches. 8 Better washing-off properties, lower water consumption. 8 Better colour yield than with the pad-batch Ecology ECONTROL is a simple, economical, efficient, energy-saving and controlled It also contributes significantly to environmental pollution control. Avoidance is always the best solution as a contribution to reducing environmental pollution. With ECONTROL high alkali, urea and salt consumption can be avoided as the process functions without these chemicals. The degree Figure 10 (above). Influence of chamber climate in the ECONTROL Figure 11 (below). Comparison of colour yield with different dyeing processes. Figure 9. ECONTROL process comparison trials. and extent of the reduction of environmental pollution can be illustrated in two examples (Figure 12). A dye shop which dyes continuously at 40m/min. using the pad-dry thermofixing or pad-dry/padsteam process consumes approx. 144.7 tonnes per annum (t/a) of urea or 18095t/a of NaC1. In threeshift the figures are: approx. 434.3t/a of urea or 542+36t/a of NaC1. In the pad-dry thermofixing process, part of the urea is discharged with the exhaust air whilst the majority enters the waste water during the washing With the pad-dry/pad-steam process, INTERNATIONAL DYER JANUARY 1996 31

the high salt volume also has ' to be washed out after the steaming By comparison, only 7.24t/a of sodium bicarbonate are discharged into the waste water in one-shift operation, or 21,71t/a in three-shift operation with the ECONTROL This means that with the ECONTROL process, waste water from the washing process contains only 4-5% of the chemical freight otherwise found in dyeing processes employing 'state-of-the-art' technology. Avoiding high volumes of chemicals means an enormous cut in exhaust air and waste water contamination. Conclusion offers the continuous dyer a simple, economical, efficient, environmentally compatible, Figure 12. Comparison of annual chemical consumption on one-shift and three-shift operation of: ECONTROL vs. Pad-dry thermofixing vs. pad-dry/pad-steam procksses. ecological, energy-saving and controlled This process is an interesting alternative to the processes commonly used to date for the dyeing of cellulose fibres using reactive dyestuffs.0 Bibliography: [11 Ciba-Geio, Switzerland, Cibacron C Documentation, Edition 1987. [2] Monforts, Germany, and Zeneca Coloun, LK, ECONll7OL process using Procion dyes. Notes: (i) Based on a paper by: Dipl.-Ing Kurt van Wench, of Monforts Textilmaschinen GmbH & Co., Germany. [ii) ECOMROL is a trademark ofzeneca, LK. Electronic Control Services Ihe Power fo Conhrol Dyeing Machine Control Finishing Machine Monitoring Central Computers Seam Detection Check Weigh Recipe Production Production ControVPlanning OUR LATEST PRODUCT RANGE... THE RESULT OF OVER 10 YEARS EXPERIENCE IN TEXTILE CONTROL SYSTEMS... TOMORROWS SYSTEMS TODAY MACHINE CONTROL MACHINE CONTROL 32 INTERNATIONAL DYER JANUARY 1996