Overview Of Dyeing And Printing Process

Overview of Dyeing and Printing Process

Textile industry is one among the important GDP contributing industries of India. It alone brings 17% of the foreign currency to India. In India, Surat, Mumbai, Indore and Ahmadabad are the prime hubs for textile industry. Surat alone contributes 45% of the total production. Thus, this sector is the biggest customer of Gujarat Gas consuming 60% of the total gas over the years in Surat LDZ. Textile industry comprises of Fibre Chips manufacturers, Yarn units, Dyers & Printers and Traders. Major sectors complimenting and facilitating for this industry are Chemicals & Dyes and Transport. India has the world’s 2nd largest capacity in yarn manufacturing. Weaving and Chips formation is what India needs to improve upon. India’s clothe quality is not as good as the leading countries of world. Surat has a large number of dyeing and printing units competing at global level. Following is the detailed explanation of Dyeing and Printing Operations carried out by Saree/Cloth Processing Units in Surat, India.

Dyeing Process: Following is the layout of dyeing process:

Fig 1: Flow Diagram of Dyeing Process Various unit operations carried out in the process are explained furtherJet/Beam Dyer: Colouring on clothes is done by two processes, Jet Dye and Beam Dye. Beam dye is for delicate clothes like Nylon. In Jet Dyer, logs of cloth of 100 m (Approx 8 kg) are inserted in the Jet dyer. Colour is inserted in the vessel in form of a jet by nozzles and it gets uniformly settled in cloth. There are various capacities of Jet dyers ranging from 200 kg to 500 kg. The cloth is heavily packed to around 90-95% of capacity. Steam is used as a medium for dyeing. In Beam Dye, cloth is revolved around a beam and inserted in the vessel. Beam is empty from inside facilitating the inward and outward path for cloth to get dyed. This method is used to cancel out the chance of possible wear and tear of cloth in Jet Dyeing.

Padding is done for multi-colouring of cloth. The equipment is similar to Zero-Zero (explained further) added with a width setter. While cloth passes between the rolls, multicoloured bands get contoured on the cloth. Drum Washer: Function of Drum washer is to provide strength to the cloth. It does so by inserting micro particles called “Dana” in the pores of cloth. These Danas can be seen by naked eye and easily differentiated from a Dana-less Cloth. It is also operated on steam. Stentor: Stentor is the most important and costliest equipment in the dyeing process. Its function is to dry and adjust the width of the cloth post dyeing operation. The cloth after dyeing operation gets wet and squeezed. After feeding to stentor, it is stretched horizontally, accordingly to the demand by customer. Each cloth has its own limits of harmless stretching and based on those this operation is carried out. After stretching, the cloth is moved on to the drying chambers. Stentors with 3-6 chambers are generally used in industries. Each chamber has 2 cylinders. A 4 chamber stentor can process 80,000 – 1, 00,000 m of cloth in a 24 hour run. Each cylinder utilizes 100 SCMD of Natural Gas for such operation making total consumption equal to 800900 SCMD. 3 chamber Stentors can process up to 75,000 m/day of cloth. Zero-Zero: It acts like a big iron press giving smoothness to the dried and crushed/wrinkled cloth coming out of stentor. It is generally operated on steam. Natural gas can also be used with necessary changes. It contains two rollers having steam enclosed in them. The cloth gets dried while passing in between the hot rollers. Folding: Folding is done to layer down the long stretches of clothes as we do with sheets in our home. These long cuboidal folds are marked with stickers notifying the length of cloth in each fold. These folds are then sent to the respective customers/ storage/ units. It is largely an electric process.

Printing Process: Printing process is a complex process with contributions from various small processes.

Fig 2: Flow Diagram of Printing Process The operation of Jet/Beam Dyer and Stentor is similar to as carried out in Dyeing. Rest of the process is explained below in detail:Printer: Printer is the part imparting complexness to the whole process. Printing operation is carried out with the help of specially designed screens. For better understanding lets divide the process in two parts: 1) Formulation of Screens 2) Printing Operation

1) Formulation of Screens: Screens perform the action to implement design on the cloth. Screen formation starts with the sketching of design on a computer. The complex design is then split into simple designs. Print out for each design is taken on a separate PMF (Plastic metal film). This PMF is placed over a transparent glass emitting light of Ultraviolet tube lights. Then, a bolting sheet is placed over the PMF and image of PMF is taken on this Bolting sheet. The sheet is then washed with water to clarify the image. This sheet is attached with a supporting iron frame similar to Photo-frames. Drying of these frames is done in sunlight or a dryer operating on Natural Gas/ alternate fuel source. Thus, photo frame for each simple design unit is made. These photo frames act as a screening and printing medium.

2) Printing Operation: The screens/ frames are placed adjacent to each other on a printing table. Printers are generally are of two types: 1. Semi automatic flat bed moving printer, 2. Fully Automatic Rotary Printers. The length of flat bed printer varies from 20-30 m. In the flat bed moving printer, cloth cyclically moves on the belt of printer. It moves for a specified distance and stops. While the belt is stagnant, operator manually passes colour onto the screen with the help of a roller. Colour gets sprinkled only from the pores in the design pattern and adjusts on the cloth. Print for each section gets contoured on the cloth and last step provides the final design. Some manufacturers use Natural gas in the printing machine to provide mild heating to the cloth while it moves between sections. Chemical Treatment: The function of chemical treatment is to apply softening chemicals and chemicals that limit the mass transfer of colour on the cloth. A printed cloth contains many colour, function of these chemicals is to refrain these colours to get carried over on each other. For this process, cubical washing ditches/ pools of 4-5 ft are used. A rotor is used to rotate the water/ chemical in these ditches for mixing with cloth. Looping: After the printing operation, cloth gets a colour that can be easily washed away. After chemical treatment, such a printed cloth is passed through a loop which helps in strengthening of the colour. It is done in the absence of moisture with the help of superheated steam. Natural gas is used as a fuel to preheat the steam to reach to its critical temperature where it looses all the moisture content. This is a 24 hour process. Stentor-2: After looping, the cloth’s width is again set and it is dried with the help of stentor. Number of chambers in the stentor vary from 3-6. Zero-Zero: It acts like a big iron press giving smoothness to the dried and crushed/wrinkled cloth coming out of stentor. It is generally operated on steam. It contains two rollers having steam enclosed in them. The cloth gets dried while passing in between the heated rollers. Natural gas can also be used with necessary changes. Folding:

Folding is done to layer down the long stretches of clothes as we do with sheets in our home. These long cubical folds are marked with stickers notifying the length of cloth in each fold. These folds are then sent to the respective customers/ storage/ units. It is largely an electric process.