Fabrics are inseparable from water during the printing and dyeing process. Apart from dyes, water quality has become one of the key factors affecting dyeing. People who know a little bit about water will know that water in nature can be divided into soft and hard water. Soft water refers to water that does not contain or contains a small amount of calcium, magnesium, and iron ions. Otherwise, it is called hard water. Hard water is divided into temporary hard water and permanent hard water.
hard water
(1) Temporary hard water: The hardness component of water, if caused by sodium bicarbonate or magnesium bicarbonate, is temporary hard water (boiling temporarily hard water decomposes sodium bicarbonate and precipitates with the insoluble carbonate generated, Water changes from hard water to soft water).
(2) Permanent hard water: If it is caused by sulfates or chlorides containing calcium and magnesium, it is permanent hard water and cannot be removed by boiling.
The above two hardnesses are collectively called total hardness, which is roughly divided according to the total hardness value of water: total hardness 0-30ppm is called soft water, total hardness above 60ppm is called hard water, high-quality drinking water does not exceed 25ppm, and high-quality soft water is generally The hardness is below 10ppm.
In natural water, unpolluted rainwater and snow water away from cities are soft water; spring water, stream water, river water, and reservoir water are mostly temporarily hard water, and some groundwater is 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 rainwater, then seeps through the soil to reach the rock layer, dissolving lime (calcium carbonate and magnesium carbonate) to produce temporary hard water. This is how hard water in and near caves in some areas is formed.
The impact of water quality on textile printing and dyeing
Due to different water sources, the water quality of printing and dyeing factories is also different. The water hardness in southern my country is lower, while the water hardness in northern areas is higher. Generally, printing and dyeing factories mostly use natural surface water or underground water and tap water.
Untreated natural water contains various chemicals, mainly 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 water quality. The consequences of hard water: it will affect the bleaching effect, uneven dyeing, poor fabric feel, and yellowing of the fabric. Adding a water softener will increase the amount of caustic soda and other auxiliaries. .
Calcium and magnesium, which are insoluble in water, will precipitate on fabrics and form scale in alkaline solutions, which will adhere to equipment and hinder production. When the iron and manganese salts in the water exceed the standard, rust spots and catalytic oxidation of cotton fibers will easily occur during cooking. When bleaching with oxidants, iron, manganese, and salt also catalyze the decomposition of the bleach.
Factors that affect the quality of dyeing include: chroma, ph value, iron ion content, calcium ion content, etc.
When dyeing with reactive dyes, the impact of water hardness is relatively small. However, when dyeing nylon with acid dyes, the impact of water hardness is more prominent. Hard water not only makes the color of the fabric poor, but the CI in the water also has a great impact on dyeing.
Suspended solids in hard water affect the bleaching whiteness of fabrics. When dyeing cheese, it is easy to reduce the color brightness of the inner and outer layers of cheese. The high pH value of water quality will affect the level dyeing of light-colored fabrics, because under alkaline conditions, the added The dye will be fixed, resulting in poor level dyeing and dyeing flowers.
If the pH value of the water is too high, the dye will be hydrolyzed during the soaping process and the reproducibility will be poor. If the water is too soft, the pH value of the cloth will exceed the standard.
Excessive iron ions will cause color spots, color flowers, and dull color. Excessive manganese ions are the main cause of yellowing of bleached fabrics.
Hard water affects the brightness of the color, causes scaling of the heat exchanger, and causes large energy losses. It can also cause alkali spots due to insoluble precipitates generated by calcium and magnesium ions and soda ash.
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