Dyeing Process

Types Of Dyeing Process
For dyeing with reactive dye mainly three types of process are available they are:-

1. Continuous Dyeing Process
2. Semi continuous Dyeing Process
3. Discontinuous Dyeing Process

Continuous Dyeing Process

The working of a continuous dyeing process is described here. The textile substrates are feeded continuously into a dye range. The speeds can vary between 50 to 250 meters per minute. According to Industry estimates Continuous dyeing is a popular dyeing method and accounts for around 60% of total yardage of the products that are dyed.

A Continuous dyeing process typically consists the following. Dye application, dye fixation with heat or chemicals and finally washing. Continuous dyeing has been found to be most suitable for woven fabrics. Mostly continuous dye ranges are designed for dyeing blends of polyester and cotton. The step of padding plays a key role in the operation of continuous dyeing. Sometimes Nylon carpets are also dyed in continuous processes, but the design ranges for them is unlike that for flat fabrics. Warps are also dyed in continuous process. Very good examples of such warp dyeing are long chain warp dyeing and slasher dyeing using indigo.

A continuous dye range has been found useful and economically sustainable for dyeing long runs of a given shade. One important factor that separates continuous dyeing from batch dyeing is the tolerance factor for color variation. That is more for continuous dyeing as compared to batch dyeing. This is so because of two reasons a) the speed of the process. b) presence of a large number of process variables which affects dye application. The process that is illustrated below is designed for dyeing of blended fabric of polyester and cotton.

Name Of Some Continuous Dyeing Process

1. Pad-steam process
2. Pad-dry process
3. Thermosol process

Pad Steam method

This technique is mainly used for scouring woven fabric and dyeing. It is particularly suitable for the application of direct, vat, sulphur and reactive dyestuffs.It includes the following steps:

• Impregnation by padding
• Steaming (at about 100 °C)
• Additional impregnation of the fabric with developing agents (e.g. reducing agents in vat or sulphur dyeing)
• Washing and rinsing.

In this process, the fabric is padded with the dye solution with 60-80⁰C and then fabric is passed through drying chamber. Then the fabric is padded with chemical (NaOH+Salt). Then the fabric is passed through a chamber at 102 C for 30 sec. Then fabric is washed in open width washer.The diagram is given below:-

Semi-Continuous Dyeing Process

In the process 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 done at room temperature while in pad-roll it is done at increased temperature by employing a heating chamber. This helps in fixation of the dyes on to the fibre. After this fixation process, the material in full width is thoroughly cleansed and rinsed in continuous washing machines. There is only one point of difference between Continuous and semi-continuous dyeing process is that in semi-continuous dyeing, the dye is applied continuously by a padding. The fixation and washing remaining discontinuous. Liquor Ratio in semi-continuous dyeing is not of much importance and is not taken as a parameter. One of the widely used techniques for semi-continuous dyeing process is the Pad Batch Dyeing a schematic diagram is given here for the semi-continuous dyeing process.

Name Of Some Semi-Continuous dyeing Process

1. Pad Batch
2. Pad-jig process
3. Pad-roll process

Pad Batch Process

Pad Batch Dyeing is one of the widely used technique for semi-continuous dyeing process. It is mainly used in the dyeing of cellulosic fibre like cotton or viscose (knit and woven fabric) with reactive dyes. Pad batch dyeing is a textile dyeing process that offers some unique advantages in the form of versatility, simplicity, and flexibility and a substantial reduction in capital investment for equipment. It is primarily a cold method that is the reason why it is sometimes referred to as the cold pad batch dyeing.

Discontinuous/Batch/Exhaust Dyeing Process

Batch Dyeing Process is the most popular and common method used for dyeing of textile materials. Batch dyeing is also sometimes referred to as Exhaust dyeing. This is because in this process, the dye gets slowly transferred from a comparatively large volume dyebath to the substrate or material that is to be dyed. The time taken is also longer. The dye is meant to 'exhaust' from dyebath to the substrate. In batch processes, textile substrates can be easily dyed at any stage of their assembly into the desired textile product. This includes fiber, yarn, fabric or garment. Some type of batch dyeing machines can  function at temperatures only up to 1000^oC. For example cotton, rayon, nylon, wool etc. can be dyed at 1000^oC or lower temperatures. While polyester and some other synthetic fibers are dyed at 1000 Centigrade or even higher temperatures. There are three general types of batch dyeing machines. The first type is the one where there is circulation of fabric. Second type is the one where the dyebath gets circulated while the material that is being dyed remains stationary, and finally the third type where both the bath and material to be dyed gets circulated. Examples of dyeing machines that utilizes batch dyeing process are Beck, Jet, Jigs, Beam Package dyeing machines etc.