E-control Dyeing Process: Features, Basic Principle and Benefits

What is E-control Dyeing Process?
E-control / Econtrol dyeing process is an energy efficient technique as it is a combination of continuous batch process and drying process. It is one of the few real inventions in process development and machinery in recent years. E-control dyeing process was introduced by Dystar and Monforts in ITMA in 1995 to provide the textile dyer with a dyeing system that would produce a simple, rapid, and economical, continuous dyeing method for cellulosic fibers with minimal chemical usage. The most significant and unique feature of this process is that it does not use a separate fixation step, i.e., steaming, curing, or dwell time, which is essential and associated with the conventional reactive dyeing methods in practice. It can be used to dye all ranges of shades that can be obtained with reactive dyes through various dyeing processes on all cellulosic fibers such as cotton, viscose, tencel, and linen.

Ecology and economy are among the most used catch words of our time, and their significance is of the greatest possible importance for the survival of textile industry. Where continuous dyeing with reactive dyes is concerned, economic efficiency means employing dyeing process and techniques, which help to withstand international price cut and stay competitive. Simplified or reliable processes with greater color yields yet with a smaller usage of auxiliaries and energy must be the aim.

To understand the emergence of the e-control process and its success, the following points are to be considered by the dye houses.

  1. The number of shades to be dyed has risen steadily with higher fastness specifications.
  2. Environmental regulations have become more stringent.
  3. Batch sizes have declined dramatically.
  4. Delivery times are reduced.

Traditionally, four dyeing processes have been employed to dye cotton and viscose with reactive dyes by continuous method (Figure 1). They are as follows:

  1. Cold pad-batch.
  2. Pad-dry Thermofix.
  3. Pad steam.
  4. Pad-dry chemical pad-steam.
dyeing methods by reactive dyes
Figure 1: Dyeing methods by reactive dyes

The characteristic features of the mentioned continuous reactive dyeing processes for cellulosic fibers are given in Table 1.

Table 1: Characteristic features of continuous reactive dyeing processes

Processes Drying Fixation (°C) Fixation medium
Pad-batch 20–35 Padding liquor
Pad-wet steam 102 Steam 100%
Pad Thermofix 110–130°C 160 Air
Pad-dry chemical pad-steam 110–130°C 102 Steam 100%

The selection of dyeing process depends upon many factors, most importantly the cost of the process. Most of the processes use high temperature (100–160°C) and hazardous chemicals (urea, sodium silicate, and salt) in order to achieve maximum yield. The limitations of these dyeing processes are listed in Table 2.

Table 2: Limitations of most common dyeing processes

Dyeing process Drawbacks
Pad-batch High fixation time, bath stability
Pad-dry Thermofix Low light fastness, damage of elastan, yellowing
Pad-wet steam Limited yield, tailing
Pad-dry chemical pad-steam Special machine necessary, high energy demand

Features of E-control Dyeing Process:
The demands made on future-oriented dyeing systems include the following criteria:

  • Economical, even when dyeing small batches
  • Rapid color changes
  • Simple to use
  • Suitable for brilliant, very pale and very heavy shades
  • High reliability due to excellent reproducibility
  • A simple lab dyeing method must be available
  • Environment friendly
  • Process should not restrict the obtainable fastness properties
  • Short processing times.

In other words, the aim is to achieve optimum results in the shortest possible time. The fewer the variables affecting the dyeing process, the higher the probability of achieving this goal. According to this definition, 25 variables mean 25 parameters that can adversely affect the outcome of the dyeing. This process contains 40% fewer variables, which means the possibility of making a mistake is reduced by 40%. That is only possible because the E-control process does not use a separate fixation step. By contrast, all other continuous dyeing processes require separate fixation of some sort. There are also a number of other variables that are not directly related to the dyeing process. As a rule, far too little attention is paid to these parameters, especially the quality of the dyes and chemicals used.

Why E-control Dyeing Process is Essential?
The necessary economical and environmental benefits, which could be achieved with respect to the other conventional processes for continuous dyeing, were assessed. The main priority was to assess the color yield achieved by different processes and to point out fastness requirement level. Since then 65 units have been installed worldwide, allowing more economical and more ecologically friendly dyeing by continuous application.

Following are the main reasons for econtrol dyeing process:

  1. The number of shades to be dyed has risen steadily
  2. At the same time, textile finishers are expected to meet higher fastness specifications
  3. Environmental regulations have become far more stringent in many parts of the world
  4. Batch sizes have declined dramatically
  5. Price pressure has risen enormously
  6. Delivery times are far shorter than in the past

One of the major challenges facing textile finishers is the reduction in batch sizes. After all, capital investments tend to be geared to a defined production capacity. Output levels thus have a lasting impact on the capacity utilization of a unit. Such changes evidently have a direct impact on textile mills. To maintain output levels, far more batches have to be dyed within the same time. Naturally, that also increases the number of lab matchings required. Let us look at capacity utilization in more detail. Many dyeing mills aim for 75% capacity utilization. Assuming an average batch size of 11,000 m, that means about 60 min are available to change shades. By contrast, if the average batch size were 1000 m, a 60 min changeover time would reduce capacity utilization to under 20%, making economical operation impossible.

To achieve 75% capacity utilization in these conditions, the changeover time would have to be cut to 5 min. Dyeing processes and products therefore have to be adjusted to reflect these conditions. Production personnel also need to adapt. That was the trigger for the development of the E-control process.

Basic Principle of E-Control Dyeing Process:
The e-control process comprises just three steps:

  1. Application of the dyes through padding
  2. Drying
  3. Washing-off as shown in Figure 2.
E-control continuous dyeing method for cellulosic fibers
Figure 2: E-control continuous dyeing method for cellulosic fibers

The dyeing system must be carefully balanced to ensure complete fixation of the Colron reactive 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. 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 E-control process uses this physical fact to fix the reactive dye during drying.

The dyeing range is a simple arrangement shown in Figure 3. The range is started with a lead fabric, which brings water into the installation through the wetting arrangement in order to establish the chamber climate. The jet temperature is 120°C. After a short time, the bath containing the dye liquor is raised and the fabric is impregnated with dyestuff. When the dye goods reach the wetting arrangement, this is turned away. A measuring device controls and regulates the steam content of the atmosphere in the hotflue. The goods dwell for 2 min in the hotflue and the reactive dyestuff is fixed to the fiber with a high yield. Owing to the mild fixation climate in the machine compared to that in other common dyeing processes, soft fabric handle is obtained. Econtrol is the registered trade mark of Dystar.

E-control process steps
Figure 3: E-control process steps (1) Feeding section, (2) pad mangle, (3) wetting unit, (4) Thermex hotflue, (5) measuring and control unit (chamber atmosphere), (6) steam injection unit, (7) outlet section

Benefits of E-control Dyeing Process:

Ecological benefits:
The E-control process simultaneously offers the following ecological benefit: The combined reduction in the quantities of chemicals (urea, salt, and sodium silicate), and dyes from the recipe, also the water used for washing-off process, greatly cuts down the effluent load discharged from the dye house to the environment.

Economical benefits:
The E-control process offers the following significant economic advantages:

Lower chemical cost: This is owing to the elimination of the usage of various chemicals and auxiliaries that include urea, salt, and sodium silicate, and are considered essential for the reactive dyeing process.

Lower dyes cost: This is due to the higher fixation yield, that is, less dye would be required to obtain the required depth of shade on the fabric.

Lower water cost: As a result of greater fiber–polymer reaction, the hydrolysis of dyes will be lower and hence, the washing-off process would definitely utilize less volume of water.

Lower energy cost: In consequence of the exclusion of the thermofixation step during the continuous dyeing process on the Thermex Hotflue, reduced thermal energy would be needed for the fiber–polymer reaction to take place.

E-control dyeing process also has a logistical benefit:
As the fabric is in dry state at the end of the E-control process, they do not have to be washed off immediately and can be stored. Now it can be said that the new dyeing technology is more economical despite its somewhat higher investment cost (hotflue plus accessories).

Conclusion:
The key issue that will concern the continuous dyer in the future would be the search for the dyeing process which must be simple to use for ranges of shade, and can provide the dyer the economy, even when dyeing small batches, and rapid color change, as the duration of the fashion trend is on fall worldwide, plus it should be reliable, due to excellent reproducibility, and without any harm to the environment. The continuous dyeing on Thermosol machine would continue to deliver all these features in the shape of economical and ecological dyeing process, that is, e-control.

References:

  1. Textile Dyeing By Dr. N. N. Mahapatra
  2. Econtrol Dyeing Process: An Ecological and Economical Approach by Shamshad Ali, Zeeshan Khatri, and Khan Muhammad Brohi (Energy, Environment and Sustainable Development)
  3. E-control: The Ecofriendly Process by Ajinkya Khot and Chandrakant Lende (Fibre2fashion.com)

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