Effect of water quality on textile printing and dyeing

（1） Difference between soft water and hard water:

Water is soft water and hard water. Water without or containing a small amount of calcium and magnesium ions is called soft water, otherwise it is called hard water.

Hard water is divided into:

(1) Temporary hard water: the hardness component of water, if caused by sodium bicarbonate or magnesium bicarbonate, is temporary hard water (boiling temporary hard water, decomposing sodium bicarbonate, precipitated by insoluble carbonate, water turns from hard water to soft water).

(2) Permanent hard water: if it is caused by sulfate or chloride containing calcium and magnesium, it is permanent hard water and cannot be removed after boiling.

The above two kinds of hardness are collectively called total hardness. According to the total hardness of water:

The total hardness of 0-30ppm is called soft water, the total hardness of more than 60ppm is called hard water, the total hardness of high-quality drinking water is less than 25ppm, and the total hardness of high-quality soft water is less than 10ppm.

In natural water, unpolluted rainwater and snow water far away from the city belong to soft water; spring water, stream water, river water and reservoir water mostly belong to temporary hard water, and some groundwater belongs to high hardness water.

When water droplets condense in the atmosphere, they dissolve carbon dioxide in the air to form carbonic acid. Carbonic acid eventually falls to the ground with rain water, then seeps through the soil to reach the rock layer, dissolves lime (calcium carbonate and magnesium carbonate) to produce temporary hard water, which is the formation of hard water in karst caves and near karst caves in some areas.

The influence of water quality on textile printing and dyeing is as follows

Due to different water sources, the water quality of printing and dyeing plants is also different. The hardness of water quality in southern China is lower, while that in northern China is higher. Generally, printing and dyeing plants use natural surface water or groundwater and tap water.

Untreated natural water has a variety of chemical substances, mainly including calcium, magnesium, iron, sodium, carbonate, sulfate and chloride, which will have a great impact on textile dyeing.

The quality of textile printing and dyeing also has certain requirements relative to the water quality. The consequence of hard water is that it will affect the bleaching effect, uneven dyeing, poor handle and yellowing of the fabric. The addition of softener will increase the dosage of caustic soda and other auxiliaries.

Calcium and magnesium, which are difficult to dissolve in water, will precipitate on the fabric and form scale in alkaline solution, which will adhere to the equipment and hinder production. When the iron and manganese salts in water exceed the standard, rust spots and catalytic oxidation of cotton fiber will easily occur during boiling. Iron, manganese and salt also catalyze the decomposition of the bleach.

The factors that affect the dyeing quality include: color, pH value, iron ion content, calcium ion content, etc.

When reactive dyes are used for dyeing, the hardness of water quality has little effect, while when acid dyes are used for dyeing nylon, the hardness of water quality is more prominent. The excellent water quality not only makes the color of fabric poor, but also the CI in water has a great effect on dyeing.

The hard water suspension affects the bleaching whiteness of the fabric. When dyeing the cheese, it is easy to reduce the brightness of the inner and outer layers of the cheese. The high pH value of the water quality will affect the levelness of the light colored fabric, because the dyes added under alkaline conditions will be fixed, resulting in poor levelness and dyeing flowers.

If the pH value of the water is too high, the dye will be hydrolyzed in the soaping process, and the reproducibility is poor. If the water is too soft, the pH value of the cloth will exceed the standard.

The main reasons for yellowing of bleached fabrics are excessive iron ions, which can cause color spots, color flowers, color fading and excessive manganese ions.

The hard water quality will affect the brightness of the color, cause scaling of the heat exchanger, cause large energy loss, and cause alkali spots due to insoluble precipitates formed by calcium and magnesium ions and soda ash.