Preparation of cotton fabric for printing:
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Gray cotton fabrics obtained from loom or knitting have to go through several steps to make printing useful. Cotton is a natural cellulosic fiber, which naturally contains proteins, pectin’s, oils, fats, waxes, and other waste products. There are also sizing items. https://bdfabric.com/history-of-textile-printing/
During spinning and weaving, various waste sticks to the fabric. The fabric is used for dyeing and printing by removing these wastes. For cotton, the preparation process is usually completed by following the steps below.
# Preparation of cotton fabric for printing-Brushing:
In this process, the dust, small fibers, and other wastes on the cloth are removed with the help of the brush.
In this process, all the projecting fibers, hairy fibers, yarn, etc. which are located on the surface of the cloth are burnt. As a result, the fabric is smooth and bright.
The importance of this process is immense for the perfect design of the cotton fabric. For this, Singeing is considered a very important and essential process from the point of view of printing. Gas singeing machines are one of the most important types of singeing machines.
This process uses two gas burners to simultaneously burn projecting fibers, hairy fibers, etc. on both surfaces of the fabric. In addition, no defects are observed in the fabric during the singeing process. It is a continuous process called production. In this case, sometimes there may be a fire in the clothes. So the singeing cloth is quickly pulled with the help of a drawing roller and immersed in the water tank or de-sizing box. As a result, there is no risk of damage to the fabric.
# Preparation of cotton fabric for printing-De-Sizing:
De-sizing is done to tighten the warp yarn before knitting or weaving the fabric in the loom and to remove the Hairiness condition of the yarn. After weaving the cloth in the loom, the gray cloth has to be used for printing through various wet processes like Scouring, Bleaching, etc. But due to the presence of sizing products in the fabric, the described processes are severely hampered. To overcome this problem, sizing products have to be removed from the fabric. Starch is the main sizing product, in fact, de-sizing means removing the starch.
The chemical method by which starch is removed from woven fabrics is called de-sizing. This increases the water absorption capacity of the fabric and saves time, labor, and chemicals in the scouring and bleaching processes.
The most interesting method of removing starch from the cloth is enzyme de-sizing. This enzyme is a type of bio-catalyst. These are high molecular weight proteins. This enzyme removes starch from fabrics under special conditions. The action of enzymes is usually controlled by the temperature, concentration, time, and PH of the solution. Temperature is a very important issue. Most enzymes cannot function above 750C.
The enzyme de-sizing method involves the de-sizing of cotton cloth in a continuous process. Hydrolysis of the enzyme is completed by treating the fabric at a temperature of 50-60°C and piling it for 3-4 hours with 0.5% to 2% malt extract by weight. The dissolved starch is then removed by washing in water. Here the PHof the solution is kept at 6 to 7.5. However, in this method, the concentration, PH, and temperature of the solution should always be kept under control. Finally, the cloth is squeezed and prepared for the next process.
After removing starch from the cloth, oil, fat, wax, and other waste products are left in the cloth as waste. The ability of the fabric to absorb all these waste products is hampered. This hinders the subsequent processing of the fabric such as dyeing and printing. The scouring process is required to overcome this problem of fabric and also to make the fabric useful for printing.
In this process oil, fat, wax, and other wastes are removed from the cloth by adding alkali or detergent. The result is that the fabric is naturally cleaner and has more water absorption capacity, which is essential for the printing process.
Cotton scouring is usually done in a Kier boiler. Kier is a special pot made of iron. It is called Kier Boiling because the cloth is boiled in Kier. The cloth is kept in the form of rope. Boiling for 2 hours at a temperature of 125°C to 130°C with 2 to 5% alkali, 2 to 3% Soda ash, and 1% wetting agent by weight of the fabric removes oil, fat, wax, and other waste from the fabric. The cloth is then washed with cold water in the kier. However, care must be taken during boiling so that the clothes do not come in contact with air. Otherwise, the cotton reacts with the oxygen in the air to form oxy cellulose and the cotton is damaged.
# Preparation of cotton fabric for printing-Bleaching:
Bleaching is the last step in the process of making cotton fabrics suitable for printing. The natural dyes are left on the fabric after all the natural and concentrated waste has been removed from the fabric through the previous processes. This natural color prevents the printing process of the fabric from being perfect and attractive. Therefore, it is necessary to remove this natural color to make the fabric suitable for printing by eliminating this problem. Therefore, through the process of bleaching, the natural colors are removed from the fabric and the fabric is whitened in a real and permanent way. As a result, after printing on the fabric, a sharp and perfect design is observed.
Hydrogen peroxide is commonly used for bleaching cotton fabrics. Also used with Caustic Soda, Sodium Silicate, and Hydrogen Peroxide. . Here the PH of the solution is 10.9 i.e. in alkali solution, and boiling temperature is present so the continuous method in J-box may result in simultaneous scouring and bleaching. The fabric is then washed first with hot water and then with cold water to prepare for the printing process.
By this process, cotton cloth is endowed with some special qualities. When printed on mercerized fabric, it creates a special kind of printing effect. With the help of this process, the cotton yarn or fabric is treated at room temperature (18°C) with the help of caustic soda with a concentration of 55 to 65 towadel.