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| Issue date:01/06/2006 |
| ATA Journal for Asia on Textile & Apparel - Jun 2006 Issue |
| Source:Journal for Asia on Textile & Apparel |
| by Franz Peter Tolksdorf |
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The Econtrol process combining Controlled Coloration from DyStar with the Monforts Thermex machine technology incorporating humidity control is a progressive continuous dyeing process and an interesting alternative to conventional processes. The simple lab process and reproducibility allow a quick response, rapid batch changes raise capacity utilization, and lower energy costs and the reduced effluent loading supports sustainability.
Basic principle of the Econtrol process
The Econtrol process comprises just three steps: Application of the dye — drying — washing-off (Figure 1). The dyeing system must be carefully balanced to ensure complete fixation of the Remazol or Levafix dyes within the drying time.
However, complete fixation of reactive dyes is not possible in normal drying conditions because of the wet bulb temperature, which is a characteristic of all convection-based drying systems. It means that during drying, the temperature of the moist goods is far lower than the surrounding temperature.
Figure 1: Econtrol process route
Figure 2: Econtrol - fabric temperature and moisture content |
In normal drying processes the temperature on the goods can drop to 50-55°C. The exact temperature depends on the humidity of the air used to dry the goods. If humidity is 25% and the air temperature is 120°C, the temperature on the surface of the goods is around 68°C. If humidity is 30%, the temperature on the goods is around 71°C.
The Econtrol process uses this physical fact to fix the reactive dye during drying. Three key variables — time, temperature and humidity — are used to ensure accurate control of the dyeing process in the Thermex hotflue. Figure 2 shows a typical drying curve and the resultant temperature of the goods throughout the Econtrol dyeing process.
The goods should spend about 2-3 minutes in the hot flue. However, it should be noted that these are average values: the actual drying time depends principally on the material to be dried.
Recommended dyes, auxiliaries and alkali systems
Evidently, the dyes used in the Econtrol process have to be suitable for the process conditions. Since dyeing is completed in approximate 2-3 minutes, reactive dyes with high to medium reactivity are particularly suitable. All Levafix and most Remazol dyes can be used.
In practice, Levafix dyes are used for pale to medium shades, while Remazol dyes are used for medium to very deep shades. Dyes with double-MCT anchors such as Procion H-EXL and Procion PX are not recommended for the Econtrol process.
Soda ash or soda ash/NaOH is normally used as the alkali system. To ensure optimum reliability, it is essential to dose the alkali and dye solutions separately. For example, the following amounts of alkali are recommended for LevafixCA dyes:
Common auxiliaries used in continuous dyeing processes can be used, e.g. wetting agents, antimigration agents and, if necessary, sequestering agents.
A mild oxidant can be added to prevent reduction of the dyes. Urea is not essential for the Econtrol process but up to 50 g/l may be advantageous in some circumstances.
Features of the Econtrol process
Figure 3: Process variables in continuous dyeing processes
Figure 4: Process variables in Econtrol
Figure 5: Mathis laboratory steamer for the Econtrol-process
Figure 6: Time consumption for lab dips |
The fewer the variables affecting the dyeing process, the higher the probability of achieving this goal. The PDPS process in Figure 3 illustrates what is meant by process variables. According to this definition, 25 variables mean 25 parameters that can adversely affect the outcome of the dyeing.
By contrast, Figure 4 shows the process variables for the Econtrol process. This process contains 40% fewer variables, which means the possibility of making a mistake is reduced by 40%. That is only possible because the Econtrol process does not use a separate fixation step. By contrast, all other continuous dyeing processes require separate fixation of some sort.
In collaboration with Mathis, DyStar has therefore developed a method that allows accurate reproduction of the Econtrol dyeing conditions in the lab. This comprises a Type DH lab steamer especially adapted for the Econtrol process. This allows regulation of all process parameters that influence the drying and dyeing results on the Monforts Thermex Hotflue (Figure 5).
As an optional extra, a radiation pyrometer can be used to monitor the temperature of the goods. This allows optimum adjustment of the dyeing parameters to meet the requirements of different types of goods.
Using the Econtrol process can greatly improve efficiency in the lab. To illustrate this, Figure 6 compares the time required for an Econtrol dyeing and a pad-dry pad-steam dyeing.
In this comparison, the Econtrol process requires 35% less time.
The process also has a logistical benefit: since the goods are dry at the end of the Econtrol dyeing process, they do not have to be washed off immediately and can be stored without problem.
If the comparison is extended to the cold pad-batch process, an additional batching time of at least eight hours per dyeing has to be taken into account.
As an alternative to this laboratory steamer, all lab processes commonly used for cold pad-batch processes can be used. However, the performance is in no way comparable and these processes greatly increase the overall time required for the process.
Figure 7: Lab to bulk reproducibility with Levafix dyes on merc. CO
Figure 8: Lab to bulk reproducibility with Levafix dyes on corduroy
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Lab-to-bulk reproducibility
A quick lab process is no use if it cannot be transferred reliably to production conditions. Special attention was therefore paid to this in the development of the process. Figure 5 shows the lab unit as used by DyStar to work out production conditions for customers.
Figures 7 and 8 compare lab and bulk dyeings on various materials. All lab dyeings were produced on the Mathis unit. The illustrations show very clearly that there is a very high standard of lab-to-bulk reproducibility on a wide variety of articles. Values below DE 1.0 (measured in accordance with CMC) can be achieved without difficulty and can be optimized on production machinery.
Econtrol can be used to dye all shades that can be obtained with reactive dyes. That includes brilliant turquoise, deep bordeaux, deep navy and, of course, black.
So far this process has been used for fabric weights from 70 g/m² to 500 g/m². All cellulosic fibers can be dyed.
Energy and chemical requirements
The Econtrol process needs far less energy than the e.g. PDPS process because it cuts out the extra fixation step (steaming).
Figure 9: Consumption of salt and alkali, Econtrol vs. PDPS |
For chemicals, unlike the PDPS process, the Econtrol process does not require any salt. The amount of alkali is similar. The calculation below shows how high the salt requirements can be in the PDPS process: A total of 61,000 kg salt is needed in the PDPS-Process, to dye 1,000,000 m of fabric assuming a fabric weight of 350 g per running meter, a liquor pick-up of 70% and 250 g/l salt (Figure 9).
Limitation
Nevertheless, like all dyeing processes, Econtrol does have its limitations.
The first is that Indanthren dyes can be dried by using the Thermex hotflue but not fixed as an air free steamer is required for this.
Pale to medium shades can be dyed on PES/CO blends using a modified one-bath TTN process but a separate thermosol step is required after the Econtrol step. Consequently, at least two Thermex chambers are required.
More experience is needed to obtain reproducible dyeings on very lightweight qualities (<60 g/m²) than on heavier fabrics.
The Econtrol process is not entirely suitable for heavyweight pile and loop pile goods such as terry towelling because there is a risk of frosting.
The appearance of some goods dyed under Econtrol conditions differs from their appearance in the PDPS process. This means the two processes are not always interchangeable.
Source: DyStar Textilfarben GmbH & Co
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| Copyright © Adsale Publishing Limited. Any party needs to reprint any part of the content should get the written approval from Adsale Publishing Ltd and quote the source "ATA Journal for Asia on Textile & Apparel", Adsale Textile English Website - www.AdsaleATA.com. We reserve the right to take legal action against any party who reprints any part of this article without acknowledgement. For enquiry, please contact Editorial Department. |
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| Copyright © Adsale Publishing Limited. Any party needs to reprint any part of the content should get the written approval from Adsale Publishing Ltd and quote the source "ATA Journal for Asia on Textile & Apparel", Adsale Textile English Website - www.AdsaleATA.com. We reserve the right to take legal action against any party who reprints any part of this article without acknowledgement. For enquiry, please contact Editorial Department. |
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