Industrial applications of reactive dyes -
Explanation -
(3) Continuous Dyeing -
The idea behind continuous dyeing is that the reaction between cellulose and reactive dye happens quickly, at a high temperature, and with a high pH level when there is water and alkali present.
There are two procedures available, depending on the dye's reactivity:
(A) Single padding process
(B) Double padding process
Explanation-
(i) Single padding process -
The pad liquor contains the dye and Alkali and fixation is finished at a Higher temperature. Urea and sodium alginate (migration inhibitor) also are added to the dye bath.
The following sequence is possible:
(a) Pad (soda ash, urea) dry bake -
In this process, reactive dye together with the Wetting agent's soda ash(10 to twenty GPL) and urea(200 GPL) is padded onto the fabric. After padding the fabric is dried at 110°C followed by a backing treatment for 3 minutes at 160°C or 30 seconds at 200°C.The main function of the area is to facilitate the dissolution of the dye and its hygroscopic properties are useful during baking when no water is present. This is most suited to heavy shades with good fixation. To avoid migration and uneven dyeing, a decent hot flur drier giving slow and even drying is critical.
This sequence is shown in the figure below-
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| Pad(soda ash + urea)- dry-bake process |
(b) Pad (bicarbonate) dry process -
This is a useful method for producing light and medium shades at an occasional cost and with ease.Heavy hues are often satisfactorily dyed by altering the procedure and adding a high quantity of urea to the padding fluid.
The dyeing process is illustrated in the fig below. Care must be taken to forestall migration and uneven dyeing by providing slow, even drying within the hot flue dryer.
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| Pad(bicarbonate) dry process |
(c) Pad (bicarbonate) steam process -
The equipment needed for dyeing is minimal during this technique. it's a high rate of productivity and is especially well matched for producing top-quality pastel colours on rayon.For optimal results, a high expression padding mangle and a reliable steamer are required. the choice would be supported by the dyes' affinity, therefore choosing the correct dyes is important.
the method flow is depicted in fig. below.
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| Pad(bicarbonate) steam process |
(d) Pad (bicarbonate) dry steam process -
This method works with all shade intensities, and quick steaming durations can be used to get the most output. It can be applied to any type of fabric to get excellent results. In the figure below, |
| Pad(bicarbonate)-dry-steam process |
(e) Pad (soda ash) dry Steam Process -
While less appealing than process (d) as previously mentioned due to the longer steaming time (8 to 10 minutes), this method is especially useful when combined with textile printing. The following set of procedures is employed.
Sequence - Pad > dry > print > dry > steam > wash off (Soda ash)
Many reactive dyes (H brands) are dischargeable, allowing the method to be used for discharge printing. To minimise facing, it is advised to resist salt L.
The figure following illustrates the order of processes when utilised for dyeing.
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| Pad(soda ash)- dry - Steam Process |
(ii) Double padding process -
In this procedure, the cloth is first padded with the dye solution, followed by another padding step (with or without intermediate drying) with an alkali solution containing a lot of salt to prevent bleeding, and finally streaming.
The figure following shows the stages in detail.
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| Pad-dry-pad(alkali)-steam process |
(a) Pad dry pad (alkali) steam process -
This process enables the employment of all the method brands whether cold dyeing or H brand thus making it possible to combine both the brands and offering the widest range of shades.
The salt within the padding bath reduces any bleeding of dyestuff from the padding material into the Alkaline bath.
After hot drying, the fabric is padded through an answer containing hydrated oxide and salt. The cloth is then passed immediately into the steam chamber.
(b) Pad (dye) pad(alkali) process (molten metal method):
This is also a double padding process.
The fabric is padded with the dye solution and goes through the alkali bath at the highest of the primary arm of the U -tube containing molten metal.
The dye is padded through the molten metal bath and it then emergers after passing through a salt, bath to be finally washed and soaped in an open soaper, as illustrated in the figure below.
The steadfast molten metal process is especially suitable for the assembly of very top quality pale to medium depth dyeing on all classes of yard goods.
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| Pad(dye)-pad(Alkali) process (molten metal method) |
Method | Equipment required |
(a)Pad(soda ash and urea)dry-bake | Padding mangle, drying equipment does not cause dye migration eg- good hot flue; backing oven giving 125°C for 3 to 5 minutes reaction time 6 to 8 box Washing range |
(b)Pad-dry(bicarb onate) | Padding mangle; drying equipment eg-good not flue, stenter or cylinders;6-8 box Washing range (open soaper) |
(c.)Pad-(carbonat e)-steam | Padding mangle giving high exhaustion, good quality steamer giving dry steaming conditions;6 to 8 box Washing range |
(d)Pad(bicarbona te)-dry-steam | Padding mangle drying equipment, preferably a good hot flue; a steamer giving at least 10 seconds steaming time;6-8 box Washing range |
(e)Pad(soda ash)-dry-steam | Padding mangle; drying equipment, preferably a hot flue, steamer giving at least 5 minutes steaming time;6 to 8 box Washing machine |
(f)Pad-dry-pad(alkali)-steam | Conventional Pad-steam range as used for vat dyeing |
(g)Pad-pad(alkali)in molten metal range | Padding mangle; Standfast molten metal machine;6-8 box Washing range |
Table - Combined and comparative study table
This table is a summary of the machines required for the different continuous methods described and the type of dyes most suitable for the process.
Questions -
- What are the Industrial applications of reactive dyes?
- Describe the continuous dyeing process for reactive dyes.
- Describe the single padding continuous dyeing process for reactive dyes.
- Describe the double padding continuous dyeing process for reactive dyes.
Continue reading,
Part 2 Classification of Reactive dyes
Part 3 The reaction of MCT and DCT of reactive dyes
Part 4 General Factors affecting the results of reactive dyeing
Part 5 Reactive dyeing method - DCT
Part 6 Bifunctional systems of reactive dyes
Part 7 Development of reactive dyes
Part 8 Reactive dyes on Silk and nylon with their application
Part 9 Industrial applications of reactive dyes
Part 10 After treatment of reactive dyes
Writer - Rushikesh Patil (Textile Engineer)
