Textile Dyeing Process, Chemistry tutorial

Introduction

In every sphere of industrial activity colour is required. Dyeing machine is the device that is employed via different industries for imparting colours. From paper to plastic to textiles everywhere there is utilize of Dyeing Machinery. According to require of each kind of substrate, different set of machines are put to utilize. The applications of this machinery give an impetus to the products related to dyeing. Though, increasing energy prices is having a knock-on effect on manufacturing expenditure for dyeing machinery. Consequently, there will be greater interest globally in machinery  that  contain  a  lower  energy  consumption  along  through  heat resurgence systems that are able to preheat the incoming cold feed water.

Types of Dyeing Process

There are dissimilar kinds of dyeing mechanism depending on convenience and choice of materials to be dyed. Nowadays computers are employed to control and monitor all features of dyeing. Over the last twenty to thirty years, increases in dye chemistry have allowed the man-made fibre to be dyed through better fastness to light and washing, and in an ever rising range of colours.

Batch dyeing process

Batch dyeing procedure is the most popular and general technique utilized for dyeing of textile substances. Batch dyeing is as well sometimes termed to as Exhaust dyeing. This is since in this procedure, the dye gets gradually transferred from a comparatively huge volume dye bath to the substrate or material that is to be dyed. The time taken is as well longer.

The dye is meant to 'exhaust' from dye bath to the substrate. In batch procedures, textile substrates can be simply dyed at any stage of their assembly into the craving textile product. This comprises fiber, yarn, fabric or garment. Several kinds of batch dyeing machines can function at temperatures only up to 1000oC. For instance cotton, rayon, nylon, wool and so on. Can be dyed at 1000oC or lower temperatures, whilst polyester and several other synthetic fibers are dyed at 1000 oC or even higher temperatures. There are 3 common kinds of batch dyeing machines.

The 1st is the one where there is circulation of fabric. Second, is the one where the dye bath gets circulated while the material that is being dyed remains stationary, and finally the third, where both the bath and material to be dyed gets circulated. Instances of dyeing machines that utilizes batch dyeing process are Beck, Jet, Jigs, and Beam Package dyeing machines and so on.

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Fig: Image Showing Popular Machines Utilizing the Batch Dyeing

Continuous dyeing process

The working of a continuous dyeing procedure is explained here. The textile substrates are fed incessantly into a dye range. The speed can fluctuate between 50 to 250 metres per minute.  According to Industry estimates continuous dyeing is a popular dyeing technique and accounts for around 60% of total average yardage of the products that are dyed. A continuous dyeing procedure classically consists of the subsequent. Dye application, dye fixation through heat or chemicals and lastly washing. Continuous  Dyeing  has  been  originate  to  be  most  suitable  for  woven fabrics. Mostly continuous dyeing is proposed for blends of polyester and cotton. The step of padding plays a key role in the process of continuous dyeing. Sometimes nylon carpets are as well dyed in continuous processes, but the design ranges for them is unlike that for flat fabrics. Warps are also dyed in continuous process. Extremely good instances of these warps dyeing are long chain warp dyeing and slather dyeing using indigo.

A continuous dye range has been originated useful and economically sustainable for dyeing long runs of a following shade. One significant feature that divides continuous dyeing from batch dyeing is the tolerance factor for colour variation. That is more for continuous dyeing as compared to batch dyeing. This is so since of 2 causes (a) the speed of the procedure; (b) presence of a huge number of procedure variables that influences dye application. The procedure that is illustrated below is designed for dyeing of blended fabric of polyester and cotton.

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Fig: Schematic Diagram of a Continuous Dyeing Machine

Several of the popular processes in continuous dyeing procedure are Pad- steam, Wet-steam, thermosol dyeing, TAK dyeing, space dyeing, and pad-steam dyeing, long chain warp dyeing and so on.

Semi-continuous dyeing

In the procedure of semi-continuous dyeing that consists of pad-batch, pad- jig, pad-roll, the fabric is first impregnated with the dye-liquor, in what is called a padding machine. Then it is subjected to batch wise treatment in a jigger. It could also be stored with a slow rotation for many hours.

In the pad-batch this treatment is completed at room temperature whilst in pad-roll it is completed at enhanced temperature via utilizing a heating chamber. This assists in fixation of the dyes on to the fibres. After this fixation procedure, the substance in full width is methodically cleansed and rinsed in continuous washing machines. There is only one point of dissimilarity between continuous and semi-continuous dyeing procedure: in semi-continuous dyeing, the dye is applied continuously via padding. The fixation and washing remain discontinuous. Liquor ratio in semi- continuous dyeing isn't of much significance and isn't taken as a parameter. One of the widely utilized techniques for semi-continuous dyeing procedure is the Pad Batch Dyeing. A schematic diagram is specified here for the semi-continuous dyeing procedure.

The following table illustrates several of the significant machinery for semi-continuous and continuous dyeing processes.

Table: Main Features of Continuous and Semi-Continuous Processes

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Pad batch dyeing

Pad Batch  Dyeing  is  one  of  the  widely  employed  techniques  for  semi- continuous dyeing process. It is mainly utilized in the dyeing of cellulosic fibre as cotton or viscose (knit and woven fabric) by reactive dyes. Pad batch dyeing is a textile dyeing procedure that offers several unique benefits in the form of versatility, simplicity, and flexibility and a substantial reduction in capital investment for equipment. It is primarily a cold technique that is the reason why it is sometimes termed to as the cold pad batch dyeing.

Workings of a Cold Pad Dyeing Process

The technique or procedure utilized in pad-batch dyeing starts by saturating 1st the prepared fabric through pre-mixed dye liquor. Then it is exceeded throughout rollers. The rollers, or padders, effectively force the dyestuff into the fabric. In the process, excess dye solution is also removed. After elimination of excess dye stuff the fabric is subsequently 'batched'. This batching is done via either storing it in rolls or in boxes. It obtains a minimum of 4-12 hours. The batches are usually enclosed through plastic films. This prevents absorption of carbon dioxide and water evaporation.

At last as the reaction is complete the fabrics are washed. This is finished via becks, beams, or any other washing machines.

Special Features of Pad Batch Dyeing Process

1. Significant cost and waste reduction as compared to additional conventional dyeing processes.

2. Total abolition of the require for salt and other specialty chemicals. For instance there is no requiring for anti-migrants, leveling agents and fixatives that are essential in conventional dye baths.

3. Optimum utilization of dyes that removes specialty chemicals cuts down chemical costs and waste loads in the effluent. All this consequences in a formidable reduction in wastewater treatment costs.

4. Admirable wet fastness properties.

5. Pad batch dyeing cuts power and water spending owing to low bath ratio (dye: water) needed for the procedure. This is since unlike other dyeing processes it doesn't function at high temperatures.

6. A uniform dye quality is attained by even colour absorbency and colour fastness.

7. As compared to rope dyeing, pad batch dyeing generates much lower defect levels.

8. In pad batch dyeing, qualities as elevated shade reliability and repeatability are common. This is since of elevated reactivity dyes via speedy fixation rate and stability.

9. Lastly pad batch dyeing can as well get better product quality. The fabric undergoing the cold pad batch dyeing procedure is able to hold a consistently coloured appearance. It illustrates added luster and provides a gentle feel. The fabric provides a brighter look in shades.

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